JPH06112123A - Method for manufacturing semiconductor device - Google Patents

Abstract

(57) [Abstract] [Objective] A method for producing a III-V group compound semiconductor using a gas source MBE method, wherein a high concentration carbon-doped p-type layer is grown using a group III element serving as a carbon doping source. It is another object of the present invention to provide a method of manufacturing a semiconductor device that can suppress the memory effect of carbon as much as possible and control the doping level of the next layer. A carbon-doped growth step of growing a carbon-doped p-type III-V compound semiconductor layer using a first group III element organic compound as a carbon doping source as a group III element source, and then carbon Using only the second group III element organic compound, which is difficult to become a doping source, as a group III element source at a growth temperature at which the first group III element organic compound is not easily decomposed,
A carbon non-doped growth step of growing a group III-V compound semiconductor layer having a low carbon content by setting the molar supply rate of the group V element to the molar supply rate of the group III element, V / III ratio, to be 10 or more.

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, and more particularly to a method for manufacturing a III-V group compound semiconductor using a gas source MBE method.

In the III-V group compound semiconductor device, in order to obtain the desired characteristics to the maximum, precise film thickness and composition control, high-quality crystal multilayer film showing a steep concentration distribution at the heterojunction interface, and the like are required. Needed. The gas source molecular beam epitaxy (MBE) method uses a molecular beam of an organometallic compound as a source of a group III element. Especially carbon
It is easy to increase the concentration when growing a layer doped as a type impurity.

[0003]

2. Description of the Related Art In the gas source MBE method, a group III element, a group V element and a dopant are basically introduced in a gas state into a gas cell. In particular, since the group III element component having a low vapor pressure is introduced under high vacuum as an organometallic compound gas capable of adjusting the flow rate, it is said that the source gas can be easily switched and it is advantageous for forming a heterojunction.

Impurities can also be supplied by a gaseous source. Since the group II element acceptor impurities such as Zn, Mg, and Be have an order of magnitude larger diffusion coefficient than the donor impurities, the profile at the interface often lacks steepness when highly doped. On the other hand, carbon impurities show a diffusion coefficient smaller by 2 to 3 orders of magnitude, and 10 ²¹ ato.
It has the characteristic that it can be uniformly doped up to about ms / cm ³ .

In the gas source MBE method, when a trimethyl group III element such as trimethylgallium is used as a group III element source, carbon impurities are highly doped as acceptors during the growth process of the group III-V compound semiconductor. Known (eg, K. Saito et al.,
J. Appl. Phys. 64 (1988) 3975).

By positively utilizing this effect, a high concentration p with a steep doping profile is formed on the n-type layer.
It is possible to grow a mold layer. That is, in the gas source MBE method, it is possible to grow a highly doped p-type and n-type multilayer thin film.
For example, it can be used for manufacturing a GaAs / GaAlAs heterojunction bipolar transistor (HBT).

In HBT, without lowering the current gain,
It is possible to reduce the resistance of the thin film p-type base region.

[0008]

As described above, when the trimethyl group III element is used as the source, the gas source M
In the BE method, the carbon acceptor is highly doped I
The II-V compound thin film layer can be grown relatively easily. The interface between the carbon-doped p-type layer and the underlying crystal exhibits a steep concentration profile as described above.

However, when the n-type layer is continuously grown on the carbon-doped p-type layer using a group III source which is difficult to serve as a carbon doping source, the concentration profile of the pn junction does not necessarily become steep. In particular, when the n-type layer is lightly doped, the effect is remarkable.

This is an effect of the carbon of the trimethyl group III element source which has already been stopped. For example, when a low-concentration n-type emitter layer is grown on a high-concentration p-type base layer of HBT, a group III element source is usually changed from a trimethyl type which is a carbon doping source to another organometallic type which is difficult to be a carbon doping source. , Switch to, for example, a triethyl source. However, the problem that the trimethyl group III element attached to the inner wall of the source cell or the like is mixed from the atmosphere during the growth of the next layer, that is, the so-called residual gas memory effect is unavoidable.

