JPH0955365A - Surface cleaning method of semiconductor substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method by which impurities such as an oxide film grown on a substrate are removed inside a chamber for regrowth the substrate without damaging the crystal of the substrate. SOLUTION: A group II-VI semiconductor epitaxial film grown by an MBE method on a group III-V semiconductor substrate or a group II-VI semiconductor substrate is used as a substrate, and a group II-VI semiconductor is grown by an MBE method on the epitaxial film. At this time, the substrate is irradiated with an He/H2 mixed-gas plasma beam inside a regrowth chamber, and the surface of the substrate is cleaned. A ZnSe bulk crystal is used as a substrate. and a group II-VI semiconductor is grown by an MBE method on the bulk crystal. At this time, the substrate is irradiated with an He/H2 mixed-gas plasma beam inside a growth chamber, and the surface of the substrate is cleaned.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a molecular beam epitaxy (MBE) method to convert II-VI group semiconductors into II-type semiconductors.
The present invention relates to a method for cleaning a substrate surface in the MBE growth chamber when growing the surface of a VI or III-V group semiconductor crystal substrate.

[0002]

BACKGROUND OF THE INVENTION Currently, a lot of research is being conducted on II-VI group semiconductor lasers produced by the MBE method, and it has been reported that they have a lifetime of about 1 hour when continuously operated at room temperature. (A. Ishibashi and S. Ito
h, IEEE LEOS 1994, PD1.1, Bo
Ston, USA (1994)).

In addition, a buried regrown type (a part of the surface of a crystal formed in a single layer or multiple layers on a substrate is etched,
A semiconductor laser of the type in which a crystal is regrown in the etched portion) is very commonly used in the field of using III-V group semiconductors (edited by Ryoichi Ito, semiconductor laser). However, such a regrowth technique has not been established for II-VI group semiconductors,
In particular, it is said that the crystal growth technique using the MBE method is difficult for the reasons described below.

That is, in general, II-VI or I
The substrate used when growing the II-V group semiconductor using the MBE method is treated with an organic compound or an inorganic compound outside the MBE growth chamber to remove the surface damage layer, and this is introduced into the MBE growth chamber. MBE crystal growth is performed after the operation of removing the oxide film formed on the substrate surface is performed in the growth chamber.

This oxide film is usually removed by raising the temperature of the substrate (for example, in the case of a GaAs substrate, raising the temperature to about 580 to 600 ° C.) and sublimating the oxide forming the film. There is.

However, it has been reported that the characteristics of the II-VI group semiconductor grown by the MBE method are rapidly deteriorated by heat treatment at a temperature higher than this growth temperature (Y. Ichimura, K. et al. Kishino, M.K.
uramoto, M .; Satake, A .; Yoshid
a, Journal of Electronic M
materials Vol. 24 (1995) 17
1).

On the other hand, a method of removing the oxide film of the crystal substrate at low temperature is also known, and one of them is RF (Radio).
Frequency) wave, microwave, or ECR
(Electron Cyclotron Reson
There is a method of irradiating hydrogen plasma excited by an (an) wave or the like. In this method, the substrate is irradiated with hydrogen activated by plasma, and the oxide film can be removed at a relatively low temperature.

However, the plasma processing method using only hydrogen gas causes a great deal of damage to the substrate. It is also possible to use low flow rate (low pressure) and low power hydrogen plasma in order to suppress damage to the substrate. However, when such plasma is generated, the plasma discharge often becomes very unstable.

[0009]

Therefore, in the present invention, the II-VI group semiconductor epitaxial crystal film grown by the MBE method is used as a substrate, and when the II-VI group semiconductor is regrown on the substrate by the MBE method, An object of the present invention is to provide a surface cleaning method capable of stably cleaning the surface of a substrate at low temperature without damaging the substrate. Further, in the present invention, Z of the II-VI group semiconductor substrate is used.
In the case of nSe, not only the above-mentioned epitaxial crystal but also a ZnSe bulk crystal grown by the bulk method is used as a substrate, and when the II-VI group semiconductor is regrown on the substrate by the MBE method, the substrate is damaged. It is another object to provide a surface cleaning method capable of stably cleaning the surface of the substrate at a low temperature without giving the above.

