U.S. patent application number 10/101341 was filed with the patent office on 2003-09-18 for rare-earth pre-alloyed pvd targets for dielectric planar applications.
Invention is credited to Demerary, Richard E., Milonopoulou, Vassiliki, Mullapudi, Ravi B..
Application Number | 20030175142 10/101341 |
Document ID | / |
Family ID | 28039991 |
Filed Date | 2003-09-18 |
United States Patent
Application |
20030175142 |
Kind Code |
A1 |
Milonopoulou, Vassiliki ; et
al. |
September 18, 2003 |
Rare-earth pre-alloyed PVD targets for dielectric planar
applications
Abstract
A target material for deposition of rare-earth doped optical
materials is described. The rare-earth ions, for example erbium and
ytterbium, is prealloyed with host materials. In some embodiments a
ceramic target material can be formed by pre-alloying
Er.sub.2O.sub.3 and/or Yb.sub.2O.sub.3 with Al.sub.2O.sub.3 and/or
SiO.sub.2. In some embodiments, a metal target material can be
formed by pre-alloying Er and/or Yb with Al and/or Si. In some
embodiments, ceramic or metallic tiles are formed which can be
mounted on a backing plate. In some embodiments, an intermetallic
mixture can be formed and flame sprayed onto the backing plate.
Inventors: |
Milonopoulou, Vassiliki;
(San Jose, CA) ; Demerary, Richard E.; (Portola
Valley, CA) ; Mullapudi, Ravi B.; (San Jose,
CA) |
Correspondence
Address: |
Skjerven Morrill MacPherson LLP
Suite 700
25 Metro Drive
San Jose
CA
95110
US
|
Family ID: |
28039991 |
Appl. No.: |
10/101341 |
Filed: |
March 16, 2002 |
Current U.S.
Class: |
419/49 ;
257/E21.274; 501/64 |
Current CPC
Class: |
B22F 1/0003 20130101;
C04B 2235/608 20130101; B22F 3/15 20130101; B22F 9/082 20130101;
B22F 9/082 20130101; C22C 1/0491 20130101; B22F 2999/00 20130101;
C04B 2235/94 20130101; C04B 2235/3224 20130101; C22C 1/0491
20130101; C04B 35/6455 20130101; C04B 2235/3222 20130101; C23C
14/3414 20130101; C04B 2235/3418 20130101; H01L 21/31604 20130101;
C04B 2235/80 20130101; C04B 2235/3427 20130101; B22F 2998/10
20130101; B22F 2998/10 20130101; C04B 35/6261 20130101; C04B 35/18
20130101; B22F 2999/00 20130101; C04B 2235/72 20130101; C04B
2235/3217 20130101 |
Class at
Publication: |
419/49 ;
501/64 |
International
Class: |
B22F 003/24 |
Claims
We claim:
1. A method of forming a target for deposition chamber, comprising:
forming a pre-alloyed material with at least one rare-earth ion
alloyed with at least one host material; forming the target from
the pre-alloyed material.
2. The method of claim 1, where forming a pre-alloyed material
includes mixing at least one rare-earth oxide material with at
least one host oxide to form mixed material; forming a green billet
from the mixed material; degassing the green billet to form a
de-gassed green billet; pressing the de-gassed green billet at high
temperatures to form a billet of the pre-alloyed material.
3. The method of claim 2, wherein pressing the de-gassed green
billet at high temperature includes applying a pressure higher than
about 20 Kpsi and temperature less than about 1000 C for a time
greater than about 1 hour.
4. The method of claim 2 wherein degassing the green billet
includes heating the green billet includes heating the green billet
to a temperature greater than about 500 C.
5. The method of claim 2, wherein mixing at least one rare-earth
oxide material with at least one host oxide includes barrel mixer
in relative concentrations such that the rare-earth ions make up
less than about 10 cat. % of the mixed material.
6. The method of claim 5, wherein the mixed material includes up to
about 37% Al.sub.2O.sub.3, about 57.0% SiO.sub.2 or less, about
2.5% of Er.sub.2O.sub.3 or less, and about 2.5% of Yb.sub.2O.sub.3
or less.
7. The method of claim 6, wherein the mixed material includes about
57.5 cat. % of SiO.sub.2, about 37.5 cat. % of Al.sub.2O.sub.3,
about 2.5 cat. % of Er.sub.2O.sub.3, and about 2.5 cat. % of
Yb.sub.2O.sub.3.
8. The method of claim 6, wherein the mixed material includes about
54.5 cat. % of SiO.sub.2, about 44.5 cat. % of Al.sub.2O.sub.3, and
about 1.0 cat. % of Er.sub.2O.sub.3.
9. The method of claim 6, wherein the mixed material includes about
54.0 cat. % of SiO.sub.2, about 44.6 cat. % of Al.sub.2O.sub.3,
about 1.0 cat. % of Er.sub.2O.sub.3, and about 0.4 cat. % of
Yb.sub.2O.sub.3.
10. The method of claim 2, wherein forming a green billet includes
pressing the mixed material at room temperature.
11. The method of claim 10, wherein pressing placing the mixed
material into a form and applying a pressure greater than about 30
Kpsi to the mixed material.
12. The method of claim 2, wherein forming the target includes
cutting and machining the billet to form tiles; mounting the tiles
on a backing plate to form the target.
13. The method of claim 12, wherein mounting the tiles on a backing
plate to form the target includes sputter coating a side of each of
a number of tiles to form a diffusion layer; tinning the diffusion
layer with a solder material; and soldering the tiles to the
backing plate.
14. The method of claim 1, wherein forming a pre-alloyed material
with at least one rare-earth ion alloyed with at least one host
material includes atomizing at least one rare-earth ion with at
least one metal host to form a pre-alloyed powder; and mixing the
pre-alloyed powder to form mixed powder.
15. The method of claim 14, wherein forming the target from the
pre-alloyed material includes flame spraying the mixed powder onto
a backing plate.
16. The method of claim 14, wherein atomizing at least one
rare-earth ion with at least one metal host includes atomizing
preselected proportions of erbium and ytterbium with aluminum.
17. The method of claim 14, further including adding silicon to the
pre-alloyed powder before barrel mixing.
18. The method of claim 17, wherein the mixed powder includes up to
about 5 cat. % of rare earth ions.
19. The method of claim 18, wherein the mixed power includes up to
about 35% of Al, about 65% Si or less, about 1.0% of Er or less and
about 1.0% Yb or less.
20. The method of claim 19, wherein the mixed powder includes about
57.4 cat. % of Si, about 41.0 cat. % of Al, about 0.8 cat. % of Er
and about 0.8 cat. % of Yb.
21. The method of claim 19, wherein the mixed powder includes about
57.4 cat. % of Si, about 41.0 cat. % of Al, and about 1.5 cat. % of
Er.
22. The method of claim 14, wherein forming the pre-alloyed
material includes degassing the mixed powder to form a green
billet; pressing the green billet to form a billet of pre-alloyed
material.
23. The method of claim 22, wherein degassing the mixed powder
includes heating the powder to a temperature of about 400 C.
24. The method of claim 23, wherein pressing the green billet
includes heating the green billet to a temperature higher than
about 450 C at a pressure higher than about 15 Kpsi.
25. The method of claim 14, wherein forming the target includes
cutting and machining the billet to form tiles; and mounting the
tiles on a backing plate to form the target.
26. A target material for a PVD deposition chamber, comprising: at
least one host constituent; and at least one rare-earth ion
pre-alloyed with some or all of the at least one host
constituent.
27. The target material of claim 26, wherein the host constituent
includes at least one metal oxide.
28. The target material of claim 27, wherein the rare-earth ions
make up less than about 10 cat. % of the mixed material.
29. The method of claim 28, wherein the target material includes
more than or equal to about 37% Al.sub.2O.sub.3, less than or equal
to about 57.0% SiO.sub.2, less than or equal to about 2.5% of
Er.sub.2O.sub.3, and less than or equal to about 2.5% of
Yb.sub.2O.sub.3.
30. The target material of claim 29, wherein the at least one host
constituent includes about 57.5 cat. % Of SiO.sub.2 and about 37.5
cat. % of Al.sub.2O.sub.3 and the at least one rare-earth ion
includes about 2.5 cat. % of Er.sub.2O.sub.3, and about 2.5 cat. %
of Yb.sub.2O.sub.3.
31. The target material of claim 29, wherein the at least one host
constituent includes about 54.5 cat. % Of SiO.sub.2 and about 44.5
cat. % of Al.sub.2O.sub.3 and the at least one rare-earth ion
includes about 1.0 cat. % of Er.sub.2O.sub.3.
32. The target material of claim 29, wherein the at least one host
constituent includes about 54.0 cat. % Of SiO.sub.2 and about 44.6
cat. % of Al.sub.2O.sub.3 and the at least one rare-earth ion
includes about 1.0 cat. % of Er.sub.2O.sub.3 and about 0.4 cat. %
of Yb.sub.2O.sub.3.
33. The target material of claim 26, wherein the host constituent
includes at least one metal.
34. The target material of claim 33, wherein the rare-earth ions
make up about 5 cat % of the mixed material.
35. The method of claim 34, wherein the target includes more than
about 35% of Al, less than about 65% Si, less than about 1.0% of Er
and less than about 1.0% Yb.
36. The target material of claim 35, wherein the at least one host
constituent includes about 57.4 cat. % of Si and about 41.0 cat. %
of Al and the at least one rare-earth ions include about 0.8 cat. %
of Er and about 0.8 cat. % of Yb.
37. The target material of claim 35, wherein the at least one host
constituent includes about 57.4 cat. % of Si and about 41.0 cat. %
of Al and the at least one rare-earth ions includes about 1.5 cat.
% of Er.
38. A method of forming a target for a PVD chamber, comprising:
melting a mixture containing rare earth ions in an Al.sub.2O.sub.3
crucible; cooling the mixture; forming a power from the cooled
mixture; HIPing the powder to form target material; and forming the
target from the target material.
39. The method of claim 38, wherein melting the mixture includes
heating with induction heating.
40. The method of claim 38, wherein melting the mixture includes
heating with e-beam heating.
Description
BACKGROUND
[0001] 1. Field of the Invention
[0002] This invention relates to deposition of doped oxide
materials and, in particular, to a target for physical vapor
deposition (PVD) of, for example, rare-earth doped oxide
materials.
