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Description  |
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FIELD OF THE INVENTION
This invention relates to a system for thin film deposition onto substrates
by vapor phase growth, such as a sputtering system, which incorporates a
means for preventing contamination of devices and formation of particles
in the deposited thin film inside the system which means can simply be
called as anti-contamination means. This invention also relates to such
anti-contamination means used in a thin film vapor deposition system and a
method for preventing contamination of devices and formation of particles
in the deposited thin film inside the system.
BACKGROUND OF THE INVENTION
Vapor phase growth techniques have been widely used in forming many
different thin films, for example, thin films for electrodes and diffusion
barriers of integrated circuits, magnetic thin films for magnetic
recording media, and indium-tin oxide (ITO) transparent conductive films
for liquid crystal display units. Thin film deposition based on the vapor
phase growth process is performed by various processes, including chemical
vapor phase process such as thermal decomposition, hydrogen reduction,
disproportionation reaction, plasma CVD technique, vacuum deposition
process, sputtering process, ion beam sputtering process, and electric
discharge polymerization process.
At the present time these processes for forming vaporphase grown thin films
are well established as mass production techniques. They have, however, a
shortcoming of accumulating coarse particulates, commonly known as
"particles", on the resulting films.
The "particles" are clustered minute or fine particulates that built up on
the substrate. They often grow to sizes as large as several microns in
diameter, and their accumulation on the substrate, for example, of an LSI
could cause shorting of interconnections, disconnection, or other trouble,
which leads to an increased percentage of rejected products. Responsible
for particle production is the deposition process itself, the equipment
involved, or other factor, and diverse efforts are under way to clarify
the mechanism and reduce the production of such particles.
The particles that are derived from the thin film deposition system are
largely those of film deposited onto and then peeled off from the
surroundings of the substrate and the inner walls (furnace walls),
shutters, shield plates, and other parts of the equipment. They scatter in
broken state and pile up on the substrate to constitute a major
contaminant source. To avoid the formation of particles due to the
peeling-off of such deposits, the inner walls of the thin film deposition
system must be kept clean.
The inner walls of the equipments, in reality, are very difficult to keep
clean. Complete cleaning takes long time, and yet the inner walls and
devices inside the equipment sometimes are practically in-accessible with
cleaners. A countermeasure has been taken to physically roughen the device
surfaces most susceptible to contamination, e.g., by spray coating with
metal in advance, so as to secure or capture the deposits inseparably in
place. It calls for elaborate, scrupulous maintenance of the system
(equipment), and still the antipeeling effect upon the deposits is quite
low. To overcome these difficulties, anti-contamination materials in the
form of disposable foil, such as A1 or electrolytic Fe foil, have been
developed. It was considered that if such a foil were affixed to the inner
walls beforehand and removed after the formation (deposition) of a thin
film on the substrate, the walls could be maintained clean.
These disposable foils have, however, been found to possess a fatal defect
in common. The film-forming substance deposited on the foils mounted in
place are liable to come off rather readily, with the result that the
formation of particles on the film deposited onto the substrate still
occured as before. Experience has revealed that in these disposable films,
the thicker the layer of the film-forming substance thereon the more
frequently the peeling-off phenomenon from the disposable film occurs. It
has also been found that the phenomenon is liable to occur specially when
the film product to be deposited is a ceramic such as silicide or ITO. A
remedy to preclude the separation is frequent replacement of the foil,
which seriously affects the operation efficiency of thin film deposition.
Another problem presented is that during thin film formation by vapor
growth the quality of the film being formed on the substrate is made
ununiform due to the fact that many contaminants flying from around the
substrate, especially accompanied with the formation of many particles.
Under the circumstances there has been a strong need for a novel, ideal
anti-contamination means for covering the inner walls of thin film
deposition systems and for preventing the particle formation in and on a
deposited thin film. The term "particles" is used herein as including
particles formed not only in a deposited thin film, but also on the
deposited thin film.
SUMMARY OF THE INVENTION
To overcome the afore-described problems, various means for preventing
contamination inside thin film deposition systems have been investigated.
It has now been found that the best results are obtained with specific
anti-contamination means, viz., (1) a treated electrolytic copper foil,
(2) a treated electrolytic copper foil coated with a material which is the
same as or is harmless and similar to the material to be deposited as a
thin film by vapor phase growth onto the substrate, (3) a corrugated metal
foil, and (4) a metal foil formed with a plurality of irregularities,
namely many recesses and protrusions by embossing.
