JP4389514B2 - Method for forming thin film semiconductor - Google Patents

Description

The present invention relates to a method for forming a thin film semiconductor having a crystalline silicon thin film.

  In recent years, research on forming a silicon crystal thin film on a non-conductive dissimilar substrate such as a glass substrate has been actively conducted. The silicon crystal thin film formed on the glass substrate is widely used for liquid crystal device TFTs (Thin Film Transistors), thin film photoelectric conversion elements, and the like.

  Thin-film photovoltaic power generation elements are made by forming a crystalline silicon thin film with good crystallinity on a low-cost substrate using a low-temperature process, and using this as a photoelectric conversion element to reduce costs and improve performance. It is. The crystalline silicon photoelectric conversion element using the crystalline silicon thin film as a photoelectric conversion element does not cause light degradation, which is a problem of the amorphous silicon photoelectric conversion element. Even long-wavelength light without (unconvertible) light can be converted into electrical energy. This technology is expected to be applicable not only to photoelectric conversion elements but also to photoelectric conversion devices such as optical sensors.

As a general manufacturing method of this crystalline silicon photoelectric conversion element, a method of directly depositing a crystalline silicon thin film on a substrate by a plasma CVD method is used. Accordingly, the crystalline silicon thin film can be formed on the substrate at a relatively low temperature, and the crystalline silicon thin film can be formed at a low cost. The film formation conditions by the plasma CVD method are that the silane source gas is diluted about 15 times or more with hydrogen, the pressure in the plasma reaction chamber is 1.33 to 1.33 × 10 ³ Pa (10 mTorr to 10 Torr), and the substrate temperature is 150. The crystalline silicon thin film can be formed on the substrate by controlling the temperature within a range of ˜550 ° C., desirably 150 ° C. to 400 ° C.

  However, it has been difficult to form polysilicon having a large crystal grain size by this plasma CVD method. In addition, the i layer (intrinsic semiconductor thin film), which is the basis of the power generation function, has a problem that the quality is drastically lowered when doping is performed to optimize the device structure. For these reasons, it has been difficult to achieve high conversion efficiency greatly exceeding 10% with a single cell advantageous for cost reduction.

  As other methods for forming the crystalline silicon thin film, various attempts have been made to crystallize the crystalline silicon thin film by scanning while irradiating laser light. In this method, an amorphous silicon layer is formed on a heterogeneous substrate, and the amorphous silicon layer is scanned while being irradiated with a continuous band laser beam, thereby melting and crystallizing the amorphous silicon layer. Thus, a polycrystalline silicon layer is obtained, and crystal grains that are long in the scanning direction can be grown (see, for example, Patent Document 1).

  This crystallization method by irradiation with continuous wave laser light is being developed for display TFT substrates. Since it is necessary to form a MOSFET on the surface of the display TFT substrate, the crystalline silicon thin film obtained by this crystallization method is required to be flat. Here, it has been reported that a very flat crystalline silicon thin film can be obtained by using a solid-state laser (see, for example, Non-Patent Document 1).

  In addition, when a crystalline silicon thin film having unevenness on the surface used for an electronic device such as a TFT is formed using laser light, the surface of the surface is average squared by irradiating the excimer laser light to amorphous silicon having a thickness of 50 nm. It has been reported that a crystalline silicon thin film having irregularities with a root (RMS) of up to 50 nm can be obtained (for example, see Non-Patent Document 2).

JP 2001-351863 A Nobuo Sasaki and 6 others, “New low-temperature poly-Si TFT technology with mobility exceeding 500 cm 2 / Vs by CW lateral crystallization (CLC) technology”, IEICE Transactions, C vol.J85-C, No.8, 2002 August, p.601-608 Katsuyuki Tsuji, 4 others, “Effect of laser irradiation atmosphere and number of irradiation on surface morphology in excimer laser annealed poly-Si film”, IEICE Transactions, C vol.J85-C, No.8, 2002 8 Moon, p.630-638

  By the way, the crystalline silicon thin film having irregularities described in Non-Patent Document 2 is obtained by performing 500 times of pulse irradiation using an excimer laser, and is a very extreme manufacturing condition. However, it was not a production method suitable for mass production. Further, since the crystalline silicon after annealing by the laser beam is aggregated and scattered, it is not suitable for use as an electronic device.

