JP2990472B2 - Low pressure vapor deposition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-pressure vapor phase growth method, and more particularly to a low-pressure MOVPE growth method for a compound semiconductor characterized by a method for extracting a liquid or solid group V material.

[0002]

2. Description of the Related Art As a storage form of raw materials used in a reduced pressure vapor phase growth method, in particular, a metal organic vapor phase epitaxy method (MOVPE), a raw material which is a gas at normal pressure is pressurized, and in some cases, is liquefied to a high pressure. There are two types: storage in a gas cylinder, and packing of a liquid or solid substance in a cylinder (container) as it is.

In the case of using these raw materials, the former employs a method in which the flow rate of a raw material gas discharged from a cylinder is controlled by a mass flow controller (MFC) and sent to a reaction tube (a reduced-pressure gas-phase growth chamber).

[0004] On the other hand, in the latter case, a method of flowing a carrier gas such as hydrogen into a cylinder (container) containing the raw material, bringing the carrier gas into contact with the raw material, and flowing the raw material contained in the carrier gas into a reaction tube is generally used. It has been used extensively.

FIGS. 5A and 5B are explanatory views of a conventional raw material take-out method. In this figure, 21 is a high-pressure gas cylinder, 22, 26, 27, 28 are throttle valves, 23, 25
Is a mass flow controller (MFC), 24 is a carrier gas introduction pipe, 29 is a cylinder, and 30 is a raw material.

FIG. 5A illustrates a method of removing a raw material which is a gas at normal pressure and stored in a high-pressure gas cylinder by pressurizing the same. By opening the throttle valve 22 as described above, FIG. The flow rate of the raw material gas coming out of the high-pressure gas cylinder 21 is controlled by a mass flow controller (MFC) 23 and sent to a reaction tube.

FIG. 5B illustrates a method of taking out a raw material, which is a liquid or solid raw material, when the raw material is packed in a cylinder as it is. A carrier gas such as hydrogen (H ₂ ) introduced from a carrier gas introduction pipe 24 is shown in FIG. Is adjusted by the MFC 25 to make contact with the liquid or solid raw material 30 in the cylinder 29 through the throttle valve 27 (bubbling when the raw material is a liquid). It was common to send to

By adjusting the openings of the throttle valves 26, 27, and 28, the source gas can be diluted to an appropriate concentration with the carrier gas, or the toxic source gas in the piping can be purged.

In this case, a carrier gas containing a source gas is ideally supplied to the reaction tube at a partial pressure equal to the saturated vapor pressure. At this time, the value obtained by converting the amount of the extracted raw material gas into a standard flow rate at a concentration of 100% is represented by fs
Then, fs is expressed by the following equation. _{fs = ηP s f c / (} P o -ηP s) ······· (1) However, eta: (a 1 if ideal) saturation P _s: saturated vapor pressure f _c of the material : standard flow P _o of the carrier gas: the cylinder outlet pressure of this equation, the flow rate f _c of the carrier gas is controlled by MFC25, saturated vapor pressure P _s of the material gas is controlled by the temperature of the cylinder 29.

The pressure _{Po at} the outlet of the cylinder 29 is
The pressure is controlled to a predetermined value by a pressure gauge (not shown) and a throttle valve 28. When changing the extraction amount fs of the raw material gas is carried out by changing the flow rate f _c of the carrier gas.

The method of extracting a source gas using a carrier gas is simple and has the advantage that a source having a low vapor pressure can be used even when the pressure of a pipe or a reaction tube is high. Has been widely adopted.

However, this method has a problem that control accuracy is deteriorated because there are many parameters to be controlled. Further, in reality, the saturation degree η in the equation (1) does not become 1, and there is a problem that the saturation degree η changes with time due to the remaining amount of the raw material gas. Not only can it not be set accurately, but also adversely affects the reproducibility of the vapor phase growth process.

In the conventional MOVPE method, the only liquid or solid raw material is a group III raw material, and the vapor pressure is 1 Torr.
Due to the low degree, such a phenomenon was not a major problem.