When GaAs or GaAlAs is doped with a carbon acceptor of the order of 10 ¹⁹ atoms / cm ³ from a trimethylgallium (TMG) source, the memory effect on the next layer is the same under the same growth conditions (underlying crystal temperature, [V] /
[III] molar ratio) is on the order of 10 ¹⁸ atoms / cm ³ .

Therefore, when growing a low concentration n-type layer on a high concentration carbon-doped p-type layer, the impurity concentration,
There is a problem that it is difficult to control the conductivity type. An object of the present invention is to grow a high-concentration carbon-doped p-type layer by using a group III element serving as a carbon doping source, and then suppress the memory effect of carbon as much as possible to control the doping level of the next layer. Is to provide a method for manufacturing the same.

[0013]

According to the method of manufacturing a semiconductor device of the present invention, carbon-doped p-type III-V is formed by using a first group III element organic compound as a carbon doping source as a group III element source. A carbon-doping growth step of growing a Group III compound semiconductor layer, and thereafter, using only a second Group III element organic compound that is difficult to become a carbon doping source as a Group III element source, the first Group III element organic compound V at a growth temperature that does not easily decompose
The ratio of the molar supply rate of the group element and the molar supply rate of the group III element,
A carbon non-doped growth step of growing a III-V group compound semiconductor layer having a low carbon content with a V / III ratio of 10 or more.

[0014]

By using the organic compound of the first group III element as the carbon doping source, the p-type group III-V compound semiconductor layer can be heavily doped with carbon.

When the first group III element organic compound serving as a carbon doping source is used, a memory effect occurs.
The memory effect is suppressed by setting the growth temperature to a temperature at which the organic compound of the first group III element, which is a carbon doping source, is not easily decomposed.

By performing the carbon dope growth step by simultaneously supplying the organic compound of the group III element, which is difficult to become a carbon dope source, a sufficient carbon dope amount can be secured and the memory effect can be further suppressed. It is considered to be a thing.

Increasing the [V] / [III] ratio decreases the density of the group V element vacancy during growth (the product of the group III element vacancy density and the group V element vacancy density at thermal equilibrium). Is constant). For this reason, the density of carbon atoms that substitute the group V element vacancies and become acceptors is further reduced.

The present invention will be described in more detail below with reference to examples.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram for explaining the manufacture of a hetero bipolar transistor (HBT) according to an embodiment of the present invention. FIG. 1 (A) schematically shows the configuration of the HBT, and FIG. 1 (B) schematically shows the configuration of a gas source MBE apparatus used for manufacturing the HBT.

In FIG. 1A, HBT is a semi-insulating G
A collector layer 2 formed of n-type GaAs or the like is arranged on a substrate 1 formed of aAs or the like, and a C-doped base layer 3 of carbon-doped p-type GaAs or the like is formed on the collector layer 2. An emitter layer 4 formed of n-type AlGaAs or the like having a wider energy gap than the base layer 3 and a contact layer 5 of n ⁺ -type GaAs or the like for forming an electrical contact are formed.

Since the emitter layer 4 has a wider bandgap than the base layer 3, even if an emitter current flows due to the emitter-base bias, substantial carriers are injected from the base layer 3 to the emitter layer 4. Absent.

Therefore, it is possible to dope the base layer 3 at a high concentration without increasing the base current, and it is possible to obtain excellent characteristics in which the base resistance is reduced and the base current is suppressed. The substrate 1 and the collector layer 2 can also be used as an n-type substrate.

If a good ohmic contact can be formed on the emitter layer 4, the contact layer 5 may be omitted. The base layer 3 is preferably doped as high as possible to reduce the base resistance.

When the emitter layer 4 is formed on the base layer 3, if the p-type impurity used for forming the base layer 3 is mixed, the emitter layer 4 does not have a desired characteristic and the HBT characteristic deteriorates. Resulting in.