[0003] 2. Discussion of Related Art
[0004] Deposition of insulating materials and especially optical
materials is technologically important in several areas including
production of optical devices and production of semiconductor
devices. In semiconductor devices, doped alumina silicates can be
utilized as high dielectric insulators.
[0005] The increasing prevalence of fiber optic communications
systems has created an unprecedented demand for devices for
processing optical signals. Planar devices such as optical
waveguides, couplers, splitters, and amplifiers, fabricated on
planar substrates, like those commonly used for integrated
circuits, and configured to receive and process signals from
optical fibers are highly desirable. Such devices hold promise for
integrated optical and electronic signal processing on a single
semiconductor-like substance.
[0006] The basic design of planar optical waveguides and amplifiers
is well known, as described, for example, in U.S. Pat. Nos.
5,119,460 and 5,563,979 to Bruce et al., U.S. Pat. No. 5,613,995 to
Bhandarkar et al., U.S. Pat. No. 5,900,057 to Buchal et al., and
U.S. Pat. No. 5,107,538 to Benton et al., to cite only a few. These
devices, very generally, include a core region, typically bar
shaped, of a certain refractive index surrounded by a cladding
region of a lower refractive index. In the case of an optical
amplifier, the core region includes a certain concentration of a
dopant, typically a rare earth ion such as an erbium or
praseodymium ion which, when pumped by a laser, fluoresces, for
example, in the 1550 nm and 1300 nm wavelength ranges used for
optical communication, amplify the optical signal passing through
the core.
[0007] As described, for example in the patents by Bruce et al.,
Bhandarkar et al, and Buchal et al., planar optical devices may be
fabricated by process sequences including forming a layer of
cladding material on a substrate; forming a layer of core material
on the layer of cladding mater; patterning the core layer using a
photolighotgraphic mask and an etching process to form a core
ridge; and covering the core ridge with an upper cladding
layer.
[0008] The performance of these planar optical devices depends
sensitively on the value and uniformity of the refractive index of
the core region and of the cladding region, and particularly on the
difference in refractive index, .DELTA.n, between the regions.
Particularly for passive devices such as waveguides, couplers, and
splitters, .DELTA.n should be carefully controlled, for example to
values within about 1%, and the refractive index of both core and
cladding need to be highly uniform, for some applications at the
fewer than parts per thousand level. In the case of doped materials
forming the core region of planar optical amplifiers, it is
important that the dopant be uniformly distributed so as to avoid
non-radiative quenching or radiative quenching, for example by
upconversion. The refractive index and other desirable properties
of the core and cladding regions, such as physical and chemical
uniformity, low stress, and high density, depend, of course, on the
choice of materials for the devices and on the processes by which
they are fabricated.
[0009] Because of their optical properties, silica and refractory
oxides such as Al.sub.2O.sub.3 are good candidate materials for
planar optical devices. Further, these oxides serve as suitable
hosts for rare earth dopants used in optical amplifiers. A common
material choice is so-called low temperature glasses, doped with
alkali metals, boron, or phosphorous, which have the advantage of
requiring lower processing temperatures. In addition, dopants are
used to modify the refractive index. Methods such as flame
hydrolysis, ion exchange for introducing alkali ions in glasses,
sputtering, and various chemical vapor deposition processes (CVD)
have been used to form films of doped glasses. However, dopants
such as phosphorous and boron are hygroscopic, and alkalis are
undesirable for integration with electronic devices. Control of
uniformity of doping in CVD processes can be difficult and CVD
deposited films can have structural defects leading to scattering
losses when used to guide light. In addition, doped low temperature
glasses may require further processing after deposition. A method
for eliminating bubbles in thin films of sodium-boro-silicate glass
by high temperature sintering is described, for example, in the
'995 patent to Bhandarkar et al.
[0010] Generally, when films are sputtered onto a target, the
rare-earth ions in the target may form aggregates of two or more
adjacent ions. These aggregates degrade the performance of the
material layer that has been deposited. Several conventional
targets have been formed with mixtures of Al.sub.2O.sub.3 and/or
SiO.sub.2, Er.sub.2O.sub.3 and/or Yb.sub.2O.sub.3 by sintering and
hot pressing. Aggregates of erbium in the deposited material, for
example, are detrimental due to up-conversion processes. In an
Er-doped amplifier, for example, the Er ion radiative coupling
processes (e.g., pair induced quenching, up-conversion), which
results from Er clusters and Er pairing, is well known to result in
inefficient amplification.
[0011] In erbium doped amplifiers, for example, an erbium
concentration of 0.3% (about 1.times.10.sup.20/cm.sup.3) results in
erbium ion separations of about 22 angstroms if they are uniformly
spaced, which is about 10 bond lengths. An ideal erbium
concentration of about 1% (about 3.times.10.sup.20/cm.sup.3),
results in a separation of about 14 angstroms or about 5-6 bond
lengths. A 0.1% erbium concentration results in a 32 angstroms
separation. It is extremely difficult to prevent the erbium ions
from pairing or clustering during deposition. Additionally, in many
target designs the erbium ions may aggregate in the target material
before deposition of the material layer and during deposition these
ions may preferential deposit in pairs or larger clusters.
[0012] Another common problem in deposition is OH impurities, which
serve to also quench the transitions required for pumping and
amplification. Targets formed by sol-gel precipitation, for
example, suffer from high OH impurities in the deposited material
layer.
[0013] Additionally, target material can be formed from glass
materials, see, e.g., M. P. Hehlen, N. J. Cockroft, T. R. Cosnell,
A. J. Bruce, C. Nykolak, and J. Shmulovich, "Uniform Upconversion
in High-Concentration Er.sup.3+-Doped Soda Lime Silicate and
Aluminosilicate Glasses", Optics Letters, Vol. 22, No. 1, p. 772
(1997), which may provide uniform non-aggregated rare-earth
concentrations, but which are mechanically brittle. Further, glass
targets usually have large concentrations of OH impurities, which
degrade the optical properties of a deposited layer.
[0014] Further, billets for forming targets have been made by flame
spraying Nd with Al, see, e.g., K. Yoshikawa, Y. Yoneda, and K.
Koide, "Spray formed aluminum alloys for sputter targets," Powder
Metallurgy, Vol. 43, no. 3 p. 198 (2000). However, with higher Nd
concentrations (e.g., greater than about 2% Nd), the Nd which has
been alloyed with the Al during the flame spraying process
precipitates out during the following HIPing process, resulting in
clusters of Nd ions.
[0015] Depositions of material films typically utilize a target for
sputtering of material onto a substrate. The material properties of
the deposited film, therefore, directly depend on the material
properties of the target. The deposition process and the materials
utilized in the deposition process of optical insulating layers
primarily determines the quality and performance of the resulting
optical structures. Therefore, there is a desire to provide
starting materials and targets for deposition processes that result
in optical devices and insulating layers of high quality.
SUMMARY
[0016] In accordance with the present invention, a target for a
Physical Vapor Deposition (PVD) process utilized for deposition of
optical layers is described. A target according to the present
invention is formed so that rare-earth dopants are pre-alloyed with
the constituent host materials, resulting in more uniform
deposition of dopants, less aggregation of the rare-earth
impurities in the target and during deposition, and higher
durability due to structure effects in the target. The alloyed
compounds, then, also act as a sintering agent, producing
physically more robust and durable target materials.
[0017] A target according to the present invention can include one
or more individual tiles mounted on a backing plate. In some
embodiments, each of the tiles can be formed in a hot isostatic
press (HIP) process. Preparation of the starting materials for the
HIPing process, and in some embodiments the HIPing process itself,
results in alloying of rare-earth impurity ions. In some
embodiments, a prealloyed starting material can be formed and that
material deposited on the backing plate, for example by flame
spraying a pre-alloyed and mixed powder to the backing plate.
[0018] In some embodiments, a ceramic tile can be fabricated in a
HIP process. The process begins by mixing oxides, including the
host oxides and oxides of rare-earth compounds. For example
SiO.sub.2, Al.sub.2O.sub.3, Er.sub.2O.sub.3 and Yb.sub.2O.sub.3 can
be mixed in predetermined relative concentrations. In some
embodiments, a total atomic percentage of up to about 10 cat % of
rare earths can be utilized. The mixture can then be poured into a
form and cold isostatic pressed (CIP), for example to a density
approximately 50% that of the theoretical density. The pressed
("green") mixture is then degassed at a high temperature, for
example a temperature greater than about 550 C, in a vacuum.
Finally, the degassed formed mixture is hot isostatically pressed,
for example at temperatures less than about 1000.degree. C. and at
pressures of about 30 Kpsi. The resulting billet can then be
machined and formed into individual tiles. The resulting tile
includes compounds alloyed compounds of ErAlO.sub.3 and YBSiO.sub.5
and little to no free Er.sub.2O.sub.3 or Yb.sub.2O.sub.3.
[0019] In some embodiments, alloying of rare earth ions such as Er
can be prealloyed in Al.sub.2O.sub.3 by melting a mixture
containing erbium in an alumina crucible. The low melting
temperature of the alumina crucible leads to alloying of the erbium
into the Al.sub.2O.sub.3. In some embodiments, a prealloyed powder
for a ceramic target can be formed in an Al.sub.2O.sub.3 crucible
by e-beam melting of a solution of Al.sub.2O.sub.3,
Er.sub.2O.sub.3, Yb.sub.2O.sub.3, and SiO.sub.2, for example.
[0020] In some embodiments, a metallic target can be fabricated in
a HIPing process. First, the atomic constituents can be atomized in
an atomization process to form intermettalics, for example Al
and/or Si and Er and/or Yb can be atomized. With Al, Er and Yb
atomization, for example, the atomized powder includes AlEr.sub.3,
AlYb.sub.3 and free aluminum. In some embodiments, there is
substantially no free Er in the intermettalic mix. The
intermettalics are then mixed. In some embodiments, further
constituents, for example silicon, can be added before mixing. The
resulting mixture can be poured into a mold and HIPed at low
temperature, for example about 600 C, to form a billet. The billet
can then be machined to form individual tiles.
[0021] In some embodiments, several tiles of target material,
either ceramic or metallic as discussed above, can be formed and
affixed to a backing plate to form a target. The target is then
utilized in a physical vapor deposition (PVD) chamber to form
material layers having composition and properties related to the
composition and properties of the target. In some embodiments, the
mixed intermettalics can be flame or plasma sprayed directly on a
backing plate to form a target.
