JPH1046326A - Method for forming thin film of calcopyrite type compound - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a thin film of a calcopyrite type compound on an inexpensive substrate at a comparatively low temp. and at a low cost. SOLUTION: In this method, the thin film of the calcopyrite type compound shown by formula: Cu(Inx Ga1-x )(SySe1-y )2 , (0<=X<=1, 0<=Y<=1) is formed on the substrate by a cluster ion beam method. In this case, the substrate 19 is placed in a hermetically sealed vacuum vessel 12 and individual materials constituting the thin film of the calcopyrite type compound are jetted in the hermetically sealed vacuum vessel 12 to form lumpy atomic groups and the Cu(Inx Ga1-x )(SySe1-y )2 film is formed on the substrate 19 by ionizing and accelerating the respective atomic groups. After start of the film-forming, at a time point when time within a range of 1/3 to 2/3 of whole period of the film-forming passes, vapor deposition rate of Cu based alloy is made relatively lower to that of InGa based alloy and, at the same time, the ionization current of the Cu based alloy is controlled so that the ionization current compared to ionization current of the InGa based alloy is changed from a relatively higher state to a lower state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a cluster ion beam.
Cu (In)_xGa_1-x) (S_ySe _1-y)
_TwoMethod for producing thin film of chalcopyrite type compound
You.

[0002]

2. Description of the Related Art For a chalcopyrite type compound which is promising as a material for an active layer of a future thin film solar cell, a material having a band gap close to 1.5 eV is desirable in order to realize high efficiency. As a material having a value close to the band gap _{Cu (In x Ga 1-x} ) (S y Se 1-y) 2 film (here, at 0 ≦ x ≦ 1, 0 ≦ y ≦ 1) can be expected.

Conventional techniques for forming a thin film of the chalcopyrite-type compound include a vapor deposition method and a precursor method.

[0004] In the vapor deposition method, each element (C
u, In, Ga, S, Se or a compound thereof) is simultaneously evaporated in a vacuum-sealed vessel to raise the substrate temperature to 500 ° C. or higher, thereby obtaining a single-phase, high-quality single-phase high-quality crystal having a grain size of 1 μm or more. A chalcopyrite type compound could be formed.

In the precursor method, the above-mentioned constituent elements are individually deposited on a substrate in order and then annealed at 500 ° C. or more in a steam atmosphere containing S or Se to obtain a chalcopyrite-type compound. did it.

[0006]

In the prior art described above, a high temperature of 500 ° C. or more is required to obtain a good crystal as a material for a thin-film solar cell. At this temperature, low-cost soda-lime glass cannot be used due to problems such as thermal deformation, and expensive glass must be used. Therefore, it becomes the most important obstacle to cost reduction as a solar cell.

The present invention provides a method for producing Cu (I) at a relatively low temperature and a low cost on an inexpensive substrate such as soda lime glass.
and to provide a _{n x Ga 1-x) (} S y Se 1-y) a method of forming a ₂ thin film.

[0008]

The method of forming a chalcopyrite-type compound thin film of the present invention is represented by Cu (In _x Ga _{1 -x} ) (S _y Se _{1 -y} ) ₂ by a cluster ion beam method. 0 ≦ x ≦ 1, 0 ≦ y ≦ 1) A method of forming a thin film of a chalcopyrite-type compound on a substrate, wherein the substrate is placed in a vacuum-sealed container, and the thin film of the chalcopyrite-type compound is removed. The constituent individual materials are sprayed in the closed container, and the supercooling effect of the adiabatic expansion in a vacuum forms a loosely bonded massive atomic group of atoms of the individual material, and the atomic groups are ionized respectively. By accelerating, the Cu (In _x Ga _{1 -x} ) (S _y
In the process of forming the Se _1-y ) ₂ film, the deposition rate of the Cu-based alloy is reduced after the start of the film formation and when a time in the range of ３ to ／ of the entire film formation period has elapsed. While lowering the deposition rate of the InGa-based alloy relatively,
Control is performed so that the ionization current of the u-based alloy is changed from a state relatively higher than that of the InGa-based alloy to a lower state.

In the step of evaporating the vapor deposition material constituting the thin film of the chalcopyrite type compound from individual vapor deposition sources and irradiating the substrate with a film to form a film, C
At the same time as changing the Cu-rich composition to the In-rich composition by lowering the deposition rate of the u-based alloy relative to the deposition rate of the InGa-based alloy, the ionization current of the Cu-based alloy is reduced with respect to the ionization current of the InGa-based alloy. Thus, by controlling the state from a relatively high state to a low state, a single-phase high-quality crystal having a large grain size can be formed at a low temperature.

[0010]

FIG. 1 shows a chalcopyrite type compound of the present invention, namely, Cu (In _x Ga _{1 -x} ) (S _y S
e _1−y ) ₂ film (where 0 ≦ x ≦ 1 and 0 ≦ y ≦ 1) cluster ion beam method (I
FIG. 3 is a diagram illustrating a schematic configuration of a film forming apparatus using a CB method.

