U.S. patent application number 09/326878 was filed with the patent office on 2001-09-06 for thin-film resistor, wiring substrate, and method for manufacturing the same.
Invention is credited to MATSUI, KOJI, SHIBUYA, AKINOBU.
Application Number | 20010019301 09/326878 |
Document ID | / |
Family ID | 26489970 |
Filed Date | 2001-09-06 |
United States Patent
Application |
20010019301 |
Kind Code |
A1 |
SHIBUYA, AKINOBU ; et
al. |
September 6, 2001 |
THIN-FILM RESISTOR, WIRING SUBSTRATE, AND METHOD FOR MANUFACTURING
THE SAME
Abstract
A thin-film resistor that enables a pattern to be simply formed
by means of wet etching, that has an excellent resistance
temperature characteristic, and that can be easily manufactured,
and a method for manufacturing this thin-film resistor, as well as
a wiring substrate with this thin-film resistor formed therein. A
thin resistor film according to this invention has a structure in
which crystal grains deposit in the matrix of amorphous titanium
nitride. The thin resistor film is formed on a substrate. The
crystal grains includes at least one of crystal titanium nitride
and crystal titanium. The thin resistor film can be manufactured
using a simple process and can provide a wide range of resistance
values with a small tolerance and a temperature coefficient of
resistance close to zero.
Inventors: |
SHIBUYA, AKINOBU; (TOKYO,
JP) ; MATSUI, KOJI; (TOKYO, JP) |
Correspondence
Address: |
LAFF WHTESEL CONTE & SARET
401 NORTH MICHIGN AVENUE
CHICAGO
IL
60611
|
Family ID: |
26489970 |
Appl. No.: |
09/326878 |
Filed: |
June 7, 1999 |
Current U.S.
Class: |
338/308 ;
338/309 |
Current CPC
Class: |
H05K 2203/0361 20130101;
H01C 7/006 20130101; H01C 3/04 20130101; H05K 2201/0317 20130101;
H01C 17/12 20130101; H05K 3/388 20130101; H05K 1/167 20130101 |
Class at
Publication: |
338/308 ;
338/309 |
International
Class: |
H01C 003/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 12, 1998 |
JP |
10-165112 |
Jun 17, 1998 |
JP |
10-170313 |
Claims
What is claimed is:
1. A thin-film resistor comprising a composite of at least either
crystal titanium nitride or crystal titanium and amorphous titanium
nitride.
2. The thin-film resistor according to claim 1, wherein the number
of nitrogen atoms in said composite is 1/3 to 2/3 of the total
number of atoms.
3. The thin-film resistor according to claim 1, wherein said
crystal titanium nitride is at least one of TiN and Ti.sub.2N.
4. The thin-film resistor according to claim 2, wherein said
crystal titanium nitride is at least one of TiN and Ti.sub.2N.
5. The thin-film resistor according to claim 1, wherein the
specific resistivity is 0.1 m.OMEGA..multidot.cm to 100
m.OMEGA..multidot.cm.
6. A method for manufacturing a thin-film resistor, wherein the
thin-film resistor according to claim 1 is manufactured using as a
process gas a nitrogen gas or a gas containing a nitrogen and using
a titanium target and DC magnetron sputtering.
7. The method for manufacturing a thin-film resistor according to
claim 6, wherein the partial pressure of said nitrogen gas is
controlled during sputtering to vary the amount of nitrogen in said
composite.
8. A wiring substrate with the thin-film resistor according to
claim 1 built in its inner layer or on its surface.
9. A wiring substrate having a wiring provided on an insulator
wherein; said wiring is placed on said insulator via a thin
titanium nitride film provided on said insulator.
10. The wiring substrate according to claim 9, wherein; said wiring
is configured by means of copper electroplating.
11. A wiring substrate having a structure in which a wiring is
connectively provided on an insulator via a resistor, wherein; said
resistor comprises a thin titanium nitride film and wherein the
thin titanium nitride film is interposed between said wiring and
said insulator.
12. The wiring substrate according to claim 11, wherein; said
wiring is configured by means of copper electroplating.
13. The wiring substrate according to claims 9, wherein; the wiring
connected via said thin titanium nitride film is placed on one of
plural layers of insulators or over a plurality of insulators.
14. A method for manufacturing a wiring substrate comprising the
steps of: forming a thin titanium nitride film on an insulator,
forming a wiring on said thin titanium nitride film, and patterning
said thin titanium nitride film.
15. A method for manufacturing a wiring substrate comprising the
steps of: forming a thin titanium nitride film on an insulator,
forming on said thin titanium nitride film a wiring having a
discontinuous portion, and patterning into the resistor a portion
of said thin titanium nitride film that is located under the
discontinuous portion of said wiring.
16. The method for manufacturing a wiring substrate according to
claim 14 comprising the steps of: after forming said titanium
nitride film, forming a thin copper film on said thin titanium
nitride film formed, forming a copper wiring on the thin copper
film, and removing said thin copper film.
17. The method for manufacturing a wiring substrate according to
claim 16, wherein; said thin titanium nitride film and thin copper
film are formed by means of sputtering.
18. The method for manufacturing a wiring substrate according to
claim 17, wherein; the process for forming said copper wiring is an
electroplating method.
19. The method for manufacturing a wiring substrate according to
any of claims 18 comprising the step of: before forming said copper
wiring, forming a resist film and patterning this resist film.
20. The method for manufacturing a wiring substrate according to
any of claims 19, wherein; in patterning said thin titanium nitride
film, the thin titanium nitride film is etched using a water
solution containing ammonia and hydrogen peroxide.
21. The method for manufacturing a wiring substrate according to
any of claims 20, wherein; said thin titanium nitride film is
formed by means of sputtering and wherein the surface temperature
is set at 150.degree. C. or more during sputtering.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention belongs to the field of electronic
technologies and relates to a thin-film resistor operating as a
passive element and its manufacturing method, and a wiring
substrate with this thin-film resistor built therein. The present
invention also relates to a wiring substrate and its manufacturing
method, and in particular, to a wiring substrate with a resistor
built therein and its manufacturing method.
[0003] 2. Description of the Prior Art
[0004] With the recent increasing demand for smaller-sized mounting
substrates, there have been an increasing number of reports on
substrates with a resistor built therein. In terms of the
structure, resistor built-in substrates are classified into
substrates with a chip resistor part built therein, substrates with
a thick-film resistor (paste) built therein, and substrates with a
thin-film resistor built therein. Chip-resistor-part built-in
substrates are limited in size reduction, and thick-film-resistor
built-in substrates do not provide an accurate resistance value.
Thin-film-resistor built-in substrates are most excellent in size
reduction and provide a relatively accurate resistance value.
[0005] Japanese Patent Application Laid-Open No. 4-174590 has
reported on a resistor used for a thin-film-resistor built-in
substrate and comprising a nichrome alloy, tantalum nitride, ITO
(Indium Tin Oxide), or metal silicide. With such a thin film,
however, in the patterning method, wet etching may degrade the
substrate due to the use of a strong acid, while dry etching may
disadvantageously increase the time required for the process. In
addition, even the wet etching method has difficulties in achieving
the selective etching between the resistor and electrodes or wiring
depending on the type of the resistor.
[0006] Thin titanium nitride films are conventionally used as
contact barriers for semiconductor elements, as reported in
Japanese Patent Application Laid-Open No. 63-156341. Japanese
Patent Application Laid-Open No. 3-276755 reports on a method for
manufacturing a semiconductor device that uses TiN as a barrier
metal and a resistor in semiconductor elements. This resistor,
however, relates to a thin TiN polycrystal film. In addition, J.
