U.S. patent application number 08/959633 was filed with the patent office on 2001-07-05 for interference layer system.
Invention is credited to BRAUER, GUNTER, SZCZYRBOWSKI, JOACHIM.
Application Number | 20010006148 08/959633 |
Document ID | / |
Family ID | 7810208 |
Filed Date | 2001-07-05 |
United States Patent
Application |
20010006148 |
Kind Code |
A1 |
SZCZYRBOWSKI, JOACHIM ; et
al. |
July 5, 2001 |
INTERFERENCE LAYER SYSTEM
Abstract
A process is provided for sputter-induced precipitation of metal
oxide layers on substrates by means of a reactive sputter process.
The plasma charge acting upon the target to be evaporated is
provided with electric power selected such that the metal oxide
layers precipitated on the substrates to be coated are deposited at
a precipitation rate of .gtoreq.4 nm/s. During the coating process
the substrate to be coated is arranged stationary in relation to
the target material to be evaporated. The electrodes are connected
in a conductive manner to the outputs of an alternating current
source whereby the alternating frequency of the alternating current
provided for the electrical supply of the plasma discharge is
selected between 10 kHz and 80 kHz. Particularly preferred is that
the precipitated oxide layer is a TiO.sub.2 layer or an SiO.sub.2
layer.
Inventors: |
SZCZYRBOWSKI, JOACHIM;
(GOLDBACH, DE) ; BRAUER, GUNTER; (FREIGERICHT,
DE) |
Correspondence
Address: |
FULBRIGHT & JAWORSKI, LLP
666 FIFTH AVE
NEW YORK
NY
10103-3198
US
|
Family ID: |
7810208 |
Appl. No.: |
08/959633 |
Filed: |
October 28, 1997 |
Current U.S.
Class: |
204/192.26 ;
204/192.12; 204/192.15; 204/192.22; 204/192.29 |
Current CPC
Class: |
C03C 2217/212 20130101;
C23C 14/10 20130101; C03C 17/366 20130101; C03C 2218/156 20130101;
C03C 17/2456 20130101; C23C 14/083 20130101; C03C 17/36 20130101;
C23C 14/3471 20130101; C03C 2217/734 20130101; C23C 14/0036
20130101; C03C 2218/155 20130101 |
Class at
Publication: |
204/192.26 ;
204/192.12; 204/192.15; 204/192.22; 204/192.29 |
International
Class: |
C23C 014/34 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 28, 1996 |
DE |
196 44 752.6 |
Claims
What is claimed is:
1. Process for sputter-induced precipitation of metal oxide layers
on substrates by means of a reactive sputter process, characterized
in that the plasma charge acting upon the target to be evaporated
is provided with electric power selected such that the metal oxide
layers precipitated on the substrates to be coated are deposited at
a precipitation rate of .gtoreq.4 nm/s, whereby during the coating
process the substrate to be coated is arranged stationary in
relation to the target material to be evaporated.
2. Process for sputter-induced precipitation of metal oxide layers
on substrates by means of a reactive sputter process, characterized
in that the oxide layers to be precipitated on the substrate to be
coated are deposited at a precipitation rate of .gtoreq.40 nm
m/min, whereby the substrate to be coated is moved along in front
of the target material to be evaporated.
3. Process according to claim 1 or 2, characterized in that the
electrodes are connected in a conductive manner to the outputs of
an alternating current source whereby the alternating frequency of
the alternating current provided for the electrical supply of the
plasma discharge is selected between 10 kHz and 80 kHz.
4. Process according to at least one of the claims 1 to 3,
characterized in that the precipitated oxide layer is a TiO.sub.2
layer or an SiO.sub.2 layer.
5. Optical-effect layer system, arranged on substrate surfaces and
produced according to at least one of the preceding claims, which
layer system exhibits an order of layers composed of alternating
low refractive and high refractive layers, where the individual
oxide layers are precipitated on the substrate surfaces to be
coated by means of a sputter-induced evaporation and precipitation
process carried out in a vacuum chamber and where the sputter
plasma is supplied by alternating current fed to the plasma
electrodes, characterized in that the predominant part of the oxide
layer exhibits a rutile structure.
6. Layer system according to claim 5, characterized in that the
metal oxide layers are deposited at a precipitation rate of >4
nm/s on the target which is arranged stationary in relation to the
sputter cathode.
