JPH0379436B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is directed to the vaporization of organic metals, which enables efficient and controlled vaporization of compound semiconductors with good controllability of film thickness and composition. It is about the method.

Conventional structure and problems It is a vapor phase epitaxial method using organic metals.
MOCVD (Metalorganic Chemical Vapor)
As a crystal growth method for compound semiconductors, the Ga _1-x Al _x It is widely used in the development of As/GaAs-based semiconductor lasers.

In this MOCVD method, for example, when growing a -V compound semiconductor layer, an organic metal is generally used as the group element, and a hydride is used as the group V element. The method of supplying this organometal to the growth reactor is to introduce a carrier gas into the liquefied organometal and bubble it, so that molecules approximately corresponding to the saturated vapor pressure at a set temperature are converted into a gas into the growth reactor. sent to.

Figure 1 shows the structure of the organometallic bubbling cylinder currently used in MOCVD growth. A liquefied organic metal (for example, triethyl indium) 2 is placed in a stainless steel bomb container 1,
A carrier gas (for example, H ₂ ) is introduced from the inlet 3. The introduced carrier gas passes through the guide 4, and bubbles 5 come out from the lower end spout 4a of the guide 4, rise in the organic metal 2 in the cylinder 1, reach the liquid level 6, burst the bubbles 5, and leave the cylinder. The organometallic gas molecules corresponding to the saturated vapor pressure at the set temperature in the cavity 7 above the liquid level in 1 are pushed away by the volume of the bubbles 5, and are pushed out to the outlet 9 via the straight T jig 8. and sent to the growth reactor. still,
The valve 10 is for ON/OFF of the flow of carrier gas. The blind screw 11 is used to cover the introduction hole for introducing the organic metal into the cylinder 1.

In this method, when the organometallic metal 2 is sufficiently filled in the cylinder 1, the cavity 7 is narrow;
Due to the violent shaking of the liquid level 6 due to the bursting of large bubbles 5 coming out from the tip of the guide 4, a considerable amount of organic metal is thrown out to the outlet, and due to the flow rate of the bubbling gas that accumulates in the supply pipe etc. after the outlet 9. It is no longer possible to control the supply amount of constituent elements of the growth layer. Even if the amount used increases and the liquid level 6 falls, the risk is still high.

The supply pipe after the outlet is often kept at room temperature, and organic metals, which have a low vapor pressure at room temperature, remain accumulated for a particularly long period of time. This is because the bubbles 5 are large. In order to alleviate this problem, a plurality of holes may be provided at the lower end of the guide 4, but since the guide 4 is straight, air bubbles are generated only from the hole near the top of the holes provided at the lower end. And it's inefficient.

Furthermore, MOCVD growth is determined by the rate of supply of group elements, for example in -V group compound semiconductors. Therefore, it is difficult to generate organometallic gas uniformly and with good controllability using conventional organometallic vaporization methods using cylinders, and it is extremely difficult to control the growth rate or composition of semiconductor crystal growth films.
It has been difficult to form a good semiconductor film using the MOCVD method.

Purpose of the Invention The present invention is capable of reducing the size of carrier gas bubbles in bubbling of an organometallic material and providing the organometallic material to a growth reactor system in a well-controlled manner.
The present invention aims to provide a vaporization method suitable for vapor phase epitaxial growth with good controllability using organic metals, using a structurally suitable vaporization apparatus.

Structure of the Invention The present invention provides a guide for introducing the gas below the liquid surface and a gas discharged from the guide when the liquefied organic metal in a stainless steel container is bubbled with a gas to gasify the liquefied metal. Separately from the stainless steel container, a bubble-forming jig with a plurality of ejection holes for ejecting from the ejection holes located outside the lower end of the guide is provided separately from the stainless steel container, and is used to vaporize the organic metal and perform epitaxy. This is what is sent to the Yaru growth reactor.

In other words, the present invention takes the above points into consideration, and the bubble forming jig is, for example, shaped like a ripple, and the diameter of the small holes is the same or becomes slightly larger as the distance from the center of the guide increases, or A control plate is used to reduce the size of the bubbles, so that small bubbles are uniformly formed within the cylinder, and as a result, the organic metal is provided to the growth reaction system in a well-controlled manner.

