JPS5912631B2 - Horizontal ribbon crystal growth method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of heating from the melt side of a growth interface from which a ribbon crystal grows in a horizontally drawn ribbon crystal growth method.

In the conventionally known horizontally drawn ribbon crystal growth method, sufficient consideration is not given to the distance between the growth interface and the heating surface of the heating device that heats it from the melt side (for example, 5choc
kley: U, S, P, 3031275.1962 and Bleil, Journal of Crysta
lGrowthll 969), relatively large distance (
1/4" or more) (for example, Bleil
.

U, S, P, 3681033.1972).

When ribbon growth is performed under such conditions, there is a large time delay in controlling temperature deviations and fluctuations at the growth interface, and the growth interface, which should be controlled to a predetermined dimension with an extremely small tolerance, is It exhibits large fluctuations both physically and temporally.

As a result, the dimensions of the grown ribbon crystals, such as width, thickness, and surface flatness, vary greatly, and the crystallinity is poor, with dislocation densities being high and bonding defects such as twin planes sometimes occurring. It has been actually experienced that this results in very low growth yields and makes the growth operation very difficult for operators.

The present invention eliminates these drawbacks of the conventional horizontally drawn ribbon crystal growth method, and uses the horizontally drawn method to produce wide and thin ribbon crystals with good dimensional accuracy and crystallinity, and a high growth yield. The purpose is to provide a method for manufacturing.

Another object of the present invention is to provide a method that can be used in mass production by making the horizontal drawing process easier when it is performed manually, and by improving its controllability when it is performed automatically. It is one purpose.

That is, the present invention provides a ribbon-shaped seed crystal that is in contact with the surface of a melt supported in a crucible or a ribbon-shaped seed crystal that is formed on all or part of the liquid-contacted surface of a growing crystal in a horizontally drawn ribbon crystal growth method for a crystalline substance. / or by providing a heating device having a heat generating surface substantially parallel to the growth interface at a position 30 mm or less below the growth interface, and adjusting the amount of heat generated by the heating device. , the gist of which is a horizontally drawn ribbon crystal growth method for crystalline materials, which is characterized by controlling the geometrical shape of the growth interface to a predetermined position and size, and to achieve the above object. It has an essential effect.

Hereinafter, the method of the present invention will be explained in detail using examples and figures.

FIG. 1 shows the main parts inside a crystal growth furnace used in an example of the horizontally drawn ribbon crystal growth method for carrying out the method of the present invention.

The figure a is a vertical sectional view parallel to the drawing direction of the ribbon crystal, and the figure b is a plan view thereof.

In the figure, reference numeral 1 denotes a thin and wide ribbon crystal of the target crystalline substance being grown (for example, a semiconductor material such as silicon), and a drawing bath 2 consisting of a melt of the crystalline substance as the raw material is free. It is pulled out horizontally from the surface as shown by the arrow.

This withdrawal bath is stably supported by a crucible (for example, a high-purity quartz crucible contained in a high-purity graphite crucible 4) made of a material that does not react with it at high temperatures and does not lose its mechanical strength. Heating device 5 installed at the bottom or side
, 6, 7, and 8 (for example, it is convenient to use a resistance heating element made of high-purity graphite) to maintain the temperature above the freezing point.

The ribbon crystal is the liquid contact surface FFBB of the ribbon 1 with the withdrawal bath 2.
The melt layer along the plane "FBGI Bc + t" (hereinafter referred to as growth interface) formed in a part of the drawing direction and intersecting at a small angle that is not parallel to the drawing direction may be cooled naturally or
By cooling it by the method of No. 136841 (Special Publication No. 57-20278) and keeping it constantly below the freezing point,
Continuous growth is achieved by causing crystal growth to occur continuously on this surface, and by pulling out in the above direction at a rate that is balanced with the growth rate in the direction opposite to the pulling direction.

The above-mentioned basic requirements are common to all horizontal drawing methods, but the method of the present invention is characterized by the following points.

