JP6044942B2 - Method for producing compound semiconductor film using supercritical fluid - Google Patents

Description

  The present invention relates to a method for manufacturing a compound semiconductor film using a supercritical fluid.

  Supercritical fluid (hereinafter referred to as SCF) has been researched and developed as an environmentally conscious solvent capable of continuously adjusting properties such as density, viscosity and dielectric constant by temperature and pressure. One of the features of supercritical fluid as a reaction solvent is that it can achieve both high density and high solubility comparable to liquid and high diffusion coefficient. Applied to the industrial field.

  Among supercritical fluids, non-associative fluids (eg carbon dioxide, fluoroform, ethane) have the advantage of a mild critical temperature, but are less or less volatile without the addition of a cosolvent Has the disadvantage that its solubility is extremely low. On the other hand, supercritical water has high solubility, but it has a disadvantage that most chemical synthesis cannot be performed except for an oxidation reaction caused by acceleration of decomposition at a high temperature. Compared with them, alcohol has a relatively mild critical point, is non-destructive than supercritical water, and is more reactive than supercritical carbon dioxide. Therefore, supercritical alcohols are used in various selective reactions such as catalytic etherification of tertiary alcohols, synthesis of p-ethyltoluene by alkylation of toluene, non-catalytic and reductive hydrogen transfer reactions of aldehydes and ketones. ing. On the other hand, in the material process, it is well known that alcohols added to supercritical carbon dioxide promote the reduction of organometallic compounds in supercritical CVD, and in recent years, metal by reduction of metal nitride in supercritical alcohols. Synthesis of fine particles has been reported.

  For example, Non-Patent Documents 1 to 3 disclose a selenization process using organometallic Se. However, a high temperature exceeding 490 ° C. is indispensable for selenization of a Cu—In or Cu—In—Ga precursor metal film. Non-Patent Document 4 discloses a CIS fine particle synthesis technique using a supercritical fluid (however, in order to obtain a CIS film, it is necessary to add a selenization treatment at 500 ° C. as a post-treatment). Yes.

S. Chichibu, S. Shirakata, S. Isomura and H. Nakanishi. Jpn. J. Appl. Phys. 36 (1997), p. 1703 S.F. Chichibu, M. Sugiyama, M. Ohbasami, A. Hayakawa, T. Mizutani, H. Nakanishi, T. Negami and T. Wada. J. Cryst. Growth 243 (2002), p. 404. S. Ando, N. Takayama1, M. Sugiyama, H. Nakanishi, and S. F. Chichibu, Phys.Status Solidi C 6, No. 5, 1038-1042 (2009) P. Luo, P. Yu, R. Zuo, J. Jin, Y. Ding, J. Song, Y. Chen, Physica B 405 (2010) 3294-3298

  A compound semiconductor film used for a solar cell is required to have a large-area, uniform, and low-cost production process with high productivity.

  In this example, a new process has been found that makes it possible to produce a large-area thin film of a compound semiconductor film at a low temperature by using a supercritical fluid as a reaction solvent and a reducing agent.

In order to solve the above problems, a method for producing a compound semiconductor film of the present invention includes:
A compound semiconductor film is manufactured by heat-treating a precursor metal film in a supercritical fluid containing an additive element source.

The method for producing the compound semiconductor film of the present invention comprises:
The supercritical fluid is characterized by being alcohol or water.

The method for producing the compound semiconductor film of the present invention comprises:
The heat treatment temperature is a critical temperature or higher and 490 ° C. or lower.

The method for producing the compound semiconductor film of the present invention comprises:
The additive element source is characterized by comprising at least one organic compound.

The method for producing the compound semiconductor film of the present invention comprises:
The additive element source is characterized by comprising at least one of organic selenium, organic sulfur, organic nitrogen, organic arsenic, and organic tellurium.

The method for producing the compound semiconductor film of the present invention comprises:
The compound semiconductor film is a CuInSe ₂ or CuInGaSe ₂ or CuInAlSe ₂ or CuGaAlSe ₂ or CuInS ₂ or CuInGaS ₂ or CuInAlS ₂ or CuGaAlS ₂ or CdS or CdSe or CdTe, or InN or GaN or InGaN, or InAs or GaAs or InGaAs It is a feature.

The method for producing the compound semiconductor film of the present invention comprises:
The precursor metal film is characterized by being CuIn, CuInGa, CuInAl, CuGaAl, Cd, In, Ga, InGa, or an oxide thereof.

