JP3487785B2 - Method for manufacturing semiconductor device - Google Patents

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 semiconductor device in which a III-V group compound semiconductor crystal is grown by a crystal growth technique using an amorphous film as a mask.

[0002]

2. Description of the Related Art Conventionally, molecular beam epitaxial growth
In the method of manufacturing a semiconductor device using the (hereinafter referred to as MBE) method, in order to improve the quality of the III-V group compound semiconductor crystal (such as GaAs), migration of the group III element during crystal growth (surface migration) It is effective to promote. In order to promote the migration of the group III element, it is necessary to make the V / III flux ratio, which is the ratio of the group V element flux amount to the group III element flux amount, as small as possible. Group element
It was general to make the value (Ga etc.) slightly larger than the upper limit of the rich value. Also, the operating rate of the MBE device is generally determined by the flux amount of the group V element,
The operating rate also increases by making the V / III flux ratio as small as possible. Therefore, also in the case of growing a III-V group compound semiconductor crystal on a substrate having a mask of an amorphous film, the same crystal growth conditions (V / III flux ratio as the upper limit value of the group III element becomes rich) Slightly larger value) was used.

[0003]

By the way, when a group III-V compound semiconductor crystal is grown on a substrate having a mask of an amorphous film, needle-like patterns are formed on the upper and side surfaces of the mask 4 as shown in FIG. The crystal 1 may grow.
In this case, there is a problem that the ungrown portion 2 is formed immediately below the needle-shaped crystal 1 because the needle-shaped crystal 1 becomes an obstacle to the III-group and V-group fluxes during the growth. In addition, when a normal photo-etching process is performed for device fabrication after growth, there is a problem that the needle-shaped crystal 1 causes uneven coating of the resist and causes a problem, or the resist remains when the resist is removed. is there. Therefore,
When the acicular crystal 1 grows when growing the III-V group compound semiconductor crystal, the characteristics of the semiconductor element deteriorate and the yield decreases.

Therefore, an object of the present invention is to provide a method of manufacturing a semiconductor device capable of suppressing the growth of needle crystals when growing III-V group compound semiconductor crystals.

[0005]

In order to achieve the above object, a method of manufacturing a semiconductor device according to a first aspect of the present invention comprises a step of partially forming an amorphous film on a semiconductor crystal substrate and a step of forming the amorphous film. III-V by a molecular beam epitaxial growth method using the amorphous film as a mask on the formed semiconductor crystal substrate.
A method for manufacturing a semiconductor device, which comprises a step of growing a group III compound semiconductor layer, wherein a group III element is formed at an early stage of the step of growing the group III-V compound semiconductor crystal layer.
Ratio of group V element flux to total flux
Crystal growth with a V / III flux ratio of 3 or more
Te, inhibit the migration of fast group III element of the migration rate of the main elements constituting the group III-V compound semiconductor crystal layer, the group III-V compound semiconductors
Group III lids except in the initial stage of the growth of the body crystal layer.
Exceeding the upper limit of 1 for the V / III flux ratio
Value and a V / III flux ratio lower than 3
It is characterized in Rukoto allowed length.

According to the method of manufacturing a semiconductor device of claim 1, the III-V group is formed at an early stage of the step of growing the III-V group compound semiconductor crystal layer by the molecular beam epitaxial growth method using the amorphous film as a mask. By inhibiting the migration of the group III element having a high migration rate among the main elements forming the compound semiconductor crystal layer, it is possible to suppress the growth of the needle-like crystals of the amorphous film. Therefore, the growth failure of the III-V group compound semiconductor crystal layer and the failure of the photolithography process due to the needle-shaped crystal are eliminated, and the semiconductor device having good characteristics can be manufactured with high yield .

Further, the group III by making the V / III flux ratio is the ratio of the flux of the group V element 3 or more with respect to the flux of the element, III-V compound semiconductor crystal layer grown initial acicular Crystal growth can be reliably suppressed, and crystal growth can be performed at a low V / III flux ratio except in the initial stage of growth, and a III-V group compound semiconductor crystal layer with good crystallinity can be formed.

