JP2647927B2 - Selective epitaxial growth method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION a) INDUSTRIAL APPLICABILITY The present invention is selectively forming a SiO ₂ film monocrystalline Si substrate, only on the portion where no Si substrate surface of SiO ₂ film is exposed And a selective epitaxial growth method for selectively growing a single crystal Si film.

B) Conventional technology A single-crystal Si layer formed on an insulating layer (including an insulating substrate) is called an SOI (Silicon on Insulator) structure, which enables easy element isolation in a narrow area and high integration. It is known that speeding up and speeding up are possible. And the traditional
Compared to semiconductor integrated circuits (ICs) in which devices are fabricated on a Si substrate, research and development are being actively conducted because the characteristics can be improved.

As a method for forming a single-crystal Si film on an insulating layer, there is a solid-phase epitaxial growth method, in which a part of the Si substrate surface is exposed as a seed on a single-crystal Si substrate to form an insulating film, and the seed is formed. Amorphous Si (hereinafter referred to as a-Si) film is deposited on the insulating film and then annealed at a low temperature of about 600 ° C., thereby allowing the a-Si film to be monocrystallized by solid phase growth in the lateral direction. It is to let.

However, in this solid phase growth, the single crystallization of the a-Si film proceeds preferentially in the <100> direction in the lateral direction, so that vertical growth from the seed to the upper side is required prior to the lateral growth. In the solid phase epitaxial growth, the thickness of the a-Si film on the seed cannot be increased, and therefore, the step between the seed and the surface of the insulating film cannot be made too large.

However, when the a-Si film is thin and the step between the seed and the insulating film surface is large (the insulating film is thick), the deposited a
-Since the step break occurs at the boundary between the insulating film and the seed in the Si film, or even if the step does not occur, the internal stress at the step becomes large, so that the solid phase growth in the lateral direction hardly occurs,
If it does, the lateral growth distance will be small.

For this reason, the step between the seed and the surface of the insulating film must be as small as possible, that is, the insulating film needs to be thinner, and usually has a thickness of 1000 mm.
It is formed below.

However, when configuring a three-dimensional circuit element with a stacked SOI structure, a device is formed under the insulating film layer.In consideration of protection for stabilizing the device structure, wiring, and electrical characteristics, an insulating material is required. A film having a thickness of 1 μm or more is required.

So, for example, "SELECTIVE EPITAXIAL GROWTH OF SI
LICON BY CVD AND ITS THERMODYNAMIC CONSIDERATION ''
(PROCEEDING OF THE TENTH INTERNATIONAL CONFERENCE
ON CHEMICAL VAPOR DEPOSITION 1987, Proceeding Vol.
87-8, PP.379-388).
SiH ₂ Cl ₂ -HCl-H is deposited on the single crystal Si substrate on which the iO ₂ film is formed.
950 ℃ at normal pressure by normal pressure CVD or low pressure CVD method of _2.
Substrate temperature of 850 ° C to 950 ° C,
Selective Epitaxial Grow to grow a single crystal Si film only on the exposed Si substrate surface
th: SEG) method is being considered.

The SEG method using a chlorine-based gas involves a single-crystal Si film and a Si film on an exposed substrate surface due to thermal decomposition of a silane-based gas.
O and the polycrystalline Si film deposited on the ₂ film, cause the etching by HCl to Si film by these simultaneously formed, the etching rate by utilizing the fact also is larger polycrystalline Si film of monocrystalline Si film Thus, the deposition of the Si film on the SiO film is eliminated.

C) Problems to be Solved by the Invention However, in the above-described SEG method using a chlorine-based gas, etching is performed by cutting Cl radicals, which are considered to be etchants, by attacking and breaking Si-Si bonds or Si-O bonds. Due to this etching, many defects occur near the surface of the deposited single crystal Si film and the surface of the polycrystalline Si film. Further, a-Si is further added on the Si film formed by the SEG method.
When a film is deposited and this a-Si film is grown by solid phase epitaxial growth, Cl atoms remaining in the a-Si film are mixed and crystallization is hindered. Then, the lateral growth distance is shortened, and as a result, a substrate having a large-area SOI structure cannot be obtained.

Furthermore, the life of a CVD apparatus (particularly, a low pressure CVD apparatus) is shortened.

The present invention has been made in view of such a point, and provides a SEG method for epitaxially growing a single crystal Si film only on an exposed single crystal Si substrate without using a chlorine-based gas. is there.