However, in the case where TBP, TBA, etc., which are liquid Group V raw materials, are used in place of arsine and phosphine used in the form of a high-pressure gas from the viewpoint of improving safety, the room temperature of these materials is reduced. The vapor pressure at 100 to 20
Since it is as high as 0 Torr, gas saturation is unlikely to occur, which has been a serious problem.

For this reason, for example, when growing an InGaAsP quaternary mixed crystal, there arises a problem that the reproducibility of the group V crystal composition is deteriorated. In addition, since the morphology, electrical, and optical characteristics of the crystal surface strongly depend on the flow rate of the group V source gas, there is also a problem that the characteristics of these crystals change due to a change in the amount of source taken out every growth. Occurs.

This phenomenon is particularly prominent when an InGaAsP quaternary mixed crystal is grown using TBP and TBA having a high vapor pressure as the group V raw material. This change over time in the degree of saturation η is a phenomenon that is in principle unavoidable as long as a carrier gas is used.

Therefore, as a method of taking out the source gas which is superior in principle, the flow rate is controlled by the MFC operating at a low differential pressure by using the differential pressure between the vapor pressure of the raw material and the internal pressure of the pipe without using a carrier gas. Then, a method of directly taking out the raw material at a concentration of 100% (direct taking-out method) has been proposed (see Japanese Patent Application Laid-Open No. 2-255595).

FIG. 6 is an explanatory view of a conventional method of directly extracting raw materials. In this figure, 31 is a constant temperature bath, 32 is a heating device, 33 is a cylinder, 34 is a raw material, 35 is a manual throttle valve, 36 and 39 are mass flow controllers (MFC),
37 is a throttle valve, and 38 is a pipe heating device.

In the direct removal method, a liquid or solid raw material 34 is charged into a cylinder 33 housed in a thermostat 31 having a heating device 32, and the raw material 34 is charged.
The raw material gas vaporized is flow-controlled by a mass flow controller (MFC) 36 through a manual throttle valve 35,
It is sent to the reaction tube via the throttle valve 37.

Then, in order to bring the differential pressure between the vapor pressure of the raw material 34 and the internal pressure of the pipe into the operating differential pressure range of the MFC 36,
Is heated by a heating device 32, and the vicinity of the MFC 36 is set to be higher than the temperature of the raw material 34 by a piping heating device 38 in order to prevent the raw material gas vaporized from the raw material 34 from cooling and aggregating in the piping including the MFC 36. Heat.

According to the direct removal method, the removal amount of the raw material gas is determined only by the accuracy of the MFC 36 and is not related to the uncertain amount such as the degree of saturation η. Even if the vapor pressure of the raw material or the internal pressure of the pipe fluctuates, if the differential pressure falls within the operating differential pressure range of the MFC 36, the amount of raw material taken out does not change.

Regarding the method for directly extracting the raw material gas,
It will be described in detail. In the above-described method of directly extracting the raw material, the amount of the raw material gas to be extracted is controlled by using an MFC capable of operating at a low differential pressure by utilizing the pressure difference ΔP between the pipe internal pressure P ₁ and the vapor pressure P ₂ of the raw material. The differential pressure ΔP need only be equal to or greater than the minimum operating differential pressure of the MFC, and precise control is not required.

[0023] Such a method of directly removing the raw material is a conventional method.
Since, SiCl which is a raw material of optical fiber _FourOr silicon oxidation
Tetraethoxysilane as a liquid source for CVD of films
(TEOS) or MOVPE III
Trimethylindium (TMI), a solid raw material of the family
It was adopted when taking out.

However, all of these raw materials are characterized in that the vapor pressure at room temperature is as low as about 1 Torr. Conventionally, the direct method of extracting raw materials is a method for extracting raw materials having low vapor pressure. It was generally recognized that the method cannot be applied to a raw material having a high vapor pressure such as TBP or TBA having a vapor pressure at room temperature exceeding 100 Torr.

[0025]

However, in the above-described method of directly extracting the raw material gas, as described above,
Heating the raw material to bring the differential pressure between the vapor pressure of the raw material and the internal pressure of the piping into the operating differential pressure range of the MFC, and piping near the MFC to prevent the vaporized raw material gas from cooling and agglomerating in the piping containing the MFC Needs to be heated to a temperature higher than the temperature of the raw material.