According to a second aspect of the present invention, there is provided a method of manufacturing a semiconductor device according to the first aspect, wherein
When inhibiting the migration of the group III element having a high migration rate at the initial stage of the growth of the step of growing the group IV compound semiconductor crystal layer, the ratio of the flux amount of the group V element to the flux amount of the group III element is V / II
The I flux ratio is characterized by being controlled by adjusting the flux amount of the group III element.

According to the method of manufacturing a semiconductor device of the second aspect , the growth rate of the III-V group compound semiconductor crystal layer is controlled by adjusting the flux amount of the III group element. By doing so, since the V / III flux ratio is controlled, the controllability is improved, and the operating rate of the MBE device can be improved by setting the use amount of the group V element to the necessary minimum.

According to a third aspect of the present invention, there is provided a method of manufacturing a semiconductor device according to the first aspect, wherein
When inhibiting the migration of the group III element having a high migration rate in the early stage of the step of growing the IV compound semiconductor crystal layer, aluminum, which is a group III element having a slow migration rate, is added to form a surface modification layer. It is characterized by being formed.

According to the method for manufacturing a semiconductor device of the third aspect , by adding aluminum, which is a group III element having a slow migration rate, at the initial stage of growth of the group III-V compound semiconductor crystal layer, the group III element Since it inhibits migration, the V / III flux ratio can be set low, and the operating rate of the MBE device can be improved by setting the use amount of the group V element to the necessary minimum.

According to a fourth aspect of the present invention, there is provided a method of manufacturing a semiconductor device, which comprises a step of partially forming an amorphous film on a semiconductor crystal substrate, and a step of processing the semiconductor crystal substrate using the amorphous film as a mask. After processing the semiconductor crystal substrate,
A method of manufacturing a semiconductor device, comprising the step of growing a III-V group compound semiconductor layer on the semiconductor crystal substrate by a molecular beam epitaxial growth method using the amorphous film as a mask, the III-V group compound semiconductor layer Flux of group III element at the beginning of the growth process
V / III which is the ratio of the flux amount of the V group element to
The crystal is grown at a flux ratio of 3 or more, and the III-V
Among the main elements constituting the group III compound semiconductor layer, the migration of the group III element having a high migration rate is inhibited, and the III-V group compound semiconductor crystal layer is grown.
V / III flag that is rich in group III except in the initial stage of process growth
The value is higher than 1 which is the upper limit of the box ratio and lower than 3.
By crystal growth at a V / III flux ratio is characterized in Rukoto.

According to the method of manufacturing a semiconductor device of the above-mentioned claim 4 , after the amorphous film is partially formed on the semiconductor crystal substrate and the amorphous film is used as a mask, the semiconductor crystal substrate is processed by, for example, etching. A III-V group compound semiconductor layer is grown on the semiconductor crystal substrate on which the amorphous film is formed by a molecular beam epitaxial growth method using the amorphous film as a mask. In the early stage of the growth of the III-V compound semiconductor crystal layer, by inhibiting the migration of the group III element having a high migration rate among the main elements constituting the III-V compound semiconductor crystal layer, the amorphous film The growth of needle crystals can be suppressed. Therefore, the growth failure of the III-V group compound semiconductor crystal layer and the failure of the photolithography process due to the needle-shaped crystal are eliminated, and the semiconductor device having good characteristics can be manufactured with high yield.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a method for manufacturing a semiconductor device of the present invention will be described in detail with reference to embodiments shown in the drawings.

(First Embodiment) FIGS. 1A and 1B are sectional views showing a method for manufacturing a semiconductor device according to a first embodiment of the present invention.

The semiconductor device manufactured in the first embodiment has a flat GaAs substrate 5 as shown in FIG.
As an amorphous film, an oxide film such as alumina (AlO
x (x; 0 to 1)) is vapor-deposited, and patterning is performed in a stripe shape by ordinary photolithography to obtain an AlOx film 4
To form.

Then, as shown in FIG. 1 (b), the resist
After removing (not shown), GaAs crystals are grown by the MBE method under the following conditions. In the initial stage of the crystal growth, the crystal growth is controlled by the V / III flux ratio (ratio of the group V molecular beam flux amount to the group III molecular beam flux amount).
Crystal growth is performed with a V / III flux ratio that is Group II-rich (Ga-rich in this case) at least three times the upper limit (V / III flux ratio> 3), for example, GaAs growth until a thickness of 0.1 μm is reached. Form layer 6. After that, the value of the V / III flux ratio is slightly higher than the upper limit (= 1) of the V / III flux ratio at which the crystal growth becomes Ga-rich, for example, 1.
The GaAs growth layer 7 is formed on the GaAs growth layer 6 by doubling (V / III flux ratio = 1.2) until the required layer thickness is reached.

