JPH0959775A - Sputtering method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the temp. of a substrate from being changed under the effect of radiation as the time elapses and to form a uniform textured electrode face at the time of forming a film on the surface of a flexible substrate through sputtering by a roll-to-roll system. SOLUTION: The temp. of the substrate 10 with a linearly stretched film formed on the surface is measured by an IR thermometer 12 or a sheet thermocouple and fed back to the output of a discharge power source to control the substrate temp. Otherwise, the measured substrate temp. is fed back, the substrate is passed between the temp.-controlled rolls, and the substrate temp. is controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sputtering method performed when an electrode layer is formed on a flexible substrate for manufacturing a thin film solar cell or the like.

[0002]

2. Description of the Related Art A thin film solar cell in which a polymer material film or stainless steel foil having a thickness of several tens to several hundreds of μm is used as a flexible substrate and a photoelectric conversion layer is formed of an amorphous silinco thin film has high mass production. Therefore, it is expected to be a low-cost solar cell. This type of solar cell usually has high reflectance such as Ag or Al in order to obtain high conversion efficiency.
Is formed on the substrate as an electrode layer. As a technique for further improving efficiency, it has been considered that texturing, that is, providing unevenness having a height of about 0.05 to 0.5 μm on the surface of the electrode layer to scatter light inside the solar cell. As a method of this texturing, as described in Japanese Patent Application No. 7-111141, a method of forming Ag at a high temperature of about 300 to 400 ° C. to aggregate and as described in Japanese Patent Application No. 7-185315. There is a method in which Al is formed at a high temperature of about 250 to 350 ° C., aggregated, and Ag is formed thereon at about 200 ° C. In each case, 300 for texturing
There is an optimum value at about ° C, and if the temperature is too low or too high, the characteristics of the solar cell are deteriorated. In particular, when a heat-resistant plastic film such as polyimide is used as the substrate, a rapid thermal contraction occurs at about 300 ° C. or more, and therefore, when forming the textured electrode, the temperature range of about 300 ° C. is extremely high at ± 10 ° C. Precise substrate temperature control is required.

2 and 3 show a roll type sputtering apparatus used for forming a metal electrode layer on a film substrate. The apparatus shown in FIG. 2 comprises three parts: a feed chamber 1, a sputter chamber 2 and a winding chamber 3. A feed roll 4 for unwinding the film is installed in the feed chamber, a take-up roll 5 is installed in the take-up chamber, and a transport guide roll 6 is installed in both chambers. The sputtering chamber 2 has a heater 9 for heating the film,
A cathode 7 and an annular anode 8 are installed.
The cathode 7 is composed of a target material 71, a backing plate 72 and a magnet 73, and is magnetron sputtered by applying a DC or high frequency voltage, and is placed on the film substrate 10 conveyed from the feed roll 4 to the winding roll 5. It is formed into a film. FIG.
In the apparatus shown in (1), the film substrate 10 is conveyed from the feed roll 4 to the take-up roll 5 while being in contact with the surface of the can roll 11. Then, the sputtering is performed by applying a voltage between the cathode 7 and the anode 8 facing the can roll 11.

[0004]

During sputtering, the substrate is heated by collision of sputtered particles and ions with the substrate and radiation from the plasma itself. Since the film substrate has a very small heat capacity, when the device of FIG. 2 is used,
The temperature of the substrate 10 instantly rises by about 100 to 200 ° C. Furthermore, the inside of the sputtering chamber 2 is gradually heated during sputtering, and the substrate temperature rises due to the secondary radiation. Normally, the backing plate 72 is provided with a cooling mechanism. However, when a discharge power supply output is controlled to be constant and a film having a length of several hundred meters is formed in a few hours, the effect of the above secondary radiation is generated. At the end of film formation, the substrate temperature rises by about 50 to 100 ° C. as compared with the start of film formation. For this reason,
It was difficult to perform precise temperature control of about ± 10 ° C.