However, when the raw material and the MFC or the MFC are heated to a temperature higher than room temperature as described above,
, The zero point or span tends to fluctuate, and as a result, the reproducibility of the amount of source gas taken out deteriorates. Further, in order to prevent the raw material gas from aggregating in the pipe including the MFC, the pipe is heated to about 80 ° C.
This had an adverse effect on the durability of valves and the like.

An object of the present invention is to provide a reduced pressure vapor phase growth method using a direct material extraction method in which the amount of material extracted does not change with time and has excellent reproducibility.

[0028]

In the reduced pressure vapor phase epitaxy according to the present invention, a raw material which is liquid or solid at normal pressure is used, and a flow rate is controlled by a mass flow controller by a differential pressure between a vapor pressure of the raw material and an internal pipe pressure. Then, in the reduced pressure gas phase growth method in which the raw material gas having a concentration of 100% is directly taken out,
A process was employed in which the mass flow controller was kept at room temperature and the raw materials were kept at a temperature lower than room temperature.

In this case, a reduced pressure MO
The tertiary butyl phosphine (TBP), tertiary butyl arsine (TB)
A) or monoethylarsine (EAs) can be used.

[0030]

The cause of the unstable zero point and span when the raw material and the MFC or the MFC are heated to a temperature higher than room temperature in the conventional method of directly extracting the raw material gas has been elucidated at present. Absent. However,
Although it cannot be detected from the outside, it is presumed that the temperature of the MFC heated to a temperature higher than room temperature is liable to fluctuate slightly due to the latent heat of vaporization accompanying the vaporization of the raw material having a high vapor pressure.

According to the experiments of the present inventors, when the MFC was kept at room temperature, such an unstable phenomenon was not observed. Therefore, the MFC is kept at room temperature, and a raw material having a high vapor pressure at a temperature lower than the room temperature is selected, and this raw material is heated to a temperature at which the differential pressure between the vapor pressure and the pipe internal pressure becomes larger than the operating differential pressure of the MFC. By cooling to
Aggregation of raw materials in the FC can be suppressed, and normal operation of the MFC can be ensured.

The minimum operating differential pressure of the currently available low differential pressure operating MFC is about 20 Torr,
In E growth, the internal pressure of the pipe is about 100 Torr,
The vapor pressure of the raw material may be 120 Torr or more.

FIG. 7 is a diagram showing the temperature dependence of the vapor pressure of TBP and TBA. According to this figure, TBP and TBA
Is not directly shown in this figure, but the vapor pressure of TBP is not less than 6 ° C. and that of TBA is not less than 20 ° C. as shown in FIG. It turns out that the extraction method can be applied.

Thus, as a raw material, TB having a high vapor pressure is used.
When P or TBA is used, the vapor pressure in the piping becomes lower than the vapor pressure of the raw material gas at room temperature, so that it becomes unnecessary to heat the piping downstream of the MFC.

As described above, when a raw material having a high vapor pressure such as TBP or TBA is used, the heating of the raw material to 50 ° C. or higher, which is indispensable for the conventional raw material having a low vapor pressure, is no longer essential, and the room temperature or Even at a temperature lower than that, a method of directly extracting the raw material gas can be adopted.

Further, the minimum operating differential pressure of the MFC is 100 To
Even in the case of using an MFC having a performance as low as about rr, a sufficient pressure difference can be obtained at a low temperature of about 35 ° C. for heating the raw material.

As described above, the operation of the MFC becomes more unstable as its temperature increases, and the durability of valves and the like also deteriorates. Is an advantage.

Further, while the conventional method of directly extracting the source gas aims at extracting a large amount of the source gas, the present invention is different in that the aim is to improve the controllability of the extraction amount of the source gas. I have.

In the present invention, in addition to the above-mentioned TBP and TBA, monoethylarsine (EAs) having a high vapor pressure at room temperature is used.
Etc. can be used similarly.