  In the present application, the additive element source refers to an organic compound that is liquid at normal temperature and pressure, which is necessary for performing a desired chemical treatment on the precursor metal film. For example, organic selenium is used for selenizing a compound, organic sulfur is used for sulfurization, organic nitrogen is used for nitriding, organic arsenic is used for arsenic, and organic tellurium is used for tellurization. Selected as additive element source. These organic compounds can be combined and used as an additive element source depending on the desired chemical treatment.

  For example, methanol, ethanol, and propanol can be used as the alcohol used as the supercritical fluid, but the alcohol is not limited thereto.

Membrane treatment process An XRD pattern (ethanol density 0.55 g / cm ³ ) of a film obtained by selenizing a Cu, In precursor at a temperature of 200 to 300 ° C. and an untreated Cu, In precursor Composition of a film obtained by selenizing a Cu, In precursor at a temperature of 200 to 300 ° C. (ethanol density 0.55 g / cm ³ ) XRD patterns of Cu and In precursors and films obtained by subjecting Cu and In precursors to selenization at an ethanol density of 0 to 0.55 g / cm ³ at 300 ° C.

  An embodiment for carrying out a method for producing a compound semiconductor film according to the present invention will be described below based on examples.

  A Cu, In precursor film was formed on a glass substrate by spin coating. A spin coating agent for indium oxide and copper oxide was prepared, and spin-coated on the substrate at 1000 rpm and 10 s after 1000 rpm and 5 s. After vacuum drying for 5 minutes, oxidation was performed at 520 ° C. in air to remove the carbon component. Thereafter, deoxygenation treatment was performed at 450 ° C. in a nitrogen + 10% hydrogen atmosphere. The above process was repeated 10 times to obtain a 2 μm film. When measured by EDX, the composition ratio of C / O / Cu / In of the precursor film is 0/20/40/40. This is because the precursor film is composed of metal and metal oxide. Is shown.

  All selenization processes were carried out in a batch type reaction vessel with an internal volume of 10 ml. A substrate is placed in the reaction vessel, and diethylselenium and ethanol are injected. In the liquid phase system in the standard state, since diethyl selenium forms a homogeneous phase with ethanol, it is considered that diethyl selenium and ethanol also form a homogeneous mixed phase in the supercritical state. The diethylselenium concentration was set to 50 mmol / l in the container. The sealed container was heated to an arbitrary temperature in a dedicated furnace. The reaction container internal temperature reaches the set temperature within 10 minutes. Therefore, the reaction time was 60 minutes after the temperature was raised for 10 minutes. The reaction was stopped by immersing the heated reaction vessel in a water bath. The treated membrane was repeatedly washed with ethanol and dried at 70 ° C. The crystallinity of the obtained film was evaluated by XRD θ-2θ measurement using Cu—Kα rays. The film composition was determined by SEM and EDX.

The XRD pattern of the film treated at 200 to 300 ° C. is shown in FIG. It is shown in 2. The density of ethanol was fixed at 0.55 g / cm ³ (twice the critical density). In the XRD pattern of the untreated precursor film, a diffraction peak derived from a Cu—In alloy or In is observed. Moreover, the film only impregnated in ethanol containing diethylselenium at room temperature showed the same XRD pattern as the precursor film.

The film treated at 200 ° C., which is lower than the critical temperature, shows the same XRD pattern as the precursor film, but the film treated at 250 ° C. exhibited a diffraction pattern seen in the chalcopyrite structure of CuInSe ₂ . Furthermore, in the film treated at 300 ° C., the peaks derived from the Cu and In precursors disappear and correspond to the (112), (204) / (220), (116) / (312) orientations of CuInSe _2. Only the peak was obtained.

Next, the composition change of the film treated at 200 to 300 ° C. measured by EDX is shown in FIG. 3 shows. It can be seen that the selenium content in the film increases as the processing temperature increases up to 300 ° C. This result suggests that the conversion reaction from the Cu, In precursor to CuInSe ₂ is promoted as the processing temperature increases. This trend is consistent with the results of the XRD analysis. Based on the above, when using diethylselenium in the previous studies, the selenization process, which required a high temperature of 490 ° C or higher, was achieved by using supercritical ethanol. Successfully achieved at a low temperature of 300 ° C.

  Furthermore, it has been found that the oxygen content in the precursor film decreases as the processing temperature increases up to 300 ° C. This fact suggests that the deoxygenation reaction proceeds at the same time as the selenization process, and we believe that the reduction ability provided by the use of supercritical fluid removes oxygen-containing components simultaneously with the decrease in selenization temperature. I think it worked effectively.