Vac. Sci. Technol. A5, p.1778 (1987) and Papers Presented at
Semiconductor Integrated Circuit Technology Symposium, 28, p.97
(1985) report a smaller and a larger resistance values of the thin
TiN polycrystal film, that is, 20 to 25 .mu..OMEGA..multidot.cm and
1,300 .mu..OMEGA..multidot.cm, respectively. In this manner, the
thin TiN polycrystal film cannot be easily formed into a thin
high-resistance film and has a large temperature coefficient of
resistance.
[0007] On the other hand, Japanese Patent Application Laid-Open No.
61-148732 reports the use as a heating resistor for a temperature
detecting element of an amorphous metal compound that is a metal
nitride such as TiN or TaN produced by means of high-frequency
magnetron sputtering. Due to the variation of the resistance value
caused by the temperature, however, this resistor was not suitable
as a typical circuit resistor such as a terminal resistor.
[0008] A composite consisting of amorphous and crystal titanium
nitride is disclosed as a surface treating layer for stainless
steel in Japanese Patent Application Laid-Open No. 3-6362, a
coating layer on a hard base substrate in Japanese Patent
Application Laid-Open Nos. 5-209120 and 9-209121, a thin
non-magnetic film for a magnetic head in Japanese Patent
Application Laid-Open No. 3-132006, or a semiconductor contact
barrier in Japanese Patent Application Laid-Open No. 4-206818. The
manufacturing methods disclosed in these applications inject Ti
ions into stainless steel in an atmosphere containing nitrogen,
inject univalent boron ions into a titanium nitride coated layer
formed on a hard base substrate by means of the arc ion plating
method using cathode arc discharge, heat the substrate to
300.degree. C. or more after ion beam sputtering, or inject ions
after the formation of a TiN crystal film. In this manner, the
process for forming a composite consisting of amorphous and crystal
titanium nitride is complicated.
[0009] In addition, due to the needs for smaller-sized mounting
substrates, there is an increasing demand for substrates such as
build-up circuit boards which have a fine wiring of a multilayer
wiring structure. Accordingly, there have been an increasing number
of reports on substrates with a resistor built therein. In terms of
the structure, resistor built-in substrates are classified into
substrates with a chip resistor part built therein, substrates with
a thick-film resistor paste built therein, and substrates with a
thin-film resistor built therein.
[0010] Of these substrates, chip-resistor-part built-in substrates
are limited in size reduction, and thick-film-resistor paste
built-in substrates do not provide an accurate resistance
value.
[0011] On the other hand, thin-film-resistor built-in substrates
are most excellent in size reduction and provide a relatively
accurate resistance value. Japanese Patent Application Laid-Open
No. 4-174590, Japanese Patent Application Laid-Open No. 6-85100,
and Japanese Patent Application Laid-Open No. 7-34510 have each
reported on a resistor used for a thin-film-resistor built-in
substrate and comprising a nichrome alloy, tantalum nitride, ITO
(Indium Tin Oxide), or metal silicide.
[0012] In addition, in order to prevent the resistance value from
being degraded over time due to the diffusion between the resistor
and an electrode or wiring, Japanese Patent Application Laid-Open
No. 4-174590 and Japanese Patent Application Laid-Open No. 7-34510
have reported on structures in which a diffusion prevention film is
formed in the interface between the resistor and the electrode or
wiring and in which the surface of a nickel chrome (nichrome) alloy
layer acting as a resistor is passivated.
[0013] Furthermore, those electrodes or wires in a build-up circuit
board which are manufactured using the photolithography technology
are allowed to adhere to the resistor by roughening the substrate,
but the roughening of the substrate is not suitable for fine
wiring.
[0014] A substrate with a fine wiring is produced by a process
using sputtering, and in this case, Cr, Ti, Mo, or Zr is generally
used as adhering ground coat metal for electrodes or wires. For
example, Japanese Patent Application Laid-Open No. 55-158697
reports on a substrate using Ti as a wiring ground coat.
BRIEF SUMMARY OF THE INVENTION
[0015] Object of the Invention
[0016] As described above, the conventional thin-film resistor has
the disadvantages of degrading a substrate on which the thin-film
resistor is formed during etching and requiring an excessive amount
of time for the thin-film resistor formation process. In addition,
if the thin polycrystal titanium nitride film is used as the
resistor, a high-resistivity film cannot be easily formed and the
thin film has a large temperature coefficient of resistance.
Furthermore, a complicated manufacturing process must be used in
order to form a composite consisting of amorphous and crystal
titanium nitride.
[0017] In addition, if a conventionally reported thin film is used
as a resistor, wet etching used to pattern the resistor may degrade
the substrate due to the use of a strong acid, while dry etching
that does not degrade the substrate may disadvantageously increase
the time required for the process.
[0018] In addition, if a passivation film is to be formed between
the resistor and the electrode or wiring, a step for forming this
film is required, thereby increasing the time required for the
entire process.
[0019] Furthermore, no ground coat metals conventionally proposed
to improve the adhesion between the wiring and an insulator are
excellent in both etching capability and adhesion.
[0020] Thus, for the conventional thin-film-resistor built-in
substrates, the following problems are desirably solved: the
degradation of the substrate during the etching of the resistor,
the increased time for the resistor formation process, the
variation of the resistance value over time which is caused by the
absence of the diffusion prevention film between the resistor and
the electrode or wiring, and the failure of the ground coat metal
for the electrodes or wiring in the conventional build-up circuit
boards to be excellent in both etching capability and adhesion.
[0021] Summary of the Invention
[0022] An object of this invention is to provide thin-film resistor
that enables a pattern to be easily formed by wet etching, that has
an excellent temperature characteristics for resistance, and that
is easy to manufacture, and a method for manufacturing this
thin-film resistor, as well as a wiring substrate with this
thin-film resistor built therein.
[0023] A thin-film resistor according to this invention consists of
a composite of at least either crystal titanium nitride or crystal
titanium and amorphous titanium nitride. In addition, in a method
for manufacturing a thin-film resistor according to this invention,
the thin-film resistor according to this invention is manufactured
using as a process gas a nitrogen gas or a gas containing a
nitrogen and using a titanium target and DC magnetron sputtering.
In this case, the partial pressure of nitrogen can be controlled
during sputtering to vary the amount of nitrogen in the composite
in order to control the resistance value.
[0024] In addition, the number of nitrogen atoms in the composite
is preferably one-third to two-thirds relative to the total number
of atoms. This is because below one-third, the amount of Ti crystal
deposited increases and the temperature coefficient of resistance
increases whereas above two-thirds, the amorphous phase becomes
unstable to vary the resistance value over time. In addition, the
specific resistivity of the thin-film resistor desirably covers a
wide range of values. For example, to obtain a resistance value of
50 .OMEGA., a material of specific resistivity 0.1
m.OMEGA..multidot.cm may be used to execute patterning so that the
thickness is 20 nm and so that the width and the length are the
same. Conversely, a material of specific resistivity 100
m.OMEGA..multidot.cm can be used with the same pattern sizes as in
the above resistor to obtain a 50-k.OMEGA. resistor. Varying the
sizes enables the resistance value to be adjusted. In general,
however, if the thin film is too thin, a defect may occur in the
film or any physical property may change due to the strong effect
of the surface structure. In addition, increasing the thickness may
increase the time required for the process or may increase the
stress of the film to release it from the substrate. Varying the
ratio between the width and length is not suitable for reducing the
size of the resistor. Although different materials are
conventionally used to cover the range of resistance values, the
thin-film resistor of this invention can use a single target to
obtain a wide range of resistance values.
