U.S. patent application number 09/864703 was filed with the patent office on 2001-10-18 for sputtering target and method for the manufacture thereof.
Invention is credited to Ohhashi, Tateo, Seki, Kazuhiro, Takahashi, Hideyuki.
Application Number | 20010030172 09/864703 |
Document ID | / |
Family ID | 11535947 |
Filed Date | 2001-10-18 |
United States Patent
Application |
20010030172 |
Kind Code |
A1 |
Takahashi, Hideyuki ; et
al. |
October 18, 2001 |
Sputtering target and method for the manufacture thereof
Abstract
A sputtering target is provided which provides early
stabilization of the film-deposition rate of the sputtering target
from its initial stage of use. The sputtering target surface
subjected to erosion is formed with a surface-deformed layer. The
surface-deformed layer is reduced by precision machining and
removed by etching. The extent of etching is controlled so that the
surface roughness (Ra) is in a range between 0.1% and 10% of the
mean crystal grain diameter of the material constituting the
target. The surface roughness (Ra) is defined as the mean roughness
on the center line of the surface.
Inventors: |
Takahashi, Hideyuki;
(Ibaraki-Ken, JP) ; Ohhashi, Tateo; (Ibaraki-Ken,
JP) ; Seki, Kazuhiro; (Ibaraki-Ken, JP) |
Correspondence
Address: |
HOWSON AND HOWSON
ONE SPRING HOUSE CORPORATION CENTER
BOX 457
321 NORRISTOWN ROAD
SPRING HOUSE
PA
19477
US
|
Family ID: |
11535947 |
Appl. No.: |
09/864703 |
Filed: |
May 24, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09864703 |
May 24, 2001 |
|
|
|
09459805 |
Dec 13, 1999 |
|
|
|
Current U.S.
Class: |
216/100 ;
204/298.12; 216/52; 216/53; 216/58; 216/63; 216/74; 216/75; 216/83;
216/96 |
Current CPC
Class: |
H01J 37/3491 20130101;
C23C 14/3414 20130101 |
Class at
Publication: |
216/100 ;
204/298.12; 216/52; 216/53; 216/58; 216/63; 216/75; 216/74; 216/83;
216/96 |
International
Class: |
B44C 001/22; C23C
014/34 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 8, 1999 |
JP |
002677/1999 |
Claims
We claim:
1. A sputtering target comprising a surface subjected to erosion,
said surface being substantially free of a surface-deformed layer,
made of a material having a predetermined mean crystal grain
diameter, and having a surface roughness (Ra) defined by a mean
roughness on a center line of said surface in a range of between
about 0.1% and 10% of said mean crystal grain diameter of said
material.
2. A sputtering target according to claim 1, wherein said surface
roughness (Ra) is in a range between 1% and 10% of said mean
crystal grain diameter of said material.
3. A method for manufacturing a sputtering target which has a
surface subjected to erosion, the surface having a surface-deformed
layer and being made of a material having a pre-determined mean
crystal grain diameter, comprising the steps of: precision
machining the surface of the sputtering target to reduce the
surface-deformed layer; and etching the surface to provide the
surface with a surface roughness (Ra) in a range of between about
0.1% and 10% of the mean crystal grain diameter of the material,
said surface roughness (Ra) being defined as a mean roughness on a
center line of the surface.
4. A method of manufacturing a sputtering target according to claim
3, wherein said surface roughness (Ra) is in a range of between 1%
and 10% of the mean crystal grain diameter of the material.
5. A method of manufacturing a sputtering target according to claim
3, wherein the surface-deformed layer has a thickness, and wherein
said thickness of the surface-deformed layer is reduced to 20 .mu.m
or less during said precision machining step.
