JP2012238637A - Sputtering method and sputtering apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sputtering method and a sputtering apparatus capable of rapidly depositing a high quality silicon thin film having a low oxygen content by using a powder target.SOLUTION: A high melting point metal filament 14 disposed in a vicinity of a target material 8 is heated in a prestage of sputter film deposition, so as to decompose gas introduced in a vacuum chamber 1 to form an active species. By performing reduction of an oxide film of a surface of the target material 8 and removing deposition film attached to a wall and a member of the vacuum chamber with the active species, oxygen amount during sputter film depositing is reduced and the high quality silicon thin film is formed.

Description

  The present invention relates to the formation of a thin film of a silicon-based material, and more particularly to a thin film formation method for forming an electronic element on a semiconductor substrate or a glass substrate used for a semiconductor device or a solar cell, a liquid crystal panel, a solar cell, or the like. The present invention relates to a sputtering method and a sputtering apparatus for forming a semiconductor thin film on a substrate to be used.

  Silicon-based thin films are widely used for thin film transistors (TFTs) such as switching elements constituting pixel circuits of liquid crystal display devices and organic EL display devices, or circuit elements for liquid crystal drive drivers, solar cells, and the like. Yes.

  Among them, the thin-film silicon solar cell is expected as a low-cost solar cell for large-scale power generation in the future because it uses an extremely small amount of material compared to a crystalline silicon solar cell. Currently, amorphous silicon solar cells are in practical use among thin-film silicon solar cells. Amorphous silicon has the advantage that low wavelength sensitivity is high and the thickness of the power generation layer is about 300 nm, but there is a problem that power generation efficiency is poor. Therefore, in order to further improve the power generation efficiency, a tandem solar cell (amorphous silicon / microcrystal silicon laminated structure) in combination with microcrystal silicon (microcrystalline silicon) with higher long wavelength sensitivity has been developed. However, the power generation layer of microcrystal silicon requires a film thickness of about 2 to 3 μm, and high-speed deposition of silicon is strongly desired from the viewpoint of production tact and production cost reduction.

As a method for forming a silicon-based thin film used for a thin-film silicon solar cell, a plasma chemical vapor deposition (CVD) method is generally used. Introducing a source gas such as SIH ₄ , Si ₂ H ₆ , SiF ₄ and a dilution gas such as H ₂ or Ar into the vacuum chamber, and applying high frequency power to the electrodes, generates plasma, and the source gas And a hydrogenated amorphous silicon film, a microcrystalline silicon film, a polysilicon film, or the like is formed on a desired substrate. Used because a p-type or n-type silicon film can be easily obtained by mixing a doping gas during film formation, and a high-quality silicon thin film with few film defects can be obtained by containing a large amount of hydrogen in the silicon film. Has been.

As other silicon-based thin film formation methods, no harmful and dangerous source gases such as SiH ₄ , Si ₂ H ₆ and SiF ₄ have been used in recent years. Also, a sputtering method capable of forming a large area on a plastic substrate or the like at a low temperature has been reviewed. (For example, refer nonpatent literature 1).

  In order to improve the film formation speed and productivity of sputtering, a sputtering method and apparatus using a powder material as a target are known. (See Patent Document 1).

  FIG. 6 shows a schematic configuration of a conventional sputtering apparatus described in Patent Document 1.

  In the figure, a vacuum chamber 1 is provided with a cathode 2 and a substrate mounting table 4 that holds the substrate 3 facing the cathode 2. The cathode part 2 is provided with a heat insulating plate 5 on a water-cooling jacket at the bottom and a heater 6 as a heating means on the heat insulating plate 5. The heater 6 is provided with a thermocouple 7 for temperature control. A tray 9 on which a powdery target material 8 can be placed is disposed above the heater 6. As the target material 8, magnesium oxide (MgO) powder (20 nm to 70 μm) was used. An earth shield 10 is installed around the target material 8, and a magnetron discharge magnet 11 is installed on the back side of the target material 8.

  In such a configuration, Ar gas is introduced into the vacuum chamber 1, the inside of the vacuum chamber 1 is adjusted to a constant pressure, and high frequency power is applied to the target material 8 from the high frequency power source 12 through the matching box 13. Generate plasma. When the plasma was generated, the surface temperature of the target material 8 rapidly increased, and when the surface temperature of the target material 8 was stabilized, a shutter (not shown) on the tray 9 was opened and film formation was started. Thus, when a powder target is used, the film-forming speed | velocity of about 4 to 5 times is obtained compared with the sputtering method using a sintered target.

