U.S. patent application number 12/202511 was filed with the patent office on 2009-01-08 for increasing an electrical resistance of a resistor by nitridization.
Invention is credited to Arne W. Ballantine, Daniel C. Edelstein, Anthony K. Stamper.
Application Number | 20090011526 12/202511 |
Document ID | / |
Family ID | 24861914 |
Filed Date | 2009-01-08 |
United States Patent
Application |
20090011526 |
Kind Code |
A1 |
Ballantine; Arne W. ; et
al. |
January 8, 2009 |
INCREASING AN ELECTRICAL RESISTANCE OF A RESISTOR BY
NITRIDIZATION
Abstract
A method for increasing an electrical resistance of a resistor.
A semiconductor structure that includes the resistor is placed in a
chamber that includes a gas including nitrogen-containing molecules
at an nitrogen concentration. A fraction F of an exterior surface
of a surface layer of the resistor is exposed to the
nitrogen-comprising molecules. A portion of the surface layer is
heated at a heating temperature. A combination of the nitrogen
concentration and the heating temperature is sufficient to
nitridize the portion of the surface layer by reacting the portion
with the nitrogen-containing molecules. Heating the portion of the
surface layer includes directing a beam of radiation or particles
into the portion of the surface layer heat the portion of the
surface layer. The portion of the surface layer is nitridized by
being reacted with the nitrogen-containing molecules such that an
electrical resistance of the resistor is increased.
Inventors: |
Ballantine; Arne W.; (Round
Lake, NY) ; Edelstein; Daniel C.; (White Plains,
NY) ; Stamper; Anthony K.; (Williston, VT) |
Correspondence
Address: |
SCHMEISER, OLSEN & WATTS
22 CENTURY HILL DRIVE, SUITE 302
LATHAM
NY
12110
US
|
Family ID: |
24861914 |
Appl. No.: |
12/202511 |
Filed: |
September 2, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11836308 |
Aug 9, 2007 |
7456074 |
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12202511 |
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10753241 |
Jan 8, 2004 |
7351639 |
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11836308 |
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09712391 |
Nov 14, 2000 |
6730984 |
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10753241 |
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Current U.S.
Class: |
438/17 ;
204/157.41; 257/E21.004; 257/E21.531; 257/E27.047; 257/E29.326;
438/382 |
Current CPC
Class: |
C23C 8/10 20130101; H01L
27/0802 20130101; C25D 11/00 20130101; Y10S 257/904 20130101; C23C
8/04 20130101; C23C 8/24 20130101; H01C 17/26 20130101; C25D 11/02
20130101; H01L 21/263 20130101; Y10S 257/914 20130101; H01C 7/006
20130101; H01L 29/8605 20130101; C23C 8/02 20130101; C25D 11/026
20130101 |
Class at
Publication: |
438/17 ;
204/157.41; 438/382; 257/E21.004; 257/E21.531 |
International
Class: |
H01L 21/66 20060101
H01L021/66; H01L 21/02 20060101 H01L021/02; B01J 19/12 20060101
B01J019/12 |
Claims
1. A method for increasing an electrical resistance of a resistor,
comprising the steps of: providing a semiconductor structure that
includes the resistor; placing the semiconductor structure in a
chamber, wherein the resistor includes a surface layer having an
exterior surface; including a gas within chamber, wherein the gas
includes nitrogen-comprising molecules at an nitrogen
concentration; exposing a fraction F of the exterior surface of the
surface layer to the nitrogen-comprising molecules; heating a
portion of the surface layer at a heating temperature, wherein an
exterior surface of said portion consists essentially of the
fraction F of the exterior surface of the surface layer, and
wherein a combination of the nitrogen concentration and the heating
temperature is sufficient to nitridize the portion of the surface
layer by reacting said portion with the nitrogen-comprising
molecules, wherein heating the portion of the surface layer
includes directing a beam into the portion of the surface layer
such that the beam causes the heating of the portion of the surface
layer, and wherein the beam is selected from the group consisting a
beam of radiation and a beam of particles; and nitridizing the
portion of the surface layer by reacting said portion with the
nitrogen-comprising molecules such that an electrical resistance of
the resistor is increased, wherein an exterior surface of said
portion consists essentially of the fraction F of the exterior
surface of the surface layer.
2. The method of claim 1, wherein the beam is the beam of
radiation, and wherein the radiation includes a laser
radiation.
3. The method of claim 2, wherein F<1.
4. The method of claim 2, wherein F=1.
5. The method of claim 2, wherein the laser radiation is a pulsed
laser radiation.
6. The method of claim 2, further comprising generating the laser
radiation by a laser whose spot size is less than a surface area of
the exterior surface of the surface layer.
7. The method of claim 1, wherein the beam is the beam of
particles.
8. The method of claim 7, wherein the beam of particles is a beam
of electrons.
9. The method of claim 7, wherein the beam of particles is a beam
of protons.
10. The method of claim 7, wherein the beam of particles is a beam
of ions.
11. The method of claim 1, wherein said nitridizing results in a
thickness of the nitridized portion of the surface layer being an
increasing function of an energy flux of the beam.
12. The method of claim 1, wherein a dimension of the exterior
surface of the surface layer is no smaller than a smallest surface
area on which the beam could be focused.
13. The method of claim 1, wherein the gas is a flowing gas.
14. The method of claim 1, wherein the gas is a non-flowing
gas.
15. The method of claim 1, wherein the method further comprises:
predetermining a target resistance R.sub.t and an associated
tolerance .DELTA.R.sub.t for the electrical resistance of the
resistor; and testing the resistor during the nitridizing step to
determine whether the electrical resistance of the resistor is
within R.sub.t.+-..DELTA.R.sub.t.
16. The method of claim 15, wherein if during the testing step the
electrical resistance of the resistor is determined to not be
within R.sub.t.+-..DELTA.R.sub.t then the method further comprises:
iterating such that each iteration of the iterating includes
additionally executing the exposing and nitridizing steps and
additionally testing the resistor during the nitridizing step to
determine whether R.sub.2'' is within R.sub.t.+-..DELTA.R.sub.t,
wherein R.sub.2'' is a latest value of the electrical resistance of
the resistor as determined by said testing; and ending the
iterating if R.sub.2'' is within R.sub.t.+-..DELTA.R.sub.t or if
(R.sub.2''-R.sub.1) (R.sub.t''R.sub.2'')<0, wherein R.sub.1 is a
latest value of the determined electrical resistance of the
resistor immediately prior to said testing.
