U.S. patent application number 09/451444 was filed with the patent office on 2001-11-15 for precision polishing apparatus for polishing semiconductor substrate.
Invention is credited to TAKAHASHI, KAZUO.
Application Number | 20010041446 09/451444 |
Document ID | / |
Family ID | 26575119 |
Filed Date | 2001-11-15 |
United States Patent
Application |
20010041446 |
Kind Code |
A1 |
TAKAHASHI, KAZUO |
November 15, 2001 |
PRECISION POLISHING APPARATUS FOR POLISHING SEMICONDUCTOR
SUBSTRATE
Abstract
A precision polishing method and a precision polishing apparatus
are adapted to be used with a chemical etching technique of
utilizing a chemical effect for polishing a metal film without
producing any process-altered layer nor any scratches on the metal
surface and without the risk of partly burying the polishing agent
near the metal surface in order to flatten and smooth or remove the
metal film. With a precision polishing method and a precision
polishing apparatus according to the invention, the surface to be
polished of a substrate 1 carrying thereon a metal film for forming
a semiconductor device is pressed against a hard polishing pad 4,
while an etching solution 7 is supplied to the surface to be
polished and that of the polishing pad 4 that are held in contact
with each other and the surface to be polished and the polishing
pad 4 are driven to move relative to each other. Then, the etching
solution on the surface to be polished gives rise to a local
temperature rise in projecting areas of the metal film found in the
surface to be polished due to the generated frictional heat and the
etching rate of the etching solution is raised in those areas to
selectively etch the projecting areas of the metal film and flatten
the surface. Thereafter, the metal film is uniformly etched and
removed.
Inventors: |
TAKAHASHI, KAZUO;
(KAWASAKI-SHI, JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Family ID: |
26575119 |
Appl. No.: |
09/451444 |
Filed: |
November 30, 1999 |
Current U.S.
Class: |
438/692 ;
257/E21.304; 257/E21.579; 438/693; 438/745; 438/753; 438/754 |
Current CPC
Class: |
H01L 21/76807 20130101;
H01L 21/3212 20130101 |
Class at
Publication: |
438/692 ;
438/693; 438/745; 438/753; 438/754 |
International
Class: |
H01L 021/302 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 30, 1998 |
JP |
10-355384 |
Nov 26, 1999 |
JP |
11-335258 |
Claims
What is claimed is:
1. A precision polishing method, comprising supplying an etching
solution to the surface to be polished comprising the metal of a
semiconductor device and flattening and removing said surface to be
polished comprising said metal by utilizing a change of etching
rate caused by the change of the temperature of the etching
solution.
2. A precision polishing method according to claim 1, wherein a
local temperature change is produced on the surface to be polished
to cause said change of etching rate of said etching solution by
locally applying heat to the semiconductor substrate having said
surface to be polished or causing it to locally emit heat in order
to produce a selective etching effect due to temperature
difference, thereby flattening and removing said surface to be
polished comprising said metal.
3. A precision polishing method according to claim 1, wherein the
temperature of the projecting areas of said metal in said surface
to be polished is set higher than the temperature of the area other
than said projecting areas of said metal in said surface to be
polished and an abutting member is made to abut on said surface to
be polished, thereby polishing and flattening said surface to be
polished comprising the metal.
4. A precision polishing method according to claim 1, wherein the
projecting areas of the surface to be polished can be selectively
caused to emit heat and raise the temperature thereof by making an
abutting member abut on the surface to be polished with or without
said etching solution interposed therebetween and driving the
abutting member to move along and relative to the surface to be
polished.
5. A precision polishing method according to claim 1, wherein said
etching solution can provide more than 5% change with respect to
said change of etching rate caused by a temperature change within a
temperature range between the room temperature and the temperature
actually used for the etching operation.
6. A precision polishing method according to claim 1, wherein said
metal of a semiconductor device is selected from the group
consisting of copper, aluminum, tungsten or an alloy containing any
of them.
7. A precision polishing method according to claim 1, wherein said
etching solution is selected from the group consisting of a
solution containing any one of iron (III) chloride and copper (II)
chloride, an alkaline aqueous solution containing a copper amine
complex as principal ingredient, and an etching solution containing
a mixture of hydrogen peroxide and a sulfuric acid type
solution.
8. A precision polishing method according to claim 1, wherein any
one of solid fine particles and fine particles to be used for a
polishing agent having a primary particle size between 0.02 and 0.5
.mu.m are added to said etching solution.
9. A precision polishing method according to claim 1 as applied to
a dual damascene process.
10. A precision polishing method according to claim 9, wherein said
dual damascene process uses copper as principal material.
11. A precision polishing method according to claim 1, wherein said
etching solution is selected from the group consisting of: (1) a
solution of a mixture of water, hydrogen peroxide and ammonium, to
which potassium hydroxide may or may not be added, (2) a solution
mainly containing water, hydrochloric acid and iron chloride, to
which ethanol may or may not be added, (3) a solution obtained by
adding hydrochloric acid and nitric acid to ultra-pure water, (4) a
solution containing ultra-pure water, nitric acid and phosphoric
acid, to which hydrochloric acid may or may not be added, (5) a
solution mainly containing ultra-pure water and nitric acid, to
which any one of silver nitride and chromium oxide may or may not
be added, (6) a solution mainly containing ultra-pure water and
phosphoric acid, to which any one of methanol, ammonium acetate and
ethylenegylcol may or may not be added, (7) a solution mainly
containing ultra-pure water and sulfuric acid, to which any one of
phosphoric acid, potassium hydroxide and sodium hydroxide may or
may not be added, (8) a solution mainly containing ultra-pure water
and nitric acid, to which any one of hydrofluoric acid and glacial
acetic acid may or may not be added, (9) a solution mainly
containing ultra-pure water and hydrogen peroxide, to which any one
of potassium hydroxide, hydrofluoric acid and methanol may or may
not be added, and (10) a solution containing ultra-pure water and
hydrochloric acid, to which any one of nitric acid, hydrofluoric
acid, and both of them may or may not be added.
12. A precision polishing method according to claim 11, wherein
said etching solution has a specific gravity between 0.79 and
2.1.
13. A precision polishing apparatus adapted to polishing the
surface to be polished comprising the metal of a semiconductor
device by making the surface to be polished comprising the metal of
a semiconductor device abut on a hard polishing pad under pressure
of a predetermined level while supplying an etching solution to the
surface to be polished and the abutment surface of said hard
polishing pad and driving said surface to be polishing to move
relative to said polishing pad, thereby polishing said surface to
be polished comprising the metal, said apparatus comprising at
least one means selected from the group consisting of a means for
locally raising the temperature of the projecting areas of said
metal in said surface to be polished and a means for cooling the
area other than said projecting areas of said metal in said surface
to be polished so as to make the temperature of the projecting
areas of said metal in said surface to be polished higher than the
temperature of the area other than said projecting areas in said
surface and utilize the change of etching rate caused by the change
of the temperature of said etching solution supplied to said
surface to be polished and the abutting surface of said hard
polishing pad, thereby flattening and removing said surface to be
polished comprising said metal.
