JPH0582442A - Manufacture of polycrystalline semiconductor thin film - Google Patents

Abstract

PURPOSE:To improve the crystallinity of a polycrystalline semiconductor thin film so as to improve the transistor characteristics of the thin film, such as mobility, ON/OFF ratio, etc., by annealing the thin film formed to crystals of a large grain size by irradiating the thin film with excimer laser light. CONSTITUTION:In the first process, a polycrystalline semiconductor layer 14 is grown by growing an amorphous semiconductor layer 13b formed on the upper surface of a substrate 11 by low-temperature solid-phase growth and, in the second process, a polycrystalline semiconductor thin film 15 is formed by reducing the thickness of the layer 14 by removing the upper layer side of the layer 14. In the third process, the thin film 15 is annealed by irradiating the thin film 15 with excimer laser light 30.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a polycrystalline semiconductor thin film.

[0002]

2. Description of the Related Art Low temperature solid phase growth of amorphous silicon is now very popular. With this low temperature solid phase growth, it is possible to increase the crystal grain size. However, high-temperature annealing is required because minute crystal defects such as twins and dislocations are present inside the silicon grains having a large grain size (having a grain size of 1 μm or more). In particular, one of the annealing treatments performed at a high temperature in a very short time is a method of performing the annealing treatment by excimer laser light irradiation without melting the entire film. This annealing method has good flatness of the film after processing and is suitable for a low temperature process. Therefore, SRAM and L
It is effective as an annealing method in the manufacturing method of CDs and the like.

[0003]

However, excimer laser light has a short wavelength and a large absorption coefficient (α) for silicon of about 10 ⁶ cm ^-1 . For this reason,
Since the excimer laser light reaches only a depth of about 10 nm in the polycrystalline silicon film, the annealing depth by the irradiation of the excimer laser light is about 40 nm in consideration of heat conduction. However, with a polycrystalline silicon film having a thickness of about 40 nm or less, a sufficiently large crystal grain cannot be obtained. Therefore, large crystal grains (for example, grain size 1 μm
When a thick polycrystalline silicon film (for example, having a thickness of 100 nm) that can obtain the above) is formed and the thick polycrystalline silicon film is annealed by irradiation of excimer laser light, the thick polycrystalline silicon film is Depth is about 40n
It is annealed only up to m. Therefore, it is difficult to form a polycrystalline silicon film having large crystal grains with excellent crystallinity over the entire thickness direction.

An object of the present invention is to provide a method for manufacturing a polycrystalline semiconductor thin film having excellent crystallinity.

[0005]

The present invention is a method for manufacturing a polycrystalline semiconductor thin film, which has been made to achieve the above object. That is, in the first step, the amorphous semiconductor layer formed on the upper surface of the substrate is subjected to low temperature solid phase growth to form a polycrystalline semiconductor layer, and then in the second step, the upper side of the polycrystalline semiconductor layer is formed. By removing, the polycrystalline semiconductor layer is thinned to form a polycrystalline semiconductor thin film. Then, in a third step, the polycrystalline semiconductor thin film is irradiated with excimer laser light and annealed.

[0006]

In the above method of manufacturing a polycrystalline semiconductor thin film, the polycrystalline semiconductor layer is formed by low temperature solid phase growth of the amorphous semiconductor layer, so that the polycrystalline semiconductor layer is formed of crystals having a large grain size.
Further, since the polycrystalline semiconductor layer is thinned and the polycrystalline semiconductor thin film is formed and then irradiated with the excimer laser light, the polycrystalline semiconductor thin film is uniformly annealed over the entire thickness direction.

[0007]

Embodiments of the present invention will be described with reference to the manufacturing process diagrams shown in FIG. As shown in the figure, first, the first step (1)
Then, a silicon oxide (SiO ₂ ) layer 12 is formed on the upper surface of a substrate (for example, a silicon substrate) 11 by, for example, a chemical vapor deposition method. Then, an amorphous semiconductor layer 13 made of amorphous silicon is formed on the upper surface of the silicon oxide layer 12 by a chemical vapor deposition method to a thickness of 40 nm or more (for example, 1
The thickness is 50 nm). Then the first step (2)
Then, by performing solid phase growth at a low temperature (for example, at about 600 ° C. for 20 hours), crystal grains are grown in the amorphous semiconductor layer 13, and a polycrystalline semiconductor made of polycrystalline silicon having a grain size of 2 μm or more, for example. Form the layer 14.