6. A method of manufacturing a sputtering target according to claim
4, wherein the surface-deformed layer has a thickness, and wherein
said thickness of the surface-deformed layer is reduced to 20 .mu.m
or less during said precision machining step.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a sputtering target which
provides a stable film deposition rate from an initial stage of
sputtering and which eliminates the need for burn-in, or
pre-sputtering, which removes substantially the entire
surface-deformed layer of the sputtering target to provide the
surface of the sputtering target in a state suitable for
sputtering. The present invention also relates to a method for
manufacturing such a sputtering target.
BACKGROUND OF THE INVENTION
[0002] Heretofore, the surface of a sputtering target has been
finished by machining, such as, cutting, grinding, or
polishing.
[0003] Due to the characteristics of machining by forcedly
processing while physically breaking metal crystal grains, a large
number of strains and defects, known as a surface-deformed layer,
remain on the surface of the target.
[0004] Since sputtering is a process for releasing metal atoms
constituting the target by using collision energy generated by
physically colliding cations, such as Ar+, to a target installed on
a cathode, the ease of releasing the metal atoms themselves differs
depending upon the arrangement of metal atoms in a crystal (crystal
orientation).
[0005] In a sputtering target having machining-affected layers as
described above still remaining on the surface of the sputtering
target, a stable surface state which provides a stable film
deposition rate is obtained only after the target has been used for
a certain period of time.
[0006] Therefore, as long as surface-deformed layers remain on the
sputtering target, the deposition rate cannot be stabilized. This
in turn causes an increase in the use of integrated input electric
energy which is required for pre-sputtering of the target.
[0007] In order to solve such problems, a method for removing
surface-deformed layers by etching the target surface has been
proposed (Japanese Patent Laid-Open No. 7-118842).
[0008] However, such a method has a problem in that the integrated
input energy required for pre-sputtering cannot be significantly
decreased by rigorous etching under conditions suitable for
removing surface-deformed layers.
OBJECTS OF THE INVENTION
[0009] In order to solve the above-described problems, in
particular to realize quick stabilization of the film deposition
rate, the object of the present invention is to provide a
sputtering target which has a surface in a desired state so that a
stable film deposition rate is provided from the initial stage of
use of the sputtering target.
[0010] Another object of the present invention is to provide a
method for manufacturing such a sputtering target.
SUMMARY OF THE INVENTION
[0011] The inventors of the present invention conducted repeated
examinations for solving the above-described problems and obtained
the following findings.
[0012] In the state where the film deposition rate of a sputtering
target is stabilized after the sputtering target has been used for
a certain period of time, a microscopic crystal surface covers the
target surface which is subjected to erosion and from which metal
atoms are easily released by sputtering. Such a crystal surface
appears one after another even after sputtering has been
proceeded.
[0013] Unless the surface of the target has been covered with a
crystal surface which can be readily sputtered at a stable film
deposition rate, integrated input electric power cannot be
decreased to zero. This is true even if the surface roughness of
the target is minimized, for example, by mirror polishing, or even
if the target surface is in a state where no surface-deformed
layers are present. (See Comparative Example 3 which is discussed
later in this application.) If a surface-deformed layer remains on
an area of the target undergoing sputtering, the film deposition
rate is higher than a stabilized film deposition rate. Therefore,
the surface-deformed layer must be removed to substantially zero to
stabilize the film deposition rate.
[0014] Even if there is no surface-deformed layer, a target having
a crystal surface that is easily sputtered cannot be obtained if
the target surface is excessively rough. Such a target requires
pre-sputtering to obtain a surface which is easily sputtered. (See
Comparative Example 5 discussed later in this application.)
[0015] A target which consumes little integrated input electric
power until the film deposition rate is stabilized can be obtained
by decreasing the surface-deformed layer to substantially zero.
This can be accomplished by precision machining the target in order
to minimize the surface-deformed layer and then by etching the
target until the surface of the target is covered with a crystal
surface that is easily sputtered.