14. A precision polishing apparatus according to claim 13, wherein
a local temperature change is produced on and near the surface of a
semiconductor substrate having said surface to be polished
comprising the metal of the semiconductor device to cause said
change of etching rate of said etching solution by locally applying
heat to said semiconductor substrate or causing it to locally emit
heat in order to produce a selective etching effect due to
temperature difference, thereby flattening and removing said
surface to be polished comprising said metal.
15. A precision polishing apparatus according to claim 13, wherein
the projecting areas of the surface to be polished are selectively
caused to emit heat and raise the temperature thereof by making the
hard polishing pad abut on the surface to be polished with or
without an etching solution interposed therebetween and driving the
abutting member to move along and relative to the surface to be
polished.
16. A precision polishing apparatus according to claim 13, further
comprising a temperature control means for controlling the
temperature of the etching solution.
17. A precision polishing apparatus according to claim 13, wherein
said metal of a semiconductor device is selected from the group
consisting of copper, aluminum, tungsten and an alloy containing
any of them.
18. A precision polishing method according to claim 13, wherein
said etching solution is selected from the group consisting of a
solution containing any one of iron (III) chloride and copper (II)
chloride, an alkaline aqueous solution containing a copper amine
complex as principal ingredient, and an etching solution containing
a mixture of hydrogen peroxide and a sulfuric acid type
solution.
19. A precision polishing method according to claim 13 as applied
to a dual damascene process.
20. A precision polishing method according to claim 19, wherein
said dual damascene process uses copper as principal material.
21. A precision polishing method according to claim 13, further
comprising a collecting means for collecting said etching solution,
a regulating means for filtering said etching solution and
regulating its ingredients and a circulating means for circulating
said etching solution.
22. A precision polishing method adapted to polish the surface, to
be polished, of a substrate by supplying liquid thereto, said
method comprising the steps of: supplying a chemical solution
having an effect of etching projecting areas of metal on said
surface to be polished as said liquid; and controlling the
temperature of said projecting areas of metal.
23. A precision polishing method according to claim 22, wherein
said step of controlling the temperature is a step of heating said
projecting areas of metal by a heating means.
24. A precision polishing method according to claim 22, wherein
said step of controlling the temperature is a step of cooling the
area other than said projecting areas of metal by a cooling
means.
25. A precision polishing method according to claim 22, further
comprising a step of polishing said surface to be polishing by
causing a hard polishing pad having a modulus of compressive
elasticity between 9.8.times.10.sup.7 Pa and 9.8.times.10.sup.10 Pa
to abut on said surface to be polished.
26. A precision polishing method according to claim 22, wherein
said step of controlling the temperature is a step of controlling
the temperature of the entire surface to be polished by causing
fluid to flow through spiral type fluid flow paths.
27. A precision polishing method adapted to polish the surface, to
be polished, of a substrate by supplying liquid thereto, said
method comprising the steps of: supplying a chemical solution
having an effect of etching projecting areas of metal on said
surface to be polished as said liquid; and polishing said surface
to be polished by causing a hard polishing pad having a modulus of
compressive elasticity between 9.8.times.10.sup.7 Pa and
9.8.times.10.sup.10 Pa to abut on said surface to be polished.
28. A precision polishing method according to claim 27, further
comprising a step of controlling the temperature of said projecting
areas of metal.
29. A precision polishing method according to claim 28, where said
step of controlling the temperature is a step of cooling the area
other than said projecting areas of metal.
30. A precision polishing method according to claim 28, wherein
said step of controlling the temperature is a step of heating said
projecting areas of metal.
31. A precision polishing apparatus having a substrate-holding
means for holding a substrate and a polishing head and adapted to
polish the surface to be polished of said substrate by supplying
liquid thereto, said apparatus comprising: a supply means for
supplying a chemical solution having an effect of etching
projecting areas of metal on said surface to be polished as said
liquid; and a temperature control means for controlling the
temperature of said projecting areas of metal.
32. A precision polishing apparatus according to claim 31, wherein
said temperature control means is a cooling means for cooling the
area other than said projecting areas of metal.
33. A precision polishing apparatus according to claim 31, wherein
said temperature control means is a heating means for heating said
projecting areas of metal.
34. A precision polishing apparatus according to claim 31, wherein
said polishing head removably holds a hard polishing pad having a
modulus of compressive elasticity between 9.8.times.10.sup.7 Pa and
9.8.times.10.sup.10 Pa.
35. A precision polishing apparatus according to claim 31, wherein
at least any one of said means for holding a substrate and said
polishing-pad-holding means is provided with said temperature
control means.
36. A precision polishing apparatus according to claim 31, wherein
said temperature control means is a fluid flow path for allowing
fluid to flow in and flow out.
37. A precision polishing apparatus according to claim 36, wherein
said flow path is of a spiral type.
38. A precision polishing apparatus according to claim 36, wherein
at least any one of said means for holding a substrate and said
polishing-pad-holding means is provided with a pair of fluid flow
paths.
39. A precision polishing apparatus having a substrate-holding
means for holding a substrate and a polishing-pad-holding means and
adapted to polish the surface to be polished of said substrate by
supplying liquid thereto, said apparatus comprising: a supply means
for supplying a chemical solution having an effect of etching
projecting areas of metal on said surface to be polished as said
liquid; said polishing pad holding means removably holding a hard
polishing pad having a modulus of compressive elasticity between
9.8.times.10.sup.7 Pa and 9.8.times.10.sup.10 Pa.
40. A precision polishing apparatus according to claim 39, further
comprising a temperature control means for controlling the
temperature of said projecting areas of metal.
41. A precision polishing apparatus according to claim 40, wherein
said temperature control means is a cooling means for cooling the
area other than said projecting areas of metal.
42. A precision polishing apparatus according to claim 40, wherein
said temperature control means is a heating means for heating said
projecting areas of metal.
43. A precision polishing apparatus having a substrate-holding
means for holding a substrate and a polishing head for polishing
said substrate held by said substrate-holding means, comprising a
spiral type flow path provided on at least any one of said means
for holding a substrate and said polishing head.
44. A precision polishing apparatus according to claim 43, wherein
at least any one of said substrate-holding means for holding a
substrate and said polishing-pad-holding means is provided with a
pair of fluid flow paths of a spiral type.
45. A precision polishing method having a step of supplying fluid
to a substrate held by a substrate-holding means for holding a
substrate and a step of polishing said substrate by means of a
polishing head, further comprising: a step of causing fluid to pass
through a spiral type fluid flow path arranged on at least any one
of said substrate-holding means and said polishing head.
46. A precision polishing method according to claim 45, wherein
said step of causing fluid to pass through is a step of causing
fluid to pass through a pair of fluid flow paths arranged on at
least any one of said substrate-holding means and said polishing
head.
47. A precision polishing method according to claim 46, wherein one
of said pair of fluid flow paths is adapted to allow fluid to flow
from the center of said polishing head to the periphery while the
other is adapted to allow fluid to flow from the periphery to the
center of said polishing pad.
Description
BACKGROUND OF THE INVENTION
[0001] b 1. Field of the Invention
[0002] This invention relates to a precision polishing method and a
precision polishing apparatus for polishing a semiconductor
substrate. More particularly, the present invention relates to a
precision polishing method and a precision polishing apparatus for
flattening or removing the wiring material film formed on an
insulating film of a semiconductor element in the process of
manufacturing a semiconductor integrated circuit.