[0022] These and other embodiments are further discussed below with
respect to the following figures.
SHORT DESCRIPTION OF THE FIGURES
[0023] FIGS. 1A and 1B show a diagram of a PVD process chamber with
a target according to the present invention.
[0024] FIG. 2 shows a plan view of a target for a PVD process
chamber according to the present invention.
[0025] FIG. 3A shows a cross-sectional view of a target for a PVD
process chamber according to the present invention.
[0026] FIG. 3B shows a planar view of one embodiment of a target
utilizing ceramic tiles according to the present invention.
[0027] FIG. 4A shows a phase diagram of Al.sub.2O.sub.3 with
Er.sub.2O.sub.3.
[0028] FIG. 4B shows a phase diagram of Er and Al ions.
[0029] FIG. 4C illustrates a waveguide amplifier formed utilizing
targets according to the present invention.
[0030] FIG. 5 illustrates manufacture of a ceramic tile for a
target according to the present invention.
[0031] FIGS. 6A through 6F show x-ray diffraction data showing
alloying of rare-earth pre-alloying in an embodiment of a ceramic
target according to the present invention.
[0032] FIGS. 6G and 6H show electron dispersion data also showing
alloying of Er and Yb with Al.sub.2O.sub.3 and SiO.sub.2.
[0033] FIGS. 7A through 7D show x-ray diffraction data of another
embodiment of a target according to the present invention showing
alloying of rare earth ions.
[0034] FIG. 8A illustrate methods of producing a metallic tile for
a metallic target according to the present invention.
[0035] FIG. 8B illustrates another method of producing a metallic
target according to the present invention.
[0036] FIG. 9 shows an x-ray diffraction spectrum of alloyed powder
utilized in an example embodiment of the present invention.
[0037] FIG. 10 shows x-ray diffraction spectrum of alloyed powder
utilized in another example embodiment of the present
invention.
[0038] In the figures, elements having the same designation have
the same or similar functions.
DETAILED DESCRIPTION OF THE FIGURES
[0039] A physical vapor deposition (PVD) process provides layers of
optical materials with controlled and uniform refractive index that
can be utilized for active and passive planar optical devices. The
process uses sputtering with a wide area target and a condition of
uniform target erosion and includes multiple approaches for
controlling refractive index. PVD processes which may utilize
targets according to the present invention are described in
application Ser. No. 09/903,050 (the '050 application) by Demaray
et al., entitled "Planar Optical Devices and Methods for Their
Manufacture," assigned to the same assignee as is the present
invention, herein incorporated by reference in its entirety.
Further, PVD processes which may utilize targets according to the
present invention are described in concurrently filed application
U.S. Application Serial No. M-12245 US} (the '245 application),
assigned to the same assignee as is the present invention, herein
incorporated by reference in its entirety.
[0040] FIG. 1A shows a schematic of an apparatus 10 for sputtering
of material from a target 12 according to the present invention. In
some embodiments, controlled refractive index material for planar
optical devices can be deposited with apparatus 10.
[0041] Apparatus 10 can include a wide area sputter source target
12, which provides material to be deposited on substrate 16.
Substrate 16 is positioned parallel to and opposite target 12.
Target 12 functions as a cathode when power is applied to it and is
equivalently termed a cathode.
[0042] In some embodiments of the invention, target 12 can include
pure materials such as quartz, alumina, or sapphire, (the
crystalline form of alumina), mixtures of compounds of optically
useful materials, or intermettalics. Optically useful materials
include oxides, fluorides, sulfides, nitrides, phosphates,
sulfates, and carbonates, as well as other wide band gap
semiconductor materials. In some embodiments, target 12 includes a
metallic target material formed from intermetalic compounds of
optical elements such as Si, Al, Er and Yb. To achieve uniform
deposition, target 12, itself can be chemically uniform, flat, and
of uniform thickness over an extended area. Target 12 can be a
composite target fabricated from individual tiles, precisely bonded
together on a backing plate with minimal separation, as is
discussed further with respect to FIG. 3A. In some embodiments, the
mixed intermetalllics can be plasma sprayed directly onto a backing
plate to form target 12. The complete target assembly can also
includes structures for cooling the target, embodiments of which
have been described in U.S. Pat. No. 5,565,071 to Demaray et al,
and incorporated herein by reference.
[0043] Substrate 16 can be a solid, smooth surface. Typically,
substrate 16 can be a silicon wafer or a silicon wafer coated with
a layer of silicon oxide formed by a chemical vapor deposition
process or by a thermal oxidation process. Alternatively, substrate
16 can be a glass, such as Corning 1737 (Corning Inc., Elmira,
N.Y.), a glass-like material, quartz, a metal, a metal oxide, or a
plastic material. Substrate 16 typically is supported on a holder
or carrier sheet 17 that may be larger than substrate 16.
[0044] In some embodiments, the area of wide area target 12 can be
greater than the area on the carrier sheet on which physically and
chemically uniform deposition is accomplished. Secondly, in some
embodiments a central region on target 12, overlying substrate 16,
can be provided with a very uniform condition of sputter erosion of
the target material. Uniform target erosion is a consequence of a
uniform plasma condition. In the following discussion, all mention
of uniform condition of target erosion is taken to be equivalent to
uniform plasma condition. Uniform target erosion is evidenced by
the persistence of film uniformity throughout an extended target
life. A uniformly deposited film can be defined as a film having a
nonuniformity in thickness, when measured at representative points
on the entire surface of a substrate wafer, of less than about 5%
or 10%. Thickness nonuniformity is defined, by convention, as the
difference between the minimum and maximum thickness divided by
twice the average thickness. If films deposited from a target from
which more than about 20% of the weight of the target has been
removed continue to exhibit thickness uniformity, then the
sputtering process is judged to be in a condition of uniform target
erosion for all films deposited during the target life.
[0045] FIG. 1B illustrates plasma conditions in apparatus 10. A
uniform plasma condition can be created in the region between
target 12 and substrate 16 in a region overlying substrate 16. The
region of uniform plasma condition is indicated in the exploded
view of FIG. 1B. A plasma 53 can be created in region 51, which
extends under the entire target 12. A central region 52 of target
12, can experience a condition of uniform sputter erosion. As
discussed further below, a layer deposited on a substrate placed
anywhere below central region 52 can then be uniform in thickness
and other properties (i.e., dielectric, optical index, or material
concentrations).
[0046] In addition, region 52 in which deposition provides
uniformity of deposited film can be larger than the area in which
the deposition provides a film with uniform physical or optical
properties such as chemical composition or index of refraction. In
some embodiments, target 12 is substantially planar in order to
provide uniformity in the film deposited on substrate 16. In
practice, planarity of target 12 can mean that all portions of the
target surface in region 52 are within a few millimeters of a
planar surface, and can be typically within 0.5 mm of a planar
surface.
[0047] Multiple approaches to providing a uniform condition of
sputter erosion of the target material can be used. A first
approach is to sputter without magnetic enhancement. Such operation
is referred to as diode sputtering. Using a large area target with
a diode sputtering process, a dielectric material can be deposited
so as to provide suitably uniform film thickness over a central
portion of an adjacent substrate area. Within that area, an area of
highly uniform film may be formed with suitable optical uniformity.
The rate of formation of films of many microns of thickness by
diode sputtering can be slow for small targets. However, in the
present method, using large targets, a disadvantage in speed of
diode sputtering can be compensated by batch processing in which
multiple substrates are processed at once.
[0048] Other approaches to providing a uniform condition of sputter
erosion rely on creating a large uniform magnetic field or a
scanning magnetic field that produces a time-averaged, uniform
magnetic field. For example, rotating magnets or electromagnets can
be utilized to provide wide areas of substantially uniform target
erosion. For magnetically enhanced sputter deposition, a scanning
magnet magnetron source can be used to provide a uniform, wide area
condition of target erosion. Diode sputtering is known to provide
uniform films.
[0049] As illustrated in FIG. 1A, apparatus 10 can include a
scanning magnet magnetron source 20 positioned above target 12. An
embodiment of a scanning magnetron source used for dc sputtering of
metallic films is described in U.S. Pat. No. 5,855,744 to Halsey,
et. al., (hereafter '744), which is incorporated herein by
reference in its entirety. The '744 patent demonstrates the
improvement in thickness uniformity that is achieved by reducing
local target erosion due to magnetic effects in the sputtering of a
wide area rectangular target. As described in the '744 patent, by
reducing the magnetic field intensity at these positions, the local
target erosion was decreased and the resulting film thickness
nonuniformity was improved from 8%, to 4%, over a rectangular
substrate of 400.times.500 mm.
[0050] A top down view of magnet 20 and wide area target 12 is
shown in FIG. 2. A film deposited on a substrate positioned on
carrier sheet 17 directly opposed to region 52 of target 12 has
good thickness uniformity. Region 52 is the region shown in FIG. 1B
that is exposed to a uniform plasma condition. In some
implementations, carrier 17 can be coextensive with region 52.
Region 24 shown in FIG. 2 indicates the area below which both
physically and chemically uniform deposition can be achieved, where
physical and chemical uniformity provide refractive index
uniformity, for example. FIG. 2 indicates that the region 52 of
target 12 providing thickness uniformity is, in general, larger
than region 24 of target 12 providing thickness and chemical
uniformity. In optimized processes, however, regions 52 and 24 may
be coextensive.
[0051] In some embodiments, magnet 20 extends beyond area 52 in one
direction, the Y direction in FIG. 2, so that scanning is necessary
in only one direction, the X direction, to provide a time averaged
uniform magnetic field. As shown in FIGS. 1A and 1B, magnet 20 can
be scanned over the entire extent of target 12 which is larger than
region 52 of uniform sputter erosion. Magnet 20 is moved in a plane
parallel to the plane of target 12.
[0052] The combination of a uniform target 12 with area larger than
the area of substrate 16 can provide films of highly uniform
thickness. Further, the material properties of the film deposited
can be highly uniform. The conditions of sputtering at the target
surface, such as the uniformity of erosion, the average temperature
of the plasma at the target surface and the equilibration of the
target surface with the gas phase ambient of the process are
uniform over a region which is greater than or equal to the region
to be coated with a uniform film thickness. In addition, the region
of uniform film thickness is greater than or equal to the region of
the film which is to have highly uniform optical properties such as
index of refraction, density, transmission or absorptivity.
