JPH0562911A - Manufacture of semiconductor superlattice - Google Patents

Abstract

PURPOSE:To form a Ge layer and an Si layer or a Ge-Si layer and an Si layer on an Si substrate, and also to put a hetero-epitaxial growth method, in which excellent crystal quality and high growth speed can be obtained, into practical use. CONSTITUTION:The title semiconductor superlattice manufacturing method is the method with which a Ge layer and an Si layer or Ge-Si layer and an Si layer are epitaxially grown on an Si substrate by conducting a depressed CVD method under the atmosphere containing oxidizing impurity gas of 1000ppb or lower using GeH4 and trisilane (Si3H8) as raw gas and also using H2 or inert gas as carrier gas.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for epitaxially growing a high-quality semiconductor superlattice comprising a silicon layer and a germanium layer or a silicon-germanium layer having a large composition ratio of the silicon layer and germanium at a high growth rate.

A crystal obtained by alternately epitaxially growing germanium (hereinafter, Ge) and Si on a silicon (hereinafter, Si) substrate has a direct transition type characteristic and is expected to be applied as an optical element.

For example, for the purpose of ultra-high speed and high integration of a hetero bipolar transistor (HBT), a light receiving element, a high electron mobility transistor (HEMT), etc. by using a material obtained by heteroepitaxially growing a superlattice crystal composed of Si and Ge. However, the application of the present method, which has few crystal defects and a high growth rate, is extremely effective.

[0004]

2. Description of the Related Art HBTs using a crystal layer formed by epitaxially growing Si and Ge or a mixed crystal of Si and Ge and Si
There is molecular beam epitaxy (MBE) as a method of forming such a device.

That is, it is possible to perform heteroepitaxial growth having a superlattice structure by measuring the signal intensity of electron beam diffraction and controlling the crystal growth rate atomically.

Here, MBE is a technique capable of performing crystal growth extremely precisely in terms of structure, but in practice, the grown crystal has a large defect density, and the defect density must be controlled. There is a problem to say.

Further, a large number of substrates cannot be processed on a large substrate, which causes a problem in productivity. On the other hand, the vapor phase growth method (CVD) is a method for forming a good quality crystal layer,
500 ° C for Si layer or mixed crystal layer with large Si composition ratio
The epitaxial growth below is difficult.

That is, if a special silane such as fluorinated silane (SiF ₂ H ₂ ) is used and a method of irradiating with ultraviolet light is used, it is possible to grow at 500 ° C. or less. The growth of mixed crystals is unknown.

Trisilane (Si ₃ H ₈ ) has a boiling point of 52.9 ° C.
As low as polycrystalline (poly) Si or amorphous (amorphous) Si
However, it is not known whether or not epitaxial growth can be performed at a low temperature by the CVD method.

Regarding Ge, it is known that when the Ge layer is thick, it can be epitaxially grown on the Si substrate by the CVD method, but since island-shaped growth occurs in the initial state of growth, lattice defects have a high density. Since it is included, it is difficult to grow a crystal having a precise structure.

[0011]

[Problems to be Solved by the Invention] CVD of Ge on Si substrate
(GeH ₄ ), diethyl germane [GeH ₂ (C ₂ H ₅ )]
Examples include dimethylgermane [GeH ₂ (CH ₃ )], but germane (GeH ₄ ) is the most common.

Since hetero-growth on a Si substrate is likely to occur in an island shape, it is necessary to lower the growth temperature to 500 ° C. or lower in order to grow a Ge film having good flatness.

Next, when disilane (Si ₂ H ₆ ) is used as a source gas for epitaxially growing Si on a Si substrate, it can be grown epitaxially at 550 ° C. or higher. It's extremely difficult.

In the case of heteroepitaxially growing a mixed crystal of Si and Ge on a Si substrate, it can be formed at a temperature of 550 ° C. or higher when the Ge composition ratio is small, and it is flat when the Ge composition ratio is large. It is difficult to form such a mixed crystal layer.

