WO2003052159A1 - Amorphous ferrosilicide film exhibiting semiconductor characteristics and method for producing the same - Google Patents

Abstract

Perfect amorphous ferrosilicide exhibiting semiconductor characteristics close to those of β-FeSi2 is not yet obtained by cluster ion beam deposition method, molecular beam epitaxial growth method, ion implantation method, or RF magnetron sputtering method. An amorphous FeSi2 film exhibiting semiconductor characteristics is obtained by growing FeSi2 as a nongranular flat film, i.e. a continuous film, on a substrate of 400˚C or below by sputtering under Ar gas pressure of 5 mTorr or below using an FeSi2 alloy target having a component atom ratio between Fe and Si of 1:2. Facing target sputtering system is especially preferable as a sputtering system.

Description

 Description Amorphous iron silicide film showing semiconductor characteristics and fabrication method

 The present invention relates to an amorphous iron silicide film exhibiting semiconductor characteristics and a method for manufacturing the same. Background art

 | 3— F e S i2 is a direct-transition semiconductor with a band gap of 0.85 eV, and is expected to be applied to solar cells and light emitting and receiving devices for communication. The present inventor has previously developed a method for depositing a three-phase FeSi 2 thin film while being deposited on a substrate by a laser ablation method (Patent Document 1: Japanese Patent Application Laid-Open No. 2000-178713). ). Disclosure of the invention

A stable solid solution is formed when Si is in the range of 69 to 72.5 at%. It has been disclosed in Japanese Patent Publication No. 1133-1453 that the amorphous film of the FeSi 2 phase exhibits semiconductor characteristics. However, this amorphous film is manufactured by a cluster ion beam evaporation method in which Fe and Si are sprayed from separate hermetically sealed crucibles and vapor-deposited. The value of the degree σ is 11 Ω— ¹ cm— ¹ at 590 ° 、, and the band gap is 1.258 eV, which does not show characteristics close to 1 F e S i 2.

In order to obtain a good quality amorphous structure film, it is necessary to use It is necessary to allow the atomic particles to reach the substrate and quench them on a substrate that is not heated or cooled at a low temperature, such as cluster ion beam evaporation, molecular beam epitaxy, ion implantation, etc. The RF magnetron sputtering method, which is considered to be the most suitable for obtaining an amorphous structure film compared to other existing methods, also requires that the plasma be in contact with the film being deposited. However, the film is damaged, and microcrystals are formed due to the effect of annealing, so that it is difficult to obtain a completely amorphous film. Not obtained until.

 The inventor of the present invention has obtained a very good quality FeSi 2 in an amorphous state by depositing a flat film that is not granular, that is, a continuous film by using a sputtering method capable of depositing particles with high energy. It has been found that FeSi 2 in the state shows semiconductor characteristics close to 3 — FeSi 2.

 That is, the present invention is an amorphous iron silicide film exhibiting semiconductor characteristics comprising an amorphous FeSi 2 film having a band gap of 0.6 to 1.0 OeV obtained by a sputtering method.

 Furthermore, the present invention uses a FeSi 2 alloy target having a component atomic ratio of Fe to Si of 1: 2, at a low Ar gas pressure of 5 mTorr or less, and at a temperature of less than 400 ° C. Has a band gap of 0.6 to 1.0 eV by depositing F e S i 2 as a continuous film on the substrate by sputtering.] 3- Shows semiconductor characteristics close to those of F e S i 2 This is a method for producing an amorphous FeSi2 film.

Amorphous FeSi 2 can be obtained by low-pressure sputtering under a low Ar gas pressure of 5 mTorr or less. In particular, the opposing target sputtering method A high quality amorphous FeSi 2 film can be grown.

 FIG. 1 is a conceptual diagram showing the principle of the opposed target type DC sputtering method. In this method, the plasma is completely confined between the target 2 and the target 3 by the magnetic field B applied in parallel with the electric field E, and the plasma does not come into contact with the substrate 1 arranged vertically with the target 2 and the target 3. However, only neutral particles are deposited on the substrate 1, and the grown film is not damaged by the plasma and does not receive an anneal effect, so that microcrystals are not generated and a better amorphous film is obtained. In addition, a continuous film (as-growth) can be grown because the surface temperature of the deposited film is small.