[0025] The composite of at least either crystal titanium nitride or
crystal titanium and amorphous titanium nitride enables a
dimensionally accurate wet etching pattern to be formed. Thus, the
time required for the process and thus costs can be reduced, and
the accuracy of the resistance value can be improved. In addition,
the use of this composite enables the ratio between titanium and
nitrogen in the thin resistor film to vary to improve the
resistance temperature characteristic while increasing the range of
resistance values.
[0026] This invention is achieved in view of the above needs, and
its object is to provide a wiring substrate having a wiring that
adheres well to an insulator.
[0027] Another object of this invention is to provide a
thin-film-resistor built-in wiring substrate that provides an
accurate resistance value and a high productivity, that does not
adversely affect the other constituent members during production,
and in which the wiring adheres well to an insulator.
[0028] Yet another object of this invention is to provide a method
for manufacturing a wiring substrate having a wiring that adheres
well to an insulator.
[0029] Still another object of this invention is to provide a
method for manufacturing a thin-film-resistor built-in wiring
substrate that provides an accurate resistance value and a high
productivity, that does not adversely affect the other constituent
members during production, and in which the wiring adheres well to
an insulator.
[0030] To attain these objects, this invention provides a wiring
substrate having a wiring on an insulator, wherein the wiring is
placed on the insulator via a thin titanium nitride film provided
on the insulator.
[0031] According to the invention of this configuration, the thin
titanium nitride film adheres well to the insulated substrate and
enables film stress to be reduced under the film formation
conditions, so it is preferably used as a wiring ground coat. A wet
etching pattern can be dimensionally accurately formed on this
film, thereby enabling a fine wiring to be formed. Besides, this
film allows wet etching using a water solution containing ammonium,
thereby preventing the substrate or wiring from being degraded
during etching. Consequently, using the thin titanium nitride film
as the ground coat for the wiring, such a wiring substrate can be
obtained that has a very reliable fine wiring.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 is a schematic sectional view showing a thin resistor
film according to this invention;
[0033] FIG. 2 is a schematic sectional view showing a first example
of a method for forming the thin-film resistor according to this
invention on a wiring substrate;
[0034] FIG. 3 is a schematic sectional view showing a second
example of a method for forming the thin-film resistor according to
this invention on a wiring substrate;
[0035] FIG. 4 is a table showing film formation conditions and
specific resistivity for an embodiment of the thin-film resistor
according to this invention;
[0036] FIG. 5 is a chart of X-ray diffraction of sample 1
manufactured on an SiO.sub.2/Si substrate at 25.degree. C. and 3
mTorr, according to the embodiment of this invention;
[0037] FIG. 6 is a chart of X-ray diffraction of sample 15
manufactured on an epoxy resin/FR-4 circuit board at 25.degree. C.
and 3 mTorr, according to the embodiment of this invention;
[0038] FIG. 7 is a chart of X-ray diffraction of sample 13
manufactured on an SiO.sub.2/Si substrate at 150.degree. C. and 3
mTorr, according to the embodiment of this invention;
[0039] FIG. 8 is a chart of X-ray diffraction of sample 27
manufactured on an epoxy resin/FR-4 circuit board at 150.degree. C.
and 3 mTorr, according to the embodiment of this invention;
[0040] FIG. 9 is a chart of X-ray diffraction of sample 11
manufactured on an SiO.sub.2/Si substrate at 25.degree. C. and 0.5
mTorr, according to the embodiment of this invention;
[0041] FIG. 10 is a chart of X-ray diffraction of sample 25
manufactured on an epoxy resin/FR-4 circuit board at 25.degree. C.
and 0.5 mTorr, according to the embodiment of this invention;
[0042] FIG. 11 is a chart of X-ray diffraction of sample 1
manufactured on an SiO.sub.2/Si substrate at 25.degree. C. and 3
mTorr and heated in a flow of nitrogen gas at 1,000.degree. C. for
five minutes, according to the embodiment of this invention;
[0043] FIG. 12 is a schematic sectional view showing a conventional
thin polycrystal titanium nitride film;
[0044] FIG. 13 shows one embodiment of a wiring substrate according
to this invention.
[0045] FIG. 13(a) is a plan view and
[0046] FIG. 13(b) is a sectional view;
[0047] FIG. 14 is a sectional view showing one embodiment of the
wiring substrate according to this invention and showing the case
in which a titanium nitride resistor is provided in a build-up
layer in a build-up circuit board;
[0048] FIG. 15 is a sectional view showing one embodiment of the
wiring substrate according to this invention and showing the case
in which the titanium nitride resistor is provided in the interface
between a base substrate and the build-up layer in the build-up
circuit board;
[0049] FIG. 16 is a sectional view showing one embodiment of the
wiring substrate according to this invention and showing the case
in which the titanium nitride resistor is provided on the surface
of the build-up layer in the build-up circuit board;
[0050] FIG. 17 is a sectional view showing one embodiment of the
wiring substrate according to this invention and showing the case
in which the titanium nitride resistor is provided on the surface
of the base substrate located on the rear surface of the build-up
layer in the build-up circuit board;
[0051] FIG. 18 is a sectional view showing one embodiment of the
wiring substrate according to this invention and showing the case
in which the titanium nitride resistor is provided on the surface
of the base substrate in the build-up circuit board from which the
build-up layer is absent;
[0052] FIG. 19 is a flowchart describing a method for manufacturing
a resistor built-in wiring substrate according to the wiring
substrate of this invention, according to a second embodiment;
[0053] FIG. 20 is a flowchart describing a method for manufacturing
a resistor built-in wiring substrate according to the wiring
substrate of this invention, according to a third embodiment;
[0054] FIG. 21 is a sectional view showing another embodiment of
the wiring substrate of this invention and showing the structure of
a wiring substrate;
[0055] FIG. 22 is a sectional view describing a conventional
semiconductor substrate using titanium nitride as a resistor;
[0056] FIG. 23 is a sectional view describing a conventional
semiconductor substrate using titanium nitride as a resistor;
and
[0057] FIG. 24 is a flowchart describing a conventional method for
manufacturing a resistor built-in wiring substrate.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0058] FIG. 12 is a schematic sectional view showing a thin
titanium nitride film according to the prior art. A thin titanium
nitride film 50 is formed on a substrate 52. The thin titanium
nitride film 50 can be easily patterned by means of wet etching.
When, however, the thin titanium nitride film 50 is used as a
resistor, the temperature coefficient of resistance is large, while
the range of the resulting specific resistivity is narrow. The
reason is as shown in FIG. 12. That is, since the thin titanium
nitride film 50 is a thin stoichiometry polycrystal film of
chemical formula TiN consisting of a large number of columnar
crystals 54, the resistance property is dominated by the
temperature coefficient of resistance and specific resistivity
value proper to TiN.
[0059] The inventor produced a thin resistor film consisting of a
composite of at least either crystal titanium nitride or crystal
titanium and amorphous titanium nitride to find that the
temperature coefficient of resistance and the specific resistivity
value significantly vary with the ratio between the amounts of
crystal and amorphous solids in the thin resistor film or the ratio
between titanium and nitrogen.