17. The method of claim 15, wherein said ending the iterating
comprises satisfying R.sub.2'' being within
R.sub.t.+-..DELTA.R.sub.t.
18. The method of claim 17, wherein the method further comprises
determining from a calibration curve the time of exposure that
results in the electrical resistance of the resistor being within
R.sub.t.+-..DELTA.R.sub.t as a result of said nitridizing, and
wherein said nitridizing is performed for the determined time of
exposure.
19. The method of claim 15, wherein said ending the iterating
comprises satisfying (R.sub.2''-R.sub.t)
(R.sub.t-R.sub.2'')<0.
20. The method of claim 15, wherein said testing comprises
continuously testing the resistor during the nitridizing step.
Description
[0001] This application is a divisional application claiming
priority to Ser. No. 11/836,308, filed Aug. 9, 2007, which is a
divisional of U.S. Pat. No. 7,351,639, issued Apr. 1, 2008, which
is a divisional of U.S. Pat. No. 6,730,984, issued May 4, 2004.
BACKGROUND OF THE INVENTION
[0002] 1. Technical Field
[0003] The present invention provides a method and structure for
increasing an electrical resistance of a resistor that is located
within a semiconductor structure such as a semiconductor wafer, a
semiconductor chip, and an integrated circuit.
[0004] 2. Related Art
[0005] A resistor on a wafer may have its electrical resistance
trimmed by using laser ablation to remove a portion of the
resistor. For example, the laser ablation may cut slots in the
resistor. With existing technology, however, trimming a resistor by
using laser ablation requires the resistor to have dimensions on
the order of tens of microns. A method and structure is needed to
increase the electrical resistance of a resistor on a wafer
generally, and to increase the electrical resistance of a resistor
having dimensions at a micron or sub-micron level.
SUMMARY OF THE INVENTION
[0006] The present invention provides a method for increasing an
electrical resistance of a resistor, comprising the steps of:
[0007] providing a semiconductor structure that includes the
resistor; and
[0008] oxidizing a fraction F of a surface layer of the resistor
with oxygen particles, resulting in the increasing of the
electrical resistance of the resistor.
[0009] The present invention provides an electrical structure,
comprising:
[0010] a semiconductor structure that includes a resistor; and
[0011] oxygen particles in an oxidizing reaction with a fraction F
of a surface layer of the resistor, wherein the oxidizing reaction
increases an electrical resistance of the resistor.
[0012] The present invention provides a method for increasing an
electrical resistance of a resistor, comprising the steps of:
[0013] providing a semiconductor structure that includes the
resistor; and
[0014] nitridizing a fraction F of a surface layer of the resistor
with nitrogen particles, resulting in the increasing of the
electrical resistance of the resistor.
[0015] The present invention provides an electrical structure,
comprising:
[0016] a semiconductor structure that includes a resistor; and
[0017] nitrogen particles in an nitridizing reaction with a
fraction F of a surface layer of the resistor, wherein the
nitridizing reaction increases an electrical resistance of the
resistor.
[0018] The present invention provides a method and structure for
increasing an electrical resistance of a resistor on a wafer
generally, and for increasing the electrical resistance of a
resistor having dimensions at a micron or sub-micron level.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 depicts a front cross-sectional view of a
semiconductor structure that includes an electrical resistor, in
accordance with embodiments of the present invention.
[0020] FIG. 2 depicts FIG. 1 at an onset of exposure of a portion
of the resistor to oxygen particles.
[0021] FIG. 3 depicts FIG. 2 after exposure of the portion of the
resistor to the oxygen particles.
[0022] FIG. 4 depicts a front cross-sectional view of a heating
chamber that includes the semiconductor structure of FIG. 2 and an
oxygen-comprising gas, wherein the heating chamber generates heat
that heats the semiconductor structure, in accordance with
embodiments of the present invention.
[0023] FIG. 5 depicts a front cross-sectional view of a chamber
that includes the semiconductor structure of FIG. 2 and an
oxygen-comprising gas, wherein the resistor of the semiconductor
structure is heated by a directed beam of radiation or particles,
in accordance with embodiments of the present invention.
[0024] FIG. 6 depicts a front cross-sectional view of a plasma
chamber that includes the semiconductor structure of FIG. 2, in
accordance with embodiments of the present invention.
[0025] FIG. 7 depicts a front cross-sectional view of an
anodization bath in which the semiconductor structure of FIG. 2 is
partially immersed, in accordance with embodiments of the present
invention.
[0026] FIG. 8 depicts a front cross-sectional view of a chemical
bath in which the resistor of the semiconductor structure of FIG. 2
is immersed, in accordance with embodiments of the present
invention.
[0027] FIG. 9 depicts FIG. 2 during exposure of the portion of the
resistor to the oxygen particles, and with the resistor coupled to
an electrical resistance measuring apparatus, in accordance with
embodiments of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0028] FIG. 1 illustrates a front cross-sectional view of a
semiconductor structure 10 that includes an electrical resistor 14
within a semiconductor substrate 12, in accordance with embodiments
of the present invention. The electrical resistor 14 includes an
electrically resistive material. The semiconductor structure 10 may
include, inter alia, a semiconductor wafer, a semiconductor chip,
an integrated circuit, etc. The substrate 12 comprises all portions
of the semiconductor structure 10 (e.g., electronic devices
including semiconductor devices, wiring levels, etc.) exclusive of
the resistor 14. The resistor 14 may have any electrical resistance
functionality within the semiconductor substrate 12 and accordingly
may exist within a semiconductor device, within an electrical
circuit, etc. The resistor 14 includes an exposed surface 19 having
a surface area S.