[0003] 2. Related Background Art
[0004] The trend in recent years of producing semiconductor
integrated circuits that are increasingly down-sized and
multilayered is accompanied by the need for improved flattening
technologies. A major advancement is brought forth in the filed of
flattening technologies by chemical mechanical polishing (CMP).
[0005] FIG. 7 of the accompanying drawings schematically
illustrates a known chemical mechanical polishing (CMP) apparatus.
As shown, it comprises a substrate-holding part 202 for removably
holding a substrate 201 that may be a wafer with the surface to be
polished facing downward and a polishing table 205 placed vis-a-vis
the substrate 201 held by the substrate-holding part 202 and
carrying a large caliber polishing pad 204 having a diameter
greater than that of the substrate 201 as the latter is bonded
thereto. The apparatus further comprises a first drive means 211
for driving the substrate-holding part 202 to revolve, a pressuring
means 212 for applying pressure to the substrate 201 so as to make
the surface, to be polished, of the substrate 201 pressed against
polishing pad 204 and a second drive means 213 for driving the
polishing table 105 to revolve, a polishing agent supply means 215
being additionally provided in order to supply the polishing pad
204 with a polishing agent 207.
[0006] With a polishing apparatus having a configuration as
described above, the substrate 201 and the polishing pad 204 are
driven to revolve respectively by the first drive means 211 and the
second drive means 213 in the directions as indicated by the arrows
in FIG. 7 so as to make the surface, to be polished, of the
substrate 201 held by the substrate-holding part 202 abut the upper
surface of the polishing pad 204 on the polishing table 205 and the
pressurizing means 212 apply pressure to the substrate 201 to a
predetermined pressure level to polish the surface while the
polishing agent supply means 215 is operated to drop the polishing
agent 207 onto the polishing pad 204. The polishing agent 207 is
normally referred to as slurry that is a suspension prepared by
mixing fine particles of silicon oxide, cerium oxide or alumina
into an aqueous solution of potassium hydroxide or ammonium. Thus,
the surface to be polished is flattened and smoothed by the
combination of the chemical effect of the polishing agent and the
physical effect of the polishing particles.
[0007] As described above, a polishing agent normally referred to
as slurry that is a suspension prepared by mixing fine particles of
silicon oxide, cerium oxide or alumina into an aqueous solution of
potassium hydroxide or ammonium is used for CMP. Such a polishing
agent is designed to be mainly used for polishing interlayer
insulating films of semiconductor devices and hence can give rise
to scratches on the metal surface when it is used for ductile
metals such as copper (Cu) and aluminum (Al) and metal alloys
containing them as principal ingredients as well as other problems
including the problem of particles of the polishing agent buried
into the metal surface. In the case of burying a tungsten (W) plug,
where the plug has a small diameter between 0.5 and 1 .mu.m while
the surface of the insulating film on the surface to be polished is
far greater than the exposed surface of the tungsten plug and both
tungsten and the material of the insulating film are fragile, the
dishing problem can be alleviated to a certain extent by using a
polishing pad showing an appropriate degree of compressibility.
[0008] However, in the process of forming wires from a metal film,
particularly in a dual damascene process mainly using copper, the
ratio of the exposed surface area of the insulating film to the
surface area of the wiring metal is closer to 1 than the above
instance so that conventional CMP techniques encounter the problem
of a remarkable dishing phenomenon appearing on the wiring metal
along with the problem of producing a process-altered layer near
the surface of the object to be polished because the surface to be
polished is subjected to pressure of a level between 200 to 500
gr/cm.sup.2 for the purpose of polishing.
SUMMARY OF THE INVENTION
[0009] In view of the unsolved problems of conventional techniques,
it is therefore the object of the present invention to provide a
precision polishing method and a precision polishing apparatus
applicable to dual damascene processes involving the use of metal,
highly ductile copper in particular, and adapted to be used with a
chemical etching technique of utilizing a chemical effect for
polishing a wiring metal film without producing any process-altered
layer nor any scratches on the metal surface and without the risk
of partly burying the polishing agent near the metal surface in
order to flatten and smooth or remove the metal film.
[0010] In an aspect of the invention, the above object is achieved
by providing a precision polishing method, comprising supplying an
etching solution to the surface to be polished comprising the metal
of a semiconductor device and flattening and removing said surface
to be polished comprising said metal by utilizing a change of
etching rate caused by the change of the temperature of the etching
solution.
[0011] Preferably, with a precision polishing method according to
the invention, a local temperature change is produced on the
surface to be polished to cause said change of etching rate by
locally applying heat to the semiconductor substrate having said
surface to be polished or causing it to locally emit heat in order
to produce a selective etching effect due to temperature
difference, thereby flattening and removing said surface to be
polished comprising said metal. Preferably, with a precision
polishing method according to the invention, the temperature of the
projecting areas of said metal in said surface to be polished is
set higher than the temperature of the area other than said
projecting areas of said metal in said surface to be polished and
an abutting member is made to abut on said surface to be polished,
thereby polishing and flattening said surface to be polished
comprising the metal.
[0012] With a precision polishing method according to the
invention, the projecting areas of the surface to be polished can
be selectively caused to emit heat and raise the temperature
thereof by making an abutting member abut on the surface to be
polished with or without an etching solution interposed
therebetween and driving the abutting member to move along and
relative to the surface to be polished.
[0013] In another aspect of the present invention, there is
provided a precision polishing apparatus adapted to polishing the
surface to be polished comprising the metal of a semiconductor
device by making the surface to be polished comprising the metal of
a semiconductor device abut on a hard polishing pad under pressure
of a predetermined level while supplying an etching solution to the
surface to be polished and the abutment surface of said hard
polishing pad and driving said surface to be polishing to move
relative to said polishing pad, thereby polishing said surface to
be polished comprising the metal, said apparatus comprising at
least either a means for locally raising the temperature of the
projecting areas of said metal in said surface to be polished or a
means for cooling the area other than said projecting areas of said
metal in said surface to be polished so as to make the temperature
of the projecting areas of said metal in said surface to be
polished higher than the temperature of the area other than said
projecting areas in said surface and utilize the change of etching
rate caused by the change of the temperature of said etching
solution supplied to said surface to be polished and the abutting
surface of said hard polishing pad, thereby flattening and removing
said surface to be polished comprising said metal.
[0014] Preferably, in a precision polishing apparatus according to
the invention, a local temperature change is produced on and near
the surface of a semiconductor substrate having said surface to be
polished comprising the metal of the semiconductor device to cause
said change of etching rate by locally applying heat to said
semiconductor substrate or causing it to locally emit heat in order
to produce a selective etching effect due to temperature
difference, thereby flattening and removing said surface to be
polished comprising said metal.
[0015] Preferably, in a precision polishing apparatus according to
the invention, the projecting areas of the surface to be polished
are selectively caused to emit heat and raise the temperature
thereof by making the hard polishing pad abut on the surface to be
polished with or without an etching solution interposed
therebetween and driving the abutting member to move along and
relative to the surface to be polished.