Based on this discovery, the present invention provides a system for thin
film deposition by vapor phase growth characterized in that the
contamination of the devices and the formation of particles in the
deposited thin film inside the system are prevented by the provision
therein of an anticontamination means which is chosen from among (1) an
electrolytic copper foil having a fine-grained thin layer of copper or/and
copper oxide formed by copper plating on the matte surface of the copper
foil, (2) an electrolytic copper foil having a fine-grained thin layer of
copper or/and copper oxide formed by copper plating on the matte surface
of the foil and coated with a material which is the same as or is harmless
and similar to the material to be deposited as a thin film by vapor phase
growth onto the substrate, (3) a corrugated metal foil, and (4) a metal
foil formed with a plurality of irregularities by embossing.
In a second aspect, this invention provides an anticontamination means used
in a thin film vapor deposition system which is selected from the group of
said (1) to (4).
In a third aspect, this invention provides a method for preventing
contamination of devices and formation of particles in the deposited thin
film inside the system using said anti-contamination means.
BRIEF DESCRIPTION OF THE DRAWING
The drawing shows a schematic view of a sputtering system with
anti-contamination means incorporated thereinto.
DETAILED DESCRIPTION OF THE INVENTION
The present invention prevents contamination of the walls inside a system
(furnace) for the deposition of vaporgrown thin film, remarkably reduces
the formation of particles caused by fugitive deposits (ones that
scattered away around a substrate and deposited on the inner walls )
coming off the inner walls, and renders it possible to produce
satisfactory thin films with less maintenance. Even at the initial stage
of vapor-phase layer growth, contaminants can be kept from flying from
around the substrate and the particle formation can be controlled, and
therefore the growth of a thin film uniform in quality is made possible.
The expression "system or means for thin film deposition by vapor phase
growth" as used herein encompasses all the system or means for effecting
thin film deposition using vapor growth technologies, including thermal
decomposition process, hydrogen reduction process, disproportionation
reaction process, transport reaction process, chemical vapor deposition
(CVD) processes such as plasma CVD and low-pressure CVD, vapor-phase
epitaxy (VPE) process, vacuum vapor deposition process, sputtering
process, molecular beam epitaxy (MBE) process, ion beam process, and
electric discharge polymerization process.
In the drawing, there is schematically shown a sputtering system as a
typical means for thin film deposition according to this invention. In a
vacuum chamber 1, there are disposed a target 3 suitably fitted by a
supporting means (not shown) and a substrate 5, for example Si wafer
located opposite to the target 1 with a shutter 7 interposed therebetween.
When the target is impinged with Ar atom, the ions of a metal or other
material composing the target are eroded out and are directed to the
substrate to form a thin film of the sputtered material thereon. The
shutter is so movable as to permit the passage of the sputtered-out
material from the target toward the substrate in a controlled manner. A
target shield 4 is disposed around the target. A substrate shield 6 is
disposed around and adjacent the substrate. Anti-contamination means 10
are so located as to cover the inner wall of the vacuum chamber and also
prevent the sputtered material from directly depositing onto the surface
of the target shield, shutter and substrate shield. In this invention,
anti-contamination means 10 is selected from among (1) an electrolytic
copper foil having a fine-grained thin layer of copper or/and copper oxide
formed by copper plating on the matte surface of the copper foil, (2) an
electrolytic copper foil having a fine-grained thin layer of copper or/and
copper oxide formed by copper plating on the matte surface of the foil and
coated with a material which is the same as or is harmless and similar to
the material to be deposited as a thin film by vapor phase growth onto the
substrate, (3) a corrugated metal foil, and (4) a metal foil formed with a
plurality of irregularities by embossing.
Explanations will be sequentially made below as to four versions embodying
this invention.
1. Treated electrolytic copper foil
In one aspect of the invention, a treated electrolytic copper foil is
employed as the anti-contamination means for preventing contamination of
devices and formation of particles. By "treated" copper foil is meant an
electrolytic copper raw foil treated to form a fine-grained thin layer
with a number of protuberances on the matte surface thereof.
The fine-grained thin layer on the matte surface of an electrolytic copper
foil can be produced, for example, by electroplating as taught in U.S.
Pat. No. 3,220,897 or 3,293,109.
Although this treatment itself is already known to the art, the present
invention achieves a surprisingly beneficial advantages using such a
treated copper foil in place of the A1 and ferrous foils that have been
considered the sole anticontamination materials in the art.