When the apparatus of FIG. 3 is used, the film 10
Is in contact with the can roll 11 having a large heat capacity, the temperature rise is suppressed, and precise temperature control becomes possible by adjusting the temperature of the can roll 11 itself.
However, the size of the device becomes large and the cost of the device also increases. Furthermore, maintenance such as replacement of the target 71 is difficult, and since the substrate temperature is limited by one roll 11, it is impossible to form a multilayer film at different film forming temperatures.

An object of the present invention is to provide a sputtering method which solves the above-mentioned problems and enables the formation of a metal electrode layer having a textured surface by precisely controlling the substrate temperature.

[0007]

In order to achieve the above-mentioned object, the present invention generates a discharge in the vicinity of a portion where a flexible substrate to be conveyed is stretched linearly, and a target is formed on the surface of the substrate. In a sputtering method for forming a thin film of a material, the substrate temperature during thin film formation is measured, and the substrate temperature is controlled based on the measured surface temperature. Accordingly, even if the substrate temperature changes after the start of film formation, the substrate temperature can be suppressed within a narrow range by following the change. The substrate temperature may be controlled by the output of the discharge power source or may be controlled by passing the substrate between rolls whose temperature can be adjusted. In either case, the substrate temperature can be set to a predetermined value with a small time delay. By combining the two control methods, it is possible to continuously form multi-layer films having different film forming temperatures on the same substrate. The temperature of the substrate surface may be measured by an infrared thermometer without contacting the substrate. Since the measurement is performed without contacting the substrate, the substrate temperature does not change due to the measurement. However, the temperature of the substrate surface may be measured by contacting a sheet-shaped thermocouple. Since the thermocouple is in the form of a sheet, it has a small heat capacity, and even if it contacts, the substrate temperature is hardly affected. At least one of the sputtering chamber and the discharge electrode may be water-cooled. This prevents the film thickness on the substrate surface from changing with time due to the change in discharge power.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the practice of the present invention, an infrared thermometer as a temperature measuring means or a sheet-like thermocouple having a sufficiently small heat capacity is installed in a conventional roll-to-roll type sputtering apparatus, and the measured temperature is discharged. It suffices if the power output or the temperature control roll has a function of making a footback. When the multilayer films are successively laminated on the same flexible substrate, different temperature control methods may be combined. Further, the temperature control type film formation according to the present invention and the normal power control type film formation can be combined.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A sputtering method according to an embodiment of the present invention will be described below with reference to the drawing in which the same parts as those in FIG. The sputtering apparatus shown in FIG. 1 is used in the sputtering method of one embodiment of the present invention.
Although it is almost the same as the sputtering apparatus of FIG. 2, a non-contact type infrared thermometer 12 is installed in the sputtering chamber 2.
It is connected to a control device for a discharge power supply (not shown). A case where a textured Ag electrode layer having an average film thickness of about 15 nm is formed on a polyimide film having a thickness of 50 μm using this apparatus will be described. The inside of the apparatus in which the film substrate 10 is set is evacuated to 10 ⁵ to 10 ⁷ Torr by a cryopump or a turbo molecular pump. The heater 9 is preheated to 250 to 300 ° C. Next, an inert gas such as Ar is introduced, and then the pressure inside the chamber is controlled to 10 ³ to 10 ² Torr by the pressure controller. While feeding the film substrate 10 at a conveying speed of 0.5 to 2 m / min, a DC or high frequency voltage is applied to the cathode 7 to start Ag film formation. The temperature of the film substrate 10 during film formation is constantly monitored by the infrared thermometer 12, and the temperature is controlled to be constant by feeding back the measured temperature to the discharge power source. Note that this apparatus can also perform film formation by normal constant power control or constant current control by mode switching. In FIG. 4, lines 41 and 42 show the relationship between the film formation time and the substrate temperature in the case of constant temperature control with feedback and normal constant power control. In both cases, the temperature rises rapidly due to radiation from the discharge at the beginning of discharge. As for the temperature change thereafter, in the case of the constant power control of the line 42, the temperature gradually continues to rise. It is considered that this is because the wall surface of the sputtering chamber and the anode were slowly heated by the discharge, and the film was heated by the secondary radiation. In the film formed by this method, the texture shape changed with time, and significant heat shrinkage was observed in the film immediately before the film formation was completed. On the other hand, when the temperature was controlled, the texture shape did not change with time, and heat shrinkage of the film was not observed. In this embodiment, since the discharge power changes with time, there is a problem that the film thickness also changes with time. In order to minimize this phenomenon, the wall surface of the sputtering chamber 2 and the anode 8 were water-cooled. In FIG. 5, lines 51 and 52 show the relationship between the film formation time and the Ag film thickness with and without water cooling. From this result, it was found that the water cooling suppresses the temperature rise inside the sputtering chamber and improves the stability of the film thickness.