[0029] FIG. 2 illustrates FIG. 1 at an onset of exposure of a
portion 15 of the resistor 14 to oxygen particles 20. The oxygen
particles 20 may comprise oxygen-comprising molecules (e.g.,
molecular oxygen O.sub.2, carbon dioxide CO.sub.2, etc.) or oxygen
ions, depending on which of several embodiments of the present
invention is operative, as will be discussed infra. The
oxygen-exposed portion 15 has an oxygen-exposed surface 17 (i.e.;
the surface 17 is exposed to the oxygen particles 20). The resistor
14 includes an oxygen-unexposed portion 16 that has an
oxygen-unexposed surface 18 (i.e.; the surface 18 is unexposed to
the oxygen particles 20). The surface 19 (see FIG. 1) comprises the
surfaces 17 and 18 which have surface areas S.sub.E and S.sub.U,
respectively. Thus the surface area S of the surface 19 (see FIG.
1) is S.sub.E+S.sub.U. In FIG. 2, the oxygen-unexposed portion 16
and the associated surface 18, if present, gives rise to a
"partially exposed" embodiment, since the surface 19 will be
partially exposed to the oxygen particles 20 (at the surface 17)
such that S.sub.U>0. The oxygen-unexposed portion 16 and the
associated surface 18, if not present, gives rise to a "totally
exposed" embodiment, since the surface 19 will be totally exposed
to the oxygen particles 20 (at the surface 17) such that
S.sub.U=0.
[0030] FIG. 3 illustrates FIG. 2 after the exposure of the portion
15 of the resistor 14 to the oxygen particles 20. The exposure of
the portion 15 of the resistor 14 for a finite time of exposure
generates an oxidized region 22 within the portion 15, wherein an
unoxidized portion 24 of the resistor 14 remains. The oxidized
region 22 is a fraction F of a surface layer of the resistor 14,
wherein the surface layer is a region defined as the oxidized
region 22 projected to the side surfaces 25 and 26 of the resistor
14. The fraction F is in a range of 0<F<1, wherein
0<F<1 corresponds to the "partially exposed" embodiment, and
F=1 corresponds to the "totally exposed" embodiment, discussed
supra. The oxidized region 22 has a thickness t that may increase
as the time of exposure increases or may reach a self-limiting
thickness. For oxidation processes which are diffusion dominated,
the thickness t may vary, inter alia, as a square root of the time
of exposure. The oxidized region 22 increases an electrical
resistance of the resistor 14 associated with current flow either
in a direction 6 or in a direction 7, in comparison with an
electrical resistance of the resistor 14 that existed before the
oxidized region 22 was formed.
[0031] The resistor 14 could be within an integrated circuit and,
accordingly, FIG. 3 also shows in of the integrated circuit above
the resistor 14. The insulative layer 11 includes an insulative
material 13 and an opening 23, wherein the opening 23 which defines
the resistor 14 that is potentially oxidizable in accordance with
the present invention. Note that there may be resistive regions 28
underneath the insulative material 13 and thus blocked by the
insulative material 13. Accordingly, the underneath or blocked
resistive regions 28 are not oxidizable in accordance with the
present invention. Although not explicated or discussed in the
embodiments described infra, the resistor 14 could be thought of as
being "partially exposed" if the total resistor is defined as the
resistor 14 in combination with the underneath or blocked resistive
regions 28.
[0032] The present invention includes five embodiments for
oxidizing the resistor 14 to increase the electrical resistance of
the resistor 14, namely: thermal oxidation using a heating chamber
(FIG. 4); thermal oxidation using a direct beam of radiation or
particles (FIG. 5); plasma oxidation (FIG. 6); anodization (FIG.
7); and chemical oxidation (FIG. 8). The following discussion will
describe these embodiments and explain how in situ testing can be
used to control the electrical resistance acquired by the resistor
14 after being exposed to the oxygen particles 20 (FIG. 9).
[0033] While the five embodiments mentioned supra and discussed
infra specifically describe oxidizing the resistor 14, the five
embodiments mentioned supra and discussed infra are each applicable
to changing an the resistance of the resistor 14 by nitridizing as
an alternative to oxidizing. Nitridizing the resistor 14, as
opposed to oxidizing the resistor 14, means reacting the resistor
14 with nitrogen particles (instead of with the oxygen particles
20) in a manner that forms a nitride of the electrically resistive
material of the resistor 14 comprises (instead of forming an oxide
of electrically resistive material that the resistor 14). As with
the oxygen particles 20, the nitrogen particles may be in molecular
or ionic form depending on the operative embodiment. "Partially
exposed" and "fully exposed" embodiments are applicable to
nitridization of the resistor 14, just as "partially exposed" and
"fully exposed" embodiments are applicable to oxidation of the
resistor 14. Unless noted otherwise herein, all features and
aspects of the five embodiments, as discussed infra, apply to
nitridization of the resistor 14 just as said all features and
aspects of the five embodiments apply to oxidation.
Thermal Oxidation Using a Heating Chamber
[0034] FIG. 4 illustrates a front cross-sectional view of a heating
chamber 30 that includes an oxygen-comprising gas 32 and the
semiconductor structure 10 of FIG. 2, in accordance with
embodiments of the present invention. The gas 32 includes an oxygen
compound such as, inter alia, molecular oxygen (O.sub.2), nitrous
oxide (N.sub.2O), carbon dioxide (CO.sub.2), and carbon monoxide
(CO).
[0035] The heating chamber 30 is heated to a heating temperature
and the resistor 14 is thus oxidized by the gas 32 to form an oxide
region within the resistor 14 such as the oxide region 22 depicted
supra in FIG. 3. A thickness of the oxidized region (see, e.g., the
thickness t of the oxidized region 22 described supra for FIG. 3)
increases as a time of exposure of the resistor 14 to the gas 32
increases. FIG. 4 exemplifies a "totally exposed" embodiment in
which the oxygen-unexposed portion 16 (see FIG. 2) of the resistor
14 does not exist (i.e., S.sub.U=0 and F=1), and the surface 17 is
the total surface 19 (see FIG. 1) that is oxidized. In FIG. 4, the
oxygen concentration in the ambient gas 32 and the heating
temperature, in combination, should be sufficient to oxidize the
resistor 14. Said combinations depend on the chemistry of the
oxidizing reaction between the resistor 14 and the gas 32. Thus,
the required oxygen concentration and heating temperature depends
on a material composition of the resistor 14 and the gas 32.
