JPH0427116A - Method of forming semiconductor heterojunction - Google Patents

Abstract

PURPOSE:To enable a thin and high-quality epitaxial growth layer to be formed while control ling a growth layer thickness accurately by forming an intermediate layer of a specific sub stance at a temperature which is lower than a growth temperature and then increasing the temperature to a growth temperature before performing the gaseous phase epitaxial growth of a second semiconductor substance. CONSTITUTION:A single crystal 3 with a second semiconductor substance which is different from a first substance is allowed to the gaseous phase epitaxial growth on a substrate 1 which consists of a first semiconductor single crystal. Before performing the gaseous phase epitaxial growth of the second semiconductor substance, the first substance, the second sub stance, and an organic metal compound or a halogen compound of a substance which is selected from a group consisting of a mixed substance of the first and second substances and a third semiconductor substance which conforms to a crystal of the substrate crystallographically are absorbed onto the substrate surface from the reaction gas of that raw material. At the same time, an intermediate layer 2 of a substance which is selected by thermal degradation reaction of the absorbed substance is formed. After that, after increas ing the temperature to a specified epitaxial growth temperature, the second semiconductor substance is subjected to gaseous phase epitaxial growth onto an intermediate layer from the reaction gas of that raw material.

Description

[Detailed Description of the Invention] [Summary] A semiconductor heterojunction is formed by vapor phase epitaxial growth of a single crystal of a second semiconductor material different from the first material on a substrate made of a single crystal of a first semiconductor material. Regarding the formation method, the purpose is to form a thin, high-quality epitaxial growth layer with good reproducibility and with precise control of the growth layer thickness.
a third semiconductor material that is crystallographically matched to the crystals of the substrate at a temperature below its epitaxial growth temperature; The structure is such that an organometallic compound or a halogenated compound of the selected substance is adsorbed onto the surface of the substrate from the raw material reaction gas, and an intermediate layer of the selected substance is formed by a thermal decomposition reaction of the adsorbed substance.

[Industrial application field]

The present invention relates to a method for forming a semiconductor heterojunction, and more specifically, the present invention relates to a method for forming a semiconductor heterojunction, and more particularly, the present invention relates to a method for forming a semiconductor heterojunction, and more particularly, a method for forming a single crystal of a second semiconductor material different from the first semiconductor material on a substrate comprising a single crystal of a first semiconductor material by vapor phase epitaxial growth. The present invention relates to a method for forming a semiconductor heterojunction.

The present invention particularly relates to improvements in a vapor phase processing method for heterojunctions using a semiconductor such as silicon as a substrate.

[Conventional technology]

It is well known that devices such as hetero-bipolar transistors (HBTs) are currently being developed using heterojunctions in which a mixed crystal with germanium is grown on a silicon substrate. Such ultra-high-speed, ultra-high-integration devices require ultra-precise and highly perfect crystal growth technology.

Although vapor phase processing has become an indispensable technology for manufacturing single conductors such as silicon, it has not necessarily been perfected in this respect. For example, the vapor phase growth method includes a process involving a chemical reaction between the vapor phase and the surface phase, that is, the surface of the semiconductor substrate, so the raw material is often used in a gaseous state, and therefore the process A chemical reaction process intervenes, and it is necessary to control this process. However, in particular, it is generally not easy to epitaxially grow a different material on a substrate.

By the way, when producing HBTs, superlattices, etc., molecular beam epitaxial growth (MBE) can be used as a crystal technology. It is also known that heterojunctions with a superlattice structure can be achieved by controlling the growth rate on an atomic layer basis by measuring the signal intensity of electron beam diffraction. However, although MBE is a crystal growth technique with extremely precise structure, from a practical point of view, the quality of the crystal is inferior.
That is, it has the drawback that the density of defects is high and uncontrolled. Another disadvantage is that productivity is poor, such as the inability to process a large number of large substrates. Although the vapor phase growth method has good quality growth layers and excellent productivity, the current situation is that the technology for forming precise structures when forming heterogeneous composites of semiconductors has not yet been perfected. be. For example, in the vapor phase growth method of silicon, it is difficult to grow at low temperature, and it is also difficult to grow precisely.

[Problem to be solved by the invention]

We will consider the problems when heterogeneously growing a germanium layer on a silicon substrate.

It is known that a heterojunction can be formed when the germanium layer has a large thickness. However, lattice defects are introduced into such a thick crystal layer at an extremely high density, and it is not a practical crystal.