In order to clarify the contribution of supercritical ethanol to the selenization process, experiments were performed with varying ethanol density. FIG. 4 shows a film XRD pattern processed at 300 ° C. by changing the ethanol density from 0 to 0.55 g / cm ³ . Under conditions not containing ethanol, diffraction patterns were observed at 22.5-24 ° and 28.5-30 ° in addition to the diffraction pattern derived from the precursor film and the chalcopyrite structure of CuInSe ₂ . The (100) and (011) peaks of selenium are known to appear at 23.4 ° 29.6 ° and are similar to the observed peaks. On the other hand, as compared with other crystal phases, these peaks show a low crystallinity or a broadening as seen in an amorphous phase. In SEM observation, it was observed that the surface was covered with a smooth film, and EDX analysis revealed that the main component (about 80%) was Se. From these facts, we conclude that the formation of an amorphous phase of selenium proceeds in parallel with the selenization process under the condition that ethanol is not included. That is, it is considered that diethyl selenium is decomposed into selenium at a high temperature, and a part of the selenium is deposited on the surface without being involved in the conversion reaction of the Cu, In precursor film.

  On the other hand, under the condition containing ethanol, no pattern resulting from the amorphous phase of selenium was observed in the XRD pattern. From this result, we have concluded that supercritical ethanol plays an essential role in this selenization process. In the selenization process in this study, it is speculated that supercritical ethanol may suppress the formation of amorphous phase by dissolving selenium species not involved in selenization reaction.

Further, with the increase of ethanol density, Cu that is not selenide it is slightly observed in the XRD pattern of 0.5Ro _c, how the peak derived from In precursor is gradually lost seen. In general, in a supercritical fluid, the pressure, solubility, and cluster state increase or improve as the density increases. Currently, we are analyzing the effects of density changes on selenium activity in more detail.

  Although it is difficult to control the crystal size, several reports have been made on the direct synthesis of semiconductor nanoparticles using a supercritical fluid. However, there is almost no report on the conversion reaction from a precursor in a supercritical fluid for the purpose of semiconductor material synthesis. When using the conversion reaction, the crystal size should depend on the state of the precursor film. By combining the more controlled precursor film with the conversion reaction in the supercritical fluid proposed in this study, It is expected that it will be possible to develop low temperature processes with controlled crystal size. This conversion reaction should be applicable to sulfidation, nitridation, etc., and it is expected that this conversion reaction in supercritical fluid will contribute to the development of low temperature and low cost processes for compound semiconductors in the future.

  In this study, CIS semiconductor films were prepared by conversion reaction (selenation reaction) of Cu and In precursor films in supercritical fluid ethanol. By using this new process, we succeeded in reducing the selenization process temperature using organometallic selenium with low toxicity compared to the conventional selenization process by heat treatment in gas atmosphere. This result contributes to low-cost production of CIS / CIGS solar cells, and further contributes to the development of a low-cost, high-quality, large-area semiconductor film production process.

Claims (6)

A compound semiconductor film is manufactured by heat-treating a precursor metal film in a supercritical fluid including an additive element source composed of at least one organic compound, and converting the precursor metal film by the additive element source. A method of manufacturing a compound semiconductor film.   The method for producing a compound semiconductor film according to claim 1, wherein the supercritical fluid is alcohol or water.   The method for producing a compound semiconductor film according to claim 1 or 2, wherein the heat treatment temperature is not lower than a critical temperature and not higher than 490 ° C. Additional element source, manufacturing method of a compound semiconductor membrane according to any one of claims 1 to 3, wherein the organic selenium, organic sulfur, organic nitrogen, in that it consists of at least one organic arsenic and organic tellurium. The compound semiconductor film is a CuInSe ₂ or CuInGaSe ₂ or CuInAlSe ₂ or CuGaAlSe ₂ or CuInS ₂ or CuInGaS ₂ or CuInAlS ₂ or CuGaAlS ₂ or CdS or CdSe or CdTe, or InN or GaN or InGaN, or InAs or GaAs or InGaAs production method of a compound semiconductor membrane according to any one of claims 1 to 4, wherein. Precursor metal film, the production of CuIn or CuInGa or CuInAl or CuGaAl or Cd or In, or Ga or InGa, or a compound semiconductor film according to any one of claims 1 to 5, characterized in that an oxide thereof Method.

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