[0010]

The present inventors SUMMARY OF THE INVENTION As a result of extensive investigations to solve the above problem, by using the He / H ₂ mixed gas plasma, than plasma using H ₂ gas alone,
It is possible to remove impurities such as an oxide film while suppressing damage to the crystal of the substrate, and as a result, it is possible to obtain a substrate surface on which regrowth of a crystal having sufficient characteristics can be performed. With the knowledge obtained, the present invention has been completed.

That is, the present invention uses [1] a II-VI group semiconductor epitaxial crystal film grown by a molecular beam epitaxy method on a III-V group semiconductor substrate or a II-VI group semiconductor substrate as a substrate, When the II-VI group semiconductor is regrown on the epitaxial crystal film substrate by the molecular beam epitaxy method, He / H in the same growth chamber is used.
_A method for cleaning a surface of a semiconductor substrate (hereinafter referred to as a first invention), which comprises irradiating the substrate with a _two- mixed gas plasma beam to clean the surface of the substrate, and [2].
When a ZnSe bulk crystal is used as a substrate and a II-VI group semiconductor is grown on the bulk crystal substrate by a molecular beam epitaxy method, the substrate is irradiated with a He / H ₂ mixed gas plasma beam in the same growth chamber. A method of cleaning a surface of a semiconductor substrate (hereinafter, referred to as a second invention) is characterized in that the surface of the substrate is cleaned.

At this time, (1) the He / H ₂ mixed gas has a volume ratio of 2/1 to 250/1, and (2) the degree of vacuum in the growth chamber is 5 × 10 ⁻⁸ to 1 × 10 ^−4. and (3) the substrate temperature is not lower than 100 ° C. in the first invention and not higher than the growth temperature of the II-VI group semiconductor epitaxial crystal film, and is 100 to 500 ° C. in the second invention. .

By the way, when a mixture of helium gas and radical nitrogen excited by an RF wave used in growing nitrogen-doped p-ZnSe: N on a GaAs substrate is used, no damage occurs. It is known that p-ZnSe epitaxial films can be grown (Take Nagatake, Hiroyuki Tosaka, Masakazu Kobayashi, Akihiko Yoshikawa: Proceedings of the 54th Annual Meeting of the Society of Applied Physics, Autumn 1993 P.256.
29P-ZL-14). However, in this document, RF
No mention is made of the case where helium is mixed with hydrogen plasma excited by microwaves, microwaves, ECR waves or the like, and from this document, when these hydrogen plasma and helium are mixed, the II-VI group It is impossible to predict that impurities such as an oxide film formed on the surface of the epitaxial film can be removed without serious damage.

Therefore, the inventor of the present invention has found that the H ₂ / He mixed gas plasma can remove impurities such as an oxide film formed on the surface of the II-VI group epitaxial film without seriously damaging the film. under the assumption, in order to confirm the stability of the H 2 _/ the He mixed gas plasma, H ₂ by RF waves
The plasma emission spectrum of the / He mixed gas plasma was analyzed.

FIG. 1 shows H ₂ / He obtained in the examples described later.
1 shows a typical example of an emission spectrum of mixed gas plasma. The intensity of the emission line due to H ₂ gas and the emission line due to He gas appearing on the plasma emission spectrum are
It represents the intensity of each plasma. In this spectrum, the emission line near 570 nm is He and 650
The bright lines near nm are due to H ₂ .

FIG. 2 shows the emission line intensities of the H ₂ gas and He gas plasmas (in relation to the He gas flow rate) when the RF wave power and the H ₂ gas flow rate are constant.

As is apparent from FIGS. 1 and 2, RF
Under conditions with a fixed flow rate of the wave power and H ₂ gas, (alpha) by introducing He gas, the plasma discharge state is stabilized, (beta) increasing the He gas flow rate, H ₂ plasma The bright line intensity also increases, (γ) H
It can be seen that there is an optimum condition of the He / H ₂ gas mixture ratio such that the emission line intensity of the e plasma and the emission line intensity of the H ₂ plasma both become maximum.