[0016] Preferably, in a precision polishing apparatus according to
the invention further comprises a temperature control means for
controlling the temperature of the etching solution. Preferably, a
precision polishing apparatus according to the invention further
comprises a collecting means for collecting said etching solution,
a regulating means for filtering said etching solution and
regulating its ingredients and a circulating means for circulating
said etching solution.
[0017] Preferably, said metal of the semiconductor device is
copper, aluminum, tungsten or an alloy containing at least one of
the above listed metals. Preferably, said etching solution is a
solution containing iron (III) chloride or copper (II) chloride, an
alkaline aqueous solution containing a copper amine complex as
principal ingredient or an etching solution containing a mixture of
hydrogen peroxide and a sulfuric acid type solution. A polishing
agent of fine solid particles with a primary particle size between
0.02 and 0.5 .mu.m may be added to the etching solution.
[0018] A precision polishing method and a precision polishing
apparatus according to the invention may be applied to a dual
damascene process, particularly to a dual damascene process mainly
using copper.
[0019] According to the invention, there is also provided a
precision polishing method adapted to polish the surface to be
polished of a substrate by supplying liquid thereto, said method
comprising the steps of supplying a chemical solution having an
effect of etching projecting areas of metal on said surface to be
polished as said liquid and controlling the temperature of said
projecting areas of metal.
[0020] Preferably, a precision polishing method according to the
invention further comprises a step of polishing said surface to be
polishing by causing a hard polishing pad having a modulus of
compressive elasticity between 9.8.times.10.sup.7 Pa and
9.8.times.10.sup.10 Pa, or 10 kgf/mm.sup.2 and 10,000 kfg/mm.sup.2
to abut on said surface to be polished. Preferably, with a
precision polishing method according to the invention, said step of
controlling the temperature of said projecting areas of metal is
conducted by heating said projecting areas of metal by a heating
means or by cooling the area of said surface to be polished other
than said projecting areas of metal.
[0021] According to the invention, there is also provided a
precision polishing method adapted to polish the surface to be
polished of a substrate by supplying liquid thereto, said method
comprising steps of supplying a chemical solution having an effect
of etching projecting areas of metal on said surface to be polished
as said liquid and polishing said surface to be polishing by
causing a hard polishing pad having a modulus of compressive
elasticity between 9.8.times.10.sup.7 Pa and 9.8.times.10.sup.10
Pa, or 10 kgf/mm.sup.2 and 10,000 kfg/mm.sup.2 to abut said surface
to be polished.
[0022] Preferably, a precision polishing method according to the
invention further comprises a step of controlling the temperature
of said projecting areas of metal.
[0023] According to the invention, there is also provided a
precision polishing apparatus having a substrate-holding means for
holding a substrate and a polishing pad holding member and adapted
to polish the surface to be polished of said substrate by supplying
liquid thereto, said apparatus comprising a supply means for
supplying a chemical solution having an effect of etching
projecting areas of metal on said surface to be polished as said
liquid and a temperature control means for controlling the
temperature of said projecting areas of metal.
[0024] Preferably, in a precision polishing apparatus according to
the invention, said temperature control means is a cooling means
for cooling the area of said surface to be polished other than said
projecting areas of metal or a heating means for heating said
projecting areas of metal. Preferably, in a precision polishing
apparatus according to the invention, said polishing pad holding
member removably holds a hard polishing pad having a modulus of
compressive elasticity between 9.8.times.10.sup.7 Pa and
9.8.times.10.sup.10 Pa, or 10 kgf/mm.sup.2 and 10,000 kfg/mm.sup.2
to abut said surface to be polished.
[0025] According to the invention, there is also provided a
precision polishing apparatus having a substrate-holding means for
holding a substrate and a polishing-pad-holding member and adapted
to polish the surface to be polished of said substrate by supplying
liquid thereto, said apparatus comprising a supply means for
supplying a chemical solution having an effect of etching
projecting areas of metal on said surface to be polished as said
liquid, said polishing pad holding member removably holding a hard
polishing pad having a modulus of compressive elasticity between
9.8.times.10.sup.7 Pa and 9.8.times.10.sup.10 Pa, or 10
kgf/mm.sup.2 and 10,000 kfg/mm.sup.2 to abut said surface to be
polished.
[0026] Preferably, a precision polishing apparatus according to the
invention further comprises a temperature control means for
controlling the temperature of said projecting areas of metal.
Preferably, in a precision polishing apparatus according to the
invention, said temperature control means is a cooling means for
cooling the area of said surface to be polished other than said
projecting areas of metal or a heating means for heating said
projecting areas of metal.
[0027] Thus, with a precision polishing method and a precision
polishing apparatus according to the invention, it is now possible
to flatten and remove the metal film formed on a substrate by using
an etching solution or a chemical solution adapted to principally
exert a chemical effect in a polishing operation and show a
selective etching rate that varies as a function of the temperature
of the etching solution or the chemical solution.
[0028] Additionally, as a result of polishing the wiring metal film
formed on an insulating film that is already flattened in a dual
damascene process by utilizing the selective etching rate of an
etching solution or a chemical solution that varies as a function
of the temperature of the etching solution or the chemical
solution, there is no risk of producing a dishing phenomenon on the
metal surface. Still additionally, since no polishing agent that
contains abrasive grains is used, there arises no risk of producing
scratches on the metal surface nor that of partly burying the
abrasive grains of the polishing agent near the metal surface.
Furthermore, since the operating pressure applied to the substrate
can be reduced unlike conventional CMP techniques, no
process-altered layer would appear on and near the metal surface as
a result of the polishing operation.
[0029] Finally, according to the invention, a substrate is polished
by means of a precision polishing apparatus comprising one or more
than on spiral type fluid flow paths as temperature control means
arranged at least in the polishing head or the substrate-holding
means. As fluid is made to flow through the flow paths, the entire
surface to be polished of the substrate can be made to show a
uniform temperature distribution. Then, the projecting areas of
metal on the surface to be polished is heated as they are scraped
by the polishing pad while the surface to be polished is held to
show a uniform temperature distribution. As a result, the
projecting areas show a high etching rate so that the metal film is
accurately flattened.
[0030] Thus, with such a method and an apparatus, it is now
possible to reliably form wires to be buried into wiring grooves or
grooves for contact holes that are arranged in the insulating film
on a semiconductor substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1 is a schematic illustration of a first embodiment of
a precision polishing apparatus according to the invention, showing
its configuration.
[0032] FIG. 2 is a schematic illustration of a second embodiment of
a precision polishing apparatus according to the invention, showing
its configuration.
[0033] FIG. 3 is a schematic illustration of a third embodiment of
a precision polishing apparatus according to the invention, showing
its configuration.
[0034] FIG. 4 is a schematic illustration of the polishing head and
the means for holding the object to be polished of the third
embodiment.
[0035] FIG. 5 is a schematic illustration of the polishing head of
the third embodiment as viewed from the side of holding the
polishing pad.
[0036] FIGS. 6A, 6B, 6C and 6D are schematic process diagrams
showing different wire forming steps in a dual damascene
process.
[0037] FIG. 7 is a schematic illustration of a known chemical
mechanical polishing (CMP) apparatus.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0038] Now, the present invention will be described by referring to
the accompanying drawings that illustrate preferred embodiments of
the invention.