  In addition, a sputtering method has been proposed in which H radicals (active species) are introduced into a vacuum chamber during sputtering film formation to form a polysilicon thin film. (For example, refer nonpatent literature 2).

FIG. 7 shows a schematic configuration of a conventional sputtering apparatus described in Non-Patent Document 2. A substrate 73 is placed in the vacuum chamber 1 so as to face the silicon target 78. Sputtering is performed by introducing Ar and H ₂ gas into the vacuum chamber 1 and applying high frequency power to the silicon target 78 from the high frequency power source 12 through the matching box 13. An inductively coupled plasma (ICP) generator 20 is newly provided in the side surface direction of the substrate 3 to supply H radicals (active species) from the plasma during sputtering film formation.

  Thereby, it is said that a highly crystalline silicon thin film can be obtained.

JP 2005-29859 A

Tadashi Sasakawa, “Si film by sputtering and high-performance polycrystalline Si thin film transistor”, IEICE technical report. SDM, silicon materials and devices 110 (15), 23-28, 2010 K. Fukaya et al. , “Enhancement of Crystal Growth in Si Thin-Film Deposition by H-Radical-Assisted Magnetron Sputtering”, Japan Journal of Applied Phys.

  However, in the sputtering method described in Patent Document 1, since a powder target material is used, the surface area of the target material is large, and the ratio of the oxide film on the surface of a natural oxide film is high. There was a problem of mixing. In addition, a long pre-sputtering (oxide film removal) step is required as a pre-sputtering step, resulting in a problem that the material use efficiency is extremely deteriorated.

  In other words, there was no problem as a sputtering method for oxides containing oxygen (for example, magnesium oxide), but as a sputtering method for forming a high-quality silicon thin film with a low oxygen content used in solar cells and thin film TFTs. Was unsuitable.

  Further, in the sputtering method described in Non-Patent Document 2, an expensive inductively coupled plasma apparatus is attached, and generation of H radicals (active species) is performed in one place, so that uniform processing over a large area is not possible. It was difficult to apply to a sputtering apparatus using a large substrate.

  The present invention has been made in view of the above-described problems, and provides a sputtering apparatus and method capable of forming a high-quality silicon thin film with a low oxygen content at high speed using a powder target. It is an object.

  In the sputtering method of the present invention, as a step before performing the sputter film formation, active species are generated by decomposing a gas by a heating means, and removal of impurities on the surface of the target material by chemical etching with the active species and It has the process of reducing the oxide film on the surface of the target material.

  With such a structure, impurities on the surface of the target material can be removed and the oxide film on the surface of the target material can be reduced, so that a film with a low oxygen content can be formed. Further, the target material is also heated by the radiant heat generated by the heating means for decomposing the gas, and the target material surface can be reduced efficiently. Also, unlike the pre-sputtering process, an oxide film is not sputtered, so that a film containing oxygen is not deposited on the vacuum chamber wall or vacuum member, and oxygen is not released from the deposited film during the sputtering film formation. Therefore, a sputtered film can be formed with a small amount of oxygen. Furthermore, since the target material is not sputtered, the material usage efficiency can be increased.

  Preferably, the target material is a material that does not contain oxygen, such as silicon.

  With such a structure, a silicon thin film used in a semiconductor device, a solar cell, a liquid crystal panel, or the like can be formed.

  Preferably, silicon powder or small pieces, chips or wafers are used as the target material.

  With such a configuration, it is possible to perform sputtering at high speed, so that improvement in productivity can be expected.

  Preferably, the gas is a gas containing hydrogen.

  With such a configuration, the quality of the silicon thin film can be improved.

  In the sputtering method of the present invention, as a pre-stage for performing sputtering film formation, active species are generated by decomposing gas with a heating means, and the deposited film on the surface of the vacuum chamber wall is removed by chemical etching with the active species. And a step of reducing the oxide film on the surface of the deposited film.

  With such a configuration, the film deposited on the vacuum chamber wall and other members can be removed and the oxide film on the surface thereof can be reduced, so that oxygen is not released from the deposited film during the sputtering film formation, so that the amount of oxygen is low. A sputtered film can be formed. Further, the vacuum chamber wall and other members are also heated by the radiant heat generated by heating for decomposing the gas, so that the deposited film can be removed and the oxide film on the deposited film surface can be efficiently reduced.

  Preferably, the gas is a gas containing hydrogen.