At this time, by setting the V / III flux ratio to 3 or more at the initial stage of the growth of the III-V compound semiconductor crystal layer (during the growth of the GaAs growth layer 6), the migration of Ga is hindered, and AlOx is prevented. Needle-like crystals do not occur near the side surface of the film 4. Therefore, there is no growth defect in which ungrown portions due to needle-like crystals occur in the GaAs growth layers 6 and 7, and the step of removing needle-like crystals can be omitted. Furthermore, G
When a normal photo-etching process is performed for device fabrication after the growth of aAs growth layers 6 and 7, needle-like crystals cause uneven coating of the resist, resulting in defects or resist remaining during resist removal. The problem of doing does not occur.

Therefore, according to the semiconductor element manufacturing method of the first embodiment, a semiconductor element having excellent characteristics and yield can be obtained.

(Second Embodiment) FIGS. 2A and 2B are sectional views showing a method of manufacturing a semiconductor device according to a second embodiment of the present invention.

The semiconductor device manufactured in the second embodiment has a flat GaAs substrate 5 as shown in FIG.
Deposited AlOx is an oxide film on, perform patterning to normal by Ri stripes photolithography to form the AlOx film 4 as a non-crystalline film.

Then, as shown in FIG.
After removing (not shown), GaAs is grown by the MBE method under the following conditions. Crystal growth rate (growth rate) is 1
When the Ga flux amount is set to be μm / hour, the V / III flux ratio is set to about 1.2.
A flux amount of s is set, and growth is performed at a growth rate of 0.4 μm / hour until an initial stage of crystal growth, for example, a thickness of 0.1 μm is reached to form a GaAs growth layer 8. After that, until the required layer thickness is reached, growth is performed at a growth rate of 1 μm / hour, and G is grown on the GaAs growth layer 8.
An aAs growth layer 7 is formed. In this case, the initial growth is 0.1 μm
The V / III flux ratio is 3 up to, and then the V / III flux ratio is 1.2.

At this time, by setting the V / III flux ratio to 3 at the initial stage of the growth of the III-V compound semiconductor crystal layer (during the growth of the GaAs growth layer 8), the migration of Ga is inhibited and the AlOx film is formed. No needle-like crystals are generated near the side surface of No. 4. Further, since the V / III flux ratio is controlled by the growth rate, the V / III flux ratio can be changed instantaneously, and the amount of As used can be set to the minimum during the growth. The operating rate can be increased.

(Third Embodiment) FIGS. 3A and 3B are sectional views showing a method for manufacturing a semiconductor device according to a third embodiment of the present invention.

The semiconductor device manufactured in the third embodiment has a flat GaAs substrate 5 as shown in FIG.
As an amorphous film, for example, AlOx which is an oxide film is vapor-deposited thereon, and patterning is performed in a stripe shape by ordinary photolithography to form an AlOx film 4.

Then, as shown in FIG. 3B, the resist
After removing (not shown), GaAs is grown by the MBE method under the following conditions. Initial stage of crystal growth, eg 0.1
Add aluminum (Al) until reaching a thickness of μm,
An AlGaAs growth layer 9 is grown as a surface modification layer. Then, the GaAs growth layer 7 is grown until the required layer thickness is reached. In this case, the V / III flux ratio is set to 1.2 through the crystal growth of the AlGaAs growth layer 9 and the GaAs growth layer 7.

At this time, in the initial stage of the growth of the III-V group compound semiconductor crystal layer (during the growth of the AlGaAs growth layer 9), aluminum (Al) which is a group III element having a slow migration rate is used.
Addition of Ga inhibits the migration of Ga, and needle crystals do not grow near the side surface of the AlOx film 4. In addition, since the addition of Al inhibits the migration of Ga, the V / III flux ratio can be set low, and the amount of As used can be set to the minimum during the growth. You can

When the AlGaAs layer 9 and the GaAs layer 7 are used as the current blocking layer, the AlGaAs layer 9 has a heterostructure, so that the current blocking effect is large.