An object of the present invention was developed in view of the above circumstances, it is to provide a method of forming a thin film semiconductor body provided with a crystalline silicon thin film having an uneven surface.

In order to achieve the above object, a method for forming a thin film semiconductor according to the present invention is a method in which a continuous wave laser beam having a light intensity distribution in a laser width direction is applied to a non-single crystal silicon thin film provided on a substrate in a direction perpendicular to the laser width direction. Irradiating a plurality of scans at predetermined intervals to completely melt and crystallize the laser light irradiation part of the non-single crystal silicon thin film, and form a plurality of protrusions on the surface, and then the protrusions The continuous wave laser beam is irradiated while scanning a plurality of times at a predetermined interval in a direction orthogonal to the longitudinal direction of the ridge, and a part of the ridge in the longitudinal direction is further raised from the ridge, thereby forming a quadrangular pyramid shape. Are formed on a crystalline silicon thin film in which a plurality of protrusions are arranged in a predetermined pattern.

Here, the continuous wave laser light has a Gaussian distribution, and its light source is a solid-state laser.

  According to the above, it is possible to form protrusions or protrusions having an average square root of surface roughness of 60 nm or more on the surface of the crystalline silicon thin film.

  According to the present invention, by providing a crystalline silicon thin film having protrusions on the surface on a substrate, an excellent effect is obtained that a thin film semiconductor having a large light confinement effect can be obtained.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, a preferred embodiment of the invention will be described with reference to the accompanying drawings.

  A perspective view of a thin film semiconductor according to a preferred embodiment of the present invention is shown in FIG.

  As shown in FIG. 1, the thin film semiconductor 10 according to the present embodiment includes a crystalline silicon thin film 14 having a plurality of saw-toothed ridges 12 with a predetermined interval P on the surface at least partially on a substrate 11. It is provided. The group of ridges 12 forms the concavo-convex portion 13.

  The mean square root of the surface roughness of the uneven portion 13 is 60 nm or more, preferably 100 nm or more.

  Next, a method for manufacturing the thin film semiconductor 10 according to the present embodiment will be described with reference to the accompanying drawings.

As shown in FIG. 2, a non-single-crystal silicon thin film 24 such as amorphous silicon or microcrystalline silicon is formed on a heterogeneous substrate 11 such as a glass substrate. Next, the non-single-crystal silicon thin film 24 is irradiated with a rectangular laser beam (semiconductor laser beam) indicated by the region A. Then, while irradiating the laser beam to scan in the direction of arrow D _S. Laser annealing is performed by this laser light irradiation and scanning, and as shown in FIG. 3, the non-single crystal silicon thin film 24 in the portion irradiated with the laser light is melted and crystallized to form a crystalline silicon thin film 34 such as polycrystalline silicon. It becomes. At this time, the laser beam, the scanning direction D _S perpendicular laser width direction (the in Figure 3 the left-right direction) can be performed by providing the intensity distribution, ridges 12 are formed on the surface of the crystalline silicon thin film 34.

Thereafter, the region irradiated with the laser beam A (see FIG. 2), by sequentially shifting at predetermined intervals P in the direction of arrow D _M, on at least a portion of the substrate 11, cross saw on the surface at predetermined intervals P A crystalline silicon thin film 14 having blade-like ridges 12 is formed, and the thin film semiconductor 10 shown in FIG. 1 is obtained.

  Here, as a laser beam used for irradiation to the non-single crystal silicon thin film 24, an intensity such as weak → strong → weak → ... → weak (in FIG. 3, weak → strong → weak → strong → weak) in the laser width direction. By forming the distribution, the portion irradiated with the laser beam having a high intensity is raised and becomes a convex portion. By projecting the laser beam, the convex portions are continuously connected to form the ridge 12.