FIG. 1 (B) shows a gas source MBE apparatus that can be used to grow the HBT shown in FIG. 1 (A). In FIG. 1B, the base crystal 16 is an undoped GaAs wafer having a plane orientation (100). After performing mirror polishing and surface chemical treatment, the wafer is fixed on a Mo block table and introduced into the reactor. In a preparation chamber (not shown), the surface is first cleaned by heating to 300 ° C., and then the holder 14 in the growth chamber 10 is set.
A heater 18 is built in below the holder 14.

The growth chamber 10 is equipped with an exhaust pipe 12 as an exhaust system in addition to the equipment related to the base crystal 16 and is connected to a diffusion pump system. Further, the RHEED gun 20 and the RHEED screen 22 for in-situ observation of the growth layer are equipped.

The gas sources are gas cells 24, 25, 26.
And 27 into the growth chamber 10.
A gas introducing pipe S is connected to each gas cell, and a valve V is connected between the gas introducing pipe and the source container so that the gas can be shut off.

Each gas cell is equipped with a heater for thermal decomposition and the like, and a shutter 28 is provided at the outlet thereof.
29, 30 and 31 are provided respectively. A liquid nitrogen shroud 32 is provided on the inner wall of the growth chamber 10.

Group V element gases such as AsH ₃ and doping gases such as Si ₂ H ₆ (diluted if necessary with hydrogen etc.) are passed through a pressure regulator from a gas cylinder and triethyl which is an organometallic source. Gallium (TEG), trimethylgallium (TMG), trimethylamine alane (TMAAl), etc. are directly connected to the gas line from the bottle without using a carrier gas, and the flow rate is adjusted using a mass flow controller.

The gas introducing pipe is first evacuated to a high degree of vacuum and sufficiently purged with each of the above gases, and then each gas is introduced into the growth chamber 10 under a stable flow rate. Using the gas source MBE apparatus of FIG. 1, p of GaAs / GaAlAs
An example of growing an epitaxial layer including an n-heterojunction will be described.

First, the GaAs substrate, which is the underlying crystal 16, is cleaned with an oxide film. The heater 18 is energized to raise the temperature of the base crystal 16, and AsH ₃ is flowed at 400 ° C. or higher to keep the temperature in the arsenic atmosphere at 650 ° C. for several minutes.

The temperature of the base crystal 16 is lowered to about 520 ° C. or lower, typically to about 500 ° C. to start the growth. The first growth layer is an n-type GaAs layer, and then a carbon-doped p ⁺ -type GaAs layer is grown. It is also possible to use an n-type GaAs substrate and directly grow a carbon-doped p ⁺ -type GaAs layer thereon.

When growing a carbon-doped p ⁺ -type GaAs layer, the corresponding valve V is opened and T
MG and TEG are simultaneously introduced into the gas cell 25.
TMAAl may be gradually supplied to gradually increase the Al composition. The gas cell temperature is 8 to keep the raw material in a gaseous state.
The temperature is 0 to 90 ° C.

The temperature of the gas cell 24 for TMAAl is set to 50.degree. The gas cell 26 is heated to about 1100 ° C., AsH ₃ is decomposed and introduced into the chamber 10. V
Supply molar ratio of group element / group III element, [V] / [II
I] ratio is about 1. Typically TEG 0.6scc
m, TMG 1.75 sccm, AsH ₃ 1 sccm.

As shown in FIG. 3, after the carbon-doped layer 40 having a thickness of 100 nm is grown on the underlying substrate 16 of n-type GaAs, the TMG valve is closed and the supply of TMG is cut off.
That is, only TEG is introduced into the gas cell 25 as a gallium source.

Furthermore, TMA is used as an aluminum source.
Al is flown and Si ₂ H ₆ is introduced into the gas cell 27 as an n-type impurity source to grow the n-type AlGaAs layer 41. The flow rate of AsH ₃ is increased to set the [V] / [III] ratio to 10 or more, and the n-type AlGaAs layer 41 is a Si-doped n-type AlGaAs layer having a carrier concentration of 5 × 10 ¹⁷ cm ⁻³ .