The fine-grained thin layer is formed on the matte surface of the
electrolytic copper (raw) foil by electroplating, typically under the
following conditions:
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Aqueous copper sulfate plating bath
CuSO.sub.4.5H.sub.2 O g/l (as Cu)
23
NaCl, ppm (as Cl) 32
H.sub.2 SO.sub.4, g/l 70
Glue, g/l 0.75
Pure water bal.
Plating conditions
Current density 60-100 A/ft.sup.2
Duration 10-60 sec.
Bath temperature 70-80.degree. F.
______________________________________
The matte (dull) surface of an electrolytic copper foil (raw foil) is
opposite to the side (lustered surface) that comes in contact with rolls
during foil production process. It is observed under an electron
microscope to have a roughened surface with numerous knobs (lumpy
protuberances).
Electron microscopic inspection also shows that, when the fine-grained thin
layer has been formed on the matte surface, fine grains (nodules) of
copper or/and copper oxide precipitate randomly on the knobby roughened
surface of the electroytic copper (raw) foil.
The copper foil formed under the foregoing conditions may further be
covered with a brass or zinc barrier layer which imparts heat resistance,
as taught in Japanese Patent Application Publication No. 6701/1979. If
desired, the covered surface may be subjected to anticorrosion treatment
so as to avoid oxidation or other deterioration during transportation or
storage of the copper foil.
Electrolytic copper foils finished through such a step or steps all come
within the contemplation of the present invention. The electrolytic copper
foil to be used is desired to have a surface roughness, Rz, in the range
between 5.0 and 10.0 .mu.m. The presence of minute protuberances
represented by the roughness produces an anchoring effect which, in turn,
improves the surface adhesion to the deposits of fugitive substance flying
toward inner walls etc. to such an extent that the possibility of peeling
is precluded.
The foil used as means for preventing contamination and particle formation
in the thin film deposition system of the invention has a thickness of
from 10 to 300 .mu.m, preferably from 15 to 100 .mu.m. If too thin, the
foil tends to crease when affixed to furnace walls. This should be avoided
because creasing can cause foil peeling-off from the wall surface. On the
other hand, the thicker the foil the less frequently it creases but the
more difficult it is to operate so as to affix and set the foil to the
walls and the greater the economic disadvantage.
Since the electrolytic copper foil is made in a glue-containing
electrolytic bath, glue sometimes remains on the foil surface. To avoid
the contamination inside the thin film deposition system with this glue,
it is advisable to use the foil after ultrasonic cleaning with an organic
solvent, such as acetone or alcohol, or with hot ultrapure water. The
cleaned surface may be heated in a vacuum to dry up. Where vacuum heating
is used, the temperature must be kept below 800.degree. C. lest the
surface protuberances further grow out of shape.
Inside the thin film deposition system that depends on vapor growth, the
copper foil may be used as corrugated or embossed beforehand.
Such processing considerably increases the surface area of the copper foil
and properly absorbs the internal stresses that result from the thin film
formation. Consequently, the particle formation in the thin film grown on
the substrate can be outstandingly reduced.
The present invention is directed also to the copper foils made in the
afore-described way.
Test examples will now be explained.
Example 1-1
Various foils listed in Table 1 were affixed to inner wall portions of a
vacuum deposition equipment (chamber), and vacuum deposition was carried
out using a conductive-film-forming Al source. After the deposition, the
foils were taken out. The foils too showed A(films formed from the
scattered A1 vapor. The films were subjected to a Scotch tape peel test.
Only the electrolytic copper foil of the invention showed no A1 film
peeling-off upon the peel test. The test materials used and the results
are summarized in Table 1.
TABLE 1
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Test materials and results of Scotch tape peel tests
Test material Test result
______________________________________
Comparative samples:
SUS 304 foil (rolled foil)
Peeled off
Pure Ti foil (rolled foil)
"
Pure Zr foil (rolled foil)
"
Pure Al foil (rolled foil)
"
Sample of this invention:
Electrolytic copper foil
No peeling
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NOTE: The designation "SUS" Type No. is used to express the kinds of
stainless steels in Japan which corresponds to "AISI" Type No. in U.S.A.
