JPH04335519A - Manufacture of semiconductor crystal - Google Patents

Abstract

PURPOSE:To form a mixed crystal thin film of high Ge concentration with little crystal defect in regard to epitaxial growth of GeSi mixed crystals by vapor growing method. CONSTITUTION:In a vapor growing method to epitaxially grow mixed crystal semiconductor crystals consisting mainly of silicon and germanium on substrate crystals, first crystal thin layers rich in silicon and second crystal thin layers rich in germanium grown within a time (period in the drawing where a crystal thin film is not grown) to grow lamellarly are piled up alternately. Semiconductor crystals manufactured by the above-mentioned method are heat-treated by diffusion to change into mixed crystals consisting mainly of germanium and silicon.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the manufacture of semiconductor crystals by epitaxially growing a mixed crystal of germanium and silicon (hereinafter referred to as GeSi mixed crystal) by a vapor phase growth method.

Heteroepitaxially grown GeSi
Mixed crystals are used in hetero bipolar transistors, HEMTs (H
high electron mobility
It is expected to be used as a material that dramatically improves the performance of optical semiconductor devices (Sistor) and optical semiconductor devices.

Mixed crystals used in such semiconductor devices are required to have a precise structure and perfect crystallinity.
It is necessary to be able to control the composition ratio over a wide range. For this reason, GeSi can be grown over a wide range of compositions using epitaxial vapor phase epitaxy, which can precisely grow thin layers with good crystallinity.
There is a need for a method of producing mixed crystals.

0004

2. Description of the Related Art A conventional method for manufacturing GeSi mixed crystal by vapor phase growth will be explained with reference to FIG.

FIG. 4 is an explanatory diagram of an embodiment of the conventional method.
It shows the relationship between the composition of a mixed crystal deposited by the D method (chemical vapor deposition method) and the composition ratio of the source gas. In FIG. 4, the composition of the mixed crystal represents the molar ratio of Ge, and the composition ratio of the source gas represents the volume ratio of germane to the source gas consisting of disilane and germane.

Conventionally, a GeSi mixed crystal having the required thickness and composition required for device formation was grown all at once. However, such a mixed crystal thin film grows in a layered manner only in the range where the composition is constant with respect to the raw material gas composition, as shown in FIG.

[0007] T500, T550, T60 in FIG.
0 represents those grown at 500°C, 550°C, and 600°C, respectively. As is clear from FIG. 4, the composition of the mixed crystal grown under layered growth conditions is such that the lower the growth temperature, the higher the germanium concentration. However, if the growth temperature is lowered to increase the germanium concentration,
The growth rate is significantly reduced.

This disadvantage can be avoided by increasing the germane concentration of the source gas. That is, under such conditions, referring to FIG. 4, a mixed crystal with a high germane concentration can be grown at high speed.

However, under such conditions, the layer does not grow, but grows as an integrated thin film after initial island-like growth. Therefore, a large number of crystal defects are introduced.

0010

[Problem to be solved by the invention] In conventional epitaxial vapor phase growth of GeSi mixed crystal, in order to grow a mixed crystal with a high germanium concentration, the growth temperature must be lowered, resulting in a slow growth rate. It has the disadvantage of becoming.

[0011] Furthermore, under conditions that allow high-speed growth of crystals with a high germanium concentration, island-like growth occurs, which has the disadvantage of deteriorating crystal quality. SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a semiconductor crystal in which a GeSi mixed crystal with a high germanium concentration is grown in a layered manner by a vapor growth method to form an epitaxial thin film with few crystal defects.

0012

[Means for Solving the Problems] In order to solve the above problems, the first aspect of the present invention is to use a vapor phase growth method for epitaxially growing a mixed crystal semiconductor crystal mainly composed of silicon and germanium on a substrate crystal. , a first silicon-rich crystal thin layer and a germanium-rich second crystal thin layer are alternately stacked, and the first and second crystal thin layers are grown such that each of the crystal thin layers is characterized by having a thickness grown within a time period of layered growth, and
The present invention is characterized in that the semiconductor crystal manufactured by the method of the first configuration is subjected to diffusion heat treatment to form a mixed crystal containing germanium and silicon as main components.

[0013]

[Operation] Figure 1 is a diagram explaining the principle of the present invention, and shows the thickness of a crystal thin film that grows within a certain growth time from the start of growth under growth conditions that result in island-like growth in the conventional vapor phase growth method. There is.