[0036] The gas 32 may be non-flowing in the form of a volumetric
distribution within the heating chamber 30. Alternatively, the gas
32 may be in a flowing form at low flow, wherein the gas 32
contacts the resistor 14. Since the flowing gas 32 originates from
a source that is likely to be substantially cooler than the heating
temperature, the oxygen flow rate should be sufficiently slow as to
minimize or substantially eliminate heat transfer from the resistor
14 to the gas 32. Such inhibition of heat transfer may by any
method known to one of ordinary skill in the art. One such method
is for the oxygen flow to be slow enough that the dominant mode of
said heat transfer is by natural convection rather than by forced
convection. An additional alternative using flowing oxygen includes
preheating the gas 32 to a temperature sufficiently close to the
heating temperature so that said heat transfer is negligible even
if said heat transfer occurs by forced convection.
[0037] The heating chamber 30 in FIG. 4 includes any volumetric
enclosure capable of heating the semiconductor structure 10 placed
therein. The heat within the heating chamber 30 may be directed
toward the semiconductor structure 10 in the direction 37 from a
heat source 34 above the semiconductor structure 10. The heat
within the heating chamber 30 may also be directed toward the
semiconductor structure 10 in the direction 38 from a heat source
36 below the semiconductor structure 10. Heat directed from the
heat source 34 in the direction 37 is transferred to the surface 17
more directly than is heat directed from the heat source 36 in the
direction 38. Accordingly, the heat directed from the heat source
34 in the direction 37 is more efficient for raising the
temperature at the surface 17 than is the heat directed from the
heat source 36 in the direction 38. Either or both of the heat
sources 34 and 36 may be utilized in the heating chamber 30. Either
or both of the heat sources 34 and 36 may be a continuous heat
source or a distributed array of discrete heat sources such as a
distributed array of incandescent bulbs. Alternatively, the heating
chamber 30 may be a furnace.
[0038] Any method of achieving the aforementioned heating
temperature in the heating chamber 30 is within the scope of the
present invention. For example, the semiconductor structure 10
could be inserted into the heating chamber 30 when the heating
chamber 30 is at ambient room temperature, followed by a rapid
ramping up of temperature within the heating chamber 30 until the
desired heating temperature is achieved therein. If the heating
temperature is spatially uniform at and near the resistor 14, then
the oxidation of the resistor 14 in the direction 37 will be
spatially uniform such that a thickness of the resultant oxide
layer is about constant (see, e.g., the thickness t of the oxide
layer 22 in FIG. 3 which is about constant). A spatially nonuniform
heating temperature which would result in a oxide layer thickness
that is not constant. Both uniform and nonuniform heating
temperature distributions, and consequent uniform and nonuniform
oxide layer thicknesses, are within the scope of the present
invention.
[0039] Suitable resistor 14 electrically resistive materials for
being oxidized in the heating chamber 30 include, inter alia, one
or more of polysilicon, amorphous silicon, titanium, tantalum,
tungsten, aluminum, silver, copper, or nitrides, silicides, or
alloys thereof.
[0040] The aforementioned method of oxidizing the resistor 14 using
the heating chamber 30 does not depend on the dimensions of the
resistor 14 and is thus applicable if the resistor 14 has
dimensions of 1 micron or less, and is likewise applicable if the
resistor 14 has dimensions in excess of 1 micron.
[0041] As stated supra, thermal nitridization using a heating
chamber could be used as an alternative to thermal oxidation using
a heating chamber. If nitridization is employed, the gas 32 would
include, instead of an oxygen compound, a nitrogen compound such
as, inter alia, molecular nitrogen (N.sub.2).
Thermal Oxidation Using a Directed Beam of Radiation or
Particles
[0042] FIG. 5 illustrates a front cross-sectional view of a chamber
40 that includes the semiconductor structure 10 of FIG. 2 and an
oxygen-comprising gas 42, wherein the resistor 14 of the
semiconductor structure 10 is heated by a directed beam 46 of
radiation or particles, in accordance with embodiments of the
present invention. The gas 42 includes an oxygen compound such as,
inter alia, molecular oxygen (O.sub.2), nitrous oxide (N.sub.2O),
carbon dioxide (CO.sub.2), and carbon monoxide (CO). The gas 42 may
be non-flowing or flowing as discussed supra in conjunction with
the gas 32 of FIG. 4.
[0043] The portion 15 of the resistor 14 is heated to a heating
temperature by the directed beam 46, and the portion 15 is thus
oxidized by the gas 32 to form an oxide region within the resistor
14 such as the oxide region 22 depicted supra in FIG. 3. A
thickness of the oxidized region (see, e.g., the thickness t of the
oxidized region 22 described supra for FIG. 3) increases as a time
of exposure of the resistor 14 to the directed beam 46 increases.
The thickness of the oxidized region also increases as an energy
flux of the directed beam 46 increases. The directed beam 46 may
include radiation (e.g., laser radiation), or alternatively, a beam
of particles (e.g., electrons, protons, ions, etc.). The directed
beam 46 must be sufficiently energetic to provide the required
heating of the resistor 14, and a minimum required energy flux of
the directed beam 46 depends on a material composition of the
resistor 14. Additionally, the directed beam 46 should be
sufficiently focused so that the aforementioned energy flux
requirement is satisfied.
[0044] If the directed beam 46 includes laser radiation, then the
laser radiation may comprise a continuous laser radiation or a
pulsed laser radiation. If the resistor 14 comprises a metal, then
the present invention will be effective for a wide range of
wavelengths of the laser radiation, since a metal is characterized
by a continuum of energy levels of the conduction electrons rather
than discrete energy levels for absorbing the laser radiation.
