JPS62235726A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To improve the electric characteristics of an SOS film by a method wherein SiF<+> ions or SiH<+> ions are implanted in specific density into a one-conductivity type silicon thin film epitaxially grown on a sapphire substrate, then another ion- implantation is performed by conducting a heat treatment at the specific temperature range so that the contamination of other ions can be prevented, and fru silicon bonds contained in the SOS film is electrically inactivated. CONSTITUTION:SiF<+> ions of the dosage of 2 X 10<15>/cm<-2> or more are implanted into an SOS substrate of silicon film thickness of 0.6 mum. As a result, an amorphous layer 14 is formed in the vicinity of the interface of silicon and sapphire. Said SOS film is heat-treated in the nitrogen atmosphere of 700-900 deg.C. Through these procedures, the crystallinity in the vicinity of the silicon-sapphire interface of the SOS film is improved, and a crystallinity-improved region 15 is formed. Subsequently, SiF<+> ions of the dosage of 2 X 10<15>/cm<-2> or more are implanted. As a result, an amorphous layer II 6 is formed in the vicinity of the surface of the SOS film. Then, the crystallinity on the region in the vicinity of the surface of the SOS film can be improved by performing a heat treatment in the nitrogen atmosphere of 700-900 deg.C, and a crystallinity-improved region II 7 is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for improving the electrical properties of silicon thin films epitaxially grown on sapphire substrates.

Conventional technology Conventionally, in SO8 films made by epitaxially growing a silicon thin film on a sapphire substrate, lattice mismatch occurs at the silicon-sapphire interface due to the difference in lattice constant between sapphire and silicon. There are many defects in the silicon film, mainly . For this reason, the MO8 type transistors fabricated on these SO8 films had disadvantages such as lower carrier mobility than MO8 type transistors fabricated on bulk silicon, and also higher drain leakage current.

In order to improve these electrical characteristics, a process according to process flowcharts as shown in FIGS. 2d to 2q has heretofore been proposed. The conventional SO
A method for improving the electrical characteristics of the 8 film will be explained.

That is, first of all, as shown in Fig. 2a, Si'' ions are ionized at a high concentration near the silicon-sapphire interface where crystal defects exist at a high density in the SO8 film, as shown in Fig. 2a. The SO8 film is implanted to amorphize the vicinity of the silicon-sapphire interface to form an amorphous layer I4.At this time, the SO8 film is kept at liquid nitrogen temperature.Subsequently, as shown in FIG. Heat treatment is performed in a nitrogen atmosphere at a temperature higher than ℃.As a result, in-phase growth occurs from the Beno plane in Table 3 toward the amorphous portion, and the amorphous layer I4 becomes a single crystal as shown in Figure 2d. As a result, the crystallinity near the silicon-sapphire interface is improved, resulting in an improved crystallinity region 5. As a result, the electrical characteristics near the silicon-sapphire interface of the SO8 film are improved, and an MO8 type transistor is formed on this SO8 film. In this case, the drain leakage current can be reduced.Next, as shown in Fig. 2e, in order to improve the electrical characteristics near the surface of the SOS film, Si+ ions were implanted at a high concentration near the surface of the SO8 film 6, and the temperature was increased to 600°C. Heat treatment is performed in the above nitrogen atmosphere.As a result, as shown in Fig. 2 f, SO8
Solid-phase growth occurs from the inside of the film toward the surface, and as shown in Figure 2, the crystallinity near the surface is improved, resulting in a crystallinity-improved region.
becomes. As a result, the electrical characteristics near the surface of the SO8 film are improved, and when an MO8 type transistor is formed on this SO8 film, the mobility is improved.

Problems to be Solved by the Invention These conventional methods mainly make the SO8 film amorphous and improve its crystallinity through the effect of in-phase growth.
This method improves the electrical properties of the film, and even after improving the crystallinity of the SO8 film by solid-phase growth, many dangling bonds of silicon atoms remain at the silicon-sapphire interface and in the film.

In conventional ion implantation using St'' ions, silicon atoms are tetravalent, so it is not possible to make silicon dangling bonds in the film electrically inactive, and crystal defects still exist in the SO8 film. Further, since the mass number of Si+ ions is 28, there is a problem of contamination by nitrogen during ion implantation.