[0053] As shown in FIG. 1A, apparatus 10 includes a power supply 14
for applying power to target 12 to generate a plasma in a
background gas. Power supply 14 can be a pulsed DC source as is
discussed in the '245 application or an RF source as is discussed
in the '050 application. An RF power supply is conventionally
operated at 13.56 MHz. Typical process conditions for RF sputter
deposition include applying high frequency RF power in the range of
about 500 to 5000 watts. Power supply 14 may include other sources
of power as well.
[0054] An inert gas, typically argon, is used as the background
sputtering gas. Additionally, with some embodiments of target 12,
oxygen may be added to the sputtering gas. Other gasses such as
N.sub.2, NH.sub.3, CO, NO, CO.sub.2, halide containing gasses other
gas-phase reactants can also be utilized. The deposition chamber
can be operated at low pressure, often between about 0.5 millitorr
and 8-10 millitorr. Typical process pressure is below about 2
millitorr where there are very few collisions in the gas phase,
resulting in a condition of uniform "free molecular" flow. This
ensures that the gas phase concentration of a gaseous component is
uniform throughout the process chamber. For example, background gas
flow rates in the range of about 30 to about 100 sccm, used with a
pump operated at a fixed pumping speed of about 50 liters/second,
result in free molecular flow conditions.
[0055] The distance d, in FIG. 1A, between target 12 and substrate
16 can, in some embodiments, be varied between about 4 cm and about
9 cm. A typical target to substrate distance d is about 6 cm. The
target to substrate distance can be chosen to optimize the
thickness uniformity of the film. At large source to substrate
distances the film thickness distribution is dome shaped with the
thickest region of the film at the center of the substrate. At
close source to substrate distance the film thickness is dish
shaped with the thickest film formed at the edge of the substrate.
The substrate temperature can be held constant in the range of
about -40.degree. C. to about 550.degree. C. and can be maintained
at a chosen temperature to within about 10.degree. C. by means of
preheating the substrate and the substrate holder prior to
deposition. During the course of deposition, the heat energy
impressed upon the substrate by the process can be conducted away
from the substrate by cooling the table on which the substrate is
positioned during the process, as known to those skilled in the
art. The process is performed under conditions of uniform gas
introduction, uniform pumping speed, and uniform application of
power to the periphery of the target as known to skilled
practitioners.
[0056] The speed at which a scanning magnet 20 can be swept over
the entire target can be determined such that a layer thickness
less than about 5 to 10, corresponding roughly to two to four
monolayers of material, is deposited on each scan. Magnet 20 can be
moved at rates up to about 30 sec/one-way scan and typically is
moved at a rate of about 4 sec/one-way scan. The rate at which
material is deposited depends on the applied power and on the
distance d, in FIG. 1A, between the target 12 and the substrate 16.
For deposition of optical oxide materials, for example scanning
speeds between about 2 sec/one-way scan across the target to 20-30
sec/scan provide a beneficial layer thickness. Limiting the amount
of material deposited in each pass promotes chemical and physical
uniformity of the deposited layer. With the typical process
conditions, the rate of deposition of pure silica can be
approximately 0.8 .ANG./kW-sec. At an applied RF power of 1 kW, the
rate of deposition is 0.8 .ANG./sec. At a magnet scan speed that
provides a scan of 2 seconds, a film of 1.8 .ANG. nominal thickness
is deposited.
[0057] A thickness of 2.4 .ANG. can be associated with one
monolayer of amorphous silica film. The impingement rate of process
gas equivalent to a monolayer per second occurs at approximately
1.times.10.sup.-6 torr. The process gas may contain oxygen atoms
ejected from the silica during sputtering in addition to the
background inert gas. For typical process conditions near 1
millitorr, 4.times.10.sup.3 monolayers of process gas impinge on
the film during the 4 second period of deposition. These conditions
provide adequate means for the equilibration of the adsorbed
sputtered material with the process gas, if the sputtered material
has a uniform composition. Uniform, wide area target erosion is
required so as to ensure that the adsorbed sputtered material has a
uniform composition.
[0058] In some embodiments, a dual frequency sputtering process, in
which low frequency RF power is also applied to the target, can be
used. Returning to FIG. 1A, apparatus 10 includes RF generator 15,
in addition to power supply 14 described previously. For RF
sputtering, power supply 14 is a high frequency source, typically
13.56 MHz, while RF generator 15 can provide power at a much lower
frequency, typically from about 100 to 400 kHz. Typical process
conditions for dual frequency RF deposition include high frequency
RF power in the range of about 500 to 5000 watts and low frequency
RF power in the range of about 500 to 2500 watts where, for any
given deposition, the low frequency power is from about a tenth to
about three quarters of the high frequency power. The high
frequency RF power is chiefly responsible for sputtering the
material of target 12. The high frequency accelerates electrons in
the plasma but is not as efficient at accelerating the much slower
heavy ions in the plasma. Adding the low frequency RF power causes
ions in the plasma to bombard the film being deposited on the
substrate, resulting in sputtering and densification of the
deposited film.
[0059] In addition, the dual frequency RF deposition process
generally results in films with a reduced surface roughness as
compared with single frequency deposition. For silica, films with
average surface roughness in the range of between about 1.5 and 2.6
nm have been obtained with the dual frequency RF process.
Experimental results for single and dual frequency deposition are
further described in Example 4 below. As discussed in the co-filed,
commonly assigned U.S. application Attorney Docket No. M-11522 US,
(the '522 application) which is incorporated herein by reference,
reducing surface roughness of core and cladding materials helps to
reduce scattering loss in planar optical devices.
[0060] Further, the dual frequency RF process can be used to tune
the refractive index of the deposited film. Keeping the total RF
power the same, the refractive index of the deposited film tends to
increase with the ratio of low frequency to high frequency RF
power. For example, a core layer of a planar waveguide can be
deposited by a dual frequency RF process, and the same target 12,
can be used to deposit a cladding layer using a single frequency RF
process. Introducing low frequency RF power in the core layer
deposition process can therefore be used to provide the difference
in refractive index between core and cladding layer materials.
[0061] It is particularly beneficial to further augment the single
frequency or dual frequency RF sputtering process by additionally
applying RF power to the substrate 16, using, for example,
substrate RF generator 18. Applying power to the substrate,
resulting in substrate bias, also contributes to densification of
the film. The RF power applied to the substrate can be either at
the 13.56 MHz high frequency or at a frequency in the range of the
low frequency RF. Substrate bias power similar to the high
frequency RF power can be used.
[0062] Substrate bias has been used previously to planarize sputter
deposited quartz films. A theoretical model of the mechanism by
which substrate bias operates, has been put forward by Ting et al.
(J. Vac. Sci. Technol. 15, 1105 (1978)). When power is applied to
the substrate, a so-called plasma sheath is formed about the
substrate and ions are coupled from the plasma. The sheath serves
to accelerate ions from the plasma so that they bombard the film as
it is deposited, sputtering the film, and forward scattering
surface atoms, densifying the film and eliminating columnar
structure. The effects of adding substrate bias are akin to, but
more dramatic than, the effects of adding the low frequency RF
component to the sputter source.
[0063] Using the bias sputtering process, the film is
simultaneously deposited and etched. The net accumulation of film
at any point on a surface depends on the relative rates of
deposition and etching, which depend respectively, on the power
applied to the target and to the substrate, and to the angle that
the surface makes with the horizontal. The rate of etching is
greatest for intermediate angles, on the order of 45 degrees, that
is between about 30 and 60 degrees.
[0064] The target and substrate powers can be adjusted such that
the rates of deposition and etching are approximately the same for
a range of intermediate angles. In this case, films deposited with
bias sputtering have the following characteristics. At a step where
a horizontal surface meets a vertical surface, the deposited film
makes an intermediate angle with the horizontal. On a surface at an
intermediate angle, there will be no net deposition since the
deposition rate and etch rate are approximately equal. There is net
deposition on a vertical surface.
[0065] Apparatus 10 may, for example, by adapted from an AKT-1600
PVD (400.times.500 mm substrate size) system from Applied Komatsu
or an AKT-4300 (600.times.720 mm substrate size) system from
Applied Komatsu may form the base reactor. The AKT-1600, for
example, has three deposition chambers connected by a vacuum
transport chamber. These Komatsu reactors can be modified such that
power at one or more RF frequencies. In addition, a pulse-DC power
supplies can be applied for purposes of pulsed DC power as
described in the '245 application.
[0066] Power supplies 14 and 15 can, for example, include a 13.56
MHz supply operating between about 500 and about 5000 Hz, a second
power supply for providing a lower frequency power to substrate 16,
and/or a pulsed DC power supply. Target 12 can have an active size
of about 675.70.times.582.48 by 4 mm in, for example, a AKT-1600
based system in order to deposit films on a substrate 16 that is
about 400.times.500 mm. The temperature of substrate 16 can be held
at between -50C and 500C. The distance between target 12 and
substrate 16 can be between 4 and 6 cm. Process gas can be inserted
into the chamber of apparatus 10 at a rate of between about 30 to
about 100 sccm while the pressure in the chamber of apparatus 10
can be held at below about 2 millitorr. Magnet 20 provides a
magnetic field of strength between about 400 and about 600 Gauss
directed in the plane of target 12 and is moved across target 12 at
a rate of less than about 20-30 sec/scan.
[0067] Therefore, any given process utilizing apparatus 10 can be
characterized by providing the power supplied to target 12, the
power supplied to substrate 16, the temperature of substrate 16,
the characteristics and constituents of the reactive gasses, the
speed of the magnet, and the spacing between substrate 16 and
target 12.
[0068] A major factor in producing uniform films for use in optical
amplifiers and in producing targets is the uniformity in chemical
composition, to the level of the metallurgy utilized to form the
powder mixtures, of target 12. In some embodiments, ceramic targets
are formed from rare-earth oxides and host oxide materials. In some
embodiments, metallic targets are formed from rare earth and
metallic ions.
[0069] In ceramic targets, typical powder sizes are between tens
and hundreds of microns. In the case of refractory oxide additions,
rare earth additions can be pre-alloyed with the refractory oxides.