The gas flow rate is typically TEG 0.6sc
cm, TMAAl 0.2sccm, AsH ₃ 10scc
m and SiH ₆ 0.7 sccm. At this time, Al
The composition of the GaAs layer 41 was Al _0.25 Ga _0.75 As, and as a result of electrical measurement, the carrier concentration was 5 × 10 ¹⁷ cm ^−3.
The n-type growth layer of was obtained. The thickness of the growth layer is 150 nm.

On top of that, a Si-doped n-type GaAs layer 42 having a thickness of 300 nm (carrier concentration: 2 × 10 ¹⁸ cm ⁻³ ).
Grow. Before the growth starts, the valve for TMAAl is closed to stop the flow of TMAAl. Other gases change the flow rate. Typical flow rate for each gas is TEG 0.8scc
m, AsH ₃ 4 sccm and Si ₂ H ₆ 5 sccm. The growth temperature is about 500 ° C. throughout.

In this way, the carbon-doped p ⁺ -type GaAs layer 40, the Si-doped and C non-doped n-type AlGaAs layer 41, and the n ⁺ -type GaAs layer 42 are grown on the n-type GaAs substrate 16.

What is important here is that the growth temperature is set to, for example, 500 ° C., which is a temperature at which TMG is not easily decomposed or hardly decomposed, and T is used when the carbon-doped layer is grown.
Supplying MG and TEG at the same time, stopping the supply of TMG when growing an n-type layer not doped with carbon, and supplying only TEG as a gallium source, and [V] / [III] Keeping the ratio high.

For comparison, a conventional growth method using the apparatus shown in FIG. 1 will be described. As shown in FIG.
A carbon-doped p ⁺ -type GaAs layer 51, an n-type AlGaAs layer 52, and an n-type GaA are formed on a base substrate 50 of type GaAs.
A case where the s layer 53 is continuously grown will be described below.

During the growth of each layer, the temperature of the base crystal 50 is TM
Set to 580 ° C. where G easily decomposes. First, in the case of the carbon-doped p ⁺ type layer 51 which is the first growth layer, the gas flow rate is TMG 1.75 sccm and AsH _{3 3} sccm. The film thickness is 100 nm. A carrier concentration of 4 × 10 ¹⁹ cm ⁻³ is obtained by carbon doping.

The first growth layer composition may be initially GaAs and grown to a thickness of about 30 nm, and Al _x Ga _1-x As having a gradually higher AlAs mixed crystal ratio may be formed, and finally x = 0.25.

Second growth layer, n-type AlGaAs layer 5
2 is the supply of TMG which becomes the C source for making it n-type
Stop, supply TEG only instead, Si doping
Do. Gas flow rate is TEG 0.8sccm, TMA
Al 0.3 sccm, AsH ₃4 sccm, SiH
₆It is 0.7 sccm. The thickness of the growth layer is 150 nm
To do. The composition obtained is Al_0.25Ga_0.75It is As.

Si doping is performed also in the growth of the n-type GaAs layer 53 which is the third growth layer. In this case, the gas flow rate is TEG 0.8 sccm, AsH _{3 4} scc
m, SiH ₆ 5 sccm. Growth layer thickness is 300
nm. The carrier concentration is 2 × 10 ¹⁸ cm ⁻³ .

In the case of this comparative example, the carrier concentration of each layer is
When measured by electrical means, p⁺Type GaAs layer 51 is 4 ×
10¹⁹cm^-3The p-type and n-type AlGaAs layer 52 is about 1 ×
10 ¹⁸cm^-32 × 10 p-type and n-type GaAs layers¹⁸cm
^-3It was n-type. As a result, carbon dope p⁺
The AlGaAs layer 52 on the mold layer 51 should be n-type
However, due to residual carbon, it has a high concentration
Suggest that it is contaminated by.

