JP4074672B2 - Sputtering method - Google Patents

Description

[0001]
BACKGROUND 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.
[0002]
[Prior art]
Thin-film solar cells that use a polymer material film or stainless steel foil with a thickness of several tens to several hundreds of micrometers as a flexible substrate and that have a photoelectric conversion layer formed of an amorphous silicon thin film must have high mass productivity. Therefore, it is expected as a low-cost solar cell. In this type of solar cell, a highly reflective Ag or Al layer is usually formed on a substrate as an electrode layer in order to obtain high conversion efficiency. As a further efficiency enhancement technique, it is considered that texturing is performed, that is, unevenness with a height of about 0.05 to 0.5 μm is provided on the electrode layer surface to scatter light inside the solar cell. As a texturing method, as described in Japanese Patent Application No. 7-111141, Ag is formed at a high temperature at about 300 to 400 ° C. for aggregation, and as described in Japanese Patent Application No. 7-185315. An example is a method in which Al is formed at a high temperature at about 250 to 350 ° C. and aggregated to form Ag at about 200 ° C. In either case, the texturing has an optimum value of about 300 ° C., which leads to deterioration of the characteristics of the solar cell if the temperature is too low or too high. In particular, when a heat-resistant plastic film such as polyimide is used as a substrate, rapid thermal shrinkage occurs at about 300 ° C. or higher. Therefore, when a textured electrode is formed, a very high temperature of about ± 10 ° C. in a temperature region of about 300 ° C. Precise substrate temperature control is required.
[0003]
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 is composed of three parts: a feeding chamber 1, a sputtering chamber 2, and a winding chamber 3. A feeding roll 4 for unwinding the film is installed in the feeding chamber, a winding roll 5 is installed in the winding chamber, and a transport guide roll 6 is installed in both rooms. In the sputtering chamber 2, a heater 9 for heating the film, a cathode 7 and an annular anode 8 are installed. The cathode 7 includes a target material 71, a backing plate 72, and a magnet 73. Magnetron sputtering is performed by applying a direct current or high frequency voltage, and the cathode 7 is transported from the feed roll 4 to the take-up roll 5 on the film substrate 10. A film is formed. In the apparatus shown in FIG. 3, 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. Sputtering is performed by applying a voltage between the cathode 7 and the anode 8 facing the can roll 11.
[0004]
[Problems to be solved by the invention]
At the time of sputtering, the substrate is heated by the collision of the sputtered particles and ions with the substrate or radiation from the plasma itself. Since the film substrate has a very small heat capacity, when the apparatus of FIG. 2 is used, the temperature of the substrate 10 instantaneously 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. Usually, the backing plate 72 is provided with a cooling mechanism. However, when the film is formed on a film having a length of several hundred meters in a few hours by controlling the discharge power output to be constant, the effect of the secondary radiation described above. At the end of the film formation, the substrate temperature rises by about 50 to 100 ° C. compared to the time of the film formation start. For this reason, it has been difficult to perform precise temperature control of about ± 10 ° C. as described above.
[0005]
When the apparatus of FIG. 3 is used, since 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 is possible by adjusting the temperature of the can roll 11 itself. Become. However, the apparatus becomes large and the apparatus cost increases. Further, there are problems that maintenance such as replacement of the target 71 is difficult, and the substrate temperature is limited by one roll 11, so that a multilayer film cannot be formed at different film formation temperatures.
[0006]
An object of the present invention is to provide a sputtering method that solves the above-described problems and enables the formation of a metal electrode layer having a textured surface by precisely controlling the substrate temperature.
[0007]
[Means for Solving the Problems]
To achieve the above object, the present invention is flexible substrate being conveyed discharge is generated in the vicinity of a portion stretched in a straight line, data on the substrate surface - Do Ri surface from target material texture In a roll-to-roll sputtering method for forming a formed electrode layer, the substrate temperature at the time of electrode layer formation is measured, and the discharge power output is controlled based on the measured temperature so that the substrate temperature becomes constant The wall surface of the sputtering chamber and the discharge electrode are water cooled. As a result, even if the substrate temperature changes after the electrode layer formation is started, the substrate temperature can be kept within a narrow range following the change, and the film thickness on the substrate surface is changed with time based on the change in discharge power. It is prevented from changing. By passing the substrate between rolls whose temperature can be adjusted, the substrate temperature can be set to a predetermined value with a small time delay, and it is also possible to continuously form multilayer films with different deposition temperatures on the same substrate. It is.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