[0039] FIGS. 1 and 2 are schematic illustrations of first and
second embodiments of precision polishing apparatus according to
the invention, showing their respective configurations, and FIG. 3
is a schematic illustration of a third embodiment of precision
polishing apparatus according to the invention, showing its
configuration.
[0040] [First Embodiment]
[0041] The first embodiment of precision polishing apparatus
according to the invention will be described by referring to FIG.
1.
[0042] As shown in FIG. 1, the first embodiment of precision
polishing apparatus comprises a substrate-holding part 2 for
removably holding a substrate 1 that may be a wafer with the
surface to be polished facing downward, a polishing table 5 (i.e. a
polishing head 5) placed vis-a-vis the substrate 1 held by the
substrate holding part 2 and carrying a large caliber hard
polishing pad 4 having a diameter greater than that of the
substrate 1 (and a modulus of compressive elasticity between
9.8.times.10.sup.7 Pa and 9.8.times.10.sup.10 Pa, or 10
kgf/mm.sup.2 and 10,000 kgf/mm.sup.2, such as that of
polytetrafluoroethylene) as the latter is bonded thereto, a first
drive means 11 for driving the substrate holding part 2 to revolve,
a pressurizing means 12 for applying pressure to the substrate 1 so
as to make the surface to be polished of the substrate 1 pressed
against polishing pad 4, and a second drive means 13 for driving
the polishing table 5 to revolve, said first drive means 11 and
said second drive means 13 being arranged to drive the substrate 1
and the hard polishing pad 4 to revolve substantially at a same
rate. Additionally, there is provided a polishing agent supply
means 15 for supplying the polishing pad 4 with a polishing agent
(chemical solution) 7. The etching solution (chemical solution) 7
is such that mainly its chemical effect (etching effect) on a metal
film may be exploited. For example, if used for copper, said
etching solution is a solution containing iron (III) chloride or
copper (II) chloride, an alkaline aqueous solution containing a
copper amine complex as principal ingredient or an etching solution
containing a mixture of hydrogen peroxide and a sulfuric acid based
solution. If the surface to be polished is that of a wiring copper
film, preferably a solution obtained by mixing iron (III) chloride
with pure water, regulating the specific gravity of the mixture to
about 1.38 and adding 1 to 5% hydrochloric acid thereto is used.
Alternatively, a solution obtained by mixing copper (II) chloride
with pure water, regulating the specific gravity of the mixture to
1.25 to 1.28 and adding hydrochloric acid to make the mixture show
an appropriate mixing ratio is also preferably used.
[0043] A mode of precision polishing mainly utilizing the chemical
effect (etching effect) of an etching solution will be discussed
below.
[0044] With conventional chemical mechanical polishing (CMP), a
polishing agent normally referred to as slurry that is a suspension
prepared by mixing particles of silicon oxide, cerium oxide or
alumina into an aqueous solution of potassium hydroxide or aqueous
ammonia is used. Such a polishing agent is designed to mainly
mechanically polish the surface to be polished and hence it is far
from directly exerting a chemical effect on the surface. To the
contrary, according to the invention, an etching solution is used
and its chemical etching effect is exploited to polish the metal
film of the wiring layer formed on a substrate so as to smooth or
remove the metal film.
[0045] While a variety of etching solutions may be used for the
purpose of the invention, the etching process with such an etching
solution proceeds uniformly over the entire surface to be polished
without selectivity so that it cannot selectively polish projecting
areas of the metal film to flatten the entire surface. However,
such etching solutions show a high etching rate when the
temperature rises. In other words, with such etching solutions, the
etching rate is highly dependent on the temperature of the
solution. Therefore, the etching solution can be provided with a
degree of selectivity when it is locally heated to locally raise
its temperature.
[0046] Now, referring back to the embodiment of precision polishing
apparatus shown in FIG. 1, the substrate 1 to be polished is fitted
to the substrate holding part 2 with the surface to be polished
facing downward and pressed against the hard polishing pad 4 placed
on the polishing table 5 under pressure of a predetermined degree
by the pressurizing means 12. At the same time, the substrate 1 and
the hard polishing pad 4 are driven to revolve respectively by the
first drive means 11 and the second drive means 13 in the
directions as indicated by arrows in FIG. 1. At this time, the
first drive means 11 and the second drive means 13 are so arranged
as to drive the substrate 1 and the hard polishing pad 4 to revolve
substantially at a same rate. Then, the etching solution 7 is
dropped onto the hard polishing pad 4 from the polishing agent
supply means 15. As the surface to be polished of the substrate 1
is pressed against the hard polishing pad 4 and they are driven to
move relative to each other, heat is generated by friction between
the hard polishing pad 4 and the surface to be polished of the
substrate 1, particularly in the projecting areas of the surface of
the substrate 1. The amount of the generated frictional heat is
proportional to the frictional force obtained by multiplying the
applied pressure by the coefficient of friction, the amount of the
relative movement and the duration of the relative movement.
Therefore, the temperature of the projecting areas of the surface
to be polished that are as high as about 1 .mu.m and held in tight
contact with the hard polishing pad 4 can be controlled by
selecting appropriate values for the above parameters. As the
projecting areas of the surface to be polished of the substrate 1
are instantaneously heated by the frictional heat generated by the
friction, the etching rate of the etching solution is raised in
those projecting areas so that the etching effect is promoted in
those areas. As a result, the projecting areas are selectively
etched and polished and the surface to be polished is consequently
polished and flattened mainly by the chemical effect (etching
effect) of the etching solution to realize precision polishing
according to the invention.
[0047] The present invention can be applied to a process of forming
metal wires on a semiconductor device, a dual damascene process in
particular. This will be discussed below.
[0048] In a dual damascene process, as shown in FIGS. 6A to 6D,
wiring grooves 103 and grooves for contact holes 104 (see FIG. 6B)
are formed in the insulating film 102 (see FIG. 6A) that is formed
on a substrate 101 where various devices are formed in advance and
flattened by CMP. Note that the wiring groove 103 and the grooves
for contact holes 104 are formed by forming respective resist
patterns having respective profiles on the insulating film 102 by
means of photolithography and then etching the insulating film 102
typically by means of an RIE technique, using the resist patterns.
Thereafter, the wiring metal of copper (Cu), aluminum (Al),
tungsten (W) or a metal compound containing any of these metals as
principal ingredient is buried into the wiring grooves 103 and the
grooves for contact holes 104 by means of a film forming technique
such as CVD or sputtering (see FIG. 6C). Before forming the film of
the wiring metal 105, a barrier film typically made of titanium
nitride (TiN) may be formed on the surface of the insulating film
102 and the inner surfaces of the wiring grooves 103 and the
grooves for contact holes 104. Thereafter, as shown in FIG. 6D, the
wiring metal film 105 is polished by a precision polishing method
according to the invention until the underlying insulating film 102
is exposed to remove the wiring metal film 105 except the film in
the wiring grooves 103 for contact holes 104 to complete the
process of forming the metal wires 106 and the contact wires 107
that are buried in the grooves 103 and 104.
