JPS6117798B2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention provides a compound semiconductor single crystal sensitive to thermal strain.
This relates to a manufacturing method and manufacturing equipment that minimizes the roughness of the crystal surface, which is a source of dislocations, and that pulls and grows with as little thermal strain as possible during growth. The aim is to obtain a single crystal with a low dislocation density by suppressing the dissociation of the sexual component elements and by reducing the strain.

(Prior art) In so-called group compound semiconductors, which are compounds of elements belonging to group B and group B of the periodic table, the group elements are volatile, so liquid encapsulation is required to obtain large single crystals. Stop lifting method (Liquid
Encapsulation Czochralski pulling method:
(commonly known as the LEC method) is used. The schematic diagram is shown in the third
As shown in the figure. Note that the heater, pressurized gas inlet, etc. are omitted. The pressure of the inert gas applied to the melt 2 of the semiconductor crystal to be obtained in the crucible 4 and the space 8 in the pressure chamber 5 is hydrostatically applied to the melt 2, and volatile components are removed from the surface of the melt 2. A liquid-sealed capsule (usually B ₂ O ₃ ) 3 used for the purpose of suppressing the dissociation of the liquid is added and melted, and a seed crystal 9 attached to a rotating pull-up shaft 6 is passed through the liquid-sealed capsule 3 to melt the liquid. In this method, the single crystal 1 is obtained by immersing the single crystal in water 2 and then starting pulling.

By the way, in such a conventional LEC method, the liquid-sealed capsule 3 is only intended to suppress the dissociation of volatile components from the surface of the melt 2 that becomes a single crystal, so its thickness is The thickness required for the sealing effect is the minimum required, and for this reason most of the grown single crystals are placed in the pressure space 8 as shown in Figure 3.
was exposed to. For this reason, convection of the inert gas within the pressure space 8 occurs, and the single crystal surface in contact with the inert gas is heated at a temperature of, for example, 80 to 150 degrees Celsius in the direction of the pulling axis.
A large temperature gradient on the order of cm will occur. When such a temperature gradient is large, thermal strain is introduced into the crystal and dislocations, which are crystal defects, ^occur .
This results in a dislocation density as high as 10 ⁵ cm ^-2 .

In view of these shortcomings, attempts have been made to improve the conventional devices. For example, a proposal has been proposed to install a preheating device such as an after-heater above the liquid-sealed capsule, but this would prevent volatile components (e.g., As if the crystal is GaAs) from the crystal surface. This promoted dissociation and severely roughened the crystal surface, conversely causing defects. this is,
Even if the temperature gradient in the direction of the pulling axis can be reduced by an after-heater, the pulled crystal will be exposed to a high-temperature pressure space, and As will dissociate on the crystal surface, resulting in many defects on the crystal surface. This is a phenomenon in which dislocations propagate within the crystal even with small thermal strain (low temperature gradient) using this as a source.
This was discovered empirically by the present inventors.

On the other hand, if an after-heater is not provided, the temperature gradient in the direction of the pulling axis of the crystal is increased, and the temperature of the pressure space around the pulled single crystal is lowered, a liquid sealed capsule can be created as shown in Figure 4. The viscosity of the agent 3 increases and it wets the surface of the growing single crystal 1, forming a coating 7.
form. However, in this case, the thermal strain is large and many defects occur due to thermal strain, and since the outer cover 7 is extremely thin, some parts are not covered, which prevents the dissociation of As. The effect was not sufficient either. Further, if an after-heater is provided in such a state, the viscosity of the outer cover (liquid sealed capsule) decreases and the outer cover cannot continue to adhere. That is, in the conventional manufacturing method and manufacturing apparatus, it has not been possible to prevent the volatile component elements from dissociating from the surface of the grown crystal. Also, by lowering the temperature gradient in the direction of the crystal growth axis (i.e.,
It was not possible to achieve both of heating the single crystal so that the ambient temperature near the melt temperature) and surrounding it with a sealant to prevent the dissociation of volatile components from the surface of the pulled single crystal. .

Furthermore, in the conventional LEC method, a method has recently been experimentally developed in which a crystal weight detection device called a load cell is installed on the pulling shaft to automatically grow the crystal, but the detection is noisy, especially for seed crystals and melt. Detection of the change in crystal weight during contact with the seed crystal and when growing the crystal from the seed crystal lacks accuracy. This can be explained using the conventional example shown in Figure 3 (however, crystal weight detection devices such as load cells are omitted).
In this way, if there is a thin liquid sealant on the melt, the crystal will come out of the liquid sealant again while receiving the buoyant force from the liquid sealant, so the change in the crystal weight due to the load cell will be due to the buoyant force. requires correction,
It becomes extremely complicated. In other words, if such a complex correction is performed with a simple correction, accuracy will be lacking.