Example 1-2
Employing a CVD system, an electrolytic copper foil of the invention and a
stainless steel (SUS) sheet sprayed with molybdenum (Mo) as a comparative
example, as listed in Table 2, were fitted inside the equipment. A
reactive gas consisting essentially of WF.sub.6 and H.sub.2 was
introduced, and a tungsten (W) film was formed on each case.
The W films thus formed on each foil were tested for peeling with Scotch
tapes and double-coated tapes as shown in Table 2. The both tapes peeled
the W skin from the Mo-sprayed SUS sheet, but none from the electrolytic
copper foil of the invention, indicating that the film bond strength was
much greater in the latter.
TABLE 2
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Results of peel tests on tungsten films
Test Type of tape used
material in peel test Test result
______________________________________
Mo-sprayed SUS sheet
Scotch tape Peeled off
Double-coated tape
Peeled off
(No. 500)
Electrolytic copper
Scotch tape No peeling
foil of the Double-coated tape
No peeling
invention (No. 500)
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As is obvious from the above examples, the thin film deposition system
having a treated copper foil as an anticontamination material fitted
inside can markedly control the formation of particles that contaminate
the thin film, as compared with the conventional systems using A(,
ferrous, or other similar foil. Another remarkable advantage is the ease
with which the copper foil is affixed and detached, thus facilitating the
maintenance of the system.
The above advantages combine with high heat conductivity and
non-electrical-chargeability to make the electrolytic copper foil ideal as
an anti-contamination material to be used inside a system for thin film
deposition by vapor phase growth.
2. Treated copper foil having a coating
The electrolytic copper foil obtained in the foregoing manner may
advantageously be coated with a substance which is the same as or is
harmless and similar to the substance to be deposited as a thin film by
vapor phase growth onto the substrate.
Examples of the substances for the above application are silicides, such as
molybdenum silicide, tungsten silicide, and titanium silicide; metals of
tungsten, molybdenum, titanium, cobalt, aluminum, and tantalum as well as
their alloys; oxides, such as indium oxide and aluminum oxide; nitrides,
and various others.
Different (or similar) substances may be employed as coatings on the
electrolytic copper foil provided the combined use (or mixing) does not
pose a problem. For example, a foil may be coated with one of the metals
constituting an alloy or tungsten silicide-coated copper foil may be used
for the deposition of molybdenum silicide. They all come within the scope
of this invention.
Coating of the electrolytic copper foil with these substances may be done
using a means for thin film deposition by vapor phase growth onto the foil
substrate. Although the thickness of the coating may be optionally chosen,
it desirably ranges from about 5,000 to about 100,000.ANG.. The coated,
treated copper foil thus keeps contaminants from flying mostly from
peripheral parts and controls the formation of particles, from the early
stage of vapor-grown thin film deposition onward. The thin film so coated
serves for the "containment" of the contaminants.
It eliminates the necessity of conventionally used precoating(pretreatment)
such as presputtering and permits further enhancement of the operation
efficiency.
Inside the thin film deposition system that depends on vapor growth, the
copper foil may be used as corrugated or embossed beforehand.
Such processing considerably increases the surface area of the copper foil
and properly absorbs the internal stresses that result from the thin film
formation. Consequently, the particle formation in the thin film grown on
the substrate can be outstandingly reduced.
The present invention is directed also to the copper foils made in the
afore-described way.
Test examples are given below.
Example 2-1
Using ITO targets for forming transparent, electrically conductive films,
various foils listed in Table 3 were affixed to the devices and inner
walls of a sputtering chamber, in such a manner that the foils
individually cover those surfaces, and then sputtering was carried out.
After the sputtering under the identical condition of 390 W.hr, the
substrates formed with ITO thin films and foils were taken out. The foils
too had ITO films formed from the flying particulates. The foils were
tested for peeling with Scotch tape. The electrolytic copper foil
according to the invention showed no separation of the ITO film. As shown
in Table 3, film separation took place with the SUS 304 foil, indicating
serious peeling of the coat that leads to particle formation. It was found
that the same electrolytic copper foils with and without an ITO film
formed in advance showed different rates of initial particle production on
substrates.
It will be seen from the foregoing that forming a film of a target material
ITO in advance will reduce the initial particle production to almost
naught and provide an excellent preventive against particle formation.