- To give an example, FIG. 5 is a graph showing the results of an experiment in which the inventors hetero-grown a germanium layer on a silicon substrate. In one experiment, the raw material germane (
GeL) gas was supplied at 10-1500 °C, and in the other experiment GeH4 gas was supplied at 10 ml 1.430 °C. From this graph, it is understood how the thickness of the grown layer changes over time at the very early stage of growth when germanium is vapor-phase treated using silicon as a substrate. At the beginning of growth, there is a so-called latent time that is not measured as a growth layer. Although it is possible to grow a thick germanium layer relatively easily, as the film thickness becomes thinner, it is very difficult to obtain a grown layer of, for example, 100 Å or less, and the reproducibility is extremely low. Therefore, it is extremely difficult to apply this vapor phase growth method to the production of crystals for devices that utilize quantum effects such as superlattices. This difficulty cannot be overcome simply by optimizing the growth conditions, such as lowering the growth temperature or lowering the concentration of source gas.

Therefore, an object of the present invention is to enable formation of a thin, high-quality epitaxial growth layer with good reproducibility and precise control of the growth layer thickness when forming a semiconductor heterojunction.

[Means to solve the problem]

According to the present invention, the above-mentioned object is achieved by applying a second semiconductor material different from the first material onto a substrate consisting of a single crystal of a first semiconductor material.
In a method for forming a semiconductor heterojunction by vapor phase epitaxial growth of a single crystal of a second semiconductor material, before performing vapor phase epitaxial growth of a second semiconductor material,
At a temperature lower than the epitaxial growth temperature, a semiconductor material comprising the first material, a second material, a mixture of the first and second materials, and a third semiconductor material that is crystallographically matched to the crystals of the substrate. An organometallic compound or a halogenated compound of the selected substance is adsorbed onto the surface of the substrate from the reaction gas as its raw material, and an intermediate layer of the selected substance is formed by a thermal decomposition reaction of the adsorbed substance, and then an intermediate layer of the selected substance is formed at a predetermined epitaxial growth temperature. This can be achieved by a method for forming a semiconductor heterojunction, characterized in that the second semiconductor material is vapor-phase epitaxially grown on the intermediate layer from its source reactant gas after the temperature is raised to .

In carrying out the method of the invention, the second semiconductor material is different from the first semiconductor material. That is, the second substance
The first substance may be a substance that is essentially different from the first substance, or it may be a mixed crystal containing only a portion of the first substance. The material forming the intermediate layer may be any one of the first semiconductor material, the second semiconductor material, a mixture of the first and second semiconductor materials, or a third semiconductor material that is crystallographically matched to the substrate crystal. It may be. The intermediate layer can be grown as a monolayer or as a few atomic layers.

In one aspect of the present invention, an organometallic compound or a halide compound of germanium is added to the surface of a substrate having a silicon single crystal in at least a surface layer at a temperature lower than the epitaxial growth temperature of germanium using a reaction gas as a raw material thereof. For example, Ge(C,H6)2H, Ge1a, etc. are adsorbed to form a germanium intermediate layer, and then, after raising the temperature to the epitaxial growth temperature of germanium, germanium is adsorbed from its raw material reactive gas, such as GeH4.
The germanium intermediate layer is grown on the germanium intermediate layer by vapor phase epitaxial growth. Here, "a substrate having at least a silicon single crystal in its surface layer" refers to a substrate made of a silicon single crystal, or a substrate made of something other than silicon and whose surface is covered with silicon. .

In another aspect of the present invention, a silicon single crystal is epitaxially grown on a substrate made of an insulating material such as sapphire, and SOI, (si
on the surface of the silicon-on-sapphire) substrate,
At a temperature lower than the epitaxial growth temperature of germanium, an organometallic compound or a halide compound of germanium is adsorbed from the raw material reaction gas to form an intermediate layer of germanium, and then, after raising the temperature to the epitaxial growth temperature of germanium, germanium is The method is characterized in that vapor phase epitaxial growth is performed on the germanium intermediate layer from a reactant gas as a raw material. The SOI substrate can be manufactured according to a method commonly used in the semiconductor manufacturing field.

In silicon vapor phase growth, it is known that immediately before epitaxial growth, the oxide film is removed by heat treatment at a high temperature of about 900°C in a hydrogen stream, and then the silicon is cooled to a predetermined growth temperature. .

In the present invention, between these two steps, as an intermediate treatment, an organometallic compound of germanium or a halogenated compound, which is adsorbed on the silicon surface at low temperature, is brought into contact. That is, an important point of the present invention is to form a germanium layer by thermal decomposition of an organic compound or the like prior to growth using germane gas, and to change the state of silicon on the substrate surface.

It is difficult to epitaxially grow germanium on a sapphire substrate. In this case, silicon is grown in advance by several atomic layers, and then germanium is grown. The properties of semiconductor crystals are highly sensitive to impurities and defects.