The present invention solves these problems by performing ion implantation without contaminating other ions, electrically inactivating silicon dangling bonds in the SO8 film, and effectively improving the electrical characteristics of the SO8 film. The purpose is to

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides a silicon thin film of one conductivity type epitaxially grown on a sapphire substrate.
iF+ ions or SiH+ ions at 2×10 crn
Provided is a method for manufacturing a semiconductor device, characterized in that ions are implanted at a high concentration as described above, and then heat treatment is performed in a temperature range of 700° C. to 900° C. after 6 pages.

Function By using SiF+ ions or SiH+ ions as implantation ions, SiF+ ions or S
In addition to the effect of improving the crystallinity of normal solid phase growth due to the amorphization of the SO8 film by iH+ ions, fluorine atoms or hydrogen atoms are present at the silicon-sapphire interface and in the SO8 film.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to process flowcharts shown in FIGS. 1a to 1q.

First, SiF" ions were applied to an SO8 substrate with a silicon film thickness of 0.6 μm as shown in FIG. Ion implantation is performed with acceleration energy such that the center of the ion range is located nearby.

As a result, an amorphous layer I4 is formed near the silicon-sapphire interface. At this time, the gas used for ion implantation is SIF4 gas, and during the implantation, the SO8 film is cooled with liquid nitrogen in order to prevent a temperature rise due to the implantation and to effectively make it amorphous. Next, as shown in FIG. 1C, this SO8 film is heat-treated for 60 minutes in a nitrogen atmosphere at 700°C. As a result, solid-phase growth occurs in the amorphous layer to form a single crystal, and at the same time, fluorine atoms electrically inactivate the dangling bonds of silicon present at the silicon-sapphire interface.

Further, during the heat treatment, excessive fluorine atoms diffuse toward the surface of the SO8 film, and at that time, the dangling bonds present in the SO8 film are electrically inactivated. Through these steps, the crystallinity near the silicon-sapphire interface of the SO8 film is improved, forming a crystallinity-improved region I5, as shown in FIG. 1d.

Subsequently, as shown in FIG. 1e, 0.0.
SiF+ ions are implanted at a dose of 5×1o15tM''-2 using acceleration energy such that the center of the ion range is around 1 μm.This allows the SiF+ ions to be implanted near the surface of the SOS film as shown in Figure 1f. An amorphous layer (6) is formed.

Next, as shown in Figure 1q, by heat-treating this SO8 film in a nitrogen atmosphere at 700°C, solid-phase growth occurs from within the SO8 film toward the surface, improving the crystallinity near the surface. , crystallinity improved region (7). The above treatment improves the crystallinity over the entire region of the silicon surface in the silicon thin film near the silicon-sapphire interface of the psos film. Although this embodiment has been described using SiF+ ions as an example, similar effects can be expected with SiH+ ions. Further, when SiF+ ions are used, since their mass number is 47, the problem of nitrogen contamination does not occur.

Effects of the Invention As described above, according to the present invention, it is possible to effectively improve the crystallinity at the silicon-sapphire interface of the SO8 film and over the entire silicon surface area in the silicon thin film. Since the drain leakage current of the HVI OS type transistor formed on the O8 film is reduced and the effective mobility is increased, it is possible to improve the performance of the MOS type integrated circuit formed on the SoS film.

[Brief explanation of drawings]

FIG. 1 is a process sectional view showing a method for manufacturing a semiconductor device according to an embodiment of the present invention, and FIG. 2 is a process sectional view showing a conventional method for manufacturing a semiconductor device. 1... Sapphire substrate, 2... Silicon epitaxial layer, 3... Silicon-sapphire interface, 4... Amorphous layer by SiF+ ion implantation. 5... Crystallinity improved region I by solid phase growth, 6... Amorphous layer ■ by SiF" ion implantation, 7... Crystallinity improved region by solid phase growth ■
. Name of agent: Patent attorney Toshio Nakao and one other person
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Claims (1)

[Claims] SiF^+ ions or SiH^+ ions are implanted at a high concentration of 2 x 10^1^5 cm^-^2 or more into a silicon thin film of one conductivity type epitaxially grown on a sapphire substrate, and then at 700°C. A method for manufacturing a semiconductor device, characterized in that heat treatment is performed in a temperature range of 900°C.