In carrying out the present invention, an infrared thermometer or a sheet-like thermocouple having a sufficiently small heat capacity is installed as a temperature measuring means in a conventional roll-to-roll type sputtering apparatus, and the measured temperature is applied to a discharge power supply output or a temperature control roll. It only has to have the function of footback. When multilayer films are continuously stacked on the same flexible substrate, different temperature control methods may be combined. Further, the temperature control type film formation and the normal power control type film formation according to the present invention can be combined.
[0009]
【Example】
Hereinafter, a sputtering method according to an embodiment of the present invention will be described with reference to a drawing in which the same reference numerals are attached to the same parts as those in FIG.
The sputtering apparatus shown in FIG. 1 is used for the sputtering method of one embodiment of the present invention, and is almost the same as the sputtering apparatus of FIG. 2, but a non-contact type infrared thermometer 12 is installed in the sputtering chamber 2. , Connected to a control device of a discharge power source (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 in the room is controlled to 10 ³ to 10 ² Torr by a pressure controller. Ag film formation is started by applying a direct current or high frequency voltage to the cathode 7 while feeding the film substrate 10 at a conveying speed of 0.5 to 2 m / min. 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. FIG. 4 shows 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 on lines 41 and 42. In both cases, the temperature rapidly increases due to radiation from the discharge at the beginning of the discharge. Looking at the temperature change thereafter, in the case of constant power control of the line 42, the temperature continues to rise gradually. This is presumably because the wall 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 thermal shrinkage was observed in the film immediately before completion of the film formation. On the other hand, when temperature control was performed, the texture shape did not change with time, and no heat shrinkage of the film was 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. FIG. 5 shows the relationship between the film formation time and the Ag film thickness when the water cooling is performed and when the water cooling is not performed. From this result, it was found that the temperature rise in the sputtering chamber was suppressed by water cooling, and the film thickness stability was improved.
[0010]
FIG. 6 shows a sputtering method according to another embodiment of the present invention. This apparatus has two sputtering chambers 21 and 22. The substrate 10 is passed between two temperature control 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, it is possible to continuously form multilayer films having different film forming temperatures in the sputtering chambers 21 and 22. Hereinafter, the case where an Al / Ag film is formed by this apparatus will be described as an example. By the above temperature control, an Al film having a textured surface with an average film thickness of 100 nm is formed in the sputtering chamber 21. The film forming temperature at that time is 300 ° C. Thereafter, it is instantaneously 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 around the winding roll 5.
[0011]
【The invention's effect】
According to the present invention, a conventional sputtering apparatus is a relatively small apparatus having a function of measuring a substrate surface temperature and a feedback function of the measurement temperature. On a flexible substrate, a roll-to-roll system has extremely good temperature controllability. Sputter deposition is possible. By using this method for forming an electrode for a solar cell, a texture electrode having a very good shape can be stably formed. This makes it possible to stably produce low-cost and high-performance amorphous silicon solar cells.
[Brief description of the drawings]
1 is a longitudinal sectional view of an apparatus used in a sputtering method according to an embodiment of the present invention. FIG. 2 is a longitudinal sectional view of an example of a conventional roll type sputtering apparatus. FIG. 3 is another example of a conventional roll type sputtering apparatus. FIG. 4 is a time-varying diagram of the substrate temperature in the case of constant temperature control according to the present invention and conventional constant power control. FIG. 5 shows the case where the wall and anode of the sputtering chamber are cooled with water and not cooled. FIG. 6 is a vertical cross-sectional view of an apparatus used in a sputtering method according to another embodiment of the present invention.
DESCRIPTION OF SYMBOLS 1 Feeding chamber 2, 21, 22 Sputtering chamber 3 Winding chamber 4 Feeding roll 5 Winding roll 7 Cathode 8 Anode 9 Heater 10 Film substrate 12 Infrared thermometer 13 Temperature control roll

Claims (2)

Flexible substrate being conveyed discharge is generated in the vicinity of a portion stretched in a straight line, the sputtering method of a roll-to-roll method for forming an electrode layer Do Ri surface is textured from the target material on the substrate surface In the above, the substrate temperature at the time of electrode layer formation was measured, the discharge power supply output was controlled so that the substrate temperature was constant based on the measured temperature, and the sputtering chamber wall surface and the discharge electrode were water cooled. A sputtering method characterized by the above.   2. The sputtering method according to claim 1, wherein the flexible substrate is passed through a temperature-adjustable roll provided between two sputtering chambers to cool and heat the flexible substrate.

Images