That is, as shown in the figure, the upper heating surface of the heating device 5 provided below the growth interface FFBGIBG□ is approximately parallel to the growth interface, and is very close to the growth interface at a distance of less than 30 dragons. It is a point.

The method of the present invention, which has these characteristics, enables the accurate formation and maintenance of a growth interface. However, before explaining its functions and effects in detail, we will explain the importance of the growth interface. It is necessary to understand the role of

That is, firstly, the applicant's earlier patent application 1986-1991
According to the method of No. 099 (Special Publication No. 57-22917),
By making the length of the growth interface sufficiently long compared to the growth ribbon thickness and making the area of the growth interface sufficiently large, the solidification heat generated in large quantities at the growth interface due to high-speed growth can be dispersed and effectively dispersed. The purpose is to dissipate heat.

Second, since crystals grow only from the growth interface, precise control of the geometry of ribbon crystals requires that the geometry of the growth interface be aligned with a given shape in both space and time. It must be precisely controlled within the error range.

In particular, the shape of the ingrowth interface of the ribbon crystal geometry primarily determines the width, thickness, and flatness of the front and back surfaces.

Among these, the width is, for example, the heating device 7 as shown in Figure 1.
The outline of the growth interface in the width direction of the ribbon crystal is Control the position and straightness of (two F-BGo).

Furthermore, for this purpose, a method is already known in which a heating device placed above the draw-out bath is used instead of the heating device 7 placed on the side of the draw-out bath; It is also good to use a heating device placed in the

Next, regarding the flatness of the surface, in the horizontal method, the liquid level and the above surface are made to match in the vertical direction using a mechanism that can adjust the relative vertical positional relationship between the crucible and the drawing device, and in the case of the small angle tilt method, By keeping the outline F of the growth interface in the growth direction (referred to as the front line) as a straight line perpendicular to the drawing direction, the flatness of the back surface can be further improved by keeping the edge BGI of the growth interface in the drawing direction ( By paying attention mainly to the heat generation distribution of the heating devices 6 and 7 so that the back line of the growth interface always lies on one plane parallel to the drawing direction, and in the small angle tilting method, the back line of the growth interface is Control is performed by keeping the line BG□ in a straight line perpendicular to the drawing direction and at a constant position.

The present invention mainly improves the remaining thickness control method, and is intended to be implemented in combination with the above-mentioned control of other geometrical shapes.

In other words, the surface is controlled so that it is flush with the liquid level in horizontal usage as described above, while the front surface is controlled to be flush with the liquid level in small angle tilt usage.
If a cooling device is used directly above the growth interface, the amount of cooling is adjusted while keeping the line F in a straight line perpendicular to the drawing direction. Control is performed by adjusting the amount of heat generated and maintaining the deviation in the thickness direction between F and Bo□ at a predetermined value.

As described above, the geometric shape of the horizontally drawn ribbon crystal is controlled to a predetermined value mainly by accurately controlling the position and shape of the growth interface.

Thirdly, controlling the growth interface to precise dimensions is even more important when growing ribbon single crystals.

In other words, near the growth interface, the grown crystal is at a high temperature close to the freezing point, so it is normally subjected to stress, which easily causes dislocations and grain boundaries even if the stress is relatively small. When the shape changes over time, there is a corresponding temperature change, and the thermal stress generated in this area causes crystal defects such as dislocations.

In particular, if the growth interface is flat and the thickness of the growing ribbon is controlled to increase as gently as possible from the front line F to the back line BGI, the ribbon crystal will have the required thickness and the solidification heat will increase due to high-speed growth. Because it has the flatness necessary for uniform dispersion within the interface, it is possible to realize a minute temperature gradient in the ribbon above the growth interface in the drawing direction, but it does not generate a temperature gradient that is large enough to cause the crystal defects mentioned above. let

As described above, accurately controlling the geometrical shape of the growth interface to a predetermined position and size, that is, adjusting the growth interface, refers to the FF and FBo et in Figure 1.