(Fourth Embodiment) FIGS. 4 (a) to (d) and FIGS. 5 (a) to (c) are AlGaInP-based red semiconductor lasers to which a method for manufacturing a semiconductor device according to a fourth embodiment of the present invention is applied. It is sectional drawing which shows the manufacturing process of an element.

As shown in FIG. 4A, the semiconductor laser device manufactured according to the fourth embodiment has an N-type GaInP buffer layer 11 and an N-type Al on an N-type GaAs substrate 10.
GaInP cladding layer 12, GaInP / AlGaInP multiple quantum well active layer 13, P-type AlGaInP cladding layer 14, GaInP etching stop layer 15, and P-type A
l GaInP cladding layer 16, P-type GaInP intermediate bandgap layer 17, and P-type GaAs cap layer 18 are M
The layers are sequentially laminated by the BE method, and the Al ₂ O ₃ film 4 is formed on the P-type GaAs cap layer 18 by vapor deposition.

After that, as shown in FIG. 4B, the AlOx film 40 is patterned into stripes by ordinary photolithography, and the AlOx film 40 is used as a mask to form a P film.
The GaAs cap layer 18, the P-type GaInP intermediate bandgap layer 17, and the P-type AlGaInP cladding layer 16 are removed by etching to form a ridge directly below the AlOx film 40.

In this way, after processing the N-type GaAs substrate 10 using the AlOx film 40 as a mask, the process shown in FIG.
As shown in (c), after removing the resist 19 (shown in FIG. 4 (a)), the second MBE growth is performed to form the N-type GaAs current blocking layers 20 and 21 under the following conditions. When the amount of Ga flux was set so that the crystal growth rate (growth rate) was 1 μm / hour, the V / III flux ratio was 1.2.
Set the flux amount of As so that
In the initial stage of crystal growth, for example, until the thickness reaches 0.1 μm, the growth rate is 0.4 μm / hour, and N
A type GaAs current blocking layer 20 is formed. After that, until the required layer thickness is reached, growth is performed at a growth rate of 1 μm / hour, and N-type GaAs is formed on the N-type GaAs current blocking layer 20.
The As current blocking layer 21 is formed. In this case, the V / III flux ratio was 3 until the initial growth of 0.1 μm, and then
This means that the V / III flux ratio is 1.2. At this time, the polycrystalline GaAs crystal 2 is formed on the surface of the AlOx film 40.
2,23 are laminated, but by setting the V / III flux ratio to 3 at the initial stage of growth of the III-V group compound semiconductor crystal layer (during the growth of the AlGaAs growth layer 9), Ga migration is inhibited, Needle-like crystals do not occur near the side surface of the AlOx film 40.

Next, as shown in FIG. 4D, a resist 19 is applied by a spinner. In this case, N-type GaAs
The resist is applied on the current blocking layer 21, but the resist is hardly applied on the GaAs layer 23 in the polycrystalline state. After that, the resist on the entire surface is covered with O3-UV.
(Ozone-ultraviolet) ashing is performed so that the resist is applied only on the N-type GaAs current blocking layer 21.

Next, as shown in FIG. 5A, the resist 1
9 as a mask, the GaAs layers 22 and 23 in the polycrystalline state (see FIG.
(shown in (d)) is removed by etching.

After that, as shown in FIG. 5B, the resist 19 and the AlOx film 40 (shown in FIG. 5A) are removed.

Then, the third MBE growth was performed, and the results shown in FIG.
As shown in (c), a P-type GaAs contact layer 24 is formed on the P-type GaAs cap layer 18 and the N-type GaAs current blocking layer 21, and an electrode 25 is formed on the P-type GaAs contact layer 24. By forming the electrode 26 on the rear surface side of the N-type GaAs substrate 10, an AlGaInP-based red semiconductor laser device is obtained.

Although AlOx is used for the non-crystalline film in the first to fourth embodiments, the non-crystalline film is not limited to this and may be SiOx or SiNx. In this case, a good quality film with few pinholes can be obtained. At the same time, it is also possible to apply by spin coating.

In the first to fourth embodiments, III
Although GaAs was used as the group-V compound semiconductor, III-V
Group compound semiconductors are InGaAlP, InGaAlN, InGaA
It may be lSb or InGaAsP.