Plasma spray, transient melting, induction melting, or electron
beam melting may be utilized to form a pre-alloyed solid which is a
solution or alloy of such materials. A powder can be formed from
the pre-alloyed solid.
[0070] FIG. 4A shows a phase diagram of Al.sub.2O.sub.3 with
Er.sub.2O.sub.3, for example. In the diagram, the designation C
refers to cubic formed rare earth oxide, G refers to garnet, P
refers to perovskite, and .alpha. refers to corundum. The 2:1 phase
refers to Er.sub.4Al.sub.2O.sub.9, the 1:1 phase refers
ErAlO.sub.3, and the 3:5 phase refers to Er.sub.3Al.sub.5O.sub.12.
As can be seen in the phase diagram of FIG. 4A, Er.sub.2O.sub.3 and
Al.sub.2O.sub.3 readily dissolve and form compounds with each
other.
[0071] In the case of mixed materials containing alumina, for
example, the low sputter yield of pure alumina can lead to
segregation of the target material during sputtering. This causes
the film to be low in aluminum with respect to the alloy target
composition. It also can lead to particle production from the
cathode. The high solubility of the rare earth material in alumina
and the high sputter efficiency of the rare earth doped alumina
suggest that practical formation of a sputter target material
proceed through a first step of alloying the rare earth dopant and
one or more of the host oxide additions to form a first material.
The remainder of the host materials can be added prior to
consolidation of the alloy target material. With this understanding
the practitioner can fabricate alloy tiles of uniform composition
having the benefit of dissolved rare earth dopant distribution.
Methods for producing tiles to form target 12 is further discussed
below.
[0072] In some embodiments, metallic target material can be
prepared by atomizing rare-earth atoms with host atoms. For
example, Er and/or Yb can be atomized with Al to form pre-alloyed
powders which can be utilized to form targets. FIG. 4B shows a
phase diagram of Er and Al ions. The phase diagram shows various
compounds of Al and Er formed. At the typical compositions of Er
utilized in formation of erbium-doped amplifier structures (e.g.,
up to 1.5 cat % erbium concentration in the amplifier), Al.sub.3Er
is formed.
[0073] In several embodiments of the invention, material tiles are
formed. These tiles can be mounted on a backing plate to form a
target for apparatus 10. FIG. 3A shows an embodiment of targets 12
formed with individual tiles 30 mounted on a cooled backplate 25.
In order to form a wide area target of an alloy target material,
the consolidated material of individual tiles 30 should first be
uniform to the grain size of the powder from which it is formed. It
also should be formed into a structural material capable of forming
and finishing to a tile shape having a surface roughness on the
order of the powder size from which it is consolidated. As an
example, the manufacture of indium tin oxide targets for wide area
deposition has shown that it is impractical to attempt to form a
single piece, wide area target of fragile or brittle oxide
material. The wide area sputter cathode is therefore formed from a
close packed array of smaller tiles. Target 12, therefore, may
include any number of tiles 30, for example between 2 to 20
individual tiles 30. Tiles 30 are finished to a size so as to
provide a margin of non-contact, tile to tile, 29 in FIG. 3A, less
than about 0.010" to about 0.020" or less than half a millimeter so
as to eliminate plasma processes between adjacent ones of tiles 30.
The distance between tiles 30 of target 12 and the dark space anode
or ground shield 19, in FIGS. 1A and 1B can be somewhat larger so
as to provide non contact assembly or provide for thermal expansion
tolerance during process chamber conditioning or operation.
[0074] The low thermal expansion and fragile condition of ideal
optical dielectric tile material can be a cause of great difficulty
in bonding and processing a wide area array of tiles 30. The
bonding process that overcomes these difficulties is illustrated in
FIG. 3A. Sputter coating a side of each of tiles 30 in region 26
prior to bonding with backing plate 25 can be accomplished with a
layer of a material such as chrome or nickel as a diffusion layer.
Such a metallurgical layer acts as a wetting layer to be tinned
with a suitable solder material such as indium or an indium alloy.
Backing plate 25 can be made of titanium or molybdenum or other low
expansion metal so as to provide a good match with the thermal
expansion of the material of tiles 30. A substantial aspect of the
formation of a tiled target is the finishing and coating of the
backing plate prior to the solder bonding of the array of tiles.
The portion 27 of the backing plate to be exposed to vacuum, either
between adjacent ones of tiles 30 or about the periphery or dark
space region 27 of target 12 should be bead blasted or otherwise
etched and plasma spray coated with a material such as alumina or
silica to prevent contamination of the process by the target
backing plate material. The portion 26 of the backing plate beneath
each of tiles 30 can be sputter coated with a material such as
nickel or chrome to enable solder bonding. Pure indium solder,
although it has a higher melting point than alloys such as
indium-tin, is much more ductile and allows the solder to yield
during cooling of the solder bonded assembly relieving stress on
the bonded tiles 30.
[0075] It is useful to provide an outer frame fixture which is
located precisely for the location of the outer tiles. It is also
useful to provide shim location, tile to tile, while the assembly
is at temperature. The actual solder application and lay up
procedure can be devised by those versed in solder assembly. To
enhance heat transfer, the solder can form a full fill of the
volume between each of tiles 30 and backing plate 25. In order to
prevent contamination of the plasma in apparatus 10, the solder not
be exposed to the plasma. There should not be any visible solder in
the region between adjacent tiles 30 or on backing plate 25. It is,
then, useful to sputter coat the wetting layer area with an offset
28 of several millimeters on both tile 30 and backing plate 25. It
is also useful to pre-solder or tin both tiles 30 and backing plate
25 prior to final assembly. The solder material should not wet
region 28 upon assembly. A mask for sputter deposition of the
diffusion barrier/wetting layer film can be useful in this process.
Finally, cleaning of the bonded target tile assembly should utilize
anhydrous cleaning rather than aqueous based cleaning methods to
prevent contamination of the material of tiles 30 with water.
[0076] In accordance with the present invention, target tiles with
pre-alloyed rare-earth impurity ions are formed. Pre-alloyed
targets can be formed either as metallic targets or ceramic
targets. Rare-earth doped material films can then be deposited on
substrate 16 of FIGS. 1A and 1B.
[0077] FIG. 3B shows a planar view of an embodiment of target 12
appropriate for an AKT-1600 system. Target 12 in FIG. 3B is
appropriate for ceramic targets according to the present invention.
Since tiles for metallic targets can be made larger in size, fewer
of them are required to form target 12 (for example, 9 instead of
20). Target 12 of FIG. 3B shows 20 tiles 30 mounted on backing
plate 25. Tiles 30 are cut and machined to appropriate shapes and
sizes for mounting on backing plate 25. In FIG. 3B, for example,
each of tiles 30 can be of dimension 134.53.times.145.05 mm, with
tiles 30 in the corner rounded with a radius R of 67.82 mm. The
separation between tiles is about 0.76 mm. The total target size is
about 675.70.times.582.48 mm. Target 12 in general can include any
number of tiles 30.
[0078] FIG. 4C shows an example of a waveguide amplifier deposited
with apparatus 10 utilizing a target according to the present
invention. A first cladding layer can be deposited on substrate 16
utilizing a target 12 with substantially no erbium content.
Substrate 16, in most cases, is a silicon substrate. An active core
40 can then be deposited and patterned to form a waveguide.
Deposition of the material layer to form the active core 40 can be
formed utilizing an erbium containing target 12 according to the
present invention. Finally, a second cladding layer 403 can be
formed over core 40. Both pump and signal light can be coupled into
core 402. First cladding layer 401 and second cladding layer 403
are often much thicker than core 402. The resulting amplified
signal can be measured as it exits core 402. The amplifier can be
described by its width W, thickness T and length L as is
illustrated in FIG. 4. Cladding layers 401 and 403 can be formed in
any fashion, for example as described in either of the '050
application or the '245 application. Core 402 is deposited
utilizing targets according to the present invention. Ceramic
Targets
[0079] FIG. 5 illustrates an embodiment of a method 500 to
manufacture of one of tiles 30 for target 12 according to the
present invention. The resulting target produced by the method
illustrated in FIG. 4 is a ceramic target.
[0080] In step 501, several oxide materials are mixed in a dry
mixing process. The oxide materials can include host oxides such as
SiO.sub.2 and Al.sub.2O.sub.3, for example, and rare earth oxides
such as Er.sub.2O.sub.3 and Yb.sub.2O.sub.3, for example. The
relative concentrations of materials can be tailored for the
particular film to be deposited on substrate 16 (FIG. 1A) with the
resulting target. In some embodiments, starting materials with
small particle sizes (a few microns or less) are utilized. In some
materials, de-agglomerated power (especially for Al.sub.2O.sub.3
and SiO.sub.2) to prevent cracking of the target due to
agglomerates can be utilized.
[0081] Higher rare earth concentrations, for example higher Er
concentrations, can result in better sintering of the resulting
ceramic tiles. However, the Er concentrations in the resulting
deposited layer on substrate 16 (FIG. 1A) will also be increased.
Erbium ion concentrations above a particular level may serve to
quench the gain of a resulting erbium amplifier based on the
deposited film. Through up-conversion processes and other dilatory
processes, pump radiation may be absorbed into processes that do
not contribute to amplification of signal light in the amplifier.
Up-conversion, for example, is a dipole-dipole processes which is
dependent on the sixth power of the separation between adjoining Er
pairs. The closer the Er ions are to each other, then, the larger
is the amount of up-conversion and the higher the required
pump-power to attain sufficient gain in a resulting amplifier. A
concentration of about 3.times.10.sup.20 atoms/cm.sup.3 uniformly
distributed in the deposited material results in an interatomic
separation between adjoining Er atoms of about 14 .ANG.. In
general, the interatomic separation is proportional to the cube
root of the inverse of the atomic concentration. As has been
discussed above, it is difficult to prevent the erbium ions to
cluster (i.e., forming either pairs or larger erbium groups). In
accordance with the present invention, target materials include
alloyed compounds of erbium, which helps to prevent the clustering
of erbium ions on deposition.
[0082] Typically, the oxide materials are high purity oxides
combined together in particular ratio compositions in order to
achieve the final target composition, which result in a particular
composition of deposited materials. In some embodiments, the oxide
materials are combined such that the mixed powder includes up to
about 10% by cation concentration of rare earth atoms. The combined
oxide materials are then mixed until the various oxide materials
are uniformly distributed throughout the mixed powder.