From the above analysis results of the plasma emission spectrum and other various experimental results, the optimum conditions in the cleaning methods of the first and second inventions are that the flow rates of He and H ₂ gases and the power of RF waves are Generally, it is confirmed that the He / H ₂ mixing ratio in (1), the vacuum degree in the growth chamber in (2), and the substrate temperature in (3) are within the respective ranges. From within the range, gas flow rate and RF
The optimum one may be appropriately selected according to the wave power.

Under the above-mentioned conditions (1) to (3), hydrogen atoms are in a radical excited by plasma or in an ionized state, and are highly reactive.
It is in a useful state for cleaning the BE growth substrate.

In the first invention, the excited hydrogen atoms are added to the MBE group II-VI group semiconductor substrate or the II-VI group semiconductor substrate by the MBE method to form an MBE grown II-VI group semiconductor epitaxial crystal film. When the II-VI group semiconductor is regrown by the method, the crystal film is irradiated in the growth chamber.

Further, in the second invention, when a group II-VI group semiconductor is grown on a ZnSe bulk crystal by the MBE method, the crystal is irradiated in the same growth chamber.

Due to the above irradiation, both the first and second inventions,
The crystal surface will be cleaned by the excited hydrogen atoms.

[0023]

【Example】

Example 1 According to the following procedure, the optimum conditions for He / H ₂ mixed gas plasma generation were first determined, and then Z grown on a GaAs substrate was used.
The surface oxide film of the nSe and MgZnSSe epitaxial film was removed, and then ZnSe was regrown.

The generation of He / H ₂ mixed gas plasma is
An RF (13.56 MHz) -radical plasma cell used for growing p-ZnSe attached to the BE growth chamber was used, and the procedure was as follows. First, 0.04 SCCM of H ₂ gas (flow rate per minute << cc >> in standard state) was introduced into this cell, and RF power was set to 350.
W added. Subsequently, He gas of 0.04 SCCM was introduced to gradually increase the flow rate of He gas. When the He gas flow rate became 0.13 SCCM, plasma of He / H ₂ mixed gas was generated. The degree of vacuum in the MBE growth chamber was about 6 × 10 ⁻⁶ Torr.

The emission spectrum of this plasma is shown in FIG. As is apparent from FIG. 1, the flow rate of He gas is increased (from 0.13 SCCM to 0.87 SC).
CM) and He gas and H on the emission spectrum
The intensity of the emission line of the _two gases increases.

FIG. 2 shows the He gas flow rate dependence of the emission line intensities of the H ₂ gas plasma and the He gas plasma when the RF power is fixed at 350 W and the H ₂ gas flow rate is fixed at 0.04 SCCM. As is clear from FIG. 2, there is an optimum value for the He gas flow rate, and under this condition, the emission line intensity of both plasmas becomes maximum when the He gas flow rate is 0.87 SCCM.

Therefore, when the H ₂ gas flow rate and the RF power are fixed to the above conditions, the He / H ₂ mixed gas plasma has the above conditions (that is, 0.87 / 0.04).
<< SCCM >> ≈20 / 1 << SCCM >>) is considered to be the most stable. However, this condition is the MBE used
It depends largely on the shape and performance of the device and radical plasma cell. For this reason, this stability condition is slightly different depending on these devices to be used, but is generally within the range (1) to (3) described above.

Next, a ZnSe and MgZnSSe epitaxial film was formed on the GaAs (substrate) at a substrate temperature of 27.
The temperature was set to 5 ° C. and the growth was performed by the MBE method.

This sample was taken out into the atmosphere and the surface was K ₂
After wet etching treatment with a mixed solution of Cr ₂ O ₇ and H ₂ SO ₄ , the sample was returned to the MBE growth chamber again.

Subsequently, the temperature of the sample was set to 275 ° C., and the He / H ₂ mixed gas plasma generated under the above conditions was applied to the surface of the sample under a vacuum degree of about 6 × 10 ⁻⁶ Torr. Irradiated. The state of the sample surface was observed by a high speed electron diffraction method (RHEED).