A10, A4, and A1 in FIG. 1 are the results when a Ge crystal layer was grown by flowing hydrogen gas containing 10% germane as a raw material gas at 10 cc/min, 4 cc/min, and 1 cc/min, respectively. represents.

Although FIG. 1 shows the results at a growth temperature of 550°C, similar results were also observed at 500°C. Figure 1
It is clear from this that there is an incubation period during which no crystal growth is observed for a certain period of time after the start of growth. and,
After a certain incubation period, crystal growth proceeds at a rapid rate.

[0016] The inventor of the present invention has discovered that several nm during the above-mentioned incubation period.
The experiment revealed that the following thin layers grow in a layered manner. In other words, it was confirmed by X-ray diffraction that the epitaxial layer, which was grown by repeating the cycle of flowing germane gas only during the incubation period and then growing a silicon layer, had a superlattice structure that suggested layered growth. Furthermore, it was confirmed through transmission electron microscopy that the composition had periodic fluctuations corresponding to the above-mentioned superlattice structure.

[0017] In heteroepitaxial growth, the fact that thin crystals grow in a layered manner at the initial stage of growth, and then changes to island-like growth when the crystal grows beyond a certain thickness, is called MBE.
This is known as the Strawskii-Klatanov growth mechanism.

The inventors of the present invention believe that this growth mechanism
The existence of vapor phase growth of Ge mixed crystals was also confirmed. The present invention was devised based on the above facts.

In the first configuration of the invention, the germanium-rich crystals are deposited within the latent period, ie, during the time during which they grow in layers. Therefore, island-like growth does not occur. Furthermore, by successively growing crystals with a low germanium concentration, the thin layer with a high germanium concentration that had grown within the incubation period was stabilized. This prevents the transition to.

[0020] In this way, by creating a multilayer structure in which layers with high germanium concentration and layers with low germanium concentration are grown alternately,
A thick epitaxial layer including a thin layer with a high germanium concentration can be stably formed.

[0021] The epitaxial layer manufactured by this structure has fewer crystal defects because it is grown in a layered manner. Furthermore, since layered growth can be performed at higher temperatures than in the MBE method, high quality crystals can be obtained.

Furthermore, since the ratio of the thickness of the layer with high germanium concentration and the layer with low germanium concentration can be controlled accurately and easily by controlling the growth time, it is possible to control the germanium concentration of the epitaxial layer over a wide range and precisely. can.

Note that the incubation time can be easily shortened by, for example, increasing the concentration of the raw material gas. Therefore, a method for rapidly switching the growth of the above two types of layers,
For example, high-speed growth can be easily achieved using the pulse jet method.

Therefore, by this method, crystals with a high germanium concentration can be grown at high speed and in a layered manner. In the second configuration of the present invention, an epitaxial layer in which layers with a high germanium concentration and a layer with a low germanium concentration are grown alternately is heat treated to diffuse Ge and Si, thereby making the epitaxial layer a mixed crystal with a uniform composition.

Since the alternately grown layers in the epitaxial layer can be easily made thin and have a period of several tenths of a nanometer, for example, they can be made to have a uniform composition even by heat treatment at a low temperature and for a short time.

According to this method, a layered crystal with few crystal defects is treated at a low temperature, so that a GeSi mixed crystal with extremely few defects can be produced. Furthermore, the ability to perform low-temperature processing has the effect of facilitating device formation.

Of course, as in the first configuration, the germanium concentration can be precisely controlled over a wide range.

[0028]

EXAMPLES The present invention will be explained with reference to examples. The vapor phase growth apparatus used was a low-pressure CVD apparatus that grows a multilayered crystal by switching a carrier gas and two types of raw material gases at high speed.

The substrate used was a silicon wafer with a plane orientation of (001) that was oxidized by immersing it in a mixture of sulfuric acid and hydrogen peroxide, and then the oxide film was removed using a hydrofluoric acid aqueous solution. First, the substrate was placed in the CVD equipment and the pressure was 10 mmHg.
A heat treatment is performed at approximately 900° C. for 10 minutes in a hydrogen atmosphere to remove the natural oxide film on the surface.

[0030] Next, the temperature is lowered to 550°C, maintained at this temperature, and growth is performed in the following procedure. FIG. 2 is a sequence explanatory diagram of an embodiment of the present invention, showing the growth procedure in time series of source gas and carrier gas.

