JPH05206028A - Semiconductor crystal growth method - Google Patents

Abstract

(57) [Summary] [Objective] The present invention is directed to a gas source molecular beam crystal growth method (G
A method for manufacturing a compound semiconductor device by SMBE),
Crystals of compound semiconductors required to create high-performance devices
The selective growth of the growth is ensured and the purity of the crystal growth layer is controlled.
The purpose is to improve it. [Configuration] Group III material irradiation and group V material irradiation are performed alternately.
After irradiation of the group III material, the stagnation of the group III material on the mask
Waiting time longer than present (τ₁) After that, irradiation of group V material is performed,
After the irradiation of the group V material, the period of stay of the group V material on the mask is less than
Waiting time on (τ ₂) It is planned to irradiate the group III material later.
To achieve.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a compound semiconductor device by a gas source molecular beam crystal growth method.

The molecular beam crystal growth method (MBE) is widely used for forming an element whose thickness is controlled in atomic layer units such as a semiconductor element using a superlattice. As a molecular beam source for generating a molecular beam, a single or a plurality of elements are prepared according to the substance to be grown, and a desired substance layer is grown by selecting and using the necessary molecular beam source.

As the source, various gas sources have been used in addition to the conventional metal source. This is called a gas source molecular beam crystal growth method (GSMBE). In this III-V group compound semiconductor by GSMBE, when an organic metal is used as a group III material, and an amorphous or polycrystalline mask is formed and grown on the substrate, the mask is not formed on the mask. The phenomenon of selective growth occurs in which only the semiconductor crystal grows without growing. This selective growth technique is used for the source / drain of the FET and is a very important technique for improving the device performance and for producing a device having a new structure.

With the recent demand for higher performance of semiconductor devices, it is necessary to improve the technique of the crystal growth method.

[0005]

2. Description of the Related Art FIG. 2 is a schematic diagram of a gas source MBE apparatus. In the figure, 1 is an ultra-high vacuum chamber, 2 is a substrate,
3 is a substrate holder, 4 is a substrate heating heater, 5 is a shutter,
Reference numeral 6 is a metal source K cell, 7 is a gas cell, 8 is a source gas, and 9 is a flow rate control device.

When epitaxially growing a crystal on the substrate 2 using the apparatus shown in FIG. 2, the metal source is heated in the K cell 6 to emit a molecular beam. In the case of a gas source, the gas is thermally decomposed into a molecular beam by the gas cell 7, or is radiated in the form of a gas molecular beam without being decomposed.

When selective growth is performed, an amorphous or polycrystalline mask such as a silicon dioxide (SiO ₂ ) film is formed on the substrate, and a portion where the substrate crystal is exposed and a portion where it is not provided are provided. For example, when selectively growing a III-V group compound semiconductor, an organic metal may be used as the III group material, and a metal or a hydrogen compound may be used as the V group material.

When growth is performed using such a material, selective growth can be realized only in the exposed portion of the substrate crystal and not on the mask. However,
Depending on conditions such as source material, growth temperature, V / III ratio, etc., polycrystals may grow on the mask or polycrystal grains may adhere to the mask, so that within the limited growth condition range where selectivity can be maintained. It was growing.

On the other hand, in order to grow a high-purity compound semiconductor crystal, the growth temperature, the V / III ratio, etc. also have a range of conditions.

[0010]

However, when selective growth is performed, the range of growth conditions that can maintain selectivity and the range of conditions for obtaining high-purity crystals do not necessarily match.

Therefore, if the growth is performed under the condition for obtaining a high-purity crystal, the selectivity cannot be maintained, and the growth also occurs on the mask. On the contrary, if the growth is carried out under the growth condition that can maintain the selectivity, the incorporation of impurities is increased, and it is not possible to obtain a high-purity crystal.

As described above, according to the conventional technique, it was not possible to grow a compound semiconductor crystal of high purity while maintaining selectivity. Therefore, an object of the present invention is to provide a selective growth method of semiconductor crystals by a gas source molecular beam crystal growth method in which the purity required for producing a high-performance device is maintained and the purity of a growth layer is remarkably improved. To do.

[0013]

FIG. 1 is a diagram for explaining the principle of the present invention, FIG. 3 is a p-type carrier concentration in a GaAs crystal, and FIG. 4 is SiO _2.
GaAs polycrystal grain density on the mask.

In FIG. 1, τ ₁ is after irradiation of the group III material,
Waiting time until group V material irradiation, τ ₂ is after irradiation of group V material, I
The waiting time until the irradiation of the group II material, J ₁ is the small irradiation amount of _the group III material during irradiation of the group V material _{, and} J ₂ is the small irradiation amount of the group III material during irradiation of the group V material.

According to the present invention, the above-mentioned object is achieved in the selective growth of a III-V compound semiconductor in which a metal is used as a group III material, a mask is formed on a substrate, and growth is performed by a gas source MBE method. As shown in Fig. 1, group III material irradiation and group V material irradiation are performed alternately, and after group III material irradiation, group V material irradiation is performed after a waiting time of the group III material on the mask or longer, and V This can be achieved by a method for growing a semiconductor crystal, which is characterized in that after the irradiation of the group material, the irradiation of the group III material is performed after a waiting time longer than the residence time of the group V material on the mask.