TABLE 3
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Initial productions of particles on substrates
and peel test results
Initial
particle
production on
Test material Peel test result
substrate
______________________________________
Comparative samples:
SUS 304 foil (rolled foil)
Peeled off Large
Electrolytic copper foil
No peeling Small
(without ITO thin film)
Sample of the invention:
Electrolytic copper foil
No peeling None
with ITO thin film
______________________________________
Example 2-2
Using silicide targets, an electrolytic iron foil and a silicide-precoated
electrolytic copper foil of the invention were separately affixed to the
devices in and inner walls of a sputtering system, in such a manner that
the foils individually cover those surfaces, and then sputtering was
likewise performed. After the sputtering, the substrates and test foils
were taken out. The both test foils had an about 10 .mu.m thick silicide
film formed thereon. These samples were tested for peeling with Scotch
tape and more adherent double-coated tape (No. 500). Only the electrolytic
copper foil of the invention did not show separation in either test. The
results are summarized in Table 4.
Initial particle formation on the substrate was not in the least observed
with the electrolytic copper foil of the invention, whereas the iron foil
exhibited initial particle formation and inclusion of contaminants.
TABLE 4
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Results of peel tests on silicide films
Type of tape Particle
Test used in peel Result of formation
material test peel test on substrate
______________________________________
Electrolytic
Scotch tape Not peeled Yes
iron foil Double-coated
Peeled off
tape (No. 500)
Electrolytic
Scotch tape Not peeled No
copper foil
Double-coated
Not peeled
of invention
(silicide-
tape (No. 500)
coated)
______________________________________
Example 2-3
An electrolytic copper foil coated with a W film in accordance with the
invention and, by way of comparison, a stainless steel (SUS) sheet spray
coated with molybdenum (Mo), as listed in Table 5, were separately affixed
to the devices and inner walls of different CVD units so as to cover them.
Reactive gases composed basically of WF.sub.6 and H.sub.2 were introduced,
and tungsten (W) films were formed on substrates under the same
conditions.
Following the formation of the W films, the substrates were taken out
together with the test foil and sheet. The substrates were inspected for
any evidence of particle formation and contamination of the thin films,
and the test foil and sheet were tested for peeling with Scotch tape and
double-coated tape. As shown in Table 5, the W film was peeled off by the
both tapes from the Mo-sprayed SUS sheet covering the devices, whereas it
did not come off from the electrolytic copper foil of the invention,
indicating much greater adhesion strength attained in the latter.
Where the electrolytic copper foil of the invention was used, there was
neither particle growth on the substrate nor contamination arising from
the devices. With the Mo-sprayed SUS sheet, by contrast, both the particle
formation on the substrate and device-related contamination were observed.
TABLE 5
______________________________________
Results of peel tests on tungsten films
Type of tape Particle
Test used in peel
Result of formation
material test peel test on substrate
______________________________________
Mo-sprayed SUS
Scotch tape Peeled off
Yes
sheet Double-coated
"
tape (No. 500)
Electrolytic
Scotch tape Not peeled
No
copper foil of
Double-coated
"
invention tape (No. 500)
(W-coated)
______________________________________
As appreciated from the examples, the treated copper foil coated in
conformity with the invention, when fitted in a thin film deposition
system, proves to be an excellent anti-contamination means. It
substantially controls the formation of particles as a contaminant to the
resulting thin film, and eliminates the ingress of contaminants or
particles into the substrate which would otherwise occur at the early
stage of coating by vapor growth.
Another notable advantage is the ease with which the foil is attached and
detached, which facilitates the maintenance of the system.
In addition, the electrolytic copper foil has high thermal conductivity and
has no possibility of being electrically charged. With these advantages,
it is a most suitable anti-contamination material for use inside a system
for thin film deposition by vapor growth.
3. Corrugated metal foil
Corrugation sharply increases the surface area of a metal foil, reduces the
amount of deposition per unit area, and inhibits the increases in internal
stresses with increased amounts of deposition. It thereby remarkably
reduces the cracking of the deposition product, warpage (camber) of the
anti-contamination material (means), and peeling-off of the deposit due to
such defects.
The corrugated form imparts flexibility to the metal foil, allowing the
latter for expansion and contraction in the direction of corrugations. It
thus prevents abnormal deformation of the anti-contamination material due
to its own internal-stress-induced warpage and hence avoids the separation
of the deposition product from the material.
Corrugating of the metal foil is implemented by roll forming or other metal
working process. There is no special limitation to the geometric shape of
corrugations, although ridges 0.1 to 5 mm high and an angle of bend in the
range of 10 to 150.degree. (preferably 30 to 100.degree. ) give good
results.