From the above, the Si layer and the Ge layer or the Si layer
In order to form a semiconductor superlattice by heteroepitaxially growing a Si / Ge mixed crystal layer, it is necessary to lower the growth temperature of the Si layer to 500 ° C or lower.

[0016]

[Means for Solving the Problems] The above-mentioned problems are caused by using trisilane (Si ₃ H ₈ ) as a source gas in an atmosphere containing GeH ₄ and an oxidizing impurity gas content of 100 ppb or less, H ₂ or an inert gas. The problem can be solved by configuring a method for manufacturing a semiconductor superlattice characterized by epitaxially growing a Ge layer and a Si layer or a Ge / Si layer and a Si layer on a Si substrate by using a gas as a carrier and a low pressure CVD method. it can.

[0017]

[Function] Superlattice of Si layer and Ge layer or Si layer on Si substrate
To form a superlattice composed of a Si / Ge mixed crystal layer, the growth temperature at the time of forming the Si film by the CVD method is set to 50 as described above.
Although it is necessary to control the temperature to 0 ° C. or less, the inventor uses trisilane (Si ₃ H ₈ ) gas and uses an oxidizing impurity gas (O ₂ ,
It was found that it is possible when the content of H ₂ O, CO, CO ₂ etc.) is 100 ppb or less.

FIG. 1 shows disilane (Si₂H₆) And trisilane (Si₃
H₈) Is used, the growth temperature and growth rate
Shows the relationship, Si₂H₆Partial pressure of 1.5 × 10^-2 torr
Si ₃H₈ The partial pressure of 1 × 10^-2 torr and 2 × 10^-2 in torr
, H₂As a carrier, the total pressure is set to 20 torr.
From this figure, Si₂H₆Growth rate at 500 ° C
Although the degree is as low as about 2Å / min, Si₃H₈ With
At 500 ℃, it is as high as several to 10 Å / min.
It shows that you can grow axially.

According to the experiment, the content of the oxidizing impurity gas such as O ₂ , H ₂ O, CO, and CO ₂ is extremely small and 100 PPB or less for performing epitaxial growth using Si ₃ H _8. Therefore, it has been found that it is essential that the low pressure CVD apparatus used has high airtightness and that the carrier gas and the purity of Si ₃ H ₈ and GeH ₄ are high.

The partial pressure of Si ₂ H ₆ and Si ₃ H ₈ is 4 ×.
At 10 ^-2 torr or more, it was observed that a polycrystal grew on the substrate surface. Next, FIG. 2 shows the period of the superlattice obtained from the X-ray diffraction measurement measured at a low diffraction angle of 0 ° to 20 °.
These are the experimental results of investigating the relationship with the flow rate of GeH ₄ gas. □ indicates the substrate temperature is 470 ℃, Si ₃ H ₈ supply rate is 100 ml / min,
When the supply time is 120 seconds and the GeH ₄ supply time is 30 seconds, the ○ mark indicates that the substrate temperature is 550 ° C and the Si ₂ H ₆ supply amount is 20 seconds.
ml / min, supply time 30 seconds, GeH ₄ supply time 10 seconds, △ indicates substrate temperature 500 ° C, Si ₂ H ₆ supply 40 ml / min, supply time 120 Second, the case where the GeH ₄ supply time is 20 seconds is shown.

Here, a white mark indicates that a superlattice is formed as a result of the measurement, and a black mark indicates that the superlattice period is not recognized. Here, no period is observed when the growth period is short and when it is long, because the Ge layer is in a mixed crystal state of SiGe when the growth period is short, and when the growth period is long, Ge It is believed that the island-like growth makes the surface uneven and becomes apparently similar to a mixed crystal.