[0083] Any mixing method which uniformly mixes the powders can be
utilized in mixing step 501. In some embodiments, the oxide
materials are placed in a barrel mixer with mixing balls, for
example about 2 cm diameter zirconia balls, over a long period of
time, for example about 4 to about 24 hours, in order that each
constituent oxide material is uniformly distributed throughout the
resulting mix. The barrel mixer turns with the balls and the
combined material, evenly distributing each of the component
materials and breaking up any aggregation of component materials.
The zirconia balls can be filtered from the mixture after the
mixing process. Dry mixing can, for example, reduce the amount of
OH impurities present in the finished tile. Further, in some
embodiments dry mixing and utilization of oxide materials that do
not agglomerate (e.g., which have anti-agglomeration agents mixed
with the component materials) can be utilized. Aggregated
materials, for example, Al.sub.2O.sub.3 clusters, can cause weak
points in the target where the target may crack during use and
further can result in non-uniform material deposition.
[0084] Once the material is mixed in step 501, it is cold pressed
in step 502. In a typical cold pressing process, the mixed material
from step 501 is placed in a rubber mold of an appropriate size and
pressed at room temperature at a pressure sufficient to reduce the
density of the mixed material to about 50-60% that of the
theoretical density to form a green billet. In some embodiments, a
pressure higher than about 30 kpsi can be applied to form the green
billet.
[0085] In step 503, the green billet is degassed. In some
embodiments, the green billet is placed in a mild steel mold lined
with graphoil during de-gassing. For example, the green billet
formed from the specific mixture described above can be de-gassed
at a temperature above about 500 C in a vacuum (about 10.sup.-6
Torr) for a period of time, for example up to about 10 hours. In
some embodiments, de-gassing can also remove de-agglomerate agents
which may have been included with the starting powders, as well as
removing some contaminants, for example water, from the green
billet. Typical degass steps in conventional HIPing processes
utilize temperatures below about 400.degree. C. Therefore, the
method of forming target tiles 30 according to the present
invention involves a degas step significantly above that utilized
in conventional processes.
[0086] When de-gassing step 503 is complete, the green billet can
be hot-isostatically pressed (HIPed) in step 504, at high
temperature and high pressure to form the billet. The degassed
green billet is sealed into the mild steel mold and heated
subjected to conditions of high temperature and high pressure. In
one example, the tile is HIPed at a temperature less than about
1000.degree. C. and a pressure higher than about 20 Kpsi. The
billet is cooled very slowly to avoid cracking the billet. Cooling
over about a 2 day period may be necessary.
[0087] The combination of high temperature de-gas and hot isostatic
pressing results in a billet of material where rare-earth ions are
alloyed with the host materials. Erbium ions, for example, form
compounds of erbium, aluminum and oxygen. Ytterbium typically forms
compounds with silicon and oxygen. In deposition, therefore, erbium
ions are deposited on substrate 16 as part of the alloyed compound
rather than an independent atomic species, which is much more
likely to cluster with other erbium ions during deposition.
Clustering of erbium, for example, in deposition results in a
degraded performance of a resulting optical device. Relatively
little of the erbium and ytterbium remains unalloyed with the
alumina and silica of the ceramic materials. Low temperature
de-gassing has not been found to be effective in forming alloyed
billets of erbium and ytterbium.
[0088] In step 505, the billet is finished, which can involve
cutting to size and machining to final dimensions to form
individual tiles 30 as shown in FIG. 3A. Once the tile is formed,
it can be mounted on a target backing 25 as described with FIG. 3A
and provided as part of target 12 for use in apparatus 10. The
resulting tile has Erbium in solution with Aluminum with few to no
aggregates of Al.sub.2O.sub.3 or Er.sub.2O.sub.3 in the tile. In
addition, the resulting target tile includes substantially no
rare-earth oxides, with substantially all of the rare-Earths being
alloyed with the SiO.sub.2 or Al.sub.2O.sub.3. In most examples,
Er.sub.2O.sub.3 combines with Al.sub.2O.sub.3 form the alloyed
material ErAlO.sub.3 and Yb.sub.2O.sub.3 combines with SiO.sub.2 to
form Yb.sub.2Si.sub.2O.sub.7. Other alloyed compounds, for example
Er.sub.2SiO.sub.5, may also be formed. Substantially all of the
Er.sub.2O.sub.3 and Yb.sub.2O.sub.3 components have been alloyed in
the resulting tile. In some embodiments, some small concentration
of one of Er.sub.2O.sub.3 and Yb.sub.2O.sub.3 components may remain
in the tile.
[0089] In summary, predetermined relative concentrations of host
oxides and rare-earth oxides are mixed in step 501 such that each
of the individual components is uniformly distributed through the
powder. Mixing in a barrel mixer with zirconia balls for a time
greater than about 4 hours suffice to thoroughly mix the
constituents. The constituents, further, may be mixed with
anti-aggregation agents to aid in insuring the each of the
constituents are uniformly distributed. In some embodiments, the
constituent oxides can include SiO.sub.2, Al.sub.2O.sub.3,
Er.sub.2O.sub.3 and Yb.sub.2O.sub.3 in any relative concentrations
such that the erbium becomes prealloyed. In some embodiments, the
relative concentration of rare earths may be as high as about 10
cat. %.
[0090] Once mixed, the mixed powder is formed by CIPing. The formed
powder is then placed in a steel form and degassed in vacuum at a
temperature greater than about 500.degree. C. The steel container
is then sealed and the powder is HIPed at high temperature, e.g.
about 1000.degree. C., and at high pressure, e.g. about 30 Kpsi, to
form individual tiles 30. Several of the individual tiles 30 can
then be mounted on a backing 25 to form target 12.
[0091] In some embodiments, a pre-alloyed powder for a ceramic
target can be formed in an Al.sub.2O.sub.3 crucible by e-beam
melting of a solution of Al.sub.2O.sub.3, Er.sub.2O.sub.3,
Yb.sub.2O.sub.3, and SiO.sub.2, for example. For example, E-beam
evaporation of Silicon oxide and Erbium oxide using 2 e-beam guns
as been accomplished by the inventors. The process for evaporation
of a metal film usually includes either aluminum oxide and
molybdenum crucibles for holding and melting the starting
materials. A Molybdenum crucible was selected to hold the oxides
because molybdenum has a higher melting temperature than Aluminum
oxide. The deposited film of silicon oxide doped with erbium oxide
was characterized for photoluminescence and lifetime. The lifetime
is estimated to be about 1 ms. In order to increase the lifetime
and photoluminescence the solubility of Erbium oxide has to be
increased in a host like aluminum oxide. Therefore, if an aluminum
oxide crucible is utilized in the evaporation process, it is
expected that the erbium ions will pre-alloy with the crucible
material. The material in the crucible can then be crushed into a
powder for formation into tiles appropriate for a ceramic target by
HIPing.
[0092] High purity starting materials can be purchased from several
manufacturers. For example, SiO.sub.2 that is 99.99% pure and has a
particle size of between about 0.02 and about 0.55 microns can be
obtained from Pred Materials, New York, N.Y. Al.sub.2O.sub.3 that
is 99.999% pure and has an average particle size of about 0.49
microns can be obtained from Ceralox, Tucson, Ariz. Yb.sub.2O.sub.3
that is 99.99% pure and has a particle size of about 3 microns can
be obtained from Stanford Materials. Er.sub.2O.sub.3 that is
99.999% pure and has an average particle size of about 9 microns
can be obtained from Stanford Materials, Aliso Vlejo, Calif.
[0093] In some embodiments, targets formed in this fashion 6 can
include up to about 37% Al.sub.2O.sub.3, about 57.0% SiO.sub.2 or
less, about 2.5% of Er.sub.2O.sub.3 or less, and about 2.5% of
Yb.sub.2O.sub.3 or less.
[0094] Several specific examples of embodiments of targets with
ceramic tiles are discussed below. Further, examples of optical
amplifiers produced utilizing the ceramic tiles according to the
present invention are presented. These examples are provided for
illustrative purposes only and are not intended to be limiting.
EXAMPLE 1
[0095] One example embodiment of the invention utilizes starting
materials in the concentration of
SiO.sub.2/Al.sub.2O.sub.3/Er.sub.2O.sub.3/Yb.sub.- 2O.sub.3 being
57.5/37.5/2.5/2.5 cat % (the "2.5/2.5 target"). As described in
step 501, the oxide materials are combined in the proportion stated
above and mixed in a barrel mixer with 2 cm diameter zironcia balls
for between about 8 and 24 hours. As described in step 502, the
resulting mixture is poured into rubber pouches and cold pressed to
appropriate size for making tiles. In some embodiments, the
finished tile size is about 5.711.times.5.296.times.4 mm in size.
The cold pressing step reduces the density of the material to about
50 to 60% of the theoretical density to form the green tile. As
described in step 503, the green billet is then placed in a mild
steel mold which has been lined with non-stick graphite and
degassed in vacuum at about 650C for about 6 to 10 h. The green
billet is then sealed into the mild steel canister and HIPed at a
temperature of about 1000C and a pressure of about 28.5 Kpsi, as
described in step 504 to form a billet. In step 505, the billet is
cut and machined to the dimensions described above to form a
tile.
[0096] FIGS. 6A-6F shows x-ray diffraction spectrum taken from a
tile produced as described in this Example. As shown in FIGS. 6A
through 6F, the tile includes ErAlO.sub.3, Yb.sub.2Si.sub.2O.sub.7,
Er.sub.2SiO.sub.5, Yb.sub.2O.sub.3, Al.sub.2O.sub.3 and SiO.sub.2
but substantially no Er.sub.2O.sub.3. FIGS. 6A through 6F point out
the x-ray spectrum from ErAlO.sub.3, Yb.sub.2Si.sub.2O.sub.7,
Er.sub.2SiO.sub.5, Yb.sub.2O.sub.3, Al.sub.2O.sub.3 and SiO.sub.2.
In other words, all of the erbium has been alloyed with Aluminum
and Silicates. FIGS. 6G and 6H show EDX data (Electron Dispersion
Spectroscopy) which also show Er and Yb alloying with Al and Si
oxides.