D) Means for Solving the Problems The present invention provides an insulating film formed on a single-crystal Si base, and an opening for exposing the surface of the single-crystal Si base is formed in the insulating film. only single-crystal Si layer on the single-crystal Si base portion exposed to a selective epitaxial growth method of selectively epitaxially grown by low pressure chemical vapor deposition by thermal decomposition of SiH ₄ in the formed opening portion, When the substrate temperature is plotted on the horizontal axis and the SiH ₄ gas partial pressure is plotted on the vertical axis, the substrate temperature is 890 ° C, the SiH ₄ gas partial pressure is 0 mTorr, and the substrate temperature is 950 ° C, the SiH ₄ gas partial pressure is 20 mTorr. the line passing through the two points as a boundary line, and performs pressure chemical vapor deposition by thermal decomposition of SiH ₄ at a substrate temperature and the SiH ₄ gas partial pressure of high side range temperature of the boundary line.

E) Action Originally, the surface of the insulating film, SiO ₂ , has fewer dangling bonds of Si than the surface of single crystal Si, so the number of kink sites to which surface adsorbed species (Si) during the reaction are bonded is small, Crystal Si nuclei hardly occur on the SiO ₂ surface. Therefore, when the base temperature is sufficiently increased, surface migration of the surface adsorbed species becomes intense, and it becomes difficult for the surface adsorbed species to be adsorbed on the kink sites. Further, by setting the partial pressure of the SiH ₄ gas to a sufficiently high degree of vacuum, the possibility that the surface adsorbed species during the surface migration is exhausted before adsorbing to the kink site is increased.

Thus, by setting the base temperature and the SiH ₄ gas partial pressure in the above ranges, the Si film does not grow on the insulating film, and the single crystal Si base exposed from the opening is formed. Only in this case, a single-crystal Si film is epitaxially grown.

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

(1) is a single crystal Si substrate as a single crystal Si base having a (100) plane as a main surface, and a film thickness of 1 μm as an insulating film on the surface thereof.
The SiO ₂ film (2) is formed by thermal oxidation or CVD (FIG. 1A). Then, an opening (2a) for exposing the surface of the Si substrate as a seed is selectively formed on the SiO ₂ film (2) by a known photolithography technique (FIG. 1B).

Next, the substrate having the patterned SiO ₂ film (2) is heated to 940 ° C. by an infrared lamp in a vacuum having a degree of vacuum higher than 1 × 10 ⁻⁶ Torr, and the temperature is kept constant. Ar gas was introduced at a flow rate of 150 cc / min and the Ar pressure was 65 mTorr.
And perform Ar sputtering to clean the substrate surface
Minutes (FIG. 1C). At this time, for example, the RF frequency is 1
A DC bias of -100 V is applied to the substrate at 3.56 MHz and an output of 50 W.

After cleaning the surface, stop supplying Ar gas while keeping the substrate temperature at 940 ° C, turn off RF and DC bias, supply SiH ₄ gas at a flow rate of 4 sccm at a pressure (partial pressure) of 13 mTorr, and open holes. The single crystal Si film (3) is selectively epitaxially grown only on the surface of the Si substrate (seed portion (1a)) exposed from the portion (2a). This single crystal Si film (3)
A film is grown to the same thickness as the O ₂ film (2) (FIG. 1D).

Subsequently, the supply of SiH ₄ gas was stopped while the substrate temperature was kept in the reaction chamber of the vapor phase growth apparatus where the selective epitaxial growth was performed, and the substrate temperature was reduced to 550 ° C. in a vacuum having a degree of vacuum higher than 1 × 10 ⁻⁶ Torr. After lowering the flow rate of Ar gas again, 500cc / mi
n, supply to Ar partial pressure 200mTorr, output 13.56MHz RF 70W
And apply a DC bias of -50 V to the substrate to clean the substrate surface by Ar sputtering for 10 minutes (first example).
Figure E).

When the surface cleaning is completed,
While maintaining the 550 ° C., to stop the supply of the Ar gas flow rate turn off the RF and DC bias, the SiH ₄ gas into the reaction chamber 20
An a-Si film (4) is deposited to a thickness of 6000 ° (growth rate 200 ° / min) on the surface of the substrate by supplying 0 sccm and a partial pressure of 6 (or 7) Torr (FIG. 1F).

Thereafter, Ar gas is introduced into the reaction chamber to exhaust the remaining SiH ₄ gas, and then the chamber is evacuated to lower the temperature to room temperature. Then, using an annealing apparatus, by performing an annealing process at a temperature of 600 ° C. for 12 hours in an atmosphere of atmospheric pressure N ₂ ,
The solid phase epitaxial growth of the a-Si film (4) is performed,
-A single-crystal Si film (4 ') is obtained by single-crystallizing the Si film (4) (FIG. 1G).