DESCRIPTION OF EMBODIMENTS FIG. 2 shows the tip of a bubble generating section according to an embodiment of the present invention. Components that are the same as those in FIG. 1 are indicated by the same symbols. The bubble forming jig 12 located immediately behind the distal end ejection part 4a of the guide 4 has a flat shape, and a plurality of gas ejection holes 13 are provided therein. This hole 1
3 is for making the gas sent from the guide 4 into fine bubbles 14, and in order to maintain uniformity in the overall amount of bubbles 14, the diameter of the hole becomes larger or the density of the hole increases as it moves away from the center. It is better to make it bigger. Of course, it is sufficient to simply provide a hole of an appropriate size. If a large amount of gas is sent, it may leak from the bottom 15 of the bubble forming jig 12, so it is better to keep the bottom 15 closed. Even when gas flows through such a structure, the bubbles 14 are formed finely and uniformly, and the bubbles 1 at the liquid level 6 are
There is little splashing of the liquefied organic metal due to the cracks in step 4, and thus stable and uniform vaporized organic metal can be sent to the next growth system.

FIG. 3 shows another embodiment of the invention. In this case, gas is fed through the same guide 4 as in the prior art, and large bubbles 5 are generated from the jetting portion 4a at the tip of the guide. A bubble control plate 16 is installed on top of this, and small bubbles 14 are uniformly formed through countless small holes 17 provided therein. This produces the same effect as the previous embodiment. control board 16
The gap between the cylinders 1 should be made as small as possible since it is not good for large bubbles to form from the gap. Further, a plurality of control plates 16 may be provided in order to form small air bubbles 14.

FIG. 4 shows yet another embodiment. This is because the bubble forming jig 12 placed immediately after the distal end jetting part 4a of the guide is made of a porous material.
By using this, innumerable small bubbles 14 are formed from innumerable small holes 18, and there is no large fluctuation of the liquid level 6, so that the vaporized organic metal can be efficiently and smoothly delivered to the outside of the cylinder.

In these embodiments, the guide 4, the bubble forming jig 12, and the control plate 16 were explained as being different.
Of course, the guide 4 and the jig may be formed integrally. As an example of integration, a guide 4 with the same diameter as the guide 4 has multiple holes, and is L-shaped connected at the lower end spout 4a of the guide 4. In other words, the guide 4 is made longer and multiple holes are provided near the lower end jet. The same effect can be obtained even if the lower end spout portion 4a is closed and bent into an L-shape.

As is clear from the above examples, when obtaining a vaporized organometal by bubbling gas through the liquefied organometal, the bubbles of the bubbling are made small and uniform to suppress fluctuations in the liquid level of the liquefied organometal. An amount of vaporized organic metal can be obtained in proportion to the flow rate of the bubbling gas, and there is no need for liquid to splash out to the outlet as in the conventional method, and the vaporized organic metal can be sent to the growth furnace with excellent controllability. usually,
The flow rate of the organic metal used in MOCVD growth is approximately 10 ^-5 mol/min, and by using the present invention, control on this order can be relatively easily performed. For example, -V group compound semiconductor
Since MOCVD growth is a rate-determining reaction of the supply of group organometallics, the film quality (thickness, composition) of the grown layer is determined by the amount of vaporized gas of group organometals supplied to the growth system. Therefore, by generating a uniform organometallic gas with good controllability using the method of the present invention, it becomes possible to control the thickness and composition of an epitaxially grown film extremely well and accurately.

For example, MOCVD of GaAs is performed at a growth temperature of 750°C.
When carrying out under the condition of 76 Torr, using the present invention, triethyl gallium [TEG (T = 15 °C)] as an organic metal was bubbled with H ₂ gas at 300 c.c./min (molar concentration 3 × 10 ^-5 mol/min),
When epitaxial growth is performed by feeding H ₂ carrier gas at 10/min into the growth furnace and mixing it with AsH ₃ at 60 c.c./min, the growth rate is ±1% at a growth rate of 1.8 μm/hr.
GaAs epitaxial films can be obtained with good reproducibility with film thickness variations within On the other hand, using the conventional method,
If there is a film thickness variation of ±5% or more and some liquid jumps out, the growth rate will fluctuate slightly thereafter.
It becomes difficult to control the thickness of the grown film.

Composition control will be described using Ga _1-x In _x P as an example. For example, x of Ga _1-x In _x P, which is lattice matched to GaAs, is 0.5
The growth conditions at this time are the growth temperature
650℃, pressure 76Torr, 300c.c./triethylgallium [TEG (T=20℃)] using the present invention
Min of H ₂ gas was bubbled to a state of 30c.c./min, and trimethylindium [TMI (T = 25℃)] generated from a solid source was added to 40c.c./min.
/min of _H2 carrier gas into the growth reactor,
It is mixed with phosphine (PH ₃ ) at 50 c.c./min in a furnace and grown at a substrate rotation rate of 10 rpm. When epitaxial growth was performed using this method, it became possible to suppress compositional variations to about ±0.1% for x=0.5. When converted into a lattice matching degree (Δa/a), this is about ±1×10 ⁻⁴ , and good crystals can be obtained with good reproducibility. On the other hand, with the conventional method, ±5
% or more (Δa/a>±3×10 ⁻³ ), making it difficult to control the crystal composition.