[0045] The directed beam 46, which is generated by a source 44, may
be directed to the oxygen-exposed portion 15 of the resistor 14 in
a manner that the oxygen-unexposed portion 16 of the resistor 14
exists. For example, the source 44 may include a laser whose spot
size area is less than the surface area S of the total surface 19
(see FIG. 1) of the resistor 14, and the associated directed beam
46 includes radiation from the laser of the source 44. Thus it is
possible for the laser beam to traverse less than the total surface
19. Similarly, the source 44 may generate the directed beam 46 as
the beam of particles, which impart energy to the resistor 14 and
thus heat the resistor 14. The directed beam 46 may be localized to
the surface 17 which requires that the directed beam 46 be
sufficiently anisotropic; i.e., sufficiently localized to the
direction 37 by the source 44, which depends on physical and
operational characteristics of the source 44. Accordingly, if the
directed beam 46 is localized to the surface 17, then FIG. 5 would
exemplify a "partially exposed" embodiment in which the
oxygen-unexposed portion 16 (see FIG. 2) exists (i.e., S.sub.U>0
and F<1). Alternatively, FIG. 5 may also exemplify a "totally
exposed" embodiment in which the oxygen-unexposed portion 16 (see
FIG. 2) does not exist (i.e., S.sub.U=0 and F=1), since the
directed beam 46 could be directed to the total surface 19. Thus,
FIG. 4 exemplifies either a "totally exposed" (F=1) or a "partially
exposed" (F<1) embodiment in which the oxygen-unexposed portion
16 (see FIG. 2) may or may not exist. A spatial extent of partial
or total exposure to, and associated reaction with, the
oxygen-comprising gas 42 may be controlled by adjusting the size
(i.e., area) of the directed beam 46 and/or by scanning the
directed beam 46 across portions of the total surface 19 (see FIG.
1).
[0046] In FIG. 5, the oxygen concentration in the gas 32 and the
heating temperature, in combination, should be sufficient to
oxidize the resistor 14, and depends on the chemistry of the
oxidizing reaction between the resistor 14 and the gas 32 as
discussed supra in conjunction with FIG. 4. An ability to achieve
the required temperature depends on the directed beam 46 being
sufficiently energetic so as to impart enough energy to the portion
15 of the resistor 14 to facilitate the heating and consequent
oxidation of the portion 15. The energy of the directed beam 46 is
controlled at its source 44.
[0047] As stated supra, an advantage of using the directed beam 46
of FIG. 5 instead of the heating chamber 30 of FIG. 4 to heat the
resistor 14 is the ability to heat less than the total exposed
surface area 19 of the resistor 14. Another advantage is that said
heating of the semiconductor structure 10 by the heating chamber 30
could potentially damage thermally-sensitive portions of the
semiconductor structure 10 which cannot tolerate the temperature
elevation caused by the heating chamber 30. In contrast, the
localized heating by the directed beam 46 advantageously does not
expose said thermally-sensitive portions of the semiconductor
structure 10 to potential thermally-induced damage.
[0048] Suitable resistor 14 electrically resistive materials for
being oxidized while being heated by the directed beam 46 include,
inter alia, one or more of polysilicon, amorphous silicon,
titanium, tantalum, tungsten, aluminum, silver, copper, or
nitrides, silicides, or alloys thereof.
[0049] If the directed beam 46 is required to be confined to the
surface 19 (see FIG. 1) of the resistor 14 (i.e., if the directed
beam 46 should not strike any surface of the resistor 14 other than
the surface 19), then dimensions of the surface 19 should be no
smaller than a smallest surface area on which the directed beam 46
could be focused. For example, if the directed beam 46 includes
laser radiation and the source 44 includes a laser, then the
dimensions of the portion 15 of the resistor 14 may be no smaller
than a laser spot dimension. Since with current and future
projected technology, laser spot dimensions of the order of 1
micron or less are possible, the portion 15 of the resistor 14 may
have dimensions of 1 micron or less (to an extent possible with
prevailing laser technology at a time when the present invention is
practiced), as well as dimensions exceeding 1 micron, when the
directed beam 46 includes the laser radiation.
[0050] As stated supra, thermal nitridization using a directed beam
of radiation or particles could be used as an alternative to
thermal oxidation using a directed beam of radiation or particles.
If nitridization is employed, the gas 42 would include, instead of
an oxygen compound, a nitrogen compound such as, inter alia,
molecular nitrogen (N.sub.2).
Plasma Oxidation
[0051] FIG. 6 illustrates a front cross-sectional view of a plasma
chamber 50 that comprises the semiconductor structure 10 of FIG. 2,
in accordance with embodiments of the present invention. The plasma
chamber 50 includes an electrode 54 and an electrode 55. The
semiconductor structure 10 has been disposed between the electrode
54 and the electrode 55. The plasma chamber 50 also includes oxygen
ions 52 which are formed in generation of a plasma gas, as will be
explained infra.
[0052] A neutral gas within the plasma chamber 50 includes an
oxygen compound such as, inter alia, molecular oxygen (O.sub.2),
nitrous oxide (N.sub.2O), carbon dioxide (CO.sub.2), and carbon
monoxide (CO). Inasmuch as a plasma gas will be formed from the
neutral gas, the plasma chamber 50 may also include one or more
noble gases (e.g., argon, helium, nitrogen, etc.) to perform such
functions as: acting as a carrier gas, providing electric charge
needed for forming ionic species of the plasma, assisting in
confining the plasma to within fixed boundaries, assisting in
developing a target plasma density or a target plasma density
range, and promoting excited state plasma lifetimes.
[0053] A power supply 56 generates an electrical potential between
the electrode 54 and the electrode 55. The power supply 56 may be
of any type known to one skilled in the art such as, inter alia: a
radio frequency (RF) power supply; a constant voltage pulsed power
supply (see, e.g., U.S. Pat. No. 5,917,286, June 1999, Scholl et
al.); and a direct current (DC) voltage source (see, e.g., U.S.
Pat. No. 4,292,384, September 1981, Straughan et al.). Pertinent
characteristics of the power supply 56 are in accordance with such
characteristics as are known in the art. For example, a RF power
supply may include, inter alia, a radio frequency selected from a
wide range of frequencies such as a commonly used frequency of
13.56 Hz. The power requirements of the RF power supply depends on
the surface area 17 of the resistor 14 and is thus case dependent.
For example, a typical range of power of the RF power supply may
be, inter alia, between about 100 watts and about 2000 watts.
[0054] The electrical potential generated by the power supply 56
ionizes the neutral gas to form a plasma between the electrode 54
and the electrode 55, wherein the plasma comprises electrons and
ions, and wherein a plasma ion polarity depends on the particular
neutral gas within the plasma chamber 50. For example, if the
neutral gas includes molecular oxygen, then a three-component
plasma may be formed including electrons, positive oxygen ions, and
negative oxygen ions, such that in the glow discharge a predominant
positive ion is O.sub.2.sup.+ and a lesser positive ionic species
is O.sup.+. See U.S. Pat. No. 5,005,101 (Gallagher et al.; April
1991; col. 6, lines 1-12).