This device is a vacuum device 11 including a vacuum pump.
And a hermetically sealable vacuum vessel 12 connected thereto. In the vacuum vessel 12, individual crucibles 13a, 13b, and 13c containing vapor deposition materials constituting a thin film are arranged. In this embodiment, in order to form a CuIn (SSe) ₂ layer, Cu crucible 13a is, Se and 13b is, an In ₂ S ₃ is placed in more 13c.

Here, the principle of film formation by the ICB method will be described.
It will be explained briefly. First, film raw materials (Cu, In, Se)
) Are placed in individual closed crucibles and placed in this crucible.
The raw material vapor is injected into the high vacuum
Let The injected raw material vapor is used for adiabatic expansion in high vacuum.
5 × 10 due to supercooling phenomenon (action)^Two~ 2 × 10 ^Three
Lumped atomic cluster (cluster) in which about atoms are loosely bonded
To form Ionizing and accelerating this cluster
For example, CuIn (SSe)_TwoFilm formed
Is done.

At the time of the film formation, the ionized cluster is broken into individual atoms upon collision with the substrate, and the incident energy is converted into diffusion energy for the atoms to migrate on the substrate surface. . At this time, the amount of ionization can be controlled by the ionization current, and the incident energy can be controlled by the acceleration voltage.

With such a migration effect,
Cu (In_xGa_1-x) (S_ySe _1-y)_TwoCarcopa
A mixed crystal of an illite type compound is obtained. Heat energy
Uses kinetic energy due to ionization instead of
Therefore, no large heat energy is required. For this reason
In addition, as a film forming condition, a low temperature of 200 to 400 ° C. or less
Relatively good crystals can be obtained.

The crucibles 13a, 13 in the vacuum vessel 12
Above the b and 13c, the ionization electron emitters 14a, 14b and 14c, the ionization electron extraction grids 15a, 15b and 15c, and the accelerating electrodes 16a and 1c, respectively.
6b and 16c are provided. Above these crucibles 13a, 13b and 13c, a film thickness sensor 17 made of a quartz crystal plate is arranged, and further above that, a substrate 19 rotated by a motor 18 is arranged. Is to be heated.
An openable and closable shutter 21 is disposed below the substrate 19, and the evaporation can be controlled by opening and closing the shutter 21.

Next, using the above ICB apparatus, CuIn
An experimental result of forming the (SSe) ₂ film will be described.
Cu in crucible 13a, Se in 13b, and 13c
Is filled with In ₂ S ₃ . The substrate 19 is soda-lime glass having Mo coated on the surface. The substrate temperature was changed between 200 and 400 ° C. under different conditions. A negative bias was applied to the acceleration electrodes 16a, 16b, 16c to accelerate the ionized cluster.

During this film forming step, the deposition rate of the Cu-based alloy is made relatively lower than the deposition rate of the InGa-based alloy (the deposition rate of the Cu-based alloy is reduced or the deposition rate of the InGa-based alloy is reduced). Is raised.)
And at the same time changed from Cu-rich composition in the In-rich composition, a relatively high state ionization current I _CU of Cu-based alloy with respect to the ionization current I _IN of InGa alloy (I _CU> I
_IN )) to a lower state (I _CU <I _IN ). Thus, the vapor deposition rate and the ionization current are controlled in synchronization. Switching of deposition rate and ionization current
After the start of vapor deposition, it is performed at a time when 1/3 to 2/3 of the total vapor deposition time has elapsed.

In an actual experiment, the total deposition time was set to 120
Min, the deposition rate of Cu is 2 ° / s, the ionization current I _CU = 150 mA, and the deposition rate of In is 2 ° / s.
To start vapor deposition at an ionization current I _IN = 50 mA, and when 40 to 80 minutes have passed since the start of vapor deposition, the deposition rate of Cu was 2 ° / s, the ionization current I _CU = 50 mA, and the vapor deposition rate of In was 4 ° / s. Then, a CuIn (SSe) ₂ film was formed at an ionization current I _IN = 200 mA. The temperature of the crucible 13a of Cu was constant at 1360 ° C. before and after the change of the deposition rate, and the temperature of the crucible 13c of In ₂ S ₃ was 740 ° C. before the change of the deposition rate and 770 ° C. after the change. Thereafter, excess CuSSe-based compounds generated on the surface were removed using KCN. As a result, a single-phase chalcopyrite-type compound having a crystal grain size of 1 μm or more was obtained.

FIG. 2A shows an SEM image (scanning electron microscope image) of the crystal surface of a chalcopyrite-type compound formed by a conventional vapor deposition method for comparison.
(B) shows an SEM image of the CuIn (SSe) ₂ film manufactured according to the example of the present invention using the ICB method. With the conventional vapor deposition method shown in FIG. 2A, only a film having a particle size of 0.5 μm or less was obtained.

