JP2698147B2 - Method of forming SOI structure - Google Patents

Description

The present invention relates to a method for forming an SOI (Silicon on Insulator) structure, and more particularly to a method for forming a Si film by a solid phase growth method.

B) Conventional technology A single-crystal Si layer formed on an insulating layer (including an insulating substrate) is called an SOI structure, which enables easy element isolation in a narrow area and high integration and high speed. Known as possible. Research and development are being vigorously conducted since the characteristics are improved as compared with a semiconductor integrated circuit (IC) in which elements are formed on a conventional Si substrate.

As a method of forming a single-crystal Si film on an insulating layer, there is a solid-phase growth method. In this method, a part of the surface of a Si substrate is exposed as a seed on a single-crystal Si substrate to form the insulating film. Formed and amorphous Si (hereinafter referred to as a-Si) on the seed and insulating film
By depositing a film and annealing at a low temperature of about 600 ° C,
The a-Si film is monocrystallized by solid phase growth in the lateral direction.

As a method of extending the lateral growth distance in solid phase growth, there is a method in which P ⁺ ions are implanted at a high concentration into an a-Si film on an insulating film and then annealing is performed (Extended Abs).
tracts of the 16th Conference on Solid State Devic
es and Materials, Kobe, 1984, pp. 507-510).

C) Problems to be Solved by the Invention However, in order to extend the lateral growth distance, P ⁺ ions are doped at a high concentration of 3 × 10 ²⁰ cm ⁻³ , so that the solid-phase grown single crystal Si film has Since the impurity (P) concentration becomes extremely high, it has been difficult to form a semiconductor device on the single crystal Si film grown by solid phase growth.

It is also considered that a single crystal Si film is epitaxially grown at a substrate temperature of about 800 ° C. on a single crystal Si film solid-phase grown by doping with P to form a Si film having a low impurity concentration. However, due to auto-doping during epitaxial growth and solid-phase diffusion during the device fabrication process,
The impurity concentration on the surface of the epitaxially grown Si film is 1
× 10 ¹⁸ cm ^-3 or more, which was again unsuitable for producing a semiconductor device. Single crystal to make semiconductor device
The impurity concentration of the Si film (base) needs to be reduced to about 10 ¹⁵ cm ^-2 .

D) Means for Solving the Problems A method for forming an SOI structure according to the present invention comprises a step of forming an insulating layer having an opening on a single crystal Si base, the opening being partially exposed on the single crystal Si base. And the single crystal exposed at the opening
Amorphous Si doped with P on Si base surface and insulating layer
A step of forming a film, a step of solid-phase growing the amorphous Si film by annealing to form a single-crystal Si film, and a step of implanting inert ions into the single-crystal Si film into the film; The method includes a step of annealing the substrate into which the inert ions have been implanted, and a step of further forming a single-crystal Si film on the annealed single-crystal Si film.

E) Action After the P-doped a-Si film is solid-phase grown by annealing to form a single-crystal Si film, inert ions are implanted into the single-crystal Si film to form a single-crystal Si base and a single-crystal Si film. A damaged region is formed at the interface of the Si film, and by annealing,
P atoms are trapped by the defects in the damaged region, and at the same time, outward diffusion occurs, so that the P concentration on the surface of the single crystal Si film is reduced.

F) Embodiment FIGS. 1A to 1G show schematic process diagrams of a first embodiment of the present invention. In this embodiment, the single crystal Si base is used as a single crystal Si base.
Although a Si substrate is used, a single crystal Si film formed on the substrate may be used.

(1) is a single-crystal Si substrate serving as a single-crystal Si base having a (100) plane as a main surface.
Causing enough for the SiO ₂ film (2) is deposited by CVD (Fig. 1 A) (SiO ₂ film may be formed by directly thermally oxidizing the Si substrate).

The opening of the <100> direction in a stripe shape of the single-crystal Si substrate (1) and (2 ') is patterned by photolithography in the SiO ₂ film (2) (Figure 1 B).

Next, a Si film is formed on the entire surface by a CVD method. First, S
The surface on which the i-film is to be formed, particularly the surface of the single crystal Si substrate (1) exposed at the opening (2 ') (that is, the seed, hereinafter referred to as seed (1')) is cleaned. The substrate was placed in a low-pressure CVD apparatus (not shown), and the temperature of the substrate was raised to about 550 ° C. under a vacuum of the order of 10 ⁻⁷ Torr. , Ar partial pressure 65mTorr)
Then, Ar plasma is generated by applying RF of 13.56 MHz using an RF oscillator. RF output at this time is 50W
(About 70 W). Then, a negative voltage of about 50 to 100 V is applied to the substrate, and Ar ⁺ ions collide against the substrate surface to perform sputter cleaning. Sputtering time required for cleaning
About 30 minutes.

