JPH07315984A - Vertical liquid phase epitaxy and device therefor - Google Patents

Abstract

PURPOSE:To provide vertical liq. phase epitaxy and device therefor capable of conducting uniform epitaxial growth on the surfaces of plural semiconductor substrates especially from a single melt, capable of growing a good-quality crystal and excellent in mass-productivity. CONSTITUTION:Plural semiconductor substrates 2 are horizontally laminated at specified intervals and supported, the substrates 2 are dipped in a melt reservoir 11 set at the lower part, pulled up and separated from the reservoir 11, only the melt 8 necessary for epitaxial growth is held on the respective substrates, and epitaxial growth is conducted outside the reservoir 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vertical liquid phase epitaxial growth method and apparatus used in the manufacture of, for example, optical semiconductor elements, and more particularly to a method for forming a single melt on the surfaces of a plurality of semiconductor substrates. Uniform epitaxial growth can be achieved, high-quality crystal growth can be obtained, and mass productivity is extremely high.

[0002]

2. Description of the Related Art Currently, a liquid phase epitaxial method (hereinafter referred to as L
An overview of the characteristics of the epitaxial device used in the PE method). The epitaxial devices are roughly classified into a horizontal type method and a vertical type method.

As the horizontal method, the slide boat method is mainly used at present. In the melt-melting step before epitaxial growth in the slide boat method, the semiconductor substrate is held at a position spatially separated from the melt, and after the melt-melting is completed, the jig is slid to expose the substrate to the bottom of the melt. The epitaxial growth is started in this state. When a large number of substrates are epitaxially grown in one batch by the slide boat method, the melt must be prepared for each substrate, so the weighing time becomes longer in proportion to the number of substrates.
Mass productivity decreases. When adopting the solid phase dope method in this slide boat method, a method of arranging a plurality of combinations (sets) of the melt and the substrate in a row or further stacking them in the vertical direction to increase the mass productivity is conceivable. If such a method is adopted, the contact area of the sliding portion increases and sliding becomes difficult, so the number of substrates to be loaded per batch cannot be increased so much. In addition, such an epitaxial device in which the behavior of the jig is slid is low in manufacturing mass productivity. Furthermore, when adopting the vapor phase dope method in the slide boat method, it is necessary to provide an opening in the upper part of the melt in order to achieve contact between the melt and the atmospheric gas, and therefore, as in the case of adopting the solid phase dope method. It is difficult to stack the combination of the substrate and the substrate in the vertical direction, and the number of substrates to be loaded per batch is smaller than that in the case where the solid phase doping method is adopted.

The vertical method includes a method of holding the substrate horizontally and immersing it in the melt, and a method of holding the substrate vertically and immersing it in the melt. In the vertical method, the number of substrates that can be put into one batch can be increased as compared with the horizontal method. An example of a horizontal substrate is, for example, Japanese Patent Laid-Open No. 5-71
558 and Japanese Patent Publication No. 54-38600 as an example of a vertical substrate. However, in each case, the specific surface area (surface area / volume) of the melt is smaller than that of the horizontal method in which the combination of the individual substrate and the melt is independent. Uptake efficiency and uniformity in the melt deteriorate. Further, in the vertical method, since the substrate is immersed in the melt reservoir, the amount of excess melt that does not contribute to epitaxial growth is greater than in the horizontal slide boat method, and the amount of melt in contact with the melt reservoir wall surface is also greater. For this reason, the amount of solute deposited on the melt reservoir wall surface becomes a non-negligible amount with respect to the total amount of the epitaxial layer (total epitaxial amount on all input substrates), and the solute deposition on the melt reservoir wall surface competes with the epitaxial growth. Therefore, delicate adjustment of the dopant concentration, meltback amount, layer thickness and the like becomes more difficult than in the horizontal method.

