JPH0136691B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field of the Invention The present invention relates to a crystal manufacturing apparatus for manufacturing a compound semiconductor having a multilayer structure having a steep impurity concentration gradient.

(b) Technical background Boron (B), aluminum (Al), gallium (Ga),
Group elements such as indium (In) and nitrogen (N),
Gallium arsenide (GaAs) is covalently bonded with group elements such as phosphorus (P), arsenic (As), and antimony (Sd) to form a regular tetrahedral coordination and has a zincblende or wurtzite crystal structure. , indium antimony (InSb), indium arsenide (InAs), etc.
Group compound semiconductors are known. Single crystals of these - group compound semiconductors can be produced by melting methods such as the horizontal Bridgeman method, zone melting method, and single crystal pulling method, or by vapor phase epitaxial methods that utilize sublimation of materials or chemical reactions with transport agents. It is cultivated using various methods. Semiconductor devices such as microwave diodes, transistors, and laser devices are manufactured by diffusing donor impurities or acceptor impurities into a single-crystal wafer, or by epitaxially growing the same type of crystal containing these impurities on a single-crystal wafer. to create semiconductor regions with different conductivity types (electron conduction, hole conduction) and conductivity.
By using this, various devices are formed.

Now, devices such as diodes and transistors that use junctions of semiconductor layers with different types of conductive carriers need to have a high rectification ratio, and this is achieved by creating semiconductor layers with steep impurity concentration gradients. It can be realized. The present invention relates to the structure of a crystal growth apparatus for epitaxially growing a compound semiconductor having a multilayer structure with such a steep concentration gradient.

(c) Prior Art and Problems Figure 1 shows a cross-sectional structure of a conventional epitaxial growth apparatus. In the figure, a wafer 1 made of a compound semiconductor single crystal is placed on a heating table 2 made of graphite, and a thermocouple 4 is inserted into a holding rod 3 inside the heating table 2. This allows the temperature of the wafer 1 to be epitaxially grown to be measured. Further, a plurality of inlet ports 6 for introducing raw material gas for epitaxially growing a compound semiconductor are provided in the upper part of the reaction container 5 made of quartz, and an outlet port 7 is provided in the lower part of the reaction container 5. ing. Here, the raw material gas and dopant for the compound semiconductor are introduced through the air supply port 6 and supplied to the wafer surface in a mixed state, and are decomposed on the surface of the wafer 1 heated by the high frequency induction heating furnace 8, resulting in epitaxial growth. The unnecessary gas that has been decomposed is removed from the exhaust port 7. In such conventional vertical vapor phase growth apparatuses, one of the following methods has been used to grow an epitaxial layer having a steep multilayer structure.

(1) Increase the flow rate of raw material gas.

(2) Introduce the source gas close to the wafer using a thin tube.

In method (1), the source gas in the reaction vessel can be exchanged quickly, but it has the disadvantage that the uniformity of epitaxial growth is impaired as a result of changes in the decomposition temperature of the wafer and source gas, the gas flow, etc. Method (2) has the disadvantage that it cannot be used when the temperature during the growth process is controlled using an infrared thermometer instead of a thermocouple because it obstructs the field of view. It has been difficult to form this by epitaxial growth.

(d) Object of the Invention The present invention provides a crystal growth apparatus for epitaxially growing a compound semiconductor multilayer structure having a steep impurity concentration distribution.

(e) Structure of the Invention According to the present invention, the object is to fix the wafer on a heating table held by a holding rod, and to provide a liner tube that loosely fits into the inner wall around the heating table; The lower reaction tube is equipped with a high-frequency induction heating coil on the outer periphery, and the inner diameter of the lower reaction tube is smaller than the lower reaction tube. It is equipped with multiple gas introduction tubes on the side for introducing different types of reaction gases, and the upper part is equipped with an infrared thermometer. It is connected to an upper reaction tube with a top part that enables the temperature measurement of the wafer, and a steep concentration gradient can be achieved by switching the type of reaction gas flowing into the device from multiple gas introduction tubes. This problem can be solved by using a crystal growth apparatus that epitaxially grows a compound semiconductor layer having a multilayer structure.

(f) Embodiments of the Invention FIG. 2 is an explanatory diagram of a compound semiconductor crystal growth apparatus according to the present invention, and FIG. 3 is a block diagram of a field effect transistor (FET) manufactured using the same.

The present invention will be described below with reference to an embodiment using GaAs as the compound semiconductor.

The microwave GaAsFET shown in Figure 3 has a thickness of approx.
A 2-3 μm thick high-resistance film doped with chromium element (Cr) is placed on a 500 μm GaAs wafer substrate 9.
There is a GaAs buffer layer 10 on top of which the thickness is approximately
N-type with 0.3μm and impurity concentration n of 1×10 ¹⁷ cm ^-3
A GaAs active layer 11 is made by epitaxial growth, and a source (S) electrode and a drain (D) electrode are formed by diffusing gold/germanium alloy (Au/Ge alloy) into this active layer 11. It has a structure in which a gate (G) electrode made of aluminum (Al) is formed in the upper part. In order for the GaAsFET to exhibit excellent electrical characteristics, it is necessary that the impurity concentration gradient from the buffer layer 10 to the active layer 11 be steep.

The device according to the present invention shown in FIG. 2 realizes this, and has the following features compared to the conventional device shown in FIG.

(1) In the reaction tube, the upper reaction tube 12 portion into which the raw material gas is introduced is formed to be thinner than the lower reaction tube 13 through which epitaxial growth is performed.