The intensity distribution such as weak → strong → weak → ... → weak is generally a Gaussian distribution. When a solid-state laser (for example, Nd: YAG laser or Nd: YVO ₄ laser) is used as the laser light source, the oscillated laser light has a circular Gaussian distribution. Therefore, since the laser light oscillated from these solid-state lasers originally has an intensity distribution, there is an advantage that the laser light can be used as it is without being optically processed. Further, when a semiconductor laser is used as a light source of laser light, laser light having a rectangular irradiation region (for example, 0.1 mm × 0.2 mm) 51 can be oscillated as shown in FIG. In this case, it is possible to provide an intensity distribution in the laser width direction (left and right direction in FIG. 5) of the laser light by partially arranging a slit, an ND filter, or the like on the optical path of the laser light. The laser beam used for laser irradiation is not particularly limited to a solid laser or a semiconductor laser, and any laser beam having a wavelength capable of melting and crystallizing the non-single-crystal silicon thin film 24 can be applied. is there.

  Next, the operation of the present embodiment will be described.

  The non-single crystal silicon thin film 24 is scanned while being irradiated with a laser beam having an intensity distribution in the laser width direction, and then the region to be irradiated with the laser beam is sequentially shifted by a predetermined interval P, whereby the ridges 12 are regulated. Therefore, it can be formed at a predetermined interval P. As a result, a V-shaped groove having a desired width can be formed between the ridges 12 in the concavo-convex portion 13 of the crystalline silicon thin film 34, and a crystalline silicon thin film 34 having a large light confinement effect is obtained. Is possible. Therefore, by applying the thin film semiconductor 10 according to the present embodiment to a device such as a solar cell, high conversion efficiency greatly exceeding 10% can be easily achieved.

  Further, the surface roughness of the concavo-convex portion 13 can be freely adjusted by adjusting the intensity of the laser beam while keeping the shape of the laser beam (the shape of the region A) as it is. Specifically, the height of the ridge 12 can be increased by increasing the laser intensity of the laser beam, and the height of the ridge 12 can be decreased by decreasing the laser intensity of the laser beam. By adjusting the average square root of the height of the ridges 12 in the crystalline silicon thin film 34 to 60 nm or more, preferably 100 nm or more, the amount of light absorption can be increased as compared with a crystalline silicon thin film having a flat surface. it can. Here, the intensity of the laser beam is within a range in which the laser beam irradiated portion of the non-single-crystal silicon thin film 24 can be completely melted, and is appropriately determined according to the material, film thickness, etc. of the non-single-crystal silicon thin film 24.

  Moreover, since the crystalline silicon thin film 34 provided with the concavo-convex portion 13 is produced using continuous wave laser light, the productivity is good and suitable for mass production. Further, the crystalline silicon thin film 34 after annealing by this laser beam is suitable for use as an electronic device because it is formed continuously and uniformly over the entire surface.

  Further, as the laser light used for laser irradiation, a non-single-crystal silicon thin film 24 having a large area is melted and crystallized in one scan by using a laser beam having a rectangular irradiation region and a very long laser width direction. Can be Thereby, the workability of the manufacturing process of the crystalline silicon thin film 34 is greatly improved, and the manufacturing cost of the thin film semiconductor 10 can be reduced.

Further, by using a solid-state laser such as Nd: YAG or Nd: YVO ₄ as the laser light used for laser irradiation, the crystalline silicon thin film 34 is crystallized, so that the running cost can be significantly reduced. It is possible to form a high-quality crystalline silicon thin film 34 (polycrystalline silicon).

  Next, another embodiment of the present invention will be described with reference to the accompanying drawings.

  FIG. 4 shows a perspective view of a thin film semiconductor according to another preferred embodiment of the present invention.

  As shown in FIG. 4, the thin film semiconductor 40 according to the present embodiment has a crystalline silicon thin film 44 in which a plurality of quadrangular pyramidal protrusions 42 are arranged at a predetermined interval P on at least a part of a substrate 41. Is provided. A group of convex portions 42 forms the concave and convex portions 43.

  The mean square root of the surface roughness of the uneven portion 43 is 60 nm or more, preferably 100 nm or more.

