JP3316828B2 - Semiconductor thin film regrowth method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor thin film regrowth method applied to a III-V semiconductor optical device used in an optical communication system.

[0002]

2. Description of the Related Art Many components are used in optical communication systems: light sources, fibers, and photodetectors. Among them, a light source and a photodetector are manufactured by a III-V group compound semiconductor thin film forming method. This thin film formation method is roughly divided into two flows. One is to form a thin film in a vacuum, and includes molecular beam epitaxy (MBE), chemical beam epitaxy (CBE), and gas source molecular beam epitaxy (GSMBE). Another flow is 0.
A method of forming a thin film in a hydrogen atmosphere of 1 to 1 atm.
The organometallic thermal decomposition (MOCVD) is a typical example.

Hitherto, MOCVD has been used to fabricate optical devices.
The law has been the most widely used. One reason is that regrowth is easy. That is, InGaAs
Taking the manufacture of a P laser as an example, first, as shown in FIG. 1, an n-type InP layer 2 and an InGaAs
P layer 3, MQW4, InGaAsP layer 5, p-type I
An nP layer 6 and finally an InGaAs cap layer are sequentially grown. This is once taken out into the air, a pattern is formed by lithography, an insulating film is formed thereon, and RIE is performed.
It is processed into a mesa shape by etching. In an MOCVD furnace, the n-type InP layer 7 is formed on the side surface of the mesa using selective growth.
Growing the mesas. Further, this is taken out into the air, the insulating film and the cap layer on the top of the mesa are removed, and the substrate is placed in a MOCVD furnace three times, so that the p-type InP layer 8 Regrow,
Finally, a contact layer 9 is grown.

[0004] Of the above processes, the selective growth is M
BE is difficult and CBE and MOCVD are equally possible. The reason is that both use an organic metal as the group III raw material. However, regarding the regrowth of the p-type InP film 8 on the p-type InP film 6, CBE has not been successful. The reason is that after removing the cap layer, the mesa surface is exposed to air, so a natural oxide film is formed,
This is because it cannot be removed in a vacuum vessel, and as a result, the regrowth interface deteriorates. Specifically, the carrier concentration at the regrowth interface is reduced to form a high resistance layer, and the operating voltage is increased and the output is reduced as an effect on device performance.

[0005] There are mainly two types of natural oxide films formed on III-V semiconductor materials. In other words, oxides of Group III elements and V
It is an oxide of a group element. Of these, the oxide of the group V element has a high vapor pressure, so that what remains at the regrowth interface is the oxide of the group III element. The easiest way to remove this is evaporation removal by high-temperature heating. From observation of RHHED or Auger analysis, it is considered that In203 evaporates at 525 degrees. However, in these assays,
Since a residue of 1% or less cannot be detected, and a hydrocarbon is attached to the surface, a temperature much higher than the above temperature is required to obtain a clean interface of device quality. I do.

[0006] As a result, when heated to a high temperature, there is a drawback that the V-group element is severely separated from the surface and the surface becomes cloudy. As a method using a reactive gas, the PC 13 has an etching effect, but has a disadvantage that the surface after etching is extremely rough. As described above, there has been no effective means for cleaning the InP-based material in a vacuum vessel and making the surface smooth.

[0007]

DISCLOSURE OF THE INVENTION The present invention has been proposed in view of the above.
An object of the present invention is to provide a semiconductor thin film regrowth method capable of cleaning a P-based material in a vacuum vessel.

[0008]

In order to achieve the above object, the present invention provides a thin film growth method for growing a III-V compound semiconductor in a vacuum vessel by heating InP exposed to air in a trisdimethylaminoarsine atmosphere. Then, heating is performed in a phosphorus atmosphere, and then InP or InGaAsP
The gist is to grow. In the above, the heating temperature is 510 to 525 degrees in a trisdimethylaminoarsine atmosphere.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention solves the problem of cleaning InP exposed to air in a vacuum vessel.
nP was first converted to trisdimethylaminoarsine (TDMA
As), and further heating in a phosphorus atmosphere.

That is, according to the literature (Journal of Crystal Grouse, Volume 175/176, 1997, pp. 387-392), trisdimethylaminoarsine (TDMAAs) thermally decomposes at 450 ° C., resulting in various radicals. And As occur. As the radical, a hydrogen radical, a methyl radical and the like are considered. Methane is used for GaAs or InP RIE etching because methyl radicals combine with group III elements to form compounds with high vapor pressure.
On the other hand, hydrogen radicals have the effect of removing oxide films,
Not as reactive as etching.

Therefore, GaAs formed by heating TDMAAs is used.
Alternatively, when InP is irradiated, TDMAAs decompose on the surface, and the generated hydrogen radicals and methyl radicals are converted into Ga radicals.
Reacts with Aa or InP. This chemical reaction becomes more severe at higher temperatures. GaAs with CBE or MBE
The temperature for growing the s film is about 600 degrees. That is, in the case of a GaAs substrate, etching occurs due to methyl radicals. This has been confirmed in many documents. For example, an etching rate of 600 degrees is about 1000 A
/ H.

On the other hand, the temperature at which InP is grown by CBE or MBE is about 500 degrees. This temperature is
Thermally decomposes TDMAAs, but not so hot as to etch methyl radicals. Therefore, if the optimum temperature is selected, in the case of InP, only the oxide film removing action by the hydrogen radical occurs, and the etching action by the methyl radical should be negligibly small.