FIG. 6 shows a sputtering method according to another embodiment of the present invention. This apparatus has two sputtering chambers 21, 2
2 The substrate 10 is passed between two temperature adjusting rolls 13 upstream of the sputtering chamber 22, where cooling and heating can be performed. The temperature of the temperature adjusting roll 13 is adjusted by a fluid medium such as water, oil or air. According to this apparatus, the sputtering chambers 21 and 2 are
In 2, it is possible to continuously form multilayer films having different film forming temperatures. Hereinafter, a case of forming an Al / Ag film with this apparatus will be described as an example. An Al film having an average film thickness of 100 nm and having a textured surface is formed in the sputtering chamber 21 by the above temperature control. The film forming temperature at that time is 300 ° C. Then, it is instantly cooled by the temperature control roll 13 and conveyed to the sputtering chamber 22. Here, an Ag film having a film thickness of 100 nm is formed at a film forming temperature of 200 ° C., and then wound on a winding roll 5.

[0011]

According to the present invention, the conventional sputtering apparatus is provided with a function of measuring the substrate surface temperature and a feedback function of the measured temperature, which is a relatively small apparatus. Sputter deposition with good temperature controllability is possible. By using this method for forming an electrode for a solar cell, a textured electrode having a very good shape can be stably formed. This enables stable production of low-cost and high-performance amorphous silicon solar cells.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of an apparatus used in a sputtering method according to an embodiment of the present invention.

FIG. 2 is a vertical sectional view of an example of a conventional roll-type sputtering apparatus.

FIG. 3 is a vertical sectional view of another example of a conventional roll-type sputtering apparatus.

FIG. 4 is a time-dependent diagram of substrate temperature in the case of constant temperature control according to the present invention and conventional constant power control

FIG. 5 is a diagram showing the change over time of the Ag film thickness with and without water cooling of the wall surface of the sputtering chamber and the anode.

FIG. 6 is a vertical sectional view of an apparatus used in a sputtering method according to another embodiment of the present invention.

[Explanation of symbols]

 1 Feed Chamber 2, 21, 22 Sputter Chamber 3 Winding Chamber 4 Feed Roll 5 Winding Roll 7 Cathode 8 Anode 9 Heater 10 Film Substrate 12 Infrared Thermometer 13 Temperature Control Roll

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H01L 31/04 H01L 31/04 M

Claims (6)

[Claims] 1. A sputtering method for forming a thin film of a target material on a surface of a substrate by causing discharge in the vicinity of a linearly stretched portion of a flexible substrate to be conveyed, and the substrate surface during thin film formation. The temperature is measured, and the substrate temperature is controlled based on the measured surface temperature. 2. The sputtering method according to claim 1, wherein the substrate temperature is controlled by the discharge power output. 3. The sputtering method according to claim 1, wherein the substrate temperature is controlled by passing the substrate between rolls whose temperature can be adjusted. 4. The sputtering method according to claim 1, wherein the temperature of the substrate surface is measured by an infrared thermometer without contacting the substrate. 5. The sputtering method according to claim 1, wherein the temperature of the surface of the substrate is measured by bringing a sheet-shaped thermocouple into contact therewith. 6. The sputtering method according to claim 1, wherein at least one of the wall surface of the sputtering chamber and the discharge electrode is water-cooled.