Now, in the step shown in FIG. 1D, SEG is performed, but a single-crystal Si film (3) for depositing an a-Si film (4)
If there are many defects on the surface, the delay time from the start of annealing of the a-Si film to the occurrence of solid phase growth becomes long, and the lateral epitaxial growth distance of the a-Si film becomes short. Further, when polycrystalline Si nuclei are generated on the SiO ₂ film (2), polycrystalline nuclei for preventing epitaxial growth are generated quickly, so that the lateral epitaxial growth distance of the a-Si film also becomes short. Therefore, in the process of FIG.
Need to do SEG.

FIG. 2 is a diagram showing the relationship between the substrate temperature and the SiH ₄ gas partial pressure when SEG occurs and does not occur. Open circles indicate the case where the single-crystal Si film epitaxially grows only on the Si substrate, and the Si film does not deposit on the SiO ₂ film (that is, SEG occurs), and black circles indicate that the single-crystal Si film epitaxially grows on the Si substrate. 3 shows a case where a Si film is deposited also on the SiO ₂ film (that is, no SEG occurs).

As can be seen from FIG. 2, the base temperature is plotted on the horizontal axis and the SiH ₄ gas partial pressure is plotted on the vertical axis. The substrate temperature is 890 ° C., and the SiH ₄ gas partial pressure is 0 mT.
A line passing through the point a of the orr and the point b of the substrate temperature of 950 ° C. and the SiH ₄ gas partial pressure of 20 mTorr is defined as a boundary line, and the substrate temperature and the SiH ₄ gas partial pressure in the range of higher temperature from the boundary line SEG is realized only when the pressure is reduced and the vapor phase growth is performed.

This is because if the base temperature is set high enough, the surface migration of the surface adsorbed species will become intense, making it difficult for the surface adsorbed species to be adsorbed on the kink sites, and the partial pressure of the SiH ₄ gas must be set to a sufficiently high vacuum. Therefore, there is a high possibility that the surface adsorbed species during the surface migration is exhausted before adsorbing to the kink site.

Thus, by setting the base temperature and the partial pressure of the SiH ₄ gas in the range shown by the oblique lines in FIG. ₂ , the Si film is not deposited on the SiO ₂ film, and the Si film is deposited only on the single crystal Si substrate. The film is deposited, ie
SEG is performed.

G) Effects of the Invention As is clear from the above description, the present invention provides a substrate temperature SiH ₄
By controlling the gas partial pressure, SEG can be performed without using chlorine gas. Therefore, generation of defects in the single crystal Si film serving as a seed for solid phase epitaxial growth can be suppressed, and the chance of impurities being mixed into the a-Si film can be reduced. As a result, when the a-Si film is subjected to solid phase epitaxial growth, the growth distance in the lateral direction can be extended, and a large-area SOI structure substrate can be provided.

Further, since a chlorine-based gas is not used, it contributes to extending the life of a growth apparatus such as a low-pressure CVD apparatus.

[Brief description of the drawings]

FIGS. 1A to 1G are diagrams for explaining the steps of an embodiment of the present invention, and FIG. 2 is a diagram showing conditions for realizing SEG. (1) Single crystal silicon substrate (1a) Seed (2)
... SiO ₂ film (insulating film), (2a) ... aperture, (3) ... single crystal Si film, (4) ... a-Si film, (4 ') ... single crystal Si
film.

Claims (1)

(57) [Claims] An insulating film is formed on a single-crystal Si base, and an opening for exposing the surface of the single-crystal Si base is formed in the insulating film. In the opening formed in the insulating film, in the selective epitaxial growth method for only the single-crystal Si layer on the single-crystal Si base portion exposed selectively epitaxially grown by low pressure chemical vapor deposition by thermal decomposition of SiH _4, the horizontal axis base temperature, SiH ₄ When the gas partial pressure is plotted on the vertical axis, a line passing through two points, a substrate temperature of 890 ° C and a SiH ₄ gas partial pressure of 0 mTorr, and a substrate temperature of 950 ° C and a SiH ₄ gas partial pressure of 20 mTorr is defined as a boundary line. A selective epitaxial growth method, comprising performing reduced-pressure vapor growth by thermal decomposition of SiH ₄ at a substrate temperature in a higher temperature range from the boundary and a SiH ₄ gas partial pressure.