[0040]

Embodiments of the present invention will be described below. (First Embodiment) FIG. 1 is an explanatory view of a low pressure vapor phase epitaxy of a first embodiment. In this example, a case where tertiary butyl phosphine (TBP) is used as a raw material will be described. In this figure, 1 is a thermostat, 2 is a cylinder, 3
Is a TBP raw material, 4 is a manual throttle valve, 5 and 7 are mass flow controllers (MFC), and 6 is a throttle valve.

In the direct extraction method of the source gas employed in the low pressure vapor phase epitaxy method of this embodiment, a liquid TBP source 3 is charged into a cylinder 2 housed in a thermostat 1,
The TBP raw material 3 is cooled to a temperature lower than room temperature by a cooling device provided in the constant temperature bath 1 so as to have an appropriate vapor pressure described later.

The vaporized raw material gas passes through a manual throttle valve 4, is flow-controlled by a mass flow controller (MFC) 5, and is supplied to a reaction tube through a throttle valve 6. Further, a carrier gas such as hydrogen whose flow rate is controlled by the mass flow controller 7 can be sent to the reaction tube.

The temperature dependence of the vapor pressure P of TBP is expressed by the following equation. lnP = 17.47-3544 / T (2) where T is the absolute temperature of TBP. Therefore, the vapor pressure of TBP at room temperature (about 20 ° C.) is 216 To
rr.

Assuming that the pipe internal pressure is about 100 Torr and the minimum operating differential pressure of the MFC is about 50 Torr, T
TBP so that the vapor pressure of BP becomes 150 Torr or more.
What is necessary is just to cool a raw material to a temperature lower than room temperature.
The temperature at which the vapor pressure of TBP reaches 150 Torr is 11 ° C. (see FIG. 7).
Works fine.

On the other hand, since a temperature difference of about 3 ° C. is required to prevent aggregation of TBP gas in the MFC, the temperature of the TBP raw material needs to be 17 ° C. or lower, which is lower than room temperature by 3 ° C. or more. In the embodiment, TBP is mainly used.
Tert-butylarsine (TBA)
When using gas, treat it in exactly the same way as TBP gas.
Can be.

From the above, it can be concluded that the optimum temperature at which both the operating differential pressure and the temperature difference have a margin is 14 to 15 ° C. Actually, when the MFC temperature was set to room temperature and the TBP temperature was set to 15 ° C and operated, it was confirmed that the MFC operates normally and stable operation without fluctuation of zero point or span can be realized. did it.

(Second Embodiment) FIG. 2 is an explanatory view of a reduced pressure vapor phase epitaxy of a second embodiment. In this figure, 11a,
11b, 11c, 11d, 11e, 11f, 11g, 1
1h is a mass flow controller (MFC), 12a, 1
2b, 12c, 12d, 12e, 12f, 12g, 12
h is an air operated valve, 13a, 13b, 13
c, 13d, 13e, 13f are hand valves, 14a,
14b, 14c, 14d are thermostats, 15a, 15b, 1
5c and 15d are cylinders, 16a and 16b are ribbon heaters, 17 is a pressure gauge, 18 is a control valve, 19 is a reaction tube, 20 is a pressure control device, and 21 is a rotary pump.

In the low pressure vapor phase epitaxy of this embodiment,
The raw material gas direct extraction method described in the first embodiment is adopted for the first system for supplying TBP and the second system for supplying TBA, and the conventional method for extracting raw material by bubbling of carrier gas is used for supplying TMI. Third system and T
Adopted in the fourth system that supplies EG.

For the first system and the second system, M
FC 11d and 11e add ribbon heater 16 for experiment
Although the points a and 16b are provided, which is different from the raw material removal apparatus described in the first embodiment, there is no point where special explanation is additionally provided.

The third system and the fourth system are the same as those used in the conventional method of removing raw materials by the bubbling method. The flow rate is controlled by the pressure gauge 17 and the control valve 18 and the reaction tube 19 is controlled. TMI and TE
The mixed gas of G is supplied.

The source gas supplied to the reaction tube 19 is In
After the InGaAsP crystal is grown on the P substrate, the gas is exhausted by the rotary pump 21 via the pressure control device 20 and the harm removal device.