BGI Adjusts the linearity and positional constancy of BG It is to maintain the straight portion so that it does not change from the position in which it was formed and that the straight portion does not bend.

Therefore, it is essential that the command to raise or lower the temperature be transmitted to the growth interface through the heating device.

The main purpose of the present invention is to improve the method of controlling the crystal thickness, and in order to achieve this purpose, the thickness of FBo□ in Fig. Despite efforts to realize this based on experience with good (i.e., linear control of FBG), using a heating device like the one shown in Figure 2 a and b, the command to raise or lower the temperature can be quickly applied to the growth interface. However, as shown in Figures 2a and 2b, there were repeated failures resulting in unevenness on the back surface of the crystal.

Therefore, as a result of various studies, the present inventor found that the positional relationship between the growth interface and the heating surface is at least 30m in Fig. 1a.
The present invention was completed after confirming that TIt could considerably reduce the difficulty of control.

As described below, the present invention has remarkable functions and effects regarding its control.

First of all, an isothermal surface extending parallel to a flat heat-generating surface is formed at a short distance, so by adjusting the amount of heat generated, a solidification isothermal surface can be easily formed at a predetermined position. It is easy to adjust to match the predetermined location of the growth interface, so that a relatively flat growth interface can be easily formed in the predetermined location.

Second, when the thermal conditions are incorrect or fluctuate due to some reason, such as a deviation in the settings of the heating device or a voltage fluctuation in the power supply device, adjusting the amount of heat generated by the heating device will allow the heating surface and the growth interface to Since the distance between the two is close, the temperature change response at the growth interface is fast, so the system can be controlled! As a result of good characteristics,
Fluctuations at the growth interface are reduced.

Thirdly, in determining the temperature of the growth interface due to the first effect mentioned above, the role of the heating device from the bottom of the withdrawal bath can be greater than that of the cooling device and others, and ultimately forced cooling from the top can be achieved. While it is possible to form a growth interface and control the dimensions even if the surface is wiped, there is no low-temperature mechanical part in the upper part of the withdrawal bath, so Si and its oxides that evaporate from the surface of the withdrawal bath can prevent the formation of abnormal crystals due to the fall of precipitates at low temperatures. Eliminate occurrence.

This also results in improved yield.

Fourth, as a result of the fast response of the temperature control of the withdrawal bath, the withdrawal operation is simplified, and excessively high temperatures are likely to occur during the withdrawal operation, especially during periods of operation when there are large changes in thermal conditions (especially at the beginning). The reduction in operating efficiency due to dissolution of seed crystals due to melting, solidification bridging with the surroundings of the crucible due to too low temperature, etc. can be greatly reduced.

An example of the horizontally drawn ribbon crystal growth method, which is different from the method of the present invention as described above and is carried out by the conventional method mentioned at the beginning, is shown in FIGS. 2a and 2b.

Figure 2a shows an example of the high-frequency induction heating method, in which a heating coil 5 made of a conductor pipe whose center is water-cooled receives controlled high-frequency power from a power supply device (not shown in the figure) and generates a heating element. Even if induced energy is generated in the high-purity graphite crucible 4, which is also used, and melted in the high-purity transparent quartz crucible 3 inside the crucible 4, as shown in the example of the resistance heating method shown in Figure 2, The high-purity quartz crucible 3 inside the high-purity graphite resistance heating element 5 receives controlled power supply from separate power supplies.
Even if the ribbon crystal 1 is melted inside, it is drawn out in the direction of the arrow while contacting the surface of the drawing bath 2 made of the formed raw material crystalline material. The temperature is controlled by the heat flow shown in , but in any case, the conventional method does not meet the requirements of the present invention that the heating surface and the growth interface are almost parallel and the distance between them is 30 mm or less. As a result, delicate temperature adjustments cannot be made.