The method for manufacturing a semiconductor device according to the present invention is a semiconductor laser device, a light emitting diode or an HBT (He
Of course, it may be applied to any III-V group compound semiconductor device such as terojunction Bipolar Transistor.

[0040]

As is apparent from the above, according to the method of manufacturing a semiconductor device of the invention of claim 1, the MBE method is used on a semiconductor crystal substrate partially having a mask of an amorphous film.
When crystal growth of a III-V group compound semiconductor is performed, a non-crystalline film is formed by inhibiting migration of a group III element having a high migration rate among the main elements constituting the III-V group compound semiconductor crystal layer in the initial stage of growth. Since needle-shaped crystals are not generated on the upper surface and the side surface of the mask of (1), growth defects due to needle-shaped crystals and defects in the photolithography process for device fabrication are eliminated, and semiconductor devices with good characteristics can be manufactured with high yield. it can.

Further, when inhibiting the migration of fast III group element initial growth of migration rate of growing on Symbol Group III-V compound semiconductor crystal layer, III
By setting the V / III flux ratio, which is the ratio of the flux amount of the group V element to the flux amount of the group element, to 3 or more, it is possible to reliably suppress the growth of needle-like crystals in the initial growth stage of the III-V compound semiconductor crystal layer. At the same time, crystal growth can be performed at a low V / III flux ratio except in the initial stage of growth, and a III-V group compound semiconductor crystal layer with good crystallinity can be formed.
Also, since the crystal growth is performed at a low V / III flux ratio except in the initial stage of growth, the amount of As used can be minimized, so that the operating rate of the MBE device can be increased.

According to the method of manufacturing a semiconductor element of the invention of claim 2, in the method of manufacturing a semiconductor element of claim 1, the migration rate is set at an initial stage of growth in the step of growing the III-V group compound semiconductor crystal layer. When the migration of the group III element having a fast growth rate is inhibited, the growth rate of the group III-V compound semiconductor crystal layer is controlled by adjusting the flux amount of the group III element to obtain V / III.
Since the flux ratio is controlled, the controllability is improved, and the operating rate of the MBE device can be improved by setting the amount of group V element used to the necessary minimum. Also, by controlling the V / III flux ratio by the growth rate,
As the amount of As used can be minimized, MBE
The operating rate of the equipment can be increased.

According to the method of manufacturing a semiconductor device of the invention of claim 3, in the method of manufacturing a semiconductor device of claim 1, the migration rate is increased in the initial stage of growth in the step of growing the III-V compound semiconductor crystal layer. When the migration of the group III element having a fast migration rate is inhibited, the migration of the group III element is inhibited by adding aluminum, which is a group III element having a slow migration rate, so that the V / III flux ratio can be set low, and The operating rate of the MBE device can be improved by setting the use amount of the element to the necessary minimum. Further, since the addition of aluminum inhibits the migration of the group III element, the amount of As used can be minimized.
The operating rate of the MBE device can be increased.

According to the method of manufacturing a semiconductor element of the invention of claim 4 , after the semiconductor crystal substrate partially having the mask of the amorphous film is processed by etching or the like, the amorphous film is formed on the semiconductor crystal substrate. By the MBE method as a mask of
When crystal growth of a III-V group compound semiconductor is performed, by inhibiting migration of a III-V group semiconductor element having a high migration rate among the main elements constituting the III-V group compound semiconductor crystal layer at the initial growth stage, the amorphous Needle-shaped crystals are not generated on the upper and side surfaces of the film mask, so that growth defects due to needle-shaped crystals and defects in the photolithography process for device fabrication are eliminated, and semiconductor devices with good characteristics can be manufactured with high yield. You can

[Brief description of drawings]

1A and 1B are process diagrams of a method for manufacturing a semiconductor device according to a first embodiment of the present invention.

2 (a) and 2 (b) are process drawings of a method for manufacturing a semiconductor device according to a second embodiment of the present invention.

3 (a) and 3 (b) are process diagrams of a method for manufacturing a semiconductor device according to a third embodiment of the present invention.

4A to 4D are process diagrams of a method for manufacturing a semiconductor laser device as a semiconductor device according to a fourth embodiment of the present invention.