[0055] In FIG. 6, a DC power supply 57 has terminals 58 and 59,
wherein the terminal 58 is positive with respect to a ground 51,
and the terminal 59 is negative with respect to the terminal 58.
The DC power supply 57 generates an electric field that is directed
from the electrode 54 to the electrode 55, and the electric field
is capable of accelerating positive ions from the electrode 54
toward the electrode 55 in the direction 37. Accordingly, if the
oxygen ions 52 are positive oxygen ions (e.g., O.sub.2.sup.+), then
the electric field accelerates the oxygen ions 52 of the plasma
toward the electrode 55 causing the oxygen ions 52 to strike the
portion 15 of the resistor. If the oxygen ions 52 are sufficiently
energetic (i.e., if the oxygen ions 52 have a minimum or threshold
energy) as required to oxidize the portion 15 of the resistor 14,
then the oxygen ions 52 will so oxidize the portion 15 and thus
form an oxidized region within the resistor 14, such as the
oxidized region 22 depicted supra in FIG. 3. A thickness of the
oxidized region (see, e.g., the thickness t of the oxidized region
22 described supra for FIG. 3) increases as a time of exposure of
the resistor 14 to the accelerated oxygen ionic species 52
increases.
[0056] If the oxygen ions 52 are negative oxygen ions to be
accelerated toward the resistor 14 and reacted with the resistor
14, then the polarities of the terminals 58 and 59 should be
reversed (i.e., the terminals 58 and 59 should have negative and
positive polarities, respectively). A factor in determining whether
positive or negative oxygen ions 52 are to be reacted with the
resistor 14 includes consideration of the chemical reactions
between said accelerated oxygen ions 52 and the electrically
resistive material of the resistor 14, since characteristics of
said chemical reactions (e.g., reaction energetics, reaction rate,
etc.) may be a function of the polarity of the reacting ionic
oxygen species 52. Nonetheless, if negative oxygen ions 52 of the
plasma are accelerated by the DC power supply 57 toward the
resistor 14, then electrons of the plasma will also be accelerated
toward the resistor 14, which in some situations may result in
undesirable interactions between said electrons and the resistor
14. Thus, each of the aforementioned considerations (e.g., material
of the resistor 14, characteristics of the chemical reactions
between the oxygen ions 52 and the resistor 14, etc.) must be
considered when choosing the neutral gas and choosing which ionic
species 52 to react with the resistor 14.
[0057] The accelerated oxygen ions 52 transfer energy to the
resistor 14 to provide at least the threshold energy required for
effectuating the chemical reaction between the oxygen ions 52 and
the resistor 14, and such energy transferred substitutes for
thermal energy (i.e., heat) provided by the heating chamber 30 of
FIG. 4, or by the directed beam 46 of radiation or particles of
FIG. 5, to the resistor 14. A voltage output of the DC power supply
57 must be sufficient to accelerate the oxygen ions 52 to at least
the aforementioned threshold energy.
[0058] FIG. 6 exemplifies a "totally exposed" embodiment in which
the oxygen-unexposed portion 16 (see FIG. 2) of the resistor 14
does not exist (i.e., S.sub.U=0 and F=1), and the surface 17 is the
total surface 19 (see FIG. 1) that is oxidized in the plasma
chamber 50.
[0059] While FIG. 6 depicts a particular plasma chamber 50
configuration for oxidizing the resistor 14, any plasma
configuration known to one of ordinary skill in the art may be
used.
[0060] Suitable resistor 14 electrically resistive materials for
being subject to plasma oxidation include, inter alia, one or more
of polysilicon, amorphous silicon, titanium, tantalum, tungsten,
aluminum, silver, copper, or nitrides, silicides, or alloys
thereof.
[0061] The aforementioned method of oxidizing the resistor 14 using
plasma oxidation does not depend on the dimensions of the resistor
14 and is thus applicable if the resistor 14 has dimensions of 1
micron or less, and is likewise applicable if the resistor 14 has
dimensions in excess of 1 micron.
[0062] As stated supra, plasma nitridization using a directed beam
of radiation or particles could be used as an alternative to plasma
oxidation using a directed beam of radiation or particles. If
nitridization is employed, the neutral gas within the plasma
chamber 50 would include, instead of an oxygen compound, a nitrogen
compound such as, inter alia, molecular nitrogen (N.sub.2).
Anodization
[0063] FIG. 7 illustrates a front cross-sectional view of an
anodization bath 60, in accordance with embodiments of the present
invention. Generally, anodizing a first conductive material such as
a semiconductor or metal requires immersing into an electrolytic
solution both the first conductive material and a second conductive
material, and passing a DC current at a sufficient voltage through
the electrolytic solution.
[0064] An anodization electrical circuit 69 includes a DC power
supply 64, an electrolytic solution 61 which includes oxygen, the
semiconductor structure 10 of FIG. 2 wherein the resistor 14 is
partially immersed in the electrolytic solution 61, and an
electrode 63 partially immersed in the electrolytic solution 61.
"Partially immersed" includes "totally immersed" (i.e., 100%
immersed) as a special case. The resistor 14 is made of the
electrically resistive material which includes the first conductive
material that serves as an anode, and the electrode 63 is made of
the second conductive material that serves as a cathode. The second
conductive material of the cathode may include any inert metal
(e.g., platinum) that does not react with the electrolytic solution
61. The resistor 14 is made anodic by electrically coupling the
resistor 14 to a positive terminal 65 of the DC power supply 64.
The electrode 63 is made cathodic by electrically coupling the
electrode 63 to a negative terminal 66 of the DC power supply 64.
The anodization may be performed at or above ambient room
temperature. A thickness of an oxide film formed with the resistor
14 is a function of a voltage output from the DC power supply 64
and the current density in the anodization circuit 69. The specific
voltage and current density is application dependent and would be
selected from known art by one of ordinary skill in the art. For
example, an anodization of tantalum or tantalum nitride at ambient
room temperature and at with a current density of about 0.1
milliamp/cm.sup.2 in an electrolytic solution of citric acid will
generate an oxide (i.e., tantalum pentoxide Ta.sub.2O.sub.5) film
thickness of 20 .ANG. per volt. Thus for an applied voltage of
about 25 volts, the Ta.sub.2O.sub.5 film thickness is about 500
.ANG..