3 (a) and 3 (b) show electron diffraction patterns of the ZnSe (a) and MgZnSSe (b) substrates immediately after being introduced into the growth chamber. 1 (a) and (b) of FIG.
As is clear from the above, both samples were relatively dark and had a pattern similar to a point, which indicates that the sample surface was not flat in atomic order.

2 (c) and 2 (d) of FIG.
ZnSe after irradiation with H ₂ mixed gas plasma for 1 hour
(C), An electron diffraction pattern of a MgZnSSe (d) substrate is shown. As is clear from 2 (c) and 2 (d) of FIG. 3, after the plasma irradiation, the intensity of the electron beam diffraction spot is increased as compared with that before the plasma irradiation, and the higher-order diffraction extended linearly. The pattern also appears. This indicates that the non-crystalline portion such as the oxide film on the surface of the sample was removed and the flatness on the atomic order was secured.

The above plasma treated ZnSe and M
On gZnSSe, 275 ° C., about 4 × 10 ⁻¹⁰ Tor
At r, a ZnSe epitaxial film was grown. 3 (e) and 3 (f) of FIG. 3 show electron beam diffraction patterns after growth. When (e) is grown on a ZnSe substrate,
(F) is a case of growing on a MgZnSSe (d) substrate. These patterns have the same quality as a ZnSe epitaxial film grown on a normal GaAs substrate.

For this ZnSe epitaxial film, a photoluminescence (PL) method was used to obtain a temperature of 1
It was evaluated at 5K (Kelvin). The result is shown in FIG.
The same figure (a) is shown for reference, and the PL spectrum of a 0.5 μm thick ZnSe epitaxial film grown on a GaAs substrate under the same conditions as above except that the above plasma treatment is not performed. Is. (B) and (c) of the figure show the above-mentioned plasma-treated ZnSe and Mg.
3 is a PL spectrum of a 0.5 μm thick ZnSe epitaxial film grown on ZnSSe.

Strong band-edge emission was observed around 2.80 eV for all the samples shown in FIGS.
It can be seen that light emission from deep levels near 2.3 eV is relatively well suppressed. On the other hand, a bright line called Y-ray emission entangled with dislocations is observed near 2.6 eV, which appears because the ZnSe epitaxial film is relatively thin at 0.5 μm, and particularly affects the crystallinity. Not something to give.

As described above, it is apparent that a relatively good crystal of the same level as ZnSe grown on the GaAs substrate can be grown on the ZnSe and MgZnSSe epitaxial film treated with the He / H ₂ mixed gas plasma. .

As described above, by using the He / H ₂ mixed gas plasma, the oxide film formed on the ZnSe, MgZnSSe epitaxial film is stabilized in the MBE growth chamber without causing a large damage to the epitaxial film. It is possible to remove ZnSe and MgZnSSe in the same growth chamber.
It can be seen that a good quality ZnSe epitaxial crystal can be regrown on the epitaxial film.

Example 2 ZnSe and MgZn were added to the GaAs (substrate) of Example 1.
Instead of the sample on which the SSe epitaxial film was grown, Z
As in Example 1, except that an nSe bulk crystal (substrate) was used, an oxide film was formed, the oxide film was removed by He / H ₂ mixed gas plasma irradiation, and ZnSe after the oxide film was removed.
The epitaxial film was grown. This result shows that, as in Example 1, a relatively good epitaxial crystal of the same level as that of the ZnSe epitaxial crystal grown on the GaAs substrate is grown on the ZnSe bulk crystal treated by the He / H ₂ mixed gas plasma. I was able to.

Therefore, even when a ZnSe bulk crystal is used as the substrate, the oxide film formed on the substrate can be removed by using the He / H ₂ mixed gas plasma.
It can be seen that the bulk crystal can be stably removed without serious damage in the MBE growth chamber, and a good quality ZnSe epitaxial crystal can be regrown on the substrate continuously in the MBE growth chamber.