7. Layer system according to claim 5, characterized in that the
oxide layer is an SiO.sub.2 layer which is deposited at a
precipitation rate of >5 nm/s on the substrate which is arranged
stationary, preferably spatially secure in relation to the sputter
cathode.
8. Layer system according to at least one of the claims 5 through
8, characterized in that the alternating frequency of the
alternating current fed to the sputter electrode lies between 10
kHz and 80 kHz.
9. A process for sputter-induced precipitation of metal oxide
layers on substrates by means of a reactive sputter process, said
process comprising: providing a target to be evaporated and
creating a plasma charge thereabout; providing electric power to
the plasma charge acting upon the target to be evaporated, said
electric power being selected such that the metal oxide layers
precipitated on the substrate to be coated are deposited at a
precipitation rate greater than or equal to 4 nm/s; and maintaining
the substrate to be coated in stationary relation to the target
material to be evaporated during the coating process.
10. A process for sputter-induced precipitation of metal oxide
layers on substrates by means of a reactive sputter process, said
process comprising: providing a target material for said sputter
process; depositing the oxide layers to be precipitated on the
substrate to be coated at a precipitation rate greater than or
equal to 40 nm m/min; and moving the substrate to be coated along
in front of the target material to be evaporated.
11. Process according to claim 9, wherein electrodes are connected
in a conductive manner to outputs of an alternating current source
whereby the alternating frequency of the alternating current
provided for the electrical supply of the plasma discharge is
selected between 10 kHz and 80 kHz.
12. Process according to claim 10, wherein electrodes are connected
in a conductive manner to outputs of an alternating current source
whereby the alternating frequency of the alternating current
provided for the electrical supply of the plasma discharge is
selected between 10 kHz and 80 kHz.
13. Process according to claim 9, wherein the precipitated oxide
layer is a TiO.sub.2 layer or an SiO.sub.2 layer.
14. Process according to claim 10, wherein the precipitated oxide
layer is a TiO.sub.2 layer or an SiO.sub.2 layer.
15. Process according to claim 11, wherein the precipitated oxide
layer is a TiO.sub.2 layer or an SiO.sub.2 layer.
16. Process according to claim 12, wherein the precipitated oxide
layer is a TiO.sub.2 layer or an SiO.sub.2 layer.
17. An optical-effect layer system comprising: a substrate having a
surface; a plurality of oxide layers applied successively over said
surface according to the process of claim 9; the layers being
applied to the substrate surface in an order such that the layers
alternate between being low refractive layers and high refractive
layers; the individual oxide layers being precipitated on the
substrate surface by means of a sputter-induced evaporation and
precipitation process carried out in a vacuum chamber, and wherein
sputter plasma is supplied alternating current fed to plasma
electrodes; the oxide layer having a predominant part having a
rutile structure.
18. A layer system according to claim 17, wherein the metal oxide
layers are deposited at a precipitation rate greater than 4 nm/s on
the target which is arranged stationary in relation to the sputter
cathode.
19. A layer system according to claim 17, wherein the oxide layer
is an SiO.sub.2 layer which is deposited at a precipitation rate
greater than 5 nm/s on the substrate which is arranged stationary
in relation to the sputter cathode.
20. A layer system according to claim 17, wherein the alternating
frequency of the alternating current fed to the sputter electrode
lies between 10 kHz and 80 kHz.
21. An optical-effect layer system comprising: a substrate having a
surface; a plurality of oxide layers applied successively over said
surface according to the process of claim 10; the layers being
applied to the substrate surface in an order such that the layers
alternate between being low refractive layers and high refractive
layers; the individual oxide layers being precipitated on the
substrate surface by means of a sputter-induced evaporation and
precipitation process carried out in a vacuum chamber, and wherein
sputter plasma is supplied alternating current fed to plasma
electrodes; the oxide layer having a predominant part having a
rutile structure.
Description
FIELD OF THE INVENTION
[0001] The invention relates to a method for sputter-induced
precipitation of metal oxide layers on substrates by means of a
reactive sputter process and also to a layer system produced
according to such a method.
DESCRIPTION OF THE PRIOR ART
[0002] Methods of manufacture of this kind and single-layer systems
manufactured according to this process are known. By means of a
sputter device as described for example in U.S. Pat. No. DE
4,106,770, substrates are coated by means of cathode sputtering,
preferably by magnetron cathode sputtering, where so-called targets
are exposed to the action of a plasma cloud which forms between two
electrodes, and where the evaporated target material which shows
affinity to the reactive gas, forms a chemical bond with the gas
and precipitates upon the substrate. In the known sputter methods
the target is for example the one electrode and the substrate the
other electrode which is connected electrically to both outputs of
an electric power supply device. As an alternative, so called
double electrodes are also used, which electrodes are alternately
switched as anode and cathode. Electric power is supplied to the
electrodes either as direct current or as alternating current, as
described for example in DE OS 3,802,852.