On the other hand, the impurity doping method in the LPE method includes a solid-phase doping method in which impurities are mixed in advance with a melt, and a vapor in which vapor generated by heating gas or solid is brought into contact with the melt to dope impurities. There is a phase doping method.
When forming a pn junction by the LPE method, p-type and n-type dopants can be independently supplied by the vapor phase doping method, so that the melt may be single. In this case, the dopant for the first layer may be solid-phase-doped in the melt. In the solid phase doping method, p-type and n-type melts are prepared separately, and the pn junction is formed by dipping the substrate from the first melt to the second melt during epitaxial growth. More than two batches of melt are required. However, when gallium arsenide (or gallium arsenide.aluminum) is doped with silicon, the conductivity type of Si, which is an amphoteric impurity, is inverted due to the epitaxial growth temperature, so it is exceptional. It is known that one melt can form a pn junction.

[0006]

Therefore, the number of substrates that can be processed at one time can be increased, and the required epitaxial growth melt can be placed only on the surface of the substrate, so that impurities can be uniformly doped. There has been a demand for improvement of the LPE method so as to be possible.

[0007]

SUMMARY OF THE INVENTION The present invention has been proposed in view of the above, and supports a plurality of semiconductor substrates horizontally and stacked at a predetermined interval and supports the semiconductor substrates on a melt reservoir installed below. After soaking, lift off from the melt reservoir,
Vertical type, characterized in that only the melt necessary for epitaxial growth is held on each semiconductor substrate, epitaxial growth is performed outside the melt reservoir, and if necessary, a dopant gas is introduced into the system during the growth process for vapor phase doping. The present invention relates to a liquid phase epitaxial growth method.

The present invention also proposes an apparatus for carrying out the above-mentioned vertical liquid phase epitaxial growth method, which is a substrate obtained by laminating a large number of support plates for horizontally supporting a semiconductor substrate at predetermined minute intervals. A vertical type liquid phase epitaxial growth apparatus comprising a cassette, a drive mechanism for moving the substrate cassette up and down, and a melt reservoir for immersing the substrate cassette, wherein the semiconductor substrate is supported by a supporting plate and the upper supporting plate. A small gap is formed between the substrate cassette and the substrate cassette, the substrate cassette is dipped in the melt reservoir to fill the gap, and the substrate cassette is lifted and separated, and only the melt filled in the gap is retained by the surface tension. A device for epitaxial growth outside the melt reservoir.

[0009]

Since the present invention has the above-mentioned structure, the melt can be held only in the minute gaps formed on the plurality of semiconductor substrates, and can be gradually cooled outside the melt reservoir for epitaxial growth. Therefore, only the required minimum amount of melt can be used, and the impurities can be easily and uniformly vapor-phase-doped as necessary.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the embodiments of the drawings.

FIG. 1 is a sectional view of an epitaxial device according to the present invention, and FIG. 2 is a side view showing a substrate cassette 9. The semiconductor substrate 2 is supported horizontally on the support plate 1, and 10 combinations of these combinations are shown in FIG.
Are stacked vertically through. This is sandwiched between the lower holding jig 3 and the upper holding jig 4, and fixing bolts 5 are fixed to fixing holes provided in the lower holding jig 3 and the upper holding jig 4, respectively, to fix the substrate cassette. 9 is composed.
An operation rod 6 which is vertically moved by a drive mechanism (not shown) is integrally connected to the upper surface of the upper holding jig 4 so that the substrate cassette 9 shown in FIG. On the other hand, the lower surface of the lower holding jig 3 has a sharpened shape for crushing the crust on the surface of the melt 8 in the melt reservoir 11 provided below the reaction tube 10.

FIG. 3 is a perspective view showing the end structure of the support plate 1 in an exploded and enlarged manner. The support plate 1 is made of graphite, quartz, p
It is a flat plate made of ceramics such as BN, and notches 1a for passing the fixing bolts 5 are provided at four corners. The substrate position fixing jig 7 is for fixing the semiconductor substrate 2 at a predetermined position on the support plate 1 and at the same time forming a predetermined space between the semiconductor substrate 2 and the support plate 1 arranged on the upper stage thereof. It is located in the four corners of. The thickness d of the substrate position fixing jig 7 is set to be about 2 mm thicker than the thickness t of the semiconductor substrate 2, and a minute gap (about 2 m) filled with the melt 8 on the semiconductor substrate 2 when assembled.
m) is formed. Further, a regulation piece 7a having a front drip shape is provided at a corner of the board position fixing jig 7, and the regulation piece 7a comes into contact with the end edge 1b of the support plate 1 when assembled.
The inner edge 7b of the substrate position fixing jig 7 fixes the semiconductor substrate 2 at a predetermined position (prevents detachment due to lateral displacement). The substrate cassette 9 is configured by stacking a plurality of stages of the support plates 1 having such an end structure.