[0040]

As described in detail above, according to the present invention,
Impurities such as an oxide film generated on the surface of the substrate can be stably removed in the MBE growth chamber while suppressing damage to the crystal of the substrate. As a result, the MBE method can be continuously performed in the growth chamber. Re-growth can be performed. Further, according to the present invention, since H ₂ is used while being mixed with He, there is no danger of H _{2 and} the surface of the semiconductor substrate can be safely cleaned.

[Brief description of drawings]

FIG. 1 is a diagram showing a typical example of an emission spectrum of H ₂ / He mixed gas plasma obtained in an example of the present invention.

FIG. 2 shows RF wave power and H ₂ obtained in the embodiment of the present invention.
When the gas flow rate constant is a diagram showing the He gas flow rate dependency of the H ₂ gas and He gas plasma emission line intensities.

FIGS. 3A and 3B are Z obtained in the embodiment of the present invention.
It is a high-speed electron beam diffraction pattern of the surface state of a nSe and MgZnSSe substrate. When (a) is a ZnSe substrate,
(B) is a case of a MgZnSSe substrate.

3 (c) and 3 (d) show He / H on these substrates.
_{2 is} an electron beam diffraction pattern of the surface state of the substrate after being irradiated with _two mixed gas plasmas. (C) is a case of a ZnSe substrate, and (d) is a case of a MgZnSSe substrate.

2 (e) and 3 (f) are electron beam diffraction patterns of the surface state of the ZnSe epitaxial film regrown after plasma irradiation. When (e) is a ZnSe substrate,
(F) is the case of the MgZnSSe substrate.

FIG. 4 shows evaluation results by a photoluminescence (PL) method for the ZnSe epitaxial film obtained in the example of the present invention, and (a) is shown for reference and G
PL spectra of 0.5 μm thick ZnSe epitaxial films grown on aAs substrate without plasma treatment according to the present invention, (b) and (c) are on ZnSe and MgZnSSe plasma treated according to the present invention. 3 is a PL spectrum of a grown 0.5 μm thick ZnSe epitaxial film.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location H01L 21/3065 H01L 21/363 21/363 21/302 N

Claims (8)

[Claims] 1. A III-V group semiconductor substrate or II
A II-VI group semiconductor epitaxial crystal film grown by a molecular beam epitaxy method on a -VI group semiconductor substrate is used as a substrate, and a II-VI group semiconductor is regrown on the epitaxial crystal film substrate by a molecular beam epitaxy method. A surface cleaning method for a semiconductor substrate, characterized in that the surface of the substrate is cleaned by irradiating the substrate with a He / H ₂ mixed gas plasma beam in the growth chamber. 2. The He / H ₂ mixed gas has a volume ratio of 2/1 to
The method for cleaning the surface of a semiconductor substrate according to claim 1, wherein the surface cleaning method is 250/1. 3. The degree of vacuum in the growth chamber is 5 × 10 ⁻⁸ to 1 ×.
10. It is ^10-4 torr, It is characterized by the above-mentioned.
A method for cleaning the surface of a semiconductor substrate as described above. 4. The semiconductor according to claim 1, wherein the temperature of the II-VI group semiconductor epitaxial crystal film substrate is 100 ° C. or higher and the growth temperature of the II-VI group semiconductor epitaxial crystal film or lower. Substrate surface cleaning method. 5. A ZnSe bulk crystal is used as a substrate,
II-V was formed on the bulk crystal substrate by molecular beam epitaxy.
When growing a group I semiconductor, He /
A method for cleaning a surface of a semiconductor substrate, which comprises irradiating the same substrate with an H ₂ mixed gas plasma beam to clean the surface of the same substrate. 6. The He / H ₂ mixed gas has a volume ratio of 2/1.
The surface cleaning method according to claim 5, wherein the surface cleaning method is about 250/1. 7. The growth chamber is 5 × 10 ⁻⁸ to 1 × 10 5.
The surface cleaning method according to claim 5, wherein the vacuum is maintained at ^-4 torr. 8. A ZnSe semiconductor bulk crystal substrate is 10
It is 0-500 degreeC, The surface cleaning method of Claims 5-7 characterized by the above-mentioned.