Here, InG is applied by a reduced pressure MOVPE method.
When growing aAsP crystal, the TBP and TB of the present invention are used.
An apparatus for supplying A to a reaction tube by a direct removal method and operating conditions tested in connection with the present invention will be described.

In this experiment, the temperature of both TBP and TBA was set to 35 ° C., and MF was set to prevent aggregation in MFC.
C was heated to 40 ° C. by a tape heater. The vapor pressure of TBP and TBA at this temperature is 388 T
orr, 220 Torr.

At 35 ° C., the vapor pressures of TBP and TBA are the above-mentioned values, respectively. Therefore, unlike the conventional direct removal method, heating of the raw material is not essential, and it can be carried out even when cooled to room temperature or lower. Is a feature of the present invention.

In this case, the heating of the MFC is also unnecessary, and the pressure in the pipe downstream of the MFC becomes lower than the vapor pressure of the raw material at room temperature. Therefore, it is unnecessary to heat the line downstream of the MFC. .

The MFCs 11a, 11b, 11c, 1
The line passing through 1f is called an acceleration line, and is used to increase the speed at which the source gas reaches the reaction tube and to improve the cut-off when the source gas is cut off. / Min gas is flowed.

Using trimethyl indium (TMI) and triethyl gallium (TEG) as group III raw materials,
Each was cooled to 16 ° C. and −10 ° C., respectively, and supplied to the reaction tube 19 by a take-out method using a normal carrier gas.

The pressure in the reaction tube 19 was controlled to a constant pressure of 20 Torr by a rotary pump 21 and a pressure controller 20. At this time, the pressure in the pipe just downstream of the MFCs 11d and 11e is about 100 Torr.

The substrate is made of InP (100) crystal, and the substrate is heated by placing the substrate on a carbon susceptor.
The carbon susceptor was heated by dielectric heating to 600 ° C. using an RF coil.

Next, a process of growing an InGaAsP crystal having a PL wavelength of 1.55 μm lattice-matched to an InP substrate will be described.

First stage Hand valves 13a, 13b, 13c, 13d, 13
e and 13f are opened in advance. First, the air operated valves 12a, 12c, 12f are opened, and 12b, 12d,
12e, 12g, and 12h are closed, and only TBP flows into the reaction tube 19. In this state, the InP substrate in the reaction tube 19 is
Raise the temperature to 00 ° C and wait for the temperature to stabilize. The flow of TBP is to prevent thermal damage due to desorption from the InP substrate, and the flow rate of TBP is 20 cc / min.

Second stage When the temperature is stabilized, the air operated valve 12
open b, 12d, 12e, 12g, 12h, 12c, 1
2f is closed, TBA, TBP, and TEG are allowed to flow through the reaction tube 19 to start the growth of the InGaAsP crystal. The flow rate of the raw material gas at this time is as follows. TMI 0.143 cc. min TEG 0.107 cc. min TBA 2.25 cc. min TBP 3.38 cc. min Under these conditions, the growth rate is about 1 μm / hr. Further, the group III composition of the obtained crystal, that is, the composition of In (In
/ (In + Ga)) is 0.57, and the group V composition, that is, the composition of P (P / (P + As)) is 0.11.

Third Step In the case of growing a crystal having a thickness of 0.3 μm for a predetermined time, for example, after growing for 18 minutes, the air operated valves 12d, 12e, 12g and 12h are closed, and the air operated valves 12c and 12c are closed. The growth is stopped by opening 12f and stopping the supply of the group III raw material. After cooling in this state and lowering the temperature to 400 ° C. or lower, the supply of the group V raw material is stopped by closing the air operated valves 12a and 12b.

Next, InGaAs is obtained by a direct extraction method.
It shows how much the reproducibility of the group V composition of the sP crystal is improved as compared with the conventional method using a carrier gas.

FIG. 3 is a graph showing the results of a conventional reduced pressure vapor deposition method.
FIG. 4 is a diagram showing the reproducibility of the group V composition of a GaAsP crystal. This figure shows that InGaAs with a PL wavelength of 1.2 μm is formed by a conventional reduced pressure vapor deposition method using bubbling of a carrier gas.
4 shows experimental results of the reproducibility of the group V composition when a P crystal is grown. The horizontal axis is the growth number measured at a fixed time interval, and the vertical axis is the group V composition (P / (P + As)). In this case, a large variation of 12% is observed in the group V composition.