In the structure of the vaporization container of the present invention, the desired bubbles are not ejected from directly below the guide end, but rather from the ejection holes (the ejection holes of the bubble forming jig) located around the guide end.
As a result, it spreads over the entire liquid surface inside the vaporization container, and the amount of vaporized gas supplied is the same as the amount of gas being sent.
Despite the small amount, it becomes easier to control. Furthermore, in the present invention, the guide and bubble forming jig are separate from the stainless steel main cylinder required for MOCVD, so it is easy to create a vaporization device consisting of the guide, jig, and cylinder, and the inside can be cleaned. It's extremely easy. Therefore, a highly pure vaporized gas free from impurity contamination is particularly required.
In MOCVD growth, it is extremely useful when performing high quality MOCVD growth. In addition, since the holes can be made in an area wider than the diameter of the guide, by making more holes, a larger number of bubbles can be formed, and the reduction in the gas passage area can be suppressed. No pressure is required, and the operability of the epitaxial growth equipment is no different from that of conventional equipment.

The shape of the bubble forming jig in the example, the shape of the control plate, the shape and size of the holes, and the shape of the cylinder do not matter, but if the filling rate of the liquefied organometallic to be filled into the cylinder is 7 to 7. The effect of the present invention will be further enhanced by setting the amount to about 80% and ensuring a sufficient cavity above the liquid level in the cylinder.

Effects of the Invention As described above, the present invention forms a blowout hole outwardly from the end of the guide that guides the gas and blows out the gas from there, thereby generating uniform air bubbles over the entire liquid surface inside the stainless steel container. By reducing the diameter of the bubbles caused by bubbling of the liquefied organic metal and making the density uniform, it is possible to supply high-purity organic metal that has been vaporized to the outside in a well-controlled manner into the vapor phase epitaxial growth reactor. Therefore, this was used
MOCVD growth improves film thickness and mixed crystal compound semiconductor (In _1-x
The group composition ratio of Ga _x As _y P _1-y , (Al _x Ga _1-x ) _y In _1-y P, etc.) can be controlled relatively easily, and a good epitaxially grown film can be formed. The MOCVD method, which is a crystal growth method using the present invention, only requires replacing the bubble forming jig, and it enables good growth without changing the epitaxial growth conditions (without changing the operability), making it possible to improve the growth of compound semiconductors. This growth method has great potential for mass production, and the present invention can also be used to control impurity doping of organic metals, and has extremely high industrial value in the field of semiconductor device manufacturing.

[Brief explanation of drawings]

FIG. 1 is a schematic structural diagram of a conventional organic metal vaporization method, and FIGS. 2, 3, and 4 are structural diagrams of a bubble generating section used in the vaporization method of an embodiment of the present invention. 4... Gas guide, 4a... Lower end spouting part, 6
. . . liquid level, 7 . . . cavity, 12 . . . bubble forming jig, 13, 17, 19 .

Claims (1)

[Claims] 1. A liquefied organic metal is placed in a stainless steel container, and in the container there is a guide that guides the gas below the liquid surface, and a guide that guides the gas below the liquid surface, and a gas that is located outside the lower end of the guide and exits from the guide. A bubble forming jig having a plurality of gas ejection holes for ejecting gas is provided separately from the container, and the liquefied organic metal is bubbled using the gas, and the liquefied organic metal is ejected from the gas ejection holes. A method for vaporizing an organic metal, comprising: ejecting and gasifying the organic metal, and sending the gasified organic metal to an epitaxial growth furnace. 2. The organic metal vaporization method according to claim 1, wherein the jig comprises a control plate having a plurality of holes above the ejection part of the guide for introducing gas. 3. The organic metal vaporization method according to claim 1, wherein the jig has an open shape and the diameter of the ejection hole becomes the same or larger as it moves away from the center of the guide. 4. The organic metal vaporization method according to claim 3, wherein the density of the ejection holes provided in the bubble forming jig increases as the distance from the center increases. 5. The organic metal vaporization method according to claim 1, wherein the material of the bubble forming jig is porous. 6. The organic metal vaporization method according to claim 1, wherein the guide and the bubble forming jig are integrated.