[0016] On the basis of the above described findings and according
to a first aspect of the present invention, a sputtering target is
provided such that it is practically free of surface-deformed
layers created by machining the target surface subjected to
erosion. This surface is provided with a surface roughness (Ra) in
a range between about 0.1% and 10% of the mean crystal grain
diameter of the material constituting the target. The surface
roughness (Ra) is defined as the mean roughness on the center line
of the surface which is subjected to erosion.
[0017] According to a second aspect of the present invention, the
surface roughness (Ra) of the above referenced target surface is in
a range between about 1% and 10% of the mean crystal grain
diameter.
[0018] According to a third aspect of the present invention, a
method for manufacturing a sputtering target is provided. The
method comprises the steps of reducing the surface-deformed layer
by precision machining the target surface and etching the target
surface to make the surface roughness (Ra) of the target surface be
in a range of between about 0.1% and 10% of the mean crystal grain
diameter of the material constituting the target.
[0019] According to a fourth aspect of the present invention, the
above described method is utilized to provide the target surface
with a surface roughness (Ra) in a range of about 1% and 10% of the
mean crystal grain diameter.
[0020] According to a fifth aspect of the present invention, the
precision machining step of the above described method is utilized
until the thickness of the surface-deformed layer is reduced to
about 20 .mu.m or less.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a graph showing the relationship between
integrated electric power consumption and film deposition rate of
the Embodiment and Comparative Embodiments of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS/METHODS
[0022] The present invention is described in detail hereinafter
referring to an Embodiment and Comparative Embodiments.
[0023] Ti targets having a purity of 99.995% by weight and a mean
crystal grain diameter of 40 .mu.m were used for five sample
targets discussed below. The five samples were prepared and
subjected, respectively, to the following surface finishing: (1)
ordinary lathe finishing; (2) ordinary lathe finishing and wet
polishing; (3) precision lathe finishing; (4) precision lathe
finishing and wet polishing and chemical etching; and (5) precision
lathe finishing and a large amount of chemical etching.
[0024] The properties of the samples are shown in Table 1. As Table
1 shows, sample (4) is the Embodiment of the present invention, and
samples (1), (2), (3) and (5) are Comparative Examples.
[0025] Surface roughness was measured by a contact roughness meter,
and the thickness of the surface-deformed layer was estimated by an
X-ray diffractometer.
[0026] Chemical etching was carried out by immersing the samples
for 60 seconds in a mixed solution of 5% by volume hydrofluoric
acid, 15% by volume nitric acid, and 80% by volume water.
1 TABLE 1 Mean Roughness Thickness of Relative ratio on the center
line machining- (%) Ra affected layer roughness/grain Symbol
(.mu.m) (.mu.m) diameter Compara- (1) 4 30 10 tive Example Compara-
(2) 0.4 15 1 tive Example Compara- (3) 0.1 20 0.25 tive Example
Example (4) 0.7 0 1.75 Compara- (5) 20 0 50 tive Example
[0027] The film deposition rates plotted for integrated electric
energy are shown in FIG. 1. For samples (1) and (2), the
surface-deformed layers are thick, and the film forming speed is
high in the initial stage of use of the sputtering target.
[0028] That is, since a large number of surface-deformed layers
remain in sample (1), the film deposition rate is high in the
initial stage, and the film deposition rate reaches almost a stable
(ie. normal) state when integrated electric energy reaches about 20
kWh.
[0029] For sample (2), less integrated electric power is required
as compared to sample (1) for the film deposition rate to reach an
almost stable state. The film deposition rate becomes almost stable
at about 10 kWh of integrated electric power.
[0030] The surface-deformed layer of sample (3) is thinner (20
.mu.m) than that of sample (1) and thus approaches a favorable
surface state. However, the surface roughness of sample (3) is
relatively small (mirror finishing). Thus, sputtering is difficult
in the initial stage of use of sample (3), and the film deposition
rate is lower than that of a stable film deposition rate. For
sample (3), the mean roughness Ra on the center line of the target
is 0.25% of the mean crystal grain diameter.