(Problems to be Solved by the Invention) As described above, the conventional techniques have not been able to prevent the volatile component elements from dissociating from the surface of the grown crystal. Furthermore, in order to lower the temperature gradient in the direction of the crystal growth axis, that is, to reduce thermal strain, and to suppress the dissociation of volatile components from the pulled single crystal surface, the crystal surface is surrounded with a sealant. It was not possible to achieve both. Furthermore, when detecting changes in crystal weight using a load cell, there is a drawback in that detection accuracy cannot be improved due to the effect of a thin liquid sealant provided on the melt.

(Means for Solving the Problems) In order to solve these drawbacks, the present invention attempts to grow compound semiconductor single crystals containing volatile component elements in a liquid encapsulation melt-pulling method (LEC method). For example, exceeding the length of the single crystal
By placing a thick layer of a liquid-tight capsule, such as B ₂ O ₃ , above the melt that becomes the single crystal,
The single crystal is constantly pulled up and grown in the liquid-sealed capsule. Furthermore, in order to realize a low temperature gradient even more effectively, the temperature of the thick liquid-sealed capsule is controlled independently of the temperature of the melt that becomes the single crystal.

FIG. 1 is a diagram explaining the basic concept of the present invention, in which 2 is a melt of a compound semiconductor crystal to be manufactured, 9 is a seed crystal, and 10 is a compound semiconductor single crystal of length c (however, the single crystal 10 It _does not depart from the basic concept of the present invention even if the length c' from the shoulder 10' of the liquid to the melt surface is defined as the _length . is a long crucible in which a semiconductor single crystal 10 and a sealant 11 are placed. The feature of this structure is that B ₂ O ₃ in a long crucible
Since the depth e is greater than the length c of the crystal, the height of the elongated crucible is therefore equal to or greater than e+m (depth of the melt).

(Function) By making the thickness of the liquid-sealed capsule equal to or greater than the length of the crystal to be grown, the crystal can prevent the dissociation of volatile component elements such as B ₂ O ₃ during the pulling and growing stage. It is completely sealed with a deterrent sealant and pulled up. Therefore, in addition to the conventional effect of suppressing the dissociation of volatile elements from the melt that becomes crystals,
A new effect can be added in that it can also suppress the phenomenon of volatile elements dissociating from the surface of the grown crystal into the pressure space.

In this case, as in the conventional example, the inert gas filled in the pressure space causes convection, and as a result, the single crystal has a large temperature gradient (for example, 80 to 150
°C/cm) does not occur. This is because since the sealant is a liquid, it is less likely to cause convection than a gas.

Furthermore, in order to actively achieve a low temperature gradient from the perspective of reducing thermal distortion, even if an independent after-heater is installed above the heater that heats the melt and a low temperature gradient environment is achieved, the single crystal surface remains Since it is always covered with a sealant such as B ₂ O ₃ that can prevent the dissociation of volatile elements, the dissociation of volatile elements such as As can be suppressed, and the crystal surface is not roughened and the generation of dislocations can be suppressed.
The after-heater in this case is capable of arbitrarily setting the temperature of the sealant such as B ₂ O ₃ independently of the temperature of the melt that becomes the single crystal.

FIG. 2 is an embodiment showing an overall view of a single crystal growth apparatus for realizing the basic concept of FIG. 1. Here, 13 is a susceptor that holds the long crucible 12, 14 is a heater that mainly heats the melt 2 (hereinafter referred to as a lower heater), and 15 is a heater that mainly heats the upper part of the liquid-sealed capsule 11 ( (hereinafter referred to as an upper heater), 16 is a lower weight detection device, 1
7 is a lower drive system that rotates and moves the susceptor 13 up and down, 18 is an upper weight detection device, 19 is an upper drive system that rotates and moves the pulling shaft 6 up and down, and 20 is a differential that processes signals from the up and down weight detection device. It is a differential amplifier. Note that in FIG. 2, the pressure chamber, an external processing system for processing signals from the upper and lower weight detectors, a control system for the upper and lower heaters, and a control system for the vertical drive device are omitted.