FIG. 4 is a plan view showing an assembled state of the support plate 1 having the above-mentioned end structure, and FIG. 5 is a side view thereof. The semiconductor substrate 2 is arranged in the center of the support plate 1, and is laterally held by substrate position fixing jigs 7 arranged at the four corners.
The semiconductor substrate 2 and the substrate position fixing jig 7 (the inner edge 7 of the
b) does not have to be in contact with each other, and may have a structure in which a part of the semiconductor substrate 2 does not protrude to the outside of the support plate 1 even if the semiconductor substrate 2 moves (horizontal shift) on the support plate 1. Further, as described above, the substrate position fixing jig 7 also serves to form a predetermined space between the substrate position fixing jig 7 and the support plate 1 arranged on the upper stage. The position of the substrate position fixing jig 7 itself is regulated by the fixing bolts 5 located outside thereof.

As shown in FIG. 1, the substrate cassette 9 having the above-described structure is installed in an epitaxial growth furnace, the inside of the reaction tube 10 is made an inert atmosphere, and the heater 12 sets the melt 8 and the upper part of the melt reservoir 11 to a predetermined temperature program (see FIG. It is advisable to adopt a division method or the like so that it can be controlled according to 6).

Other configurations will be described below along with specific operations. First, the substrate cassette 9 is positioned above the reaction tube 10 as shown in FIG. Next, the melt 8 charged with gallium phosphide or gallium arsenide (aluminum) as a solute, silicon and tellurium as a dopant, and metal gallium as a solvent is heated to the raw material melting temperature T1 according to the temperature program of FIG. , Solute and dopant are uniformly dissolved. At this time, the amount of solute charged is adjusted so as to be saturated between the dissolution temperature T1 and the immersion temperature T3 described later. Then, when the temperature of the furnace is lowered to the immersion temperature T3 and kept at a constant temperature, a saturated solution having a slight crust on the surface of the melt 8 is formed. Continuing with FIG.
At time (A), the operating rod 6 is lowered to immerse the substrate cassette 9 in the melt 8. Then, as shown in FIG. 7, the melt 8 fills the space between the support plates 1 and 1. 0 to 10 minutes after the completion of the immersion, the operating rod 6 is lifted at the time point of FIG. 6B to lift and separate the substrate cassette 9 from the melt 8.
At that time, as shown in FIG.
The melt 8 on the semiconductor substrate 2 flows out from the space between the two.
Only is retained without spilling. This is because, in the region where the semiconductor substrate 2 is present, the space is a gap narrower than the surroundings by the thickness of the semiconductor substrate 2, and therefore the surface tension is increased by that amount, so only the melt 8 in this gap is formed. Are retained without spilling. Needless to say, such a phenomenon depends on the thickness of the space between the support plates 1 and 1 and the thickness of the semiconductor substrate 2 (that is, the above-mentioned gap). As a result of experiments on this point, the semiconductor substrate 2 Thickness is 25
In the case of 0 to 400 μm, if the thickness of the space between the support plates 1 and 1 is 2.5 mm or less, preferably 2 mm or less, the excess of the melt 8 is left only on the semiconductor substrate 2 as described above. It was found that the melt 8 can be removed (flowed out) from the substrate cassette 9 by its own weight. After (B) point in FIG. 6,
The temperature is lowered according to the conventional LPE method to continue the epitaxial growth, and if necessary, a dopant gas is caused to flow into the atmosphere to dope the impurities by a vapor phase doping method. If necessary, meltback may be carried out.

An example of manufacturing an epitaxial wafer using the above epitaxial growth apparatus is shown below.