Therefore, in order to confirm this, each sample in the case of the above-mentioned example and the case of the comparative example was analyzed by SIMS to examine the profile of carbon impurities mixed in each layer.

FIG. 2 shows S in the depth direction of the sample of the comparative example.
The IMS analysis data is shown. Due to the memory effect of the TMG used as the carbon doping source in the p ⁺ -type GaAs layer 51, the Al _0.25 Ga _0.75 As layer 52 _thereabove also has 1
× It can be seen that the residual carbon in excess of 10 ¹⁸ atoms / cm ³ is mixed.

Therefore, in the AlGaAs layer 52, the n-type conversion cannot be achieved even if Si of about 1 × 10 ¹⁸ atoms / cm ³ is doped. Such a sample cannot be used as a material for a device.

Also in the GaAs layer 53, 5 × 1
Residual carbon of about 0 ¹⁷ atoms / cm ³ was detected, but this layer was a high-concentration Si doped layer and was converted to n-type with a carrier concentration of 2 × 10 ¹⁸ cm ⁻³ .

On the other hand, SIMS of the above-mentioned example samples
The analysis result is shown in FIG. FIG. 3 shows data analyzed specifically for carbon concentration only. p ⁺ type GaAs
Mixing of carbon doped at about 4 × 10 ¹⁹ cm ^{−3 in the} layer 40 into the n-type Al _0.25 Ga _0.75 As layer 41 is suppressed to below the detection limit (2 × 10 ¹⁷ atoms / cm ³ or less). I understand. Carbon contamination of the n-type GaAs layer 42 is also suppressed below the detection limit.

When carbon is doped into the p-type growth layer using TMG, only TMG can be used as the gallium source. However, the amount of TMG used increases. In order to dope a predetermined amount of carbon without lowering the growth rate of the growth layer and further reduce the carbon memory effect on the layer grown on the growth layer, supply at the time of carbon doping II
More preferably, the group I element source is a mixed source of TMG and TEG.

According to the research conducted by the present inventors, particularly when the supply amount of TEG is larger than that of TMG and the underlayer crystal temperature during growth is maintained at 520 ° C. or lower, the carbon memory effect to the second growth layer is obtained. It has been found that the above can be suppressed. T
By simultaneously supplying TEG even if the supply amount of MG is reduced, it is possible to secure a growth rate and dope carbon of a predetermined concentration into the growth layer.

In the above example, the [V] / [III] ratio during the growth of the AlGaAs layer 41 was 12.5.
In this case, it was stated that sufficient suppression of the carbon memory effect can be obtained. Further, FIG. 4 shows the residual carbon concentration during the growth of the AlGaAs layer 41 as a function of the [V] / [III] ratio.

The carbon contamination concentration was examined by an analysis with higher sensitivity than SIMS. In FIG. 4, [V] /
[III] When the ratio is 20, the black circle data (1.5 × 10 ¹⁶ atoms / cm ³ ) located below indicates that the amount of TMG supplied is further reduced to about 0.5 sccm (about 1/5). Show the data.

FIG. 4 shows that the carbon-doped growth layer material is Ga.
In the case of As or AlGaAs system, the residual carbon concentration is 3 to 4 × 10 ¹⁷ atoms / c by setting the [V] / [III] ratio supplied at the time of growth under the above conditions to 10 or more.
m ³ or less, that is, 5 × 10 ¹⁷ cm ⁻³
It is shown that the conductivity type and carrier concentration of the growth layer having the above carrier concentration can be controlled. It is considered that similar results can be obtained when other conditions such as TMG supply amount are changed.

In the case of producing the HBT, the case where the carbon-doped p ⁺ type base region and the n-type emitter region are grown at the same growth temperature has been described, but if the growth temperature of the carbon doped base region is different from the growth temperature of the emitter region. You may let me.

However, in the growth of the n-type layer or the low impurity concentration layer following the carbon-doped layer, the growth temperature is preferably about 520 ° C. or lower in order to reduce the memory effect of TMG. It is considered that when the growth temperature is lowered, even if the TMG remaining on the cell wall or the like is re-evaporated, it is decomposed and the probability of being taken into the growth layer is reduced.