[0065] Suitable resistor 14 electrically resistive materials for
being anodized include, inter alia. Suitable cathode 63 materials
include, inter alia tantalum, titanium, polysilicon, aluminum,
tungsten, nitrides thereof, and alloys thereof. A electrolyte
containing oxygen that can be used depends on the electrically
resistive material to be anodized and is therefore case specific.
Thus, any electrolyte containing oxygen that is compatible with
said electrically resistive material may be selected as would be
known or apparent to one of ordinary skill in the art.
[0066] Upon activation of the DC power supply 64 (i.e., the DC
power supply 64 is turned on), and under the voltage output (and
the associated current) from the DC power supply 64, an
electrolytic reaction occurs at the surface 17 of the resistor 14
to generate hydrogen ions, electrons, and oxygen ions 62 from the
electrolytic solution. The oxygen ions 62 chemically react with the
portion 15 of the resistor 14 such that an oxidized region, such as
the oxidized region 22 depicted supra in FIG. 3, forms within the
portion 15 of the resistor 14. The generated hydrogen ions and
electrons combine at the cathode 63 to form hydrogen gas.
[0067] FIG. 7 shows the portion 16 of the resistor 14 above an
electrolyte level 67. Accordingly, FIG. 7 may exemplify a
"partially exposed" embodiment in which the oxygen-unexposed
portion 16 (see FIG. 2) exists (i.e., S.sub.U>0 and F<1).
Alternatively, FIG. 7 may also exemplify a "totally exposed"
embodiment in which the oxygen-unexposed portion 16 (see FIG. 2)
does not exist (i.e., S.sub.U=0 and F=1) if the resistor 14 is
totally immersed in the electrolytic solution 61. Thus, FIG. 7
exemplifies either a "partially exposed" embodiment or a "totally
exposed" embodiment in which the oxygen-unexposed portion 16 (see
FIG. 2) exists or does not exist, respectively.
[0068] A thickness of the oxidized region (see, e.g., the thickness
t of the oxidized region 22 described supra for FIG. 3) increases
as a time of the electrolytic reaction increases. As the thickness
of the oxidized region increases, a current drawn by the anodizing
bath 60 decreases due to increasing isolation of the portion 15 of
the resistor 14 from the electrolytic solution 61 as the thickness
of the oxidized layer increases. For certain resistor 14 materials
(e.g., aluminum), the anodization process may eventually self
terminate, because said current is eventually reduced to a
negligible value.
[0069] The aforementioned method of oxidizing the resistor 14 using
anodization does not depend on the dimensions of the resistor 14
and is thus applicable if the portion 15 of the resistor 14 has
dimensions of 1 micron or less, and is likewise applicable if the
portion 15 of the resistor 14 has dimensions in excess of 1
micron.1
[0070] As stated supra, anodization that causes nitridization of
the resistor 14 could be used as an alternative to anodization that
causes oxidation of the resistor 14. If anodization with
nitridization is employed instead of anodization with oxidation,
then the electrolytic solution 61 would include nitrogen instead of
oxygen. An electrolyte containing nitrogen that can be used depends
on the electrically resistive material to be anodized and is
therefore case specific. Thus, any electrolyte containing nitrogen
that is compatible with said electrically resistive material may be
selected as would be known or apparent to one of ordinary skill in
the art.
Chemical Oxidation
[0071] FIG. 8 illustrates a front cross-sectional view of a
chemical bath 70, in accordance with embodiments of the present
invention. The chemical bath 70 comprises a chemical solution 71.
The semiconductor structure 10 of FIG. 2 is immersed in the
chemical solution 71. The chemical solution 71 includes oxygen
particles 72 in such form as oxygen-comprising liquid molecules,
oxygen ions, or an oxygen-comprising gas (e.g., oxygen gas or ozone
gas) dissolved in the chemical solution 71 under pressurization.
The oxygen particles 72 chemically react with the resistor 14 to
form an oxidized region within the resistor 14 such as the oxidized
region 22 depicted supra in FIG. 3. A thickness of the oxidized
region (see, e.g., the thickness t of the oxidized region 22
described supra for FIG. 3) increases as a time of the chemical
reaction increases. The chemical reaction may be exothermic or
endothermic, depending on the electrically resistive material of
the resistor 14 and the oxygen particles 72. If the chemical
reaction is endothermic, an addition of a sufficient amount of heat
is required. Additionally, a suitable catalyst may be utilized to
accelerate the chemical reaction. The catalyst may be any catalyst
known to one of ordinary skill in the art for the particular
chemical reaction.
[0072] Suitable resistor 14 electrically resistive materials for
being chemically oxidized include, inter alia, copper, tungsten,
aluminum, titanium, nitrides thereof, and alloys thereof. Suitable
chemical solutions 71 include, inter alia, hydrogen peroxide,
ferric nitrate, ammonium persulphate, etc.
[0073] FIG. 8 shows the resistor 14 as totally immersed in the
chemical solution 71, which exemplifies a "totally exposed"
embodiment in which the oxygen-unexposed portion 16 (see FIG. 2) of
the resistor 14 does not exist (i.e., S.sub.U=0 and F=1), and the
surface 17 is the total surface 19 (see FIG. 1) that is oxidized in
the chemical solution 71. Nonetheless, the resistor 14 could be
rotated 90 degrees (within the cross-section plane illustrated in
FIG. 8) and moved upward in a direction 75 such that a portion of
the resistor 14 would be above the level 77 of the chemical
solution 71 just as the portion 16 is above the electrolyte level
67 in FIG. 7. Under such 90 degree rotation and upward movement,
FIG. 8 would represent a "partially exposed" embodiment in which
the oxygen-unexposed portion 16 (See FIG. 2) exists (i.e.,
S.sub.U>0 and F<1). Accordingly, FIG. 8 exemplifies either a
"partially exposed" embodiment or a "totally exposed" embodiment in
which the oxygen-unexposed portion 16 (see FIG. 2) exists or does
not exist, respectively.
[0074] The aforementioned method of oxidizing the resistor 14 using
chemical oxidation does not depend on the dimensions of the
resistor 14 and is thus applicable if the resistor 14 has
dimensions of 1 micron or less, and is likewise applicable if the
resistor 14 has dimensions in excess of 1 micron.
