JPH0470771B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a semiconductor substrate in which a silicon epitaxial layer is selectively grown on a single crystal substrate having an insulating film region.

In conventional semiconductor devices, a silicon substrate is made into a desired P-type or N-type conductivity type by using ion implantation or impurity diffusion to become an active element, and isolation between active elements is achieved by using a PN junction or partial oxidation (LOCOS).
was using the law. However, there is an increase in the stray capacitance of the junction and a dimensional change due to the partial oxidation process, which has been an obstacle to increasing the speed and density of devices.

SOS (Si on) is a technology that compensates for the above drawbacks.
There is a method using Sapphire as a substrate. Since the substrate is an insulator, there is little stray capacitance, which is advantageous for increasing the speed of the device. On the other hand, since the substrate and the silicon epitaxial layer are bonded with different types, there are many lattice defects at the substrate-silicon interface due to lattice constant mismatch.
The drawback was the generation of leakage current.

Furthermore, there are graphite epitaxy technology and bridging epitaxy technology as new single crystallization technologies for silicon films on insulating substrates.

The former is Applied Fixtures Letters No. 35.
Volume 1, pages 71-74, 1979 (Applied Physics
Letters, Vol. 35, No. 1, pp. 71-74 1979), a method is described in which a groove is formed on a quartz substrate, a CVD film of polycrystalline silicon is grown on the entire surface of the substrate, and it is made into a single crystal by laser irradiation. That is.

The latter is published in Japan Journal of Applied Physics, Vol. 19, Pages 1, L23-L26, 1980 (Japan Journal of Applied Physics, Vol. 19,
No. 1, ppL23-L26, 1980),
According to this, an insulating film is formed partially on a semiconductor single crystal substrate, a polycrystalline silicon film is further deposited on the entire surface of the substrate, and re-crystallization is performed using the substrate as a seed crystal by laser irradiation. The aim is to form a single crystal layer. However, each method has problems with the degree of single crystallization, crystal defects on the insulating film, etc., and has not reached the point where it has reached the point where device characteristics that can withstand practical use are obtained.

In contrast to these techniques, there is a selective epitaxial technique. In this method, an insulating film is partially formed on a semiconductor single crystal substrate, and epitaxial growth is performed only on the exposed substrate region without depositing on the insulating film, thereby forming the active region of the device. Since this epitaxial method uses homogeneous bonding, it exhibits extremely high quality crystallinity, and has excellent characteristics such as being simple and easy to manufacture in bulk.

However, the substrate used in conventional selective epitaxy is formed by forming an insulating film on a single crystal substrate and then partially opening the insulating film, so the interface between the insulating film and the epitaxial film is affected by interfacial tension. A facet is formed by being strongly affected by For example (100)
The use of a substrate produces a 4-fold symmetrical facet with (113) planes. When a (111) plane substrate is used, a (111) plane with a different orientation appears. When a (110) plane substrate is used, a (111) plane appears. As described above, an insulated gate field effect transistor formed on a substrate with a conventional structure has a drawback that the gate insulating film has a low withstand voltage and wires are easily disconnected due to the unevenness of the surface.

The present invention provides a method for obtaining a selective epitaxy growth substrate that provides an extremely flat surface independent of the orientation of the single crystal substrate, and is based on the following three principles.

The size of the facet is proportional to the epitaxial film thickness. The mechanism is that, as shown in Figure 1 in the case of a 100 substrate, the (100) plane grows at a growth rate α from the lower side of the opening, and near the sidewalls, a facet with a slow growth rate β occurs at the same time as the growth starts. Thereafter, the points X and Y, which are the intersection points of these, move upward and to the right as the child grows, resulting in the development of the facet. In fact, in Figure 1, the (100) plane is y=
Let αt be the facet plane y=(tanθ)x+βt/
If cos θ, facet width W and epitaxial growth film thickness αt
The relationship is W=(tanθ)(1-β/αcosθ)·αt (1), which agrees with the experimental result shown in FIG. 2 in which the facet width W and the epitaxially grown film αt are in a proportional relationship.

The size of the facets depends on the amount of HCl injected. As shown in equation (1), the size of the facet depends on β/α, which indicates the crystal orientation dependence of the growth rate. At the same time, the ratio of growth rate due to crystal orientation is
It also depends on the amount of injection. Figure 3 shows how the growth rate changes as the crystal orientation moves away from the (100) plane growth rate.
This is a view using the amount of HCl as a parameter. The horizontal axis is the angle between the (100) plane and other planes, and the (111)
The plane is about 50 degrees. When HCl is not injected, the ratio of growth rates of (100) and (111) is 0.5, but
When injected at 1.31/min, it decreases to 0.1. Therefore,
The facet becomes larger as the HCl injection amount increases.