[Manufacturing Example 1] In summary, an infrared light emitting diode was prepared by stacking a silicon-doped gallium arsenide layer on a gallium arsenide substrate. As a melt,
Metallic gallium 5 kg as a solvent, gallium arsenide polycrystal 715 g as a solute, and silicon 10 as a dopant.
The solution which mix | blended each g was used. The saturation temperature (T2 in FIG. 6) of this melt is 908 ° C. An n-type gallium arsenide single crystal substrate was used as the semiconductor substrate. A substrate cassette made of graphite was used, and ten semiconductor substrates were attached. The substrate cassette was positioned above the melt reservoir according to the illustrated embodiment, and the melt was heated to 910 ° C. (melt melting temperature) according to the program shown in FIG. The gallium arsenide polycrystal was uniformly melted by maintaining this temperature for about 1 hour, and then the temperature was lowered to 905 ° C. After keeping the temperature constant for 15 minutes,
The substrate cassette was immersed in the melt. After the lapse of 5 minutes, the substrate cassette was lifted and separated, and was placed on the melt reservoir. Then cool down to 785 ° C at a cooling rate of 1 ° C / min,
The epitaxial layer was grown. In this epitaxial system, the conductivity type of silicon naturally inverts from n-type to p-type with epitaxial growth, so a pn junction is formed by this step. After reaching 785 ° C., the atmosphere gas was switched to an inert gas, the heater was turned off, and the mixture was allowed to cool.

Using the epitaxial wafer obtained in Production Example 1 above, a light emitting diode was manufactured and its characteristics were evaluated. The thicknesses of the n layer and the p layer are 50 μm and 80 μm, respectively.
The emission wavelength was 930 nm. Further, when comparing the light emission output (relative value) at a forward current of 20 mA, it is 0.50 in the conventional method of epitaxial growth while being immersed in the melt pool, whereas it is 0.5 in Production Example 1.
5, which was an improvement of 10%. Further, the in-plane variation within one wafer was extremely small, and the variation between the ten wafers was not recognized, and the wafer having extremely excellent uniformity was obtained.

[Production Example 2] Briefly, a gallium phosphide layer doped with silicon is formed on an n-type gallium phosphide substrate.
A yellow-green light emitting diode was prepared by stacking a nitrogen-doped n-type gallium phosphide layer and a zinc-doped p-type gallium phosphide layer. As the melt, 5 kg of metal gallium as a solvent and gallium phosphide polycrystal 190 as a solute were used.
g and 26 mg of silicon as a dopant were used. The saturation temperature (T2 in FIG. 6) of this melt is 1010 ° C. As in the case of Production Example 1, a graphite cassette was used as the substrate cassette, and ten semiconductor substrates were attached. The substrate cassette was positioned above the melt reservoir according to the illustrated embodiment, and the melt was heated to 1020 ° C. (melt melting temperature) according to the temperature program of FIG. The gallium phosphide polycrystal was uniformly dissolved by holding at this temperature for about 1 hour, and then the temperature was lowered to 1000 ° C. After holding for 15 minutes, the substrate cassette was immersed in the melt.
After the lapse of 5 minutes, the substrate cassette was lifted and separated, and was placed on the melt reservoir. Then, at a cooling rate of 2.5 ° C / min, 9
The temperature was lowered to 00 ° C. to grow an epitaxial layer. Ammonia gas was introduced into the reaction tube when the temperature reached 960 ° C. during the epitaxial growth process. Further cooling was continued, and when the temperature reached 900 ° C., the temperature was maintained and metallic zinc was charged into the melt reservoir to grow a p-type gallium phosphide layer, and zinc vapor was generated. After sufficient zinc is supplied to the melt held on the semiconductor substrate, 2.5 ° C
The gallium phosphide layer was grown by lowering the temperature to 800 ° C./min. Then, cooling was continued, and after reaching 800 ° C., the atmosphere gas was switched to an inert gas, the heater was turned off, and the mixture was allowed to cool.

A light emitting diode was manufactured using the epitaxial wafer obtained in the above Production Example 2 and its characteristics were evaluated. The thicknesses of the n-layer and the p-layer are 50 μm (20 μm in the region doped with nitrogen) and 20 μm, respectively.
Met. In addition, the light emission output (relative value) is set to the forward current 20.
When compared in mA, it was 0.25 in Production Example 2, and an improvement of 20% was recognized as compared with the conventional method of epitaxial growth while being immersed in a melt pool. Furthermore, 1
The variations in the wafers were extremely small, and the variations among the 10 wafers were not recognized, and the wafers with excellent uniformity were obtained.