[0075] As stated supra, chemical nitridization of the resistor 14
could be used as an alternative to chemical oxidation of the
resistor 14. If chemical nitridization is employed instead of
chemical oxidation, then the chemical solution 71 would include
nitrogen particles instead of the oxygen particles 72.
Resistance Testing
[0076] The resistor 14 may be tested prior to being oxidized or
nitridized, while being oxidized or nitridized (i.e., in situ),
and/or after being oxidized or nitridized. The resistance testing
may be accomplished by a conventional test apparatus, such as with
a four-point resistance test having four contacts to the resistor
with two of the contacts coupled to a known current source
outputting a current I and the other two contacts coupled to a
voltage meter that measures a voltage V across the resistance to be
determined, and the measured resistance is thus V/I. Alternatively,
the resistance testing may be accomplished with an inline measuring
circuit within the same integrated circuit that includes the
resistor, wherein the measuring circuit is coupled to
instrumentation that outputs the measured resistance.
[0077] FIG. 9 illustrates FIG. 2 during exposure of the portion 15
of the resistor 14 to the oxygen particles 20, and with the
resistor 14 coupled to an electrical resistance measuring apparatus
85. The electrical resistance measuring apparatus 85 may include
the conventional test apparatus or the inline measuring circuit,
mentioned supra. The electrical resistance measuring apparatus 85
may be conductively coupled to surfaces 81 and 82 of the resistor
14 by conductive interconnects (e.g., conductive wiring) 86 and 87,
respectively. Accordingly, the electrical resistance measuring
apparatus 85 is capable of measuring an electrical resistance of
the resistor 14 (before, during, and after oxidation or
nitridization of the resistor 14) associated with current flowing
in the direction 7 through the resistor 14. Alternatively, the
electrical resistance measuring apparatus 85 may be used to measure
an electrical resistance of the resistor 14 associated with current
flowing in the direction 6 through the resistor 14 (before, during,
and after oxidation or nitridization of the resistor 14) if the
conductive interconnects 86 and 87 are coupled to bounding surfaces
83 and 84 of the resistor 14 instead of to the surfaces 81 and 82,
respectively. The surface 83 in FIG. 9 corresponds to the surface
19 in FIG. 1. In FIG. 9, the resistor 14 includes an oxidized (or
nitridized) region 21, which corresponds to the oxidized (or
nitridized) region 22 of FIG. 3. The semiconductor structure 10 is
within an oxidizing (or nitridizing) environment 80, which includes
any oxidizing (or nitridizing) environment within the scope of the
present invention such, inter alia, the heating chamber 30 of FIG.
4, the chamber 40 of FIG. 5, the plasma chamber 50 of FIG. 6, the
anodization bath 60 of FIG. 7, and the chemical bath 70 of FIG. 8.
The electrical resistance measuring apparatus 85 is any apparatus,
as is known to one of ordinary skill in the art, capable of
measuring an electrical resistance of the resistor 14.
[0078] The following discussion describes how the electrical
resistance measuring apparatus 85 of FIG. 9 can be used for in situ
testing to control the electrical resistance acquired by the
resistor 14 after being exposed to the oxygen particles 20. The
following discussion applies to any of the embodiments described
supra ( i.e., thermal oxidation or nitridization using a heating
chamber, thermal oxidation or nitridization using a directed beam
of radiation or particles, plasma oxidation/nitridization,
anodization, and chemical oxidation/nitridization).
[0079] Let R.sub.1 denote an electrical resistance of the resistor
14 prior to being oxidized or nitridized. Let R.sub.2 denote a
final electrical resistance of the resistor 14 (i.e., an electrical
resistance of the resistor 14 after being oxidized or nitridized).
Let R.sub.t denote a predetermined target electrical resistance
with an associated resistance tolerance .DELTA.R.sub.t for the
resistor 14 after the oxidation (or nitridization) has been
completed (i.e., it is intended that R.sub.2=R.sub.t within the
tolerance .DELTA.R.sub.t). The target electrical resistance R.sub.t
is application dependent. For example, in an analog circuit R.sub.t
may be a function of a capacitance in the circuit, wherein for the
given capacitance, R.sub.t has a value that constrains the width of
a resonance peak to a predetermined upper limit. In practice, the
predetermined resistance R.sub.t, together with the associated
resistance tolerance .DELTA.R.sub.t, may be provided for the
intended application.
[0080] The resistor 14 may have its electrical resistance tested
during or after the exposure of the resistor 14 to the oxygen
particles 20. As stated supra, the thickness t of the oxidized (or
nitridized) region 22 (see FIG. 3) increases as the time of said
exposure increases, and the electrical resistance of the resistor
14 increases as the thickness t increases. Thus, the final
electrical resistance may be controlled by selection of the time of
exposure. The time of exposure may be selected based on any method
or criteria designed to obtain R.sub.2 as being within
R.sub.t.+-..DELTA.R.sub.t (i.e.,
R.sub.t-.DELTA.R.sub.t.ltoreq.R.sub.2.ltoreq.R.sub.t+.DELTA.R.sub.t).
For example, calibration curves derived from prior experience may
be used for determining the time of exposure that results in
R.sub.2 being within R.sub.t.+-..DELTA.R.sub.t.
[0081] An iterative testing procedure may be utilized such that the
electrical resistance of the resistor 14 is tested during the
exposing of the resistor 14 to the oxygen particles 20 and thus
during the oxidizing (or nitridizing) of the resistor 14. The
testing during the exposing of the resistor 14 to the oxygen
particles 20 determines continuously or periodically whether
R.sub.2'' is within R.sub.t.+-..DELTA.R.sub.t, wherein R.sub.2'' is
the latest resistance of the resistor 14 as determined by the
testing. The testing is terminated if R.sub.2'' is within
R.sub.t.+-..DELTA.R.sub.t or if
(R.sub.2''-R.sub.1)(R.sub.t-R.sub.2'').ltoreq.0.
[0082] While particular embodiments of the present invention have
been described herein for purposes of illustration, many
modifications and changes will become apparent to those skilled in
the art. Accordingly, the appended claims are intended to encompass
all such modifications and changes as fall within the true spirit
and scope of this invention.
* * * * *