In addition to the above, a small amount of group V material irradiation is performed during the irradiation of the group III material, and a small amount of the group III material irradiation is performed during the irradiation of the group V material. To be done.

[0017]

In the present invention, the group V material is not irradiated or the irradiation amount is reduced during the irradiation of the group III material, and the group III material is not irradiated or the irradiation amount is reduced during the irradiation of the group V material. By placing a waiting time longer than the residence time of each material on the mask, it is possible to prevent the growth of polycrystals or the adhesion of polycrystal grains on the mask, and to prevent the carbon impurities in the grown crystal from growing. Capturing can be suppressed.

In FIG. 3, triethylgallium (TEGa) and metal arsenic (As) are used as the source material, and gallium arsenide (GaAs) is used.
Dependence of residual impurity concentration in GaAs crystal on growth temperature and V / III ratio is shown by p-type carrier concentration.

In FIG. 3 (a), the p-type carrier concentration increases on the high temperature side because the hydrocarbon group of the organic metal is easily decomposed on the high temperature side, and the resulting carbon is incorporated into the crystal. It is thought to be because it is done.

In FIG. 3 (b), p on the high V / III ratio side
It is considered that the type carrier concentration decreases because an excessive group V element bonds with the hydrocarbon group and is desorbed. Also, V
When a group V hydrogen compound is used as the group material, in addition to the above-described effect, a hydrogen radical resulting from the decomposition of the group V hydrogen compound is combined with a hydrocarbon group to be eliminated.

FIG. 4 shows the crystal growth selectivity growth temperature, V /
III Ratio dependence and growth rate dependence are shown by the density of GaAs crystal grains on the mask. If the conditions are not satisfied and the density of GaAs polycrystal grains greatly exceeds ^{1x10 7} cm ^-2 , the GaAs polycrystal grows over the mask surface.

As shown in FIG. 4A, the As pressure is 8.5 × 10 ⁻⁶ Tor.
The growth temperature dependence of the density of GaAs polycrystal grains on the SiO ₂ film mask when GaAs crystals are grown on a substrate under the conditions of r and GaAs growth rate of 0.55 μm / h is shown.

On the low temperature side, the density of the GaAs polycrystal grains becomes high because the staying time of the group III material molecules and the group V material molecules on the mask is long on the low temperature side, and the probability of collision and binding of both is high. This is because On the high temperature side, the two are re-evaporated before they collide with each other, so that growth on the mask does not occur.

In FIG. 4B, the GaAs growth rate is 0.55 μm.
As of the density of GaAs polycrystal grains on the SiO ₂ film mask when GaAs crystals were grown on the substrate under the conditions of m / h and growth temperature of 550 ° C.
Shows pressure dependence.

On the high V / III ratio side, the density of GaAs polycrystal grains increases because the beam intensity of the V group material or the flow rate of the V group material increases the V group concentration on the mask. This is because the probability of collision and binding with molecules increases.

As shown in FIG. 4C, the As pressure is 8.5 × 10 ^-6 Tor.
The growth rate dependence of the density of GaAs polycrystal grains on the SiO ₂ film mask when GaAs crystals are grown on a substrate at r and a growth temperature of 550 ° C is shown.

The higher the growth rate, the higher the density of GaAs polycrystal grains is that as the flow rate of the group III material increases, the concentration of the group III material molecules on the mask increases and collides with the group V material molecules. This is because the probability of combination increases. If the growth rate is lowered, the density of GaAs polycrystal grains will be reduced, but the growth time will be longer, which is not practical.

FIG. 1 shows the growth method of the present invention. At the time of irradiating the group III material, the group V material is not irradiated or the irradiation amount is reduced, so that the polycrystalline growth on the mask does not occur. At that time, since group V atoms exist in the mask opening, crystal growth occurs when there is adsorption of group III material molecules or irradiation of a small amount of group V material. At this time on the surface
Hydrocarbon groups are present due to incomplete decomposition of group III material molecules. Since this hydrocarbon group is removed during the next irradiation of the group V material, it is preferable that the irradiation amount of the group III material does not greatly exceed one atomic layer.

At the time of irradiating the group V material, the group III material is not irradiated or the irradiation amount is reduced, so that no polycrystal growth on the mask occurs. At the mask opening, the hydrocarbon groups remaining on the surface are removed by the irradiation of the group V material, and the crystal growth occurs when the group V atomic plane is formed or a small amount of the group III irradiation is performed. By setting the ratio of the group V material and the group III material to be supplied per cycle to be approximately the same as the V / III ratio at which the desired purity can be obtained in the case of continuous supply growth,
Growth with less carbon uptake is possible.

The waiting time between each is the time for each switching to be surely performed, and it is better to exceed the staying time of each material on the mask. By repeating these steps, a high-purity crystal can be grown while maintaining the crystal growth selectivity.