Therefore, even if an intermediate crystal layer is provided, it is necessary that it does not have any adverse effects. but,
The combination of germanium and silicon is practical because they are both group IV elements and do not become electrically active impurities.

In such a case, in order to precisely grow the crystal, a method using a reactive gas having an adsorption effect is used, as in the case described above.

[For production]

As previously explained with reference to FIG. 5, when germanium is vapor-phase grown on a silicon substrate according to the conventional method, a latent period during the initial stage of growth cannot be avoided. This is because hydrogen terminates dangling bonds of atoms on the substrate surface during high-temperature heat treatment of the substrate surface, and it takes time to replace this hydrogen with germane gas. In the present invention, in order to eliminate the incubation time,
We propose to eliminate the state in which silicon atoms are terminated with hydrogen, for example to deposit even one atomic layer of germanium.

When germanium is grown on a germanium intermediate layer (buffer layer), there is no incubation time as described above. Furthermore, since there is no incubation time, the thickness of the grown layer can be precisely controlled.

〔Example〕

FIG. 1 is a cross-sectional view showing an example of a semiconductor heterojunction formed according to the present invention. In the figure, the first semiconductor material is silicon, designated by the reference number 1, and the second semiconductor material is germanium, designated by the reference number 3. A germanium intermediate layer 2, which is referred to as an intermediate layer or buffer layer in the present invention, is interposed between the silicon substrate 1 and the germanium epitaxial growth layer 3. Here, the thickness of the germanium intermediate layer 2 is preferably on the order of several layers, and the thickness of the germanium growth layer 3 can be arbitrarily changed depending on the desired bonding state.

The heterojunction illustrated in FIG. 1 can preferably be formed according to a reduced pressure vapor deposition method and can be carried out, for example, using a vapor deposition apparatus as schematically illustrated in FIG. 3. . In FIG. 3, a quartz reaction tube 10 is equipped with a high frequency coil 11 surrounding it and serving as a heating means. Silicon substrate 1 is placed on susceptor 12 and housed in quartz reaction tube 10 . As shown in the figure, the quartz reaction tube 10 is connected to piping for supplying various raw material gases thereto. Hydrogen (H2) is a carrier gas, silane (SiHl) gas is a raw material gas for forming the silicon intermediate layer, and diethyl germane (Ge
(C2H5) 2H2) gas is a raw material gas for forming a germanium intermediate layer, and germanium (GeH2) gas is a raw material gas for forming a germanium intermediate layer.
, ) gas is the raw material gas for forming the germanium growth layer. The waste gas from the quartz reaction tube 10 is extracted by the rotary vacuum pump 12, treated by a waste gas treatment device (not shown) connected thereto, and discharged into the atmosphere after purification.

FIG. 2 is a cross-sectional view showing another example of a heterojunction formed according to the present invention. In the illustrated example, a sapphire substrate 4 is used instead of the silicon substrate, so that the silicon layer 5 is grown to a thickness of ≦300 nm. Above the silicon layer 5, a germanium intermediate layer 2 and a germanium growth layer 3 are successively formed, as in the case of the example shown in FIG. 1 described above.

Example 1 (Comparative Example) Germanium was grown in a vapor phase on a silicon substrate according to a conventional method.

A silicon substrate with a (001) plane orientation was prepared, and its surface was oxidized with a sulfuric acid/hydrogen peroxide mixture, and then a wet oxide film was removed using a hydrofluoric acid aqueous solution. Next, the surface-treated silicon substrate was placed in a vapor phase growth apparatus and heated at about 900° C. for about 10 minutes as a pretreatment for growth. Next, the growth temperature was maintained at 500° C., and germanium was epitaxially grown using germanium (GeHa) gas. FIG. 5 shows the temporal change of the epitaxial layer.

No germanium growth was observed in the early stages;
It was first observed about 4 minutes after the germane gas supply started. After more than 10 minutes, a nearly proportional relationship was established between the growth layer thickness and time, but this relationship broke down in the early stages of growth, making it difficult to precisely grow a germanium layer of 100 Å or less. Met.

Example 2 A silicon substrate with a (001) plane orientation was prepared, and its surface was oxidized with a sulfuric acid/hydrogen peroxide mixture, followed by wet oxide film removal using a hydrofluoric acid aqueous solution. Next, the silicon substrate after the surface treatment was placed in a vapor phase apparatus shown in FIG. 3, and a germanium intermediate layer and a germanium growth layer were sequentially formed according to the present invention. Here, the total pressure of hydrogen as a carrier gas was approximately 10 mmHg.

First, the substrate is cooled to around 700°C, and then silane (S
A very thin silicon buffer layer was grown by introducing iH4) gas. Then, after further cooling to 300°C or less, diethylgermane (Ge(C,H,),)l,
) A germanium intermediate layer was formed by supplying gas at a concentration of about I x 10'atm for about 1 minute.

