JPS63297297A - Production of compound semiconductor single crystal - Google Patents

Abstract

PURPOSE:To obtain a compound semiconductor single crystal with hardly any crystal defects, such as dislocation, by using a heater having an inwardly curved heat radiation surface in a liquid encapsulated Czochralski (LEC) method using heaters in plural stages and concentrating heating energy with the heater in a solid-liquid interfacial part. CONSTITUTION:A heater 2 is provided on the periphery of a crucible 3 corresponding to a melt 6 and a heater 11 is placed corresponding to a liquid encapsulating agent 5 and solid-liquid interface 9. An annular heater 11 having an inwardly curved heat radiation surface is used as the heater 11 and heating energy with the heater 11 is concentrated in the solid-liquid interfacial part 9 to grow a compound semiconductor single crystal 4 by the LEC method. Thereby the temperature of the surface of the liquid encapsulating agent 5 can be kept at a low value while reducing temperature gradient in the interface of the liquid encapsulating agent 5 and the single crystal 4. As a result, the single crystal 4 with hardly any crystal defects, such as dislocation, can be produced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for growing compound semiconductor single crystals such as InP and GaAs used as substrates for light emitting and light receiving devices and high speed ICs.

[Prior art] In the growth of compound semiconductor single crystals such as InP and GaAs, liquid sealants such as B2O3 and solid solutions of NaCQ-KCQ are used to suppress the evaporation of elements with high dissociation pressure at the melting point of the compound such as P and As. using LEC (Llquld
Encapsulated Czochralskl
) law is widely applied.

FIG. 3 shows a compound semiconductor single crystal growth apparatus using a conventional heater.

A heater 2 is arranged surrounding the crucible 3 and corresponds to the growth melt 6, a heater 1 is arranged corresponding to the liquid sealant 5 and the solid-liquid interface 9, and the crucible 3 is moved up and down by the lower axis lO and rotated. configured to be able to do so.

Further, the upper shaft 8 is configured to be able to move up and down and rotate, and a seed crystal 7 is attached to the tip of the upper shaft 8, and the ingot 4 is grown at the solid-liquid interface 9 that is in contact with the lower surface of the liquid sealant 5, and is successively pulled up. . Although not shown, the entire device is housed in a reaction container.

Not limited to the LEC method mentioned above, when growing single crystals, it is extremely important to reduce the temperature gradient near the interface between the grown ingot and the raw material melt in order to suppress crystal defects such as dislocations. In order to achieve this objective, various efforts have been made, such as using a shielding plate and a multi-segmented heater, and these efforts have been reported in Collection P, 588, etc.

Furthermore, j'E'c (Fu
ll,y Encapsulated Czochra
lskl) method has also been attempted. This is, for example, the Tokuko Sho 6
1-31381.

[Problems to be solved by the invention] In the LEC method, the general growth condition is to set the liquid sealant to about 1 to 3 cm, but under such conditions, it is necessary to adjust the furnace environment. When the temperature gradient at the solid-liquid interface is reduced, the surface temperature of the liquid encapsulant is kept high, so elements with high dissociation pressure evaporate from the surface of the ingot that has come out of the liquid encapsulant after growth. It ends up. As a result, the missing element becomes a source of crystal defects, or the remaining elements with low dissociation pressure gather, become a liquid, and drip downward, eventually reaching the solid-liquid interface and causing crystal defects. There is a problem in that the temperature gradient at the solid-liquid interface cannot be freely set.

In addition, the FEC method proposed as a method to solve these problems still has problems with seeding and crystal diameter control because the layer of liquid sealant is thick and it is difficult to visually observe the melt. .

[Structure of the Invention] The present invention has been made for the purpose of solving the above-mentioned problems, and among the multi-stage divided heaters surrounding the crucible, heat radiation is applied to the heaters corresponding to the liquid sealant and the solid-liquid interface in particular. By using a heater whose surface is curved inward, it is possible to concentrate heater heating energy near the solid-liquid interface of the growing ingot or around the bottom of the liquid sealant, thereby reducing the temperature gradient at the solid-liquid interface. is kept small and the temperature of the surface of the liquid sealant is set at a relatively low temperature.

The present invention will be explained in detail below using the apparatus shown in FIG.

The same parts as in FIG. 3 are indicated by the same reference numerals.

A heater 2 is disposed surrounding the crucible 3 and corresponds to the melt 6, and has an inwardly curved heat radiation surface so as to concentrate heating energy corresponding to the liquid sealant 5 and the solid-liquid interface 9. An annular heater 11 is arranged. Although the vertical distance between the heater 11 and the heater 2 is not shown, it is configured to be adjustable.

Furthermore, the number of heaters is not limited to two as shown in the figure, but any heater may be provided in multiple stages.

The crucible 3 is configured to be able to move up and down and rotate by a lower shaft 10, and the upper axis 8 is configured to be able to move up and down and rotate. A growing ingot is grown at a certain solid-liquid interface 8 and pulled up sequentially.

Now, as shown, the heater l! has a heat radiation surface curved inward, and serves to intensively heat the area near the solid-liquid interface between the growing ingot 4 and the melt 6, or the lower surface of the liquid sealant 5. There is. Furthermore, the heater 2 is a heater that mainly serves to heat the growth melt 6, and the heater 2 and the heater 2 complement each other to heat the ingot 4, the growth melt 6, and the liquid sealant 5, and both heaters 11.2 plays an important role of arbitrarily setting the growth diameter of the ingot by minutely adjusting its output.