[0049] As discussed above, when polishing the surface of a
substrate 101, wiring grooves 103 and grooves for contact holes 104
have been formed in the insulating film 102 formed as flattened on
the surface to be polished of the substrate 101 and a layer of the
wiring metal 105 that is mostly copper has been formed on the
insulating film 102 to bury the grooves (see FIG. 6C). Then, also
as discussed above, an etching solution obtained by mixing iron
(III) chloride with pure water, regulating the specific gravity of
the mixture to about 1.38 and adding 1 to 5% hydrochloric acid
thereto is preferably used to flatten and remove the wiring metal
film 105. If a different wiring material is used, a different
etching solution (chemical solution) that matches the properties of
the wiring material will be selected.
[0050] In the process of flattening and removing the wiring metal
film formed on a substrate, frictional heat will be generated by
the friction between the hard polishing pad 4 and the surface of
the wiring metal film on the substrate 1, particularly in the
projecting areas of the metal film, as the surface of the wiring
metal film that is the surface to be polished of the substrate 1 is
pressed against the hard polishing pad 4 and they are driven to
revolve relative to each other. Particularly, in the case of a dual
damascene process where the insulating film underlying the wiring
metal film shows a very low thermal conductivity relative to that
of the wiring metal, or copper, the frictional heat generated
locally on the surface of the metal film in areas held in tight
contact with the pad 4 (projecting areas of the metal film) is
stored in the wiring metal layer typically made of copper. As a
result, even if the pressure applied to the substrate 1 is
remarkably lower than the pressure used in comparable conventional
processes, the temperature at and near the surface will be highest
in the areas held in tight contact with the polishing pad 4 and
falls in areas remote from those areas that are held in tight
contact. With this arrangement of raising the temperature in the
projecting areas of the surface of the wiring metal film on the
substrate by means of frictional heat, the etching solution will
produce an enhanced etching rate in the heated areas (projecting
areas) to promote the etching effect in those areas by far more
than the remaining area so that those areas are selectively etched
to flatten the entire surface of the wiring metal film.
Additionally, in a dual damascene process where the insulating film
underlying the wiring metal film is already flattened, the
projecting areas are not very steep and all the surface of the
wiring metal film is relatively flat so that it is relatively easy
to etch and polish the slightly projecting areas of the wiring
metal film at a high etching rate in order to flatten the entire
surface of the wiring metal film.
[0051] As described above, with this arrangement of etching and
polishing the projecting areas of the wiring metal film at a high
etching rate, the entire surface of the wiring metal film can be
flattened. Thereafter, the wiring metal film is etched and removed
uniformly by the etching solution until the underlying insulating
film comes to be exposed. The operation of flattening and removing
the wiring metal film is completed when the wiring metal film no
longer shows any residue thereof on the surface of the substrate 1.
Since the etching solution does not affect the insulating film, no
overpolishing problem occurs and hence, advantageously, the use of
an independent stopper is not necessary for the purpose of the
invention.
[0052] In the case of a dual damascene process where the insulating
film underlying the wiring metal film is reliably flattened, the
undulations, if any, of the surface of the wiring metal film are
not very remarkable and hence, by supplying the etching solution
under control in such a way that the heat in the non-contact area
can be discharged satisfactorily, the surface can be reliably
flattened only if the temperature dependency of the etching effect
is varied by more than 5%.
[0053] Additionally, for the purpose of the invention, the pressure
required to generate frictional heat to a necessary level will be
such that it produces a temperature rise only between several to
less than twenty .degree. C. for realizing the thermal selectivity
if the polishing pad is made of a relatively hard material such as
polytetrafluoroethylene- . Thus, the pressure required for pressing
the substrate against the polishing pad in a precision polishing
apparatus according to the invention will be far lower than the
pressure required for comparable polishing methods.
[0054] While the temperature of the projecting areas of the surface
(of the metal film) to be polished is raised by the frictional heat
mostly generated by the friction between the projecting areas and
the polishing pad to selectively etch the projecting areas and
flattens the surface to be polished in the above description, the
present invention is not limited to the use of such frictional heat
and it is also possible for the purpose of the invention to use a
heat control means such as a heating means or a cooling means to
selectively etch the projecting areas by controlling the
temperature difference between the areas to be etched at a high
etching rate and the remaining area of the surface. More
specifically, the etching rate of the etching solution is raised in
the projecting areas of the surface to be polished (of the metal
film) to selectively etch them by using a heat control means such
as a heating means or a cooling means and raising the temperature
of the etching solution in the projecting areas of the surface to
be polished (of the metal film) to a level higher than temperature
level of the remaining area of the surface or lowering the
temperature of the etching solution in the area other than the
projecting areas than that of the projecting areas, whichever
appropriate.
[0055] For the purpose of the present invention, any of the ten
types of etching solutions as listed below may alternatively be
used in place of the above described etching solution.
[0056] (1) A solution of a mixture of ultra-pure water, hydrogen
peroxide and ammonia, to which potassium hydroxide may or may not
be added.
[0057] (2) A solution mainly containing ultra-pure water,
hydrochloric acid and iron chloride, to which ethanol may or may
not be added.
[0058] (3) A solution obtained by adding hydrochloric acid and
nitric acid to ultra-pure water.
[0059] (4) A solution containing ultra-pure water, nitric acid and
phosphoric acid, to which hydrochloric acid may or may not be
added.
[0060] (5) A solution mainly containing ultra-pure water and nitric
acid, to which silver nitrate or chromium oxide may or may not be
added.
[0061] (6) A solution mainly containing ultra-pure water and
phosphoric acid, to which methanol, ammonium acetate or ethylene
glycol may or may not added.
[0062] (7) A solution mainly containing ultra-pure water and
sulfuric acid, to which phosphoric acid, potassium hydroxide or
sodium hydroxide may or may not be added.
[0063] (8) A solution mainly containing ultra-pure water and nitric
acid, to which hydrofluoric acid or glacial acetic acid may or may
not be added.
[0064] (9) A solution mainly containing ultra-pure water and
hydrogen peroxide, to which potassium hydroxide, hydrofluoric acid
or methanol may or may not be added.
[0065] (10) A solution containing ultra-pure water and hydrochloric
acid, to which nitric acid, hydrofluoric acid of both may or may
not be added.
[0066] If the required level of purity is satisfied, ultra-pure
water may be replaced by ordinary clean water in any of the above
solutions.
[0067] For the purpose of the invention, hydrochloric acid in any
of the related ones of the above solutions refers to hydrogen
chloride.
[0068] A surface active agent and/or an etching promoting agent or
an etching suppressing agent may be added to any of the above
listed solutions.
[0069] Preferably, the etching solution has a specific gravity
between 0.79 and 2.1 for realizing an improved etching effect for
the purpose of the invention.
[0070] The etching solution may contain microparticles in order to
improve the etching effect. Then, the etching solution can provide
a physical polishing effect through the use of microparticles
contained in it as abrasive grains in addition to the chemical
etching effect of the etching solution on the surface to be
polished of the metal film.
[0071] Such microparticles preferably have a spherical profile.
[0072] The primary particle diameter of the microparticles
contained in the etching solution is preferably between 0.02 and
0.5 .mu.m. Then, a high polishing rate will be achieved without
significantly damaging the surface to be polished.
[0073] If the etching solution contains microparticles, its
specific gravity preferably shows a value greater than the value it
shows when the etching solution does not contain
microparticles.
[0074] The microparticles contained in the etching solution are
preferably not soluble or hardly soluble in the etching
solution.