[0097] The resulting tiles 30 formed in the above described
procedure can then formed on a backing 25 to form a ceramic target
12. Positioning about 20 of tiles 30 onto backing 20 results in a
target 12 with dimensions of about 675.70.times.582.48.times.4 mm
(neglecting the thickness of backing 25). Tiles 30 are mounted on
backing plate 25 as is described with FIG. 3.
[0098] Target 12 formed by this example can then be mounted in
apparatus 10 and utilized to form an optical amplifier layer.
Material from target 12 may be deposited onto a substrate held at
T=350C with an RF power at 13.56 MHz of 2000W and a sputtering gas
flow of 40 sccm of Ar. Substrate 16 is a silicon substrate. No bias
is applied to substrate 16 (i.e., substrate 16 is grounded) and no
lower frequency power is applied to target 12. The spacing betwee
substrate 16 and target 12 is 6 cm. The magnet is swept at a rate
of 4 s/scan.
[0099] A material layer of thickness about 0.8 .mu.m can then be
formed. The Er concentration, which can be verified by EDS
(electron dispersion spectroscopy) corresponds to about
7.times.10.sup.20 atoms/cm.sup.3 (which is the highest Er
concentration reported to date). Similarly, the Yb concentration
corresponds to about 7.times.10.sup.20 atoms/cm.sup.3.
[0100] For measurement purposes, the film deposited from target 12
can be etched to form an active core of about 5 .mu.m wide and
about 1.1 cm in length. A cladding layer can then be deposited over
the active waveguide. Substrate 16 is then annealed at 800 C for
about 30 min. Signal and pump light can be coupled into the active
core in order to measure amplifier parameters.
[0101] The core material has an as-deposited refractive index of
about 1.563, which becomes 1.5497 after annealing. The deposited
cladding layers 401 and 403 (see FIG. 4) have an index of 1.445.
The net Gain of the amplifier formed is about 2.8 dB/1.1 cm, which
corresponds to a gain of 2.5 dB/cm, at an internal pump power of
about 30 mW and wavelength of 980 nm and input signal power of
about -15 dBm and wavelength 1550 nm. The Er transition lifetime is
about 5 ms. The upconversion coefficient is about
1.4.times.10.sup.-17 cm.sup.3/s.
EXAMPLE 2
[0102] Another example embodiment of the invention utilizes
starting materials in the concentration of
SiO.sub.2/Al.sub.2O.sub.3/Er.sub.2O.sub- .3/Yb.sub.2O.sub.3 being
54.5/44.5/1.0/0.0 cat % (the "1/0 target"). The starting oxide
materials are the same as those described with Example 1. As
described in step 501, the oxide materials are combined in the
proportion stated above and mixed in a barrel mixer with 2 cm
diameter zironcia balls for between about 8 and 24 hours. As
described in step 502, the resulting mixture is poured into rubber
pouches and cold pressed to appropriate size for making tiles. In
some embodiments, the finished tile size is about
5.711.times.5.296.times.4 mm in size. The cold pressing step
reduces the density of the material to about 50 to 60% of the
theoretical density to form the green tile. As described in step
503, the green tile is then placed in a mild steel mold which has
been coated with non-stick graphite and degassed in vacuum at about
650C for about 6 to 10 h. The green tile is then sealed into the
mild steel canister and HIPed at a temperature of about 1000C and a
pressure of about 28.5 Kpsi, as described in step 504.
[0103] FIGS. 7A through 7D show x-ray diffraction data for this
example with the individual peaks for ErAlO.sub.3,
Er.sub.2SiO.sub.5, Al.sub.2O.sub.3, and SiO.sub.2, respectively,
identified. The target material according to this example includes
ErAlO.sub.3, Er.sub.2SiO.sub.5, Al.sub.2O.sub.3, and SiO.sub.2, but
substantially no Er.sub.2O.sub.3. Again, the erbium is completely
alloyed into the Al.sub.2O.sub.3 and SiO.sub.2 host with little to
no free Er.sub.2O.sub.3 present in the finished tile 30 for target
12.
[0104] The resulting tiles 30 formed in the above described
procedure can then formed on a backing 25 to form a ceramic target
12. Positioning about 20 of tiles 30 onto backing 20 results in a
target 12 with dimensions of about 675.70.times.582.48.times.4 mm
(neglecting the thickness of backing 25). Tiles 30 are mounted on
backing plate 25 as is described with FIG. 3.
[0105] Target 12 formed by this example can then be mounted in
apparatus 10 and utilized to form an optical amplifier layer.
Material from target 12 may be deposited onto a substrate held at
T=200 C with an RF power at 13.56 MHz of 2.5 kW and a sputtering
gas flow of 60 sccm of Ar. No bias is applied to substrate 16
(i.e., substrate 16 is grounded) and no lower frequency power is
applied to target 12. Separation between substrate 16 and target 12
is about 6 cm. The magnet is swept at a rate of about 4 s/scan.
[0106] A material layer of thickness about 1.17 .mu.m can then be
formed. The Er concentration, verified by EDS, corresponds to about
2.9.times.10.sup.20 atoms/cm.sup.3.
[0107] For measurement purposes, the film deposited from target 12
can be etched to form an active core about 5-6 .mu.m wide and about
1.6 cm in length. A cladding layer can then be deposited over the
active waveguide. The sample is then annealed at 725 C for 30 min.
Signal and pump light can be coupled into the active core in order
to measure amplifier parameters.
[0108] The net gain of the resulting amplifier is about 17 dB/20 cm
at an internal pump power of about 260 mW, pump wavelength of 976
nm and input signal of about -20 dBm at 1550 nm. The Er transition
lifetime is about 2.9 ms. The upconversion coefficient is about
4.5.times.10.sup.-18 cm.sup.3/s.
EXAMPLE 3
[0109] Another example embodiment of the invention utilizes
starting materials in the concentration of
SiO.sub.2/Al.sub.2O.sub.3/Er.sub.2O.sub- .3/Yb.sub.2O.sub.3 being
54.0/44.6/1.0/0.4 cat % (the "1/0.4 target"). The starting oxide
materials are the same as those described with Example 1. As
described in step 501, the oxide materials are combined in the
proportion stated above and mixed in a barrel mixer with 2 cm
diameter zironcia balls for between about 8 and 24 hours. As
described in step 502, the resulting mixture is poured into rubber
pouches and cold pressed to appropriate size for making tiles. In
some embodiments, the finished tile size is about
5.711.times.5.296.times.4 mm in size. The cold pressing step
reduces the density of the material to about 50 to 60% of the
theoretical density to form the green tile. As described in step
503, the green tile is then placed in a mild steel mold which has
been coated with non-stick graphite and degassed in vacuum at about
650C for about 6 to 10 h. The green tile is then sealed into the
mild steel canister and HIPed at a temperature of about 1000C and a
pressure of about 28.5 Kpsi, as described in step 504.
[0110] The resulting tiles 30 formed in the above described
procedure can then formed on a backing 25 to form a ceramic target
12. Positioning about 20 of tiles 30 onto backing 20 results in a
target 12 with dimensions of about 675.70.times.582.48.times.4 mm
(neglecting the thickness of backing 25). Tiles 30 are mounted on
backing plate 25 as is described with FIG. 3.
[0111] Target 12 formed by this example can then be mounted in
apparatus 10 and utilized to form an optical amplifier layer.
Material from target 12 may be deposited onto a substrate held at
T=350.degree. C. with an RF power at 13.56 MHz of 2.0 kW and a
sputtering gas flow of 60 sccm of Ar. Substrate 16 is biased with
about 100 W of 1.2 MHz RF power. The separation between substrate
16 and target 12 is about 6 cm. The magnet is swept at a rate of 4
s/scan. The formed amplifier is annealed at 800 C for 30
minutes.
[0112] A material layer of thickness about 1.2 .mu.m can then be
formed. The Er concentration, verified by erbium dispersion
spectroscopy, corresponds to about 2.9.times.10.sup.20
atoms/cm.sup.3.
[0113] For measurement purposes, the film deposited from target 12
can be etched to form active cores of between 2 and 5 .mu.m wide
and about 9.1 cm in length. A cladding layer can then be deposited
over the active waveguide. The sample can then be annealed at 800 C
for 30 minutes. As shown in FIG. 4, a bottom cladding layer 401 of
thickness approximately 15 .mu.m and a top cladding layer 403 of
approximately 10 .mu.m can be deposited.
[0114] Signal and pump light can be coupled into the active core in
order to measure amplifier parameters. The waveguide formed in this
manner can be double pumped (i.e., pumped forward and backward
through the waveguide) with a 976 nm pump at 250 mW in the forward
direction and a 974 nm pump at 147 mW in the backward direction.
The resulting gain is about 3.8 dB with a 1530 nm signal at input
power of -20 dB. The up-conversion constant for this deposited
layer is about 5.61.times.10.sup.-18 cm.sup.3/s and the lifetime of
the erbium states is about 3.29 ms.
Metallic Targets
[0115] Metallic targets tend not to be as brittle as the Ceramic
targets discussed above and therefore tiles 30 can be formed in
larger sizes. Metallic targets can also be utilized for higher
sputtering rates than ceramic targets. A fewer number of tiles 30,
therefore, may be necessary to form target 12. In addition, in some
embodiments metallic constituents can be plasma sprayed or flame
sprayed directly onto backing 25 with the necessity of forming
tiles 30 through the HIPing process.
[0116] FIG. 8A shows an embodiment of a method 800 of fabricating
one of tiles 30 of target 12 according to the present invention. In
step 801, constituent powders are pre-alloyed in an atomization
process. In some embodiments, rare earth ions are alloyed with
aluminum, for example. In an atomization process, liquid is broken
up into fine drops. The desired metal composition of host with
rare-earth material (e.g., aluminum with erbium and ytterbium) is
inserted into a vacuum induction furnace and brought to a
temperature of about 1500.degree. C. The molten material is then
poured into a tundish where it is rapidly cooled by argon flow. A
solid powder is formed which has compounds of the rare-earth
components with the host material.
[0117] In general, metallic targets can be formed with a
combination of any metallic or semiconductor material and rare
earths. For example, target 12 can have any composition and can
include ions other than Si, Al, Er and Yb, including: Zn, Ga, Ge,
P, As, Sn, Sb, and Pb and rare earths Ce, Pr, Nd, Pm, Sm, Eu, Gd,
Tb, Dy Ho, Er, Tm Yb and Lu.