FIG. 4 is a graph showing the relationship between I and I obtained by the reduced pressure vapor deposition method of the present invention.
FIG. 4 is a diagram showing reproducibility of a group V composition of an nGaAsP crystal.

This figure shows that the raw material was taken out by the direct take-out method according to the present invention, and InGaAs with a PL wavelength of 1.55 μm was used.
4 shows experimental results of the reproducibility of the group V composition when a P crystal is grown. According to this figure, the variation of the group V composition is 0.8
%, Which is very small.

As described above, the method of using the carrier gas bubbling and the method of direct extraction of the raw material of the present invention show a difference of more than one digit in the variation of the composition for each growth. It is evident that the reproducibility of the group V composition is greatly improved by the adoption of, and the effect of the reduced pressure vapor deposition method of the present invention is high.

Further, in the crystal grown by the direct extraction method, since the supply amount of the group V itself is stable, the reproducibility of the surface morphology, electric characteristics and engineering characteristics has been remarkably improved.

[0070]

As described above, according to the reduced pressure vapor growth method such as the reduced pressure MOVPE method using the direct material extraction method according to the present invention, the composition and surface A layer having no variation in morphology, electrical characteristics, optical characteristics, etc. can be grown with good reproducibility, and a heating mechanism with a temperature control function of the MFC is not required, so that the apparatus can be simplified. Also, since the MFC or the like is not heated to a high temperature, there is an advantage that the life of the apparatus can be extended.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a reduced pressure vapor deposition method of a first embodiment.

FIG. 2 is an explanatory view of a reduced pressure vapor deposition method of a second embodiment.

FIG. 3 is a diagram showing the reproducibility of the group V composition of an InGaAsP crystal obtained by a conventional reduced-pressure vapor deposition method.

FIG. 4 shows InGaAsP prepared by the reduced pressure vapor deposition method of the present invention.
FIG. 3 is a view showing reproducibility of a group V composition of a crystal.

FIGS. 5A and 5B are explanatory views of a conventional raw material removal method.

FIG. 6 is an explanatory view of a conventional method for directly removing raw materials.

FIG. 7 is a diagram showing the temperature dependence of the vapor pressure of TBP and TBA.

[Explanation of symbols]

Reference Signs List 1 constant temperature bath 2 cylinder 3 TBP raw material 4 manual throttle valve 5, 7 mass flow controller (MFC) 6 throttle valve 11a, 11b, 11c, 11d, 11e, 11f, 1
1g, 11h Mass flow controller (MFC) 12a, 12b, 12c, 12d, 12e, 12f, 1
2g, 12h Air operated valve 13a, 13b, 13c, 13d, 13e, 13f Hand valve 14a, 14b, 14c, 14d Constant temperature bath 15a, 15b, 15c, 15d Cylinder 16a, 16b Ribbon heater 17 Pressure gauge 18 Control valve 19 Reaction tube Reference Signs List 20 pressure control device 21 rotary pump

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-255595 (JP, A) JP-A-63-190330 (JP, A) JP-A-62-259429 (JP, A) (58) Investigation Field (Int.Cl. ⁶ , DB name) H01L 21/205 C23C 16/02

Claims (3)

(57) [Claims] 1. Using tertiary butyl phosphine (TBP) and tertiary butyl arsine (TBA), which are liquid or solid at normal pressure, and controlling the flow rate by a mass flow controller by the differential pressure between the vapor pressure of the raw material and the pressure in the pipe. A low-pressure vapor phase epitaxy method wherein the mass flow controller is kept at room temperature and the raw material is kept at a temperature lower than room temperature in a low-pressure vapor phase epitaxy method in which a raw material gas having a concentration of 100 % is directly taken out. 2. The temperature difference between a temperature lower than room temperature and room temperature is 3
2. The method of claim 1, wherein the temperature is [° C.] or higher. 3. The reduced pressure vapor deposition method according to claim 1, wherein the reduced pressure vapor deposition method is a reduced pressure MOVPE method.