  Next, a method for manufacturing the thin film semiconductor 40 according to the present embodiment will be described with reference to the accompanying drawings.

  First, the thin film semiconductor 10 shown in FIG. 1 is formed. Next, the thin film semiconductor 10 is rotated 90 ° horizontally with respect to the longitudinal direction of the ridges 12. Thereafter, scanning is performed while irradiating the laser beam again in the direction orthogonal to the longitudinal direction of the ridges in the same procedure as the procedure for forming the crystalline silicon thin film 34 described in the previous embodiment. At this time, the portion irradiated with the laser beam having a high intensity is further raised at a part of the longitudinal direction of each ridge 12. Thereby, a part of the longitudinal direction of each ridge 12 is formed into a quadrangular pyramid-shaped convex portion 42 that is further raised than the ridge 12.

  Thereafter, by sequentially moving the region to be irradiated with the laser beam at a predetermined interval P in a direction orthogonal to the scanning direction of the new laser beam, at least part of the substrate 41 has a quadrangular pyramid on the surface. A crystalline silicon thin film 44 in which a plurality of convex portions 42 are arranged at a predetermined interval P is formed, and the thin film semiconductor 40 shown in FIG. 4 is obtained.

  Also in the thin film semiconductor 40 according to the present embodiment, the same effects as the thin film semiconductor 10 according to the previous embodiment can be obtained.

  In addition, the thin film semiconductor 40 according to the present embodiment has a V-shaped groove having a desired width between the convex portions 42 of the concave and convex portions 43 of the crystalline silicon thin film 44. The number of grooves reaches about twice the number of grooves in the thin film semiconductor 10 according to the previous embodiment. Moreover, the mean square root of the surface roughness of each convex part 42 in the uneven part 43 of the crystalline silicon thin film 44 is larger than that of each convex line 12 in the uneven part 13 of the thin film semiconductor 10 according to the previous embodiment. As a result, a crystalline silicon thin film 44 having a greater light confinement effect than the crystalline silicon thin film 34 of the thin film semiconductor 10 according to the previous embodiment can be obtained.

  As mentioned above, it cannot be overemphasized that embodiment of this invention is not limited to embodiment mentioned above, and various things are assumed in addition.

  Next, embodiments of the present invention will be described based on examples, but the embodiments of the present invention are not limited to these examples.

An amorphous silicon thin film having a thickness of 300 nm was formed on a quartz substrate using a vacuum deposition method in a UHV (Ultra High Vacuum) atmosphere of 1 × 10 ⁻⁷ Pa. The amorphous silicon thin film was irradiated with laser light using a semiconductor laser as an oscillation source. This semiconductor laser beam has a Gaussian distribution and has a wavelength of 800 nm. When this laser beam was scanned linearly at a scanning speed of 1 cm / sec, the amorphous silicon thin film was melted and then crystallized to obtain a polycrystalline silicon thin film. This polycrystalline silicon thin film had a width of several μm or more and a length of several tens of μm or more.

  This polycrystalline silicon thin film has a different film thickness in the laser width direction perpendicular to the scanning direction of the laser beam. As shown in FIG. 6, the central portion of the laser beam irradiation portion is raised to a height of about 1 μm. It was found from the step measurement. This ridge appeared when the laser intensity was such that the portion irradiated with the laser beam was completely melted. Further, by reducing the laser intensity without changing the shape of the laser beam, it was possible to produce a protrusion with a height of 100 nm (0.1 μm).

A quartz substrate on which an amorphous silicon thin film similar to that in Example 1 was formed was irradiated with laser light using an Nd: YVO ₄ laser as an oscillation source. This semiconductor laser beam has a Gaussian distribution, and has a wavelength of 532 nm and a laser beam diameter of 10 μm. When this laser beam was scanned linearly at a scanning speed of 2 cm / sec, the amorphous silicon thin film was melted and then crystallized to obtain a polycrystalline silicon thin film. Thereafter, the laser beam irradiation region was shifted by 9 μm in the laser width direction, and scanning while irradiating the laser beam was repeated 100 times. As a result, a crystallized region having a width of 900 μm was formed. In the crystallized region, ridges were continuously formed at a pitch of 9 μm in the laser width direction perpendicular to the laser beam scanning direction.

