JPH0151050B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a thin film. Generally, amorphous silicon is widely used in photoelectric materials such as contact image sensors and solar cells. FIG. 1 shows a cross-sectional view of an image sensor manufactured using amorphous silicon. This has a structure in which an amorphous silicon film 2 is formed on the surface of a substrate 1, and an upper electrode 3 and a lower electrode 4 are provided. Methods for depositing this type of amorphous silicon include the so-called plasma CVD method or sputtering method, which incorporates discharge into film formation by CVD (vapor phase growth accompanied by chemical reactions). To deposit amorphous silicon only on desired portions of the substrate using these methods, there are methods using photolithography and etching, methods using a mask, and the like. In this method using photolithography and etching, amorphous silicon is deposited over the entire surface of the substrate by the plasma CVD method or sputtering method, and then unnecessary parts of the amorphous silicon film are removed. It is removed by photolithography and etching. Further, in the method using a mask, a mask is attached to a substrate and amorphous silicon is deposited only on desired portions of the substrate from the beginning. FIG. 2 is a sectional view showing the main parts of an apparatus for producing an amorphous silicon film by sputtering using a mask. In the figure, a target 7 for emitting silicon atoms is placed in a vacuum chamber 5 filled with argon, facing a substrate 6 on which amorphous silicon is to be deposited. Further, as shown in FIG. 3, a mask 8 is attached to the substrate 6. This mask 8 has an opening 8a corresponding to the shape of the amorphous silicon film to be formed on the substrate 6. Further, the substrate 6 side is cooled with liquid helium or liquid nitrogen. In this state, when an appropriate voltage is applied to the substrate 6 side and the target 7 side, ionized argon particles collide with the target 7, and the impact releases silicon atoms A, causing them to form on the mask 8 and substrate 6. Amorphous silicon is deposited on the surface. Furthermore, by removing the mask 8, an amorphous silicon film having a desired shape is formed on the substrate 6. By the way, stainless steel has traditionally been widely used as the material for the mask 8, but as a matter of course, silicon atoms A released from the target 7 also collide with the mask 8, and atoms B are released from the mask 8. . Atoms B emitted from this mask 8 are incorporated into the amorphous silicon film being formed on the substrate 6 as impurities. Therefore, when an image sensor as shown in FIG. 1 is manufactured using the above-described apparatus, impurities incorporated into the amorphous silicon film cause deterioration of various characteristics of the image sensor. There was also the problem of defects occurring. The present invention was made in view of the above circumstances, and
It is an object of the present invention to provide a method for producing a thin film so as to suppress as much as possible the incorporation of impurities into the formed thin film. By the way, the release of atoms from a solid is basically caused by the impact of sputtering ions in the sputtering method or ions or radicals in the plasma material colliding with the solid in the plasma CVD method. This is done by knocking out atoms on the surface of the solid. In this case, the sputter rate of solid atoms by ions (the number of atoms ejected by each ion incident on the solid) depends on the type of ion, the kinetic energy of the ion, the angle of incidence of the ion, and the distance between atoms in the solid. It depends on the binding energy of Therefore, by using a mask made of a substance with a small sputter rate, a thin film containing no impurities can be produced. Therefore, in the present invention, a material with a smaller sputter rate than stainless steel is used as the mask material to prevent impurities from entering the thin film. Hereinafter, one embodiment of the present invention will be described in detail with reference to the accompanying drawings. FIG. 4 shows an example in which an amorphous silicon film was manufactured by applying the thin film manufacturing method according to the present invention. In FIG. 4, the same reference numerals are used for parts that perform the same functions as in FIG. 2. A vacuum chamber 5 filled with argon gas contains a substrate 6 on which amorphous silicon is deposited, and the substrate 6
A target 7 that emits spatter ions is disposed facing the target. Further, a mask 9 having an appropriately shaped opening 9a is attached to the substrate 6. This mask 9 is made of tungsten (W), tantalum (Ta), molybdenum (Mo), glass, etc., which have a small sputter rate in an argon gas atmosphere and are available at relatively low cost. uses tungsten. Note that the substrate 6 side is cooled with liquid helium, liquid nitrogen, or the like. When a suitable voltage is applied to the substrate 6 side and the target 7 side in the above state, silicon atoms A are emitted from the target 7, and amorphous silicon is deposited on the mask 9 and the substrate 6. Furthermore, mask 9
By removing this, an amorphous silicon film having a desired shape is formed on the substrate 6. Next, an amorphous silicon film is formed using conventional stainless steel and tungsten according to the present invention as mask materials, and electrodes are provided by an appropriate method to produce an image sensor. The results of determining the number of defects will be explained. The fabricated image sensor had a sandwich structure as shown in Fig. 1, and three samples of each (1056) pieces of this were arranged on a substrate were fabricated, and each sample was inspected for defects one by one. The presence or absence of defects was checked and the number of defects generated was investigated. The results are shown in Table 1.

[Table] As is clear from Table 1, when tungsten is used as a mask, no defects are observed in the image sensor. Further, another example using tantalum as the mask material will be described. Similar to the above-mentioned example, image sensors were manufactured using conventional stainless steel and tantalum according to the present invention as mask materials (see Figure 1), and the number of defects was determined for each image sensor. A large number (1056) of the image sensors shown in FIG. 1 were arranged on a substrate using stainless steel and tantalum as a mask, and three samples of each were prepared, and each sample was examined for defects one by one. was checked to determine the number of defects. The results are shown in Table 2.

[Table] As is clear from Table 2, when an image sensor is manufactured using tantalum as a mask material, the number of defects in the image sensor is much smaller than when stainless steel is used as a mask material. In this example, a method for manufacturing a thin film using a sputtering method has been described, but the method is not limited to this, and the same effects as in this example can be obtained by using other methods, such as plasma CVD. Further, the thin film to be produced is not limited to amorphous silicon, but other thin films may be produced. As explained above, according to the present invention, when producing a thin film with a desired shape by sputtering method, plasma CVD method, etc., a material with a small sputter rate is used as a mask material, so a thin film with less contamination of impurities can be produced. can do.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of an image sensor, FIG. 2 is an amorphous silicon film manufacturing apparatus using stainless steel as a mask, and FIG. 3 is a plan view showing a state in which a mask 8 is attached to a substrate 6 in FIG. 2. FIG. 4 shows a thin film manufacturing apparatus to which the thin film manufacturing method according to the present invention is applied. 1, 6... Substrate, 2... Amorphous silicon film, 3, 4... Electrode, 5... Vacuum chamber, 7... Target, 8, 9... Mask.

Claims (1)

[Scope of Claims] 1. A method for producing a thin film, in which a mask is mounted on a substrate, sputtered atoms are attached to the substrate, and then the mask material is removed to form a thin film in a desired shape on the substrate. . A method for producing a thin film, characterized in that a material with a smaller sputter rate than stainless steel is used as the material of the mask to prevent impurities from entering the thin film. 2. The thin film manufacturing method according to claim 1, wherein the material of the mask is tungsten. 3. The thin film manufacturing method according to claim 1, wherein the material of the mask is tantalum.