[0060] FIG. 1 is a schematic sectional view showing a thin resistor
film according to a first embodiment of this invention. A thin
resistor film 10 is assumed to have a structure in which crystal
grains 14 deposit in the matrix of amorphous titanium nitride 12. A
thin resistor film 10 is formed on a substrate 16. The crystal
grains 14 comprise at least one of crystal titanium nitride and
crystal titanium. Although FIG. 1 clearly shows the crystal grains
14 for easy understanding, the actual crystal grains 14 are assumed
to be finer and to have no definite interfaces with the amorphous
solid. The etching time for the thin resistor film 10 tends to
increase with the increasing rate of nitrogen, but the thin film 10
is well suited for wet etching.
[0061] If a thin titanium nitride film consisting of only amorphous
solids is subjected to heat history after manufacturing, crystals
may deposit in the thin film to substantially vary the resistance
value. In contrast, the thin resistor film 10 is formed by
depositing the composite, thereby reducing the variation of the
resistance value caused by thermal history of 500.degree. C. or
less. This may be because the amorphous and crystal solids are
balanced in the composite. The crystal titanium nitride that can be
contained in the composite is preferably TiN or Ti.sub.2N, but this
invention is not limited to such a crystal.
[0062] In addition, the thin resistor film 10 is preferably used as
an alternative to a chip resistor used for a mounting substrate,
and enables a resistor to be formed on the surface of the substrate
16 or inside it. The substrate 16 preferably comprises an Si
substrate with an insulating layer, a printed circuit board, a
build-up circuit board, or a ceramic substrate, and the thin-film
resistor 10 may be formed either in its inner layer wiring or on
its surface. In addition, the preferable Si and ceramic substrates
include a multilayer wiring substrate having an organic insulating
layer on its surface. In this case, the resistor may be formed
either in the inner layer wiring in the organic multilayer portion
or on the surface of the substrate. In particular, if the resistor
is formed in the inner layer of the substrate, the mounting area of
the substrate surface can be substantially reduced without changing
the substrate thickness, thereby noticeably contributing to
reducing the size of the substrate. The substrate 10 may also be,
for example, an organic film, a glass plate, or a metal foil.
[0063] The following two methods can be used to form the thin-film
resistor of this invention in a circuit in a wiring substrate. A
first method forms the thin-film resistor 10 on the substrate 16,
forms a pattern by means of photolithography, and then forms a
wiring 18, as shown in FIG. 2. A second method forms the thin-film
resistor 10 on the substrate 16 with the wiring 18 pre-formed
therein and then forms a pattern by means of photolithography, as
shown in FIG. 3. Of course, this invention is not limited to these
formation methods.
[0064] A preferable method for forming the thin-film resistor 10 is
preferably DC magnetron sputtering using titanium target and a
nitrogen gas. In this case, the gas pressure during sputtering can
be used to control the ratio between titanium and nitrogen in the
thin-film resistor 10. Furthermore, the gas pressure, substrate
temperature, or sputter power can be controlled during sputtering
to control the type and amount of crystal in the thin film. In
particular, by heating the substrate 16 up to a certain temperature
during sputtering, the variation of the resistance value can be
reduced when the thin film is subjected to thermal history. The
substrate temperature during sputtering is preferably 500.degree.
C. or less, and in particular, a good resistance characteristic can
be obtained when the film is formed at a substrate temperature of
200.degree. C. or less.
[0065] Next, examples of this invention will be described.
[0066] Thin-film resistors each comprising of a titanium nitride
composite were formed on an Si wafer with an oxide film formed on
its surface and on a printed circuit board FR-4 with an epoxy resin
coated on its surface. In this case, a sputter-up type inline DC
sputter apparatus was used to execute reactive sputtering using a
titanium target and a nitrogen gas, thereby forming thin-film
resistors. The pressure in the chamber of the sputter apparatus was
evacuated down to 9.9.times.10.sup.-7 Torr or less, and was then
maintained between 0.5 and 10 mTorr during film formation by
introducing 50 sccm of nitrogen gas into the chamber while
controlling an evacuation orifice. The surface temperature was set
at 25 to 200.degree. C., the speed at which the substrate moved
over a target was set at 100 to 500 mm/min., and the sputter
current was set at 2.5 to 8 A. These thin-film resistors (hereafter
referred to as "samples" were evaluated by means of sheet
resistivity measurements using the Van der Pauw method, thickness
measurements using a contact probe film thickness meter, and
thin-film structure analysis using X-ray diffraction.
[0067] FIG. 4 shows film formation conditions for the produced
samples, and their film thicknesses and resistivity values. Under
each set of film formation conditions, 50 samples obtained by
cutting the substrate into squares of 10 mm side were measured at
the room temperature, and their average was determined as the
specific resistivity value. The film thickness on the printed
circuit board could not be measured due to the large roughness of
the surface of the substrate. Thus, the specific resistivity of the
sample formed on the printed circuit board was calculated from the
measured sheet resistivity value by assuming that this sample had
the same film thickness as the sample on the Si substrate
simultaneously produced.
[0068] The specific resistivity of the samples under the film
formation conditions in FIG. 4 was between 0.209 and 13.315
m.OMEGA..multidot.cm for the Si substrate and between 0.280 and
21.147 m.OMEGA..multidot.cm for the FR-4 circuit board. In either
substrate, a wide range of resistance values could be obtained by
varying the film formation conditions. In particular, the samples
produced at a nitrogen gas pressure of 10 mTorr exhibited a very
large resistance value exceeding 10 m.OMEGA..multidot.cm. The large
variation of the resistance value of the samples by means of the
film formation conditions is presumably caused by the different
ratios between titanium and nitrogen in the thin film or the
different types or amounts of crystal in the thin film. In
addition, the accuracy of the resistance value of each sample
corresponded to a tolerance within .+-.5%. In particular, the
accuracy of samples 13, 14, 27, and 28 under the substrate
temperature condition of 150.degree. C. or more was high and
corresponded to a tolerance within .+-.2%. This is assumed to be
because the uniformity of the thin titanium nitride film is
improved better by heating the substrate.
[0069] In addition, samples 10, 13, 24, and 27 were measured for
the temperature characteristic of the resistor by measuring the
resistance value at 20 and 15.degree. C. As a result, the
temperature coefficients of resistance of these samples were 87.4
ppm/.degree. C., 186.2 ppm/.degree. C., -24.3 ppm/.degree. C., and
137.8 ppm/.degree. C., indicating a good temperature
characteristic. As described above, the sign of the temperature
coefficient of resistance was clearly shifted between plus and
minus depending on the variation of the nitrogen gas pressure
within the film formation conditions. Accordingly, the temperature
coefficient of resistance can be allowed to approach zero by
optimizing the film formation conditions.
[0070] Next, the results of evaluation of the structures of the
produced samples using X-ray diffraction will be described.
[0071] FIGS. 5, 6, 7, 8, 9, and 10 show the results of X-ray
diffraction for samples 1, 15, 13, 27, 11, and 25 in FIG. 4. FIG.
11 shows the results of X-ray diffraction for sample 1 in FIG. 4,
which was heated in a flow of nitrogen gas at 1,000.degree. C. for
five minutes. The X-ray diffraction used CuKa beams.
[0072] The diffraction patterns in FIGS. 5 to 11 all show a broad
and feeble diffracted beam near 2.theta.=36.degree.. The figures
show spacing (d) at the peak of the diffracted beam near
2.theta.=36.degree.. These diffracted beams are presumably emitted
from the crystal titanium nitride, and are broad and feeble because
the titanium nitride has a low crystallinity and includes an
amorphous solid.