[0003] For precipitation of dielectric layers such as for example
SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2, TiO.sub.2, ZnO.sub.2, the
target to be evaporated is composed of the corresponding metal
components present in the above compounds and is acted upon by the
plasma cloud composed for example of Ar/O.sub.2 or Ar/N.sub.2 mix,
which action evaporates the metal target.
[0004] A problem long known in the use of the generic sputter
methods has been to provide homogenous and uniformly composed
layers of high optical quality reproducible for industrial use.
Thus dielectric layers such as for example SiO.sub.2,
Al.sub.2O.sub.3, or especially TiO.sub.2, deposited for example by
the DC sputter method on glass surfaces or optical components, have
shown less than the desired resistance to environmental conditions,
such as for example humidity acting upon the layers. Sputter and
coating techniques realized by means of the DC sputter method
additionally cause in a disadvantageous manner long and therefore
expensive coating times during which the process parameters
defining the coating process must be held constant. In addition,
the optical properties of layer systems produced using conventional
sputter methods have proved inadequate increasingly exacting
requirements.
SUMMARY OF THE INVENTION
[0005] An object of the present invention is to provide a method of
sputter-induced production of metal oxide layers on substrates by
means of a reactive sputter process through which metal oxide
layers of high optical quality can be made available for industrial
manufacture in a reproducible and cost-efficient manner.
[0006] According to the invention, the object is accomplished by a
method of this kind as mentioned in the introduction according to
claim 1 in that electric power is applied to the plasma charge
acting upon the sputter target to be evaporated by means of at
least two electrodes arranged in the vicinity of each other in the
plasma reaction space, and where electric power is selected such
that oxide layers to be precipitated on the substrate to be coated
are deposited at a coating rate of >4 m/s, whereby during the
coating process the substrate to be coated is arranged stationary
in relation to the target material to be evaporated. A coating rate
of >40 nm m/min is proposed for substrates which during the
coating process are to be moved in front of the sputter target as
in so-called continuous systems. Metal oxide layers produced
according to the method characteristics of claim 1 or claim 2
exhibit, surprisingly enough, several advantages vis--vis metal
oxide layers produced by conventional sputtering. Thus it was found
that TiO.sub.2 layers produced according to the invention had a
refractive index n between 2.55 and 2.60. Conventional DC technique
only produced n values between 2.35 and 2.45. Metal oxide layers
having a high n value advantageously allow a thinner metal oxide
layer than one produced by conventional methods in order to achieve
an effect dependent on the refractory value. In addition, thinner
metal oxide layers have the advantage of high light transmission
and color neutrality in the visible spectrum. Moreover, thin metal
oxide layers can be produced more cost-effectively than
conventional metal oxide layers.
[0007] Layers produced according to the invention also
advantageously exhibit a very smooth surface, as indicated in claim
5. Surface structure morphology of metal oxide layers produced
according to the invention exhibits a very compact crystalline
definition which demonstrates high resistance to chemically
reactive substances. Metal oxide layers produced according to the
invention are correspondingly more resistant to the effects of
humidity than conventional sputter layers produced for example by
means of a plasma discharge. Furthermore it was found that by using
sputter plasma operated with alternating current the precipitated
TiO.sub.2 layers crystallized primarily in a rutile structure.
Contrary to the anatase structure of the TiO.sub.2 layer which
primarily forms in DC sputter process, the rutile structure is
temperature-stable up to 1855.degree. C., while the anatase
structure undergoes a phase conversion at 642.degree. C. and
exhibits an unstable structure. It has been further shown that
given equal plasma output, the process according to the invention
achieves a sputter rate about 6 to 7 times higher than that of
conventional DC sputter process.
[0008] Metal oxide layers produced according to the invention can
also be used for improved low-E layer systems and for so-called
solar-control systems with improved optical properties. In the case
of low E layers the possibility is created advantageously to forgo
tin as the target material in favor of economical titanium. Since
SnO.sub.2 layers produced by the sputter process disadvantageously
tend to develop islands, it is desirable to substitute TiO.sub.2
for SnO.sub.2. In the case of low-E layer systems the base layer
applied directly on the substrate exhibits according to the
invention a smooth and compact surface structure onto which the
actual low E layer is applied, for example a silver or gold layer.