5A to 5C are process diagrams of the method for manufacturing the semiconductor laser device, following FIG.

FIG. 6 is a diagram showing a generation state of needle-shaped crystals when a conventional method is used.

[Explanation of symbols]

1 ... Needle crystal, 2 ... Ungrown part, 3 ... GaAs growth layer, 4 ...
AlOx film, 5 ... GaAs substrate, 6 ... GaAs growth layer, 7 ... G
aAs growth layer, 8 ... GaAs growth layer, 9 ... AlGaAs layer, 1
0 ... N-type GaAs substrate, 11 ... N-type GaInP buffer layer, 12 ... N-type AlGaInP cladding layer, 13 ... Multiple quantum well active layer, 14, 16 ... P-type AlGaInP cladding layer, 15 ... Etching stop layer, 17 ... Intermediate Band gap layer, 18 ... P-type GaAs gap layer, 19 ... Resist, 20 ... N-type GaAs current blocking layer, 21 ... N-type Ga
As current blocking layer, 22 ... Polycrystalline GaAs layer, 2
3 ... Polycrystalline GaAs layer, 24 ... P-type GaAs contact layer, 25, 26 ... Electrodes.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A 54-16177 (JP, A) JP-A 63-2890 (JP, A) JP-A 7-94409 (JP, A) JP-A 4- 130688 (JP, A) JP 8-97140 (JP, A) JP 2-288223 (JP, A) JP 63-60197 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01L 21/203 C30B 23/08 C30B 29/40-29/44

Claims (4)

(57) [Claims] 1. A step of partially forming an amorphous film on a semiconductor crystal substrate, and a step of forming the amorphous film on the semiconductor crystal substrate by the molecular beam epitaxial growth method using the amorphous film as a mask III- A method for manufacturing a semiconductor device, which comprises a step of growing a group V compound semiconductor layer, wherein the amount of flux of the group III element relative to the amount of flux of the group III element at the initial growth stage of the step of growing the group III-V compound semiconductor crystal layer
V / III flack, which is the ratio of the amount of flux of group V element
The crystal growth is performed at a ratio of 3 or more to inhibit migration of a group III element having a high migration rate among the main elements constituting the group III-V compound semiconductor crystal layer.
Of the group III-V compound semiconductor crystal layer
V / III flux ratio that is rich in group III except in the initial stage of growth
V / II higher than the upper limit of 1 and lower than 3
A method for manufacturing a semiconductor device, characterized in that a crystal is grown at an I flux ratio . 2. The method for manufacturing a semiconductor device according to claim 1, wherein when the migration of the group III element having a high migration rate is inhibited at an early stage of growth in the step of growing the group III-V compound semiconductor crystal layer, A method for manufacturing a semiconductor device, wherein a V / III flux ratio, which is a ratio of a flux amount of a group V element to a flux amount of a group III element, is controlled by adjusting a flux amount of the group III element. 3. The method of manufacturing a semiconductor device according to claim 1, wherein when the migration of the group III element having a high migration rate is inhibited at an early stage of growth in the step of growing the group III-V compound semiconductor crystal layer, A method for manufacturing a semiconductor device, characterized in that a surface modification layer is formed by adding aluminum which is a group III element having a slow migration rate. 4. A step of partially forming an amorphous film on a semiconductor crystal substrate, a step of processing the semiconductor crystal substrate using the amorphous film as a mask, and a step of processing the semiconductor crystal substrate and then the semiconductor. A method for manufacturing a semiconductor device, comprising: growing a III-V group compound semiconductor layer on a crystalline substrate by a molecular beam epitaxial growth method using the amorphous film as a mask, wherein the III-V group compound semiconductor layer is grown. In the initial stage of the growing process, the amount of V group to the amount of III group element flux
V / III flux ratio, which is the ratio of the amount of elemental flux
Was crystallized grown in 3 above, to inhibit the migration of fast group III element of the migration rate of the main elements constituting the group III-V compound semiconductor layer, growing the group III-V compound semiconductor crystal layer Of the process
V / III flux ratio that is rich in group III except in the initial stage of growth
V / II higher than the upper limit of 1 and lower than 3
A method for manufacturing a semiconductor device, characterized in that a crystal is grown at an I flux ratio .