  With such a configuration, the quality of the silicon thin film can be improved.

  In the sputtering method of the present invention, during sputtering film formation, a gas is decomposed by a heating means to generate active species, and the sputtering rate of the target is improved by the chemical etching effect, and the active species are formed in the film formed by sputtering. It is characterized by having it taken in.

  With such a configuration, it is possible to perform sputtering at high speed due to the chemical etching effect by the active species, and it is possible to form a high-quality film. In addition, the target material is also heated by the radiant heat generated by heating for decomposing the gas, and film formation at a higher speed becomes possible.

  Preferably, the target material is a material that does not contain oxygen, such as silicon.

  With such a structure, a silicon thin film used in a semiconductor device, a solar cell, a liquid crystal panel, or the like can be formed.

  Preferably, silicon powder or small pieces, chips or wafers are used as the target material.

  With such a configuration, it is possible to perform sputtering at high speed, so that improvement in productivity can be expected.

  Preferably, the gas is a gas containing hydrogen.

  With such a configuration, the quality of the silicon thin film can be improved.

The sputtering apparatus of the present invention has a vacuum chamber, a gas inlet for supplying gas into the chamber, a target, and a substrate mounting table for holding a substrate placed opposite to the target, A sputtering apparatus for forming a thin film of the target material on a substrate,
A refractory metal filament is provided in the vicinity of the sputtering target,
It has a mechanism capable of heating the refractory metal filament.

  With such a structure, by heating the refractory metal filament in the pre-sputtering film formation stage, removal of impurities on the surface of the target material and reduction of the oxide film on the surface of the target material reduce the oxygen content. Can be formed. Further, since the film deposited on the vacuum chamber wall and other members and the oxide film on the surface thereof can be removed, oxygen is not released from the deposited film during the sputtering film formation, so that the sputtered film is formed in a state where oxygen is low. be able to. Further, by heating the refractory metal filament during sputtering film formation, sputtering can be performed at high speed, and a high-quality film can be formed.

  Preferably, the refractory metal filament is installed between the target and the chamber wall so as to surround the target.

  With such a configuration, it is possible to remove the film deposited on the vacuum chamber wall and other members and the oxide film on the surface thereof, so that oxygen is not released from the deposited film during the sputtering film formation. A film can be formed.

  Preferably, the refractory metal filament may be installed between the target and the substrate mounting table.

  With such a configuration, the impurity of the target material and the oxide film on the surface of the target material can be more effectively removed.

  Preferably, there may be provided a moving mechanism that is installed between the sputtering target and the substrate mounting table and is movable other than between the sputtering target and the substrate mounting table.

  With such a configuration, it is possible to reduce contamination from the refractory metal filament during sputter deposition.

  ADVANTAGE OF THE INVENTION According to this invention, the sputtering method and sputtering apparatus which can form a high quality silicon thin film with little oxygen content rate at high speed using a powder target are realizable.

Sectional drawing which shows the structure of the sputtering device in Embodiment 1 of this invention The top view which shows the structure of the sputtering device in Embodiment 1 of this invention Sectional drawing which shows the structure of the sputtering device in Embodiment 2 of this invention Sectional drawing which shows the structure of the sputtering device in Embodiment 3 of this invention The top view which shows the structure of the sputtering device in Embodiment 3 of this invention. Sectional drawing which shows the structure of the sputtering device in patent document 1 Sectional drawing which shows the structure of the sputtering device in a nonpatent literature 2.

  Hereinafter, a sputtering apparatus according to an embodiment of the present invention will be described with reference to the drawings.

(Embodiment 1)
Hereinafter, Embodiment 1 of the present invention will be described with reference to FIG. 1 and FIG.

  1 and 2 show a configuration of a sputtering apparatus according to Embodiment 1 of the present invention. FIG. 1 is a schematic cross-sectional view, and FIG. 2 is a schematic view seen from above.

  In FIG. 1, in the vacuum chamber 1, a cathode unit 2 and a substrate mounting table 4 that holds the substrate 3 facing the cathode unit 2 are installed. The cathode 2 is provided with a heat insulating plate 5 on a water-cooling jacket at the bottom, and a heater 6 for heating the target material 8 thereon. The heater 6 is provided with a thermocouple 7 for temperature control. A tray 9 on which a powdery target material 8 can be placed is disposed above the heater 6. Silicon powder (about 1 μm) was used as the target material 8.