Morphology of the base layer produced according to the invention
also advantageously promotes the forming of an applied metal layer
which exhibits high conductivity or a low k value,
respectively.
[0009] It has been shown to be advantageous for the production of
layers according to the invention to select a frequency of the
alternating current supplying the sputter plasma between 10 kHz and
80 kHz, as indicated in claim 8.
[0010] Additional advantageous features of the method and possible
uses of metal oxide layers according to the invention are
characterized in more detail in the subclaims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The invention includes various possible embodiments. Several
especially advantageous exemplary emdodiments are represented in
the drawings and are described in more detail below.
[0012] There are shown in
[0013] FIG. 1a Scanning electron microscope image of the surface of
a TiO.sub.2 layer produced according to prior art, viewed at an
angle;
[0014] FIG. 1b enlarged portion of the TiO.sub.2 layer shown in
1a;
[0015] FIG. 2 an X-ray diffraction spectrum of the TiO.sub.2 layer
shown in 1a, 1b;
[0016] FIG. 3a a scanning microscope image of a TiO.sub.2 layer
applied at a dynamic coating rate of 21 nm m/min and a viewing
angle of 60.degree. in relation to the normal of the surface;
[0017] FIG. 3b a scanning microscope image of a cross-section of
the TiO.sub.2 layer shown in 3a;
[0018] FIG. 4 an X-ray diffraction spectrum of the TiO.sub.2 layer
shown in 3a, 3b;
[0019] FIG. 5a a scanning microscope image of a TiO.sub.2 layer
applied at a dynamic coating rate of 37 nm m/min;
[0020] FIG. 5b a scanning microscope image of a cross-section of
the TiO.sub.2 layer shown in 5a;
[0021] FIG. 6 an X-ray diffraction spectrum of the TiO.sub.2 layer
shown in 5a, 5b;
[0022] FIG. 7a a scanning microscope image of a TiO.sub.2 layer
applied by reactive sputter at a layer growth rate of 49 nm
m/min;
[0023] FIG. 7b a scanning microscope image of a cross-section of
the TiO.sub.2 layer shown in 7;
[0024] FIG. 8 an X-ray diffraction spectrum of the TiO.sub.2 layer
shown in 7a, 7b;
[0025] FIG. 9 the characteristic curve of a high output DC
cathode;
[0026] FIG. 10 the characteristic curve of a dual magnetron cathode
and
[0027] FIG. 11 output curve and sputter rate measured as a function
of the probe voltage for a sputter process according to the
invention.
DETAILED DESCRIPTION
[0028] A TiO.sub.2 layer 4, 6 produced by conventional DC sputter
method in shown in FIGS. 1a and 1b in various enlargements of a
scanning microscope image. The TiO.sub.2 layer is applied on an Si
wafer 2 and exhibits a layer thickness of approximately 500 nm. The
TiO.sub.2 layer 4,6 grown by means of reactive DC magnetron
sputtering with addition of an Ar/O.sub.2 gas mixture consists of
single columnar microcrystallites which are arranged substantially
parallel to each other on the substrate. The surface of the
TiO.sub.2 layer 4, 6 possesses a pronounced surface roughness. The
X-ray crystallographic analysis of the TiO.sub.2 layer 4, 6 shown
in FIGS. 1a, 1b is represented as a Debye-Scherer diagram in FIG.
2. Diffraction reflexes A.sub.1, A.sub.2 and A.sub.3 which dominate
in FIG. 2 are characteristic of the anatase structure of TiO.sub.2.
Accordingly, reflex A.sub.1 represents grid net planes assigned to
the anatase structure 101 and fulfilling the Bragg reflexion
conditions, reflex A.sub.2 those of anatase structure 004, and
reflex A.sub.3 those of anatase structure 112.
[0029] A TiO.sub.2 layer produced by means of a reactive sputter
process with a coating rate of 21 nm m/sec as proposed according to
the invention is shown in FIGS. 3a and 3b. TiO.sub.2 layer 14 (see
FIG. 3b) has a thickness of about 500 nm and in comparison to the
layer structure shown in FIG. 1b, exhibits only weakly defined and
locally limited columnar TiO.sub.2 microcrystallites. Surface 16
shown in FIG. 3a exhibits in places surface sites which have only a
small depth of roughness. The crystalline composition of TiO.sub.2
layer 14 shown in FIGS. 3a, 3b, applied to a glass substrate, is
evident in the Debye-Scherrer diagram (FIG. 4), which, beside the
known anatase 101 structure (A.sub.1), also shows the diffraction
reflex R.sub.1, which corresponds to the Bragg reflection in a 110
grid net plane of a TiO.sub.2 layer crystallized in a rutile
structure. The rutile structure therein corresponds to the areas of
low surface roughness appearing in FIG. 3a, while in contrast, the
anatase 110 structure corresponds to the island formations
appearing in FIG. 3a.