Although the probability of capturing carbon does not always decrease as the growth rate decreases, it is possible to reduce the memory effect of TMG while ensuring the growth rate by using a source gas such as TEG which is unlikely to become a carbon source. Become.

The structure of the HBT to be manufactured is not limited to that described above. For example, the composition of the collector layer may be continuously changed from GaAs to AlGaAs. Also, H
Besides BT, other semiconductor devices can be formed.
For example, it is also possible to form an electronic device or an optical device having a diode structure in which a carbon-doped p-type layer and an undoped carbon n-type or i-type layer are adjacent to each other.

As described above, the carbon-doped p ⁺ -type growth layer is G
The case of aAs has been described, but AlGaAs and InG
It goes without saying that the present invention can be similarly applied to aAs and the like. It will be apparent to those skilled in the art that various changes, improvements, combinations, and the like can be made.

[0062]

As described above with reference to the embodiments, according to the present invention, after forming a high-concentration carbon-doped p ⁺ -type layer by the gas source MBE method, the residual carbon concentration mixed in the upper layer is effective. Can be suppressed.

Therefore, a semiconductor device having a high-concentration p ⁺ -type layer as an active layer, such as HBT, can be manufactured with high precision.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention. FIG. 1A is a cross-sectional view of the HBT, and FIG. 1B is a cross-sectional view showing the structure of the growth chamber of the gas source MBE device used for manufacturing.

2 is a graph showing a SIMS analysis result in the thickness direction of a comparative example sample grown by the prior art using the apparatus of FIG.

3 is a graph of carbon distribution data (SIMS analysis) in the thickness direction of an example sample grown by the apparatus of FIG.

FIG. 4 High concentration carbon-doped GaA supplied by TMG
Supply [V] / [I for GaAs-based growth layer on s layer
II] A graph of data showing the relationship between the ratio and the residual carbon concentration in the growth layer.

[Explanation of symbols]

1 substrate 2 collector layer 3 base layer 4 emitter layer 5 contact layer 10 growth chamber 12 exhaust pipe 14 holder 16 base crystal 18 heater 20 RHEED gun 22 RHEED screen 24, 25, 26, 27 gas cell 28, 29, 30, 31 shutter 32 Liquid nitrogen shroud 40 Carbon-doped p ⁺ -type GaAs layer 41 n-type AlGaAs layer 42 n-type GaAs layer 50 Base crystal 51 Carbon-doped p ⁺ -type GaAs layer 52 AlGaAs layer 53 n-type GaAs layer S Gas inlet tube V valve

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location H01L 29/73

Claims (4)

[Claims] 1. A first III as a carbon doping source
A carbon-doping growth step of growing a carbon-doped p-type III-V compound semiconductor layer by using an organic compound of a group III element as a source of a group III element, and a second organic group III element that is difficult to become a carbon doping source Using only the compound as a group III element source, the organic compound of the first group III element is easily decomposed at a growth temperature, and the molar supply rate of the group V element and
A method of manufacturing a semiconductor device, comprising: a carbon non-doped growth step of growing a group III-V compound semiconductor layer having a low carbon content, with a molar supply ratio of a group element, a V / III ratio, of 10 or more. 2. The method of manufacturing a semiconductor device according to claim 1, wherein the growth temperature is about 520 ° C. or lower. 3. The organic compound of the first group III element is trimethylgallium, the p-type group III-V compound semiconductor layer is a p-type GaAs layer, and the second group III.
3. The method of manufacturing a semiconductor device according to claim 1, wherein the organic compound of the group element is triethylgallium, and at the same time, the organic compound of aluminum and the n-type impurity source are supplied as the group III element. 4. The manufacturing of a semiconductor device according to claim 1, wherein the carbon doping growth step is performed at the growth temperature by simultaneously supplying the organic compound of the second group III element using the group III source. Method.