From the figure, in the superlattice 4 represented by the mark ○, which was grown at 550 ° C. using Si ₂ H ₆ , the period was 6 Å or less and 20 Å.
Although not observed above, in the superlattice 5 represented by □ grown using Si ₃ H ₈ at 470 ℃, the period is less than 4Å and 30
Although it is not observed above Å, it is understood that the range of the period width can be widened by using Si ₃ H ₈ .

Further, it was determined from the result of X-ray diffraction of the (004) plane.
From the average composition of the SiGe superlattice₂H ₆And GeH_FourUsing, 55
Superlattice 4 grown at 0 ℃ and marked with ○ and grown at 500 ℃
In the superlattice 6 represented by Δ, the Ge composition ratio in the Ge layer is high.
50% each, but Si₃H₈And GeH _FourGrown at 450 ° C
The Ge composition in the Ge layer of the superlattice 5 indicated by □ is 80% or more.
Can be estimated and found to be significantly improved.
It

[0024]

EXAMPLES Example 1: (Example of multi-layer growth of Ge layer and Si layer)
After using Si having a plane orientation of (001) as a substrate and immersing it in a mixed solution of sulfuric acid (H ₂ SO ₄ ) and hydrogen peroxide (H ₂ O ₂ ) to oxidize the surface, hydrofluoric acid ( (HF) aqueous solution to remove the oxide film for cleaning, then place this substrate in a vapor phase epitaxy apparatus and immediately before processing, use a high-purity vacuum with a degree of vacuum of 10 torr.
The oxide film was removed by performing a heat treatment at a temperature of 900 ° C. for 10 minutes in an H ₂ atmosphere.

After that, the substrate temperature was set to 450 ° C. by air cooling, the partial pressures of Si ₃ H ₈ and GeH ₄ were each set to 2 × 10 ^-2 torr, and the total pressure was set to 20 torr by using H ₂ as a carrier, and alternately supplied. To grow Si layers and Ge layers alternately,
The superlattice could be formed. Example 2: (Example of growth of Ge / Si layer and Si layer) After performing cleaning treatment of Si substrate and removal of oxide film in the same manner as in Example 1, a gas supply program as shown in FIG. The gas of GeH ₄ and Si ₃ H ₈ was independently supplied for a short time.

That is, in this case, GeH ₄ was supplied for 1 minute, Si ₃ H ₈ was supplied for 4 minutes at an interval of 20 seconds, and GeH ₄ was supplied for 1 minute at an interval of 20 seconds. repeat.
When the GeH ₄ supply time is shortened in this way, a mixed crystal layer having a thickness of about several Å can be formed due to the averaging of the composition due to the mutual diffusion of Ge and Si.

Also, the Si layer is up to the time corresponding to its thickness.
It can be made by supplying Si ₃ H ₈ . A superlattice could be made by the above method.

[0028]

According to the present invention, a superlattice structure composed of a Ge layer and a Si layer, or a Ge / Si mixed crystal layer containing a high concentration of Ge and a Si layer can be grown with high quality at a high growth rate.

[Brief description of drawings]

FIG. 1 is a relationship diagram between a growth temperature and a growth rate.

FIG. 2 is a relationship diagram between a GeH ₄ flow rate and a superlattice period.

FIG. 3 is an example of a gas supply program for forming a superlattice structure.

Claims (3)

[Claims] 1. A germanium layer on a silicon substrate by a low pressure vapor deposition method using trisilane and germane as source gases and hydrogen or an inert gas as a carrier in an atmosphere having an oxidizing impurity gas content of 100 ppb or less. And a silicon layer, or a germanium / silicon layer and a silicon layer are epitaxially grown. 2. A period in which the repeated growth of the silicon layer and the germanium-silicon layer stops the growth of the silicon layer and the germanium layer is sandwiched, and trisilane gas and germane gas are independently supplied to the silicon substrate. The method for manufacturing a semiconductor superlattice according to claim 1, wherein the method is performed. 3. The method for manufacturing a semiconductor superlattice according to claim 2, wherein the composition ratio of germanium in the germanium / silicon layer is 50% or more.