[0075] [Second Embodiment]
[0076] FIG. 2 is a schematic illustration of the second embodiment
of precision polishing apparatus according to the invention,
showing its configuration. This embodiment of precision polishing
apparatus comprises a cooling means for cooling the substrate 1 as
heat control means 10, which cooling means (heat control means) 10
controls the temperature of the area of the metal film other than
the projecting areas to a level lower than the temperature level of
the projecting areas so as to consequently keep the temperature of
the projecting areas higher than that of the remaining area during
the polishing process. Otherwise, this second embodiment is
identical with the above described first embodiment.
[0077] In a dual damascene process, wiring metal that is normally
copper is buried in the wiring grooves and the grooves for contact
holes formed in the insulating film to such an extent that it
partly passes through the insulating film layer and gets to the
device forming layer and the underlying lower wiring layer. Then,
the temperature of the area other than the areas projecting high
from the wiring metal layer having a high thermal conductivity is
held lower than that of the projecting areas by controlling the
rear surface of the substrate by the cooling means arranged for
this purpose. As a result, the etching rate of the projecting areas
can be raised from that of the remaining area for the purpose of
selective etching.
[0078] As described above, the surface of a substrate is polished
mainly by relying on the chemical effect of the etching solution
when the temperature of the projecting areas of the wiring metal
layer on the surface to be polished is controlled or the frictional
heat generated by the friction between the hard polishing pad is
utilized. Additionally, in a dual damascene process where the
insulating film underlying the wiring metal film is already
flattened, the projecting areas are not very steep nor high and all
the surface of the wiring metal film is relatively flat so that the
pressure required for pressing the substrate against the polishing
pad in order to generate frictional heat can be reduced by using a
relatively hard polishing pad if compared with conventional
polishing techniques. Still additionally, by supplying the etching
solution under control in such a way that the heat in the
non-contact area can be discharged satisfactorily, the surface of
the wiring metal layer can be held free from the problem of a
dishing phenomenon. Still additionally, since no polishing agent
that contains abrasive grains is used, there arises no risk of
producing scratches on the metal surface nor that of partly burying
the abrasive grains of the polishing agent into the wiring
material. Furthermore, since the operation mainly relies on the
chemical effect and the operating pressure applied to the substrate
can be reduced unlike conventional CMP techniques, no
process-altered layer would appear on and near the metal surface as
a result of the polishing operation. Therefore, buried wires can be
reliably formed in the wiring grooves and the grooves for contact
holes formed in the insulating film on a semiconductor device.
[0079] Finally, a polishing agent of fine solid particles or fine
abrasive particles with a primary particle diameter between 0.02
and 0.5 .mu.m or a stabilizer agent may be added to the etching
solution in order to promote or suppress, whichever appropriate,
the heat generation caused by friction. Even if such fine solid
particles or fine abrasive particles are added, the pressure
required for pressing the substrate against the polishing pad in
order to generate frictional heat can be reduced if compared with
conventional polishing techniques.
[0080] [Third Embodiment]
[0081] Now, the third embodiment of precision polishing apparatus
according to the invention will be described by referring to FIG.
3.
[0082] The third embodiment of precision polishing apparatus is
also characterized in that a polishing pad having a size greater
than the substrate that may be a wafer can be used for polishing
the substrate. More specifically, the third embodiment of precision
polishing apparatus comprises a substrate table 23 provided with a
substrate-holding part 22, which may be a wafer chuck, for holding
a substrate 21, which may be a wafer, with the surface to be
polished facing upward, a polishing head 25 arranged vis-a-vis the
substrate 21 held by the substrate holding part 22 and carrying a
large caliber hard polishing pad 24 having a diameter greater than
that of the substrate 21 as the latter is bonded thereto, a first
drive means 31 for driving the substrate table 23 to revolve, a
reciprocating means 32 for driving both the substrate table 23 and
the substrate 21 to reciprocate, a second drive means 33 for
driving the polishing head 25 to revolve, and a polishing pad
vertically driving means/pressurizing means 34 for driving the
polishing head 25 and the hard polishing pad 24 to move vertically
and pressing the hard polishing pad 24 against the surface to be
polished of the substrate 21 under pressure of a predetermined
level, said first drive means 31 and said second drive means 33
being arranged to drive the substrate 21 and the hard polishing pad
24 to revolve substantially at a same rate. Additionally, there is
provided a polishing agent supply means 35 for feeding a polishing
agent 27 to a solution supply system 36 running through the center
of the polishing head 25 and the hard polishing pad 24 and then
further to between the substrate 21 and the hard polishing pad
24.
[0083] With the embodiment of precision polishing apparatus having
the above described configuration, the substrate 21 to be polished
is fitted to the substrate holding part 22 of the substrate table
23 with the surface to be polished facing upward and moved to a
position directly below the polishing head 25 that carries the hard
polishing pad 24 bonded to the lower surface thereof as shown in
FIG. 3. Then, the etching solution 27 is fed from the etching
solution supply means 35 to the surface of the substrate 21 by way
of the solution supply system 36 and the center of the hard
polishing pad 24. At the same time, the substrate 21 and the hard
polishing pad 24 are driven to revolve respectively by the first
drive means 31 and the second drive means 33 in the directions as
indicated by arrows in FIG. 3. Additionally, the hard polishing pad
24 is made to abut the surface to be polished of the substrate 21
and pressed against the latter under pressure of a predetermined
level by the polishing pad vertically driving means/pressurizing
means 34. At this time, it is possible to cause the substrate 21 to
make a reciprocating motion by the reciprocating means 32 to an
extent that does not affect the respective revolutions per unit
time of the hard polishing pad 24 and the substrate 21. It is also
possible to cause the hard polishing pad 24 to make a reciprocating
motion by a reciprocating means (not shown).
[0084] In this way, the etching solution 27 is supplied to between
the surface to be polished of the substrate 21 and the hard
polishing pad 24 while they are moved relative to each other as in
the case of the above described first embodiment. Thus, the
projecting areas of the surface to be polished is selectively
etched due to the temperature difference in the etching solution 27
to flatten the metal film, which is then removed by the uniform
etching effect as in the case of the first embodiment.
[0085] The etching solution is supplied to between the surface to
be polished of the substrate and the polishing pad and used for the
operation of etching the surface. However, what is remarkable about
this embodiment is that the used etching solution is collected,
filtered and then regulated for the contents of the ingredients so
that it can be recirculated for reuse. With this arrangement of
recirculating used etching solution, the running cost of the
embodiment can be greatly reduced.
[0086] In the case of a dual damascene process where a barrier film
typically made of TiN is used in order to prevent diffusion of
copper ions, an etching solution adapted to etch TiN may have to be
used after the ordinary etching solution.
[0087] FIG. 4 is a schematic illustration of the polishing head 25
and the means for holding the object to be polished 22 of the third
embodiment shown in FIG. 3.
[0088] Referring to FIG. 4, both the polishing head 25 and the
means for holding the object to be polished 22 of this embodiment
of precision polishing apparatus are provided with respective fluid
flow paths 255 as heat control means. The fluid flow paths are
tubes and the fluid is water in this embodiment, although the fluid
may be gas or liquid. The polishing head 25 is provided with a pair
of fluid paths 255 that are arranged at the surface for holding the
hard polishing pad 24. It is also provided with a pair of inlet
holes 251 and 252 for introducing fluid into the respective fluid
flow paths 255 and a pair of outlet holes 253 and 254 for
delivering fluid to the outside from the respective fluid flow
paths 255.