For example, with a circular target or circular substrate in a sputtering
system, the corrugations may be concentric, with the ridgelines extending
radially in conformity with the configuration of the substrate shields or
shutters. With a rectangular target or substrate, the corrugations may be
so aligned that their ridgelines are in parallel.
Metal foils 10 to 300 .mu.m thick can be employed, but those usually used
have a thickness of 18 to 300.mu.m, preferably 18 to 250.mu.m, more
preferably 18 to 100.mu.m.
If the metal foil is too thin, a strength problem arises and, in addition
to having inadequate rigidity, the foil becomes difficult to corrugate.
Conversely if the foil is too thick, excessive rigidity makes it no longer
flexible enough to absorb the internal stresses of the deposition product.
As a consequence, separation tends to occur between the anti-contamination
metal foil and the deposition product, giving rise to particles.
The corrugated anti-contamination material is preferably fitted in the
vicinity of the substrate where deposition takes place most actively, for
example, around the shutter, substrate shield and magnetic shield of a
sputtering system. Alternatively, it may be affixed to the surfaces of the
inner walls and other devices inside the system.
For the fitting of the anti-contamination material to the devices inside
the thin film deposition system, spot welding is advisable. Fitting by
means of pins does not produce sufficient fastening strength, and the
geometry of some devices provides locations inaccessible for pinning. The
deposition product can come off, and from around, the pins.
Where bolting is resorted to, it is necessary to drill holes in the parts
to be joined and in the anti-contamination material too, causing the
danger of rupture starting with such holes. This, along with the same
drawbacks as with pinning, makes bolting undesirable.
Spot welding may be carried out, when necessary, with a brazed copper-base
alloy (Cu-10-30wt%Sn) foil interposed between the device and the thin film
deposition system.
This permits joining with a low power output and reduces the possibility of
damaging of the devices and the anticontamination material inside the thin
film deposition system.
Covering operation involves no separation (poor adhesion) but ensures
stable fitting. A further advantage is that when replacement becomes
necessary, the anti-contamination material can be easily removed from
devices by hand.
The metal foil to be used may consist of stainless steel, iron, aluminum,
or the like. Above all, a surface treated electrolytic copper foil as
described in 1. or 2. above is desirable. Such a copper foil
advantageously gains added ductility on annealing.
The treated electrolytic copper foil exhibits outstanding adhesion strength
and effectively controls the exfoliation of the deposition product. In
these respects the foil proves quite useful because its own anchoring
effect combines with the corrugation effect.
A rolled copper foil attains beneficial effects comparable to those of the
electrolytic copper foil upon surface treatment. The treatment imparts
greater ductility to the rolled copper foil and allows the foil to absorb
the internal stresses of the deposition product efficiently.
Test examples are given below.
Example 3-1
Various foils listed in Table 6 were fitted inside a sputtering system and
sputtering was conducted using a tungsten alloy (W-10wt%Ti) target 3 in.
in diameter. The foils were taken out after the sputtering under identical
conditions, i.e., at the distance of 40 mm from the target, with a power
output of 100 W.hr, and at a film forming rate of 12 .mu.m/hr.
TABLE 6
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Test material Peelability
Deformation
______________________________________
Comparative samples:
Flat 70 .mu.m-thick
Peeled after
Warpage with a radius
copper foil 12 hrs. of of curvature of ab.
sputtering 100 mm after
12-hr sputtering
Flat 70 .mu.m-thick
Peeled after
Warpage with a radius
rolled copper foil
16-hr of curvature of ab.
sputtering 120 mm after 16-hr
sputtering
Samples of the
invention:
Corrugated 70 .mu.m-
Peeled after
Practically no warpage
thick copper foil
50-hr even after 50-hr
(Ridge height 3 mm)
sputtering sputtering
Corrugated 70 .mu.m-
Partly peeled
No warpage even after
thick copper foil
after 50-hr
50-hr sputtering
(Ridge height 1 mm)
sputtering
______________________________________
As table 6 clearly indicates, the both corrugated copper foils (of
electrolytic copper) provided quite superior in that they peeled far less
than the flat foils and, because the corrugations absorbed the internal
stresses of the deposition product, the foils underwent little or no
deformation after 50 hours of sputtering.
Thus, the corrugated foils according to the invention have a service life
several times as long as the flat copper foils and act amazingly as
anti-contamination means inside sputtering systems. They permit prolonged
sputtering to get both technical and economical advantages.
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