[0118] In step 802, the pre-alloyed powder can be mixed. Further,
other component materials such as, for example, Si can be added
during step 802. In some embodiments, the constituent powders are
mixed in a barrel mixer for some time, for example between 2 and 8
hrs, with large (about 2 cm diameter) zirconia balls.
[0119] In some embodiments, the mixed power formed in step 802 can
include up to about 35% of Al, about 65% Si or less, about 1.0% of
Er or less and about 1.0% Yb or less.
[0120] Since the packing density of metallic powders is in general
higher than ceramic powders, no CIPing process is required with
metallic targets. However, some embodiments of the invention may
include a separate CIPing step similar to that described in the
formation of ceramic targets according to the present
invention.
[0121] In step 803, the material is degassed in vacuum. In some
embodiments of the process, the mixed powder is placed into a mild
steel canister lined with graphoil and heated in a vacuum. In some
embodiments, the degass process occurs at a temperature of about
400 C at a pressure of about 10.sup.-6 Torr range. In step 804, the
mild steel canister can be sealed in vacuum and the material HIPed
at low temperature to form a billet In some embodiments, HIPing can
be performed at temperatures above about 450 C and pressures above
about 15 Kpsi for longer than about 1 hour. If, after HIPing step
904, the billet is cooled too slowly, the billet may be
non-alloyed. Therefore, the billet should be cooled in a time less
than about 5 hours to avoid Er precipitation. Note that cooling too
fast may result in cracking of the billet. The billet is typically
cooled to room temperature in about 2 to 3 hours.
[0122] In step 805, the billet can be cut and machined to form
tiles 30. In some embodiments, tiles 30 of the size
213.91.times.182.91.times.4 mm are produced. Tiles 30 according to
this embodiment can be formed into target 12 as is described with
FIG. 3.
[0123] Pre-alloying of tiles 30 can be shown with x-ray diffraction
data taken on powders formed by the prealloying step 801 of method
800. In embodiments where Er and Yb are prealloyed with Al in step
801, x-ray diffraction data typically shows Al.sub.3Er, Al.sub.3Yb,
and Al in the powder before mixing with a very small to
substantially no concentration of free Er. In some embodiments, the
alloyed powder from step 801 is mixed with Si in step 902 in order
that the final powder mixture is appropriate for the material. In
some embodiments, total rare-earth ion concentrations are up to
about 5 cat %. The resulting deposited material layer, then, has a
uniform distribution of Er and, because aggregates are reduced,
target 12 can be longer lasting.
[0124] Rare earth elements can be obtained from Stanford Materials,
Aliso Vlejo, Calif. Ceram Research can provide Aluminum of the
appropriate purity. Si powder can be provided from Noah
Technologies Corporation, San Antonio, Tex.
[0125] The overall purity of materials can be approximately 99.99%
pure. Special care can be taken to reduce the concentration of
transition metals included, for example to no more than a few ppm
and the concentration of hydrogen. Both transition metals and OH
impurities in target 12 can act as photoluminesance quenchers,
which detract from the performance of an amplifier produced with
target 12.
[0126] FIG. 8B shows another method 910 of forming target 12.
Instead of producing tiles 30 and mounting tiles 30 onto backing 25
as is described with respect to FIG. 3A, the mixed powder can be
plasma sprayed directly onto backing 25. In method 810, powder
pre-alloy 801 and mixing 802 are the same as in method 800 of FIG.
8A. In step 813, however, the mixed powder is plasma sprayed in an
inert atmosphere directly onto backing plate 25. In some
embodiment, the resulting coating on backing plate 25 can be as
thick as about 1.5 mm and as dense as about 95% of the theoretical
density. Method 810 of FIG. 8B may be a very fast and simple
process for forming metallic targets without the need for tiles.
Another advantage is an extremely fast cooling rate, which avoids
erbium precipitation from the intermetallics during cooling.
EXAMPLE 4
[0127] A target tile with composition Si/Al/Er/Yb being
57.4/41.0/0.8/0.8 cat % (the "0.8/0.8 target") can be produced by
the above method. The proper proportional amounts of Al, Er and Yb
powder are placed in the vacuum induction furnace in step 801 and
heated to about 1500.degree. C. The atomized powder is mixed with
the proper proportional amount of Si in mixing step 802. The
powders are mixed in a barrel mixer for about 4 hours with large
zironcia balls (approximately 2 cm in diameter). In step 802, the
mixed powder is poured into a rubber mold of the right size to
produce finished tiles of the size 213.91.times.182.91.times.4 mm.
Nine (9) such tiles will form a target for apparatus 10 of FIG. 1A.
The formed powder is inserted into a mild steel canister and
degassed at about 400 C in a vacuum (about 10.sup.-6 Torr) in step
803. The degassed tile is then sealed into the steel canister and
HIPed at low temperature and high pressure (about 600 C at 20 Kpsi
for about 4 hours) to form billets. The billets are then cut and
machined to size in setp 805. The individual tiles 30 are mounted
as is described with FIG. 3A to form target 12.
[0128] FIG. 9 shows an x-ray diffraction spectrum of the atomized
powder before mixing step 902 is performed. As is shown in FIG. 10,
compounds of YbAl.sub.3, Al.sub.3Er, and Al are present but
substantially no free Er or Yb are observed. This shows that
virtually all of the rare-earth compounds are alloyed with the
aluminum during the atomization process. Target 12 produced
according to this example results in Yb--Al, Er--Al, Yb--Si, and
Er--Si alloys but found substantially no free Er.
[0129] In formation of an amplifier utilizing target 12 of this
Example, an undercladding layer 401 is deposited with about 10
.mu.m thickness, then a layer can be deposited utilizing target 12
according to this example and patterned to form a core 402. Then a
second cladding layer of about 10 .mu.m thickness 403 is formed
over core 402. The amplifier can then be annealed at about 725 C
for about 30 min.
[0130] A film of material from which core 402 can be formed can be
deposited in apparatus 10 using the 0.8/0.8 target as target 12. A
pulsed DC power is applied through power supply 15 to the target.
About 6 KW of 120 KHz pulsed DC power is supplied. Substrate 16 is
biased with about 100 W of 2 MHz frequency power. An argon gas flow
at 60 sccm and an oxygen gas flow at about 28 sccm is supplied to
reactor apparatus 10. The deposited layer can be of any thickness,
for example 1.1 .mu.m
[0131] FIG. 10B shows an SEM of a cross section of a 3.5 .mu.m wide
waveguide formed utilizing target 12 according to this Example and
the deposition process described above. FIG. 10B shows core 402
deposited with target 12 according to the present Example and
cladding layers 401 and 402. Core 402 is deposited at a 1.1 .mu.m
thickness.
[0132] The deposition results in an erbium and ytterbium
concentrations of about 2.3.times.10.sup.20 cm.sup.-3. The
resulting up-conversion coefficient is 5.times.10.sup.-18
cm.sup.3/s and the erbium excited state lifetime is about 3 ms. At
an internal pumping power of about 200 mW at a wavelength of 982 nm
and with an input signal of about -28 dBm, the internal gain across
the C-band is aobut 8.9 dB for a 10.1 cm amplifier produced
according to this example. The power level of 1060 nm signal light
in FIG. 10C is about -25 dB and the power level of signal light in
FIG. 10D is 0 dB.
EXAMPLE 5
[0133] A target tile with composition Si/Al/Er/Yb being
57.4/41.0/1.5/0.0 cat % (the "1.5/0.0 target") can be produced by
the above method. The proper proportional amounts of Al, and Er
powder are placed in the vacuum induction furnace in step 801 and
heated to about 1500.degree. C. The atomized powder is mixed with
the proper proportional amount of Si in mixing step 802. The
powders are mixed in a barrel mixer for about 4 hours with large
zironcia balls (approximately 2 cm in diameter). In step 803, the
mixed powder is poured into a rubber mold of the right size to
produce finished tiles of the size 213.91.times.182.91.times.4 mm
and degassed at about 400 C in a vacuum (about 10.sup.-6 Torr). In
step 804, the degassed billet is then sealed into the steel
canister and HIPed at low temperature and high pressure (about 600
C at 20 Kpsi for about 4 hours) to form a billet. In step 805, the
billets are cut and machined to size to form a tile. The individual
tiles 30 are mounted as is described with FIG. 3 to form target
12.
[0134] FIG. 10 shows x-ray diffraction data of the power formed in
step 802 of this example. The x-ray diffraction data shows the
existence of Er.sub.xSi.sub.y and Er.sub.xAl.sub.y alloys with Al
and Si.
[0135] In producing an amplifier waveguide, an under cladding layer
401 is first deposited. The under cladding layer is of thickness
around 10 .mu.m. Then a layer of material utilizing target 12 of
the present example is deposited and patterned to form a core 402.
Finally, an upper cladding layer of thickness around 10 .mu.m is
deposited. The cladding layers can be deposited in any fashion, for
example as is described in the '050 application or the '245
application.
[0136] The material layer utilized for forming core 402 is, in this
example, deposited using the 1.5/0 target described above. Six (6)
KW of pulsed DC power at 120 KHz is applied to target 12. The
reverse pulsing time is 2.3 .mu.s. One hundred (100) watts of bias
power at 2 MHz bias frequency is supplied to substrate 16. Gas
flows of 60 sccm of Ar and 28 sccm of oxygen is flowed through the
reaction chamber of apparatus 10. The amplifier is annealed at a
temperature of 725 C for 30 min.
[0137] The up conversion constant Cup is measured to be about
8.0.times.10.sup.-18 cm.sup.3/s with a lifetime at 1530 nm is about
1.55 ms. The internal gain across the C-band is about 13.7 dB in a
10.1 cm waveguide double pumped with 978 nm light at an internal
pumping power of around 150 mW. The erbium concentration is about
4.5.times.10.sup.20/cm.s- up.3.
[0138] The examples and embodiments discussed above are exemplary
only and are not intended to be limiting. One skilled in the art
can vary the processes specifically described here in various ways.
Further, the theories and discussions of mechanisms presented above
are for discussion only. The invention disclosed herein is not
intended to be bound by any particular theory set forth by the
inventors to explain the results obtained. As such, the invention
is limited only by the following claims.
* * * * *