FIG. 3 shows a CuIn (SSe) ₂ film obtained by conducting experiments at a substrate temperature of 200 ° C. (FIG. 2A) and 350 ° C. (FIG. 2B) by the ICB method of the above embodiment. S
3 shows an EM image. From this photograph, it can be seen that when the substrate temperature is 200 ° C., the crystallinity is worse than when the substrate temperature is 350 ° C. CuIn (S
Se) From the SEM image of the _two films, set the substrate temperature at the time of vapor deposition to 200 ° C.
It has been found that it is preferable to make the height higher than the above.

In order to use inexpensive soda glass or the like as the substrate, the substrate temperature is preferably set to 400 ° C. or less.

FIG. 4 shows the measurement results of the X-ray diffraction spectrum (112) of the CuIn (SSe) ₂ film produced by changing the substrate temperature by the method of the embodiment. From this result, it was confirmed that the peak corresponding to (112) was weakened when the substrate temperature was 200 ° C.

In the above embodiment, C before the deposition rate is changed
u: In_TwoS_ThreeOf 1: 1, and the changed Cu:
In_TwoS_ThreeThe deposition rate was 1: 2, but the deposition rate was
In after change_TwoS_ThreeDeposition rate of Cu with respect to deposition rate of
Rate is lower than before changing the deposition rate
What should I do? Cu: In before changing the deposition rate_TwoS
_ThreeThe preferred range of the evaporation rate is 1: (1-2) evaporation rate.
After the change, it is 1: (2-3).

In the embodiment, the case of forming a CuIn (SSe) ₂ film has been described as an example.
chalcopyrite-type mixed crystal represented by u (In _x Ga _1-x ) (S _y Se _1-y ) ₂ (where 0 ≦ x ≦ 1, 0 ≦ y
Needless to say, the present invention can be applied to the case of producing a thin film of ≦ 1) and the same effect can be obtained. In that case, the raw materials and the number of the crucibles, the ionization current and the deposition rate will be appropriately selected according to the crystal to be formed.

The materials and numerical values in the above description are merely examples, and the present invention is not limited to the described embodiments. Various modifications and changes can be made by those skilled in the art based on the above disclosure. Needless to say.

[0026]

According to the present invention, the deposition rate of the Cu-based alloy is made relatively lower than the deposition rate of the InGa-based alloy during the film forming process by the ICB method, so that the Cu-rich composition can be changed to the In-based alloy.
At the same time as changing to a rich composition, a single phase having a large grain size is controlled by changing the ionization current of the Cu-based alloy from a state relatively higher than that of the InGa-based alloy to a lower state. Can be formed at a low temperature.

Therefore, inexpensive soda lime glass can be used for the substrate, and when the thin film of the present invention is used for a solar cell or the like, a highly efficient and inexpensive solar cell can be manufactured.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a cluster ion beam apparatus used in a film forming method of the present invention.

FIG. 2 shows SEM images of the surface of a film produced by a conventional vapor deposition method and the surface of a film produced by the method of the present invention.

FIG. 3 shows the SE of the film surface when the substrate temperature during film formation is changed.
An M image is shown.

FIG. 4 shows CuIn (SSe) ₂ for a change in substrate temperature.
It is an X-ray diffraction spectrum (112) pattern of a film.

[Explanation of symbols]

11 vacuum device 12 closed container 13a, 13b, 13c crucible 14a, 14b, 14c electron emitter 15a, 15b, 15c electron for ionization Drawing grit 16a, 16b, 16c Accelerating electrode 17 Film thickness sensor 18 Motor 19 Substrate 20 Heating Lamp

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor, Nakamura Satoru 6-12-27, Shimoda-cho, Kohoku-ku, Yokohama, Kanagawa Prefecture (72) Inventor, Katsuaki Sato 1087-169, Kami-Aso, Aso-ku, Kawasaki, Kanagawa Prefecture

Claims (2)

[Claims] 1. The method according to claim 1, wherein Cu (I) is formed by a cluster ion beam method.
_nx Ga _1-x ) (S _y Se _1-y ) ₂ (0 ≦ x
≦ 1, 0 ≦ y ≦ 1) A method of forming a thin film of a chalcopyrite-type compound on a substrate, wherein the substrate is placed in a vacuum-sealed container to form an individual thin film of the chalcopyrite-type compound. Is sprayed in the closed container, and a supercooling effect due to adiabatic expansion in a vacuum forms a massive atomic group in which atoms of the individual materials are loosely bonded, and ionizes and accelerates each atomic group. In the step of forming the Cu (In _x Ga _1-x ) (S _y Se _1-y ) ₂ film on the substrate by When the time in the range of 3 has passed,
The deposition rate of the Cu-based alloy is made relatively lower than the deposition rate of the InGa-based alloy, and at the same time, the ionization current of the Cu-based alloy is relatively lower than that of the InGa-based alloy. A method for forming a chalcopyrite-type compound thin film that is controlled to change to a state. 2. The method for forming a chalcopyrite-type compound thin film according to claim 1, wherein in the step of forming the film, the temperature of the substrate is controlled to be 400 ° C. or lower and higher than 200 ° C.