After completely eliminating the diethylgermane gas in the gas phase, which actually takes more than 30 seconds, the temperature is quickly raised (at least 200°C/min) to reach the growth temperature of 500°C.
It was kept at ℃. Next, germane (Ge) I4) gas 1
0mI! Epitaxial growth of germanium was performed using the following method. In this example, an extremely thin germanium layer was formed on the silicon substrate surface by thermal decomposition of diethylgermane, so that, in contrast to Example 1, germanium growth was initiated without requiring any incubation time. Also, increase the growth temperature to 5
When the temperature was lowered from 00°C to 430°C, good results could be obtained while suppressing the growth rate of the Ge layer. FIG. 4 is a graph plotting the relationship between the film thickness of the germanium layer on the silicon substrate and the growth time.

Example 3 The procedure described in Example 2 above was repeated, but in this example a sapphire substrate was used instead of a silicon substrate, and therefore the sapphire substrate was heated to 1100° C. and then treated with silane (St) gas. Silicon was grown at 950°C. A silicon layer with a thickness of approximately 300 nm was formed on a sapphire substrate. After cooling the sapphire substrate to 200° C., a germanium intermediate layer and a germanium growth layer were sequentially grown in the same manner as in Example 1 above. A semiconductor heterojunction having a cross-sectional shape as shown in FIG. 2 was obtained.

Here, an organic compound may be used as a raw material for germanium, but in crystal growth of silicon, it becomes a source of contamination of impurity carbon, so it can be used only for forming an adsorption intermediate layer.

〔Effect of the invention〕

According to the present invention, since the surface properties of the base substrate are changed using a substance that adsorbs at low temperatures, crystal growth of a heterojunction can be precisely controlled. Further, according to the present invention, a superlattice structure combining silicon and germanium can be formed by a vapor phase growth method. Furthermore, according to the present invention, a precisely controlled germanium layer or a heterojunction crystal of germanium and silicon can be formed on a sapphire substrate.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an example of a semiconductor heterojunction formed according to the present invention, FIG. 2 is a cross-sectional view showing another example of a semiconductor heterojunction formed according to the present invention, and FIG. 4 is a schematic diagram showing an example of a vapor phase growth apparatus used in carrying out the present invention, and FIG. 4 shows the growth time and germanium layer film when a germanium layer is grown on a silicon substrate according to the method of the present invention. FIG. 5 is a graph showing the relationship between the growth time and the thickness of the germanium layer when the germanium layer is grown on a silicon substrate according to the conventional method. In the figure, 1 is a silicon substrate, 2 is a germanium intermediate layer, and 3 is a silicon substrate.
is a germanium growth layer, 4 is a sapphire substrate, and 5 is a germanium growth layer.
is a silicon layer.

Claims (1)

[Claims] 1. A method of forming a semiconductor heterojunction by vapor phase epitaxial growth of a single crystal of a second semiconductor material different from the first material on a substrate made of a single crystal of a first semiconductor material. Before performing the vapor phase epitaxial growth of the second semiconductor material,
a third semiconductor material that is crystallographically matched to the crystals of the substrate at a temperature below its epitaxial growth temperature; An organometallic compound or a halogenated compound of the selected substance is adsorbed onto the surface of the substrate from the reaction gas as its raw material, and an intermediate layer of the selected substance is formed by a thermal decomposition reaction of the adsorbed substance, and then an intermediate layer of the selected substance is formed at a predetermined epitaxial growth temperature. A method for forming a semiconductor heterojunction, characterized in that the second semiconductor material is vapor-phase epitaxially grown on the intermediate layer from a reactant gas as its raw material after the temperature is raised to . 2. An intermediate layer of germanium is formed by adsorbing a germanium organometallic compound or a halide compound from the raw material reaction gas onto the surface of a substrate having a silicon single crystal in at least the surface layer at a temperature lower than the epitaxial growth temperature of germanium. 2. The method according to claim 1, wherein germanium is vapor-phase epitaxially grown on the germanium intermediate layer from a raw reactant gas after the temperature is raised to a germanium epitaxial growth temperature. 3. A silicon single crystal is epitaxially grown on a substrate made of an insulating material, and an organometallic compound or a halide compound of germanium is added to the surface of the formed SOI substrate at a temperature lower than the epitaxial growth temperature of germanium with its raw material reactive gas. 2. The method according to claim 1, wherein a germanium intermediate layer is formed by adsorption from germanium, and then, after the temperature is raised to a germanium epitaxial growth temperature, germanium is vapor-phase epitaxially grown on the germanium intermediate layer from a reactant gas as its raw material.