First, referring to FIG. 2, the inflow H0 of carrier gas H2 is stopped. Then, for example,
Germane (Ge) is added to hydrogen carrier gas at a pressure of 10 mmHg.
The raw material gas for Ge layer growth mixed with
cc inflow G1 to grow a germanium crystal thin film.

The growth time is within the incubation period, for example 10 seconds when the incubation period is 15 seconds. In addition, the incubation period is 1 minute when the flow rate of the raw material gas is 4 cc per minute, and 1 c per minute.
It was 2 minutes at c.

[0033] If the incubation period is long, the time required for one growth cycle becomes longer, and growth becomes slower. Also, if the length is too short, it will be difficult to switch gases. Since the incubation period can be controlled by the concentration of the raw material gas, it can be set to an appropriate period taking into consideration the equipment, etc.

Next, hydrogen carrier gas is introduced H1a for 10 seconds for purging. Then, for example, a pressure of 10 mm
A silicon crystal thin film is grown by flowing a raw material gas for Si layer growth, which is a mixture of Hg hydrogen gas and disilane (Si2H6), at a rate S1 of 10 cc per minute.

Next, hydrogen carrier gas is introduced H1b for 10 seconds for purging. After that, the cycle from the growth of the germanium crystal thin film to the growth of the silicon crystal thin film and the verging is repeated, for example, for about 300 nm.
An epitaxial layer of m thickness is grown.

Since the epitaxial layer manufactured by the above process had a mirror surface, it was confirmed that the epitaxial layer was grown in a layered manner. Note that in the present invention, one of the source gases may be one for growing a crystal containing germanium, and is not limited to one for growing a germanium crystal.

FIG. 3 is an explanatory diagram of the results of an example of the present invention, showing the distribution of the Ge composition ratio of the epitaxial layer in the thickness direction. The Ge composition was determined from the density of the transmission electron microscope image.

In FIG. 3, a shows a silicon crystal thin film grown for 2 minutes in the above example, and b shows a film grown for 1 minute. In addition, c is after growing a silicon crystal thin film for 20 seconds and growing an epitaxial layer at 700℃, 1
It was subjected to diffusion heat treatment for 0 minutes.

A periodic compositional variation in thickness corresponding to the growth cycle was observed, indicating that an epitaxial layer with a multilayer structure was grown in accordance with the growth time. This multilayered structure was confirmed by X-ray analysis.

Furthermore, the fact that the peak Ge concentrations are approximately the same for a and b suggests that crystal thin films having the same concentration and thickness were grown. The result of c is Ge0.6
A mixed crystal epitaxial layer of Si0.4 has been manufactured, and it has been shown that when the period of the multilayer structure is short, a mixed crystal with a uniform composition can be easily formed by low-temperature diffusion heat treatment.

[0041] Furthermore, according to the present invention, G can be easily produced at a high concentration.
A GeSi mixed crystal containing e can be manufactured.

[0042]

Effects of the Invention According to the present invention, a thin crystal layer containing a high concentration of germanium can be grown rapidly in a layered manner by a vapor phase growth method. This makes it possible to manufacture crystals precisely and quickly, which greatly contributes to improving the performance of semiconductor devices.

[Brief explanation of drawings]

[Figure 1] Diagram explaining the principle of the present invention

[Figure 2] Example sequence explanatory diagram of the present invention

[Figure 3]
Explanatory diagram of the results of examples of the present invention

[Figure 4] Illustration of an example of the conventional method

[Explanation of symbols]

A1, A4, A10 raw material gas flow rate is 1 and 4 respectively
, Result at 10 cc/min H0 , H1a, H1b, ~ Hydrogen gas inflow G1
, G2 , ~ Inflow S of hydrogen gas mixed with germane
1, S1, ~ Inflow of hydrogen gas mixed with disilane T500, T550, T600 Results at growth temperatures of 500, 550, and 600°C, respectively

Claims (2)

[Claims] Claim 1: In a vapor phase growth method for epitaxially growing a mixed crystal semiconductor crystal mainly composed of silicon and germanium on a substrate crystal, a first crystal thin layer rich in silicon and a second thin crystal layer rich in germanium are used. A semiconductor characterized in that the first and second thin crystal layers have a thickness that is grown within the time period for each of the thin crystal layers to grow in a layered manner. Method of manufacturing crystals. 2. A method for manufacturing a semiconductor crystal, comprising subjecting the semiconductor crystal manufactured by the method according to claim 1 to a diffusion heat treatment to form a mixed crystal containing germanium and silicon as main components.