 In addition, since re-sputtering due to plasma contact does not occur, the resulting film has a very small composition deviation from the target, and a FeSi 2 alloy target can be used similarly to the laser ablation method. Furthermore, since low-pressure sputtering of 5 mTorr or less, preferably 1 mTorr or less, is possible, the emitted particles (atoms) from the target maintain high energy without substantially colliding with the Ar gas for sputtering. To reach. Even with the same sputtering method, the above two improvements over the RF magnetron sputtering method enable the growth of higher quality amorphous iron silicide films. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a conceptual diagram showing the principle of the facing target type DC sputtering method. (A) and (b) in FIG. 2 are photographs substituted for drawings showing surface SEM images of amorphous iron silicide and polycrystalline] 3 _FeSi 2 films produced by the method of the present invention, respectively. . FIG. 3 shows an X-ray diffraction pattern of iron silicide produced by the method of the present invention. 6 is a graph showing substrate temperature dependence of a turn. FIG. 4 is a graph showing the substrate temperature dependence of the light absorption spectrum and absorption coefficient α of iron silicide produced by the method of the present invention. FIG. 5 is a graph showing the substrate temperature dependence of the optical absorption spectrum and the optical band gap E g of the iron silicide produced by the method of the present invention. FIG. 6 is a graph showing the substrate temperature dependence of the sheet resistance and specific resistance P of iron silicide produced by the method of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

 (Example 1)

 Using a facing target type DC sputtering device (Mitsurin Soft Co., Ltd., Millertron sputtering device MTS-L2000-2T), the sputtering was performed by the sputtering method.

(100), (111) An iron silicide thin film having a thickness of about 240 ηm was formed on a substrate in a temperature range from room temperature to 400 ° C. For comparison, an iron silicide thin film was similarly prepared at a temperature range of 400 ° C or higher. The target used was a FeSi 2 alloy (99.99%) having a composition ratio of 1: 2. The sputtering chamber in one was evacuated to less 10- ⁴ P a with a turbo-molecular pump, the time of film formation gas pressure of 1. OmTorr flows into the A r gas 15. Osccm, applied voltage, current, respectively 95 OmV, 6.0 mA. The deposition rate was 1.0 nmZmin.

The prepared films were evaluated by SEM observation, X-ray diffraction, light absorption spectrum measurement, and electrical resistance measurement. X-ray diffraction measurement showed that the film was amorphous when the substrate temperature was less than 400 ° C. According to the absorption spectrum measurement, the amorphous FeSi2 was 0.6 to 0.7 e. FIG. 2 shows an SEM image showing a change in the surface shape of the iron silicide with respect to the substrate temperature. The sample surface is extremely smooth regardless of the substrate temperature. At 800 ° C, slight undulation-like irregularities were observed. Figure 3 shows the substrate temperature dependence of the X-ray diffraction pattern. It can be seen that when the substrate temperature is lower than 400 ° C., amorphous Fe S i 2 is obtained, and when the substrate temperature is 400 ° C. or higher,] 3—F e S i 2 is obtained.

Figure 4 shows the substrate temperature dependence of the light absorption spectrum and absorption coefficient. Α-Fe S i 2 film is α = 1.3 to 1.6 × 10 ⁵ cm— ¹ , polycrystalline] 3 — F e S i 2 film is α = 5.0 to 7.8 X 10 ⁴ cm— ^one . Figure 5 shows the substrate temperature dependence of the optical absorption spectrum and optical band gap Eg. The amorphous FeSi 2 film has a thickness of 0.64 to 0.82 eV, and the polycrystalline 3-FeSi 2 film has a thickness of 0.84 to 0.94 eV. FIG. 6 shows the substrate temperature dependence of the sheet resistance and the specific resistance p. Amorufasu F e S i 2 the resistivity p of the film, 3. a ^{2~7. 3 X 10- 3 Q cm} , the resistivity of the polycrystalline j3- F 6 3 12 film is from 1.0 to 3.2 it is an X 10- ¹ Ω cm.

Industrial applicability

 Similar to the laser ablation method, the facing target sputtering method can easily realize the property improvement by adding another element which is effective for the amorphous film. In a normal sputtering method, a high-quality amorphous film can be obtained by preventing the plasma from coming into contact with the film being formed, thereby preventing the effect of the anneal from acting. Since the method is plasma-free, an amorphous film can be easily obtained. Therefore, lamination is easy. Suitable for large area, easy for industrial application.

In addition, amorphous iron silicide has a magnetic semiconductivity by adding a magnetic element. It is possible to adjust the carrier concentration by solidification and hydrogenation. further,

Iron silicide does not require a substrate heating mechanism because it grows at room temperature.

 The amorphous iron silicide film exhibiting the semiconductor characteristics of the present invention can be applied to a solar cell element and a communication light emitting / receiving element.

Claims

The scope of the claims 1. 0.6 to 1. Oe obtained by sputtering method Amorphous iron silicide film with semiconductor characteristics consisting of an amorphous FeSi 2 film.  2. Using a FeSi 2 alloy target with a component atomic ratio of Fe and Si of 1: 2, sputtering on a substrate under 400 ° C under a low Ar gas pressure of 5 raTorr or less. 2. The method for producing an amorphous iron silicide film according to claim 1, wherein an amorphous Fe Si 2 film exhibiting semiconductor characteristics is obtained by depositing F e Si 2 as a continuous film.  3. The method for producing an amorphous iron silicide film according to claim 2, wherein the sputtering method is a facing target type sputtering method.