[0073] On the other hand, the peak at 2.theta.=36.7.degree. of the
sample in FIG. 11 which was heated at 1,000.degree. C. is sharp and
strong, so it is identified as a diffracted beam from the (111)
face of the TiN crystal. This indicates that the heating caused the
amorphous solid of the titanium nitride to be crystallized.
[0074] According to JCPDS cards 38-1420, 17-0386, and 44-1294, the
spacings of TiN(111), Ti.sub.2N(200), and Ti(100) are 0.245 nm,
0.247 nm, and 0.256 nm, respectively. Thus, the broad peaks near
2.theta.=36.degree. in FIGS. 5 to 10 indicate the presence of all
of TiN, Ti.sub.2N, and Ti crystals. The spacing (d) at the peak of
the diffracted beam varies depending on the manufacturing
conditions, due to the different rates of these crystals contained
in the thin film, the different structures of the amorphous solid,
or the different ratios between titanium and nitrogen.
[0075] Since the thin-film resistor according to this invention
comprises at least either crystal titanium nitride or crystal
titanium and amorphous titanium nitride, it can be manufactured
using a simple process and can provide a wide range of resistance
values with a small tolerance and a temperature coefficient of
resistance close to zero.
[0076] In the method for manufacturing the thin-film resistor
according to this invention, the thin-film resistor according to
this invention can be manufactured by a simple process using as a
process gas a nitrogen gas or a gas containing nitrogen and using a
titanium target and DC magnetron sputtering. In addition, the
partial pressure of nitrogen can be controlled to easily
manufacture the thin-film resistor providing a wide range of
resistance values.
[0077] A second embodiment of this invention will be described with
reference to the drawings.
[0078] FIG. 13 shows one embodiment of a resistor built-in wiring
substrate according to this invention. FIG. 13(a) is a plan view
and FIG. 13(b) is a sectional view taken along A-A in FIG.
13(a).
[0079] In a wiring substrate B1, a resistor B11a comprising of a
thin titanium nitride film B11 is provided on an insulated
substrate B10, and a pair of electrodes B12 are provided across the
resistor B11 and have a wiring B13 connected thereto. The overall
bottom surface of the electrodes B12 and wiring B13 is wired on the
insulated substrate B10 using as a ground coat a thin titanium
nitride film B11 configurating the resistor B11a.
[0080] Thus, the thin titanium nitride film B11 exists not only in
the resistor pattern portion B11a but also under the overall bottom
surface of the pattern of the electrodes B12 or wiring B13, as
clearly shown in the sectional view in FIG. 13 (b). Accordingly,
the wiring B13 including the electrodes B12 of the wiring substrate
B1 forms a laminated structure with the thin titanium nitride film
B11, and the electrodes B12 and the wiring B13 are placed on the
insulated substrate B10 via the thin titanium nitride film B11.
[0081] The insulated substrate B10 comprises a build-up circuit
board, printed circuit board, Si substrate with an insulating
layer, a ceramic substrate, an organic film, a glass plate, or a
metal plate or foil with an insulating layer and may or may not
have an internal wiring, vias, or through-holes.
[0082] In addition, the titanium nitride preferably comprises a
thin film formed by means of PVD or CVD such as sputtering but is
not limited. Its shape or composition is neither limited. The
thickness of the thin titanium nitride film is selected to provide
a desired resistance value based on the width and length of the
resistor, which determine the resistance value.
[0083] The metal or alloy used for the electrodes or the wiring
preferably comprises copper formed by means of electroplating, but
its type or composition is not limited. In addition, the metal or
alloy used for the electrodes or the wiring may comprise a
plurality of metal or alloy layers. In particular, if copper is
used for the electrodes in the topmost layer, a barrier metal or an
oxidation preventing or a wettability improving metal is
effectively provided on the metal used for the wiring.
[0084] As reported in Japanese Patent Application Laid-Open No.
63-156341, the titanium nitride film is used as a contact barrier
for semiconductor elements. In addition, Japanese Patent
Application Laid-Open No. 3-276755 reports on a method for
manufacturing a semiconductor device, including the use of TiN as a
barrier metal and resistor in the semiconductor element.
[0085] FIGS. 22 and 23 show sectional views of a process for
manufacturing a semiconductor substrate that uses titanium nitride
as a resistor, which is disclosed in the conventional Japanese
Patent Application Laid-Open No. 3-276755.
[0086] This method for manufacturing a semiconductor device forms
an insulating film B110 on the surface of a semiconductor substrate
B100, forms an opening in the insulating film B110, provides a
contact portion B101 therein, and further forms a film of a barrier
metal B111 to form a structure in which the barrier metal B111
contacts the semiconductor substrate B100 in the contact portion
B101, as shown in (a). Next, the barrier metal B111 is patterned so
as to produce a barrier layer B112 and a resistor B113, and wiring
B120 is further formed, as shown in (b) According to this method
for manufacturing a semiconductor device, the steps of producing
the TiN resistor and the metal wiring are independent of each
other, and the metal wiring is directly formed on the insulating
film and inter-layer insulating film of the semiconductor
substrate. Consequently, the thin titanium nitride film does not
exist under certain portions of the wiring connected to the
resistor, so this structure is evidently different from the
structure of this invention.
[0087] The wiring substrate B1 is characterized by using the thin
titanium nitride film B11 as the resistor B11a, and in that the
thin titanium nitride film B11 functions as the ground coat for the
wiring B13 and electrodes B12 over the insulated substrate B10.
[0088] In addition, the method for manufacturing a semiconductor
device as shown in FIG. 23 forms the insulating film B10 on the
surface of the semiconductor substrate B100, forms the wiring B121
on the insulating film B110 via the resistor B114, and coats the
resistor B114 and wiring B121 with the inter-layer insulating film
B115. Next, via holes B116 are formed in the inter-layer insulating
film B115 so as to lead to the wiring B121, further forms a film of
the barrier metal B111, pattern the barrier metal B111 so as to
produce the barrier layer B112 and the resistor B113, and then
forms a wiring B122.
[0089] According to such a wiring substrate, the thin titanium
nitride film can reduce the film stress depending on the film
formation conditions and enables a uniform thin film to be formed
while enabling a dimensionally accurate pattern to be formed by wet
etching. Consequently, the accuracy of the resistance value can be
improved.
[0090] In addition, titanium nitride is etched using a water
solution containing ammonia and hydrogen peroxide and is
unsusceptible to acids. Thus, titanium nitride enables selective
etching between the resistor and the wiring or electrodes composed
of a conductive material such as metal copper. When the thin
titanium nitride film is patterned by means of etching, this
component prevents the wiring or the electrodes from being degraded
to avoid damaging the fine wiring. As a result, it is suitable for
recent wiring substrates such as build-up circuit boards which have
a fine wiring.
[0091] Besides, titanium nitride has a high barrier capability and
reduces the diffusion of the metal or the insulating material used
for the insulated substrate. Accordingly, the resistance value does
not significantly vary over time even without a passivation film,
so a stable resistance value is maintained.
[0092] The thin titanium nitride film is characterized in that by
varying the film formation conditions, the composition of the film
or the morphology of the crystal film can be varied to adjust the
stress of the thin film correspondingly. The adjustments of the
stress can provide good adhesion for any substrate. The stress can
be easily adjusted particularly by using reactive sputtering that
uses a titanium target and that introduces a nitrogen gas or a
mixed gas of nitrogen and argon and controlling the pressure during
sputtering and the temperature of the substrate.