In the first step (1), a polycrystalline silicon layer is formed on the upper surface of the substrate 11 by the chemical vapor deposition method, and then the formed polycrystalline silicon layer is ion-implanted with silicon (Si ⁺ ). Then, the polycrystalline silicon layer may be made amorphous to form the amorphous semiconductor layer 13. Alternatively, without forming the silicon oxide layer 12 on the upper surface of the substrate 11, the substrate 11 is formed of quartz glass, and the substrate 11 is formed.
Further, similarly to the above, it is possible to form the amorphous semiconductor layer 13 made of amorphous silicon by the chemical vapor deposition method.

Then, in a second step, the polycrystalline semiconductor layer 14 is formed.
The upper layer side is etched to form a polycrystalline semiconductor thin film 15 made of the polycrystalline semiconductor layer 14. The polycrystalline semiconductor thin film 15 is formed to have a thickness of, for example, 40 nm or less as a thickness that is annealed over the entire region of the polycrystalline semiconductor thin film 15 in the film thickness direction by irradiating the excimer laser light 30. Further, the above-mentioned etching is carried out by, for example, ordinary plasma etching with little etching damage or ammonia (NH ₃ ) and hydrogen peroxide solution (H ₂ O ₂ + H ₂ ) so that the surface to be etched of the polycrystalline semiconductor thin film 15 does not become rough. Wet etching with a mixed solution with O) is performed.

Then, in a third step, the polycrystalline semiconductor thin film 1
The entire surface of 5 is irradiated with excimer laser light 30 (for example, energy density is about 280 mJ / cm ² ) to anneal the polycrystalline semiconductor thin film 15. By this annealing treatment, crystal defects such as twins and dislocations in the polycrystalline semiconductor thin film 15 are reduced, and the crystallinity of the polycrystalline semiconductor thin film 15 is improved.

In the polycrystalline semiconductor thin film 15 formed as described in the above embodiment, one crystal grain is large (for example, the grain size is 2 μm or more), and the crystallinity of the crystal grain is improved. When a thin film transistor (not shown) is formed on one crystal grain of such a polycrystalline semiconductor thin film 15 or when a thin film transistor (not shown) is formed over a plurality of crystal grains, the leakage current is small and the mobility is low. Is a thin film transistor having characteristics such as a high value, a low swing, and a large ON / OFF ratio. Further, in the annealing treatment by irradiation with excimer laser light, the surface of the polycrystalline semiconductor thin film 15 is substantially flat and there is almost no surface roughness, so that the subsequent process treatment becomes easy.

[0012]

As described above, according to the present invention,
Since the polycrystalline semiconductor layer is formed by low-temperature solid-phase growth of the amorphous semiconductor layer on the substrate, the polycrystalline semiconductor layer having large crystal grains can be generated. Further, since the excimer laser light irradiation is performed after thinning the polycrystalline semiconductor layer to form the polycrystalline semiconductor thin film, the polycrystalline semiconductor thin film is uniformly annealed over the entire area in the film thickness direction. Therefore, the grain size of the crystals forming the polycrystalline semiconductor thin film is large, and the crystal defects in each crystal grain are small. Therefore, when the transistor is formed in each crystal grain, the transistor characteristics can be improved.

[Brief description of drawings]

FIG. 1 is a manufacturing process diagram of an example.

[Explanation of symbols]

11 substrate 13 amorphous semiconductor layer
14 Polycrystalline semiconductor layer 15 Polycrystalline semiconductor thin film 30 Excimer laser light

Claims (1)

[Claims] 1. A first step of forming a polycrystalline semiconductor layer by low-temperature solid-phase growth of an amorphous semiconductor layer formed on an upper surface of a substrate, and removing an upper layer side of the polycrystalline semiconductor layer. A second step of thinning the polycrystalline semiconductor layer to form a polycrystalline semiconductor thin film, and a third step of irradiating the polycrystalline semiconductor thin film layer with an excimer laser beam for annealing treatment. And a method for manufacturing a polycrystalline semiconductor thin film.