When the cleaning with Ar ⁺ ions is completed, Ar gas, R
Stop F output and bias application, and flow SiH ₄ gas to a-S
An i-film (3) is deposited (FIG. 1C). At this time, the substrate temperature was maintained at 550 ° C., and the deposition rate was about 250 ° / m.
Deposit about 3000mm in thickness.

After that, the whole surface of the substrate (the implantation is in the a-Si film (3))
With an acceleration energy of 180 keV and a dose of 7 × 10 ¹⁵ particles / cm ² ,
P ⁺ ions are implanted in three stages under the conditions of an acceleration energy of 100 keV and a dose of 3 × 10 ¹⁵ / cm ^2, and an acceleration energy of 50 keV and a dose of 2 × 10 ¹⁵ / cm ² (FIG. 1D).

Then, an annealing treatment is performed for 12 hours in an electric furnace in a nitrogen atmosphere maintained at 600 ° C. Then, while inheriting the crystal orientation of the seed (1 ′), lateral solid phase growth of 20 μm or more occurs, and the a-Si film (3) is monocrystallized to become a single crystal Si film (3 ′) ( FIG. 1E).

Into this single-crystal Si film (3 '), Si ions as ions inert to the film are implanted under the conditions of an acceleration energy of 200 keV and a dose of 2 × 10 ¹⁵ / cm ² . By this ion implantation, a high-concentration damaged region (3a) is formed near the interface between the SiO ₂ film (2) and the single-crystal Si film (3 ′) (FIG. 1F).

This substrate is annealed again in a nitrogen atmosphere at a substrate temperature of 900 ° C. for 60 minutes. By this annealing treatment, P doped in the single-crystal Si film (3 ') is targeted to the damaged region (3a) and simultaneously diffused outward.

As a result, the impurity concentration on the surface of the single crystal Si film (3 ') becomes
It is reduced to about 10 ¹⁹ cm ^-3 .

Finally, a substrate temperature of 800 ° C. is placed on this single crystal Si film (3 ′).
The MBE (Molecular Beam Epitaxy) method (or CVD method, etc.) is used to epitaxially grow a single crystal Si film (4) inheriting the crystal orientation of the single crystal Si film '3') to a thickness of, for example, 1 μm. (FIG. 1G), an SOI structure is formed.

At this time, the impurity concentration on the surface of the single crystal Si film (3 ') becomes
Since it is reduced to about 10 ¹⁹ cm ^-3, the impurity concentration near the surface of the single crystal Si film (4) is 10 ¹⁴ cm even if auto-doping (or solid phase diffusion) occurs during epitaxial growth.
^-3 can be suppressed.

G) Effects of the present invention As is apparent from the above description, the present invention provides a method for implanting an inert ion into a single crystal Si film which has been solid-phase grown by doping with P, and annealing the single crystal Si film. The impurity concentration on the surface is suppressed to about 10 ¹⁹ cm ⁻³ , and a single-crystal Si film is epitaxially grown on the single-crystal Si film. As a result, the impurity concentration near the surface is reduced to about 10 ¹⁴ cm ^-3 ,
We can provide a substrate with SOI structure suitable for making semiconductor devices,
It can contribute to high integration and improvement of characteristics in a semiconductor integrated circuit.

[Brief description of the drawings]

FIGS. 1A to 1G are process explanatory views of one embodiment of the present invention. (1) ... single crystal Si substrate (single crystal Si base), (1 ') ...
... sheet, ₍₂₎ ...... SiO 2 film (insulating film), (2 ') ...
Opening, (3) ... a-Si base film, (3 ') ... single crystal Si
Film, (4) ... single crystal Si film.

Claims (1)

(57) [Claims] A step of forming an insulating layer on a single crystal Si base having an opening exposing a partial surface of the single crystal Si base; and a step of exposing the single crystal Si base exposed at the opening. A step of forming a P-doped amorphous Si film on the surface and the insulating layer;
A step of forming a film; a step of implanting inactive ions into the single crystal Si film into the film; a step of annealing the substrate into which the inert ions are implanted; And forming a single crystal Si film.