Figure 2 shows the temperature distribution near the top of the liquid sealant and melt during crystal growth using the conventional apparatus shown in Figure 3.
), (line I)), and the same temperature distribution during crystal growth using the apparatus shown in FIG. 1 for carrying out the present invention (line I).

The figure is for the growth of a single crystal of GaAs.
B2O3 is used as the liquid sealant.

According to the apparatus using the conventional heater shown in FIG. 3, which has already been described, a temperature distribution as shown in (1) is typically obtained. Also, in this device, the growth melt 6 and the crucible 3
By adjusting the relative position of the heaters 1 and 2 and applying a larger output to the upper heater 1, the temperature distribution with a small temperature gradient at the interface between the encapsulant B2O3 and GaAs can be achieved, as shown by the (eye) in Figure 3. It is possible to achieve this. However, B2
At the same time, the O3 surface temperature increases, making it impossible to obtain a good ingot.

On the other hand, if a curved upper heater is used as in the apparatus of the present invention, the temperature of the B2O3 surface can be lowered without reducing the temperature gradient at the interface between B2O3 and GaAs, as shown in (Ill). can be kept.

The origin of this aspect will be explained using the apparatuses shown in FIGS. 1 and 3. In the figure, the arrows coming out from the side walls of the heaters 1 and 11 and the crucible 3 are calibrated representations of radiation from the upper heater 1°I1. In other words, even if the same output is applied to heaters 1 and 11 in both figures and the surface temperatures of heaters 1 and 11 become similar, in the case of heater 11 in Figure 1, since the heater is curved, It becomes possible to concentrate the heating energy from the crucible 3 in a narrower portion of the side wall of the crucible 3 compared to the heater 1 shown in FIG.

As a result, the temperature environment of the system including the growth melt, liquid sealant, and growth ingot becomes steep.

By adjusting the relative positions of the heaters 1 and II and the crucible 3, the temperature gradient between the growing ingot and the melt is small, and the temperature of the surface of the liquid sealant is low.
An ideal temperature distribution as shown in Figure (1) can be obtained.

[Example] An undoped GaAs single crystal was grown using B2O3 as a liquid sealant. As raw materials, metallic gallium and metallic arsenic with a purity of 6N were used, and they were weighed and introduced so that a stoichiometric composition could be achieved with a total amount of 3 kg. B
For 2O3, 400 g of a substance with a moisture content of 1100 pp was used. The crucible is made of PBN and has a diameter of 125 m and a height of 200 mm.

As for the growth conditions, high-purity Ar gas was used as the atmospheric gas, and the pressure was set at 15 kg/cJ during growth. The growth ingot and crucible were rotated in opposite directions at IOrpm and 2Orpm, respectively. The pulling speed is I2 mm/hour. In addition, in order to keep the height of the interface between B2O3 and the GaAs melt unchanged throughout the growth, the crucible was raised as much as possible to catch the drop in the melt as the ingot grew.

The growth diameter of the crystal was set to 55 mm in the diameter of the straight body.

In order to obtain an ingot of the desired diameter, the weight of the growing ingot is measured using a load cell installed at the top of the upper shaft (pulling shaft), the growing diameter is calculated from the time change, and the information is A method is adopted in which feedback is given to the heater power.

The diameter control, growth rate, crucible rising rate, etc. are all centrally controlled by a single computer.

In order to clarify the difference from the conventional heater, the relative positional relationship between the heater and the melt was kept the same.

In addition, we attempted to adjust the current flowing through the heater to be as similar as possible between growth using a conventional heater and growth using the curved heater of the present invention, but growth using the curved heater was not stable. Diameter control was not possible.

Therefore, by slightly suppressing the current flowing through the curved heater, we were able to perform growth with good diameter control.

This suggests that radiation is effectively concentrated by turning the heater once.

The grown ingot was sliced, etched with KOH, and the number of pits associated with dislocations was counted.
Average of 7.3 x 1G' using conventional heater
/cJ 1 for a curved heater. G X In' /c
The result was J.

Furthermore, when the surface of the grown ingot was observed, the surface roughness of the ingot using the curved heater was less than that of the conventional ingot, and it is presumed that the temperature of the B2O3 surface was lower than that of the conventional ingot.

[Effects of the Invention] As described above, by simply changing the shape of the heater by curving it, crystal defects such as dislocations can be significantly reduced compared to the conventional method.

In the fabrication of semiconductor devices, the dislocation density of the substrate crystal is an important factor that greatly influences the performance of the device. For example, when transistors are integrated in a single chip at a high density, it is known that the operating voltage of each transistor is directly affected by the presence of dislocations, and even when making semiconductor lasers, the emission intensity of the locations with dislocations is considered not to contribute. That is, reducing crystal defects is an essential direction toward improving device performance, and the present invention is effective as a manufacturing technology for compound semiconductor single crystals with few crystal defects.

[Brief explanation of drawings]

FIG. 1 shows an example of a lifting device implementing the present invention. FIG. 2 shows the temperature distribution in the longitudinal direction inside the furnace in an apparatus implementing the present invention and a conventional apparatus. FIG. 3 shows an example of a conventional lifting device. 1, 2... Heater, 3... Crucible, 4... Ingot, 5... Liquid sealant, 6... Melt, 7...
・Seed crystal, 8...upper axis, 9...solid-liquid interface, 1G...
・Lower shaft, 11...Curved heater. ) 1 Figure dice 3 Figures

Claims (1)

[Claims] (1) In the LEC method, which uses multi-stage heaters, a heater whose heat radiation surface is curved inward is used.
A method for producing a compound semiconductor single crystal, comprising concentrating heating energy by the heater on a solid-liquid interface.