[0093] In addition, due to its high barrier capability, titanium
nitride is characterized to preclude the diffusion of the metal or
alloy to the substrate used for the wiring. Thus, using the thin
titanium nitride film as the ground coat for the wiring and
electrodes over the insulated substrate, a very reliable wiring
substrate with a fine wiring can be provided.
[0094] The wiring substrate shown in FIG. 13 is a structure with
the thin titanium nitride film formed on the insulated
substrate.
[0095] The structure in which the thin titanium nitride film of
this invention is used as the resistor and as the ground coat layer
for the wiring can be applied to substrates of any structure and
even to build-up circuit boards of a multilayer wiring
structure.
[0096] FIGS. 14 to 18 show an embodiment in which this invention
has been applied to a build-up circuit board, and FIG. 14 shows the
case in which a resistor lies in a build-up layer. The build-up
layer B21 is formed by laminating a plurality of build-up resin
layers B21a on a base substrate B20, providing a wiring B23 on the
surface of each of the build-up resin layers, and connecting the
wirings between the build-up resin layers B21a together via the via
holes B24 provided in the build-up resin layer B21a.
[0097] The wiring layer B23 with the thin titanium nitride film B11
provided as the resistor B11a forms a laminated film with the thin
titanium nitride film B11. Thus, the layer B23 is connected to the
wiring in the underlying build-up layer via the thin titanium
nitride film B11, which functions as a barrier layer. The build-up
resin layer B21a is composed of, for example, a polyimide resin
obtained by spin-coating a solution containing a polyimide
precursor and heating the solution at about 400.degree. C.
[0098] In addition, FIG. 15 shows a mode in which the resistor is
placed in the interface between the base substrate and the build-up
layer, FIG. 16 shows a mode in which the resistor is placed on the
surface of the build-up layer, FIG. 17 shows a mode in which the
resistor is placed on the surface of the base substrate located on
the rear surface of the build-up layer, and FIG. 18 shows a mode in
which the resistor is placed on the surface of the base substrate
with no build-up layer provided thereon.
[0099] As clearly shown in these figures, the place in which the
resistor is formed is not limited. In addition, the resistor may be
formed in a plurality of layers. Furthermore, the ground coat for
the electrode or wiring in a layer with no resistor formed therein
may be the thin titanium nitride film or another thin film, or no
ground coat may be provided. The use of titanium nitride for the
ground coat for the wiring is effective in improving reliability
because titanium nitride can maintain adhesion with the substrate
and because it can prevent metal ions such as copper used for the
wiring from diffusing to the substrate.
[0100] Next, a method for manufacturing a wiring substrate
according to the embodiment shown in FIG. 13 will be described.
First, a first embodiment of the manufacturing method will be
described with reference to the flowchart in FIG. 19.
[0101] First, titanium nitride and copper are continuously
sputtered on the insulated substrate B10 in this order to form a
titanium nitride sputtered film B11 and a copper sputtered film.
The method for sputtering titanium nitride during this step is
preferably reactive DC sputtering that uses a titanium target and
that introduces a nitrogen gas or a mixed gas of nitrogen and
argon. The method, however, may be RF sputtering or other method
and is not limited.
[0102] Next, a photoresist film is formed by means of spin coating
and then patterned, and the pattern of electrodes and wiring is
removed from the photoresist film. At this point, if a
thin-film-resistor built-in substrate is to be obtained, electrodes
are formed at positions at which a resistor is placed and
disconnected portions are formed in the wiring.
[0103] Next, for example, a copper film is formed by means of
electroplating using thin copper films as electrodes.
[0104] Next, the photoresist film is stripped by the ash method to
leave the copper film in a pattern of electrodes and wiring using
the semi-additive method.
[0105] Subsequently, the copper sputtered film is etched and
removed using, for example, a mixed water solution of sulfuric acid
and hydrogen peroxide.
[0106] Next, the photoresist film is formed and patterned into a
resistor.
[0107] Then, the titanium nitride sputtered film Bl is etched using
a mixed water solution of ammonia and hydrogen peroxide. In this
case, the photoresist film, the wiring, and the electrodes function
as an etching mask.
[0108] Finally, the photoresist film is stripped by the ash method
to manufacture a wiring substrate such as that shown in FIG.
13.
[0109] In addition, a second embodiment of a method for
manufacturing a wiring substrate according to the embodiment shown
in FIG. 13 will be described with reference to the flowchart in
FIG. 20.
[0110] First, a thin titanium nitride film is formed by the
sputtering method to form a titanium nitride sputtered film.
[0111] Next, a photoresist film is formed by spin coating and then
patterned to form a pattern of electrodes and wiring opened in the
photoresist form.
[0112] Next, for example, a copper film is formed by the
electroless plating method.
[0113] Next, the photoresist film is stripped by the ash method to
leave the copper film into a pattern of electrodes and wiring using
the lift method.
[0114] Next, the photoresist film is formed and patterned into a
resistor.
[0115] Then, the titanium nitride sputtered film is etched using a
mixed water solution of ammonia and hydrogen peroxide.
[0116] Finally, the photoresist film is stripped by the ash method
to manufacture a wiring substrate such as that shown in FIG.
13.
[0117] Although the above manufacturing methods form the
photoresist film prior to the formation of the conductor film and
thus the wiring, the photoresist film may be formed after the
formation of the conductor film and prior to the etching of the
conductor film executed to form the wiring.
[0118] According to these methods for manufacturing a wiring
substrate, the first embodiment requires only a single sputtering
step due to the formation of both the thin titanium nitride film
and the thin copper film by means of continuous sputtering, and the
second embodiment also requires only a single sputtering step.
[0119] FIG. 24 shows a flowchart of an example of a process for
manufacturing a conventional substrate with a resistor built
therein.
[0120] In this manufacturing process, a film of resistor is formed
by sputtering, a photoresist film is then formed and patterned, and
a resistor is produced by means of etching. Subsequently, the
photoresist is stripped, a copper sputtered film is then formed,
and a photoresist film is formed and patterned. A copper film is
formed by the plating method, and the photoresist film is then
stripped to form electrodes and wiring composed of copper.
[0121] If the sputtering step is used for both the resistor and the
wiring, such a conventional method for manufacturing a wiring
substrate requires two sputtering steps. Even if the wiring is
formed prior to the formation of the resistor, two sputtering steps
are also required.
[0122] The present process for manufacturing a wiring substrate,
which is shown in FIGS. 19 and 20, requires only a single
sputtering step. Thus, the present method for manufacturing a
wiring substrate evidently has a shorter process than the
conventional method. This process is possible because titanium
nitride is insoluble in an acid such as a sulfuric acid used as an
etchant for the wiring metal such as copper whereas it is soluble
in a solution containing ammonia and hydrogen peroxide, thereby
preventing the etching liquid from attacking the wiring metal such
as copper, the electrode metal such as Ni or Au used for the
topmost layer, and the substrate.
[0123] In addition, in order to prevent the resistance value from
varying over time due to the diffusion between the resistor and the
electrodes or wiring, Japanese Patent Application Laid-Open No.
4-174590 and Japanese Patent Application Laid-Open No. 7-34510
disclose a structure having a diffusion prevention film in the
interface between the resistor and the electrode or wiring and a
structure in which the surface of a nickel chrome (nichrome) alloy
layer that is a resistor is passivated, respectively. Due to the
excellent barrier capability of titanium nitride, however, this
invention eliminates the needs for such passivation processing to
reduce the number of required steps, thereby contributing to
improving productivity.
[0124] Next, another embodiment of this invention will be described
in detail with reference to the drawings.