In selective epitaxial growth using Sih ₂ Cl ₂ /H ₂ /HCl, the required amount of HCl injection varies depending on the ratio of the total area of the openings to the total area of the wafer. In the SiH ₂ Cl ₂ /H ₂ system, Si does not nucleate near the opening even if HCl is not injected. One reason for this is that HCl, which is formed by decomposition from SiH ₂ Cl ₂ , exists and therefore has a certain degree of selectivity, and the other reason is that there is a reaction between the area near the opening and the top of the field oxide film. It is thought that there is a concentration gradient of the species SiCl ₂ . In any case, the HCl injection is performed on the field oxide away from the opening.
This is necessary to suppress the generation of Si nuclei, and if the opening area increases and the field oxide film portion decreases, the amount of HCl injected can be reduced. In fact, as shown in Figure 4, the horizontal axis represents the ratio σ of the total area of the openings to the total area of the wafer, and the vertical axis represents the selective epitaxial growth (Si
If the minimum amount of HCl injection is taken (no nuclei are generated), the larger the value of ratio σ, the more selective epitaxial growth is possible even with a smaller amount of HCl injection. If the ratio σ is about 0.8 or higher, no injection amount of HCl is necessary.

In actual selective epitaxial growth for device fabrication, a certain level of epitaxial growth film thickness is desired, but the facet is desired to be as small as possible.
Furthermore, the area of the opening is often not so large compared to the area of the entire substrate. In addition to the openings created for the purpose of creating devices based on the above findings, openings not intended for device creation can be created to increase the ratio σ and reduce the amount of HCl injection as much as possible to bring the facet to an acceptable size. It is possible to achieve flat selective epitaxial growth. That is, the relationship between the ratio σ of the total area of the openings to the total area of the wafer and the width W of the facet is as shown in FIG. Changing the epitaxial growth film thickness increases the facet width, but increases the ratio σ and increases the HCl
The injection volume can be reduced and the facet size can be reduced to an almost negligible level for device fabrication. For example, when selective epitaxial growth is performed for the purpose of CMOS, the film thickness is at most 2 μm. In practical terms, the facet width should be about 3000 Å or less to prevent the gate wiring from breaking. At this time, the ratio σ
The desired selective epitaxial growth can be achieved by increasing the HCl injection rate to 50% or more and reducing the HCl injection rate to 0.32/min. The present invention will be explained in detail below based on examples.

FIGS. 6a and 6b are schematic cross-sectional views showing the manufacturing process of a semiconductor substrate manufacturing method according to the present invention in order.

First, a (100) silicon substrate 1 having a resistivity of, for example, about 1 Ω cm is thermally oxidized at 1000°C.
After depositing a SiO ₂ film with a thickness of approximately 2 μm, the sixth
As shown in Figure a, a SiO ₂ film pattern 2 is formed.
An opening 15 used as an active region and an opening 25 for increasing the ratio σ, which is not intended for device fabrication, are formed in this step. Opening 25 is 100μm×
A rectangular pattern of 100 μm was distributed over the entire surface of the substrate. In this substrate, the total area of the openings 15 is 19.6% of the total area of the wafer, but because the openings 25 are provided, the total area is 55%. _{SiH2Cl2 _}
Approximately 1 vol of HCl is added to the gas system consisting of
% and selectively epitaxially grows in the temperature range of 900°C to 1100°C, the single crystal Si film 5 becomes
It does not deposit on the surface of the SiO ₂ film 2, but grows only on the exposed silicon substrate (FIG. 6b). When the facet width was measured after growth, it was approximately 2500 Å.

Furthermore, if selective epitaxy is grown at high temperature, SiO ₂
The film 2 may peel off, but if a thin Si ₃ N ₄ film is formed on the side wall of the SiO ₂ film 2 and then grown, this will not occur. Further, if a thin polysilicon film is formed on the sidewalls and then grown, the facet width becomes smaller, and in the case of the above embodiment, it can be made approximately 2000 Å.

As described above, the present invention increases the ratio of the opening to 50% or more of the total area of the substrate by providing an opening in which no device is fabricated, thereby achieving a flat selective epitaxial layer that could not be obtained conventionally. Provides a method for obtaining a grown film,
Its industrial value is great.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram for explaining the process of forming a facet. FIG. 2 is a diagram showing experimental results regarding the relationship between epitaxial film thickness and facet width W. Figure 3 is based on the growth rate of the (100) plane,
This is a diagram showing how the growth rate changes as the crystal orientation moves away from it, using the amount of HCl as a parameter. FIG. 4 is a diagram showing the relationship between the ratio of the total area of openings to the total area of the wafer and the minimum amount of HCl implanted for selective epitaxial growth. FIG. 5 is a diagram showing the relationship between the area ratio and the facet width W, and the HCl injection amount is the minimum HCl amount with respect to the ratio in FIG. 6a and 6b are schematic cross-sectional views for explaining the manufacturing process of a semiconductor substrate in the present invention, where 1 is a (100) silicon substrate, 2 is a SiO ₂
Insulating film pattern 5 is single crystal silicon grown selectively epitaxially. 15 is an opening used as an active region, and 25 is an opening not intended for device fabrication.

Claims (1)

[Claims] 1. An insulating film is provided on a silicon single crystal substrate, then an opening is provided in the insulating film to expose the substrate single crystal silicon, and then chlorosilane is flowed to selectively epitaxially grow a silicon film in this opening. A method for manufacturing a semiconductor substrate, characterized in that the selective epitaxial growth is performed by increasing the ratio of the opening to the total area of the substrate to 50% or more by providing an opening in which no device is to be formed. .