  This time, a silicon powder material is used, but a silicon material such as a silicon sintered target, a silicon wafer, a silicon chip, or a silicon piece may be used. The silicon material may be a silicon material doped with a small amount of impurities such as boron (B), aluminum (Al), phosphorus (P), arsenic (As), or a silicon material not doped with impurities. Thereby, p-type, n-type silicon, i-layer silicon thin film, etc. used for solar cells and the like can be formed.

  An earth shield 10 is installed around the target material 8, and a magnetron discharge magnet 11 is installed on the back side of the target material 8. A refractory metal filament 14 (tungsten) was placed in the vicinity of the target material 8 so as to surround the target material 8.

  This time, tungsten (W) was used for the refractory metal filament 14, but platinum (Pt), palladium (Pd), molybdenum (Mo), titanium (Ti), niobium (Nb), tantalum (Ta), cobalt (Co), nickel (Ni), chromium (Cr) or an alloy thereof may be used.

  A DC power source 15 is attached to the refractory metal filament 14, and the temperature of the refractory metal filament 14 can be adjusted to about 1500 to 2200 ° C. by the current of the DC power source 15.

Ar and H ₂ gas were introduced into the vacuum chamber 1 through a mass flow meter (0 to 200 sccm each), and the inside of the chamber was regulated to a constant pressure (0.1 to 100 Pa). Thereafter, the refractory metal filament 14 is heated to about 2000 ° C., and H ₂ gas collides with the heated refractory metal filament 14 to be decomposed to generate H radicals (active species). By using this H radical, impurities on the surface of the target material 8 can be removed and the oxide film on the surface of the target material 8 can be reduced. Further, since the refractory metal filament 14 is heated to about 2000 ° C., the target material 8 is also heated by the radiant heat, and the surface of the target material 8 can be efficiently reduced. Further, it is possible to efficiently remove the film deposited on the vacuum chamber wall and other members and reduce the oxide film on the surface thereof.

  When the increase in the surface temperature of the target material 8 and the decrease in signal intensity contributing to oxygen atoms and oxygen molecules in the vacuum chamber 1 by the quadrupole mass spectrometer (QMS) become stable, a high frequency power of 13.56 MHz is supplied as a high frequency power source. 12 is applied to the target material 8 through the matching box 13 to start sputtering of a silicon thin film on the substrate 3. As a result, the oxide film on the surface of the target material 8, the film deposited on the vacuum chamber wall and other members, and the oxide film on the surface can be removed, so that oxygen is not released from the deposited film during the sputtering film formation. A sputtered film can be formed with less oxygen.

Even during the sputtering film formation, the refractory metal filament 14 is heated to decompose the H ₂ gas in the vacuum chamber 1 to generate a lot of H radicals (active species). The quality can be improved and the crystallinity of the silicon film can be improved. In addition, the target material 8 is heated by the radiant heat from the refractory metal filament 14, and film formation at higher speed becomes possible.

In Patent Document 1, the surface oxide film of the powder target material is not suitable for forming a high-quality silicon thin film having a low oxygen content. In the present embodiment, however, the H.sub. _{Since the two} gases are decomposed to generate a large amount of H radicals, removal of impurities on the surface of the target material and reduction of the oxide film on the surface of the target material can form a film with a low oxygen content. In addition, the target material is also heated by the radiant heat generated by heating the refractory metal filament 14, and the surface of the target material can be reduced efficiently.

  Furthermore, since the film deposited on the vacuum chamber wall and other members and the oxide film on the surface thereof can be removed, oxygen is not released from the deposited film during the sputtering film formation, so the sputtered film is formed with a low oxygen content. be able to.

  In Non-Patent Document 2, an expensive inductively coupled plasma apparatus is attached, and generation of H radicals (active species) is one place, so uniform processing over a large area is difficult. In the form, an expensive apparatus is not required, and it is easy to form H radicals (active species) uniformly in a large area by the shape of the refractory metal filament 14.

  Unlike the general pre-sputtering process, the oxide film is not sputtered, so that no oxygen-containing film is deposited on the vacuum chamber wall or vacuum member, and the deposited film is removed, so that sputtering is in progress. In addition, since oxygen is not released from the deposited film, a sputtered film can be formed with a small amount of oxygen. Furthermore, since the target material is not sputtered, the material usage efficiency can be increased.

(Embodiment 2)
The second embodiment of the present invention will be described below with reference to FIG.

  FIG. 3 is a cross-sectional view of the sputtering apparatus according to the second embodiment of the present invention.