[0125] FIG. 21 shows the structure of a wiring substrate according
to another embodiment of this invention. This figure shows an
example of an application to a build-up circuit board. This wiring
substrate is characterized in that a ground coat for a wiring
provided on an insulator such as the base substrate B20 or build-up
layer B21 and comprising metal or alloy comprising a thin titanium
nitride film and in that the wiring B23 forms a laminated structure
with the thin titanium nitride film B11.
[0126] As in the resistor build-in circuit board, the insulated
substrate comprises a build-up circuit board, a printed circuit
board, an Si substrate with an insulating layer, a ceramic
substrate, an organic film, a glass plate, or a metal plate or foil
with an insulating layer, and may have an internal wiring, vias, or
through-holes.
[0127] In addition, titanium nitride preferably comprises a thin
film formed by PVD or CVD but is not limited. Its shape or
composition is neither limited.
[0128] The metal or alloy used for the wiring can be preferably
formed by means of plating but its type or composition is not
limited. In addition, the metal or alloy used for the wiring may be
a plurality of metal or alloy layers. In particular, if such metal
or alloy is used for the electrodes in the topmost layer, a barrier
metal or an oxidation preventing or a wettability improving metal
is effectively provided on the metal used for the wiring.
[0129] According to the structure of the wiring substrate shown in
FIG. 21, the ground coat for the wiring may be titanium nitride to
enable easy wet etching in order to provide a wiring with an
excellent adhesion.
[0130] The wet etching method for titanium nitride is not limited,
but the etchant is preferably a water solution of ammonia and
hydrogen peroxide. Such an etchant can prevent the substrate from
being degraded. A substrate using Ti as the ground coat allows the
use of a similar etchant, but the present titanium nitride is
characterized in that by varying the film formation conditions, the
composition of the film or the morphology of the crystal film can
be varied to adjust the stress of the thin film correspondingly.
The adjustments of the stress can provide good adhesion for any
substrate.
[0131] The stress can be easily adjusted particularly by using
reactive sputtering that uses a titanium target and that introduces
a nitrogen gas or a mixed gas of nitrogen and argon and controlling
the pressure during sputtering and the temperature of the
substrate. In addition, due to its high barrier capability,
titanium nitride is characterized to preclude the diffusion of the
metal or alloy to the substrate used for the wiring according to
the present structure, resulting in a high reliability.
EXAMPLES
[0132] Next, examples of this invention will be described.
[0133] The results of production of resistance-measuring testing
elements groups (TEGs) having the structure of the wiring substrate
with the titanium nitride resistor built therein according to this
invention shown in FIG. 13 will be explained.
[0134] Sets of wires and sets of two resistors having the
respective pattern sizes resistor width WR and resistor length LR
shown in Table 1 at Nos. 1 to 27 were produced in a single
insulated substrate to produce the substrate with the 54 resistors.
Referencing FIG. 13, an electrode width WE and electrode length LE
corresponding to the connection with the resistor were set at 2 mm
and 100 .mu.m, respectively, and in patterns Nos. B1 to B3, the
resistor was not formed and the substrates were used to measure
contact and wiring resistance.
1 TABLE 1 Wiring Resistor Resistor Pattern No. width (.mu.m) width
(.mu.m) length (.mu.m) No. B1 25 -- -- No. B2 50 -- -- No. B3 100
-- -- No. 1 25 0.1 0.1 No. 2 25 0.2 0.2 No. 3 25 0.1 0.2 No. 4 25
0.2 0.2 No. 5 25 0.4 0.2 No. 6 25 0.2 0.4 No. 7 25 0.4 0.4 No. 8 25
0.8 0.8 No. 9 25 1.6 1.6 No. 10 50 0.1 0.1 No. 11 50 0.2 0.1 No. 12
50 0.1 0.2 No. 13 50 0.2 0.2 No. 14 50 0.4 0.2 No. 15 50 0.2 0.4
No. 16 50 0.4 0.4 No. 17 50 0.8 0.8 No. 18 50 1.6 1.6 No. 19 100
0.1 0.1 No. 20 100 0.2 0.1 No. 21 100 0.1 0.2 No. 22 100 0.2 0.2
No. 23 100 0.4 0.2 No. 24 100 0.2 0.4 No. 25 100 0.4 0.4 No. 26 100
0.8 0.8 No. 27 100 1.6 1.6
[0135] The sputter-up type inline DC sputter apparatus was used to
continuously form thin films of titanium nitride and copper in this
order, on a 100-mm.sup.2 printed circuit board FR-4 coated with an
epoxy acrylate having a fluorene skeleton and described in Japanese
Patent Application Laid-Open No. 9-214141 and on an Si wafer of 5
inch diameter with an oxide film formed on its surface.
[0136] The pressure in the chamber of the sputter apparatus was
evacuated down to 9.9.times.10.sup.-7 Torr or less and was then
maintained between 0.5 and 10 mTorr during the formation of a thin
titanium nitride film by introducing 50 sccm of nitrogen into the
chamber while controlling an evacuation orifice. The temperature of
the substrate was set between 25 and 200.degree. C., the speed at
which the substrate moved over a target was set between 100 and 500
mm/min., and the sputter current was set between 2.5 and 8 A.
[0137] During the formation of a copper film, the pressure was
maintained at 3 mTorr by introducing 50 sccm of argon while
controlling the evacuation orifice. The temperature of the
substrate was set at 60.degree. C., the speed at which the
substrate moved over the target was set at 300 mm/min., and the
sputter current. was set at 4 A.
[0138] Next, photoresist coating, patterning, and copper
electroplating were executed on these substrates to form electrodes
and wires, and the resist was then stripped. The copper sputtered
film was etched using a mixed water solution of sulfuric acid,
hydrogen peroxide, and water.
[0139] Next, a photoresist was coated and patterned, and the
titanium nitride film was etched using a mixed water solution of
ammonia and hydrogen peroxide. Then, the resist was stripped to
obtain a pattern of titanium nitride resistor.
[0140] Finally, only measuring pads were opened and the epoxy
acrylate having the fluorene skeleton was coated to produce
resistance-measuring TEGs.
[0141] Table 2 shows the types of the produced TEG substrates, the
titanium nitride film formation conditions, the mean value of the
sheet resistivity converted from the measured resistance values
from the 54 positions, and the tolerance of the sheet
resistivity.
2TABLE 2 Sheet Substrate N.sub.2 Substrate Sheet resistivity
Substrate Current speed pressure temperature resistivity tolerance
No. Substrate (A) (mm/min) (mTorr) (.degree. C.) (.OMEGA./square)
(%) 1 FR-4 4 100 3 25 75 .+-.7 2 FR-4 4 200 3 25 186 .+-.10 3 FR-4
4 300 3 25 325 .+-.20 4 FR-4 4 400 3 25 480 .+-.6 5 FR-4 8 100 3 25
25 .+-.6 6 FR-4 8 200 3 25 50 .+-.3 7 FR-4 8 300 3 25 81 .+-.3 8
FR-4 8 400 3 25 143 .+-.5 9 FR-4 8 500 3 25 206 .+-.8 10 FR-4 4 100
10 25 3204 .+-.20 11 FR-4 2.5 100 0.5 25 44 .+-.5 12 FR-4 4 100 3
100 65 .+-.8 13 FR-4 4 100 3 150 60 .+-.5 14 FR-4 4 100 3 200 82
.+-.5 15 Si 4 100 3 25 54 .+-.6 16 Si 4 200 3 25 126 .+-.4 17 Si 4
300 3 25 209 .+-.2 18 Si 4 400 3 25 252 .+-.2 19 Si 8 100 3 25 15
.+-.10 20 Si 8 200 3 25 38 .+-.6 21 Si 8 300 3 25 60 .+-.3 22 Si 8
400 3 25 95 .+-.3 23 Si 8 500 3 25 124 .+-.4 24 Si 4 100 10 25 2017
.+-.10 25 Si 2.5 100 0.5 25 36 .+-.8 26 Si 4 100 3 100 46 .+-.3 27
Si 4 100 3 150 42 .+-.2 28 Si 4 100 3 200 56 .+-.2
[0142] These results indicate that depending on the titanium
nitride film formation conditions, the sheet resistivity of the
FR-4 circuit board can be controlled to between 25 .OMEGA./square
and 3.2 k.OMEGA./square while the sheet resistivity of the Si
substrate can be controlled to between 15 .OMEGA./square and 2.0
k.OMEGA./square. Under the same titanium nitride film formation
conditions, the FR-4 circuit board has a larger sheet resistivity
value and tolerance than the Si substrate. This is assumed to be
due to the difference in surface flatness.