Conventional LEC does not have an upper heater, and
Since B ₂ O ₃ is used solely for the purpose of preventing the dissociation of volatile components from the melt, its thickness is usually 10 to 15 mm. direction). For this reason, the temperature gradient at the boundary between the melt and B ₂ O ₃ is large, and the pulled single crystal is exposed to a pressure space above the B ₂ O ₃ , and the inert gas filled therein is convected. This causes rapid cooling and increases thermal strain. However, in the present invention, the B ₂ O ₃ layer is sufficiently thick and the pulled single crystal is always in B ₂ O ₃ , so there is little convection and the temperature is stable. Furthermore, if an upper heater is provided as shown in Fig. 2, the temperature of B ₂ O ₃ can be set arbitrarily with this upper heater, so that the melt and
The temperature distribution near the boundary of B ₂ O ₃ is further softened,
In addition, since the pulled single crystal is at a constant temperature of B ₂ O ₃ , rapid cooling is avoided, so thermal strain entering the crystal is extremely small compared to A.

Furthermore, according to the present invention, since the entire crystal is always in a sealant such as B ₂ OC, correction of buoyancy becomes simple.
Therefore, the change in crystal weight can be determined accurately.

(Example) An example using the compound semiconductor single crystal manufacturing apparatus shown in FIG. 2 will be described in detail.

Approximately 1000 g of GaAs master alloy and 1250 g of B ₂ O ₃ were placed in a transparent quartz long crucible with a diameter of approximately 7.6 cm and a depth of approximately 20 cm.
and heat the upper heater 15 to bring the temperature of B ₂ O ₃ to approx.
Bring to 1100℃. Next, heat the lower heater 14
The temperature is raised to 1250°C, which is slightly higher than the melting point of GaAs, 1237°C, to form a GaAs melt. At this time, GaAs
Forms a melt. At this time, the depth m of the GaAs melt is approximately 4.4 cm, and the thickness e of _{the B 2} O ₃ is approximately 15 cm, which fits within the crucible. Next, the pulling rotation shaft 6 with the seed crystal 9 attached thereto is gradually lowered to bring the seed crystal 9 into contact with the melt 2. If the temperature of the melt is optimal during this contact, a so-called meniscus will be formed between the melt and the seed crystal, and a change in weight will be detected through the upper and lower weight detectors according to the tension, so a deep crucible is used. contact can be confirmed even if When the melt temperature is low, crystals grow rapidly at the tip of the seed crystal, the signal of the upper weight detector increases, and the signal of the lower weight detector decreases. When the melt temperature is high, the above phenomenon is reversed. By providing two vertical detection devices, upper and lower, as described above, it was possible to reliably confirm the contact of the seed crystal, and it was possible to easily control the lower heater through the differential differential amplifier.

Next, while pulling the pulling shaft at a speed of 10 mm/hour, the temperature of the GaAs melt is gradually lowered by the lower heater to form a so-called crystal shoulder, and the melt temperature is adjusted to change the crystal weight and melt weight. By making appropriate adjustments, a single crystal with a diameter of approximately 5 cm and a length of 10 cm was pulled and grown. At this time, since the entire single crystal is in B ₂ O ₃ maintained at about 1100°C to a depth of about 15 cm, the crystal being pulled is gradually cooled, which is a phenomenon that occurs in the conventional LEC method. Never. After the pulling of the single crystal was completed, the upper and lower heaters were gradually cooled, and when the temperature of B ₂ O ₃ reached approximately 300°C, the single crystal was pulled upward from the B ₂ O ₃ and emptied. . Since the GaAs single crystal surface obtained in this way is surrounded by B ₂ O ₃ during this pulling growth, As is removed from the crystal surface even when the temperature around the crystal is as high as approximately 1100°C. There was no dissociation, and the surface was extremely smooth and had a metallic luster. Also, during cooling
Since B ₂ O ₃ covers the crystal surface, the crystal surface has extremely little roughness and problems such as oxidation were avoided. It goes without saying that the device shown in FIG. 2 is installed inside a pressure chamber.

The single crystal wafer cut perpendicular to the pulling axis is
As a result of etching with KOH and examining the in-plane distribution of etchipts corresponding to dislocations, it was found that the dislocation distribution in conventional LEC crystals is W-shaped and non-uniform, but the dislocation distribution in the crystal grown by the present invention is V-shaped. Alternatively, a dish-shaped region with a low dislocation density of 70 to 80%, which is one to two orders of magnitude lower than that obtained using conventional methods, was obtained.

In the above examples, a GaAs base material was used, but instead of this, the raw materials Ga and As were used in a stoichiometric ratio of 1:1.
It is clear that the same effect can be obtained even if it is placed in a long crucible together with the basis weight Shiso B ₂ O ₃ . In addition, other than GaAs such as GaP, InP, InAs
Alternatively, even in the case of these mixed crystal compounds, by using the method of the present invention, there is no dissociation of the surface, that is, there is extremely little roughness on the crystal surface that becomes a source of dislocation.
Therefore, it goes without saying that a single crystal with low dislocations can be obtained.