  A microcrystalline silicon thin film having a thickness of 1 μm was formed on a quartz substrate by plasma CVD. The source gas was 50 ccm of hydrogen relative to 1 ccm of monosilane, and the substrate temperature was 400 ° C. Thereafter, the quartz substrate was heat-treated at 600 ° C. for 30 minutes. Next, laser annealing was performed on the microcrystalline silicon thin film using semiconductor laser light. Here, the semiconductor laser light has a rectangular shape with a length of 0.1 mm and a width of 0.2 mm, and the length direction is taken as the scanning direction. Further, 100 ND filters are periodically inserted in the optical path of the laser beam so that the output laser beam has a periodic strength of 100 times in the width direction.

  When scanning was performed using such a laser beam, a polycrystalline silicon thin film (crystalline silicon thin film) having periodic ridges corresponding to the intensity of light as shown in FIG. 1 was formed. As a result of measuring the absorption spectrum of this polycrystalline silicon thin film, as shown in FIG. 7, the light absorption increased remarkably as the height of the ridges increased as compared with the polycrystalline silicon thin film having a flat surface. The height of the ridge could be freely adjusted in the range of 60 to 500 nm by changing the laser power. In addition, a light confinement effect of about 1.2 times was confirmed in the wavelength region of 300 to 1200 nm. From the measurement result of the absorption spectrum, it was confirmed that the light absorption amount increased when the average square root of the height of the ridge was 100 nm or more.

  The quartz substrate having the polycrystalline silicon film of [Example 3] is rotated by 90 ° with respect to the longitudinal direction of the ridges. Thereafter, in the same procedure as in Example 3, the semiconductor laser light is again oscillated with an appropriate output in the direction orthogonal to the longitudinal direction of the ridges, and scanning is performed while irradiating.

  As a result, a polycrystalline silicon thin film having a plurality of quadrangular pyramidal projections arranged at predetermined intervals on the surface as shown in FIG. 4 was formed. As a result of measuring the absorption spectrum of this polycrystalline silicon thin film, an optical confinement effect of about 1.27 times was confirmed in the wavelength region of 300 to 1200 nm as compared with the polycrystalline silicon thin film having a flat surface.

1 is a perspective view of a thin film semiconductor according to a preferred embodiment of the present invention. It is a figure for demonstrating the manufacturing method of the thin film semiconductor of FIG. It is a figure for demonstrating the manufacturing method of the thin film semiconductor of FIG. It is a perspective view of the thin film semiconductor which concerns on other suitable one Embodiment of this invention. It is a schematic diagram of the semiconductor laser beam used for laser annealing of a non-single crystal silicon thin film. It is a figure which shows the protruding state in the laser width direction of a laser irradiation part. It is a figure showing the relationship between the height of a protruding item | line and the amount of light absorption. The vertical axis represents the relative value when the light absorption amount of the flat polycrystalline silicon thin film is 1.0.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Thin-film semiconductor 11 Substrate 12 Projection 14 Crystalline silicon thin film P Predetermined interval

Claims (2)

A non-single-crystal silicon thin film provided on a substrate is irradiated with a continuous wave laser beam having a light intensity distribution in the laser width direction while scanning a plurality of times at predetermined intervals in a direction perpendicular to the laser width direction. The laser light irradiation part of the single crystal silicon thin film is completely melted and crystallized to form a plurality of ridges on the surface, and then the continuous wave laser light is spaced at a predetermined interval in a direction perpendicular to the longitudinal direction of the ridges. Irradiated while scanning a plurality of times apart from each other, a part in the longitudinal direction of the ridge is raised further than the ridge, and formed into a crystalline silicon thin film in which a plurality of quadrangular pyramidal protrusions are arranged in a predetermined pattern A method for forming a thin film semiconductor. 2. The method of forming a thin film semiconductor according to claim 1, wherein the light source of the continuous wave laser beam is a solid-state laser, and the continuous wave laser beam has a Gaussian distribution.

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