  In the second embodiment of the present invention, the difference from the first embodiment is the difference in the installation position of the refractory metal filament 14, and the other description is omitted.

  The refractory metal filament 14 is disposed between the target material 8 and the substrate 3 above the target material 8. Thereby, since the place where H radicals (active species) are generated is close to the target material, it is possible to more effectively remove impurities on the surface of the target material and reduce the oxide film on the surface of the target material. In addition, since the distance between the refractory metal filament 14 and the target material 8 can be set close, the radiant heat from the refractory metal filament 14 also increases, removing impurities on the surface of the target material and reducing the oxide film on the target material surface. Can be done effectively.

  During sputter deposition, the refractory metal filament 14 may be moved to a location other than between the target material 8 and the substrate 3. As a result, contamination due to the material of the refractory metal filament 14 can be reduced during the sputtering film formation, so that a higher quality silicon thin film can be formed.

(Embodiment 3)
Hereinafter, Embodiment 3 of the present invention will be described with reference to FIG. 4 and FIG.

  4 and 5 show the configuration of the sputtering apparatus according to Embodiment 3 of the present invention. FIG. 4 is a schematic cross-sectional view, and FIG. 5 is a schematic view seen from above.

  In the third embodiment of the present invention, the difference from the first embodiment is a large apparatus when a large substrate used for a solar cell, a liquid crystal panel, or the like is used.

  As shown in FIGS. 4 and 5, the large substrate 3 in the large vacuum chamber is formed with a silicon thin film when passing over the upper surface of the cathode portion 2 while moving from the left side to the right side of the drawing. The Thereby, a silicon thin film can be uniformly formed in a large area at high speed without requiring an expensive apparatus.

  As described above, the present invention relates to a thin film formation of a silicon-based material, and in particular, a thin film formation method for forming an electronic element on a semiconductor substrate or a glass substrate used for a semiconductor device or a solar cell, a liquid crystal panel, The present invention is useful as a sputtering film forming apparatus and method for forming a semiconductor thin film on a substrate used in a solar cell or the like.

DESCRIPTION OF SYMBOLS 1 Vacuum chamber 2 Cathode part 3,73 Substrate 4 Substrate mounting base 5 Heat insulation plate 6 Heater 7 Thermocouple 8 Target material 9 Tray 10 Earth shield 11 Magnetron discharge magnet 12 High frequency power supply 13 Matching box 14 Refractory metal filament 15 DC power supply

Claims (14)

As a pre-stage for performing sputtering film formation, active species are generated by decomposing gas by a heating means, and impurities attached to the surface of the target material are removed by chemical etching with the active species and the oxide film on the surface of the target material is removed. Having a step of reducing,
Sputtering method characterized. The sputtering method according to claim 1, wherein the target material is a material that does not contain oxygen. The sputtering method according to claim 1, wherein the target material is one of silicon powder, small pieces, chips, and wafers. The sputtering method according to claim 1, wherein the gas is a gas containing hydrogen. As a pre-stage for performing the sputter film formation, active species are generated by decomposing the gas by a heating means, and the deposited film on the surface of the vacuum chamber wall is removed and the oxide film on the deposited film surface is chemically etched by the active species. Having a step of reducing
Sputtering method characterized. The sputtering method according to claim 5, wherein the gas is a gas containing hydrogen. During sputtering film formation, gas is decomposed by heating means to generate active species, the chemical etching effect improves the sputtering rate of the target, and the active species are incorporated into the film formed by sputtering,
Sputtering method characterized. The sputtering method according to claim 7, wherein the target material is a material that does not contain oxygen. The sputtering method according to claim 7, wherein the target material is one of silicon powder, small pieces, chips, and wafers. The sputtering method according to claim 5, wherein the gas is a gas containing hydrogen. A vacuum chamber; a gas inlet for supplying gas into the vacuum chamber; a target; and a substrate mounting table for holding a substrate placed opposite to the target. A sputtering apparatus for forming a thin film,
A refractory metal filament is provided in the vicinity of the target,
A sputtering apparatus having a mechanism capable of heating the refractory metal filament. The refractory metal filament is
The sputtering apparatus according to claim 11, wherein the sputtering apparatus is installed so as to surround the target between the target and the chamber wall. The refractory metal filament is
The sputtering apparatus of Claim 11 or 2 installed between the said target and the said substrate mounting base. The refractory metal filament is
Installed between the target and the substrate mounting table;
The sputtering apparatus according to claim 11, further comprising a movement mechanism that allows movement other than between the target and the substrate mounting table.

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