[0030] A TiO.sub.2 layer 24, 26, applied to a glass substrate with
a application rate of 37 nm m/min is shown in FIG. 5a. In
comparison to TiO.sub.2 surfaces 14, 4, 6 shown in FIG. 3a and FIG.
1a, only occasional micro-crystalline island formations appear with
the higher coating rate. Column formations corresponding to the
micro-crystalline island formations are no longer present in the
cross-sectional view shown in FIG. 5b. This result is also
confirmed by the corresponding X-ray diffraction spectrum (see FIG.
6). Accordingly, in the corresponding I(2.theta.) diagram, the
rutile structure clearly dominates vis--vis the competing anatase
101 structure.
[0031] An even stronger definition of the rutile structure can be
seen in FIGS. 7a and 7b. The TiO.sub.2 layer, with a thickness of
approximately 500 nm, applied on a glass substrate, is composed
almost entirely of rutile structures, as can be deduced from the
corresponding X-ray diffraction spectrum in FIG. 8 on the basis of
the rutile 110 reflex which is the only one present. Surface 36 of
the TiO.sub.2 layer, applied at a rate of 49 nm m/min, is nearly
homogeneously smooth and exhibits only occasional island formations
38. Microcrystalline anatase structures which form columns during
growth are no longer visible in the cross-section shown in FIG.
7b.
[0032] The substantial difference between reactive sputter process
according to prior art and the proposed sputter process according
to the invention follows from the comparison of the course of the
respective characteristic curves of the cathode of a DC sputter
process (see FIG. 9) and a AC sputter process (FIG. 10). FIG. 9
shows the characteristic curve of a high output cathode supplied
with direct current, into which cathode a titanium target is
integrated. What is shown is the total pressure in the sputter
chamber as a function of the O.sub.2 gas volume M flowing into the
plasma reaction space. The p(M) curve exhibits a hysteresis loop
between working points M.sub.1 and M.sub.2. Two sputter conditions
for the DC cathode are possible in the transitional area between
the points M.sub.1 and M.sub.2, i.e. a metallic one which will
proceed along route W.sub.1, and an oxide sputter condition which
is present if following the hysteresis loop in the direction
W.sub.2. A cathode supplied with direct current uncontrollably
jumps between the two modes in the transitional area between the
points M.sub.1 and M.sub.2. Due to the broad transitional area of
the hysteresis loop of the p(M) curve shown in FIG. 9, stable
sputter conditions needed for high-quality metal oxide layers can
only be achieved with the help of expensive process control
devices. To achieve maximum sputter rates with a high output DC
cathode, a value of the oxygen volume supply is sought in the
M.sub.1 area, for the selection of the sputter working point, where
the metal oxide layers can be produced in the oxide mode.
[0033] FIG. 10 shows the characteristic curve of a high output
magnetron cathode supplied with alternating current, according to
the invention. The figure clearly shows that the transitional area
between the working points M.sub.3 and M.sub.4 has a width of only
10 sccm and is therefore narrower by a factor of 7 than in the case
of conventional sputter process (see FIG. 9):
[0034] FIG. 11 shows measured sputter rates Y.sub.sp and cathode
output L at a constant oxygen supply of 120 sccm as a function of
probe voltage U.sub.s for a sputter process according to the
invention. According to the measuring process a higher probe
voltage U.sub.s corresponds to a lower oxygen proportion in the
sputter chamber. It can be observed that the higher the probe
voltage U.sub.s, the more metallic the burning of the cathode. The
sputter rate rises advantageously with falling oxygen volume and at
the same time the cathode output falls (see curve run A). An oxygen
sensor serves for the regulation of the sputter process, which
sensor provides the probe voltage U.sub.s as an actual value
assigned to a control circuit. FIG. 11 shows that rising sputter
rates Y.sub.sp are realized with a smaller cathode output L. This
significantly increases the efficiency of the sputter arrangement
according to the invention.
* * * * *