[0031]

EXAMPLE FIG. 2 is a schematic view of a gas source MBE apparatus used in the present invention. In the figure, 1 is an ultra high vacuum chamber,
2 is a substrate, 3 is a substrate holder, 4 is a substrate heater, 5 is a shutter, 6 is a metal source K cell, 7 is a gas cell, 8
Is a source gas, 9 is a flow controller, 10 is a liquid nitrogen shroud, and 11 is a vacuum pump.

As a source material, triethylgallium (T
An example is shown in which GaAs is grown using EGa) and metallic arsenic (As). After cleaning the GaAs substrate, a SiO ₂ mask is formed by the CVD method and the photolithography method. This board is shown in Figure 2.
It is introduced into the growth chamber of the gas source MBE device shown in. While irradiating As, the native oxide film on the GaAs substrate surface was removed at a substrate temperature of 600 ° C for 3 minutes, and the substrate temperature was set to a growth temperature of 550
At ℃, the growth of GaAs crystal was started.

The As pressure was 1.5 × 10 ⁻⁴ Torr. TEGa was introduced into the growth chamber using a hydrogen carrier. TEGA flow rate is 2.5
When the growth rate is 0.6 μm / h when the growth is performed in the normal growth mode, that is, the simultaneous supply mode, with sccm, the As
Since the pressure was high, the entire surface of the mask was covered with the polycrystalline film.

Further, when the growth is performed at the same effective growth rate of 0.28 μm / h as in the first embodiment, the entire surface of the mask is Ga
As covered with a polycrystalline film. In the first embodiment of the present invention, the TE
Irradiation time of Ga and As is required for growth of one layer
It was set to 1.8 seconds. TEGa irradiation was not performed during As irradiation.

As a result of studies conducted by the present inventors, the residence time of TEGa and As on SiO ₂ at 550 ° C. has been found to be several tens of milliseconds or less. In the example, after irradiation of each material,
A waiting time of 0.1 seconds was provided.

This is performed for 947 cycles (59 minutes 58.6 seconds),
Observation of a sample on which 0.28 μm GaAs was grown revealed that Ga
As polycrystalline grain density was less than 500 cm ^-2 . The residual impurity concentration was 1 × 10 ¹⁵ cm ^-3 or less as the p-type carrier concentration, and high-purity crystals were obtained.

Next, in the second embodiment of the present invention, the irradiation time of As and the waiting time are the same as those in the first embodiment, and TEGa
The irradiation time was 7.5 sccm and the waiting time was 0.6 seconds. Even in this case, the TEGA irradiation dose for one time becomes equal to that in the first embodiment.
By doing this, the effective growth rate becomes 0.42 μm / h, and
As growth time can be shortened.

In the first and second embodiments, the dose of material is set to the amount required for growth of one layer, but it is not necessary to determine as such, and the dose must greatly exceed one layer. For example,
You can set it arbitrarily.

However, in order to remove the hydrocarbon groups remaining on the surface, it is necessary that the irradiation amount of As be approximately the same as the V / III ratio that gives the desired purity in the case of continuous supply growth. Further, in the example, As irradiation was not performed during TEGa irradiation and TEGa irradiation was not performed during As irradiation, but even a small amount of irradiation that does not increase the density of GaAs polycrystal grains may be performed. good.

[0040]

As described above, according to the present invention,
Since it is possible to grow high-purity compound semiconductor crystals such as GaAs while maintaining the selectivity of masks such as SiO ₂ without sacrificing productivity, it greatly contributes to the performance improvement of compound semiconductor devices. ..

[Brief description of drawings]

FIG. 1 is an explanatory view of the principle of the present invention.

FIG. 2 is a schematic diagram of a gas source MBE device.

FIG. 3 Concentration of p-type carrier in GaAs crystal

FIG. 4 GaAs polycrystal grain density on SiO ₂ mask

[Explanation of symbols]

 1 Ultra High Vacuum Chamber 2 Substrate 3 Substrate Holder 4 Substrate Heater 5 Shutter 6 K Cell for Metal Source 7 Gas Cell 8 Source Gas 9 Flow Control Device 10 Liquid Nitrogen Shroud 11 Vacuum Pump

Claims (3)

[Claims] 1. A selective growth of a III-V group compound semiconductor in which a metal is used as a group III material, a mask is formed on a substrate, and growth is performed by a gas source MBE method.
Irradiation of group I material and irradiation of group V material are performed alternately. After irradiation of group III material, irradiation of group V material is performed after waiting time (τ ₁ ) longer than the staying time of group III material on the mask (τ ₁ ). A method for growing a semiconductor crystal, characterized in that after the irradiation, the irradiation of the group III material is performed after a waiting time (τ ₂ ) longer than the residence time of the group V material on the mask. 2. A small amount of group V material is also irradiated during the irradiation of the group III material, and a small amount of II is irradiated during the irradiation of the group V material.
2. The method for growing a semiconductor crystal according to claim 1, wherein the irradiation with the group I material is also performed. 3. The ratio (V / III) of the group III material to the group V material fed per cycle is such that the desired purity in the case of continuous feeding can be obtained by the group III material and the group V material. 3. The method for growing a semiconductor crystal according to claim 1, wherein the ratio is about the same as the ratio.