(Effects of the Invention) As explained above, according to the present invention, by making the thickness of the liquid encapsulant equal to or greater than the length of the crystal to be grown, volatile elements can be extracted from the melt that becomes the crystal. A novel effect can be obtained in that it is possible to suppress the dissociation of volatile elements from the surface of the grown and solidified crystal and also to suppress the dissociation of volatile elements from the surface of the grown and solidified crystal into the pressure space.

Furthermore, it is possible to make the pulled crystal always exist in a sealant such as B ₂ O ₃ independently of the temperature gradient conditions in the direction of the crystal pulling axis. Therefore, if a heater that mainly heats only the upper part of the sealant is installed above the heater that heats the melt, and the temperature gradient in the direction of the pulling axis is actively reduced (this is Even in this case, the surface of the crystal is always covered with a sealant such as B ₂ O ₃ , which has the function of preventing the dissociation of volatile elements. Since it is covered, surface roughness can be suppressed, and therefore, a remarkable effect can be obtained in that it is possible to suppress the phenomenon of dislocation generation under a low temperature gradient environment discovered by the inventors.

Furthermore, according to the present invention, since the entire crystal is always in a sealant such as B ₂ O ₃ , if an independent weight detection device is provided at the lower end of the susceptor that holds the rotational pulling shaft of the crystal and the elongated crucible, Since the correction of buoyancy is simplified and the weight change of the crystal can be determined accurately, there is also the effect that highly accurate automation of the crystal growth process can be easily achieved.

[Brief explanation of the drawing]

Figure 1 is a drawing for explaining the basic concept of the present invention, Figure 2 is a single crystal manufacturing apparatus according to the present invention, and Figure 3 is a diagram for explaining the basic concept of the present invention.
The figure shows a single crystal production apparatus using the conventional LEC method (general case, when the temperature gradient in the pressure space is small). Figure 4 shows a single crystal production apparatus using the conventional LEC method (when the temperature gradient in the pressure space is small). if large),
FIG. 5 is a diagram comparing the temperature distribution in the pulling axis direction in the conventional method and the embodiment of the present invention. 1... Single crystal, 2... Melt, 3... Liquid sealant, 4...
Crucible, 5... Pressure chamber, 6... Pulling rotation shaft,
7... Capsule envelope, 8... Pressure space, 9... Seed crystal, 10... Single crystal, 10'... Single crystal shoulder, 11
...Liquid sealant, 1... Long crucible, 13... Susceptor, 14... Lower heater, 15... Upper heater, 16
...Lower weight detection device, 17...Rotating vertical drive device,
18... Upper weight detection device, 19... Rotating vertical drive device, 20... Differential differential amplifier.

Claims (1)

[Claims] 1. In the liquid encapsulation melting and pulling method (LEC method) of compound semiconductor single crystals containing volatile component elements, for example, B ₂ O ₃ which exceeds the length of the single crystal to be grown. A compound semiconductor single crystal characterized in that a thick layer of a liquid-sealed capsule is placed above the melt that forms the single crystal, so that the single crystal is constantly pulled and grown in the liquid-sealed capsule. manufacturing method. 2. In a manufacturing device that grows compound semiconductor single crystals containing volatile component elements using the liquid-sealed capsule sealing melt-pulling method, a device is placed above the melt that will become the single crystal, and is used to control the length of the single crystal to be grown. liquid-sealed capsules, such as B ₂ O ₃ , with a thickness exceeding
It comprises at least a long crucible filled with the thick liquid sealed capsule and a melt to form a single crystal, and a means for controlling the temperature of the thick liquid sealed capsule surrounding the single crystal to be grown. A compound semiconductor single crystal manufacturing device characterized by: 3 In manufacturing equipment that pulls and grows compound semiconductor single crystals containing volatile component elements using the liquid encapsulation melt-pulling method, a single crystal is placed above the melt that will become the single crystal, and the length of the single crystal exceeds the length of the single crystal to be grown. A long crucible filled with a thick liquid-sealed capsule such as B ₂ O ₃ , the thick liquid-sealed capsule and a melt to form a single crystal, and the above-mentioned crucible that surrounds the single crystal to be grown. A compound characterized in that it comprises at least a means for controlling the temperature of the thick liquid-sealed capsule, and two independent weight detection means provided at the lower end of the susceptor that holds the rotational pulling axis of the crystal and the crucible. Semiconductor single crystal manufacturing equipment.