[0089] The means for holding the object to be polished 22 is also
provided with a pair of fluid flow paths 223, which have an inlet
hole 221 for introducing fluid into them and an outlet hole 222 for
delivering fluid to the outside from the fluid flow paths 223. Note
that a single inlet hole 221 is provided to introduce fluid into
two fluid paths and a single outlet hole 222 is provided to deliver
fluid to the outside from the two fluid path for the purpose of
simplifying the configuration of the apparatus.
[0090] Thus, the temperature of the surface to be polished can be
controlled during the polishing, or etching, operation by means of
the fluid flow paths 255 arranged in the polishing head 25 that
carries a hard polishing pad.
[0091] The temperature of the surface to be polished can also be
controlled during the polishing, or etching, operation by means of
the fluid flow paths 223 arranged in the means for holding the
object to be polished 22. Particularly, when the substrate 21
carries a metal film formed on an insulating layer and the metal
film fills the grooves of the insulating layer, the projecting
areas of the metal film, particularly those on the grooves, can be
selectively heated or cooled to selectively polish the metal film
in those areas by utilizing the high thermal conductivity of
metal.
[0092] FIG. 5 is a schematic illustration of the polishing head 25
of FIG. 4 as viewed from the side of holding the polishing pad. In
FIG. 5, the components same as those of FIG. 4 are denoted
respectively by the same reference symbols. As shown in FIGS. 4 and
5, the fluid flow paths 255 arranged in the polishing head 25 are
of a spiral type. A pair of fluid flow paths 255 are arranged in
the polishing head 25. One of the fluid flow path 255 is spirally
arranged along the other fluid flow path 255. With this
arrangement, the polishing head 25 is provided with a pair of
spiral fluid flow paths 255 that are wound in the same sense. Note
that the means for holding the object to be polished 22 is also
provided with a pair of spiral fluid flow paths 223 that are
similar to the fluid flow paths 255 of the polishing head 25.
[0093] Referring to FIG. 5, one of the fluid flow paths 255 is
provided with the inlet hole 251 and the outlet hole 253, while the
other fluid flow path 255 is provided with the inlet hole 252 and
the outlet hole 254. The inlet hole 251 is disposed at the
periphery of the polishing head 25 and hence at a position remote
from the axis of rotation of the latter. On the other hand, the
outlet hole 253 is located at the center of the polishing head 25
and hence at the axis of rotation of the latter. The other inlet
hole 252 is arranged at the center of the polishing head 25 and
hence at the axis of rotation of the latter. On the other hand, the
outlet hole 254 is located at the periphery of the polishing head
25 and hence at a position remote from the axis of rotation of the
latter.
[0094] With this arrangement of juxtaposing a pair of fluid flow
paths, one of which leads fluid from the axis of rotation to the
periphery remote from the axis while the other leads fluid from the
periphery remote from the axis of rotation to the axis, the
temperature difference that may arise in each of the fluid flow
paths can be offset by that of the other. As a result, the
temperature difference on the surface to be polished that may arise
between a peripheral area and an axial area thereof can be
minimized to produce a uniform temperature distribution over the
entire surface to be polished. Then, the projecting areas of the
surface to be polished showing a uniform temperature distribution
give rise to a temperature rise due to the friction between them
and the polishing pad to consequently produce a high etching rate
there so that the metal film is accurately flattened. The
projecting areas are those that are abraded by the polishing pad
and may include both large projections produced when the substrate
is warped and micro-projections of the sizes of semiconductor
devices to be formed on the substrate as described earlier by
referring to FIG. 6C.
[0095] The temperature of the surface to be polished can be
controlled to show a uniform temperature distribution simply by
using spiral fluid flow paths that are by no means costly. If water
is used as fluid, the running cost will be further reduced.
[0096] The inlet holes of both of the two fluid flow paths 255 of
the polishing head 25 may be arranged at the periphery of the
polishing head 25 and the outlet holes of the two fluid flow paths
255 may be arranged at the axis of rotation of the polishing head
25. Alternatively, the inlet holes of both of the two fluid flow
paths 255 may be arranged at the axis of rotation of the polishing
head 25 and the outlet holes of the two fluid flow paths 255 may be
arranged at the periphery of the polishing head.
[0097] While the polishing head 25 is provided with a pair of fluid
flow paths 255 in this embodiment, it may alternatively be provided
with a single fluid flow path 255 for the purpose of the
invention.
[0098] While both the polishing head 25 and the means for holding
the object to be polished 22 are provided with respective fluid
flow paths in this embodiment, only either of them may be provided
with one or more than one fluid flow paths for the purpose of the
invention.
[0099] As described above in detail, with a chemical mechanical
polishing (CMP) method mainly relying on the chemical effect of the
polishing agent, or the etching solution, according to the
invention, the wiring metal film produced by a dual damascene
process can be flattened and then removed by means of selective
etching utilizing an etching rate that varies as a function of the
temperature of the etching solution. Additionally, the pressure
applied to the surface to be polished and the polishing pad may be
sufficient if it generates heat by friction so that it may be far
lower than the pressure required for comparable conventional
polishing methods. The pressure can be further reduced by using a
relatively hard polishing pad. As a result, the surface to be
polished is made free from the problem of a dishing phenomenon.
Still additionally, since no polishing agent that contains abrasive
grains is used, there arises no risk of producing scratches on the
metal surface nor that of partly burying the abrasive grains of the
polishing agent into the wiring material.
[0100] Furthermore, since the operating pressure applied to the
substrate can be reduced unlike conventional CMP techniques, no
process-altered layer would appear on and near the metal surface as
a result of the polishing operation, whereby ideal flattening and
removal of metal films can be realized.
[0101] A polishing agent of fine solid particles or fine abrasive
particles may be added to the etching solution in order to promote
or suppress, whichever appropriate, the heat generation caused by
friction. Even if such fine solid particles or fine abrasive
particles are added, the pressure required for pressing the
substrate against the polishing pad can be reduced further so that
there arises no risk of producing scratches on the metal surface
nor that of partly burying the abrasive grains of the polishing
agent into the wiring material.
[0102] Additionally, since the etching solution does not affect the
insulating film, no overpolishing problem occurs and hence,
advantageously, the use of an independent stopper is not necessary
for the purpose of the invention.
[0103] Thus, according to the invention, buried wires can be
reliably formed in the wiring grooves and the grooves for contact
holes formed in the insulating film on a semiconductor device in a
dual damascene process.
[0104] Finally, according to the invention, the substrate is
polished by a precision polishing apparatus where at least either
the polishing head or the means for holding the substrate is
provided with one or more than one spiral type fluid flow path as
temperature control means. Then, the entire surface to be polished
of the substrate is made to show a uniform temperature distribution
as fluid is made to flow through the fluid flow paths. Then, the
projecting areas of the surface to be polished showing a uniform
temperature distribution give rise to a temperature rise to
consequently produce a high etching rate there so that the metal
film is accurately flattened.
* * * * *