[0031] Thereafter, since surface deformed layers of about 20 .mu.m
remain in sample (3), the film deposition rate increases before it
stabilizes at which time the integrated electric energy reaches
about 16 kWh. Such variations in the film deposition rate are not
preferable.
[0032] With respect to sample (4), which is the Embodiment of the
present invention, almost all of the surface-deformed layer has
been removed by etching, and the film deposition rate is low until
integrated electric power reaches about 1 kWh when the naturally
oxidized layer on the uppermost surface is removed. Thereafter, the
film deposition rate is highly stabilized. In sample (4), the
surface roughness Ra is 1.75% of the mean crystal grain
diameter.
[0033] It is shown that the stable film deposition rate is obtained
from the very initial stage of use of the sputtering target
according to the present invention.
[0034] Although the Comparative Example (5) has no surface-deformed
layers, the amount of etching is large and surface roughness is
large. Therefore, the film deposition rate is low in the initial
stage of use, and thereafter, it is almost stabilized as integrated
electric energy reaches about 14 kWh.
[0035] As described above with respect to the samples, after the
surface-deformed layer of the surface of the sputtering target has
been decreased and then adequately etched thereby obtaining a state
close to the state where the surface is covered with an orderly
crystal surface suitable for sputtering, the film deposition rate
is stabilized from an initial stage of use.
[0036] Turning to Table 2, it shows the relationship between the
surface roughness Ra, the ratio of the surface roughness Ra to the
particle diameter, and the integrated electric power required for
the film deposition rate to stabilize. In Table 2, A, B, F and G
are Comparative Examples and C, D and E are the Embodiments of the
present invention.
2 TABLE 2 Mean Roughness Relative ratio Integrated Thickness of on
the center line (%) power machining- Ra roughness/grain consumption
affected layer (.mu.m) diameter (kWh) (.mu.m) A 0.004 0.01% 20 10 B
0.02 0.05% 16 10 C 0.04 0.1% 8 0 D 0.4 1.0% 2 0 E 4 10% 3 0 F 20
50% 14 0 G 32 80% 18 0
[0037] Comparative Examples A and B correspond to previously
described Comparative Example (3). However, the surface roughnesses
of Comparative Examples A and B have been further reduced, that is,
mirror polished. The film deposition rate of Comparative Example B
stabilizes when integrated electric power reaches 16 kWh which is
almost the same as Comparative Example (3). The film deposition
rate of Comparative Example A stabilizes when integrated electric
power reaches 20 kWh, which is an increase in comparison to
Comparative Example (3).
[0038] Examples C, D and E and Comparative Examples F and G
correspond to previously discussed Example (4), except that their
surface roughnesses are different than Example (4) because their
etching times were altered. Comparative Example F corresponds to
previously discussed Comparative Example (5).
[0039] The film deposition rates of Examples C, D and E and
Comparative Examples F and G stabilize when the integrated electric
power is 8, 2, 3, 14 and 18 kWh, respectively. Thus, it is
demonstrated that the preferable ratio of the surface roughness Ra
to the grain diameter is within a range of between 0.1% and 10%,
and more preferably, between a range of 1.0% and 10%.
[0040] It is shown from this that excessive etching of target
materials does not provide favorable and quickly stabilized film
deposition rates.
[0041] As described above, the present invention provides, in an
initial stage of manufacturing the target, a surface which
approximates the surface of a sputtering target during a normal
state of sputtering. This is a sputtering target surface with an
exposed uneven texture of crystal grains.
[0042] In the target thus manufactured, sputtering proceeds as
ordinary sputtering, and the surface is the same as, or similar to,
the sputtered surface in a normal state.
[0043] According to the present invention, as described above, a
sputtering target useful in providing a stabilized film deposition
rate from an initial stage of sputtering can be provided by making
a sputtering target surface in a state close to a state where the
surface has an exposed uneven texture of grains, rather than
removing almost all of the surface-deformed layers and mirror
polishing the surface.
* * * * *