As is clear from the illustrated embodiment and manufacturing examples 1 and 2, according to the present invention, it is not necessary to separately prepare the melt for each semiconductor substrate, and one melt reservoir can automatically prepare the melt without excess or deficiency. It is now possible to supply saturated melt onto semiconductor substrates. For this reason, the melt weighing time does not increase even if the number of semiconductor substrates to be added per batch increases, and as a result, it contributes to the improvement of production efficiency. Further, after the time point of FIG. 6B, since the periphery of the melt on the semiconductor substrate is in contact with the atmospheric gas, the vapor phase doping can be efficiently performed even if a large number of semiconductor substrates are charged in one batch. It is also possible to improve the mass productivity. Furthermore, since the jig behavior (operation) does not involve sliding, it is possible to realize an epitaxial device with high productivity in mass production.

Although the present invention has been described above based on the embodiments, the present invention is not limited to the above-mentioned embodiments, and may be carried out in any manner as long as the configuration described in the claims is not changed. You can

[0023]

As described above, according to the vertical liquid phase epitaxial growth method of the present invention, when supplying a saturated melt to the surfaces of a plurality of semiconductor substrates, only one melt reservoir needs to be prepared. Since the melt is not wasted because only the necessary melt is held on the semiconductor substrate by surface tension, mass productivity and production efficiency are extremely high.

Further, when the impurities are uniformly doped, if necessary, the vapor phase doping can be easily and efficiently carried out by only introducing the dopant gas into the atmosphere gas, so that the mass productivity is improved. Can be improved.

Further, in the growth apparatus of the present invention, the behavior (operation) of the jig is not accompanied by sliding unlike the conventional slide boat method, so that an epitaxial apparatus with high productivity in mass production can be realized. it can.

[Brief description of drawings]

FIG. 1 is a side view schematically showing an apparatus of the present invention.

FIG. 2 is a side view showing an assembled state of a substrate cassette used in the apparatus shown in FIG.

FIG. 3 is an exploded perspective view showing an example of an end structure of a support plate.

FIG. 4 is a plan view showing an assembled state of the semiconductor substrate on the support plate of FIG.

FIG. 5 is a side view of FIG.

FIG. 6 is a graph showing an example of a temperature program for epitaxial growth.

FIG. 7 is a partial side sectional view showing a state in which the substrate cassette is immersed in the melt reservoir.

FIG. 8 is a partial side view showing a melt state during epitaxial growth.

[Explanation of symbols]

 1 Support plate 2 Semiconductor substrate 3 Lower holding jig 4 Upper holding jig 5 Fixing bolt 6 Operation rod 7 Spacer 8 Melt 9 Substrate cassette 10 Reaction tube 11 Melt reservoir 12 Heater

Claims (3)

[Claims] 1. A plurality of semiconductor substrates are horizontally stacked and supported at predetermined intervals, the semiconductor substrates are immersed in a melt reservoir installed below, and then separated from the melt reservoir.
A vertical liquid phase epitaxial growth method characterized in that only a melt necessary for epitaxial growth is held on each semiconductor substrate, and epitaxial growth is performed outside the melt reservoir. 2. A plurality of semiconductor substrates are stacked horizontally and supported at predetermined intervals, the semiconductor substrates are immersed in a melt reservoir installed below, and then lifted and separated from the melt reservoir,
A vertical liquid phase epitaxial growth method characterized in that only a melt necessary for epitaxial growth is held on each semiconductor substrate, epitaxial growth is performed outside the melt reservoir, and a dopant gas is introduced into the system during the growth process to perform vapor phase doping. . 3. A substrate cassette in which a plurality of support plates for horizontally supporting a semiconductor substrate are stacked at predetermined minute intervals,
A vertical liquid phase epitaxial growth apparatus comprising a drive mechanism for moving the substrate cassette up and down and a melt reservoir for immersing the substrate cassette.