[0143] In addition, FR-4 circuit board Nos. 2 and 3 had extremely
high sheet resistivity tolerances because cracks or wrinkles
occurred in the produced resistor pattern. However, circuit boards
Nos. 10 and 24, which exhibited high resistance values of a
k.OMEGA. order, had large sheet resistivity tolerances despite the
absence of cracks or wrinkles.
[0144] On the other hand, the FR-4 circuit boards of substrate Nos.
13 and 14 had very small sheet resistivity tolerances within +5%,
and the Si substrates with substrate Nos. 27 and 28 had very small
sheet resistivity tolerances dispersing .+-.2%.
[0145] Thus, assuming that heating at 150.degree. C. or more is
effective in reducing the tolerance in resistance values, the
titanium nitride film was formed by varying the sputter chamber
pressure under each set of conditions including the target
substrate temperature of 150.degree. C. shown in Table 3 below. As
in Table 2, Table 3 shows the types of the substrates, the titanium
nitride film formation conditions, the mean value of the sheet
resistivity, and the tolerance of the sheet resistivity.
3TABLE 3 Sheet Substrate N.sub.2 Substrate Sheet resistivity
Substrate Current speed pressure temperature resistivity tolerance
No. Substrate (A) (mm/min) (mTorr) (.degree. C.) (.OMEGA./square)
(%) 29 FR-4 2.5 100 0.5 150 32 .+-.5 30 FR-4 2.5 500 0.5 152 383
.+-.10 31 FR-4 4 100 1 152 30 .+-.7 32 FR-4 4 500 1 153 298 .+-.9
33 FR-4 4 100 3 152 58 .+-.5 34 FR-4 4 500 3 151 636 .+-.3 35 FR-4
8 100 3 151 34 .+-.4 36 FR-4 8 500 3 153 138 .+-.3 37 FR-4 4 100 6
147 424 .+-.9 38 FR-4 4 500 6 150 1652 .+-.11 39 FR-4 8 100 6 153
71 .+-.8 40 FR-4 8 500 6 151 311 .+-.6 41 FR-4 4 100 10 150 2115
.+-.15 42 FR-4 4 500 10 153 2753 .+-.8 43 FR-4 8 100 10 152 224
.+-.5 44 FR-4 8 500 10 153 535 .+-.8 45 Si 2.5 100 0.5 150 25 .+-.5
46 Si 2.5 500 0.5 152 180 .+-.5 47 Si 4 100 1 152 25 .+-.4 48 Si 4
500 1 153 161 .+-.3 49 Si 4 100 3 152 42 .+-.2 50 Si 4 500 3 151
300 .+-.2 51 Si 8 100 3 151 15 .+-.5 52 Si 8 500 3 153 87 .+-.1 53
Si 4 100 6 147 439 .+-.4 54 Si 4 500 6 150 849 .+-.2 55 Si 8 100 6
153 56 .+-.8 56 Si 8 500 6 151 198 .+-.3 57 Si 4 100 10 150 1561
.+-.3 58 Si 4 500 10 153 2171 .+-.3 59 Si 8 100 10 152 201 .+-.5 60
Si 8 500 10 153 464 .+-.5
[0146] As clearly shown in Table 3, heating the substrate slightly
changed the mean value of the sheet resistivity compared to the
absence of heating, and this value could be controlled to between
30 .OMEGA./square and 2.8 k.OMEGA./square for the FR-4 circuit
board and to between 15 .OMEGA./square and 2.2 k.OMEGA./square for
the Si substrate. The tolerance of sheet resistivity was reduced
compared to each set of conditions without heating. Although a few
cracks were observed in the titanium nitride resistor in substrate
No. 39, no cracks or wrinkles were found in the other titanium
nitride resistors and they exhibited a uniform external
appearance.
[0147] The FR-4 circuit boards of substrate Nos. 29, 33, 34, 35,
36, and 43had sheet resistivity tolerances within .+-.5%, and
within this range of tolerance, their sheet resistivity could be
controlled to between 32 .OMEGA./square and 636 .OMEGA./square. The
Si substrates of substrate Nos. 45 to 60 except No. 55 had sheet
resistivity tolerances within .+-.5%, and within this range of
tolerance, their sheet resistivity could be controlled to between
15 .OMEGA./square and 2.2 k.OMEGA./square. Heating the substrate
during film formation enabled both the FR-4 circuit boards and the
Si substrates to be controlled to a wider range of sheet
resistivity values than the absence of heating.
[0148] The structure of this invention is assumed to provide the
above accurate resistance because the use of the titanium nitride
resistor enables the use of an etchant that is unlikely to damage
the substrate, because the single use of a thin-film formation
apparatus such as a sputter reduces the degradation such as
oxidation of the surface of titanium nitride, and because the
continuous sputtering of titanium nitride/copper provides an
excellent adhesion between the titanium nitride resistor and the
wiring metal.
[0149] According to the wiring substrate of this invention, the
wiring is laminated on the thin titanium nitride film so that the
thin titanium nitride film excellent in adhesion and barrier
capability functions as an effective ground coat layer, thereby
reducing the number of required manufacturing steps and providing a
reliable wiring substrate.
[0150] In addition, according to the wiring substrate of this
invention, the thin titanium nitride film is used as the ground
coat layer for both the resistor and the wiring, thereby providing
a thin-film-resistor built-in wiring substrate of a fine wiring
structure that can provide an accurate resistance value, that
includes a reliable wiring layer, and that can reduce the number of
required manufacturing steps.
[0151] In addition, the present method for manufacturing a wiring
substrate enables a reliable wiring substrate to be manufactured
using a small number of steps.
[0152] Furthermore, according to the present method for
manufacturing a wiring substrate, a small number of steps can be
used to provide a thin-film-resistor built-in wiring substrate of a
fine wiring structure that has an accurate resistance value and a
reliable wiring layer. The invention may be embodied in other
specific forms without departing from the spirit or essential
characteristic thereof. The present embodiments are therefore to be
considered in all respects as illustrative and not restrictive, the
scope of the invention being indicated by the appended claims
rather than by the foregoing description and all changes which come
within the meaning and range of equivalency of the claims are
therefore intended to be embraced therein.
[0153] The entire disclosure of Japanese Patent Application No.
10-165112 (Filed on Jun. 12, 1998) and Japanese Patent Application
No. 10-170313 (Filed on Jun. 17, 1998) including specification,
claims, drawings and summary are incorporated herein by reference
in its entirety.
* * * * *