Further, as is well known, when an As beam is irradiated on the InP surface, P and As are replaced, and InAs is formed on the surface. As is generated when TDMAAs are decomposed, InAs is formed on the cleaned InP surface. Therefore, TD under optimal conditions
After the MAAs treatment, a P beam is applied to
Needs to be changed back to InP

[0014]

Embodiment 1 Hereinafter, InP according to a first embodiment of the present invention will be described.
The regrowth of InP on the film will be described. In the present invention, CBE is used for the film growth method. TEG was used as a Ga source, TMI was used as an In source, and thermally decomposed arsine and phosphine were used as As and P sources, respectively. Be was used as the p-type dopant.

In regrowth of InP, first,
An InP buffer layer is grown on the n-type InP substrate, and then Be is doped with p = 10 ¹⁸ cm ⁻³ doped InP.
000 A, and finally the InGaAs cap layer is
It grew 0A. This was taken out into the air, and the cap layer was wet-etched using a mixed solution of sulfuric acid and hydrogen peroxide. This was put back into the CBE device, and two methods were studied to clean the surface. One is a method of heating to high temperature in TDMAAs or P atmosphere, and the other is
After heating in a TDMAAs atmosphere, it is heated and held in a P atmosphere for several minutes. After the cleaning, the InP doped with Be at p = 10 ¹⁸ cm ⁻³ at 505 ° C. was heated to 30 ° C.
00A regrown.

FIG. 2 shows the carrier concentration distribution in the depth direction of the regrown InP film when heated only in the P atmosphere. It can be seen that the carrier concentration is reduced by about one digit at the regrowth interface. When the heating temperature (cleaning temperature: Tc) was in the range of 500 to 525 degrees, this decrease in carrier concentration could not be eliminated. In addition,
At a cleaning temperature of 525 ° C. or higher, the film became cloudy.

On the other hand, FIG. 3 shows a carrier concentration distribution in the depth direction when heating is performed in a PDMA atmosphere after heating in a TDMAAs atmosphere. When the cleaning temperature is 510 ° C. or higher, an almost ideal carrier concentration distribution is obtained. AFM
It was found from the measurement that the surface when InP was heated to 515 degrees in a TDMAAs atmosphere was flat at the primitive level. Therefore, the optimum cleaning temperature is 5
10-525 degrees.

[0018]

Embodiment 2 The present invention was applied to a laser. First, MOCV
Using method D, an n-type InP buffer layer (0.4 μm), 1.3 Q (0.1 μm), InG
aAsP-MQW, 1.3Q (0.1um), p-InP
(0.3 μm), and finally an InGaAs cap layer was grown. Here, Q is InGaAsP quaternary mixed crystal.

Thereafter, the substrate is once taken out into the air, a pattern is formed by lithography, an insulating film is formed thereon, and processed into a mesa by RIE etching. MO
Put into a CVD furnace and use selective growth to add n
A type InP layer is grown and mesas are buried. Further, this was taken out into the air, and the insulating film and the cap layer on the top of the mesa were removed. Thereafter, the apparatus was mounted on a CBE apparatus, heated at 515 ° C. for 5 minutes in a TDMAAs atmosphere, the supply of TDMAAs was stopped, and heated at 505 ° C. for 1 minute in a phosphine atmosphere. Then, Be doped with p = 10 ¹⁸ cm ⁻³
nP was regrown by 1 μm, and finally an InGaAs contact layer doped with carbon at a concentration of 10 ²⁰ cm ⁻³ was grown.
At that time, CBr4 was used as a raw material for carbon doping.
TiPtAu was deposited on the contact layer to form a non-alloy electrode.

As a result of comparing this laser with a laser produced by conventional MOCVD regrowth, the threshold current and the output of both were almost the same. However, as a result of the aging test at a high temperature, almost no change was observed in the case of the non-alloy electrode, whereas in the case of the alloy electrode of the MOCVD regrowth, a device which rapidly deteriorated was observed.

[0021]

As described above, according to the present invention, InP exposed to air is first heated with TDMAAs, further heated in a phosphorus atmosphere, and then InP is regrown. Has the effect of cleaning.

In the above embodiment, the InP on InP
The regrowth of P was described, but InGaAs on InP
It goes without saying that the present invention can be applied to the regrowth of the sP film. Further, although the embodiment has described that the present invention is effective for improving the laser, the present invention can be applied to the improvement of the characteristics of an optical device requiring regrowth, for example, a photodetector.

[Brief description of the drawings]

FIG. 1 shows a cross-sectional view of the structure of an embedded laser.

FIG. 2 is an explanatory diagram of a carrier concentration distribution of an InP regrown film by heating cleaning.

FIG. 3 is an explanatory diagram of a carrier concentration distribution of an InP regrown film made of TDMAAs.

[Explanation of symbols]

 Reference Signs List 1 n-type InP substrate 2 n-type InP buffer layer 3 InGaAsP guide layer 4 MQW 5 InGaAsP 6 p-type InP layer 7 n-type InP buried layer 8 p-type InP layer 9 regrowth 9 electrode contact layer

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-8-55799 (JP, A) JP-A-8-88185 (JP, A) JP-A-9-213639 (JP, A) JP-A-9-98 289171 (JP, A) JP-A-1-197398 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/205

Claims (2)

(57) [Claims] In a thin film growth method for growing a III-V compound semiconductor in a vacuum vessel, InP exposed to air is heated in a trisdimethylaminoarsine atmosphere, subsequently heated in a phosphorus atmosphere, and then InP or InGaAs is heated.
A semiconductor thin film regrowth method comprising regrowing P. 2. The method according to claim 1, wherein the heating temperature is 510-525 ° C. in a trisdimethylaminoarsine atmosphere.