(2) A liner tube 14 is provided inside the lower reaction tube 13.

(3) The top portion 15 of the upper reaction tube 12 is made optically transparent.

Here, the reaction tube is made of quartz, and a plurality of gas inlets (four in this example) are provided on the outer peripheral side of the upper reaction tube ₁₂ . 16. Trimethyl gallium Ga
Raw material gases such as (CH ₃ ) ₃ 17, hydrogen sulfide (H ₂ S) 18, and chromium carbonyl Cr (CO) ₆ 19 are supplied, and are mixed in the upper reaction tube 12 and sent to the heating table 2. It is designed to be supplied perpendicularly to the GaAs wafer 1 placed above. Here
AsH ₃ and Ga(CH ₃ ) ₃ are used for vapor phase growth of GaAs through the reaction Ga(CH ₃ ) ₃ +AsH ₃ →GaAs+3CH ₄ (1), and Cr(CO) ₆ is used as a third The dopant or H ₂ S for growing the buffer layer 10 in the figure is N
This is a dopant for growing the type operation layer 11.

The reason why the upper reaction tube 12 is made thin in FIG. 2 is that the wafer 1
By reducing the volume of the reaction tube, gas exchange is facilitated, and this enables a multilayer structure with a steep rise distribution. In other words, the buffer layer 10 of the GaAsFET shown in FIG.
AsH ₃ 16, Ga(CH ₃ ) ₃ 17 and Cr(CO) ₆ 19
The active layer 11 is formed by epitaxial growth using source gases supplied from three inlets 16 to 18. Now, in the case of the example,
The reaction vessels are all made of quartz, but the second
A feature of this is that a liner tube 14 is provided inside the lower reaction tube 13 that is continuous with the upper reaction tube 12, and this liner tube 14 is made of quartz like the container, and its upper end is loosely fitted into the upper reaction tube 12. It's starting to match. The purpose of providing this liner tube 14 is to restrict the flow path of the raw material gas, reduce the gas volume, and enable a steep change in impurity concentration distribution, while also preventing the lower reaction tube 13 from being contaminated by thermal decomposition products. It prevents that. In other words, the raw material gas is in the liner tube 1.
4 to the wafer 1, the result is the same as when the raw material gas is guided directly above the wafer using a thin tube, and a steep concentration gradient is possible.

Next, the third feature is the top portion 15 of the upper reaction tube 12.
By forming the wafer 1 from a transparent material (transparent quartz in this case), the temperature of the wafer 1 can be directly controlled using the infrared thermometer 20. Note that this may be a structure in which a thermocouple is provided inside the holding rod 3 as in the conventional example shown in FIG. 1, but it is better to directly measure the temperature of the epitaxial growth surface to control crystal growth more accurately. can. In FIG. 2, reference numeral 21 denotes a high-frequency induction heating coil for heating the wafer 1. As shown in FIG.

According to such a configuration, it is easy to rotate the holding rod in order to uniformly grow on the wafer surface, but it is difficult to handle this with a structure including a thermocouple.

As described above, the present invention is an apparatus for obtaining an epitaxially grown layer in which the impurity concentration distribution changes sharply, and although the manufacturing of GaAsFET has been explained, the number of introduction ports in the apparatus according to the present invention shown in FIG. By increasing the number of layers, it is possible to create a multilayer structure with different compositions. For example, if trimethylaluminum Al(CH ₃ ) ₃ is introduced through the inlet at the same time as Ga(CH ₃ ) ₃ and AsH ₃ , a semiconductor layer having a composition of GaAlAs can be epitaxially grown, and these multilayer structures Effective for producing optical elements. Although the above embodiments have been described with respect to a vertical crystal growth apparatus, the present invention is not limited thereto, and can also be applied to a horizontal crystal growth apparatus.

(g) Effects of the Invention According to the present invention, the upper reaction tube is made elongated, the lower reaction tube is provided with a liner tube, the top of the head is made transparent, and the temperature is adjusted using an infrared thermometer. A growth apparatus is provided that enables the growth of multilayer compound semiconductor layers with concentration gradients.

[Brief explanation of drawings]

FIG. 1 shows a conventional crystal growth apparatus, FIG. 2 shows a crystal growth apparatus according to the present invention, and FIG. 3 shows an embodiment of a field effect transistor. In the figure, 1 is a wafer, 2 is a heating table, 4 is a thermocouple, 5 is a reaction vessel 6, 16, 17, 18, 19 is an inlet, 9 is a GaAs wafer, 10 is a buffer layer,
11 is a working layer, 12 is an upper reaction tube, 13 is a lower reaction tube, and 14 is a liner tube.

Claims (1)

[Claims] 1. A wafer 1 is fixed on a heating table 2 held by a holding rod 3, and a liner tube 14 is provided that fits loosely into the inner wall around the heating table 2, and a liner tube 14 is provided on the outer periphery. A lower reaction tube 13 equipped with a high-frequency induction heating coil 21, and a plurality of gas introduction tubes 16, 17, 18, 19 having a smaller inner diameter than the lower reaction tube 13 and into which different types of reaction gases are introduced into the side surfaces. , an upper reaction tube 12 having a top portion 15 that enables temperature measurement of the wafer 1 with an infrared thermometer 20 is connected to the upper reaction tube 12, and the plurality of gas introduction tubes 16, 17, 18, 19 are connected to each other.
A crystal growth apparatus characterized by epitaxially growing a compound semiconductor layer having a steep concentration gradient and a multilayer structure by switching the type of reactive gas flowing into the apparatus.