In other words, as shown in Figure 2 a, the heating surface is not parallel to the prescribed growth interface (indicated by a dashed line), or even if it is parallel as shown in b, the distance is large and the thermal resistance is large, resulting in a delay in response to temperature adjustment. Because of the large thickness, the thickness of the grown ribbon crystal varies greatly, and there are correspondingly many areas with poor crystallinity.

Not only was the growth yield extremely low, but the initial draw operation was extremely difficult and the success rate was low even for experienced personnel.

As is clear from the above description, it has been experimentally confirmed that the method of the present invention described in the claims is extremely effective when used in actual growth of ribbon crystals by the horizontal drawing method.

In particular, in the case of ribbon crystal growth of silicon, it was confirmed that the effect is remarkable when the distance between the growth interface and the heat generating surface is set to 30 mrrt or less.

Further, as an embodiment of the present invention, Japanese Patent Application No. 50-155814 (Japanese Patent Publication No. 57-21516) is an earlier application of the present applicant.
There is also a method in which heat is generated directly in the molten material directly below the growth interface held by a solid raw material crystalline material, such as the method of No. 1, the so-called crucibleless method.

That is, it is obvious that the same effects and effects of the method of the present invention can be obtained even in this case.

In addition, it was actually confirmed that the parallelism between the growth interface and the heating surface does not need to be very strict, but this is because the amount of solidification heat generated per unit area at the growth interface flows from the molten material below. In fast growth where the amount of heat is large compared to the amount of sensible heat,
This is thought to be because the heating unevenness caused by the heating device at the growth interface is canceled out by the solidification heat uniformly generated due to the self-control property of high-speed growth, and in fact, the intersection angle between the growth interface and the top surface of the ribbon crystal in normal high-speed growth is 1O Under conditions of less than 100°C, it was sufficient to make the top surface of the ribbon crystal parallel to the heat generating surface.

However, if the thickness of the ribbon crystal to be grown is very small and the growth rate is to be relatively slow, it is recommended to provide a heat generating surface parallel to the predetermined growth interface as shown in Figure 3. It was desirable.

Next, an example will be explained.

The dimensions of the part that holds the melt are width 120 mm and length 15 mm.
A graphite resistance heating element was arranged as shown in FIG. 1 using a quartz crucible with a size of 0 mm and a depth of 15 mm.

The power supply was controlled to adjust the amount of heat generated, and the growth was performed while observing the desired shape of the growth interface near the silicon melting temperature of 1430°C.

At this time, the heating bodies 5 and 6 are parallel to the free surface of the silicon melt supported in the crucible, and the distance between them is 30 mm.
6 were almost parallel and had a distance relationship of 29 mm to 30 mm.

As a result, the thickness was Lm4 and the width was 40 mm at a withdrawal speed of 300 dragons/min.
A high quality silicon ribbon single crystal of mrtt was obtained.

In this example, 57 out of 76 cases achieved the intended purpose (success rate: 75).
In the case of m, only 27 out of 75 cases (success rate: 36) were successful.

[Brief explanation of the drawing]

The drawings are schematic diagrams showing aspects of various embodiments for explaining the technical idea of the present invention. FIG. 1a is a vertical sectional view parallel to the drawing direction near the ribbon crystal drawing part, and FIG. 1 is a plan view of the part shown in FIG. The mutual arrangement of Bo□ is shown. FIGS. 2a and 2b are vertical cross-sectional views of the vicinity of the extraction part when the relationship between the heating device 5 and the growth interface F-BG□ is unfavorable, and FIG. When the length of is not much larger than the thickness of the ribbon crystal,
FIG. 3 is a vertical cross-sectional view of the vicinity of the lead-out portion when the heat generating surface of the heating device 5 is arranged parallel to the growth interface. In the figure, 1 is a ribbon-shaped seed crystal or growing crystal, 2 is a withdrawal bath made of raw material crystalline material, 3 is a high-purity quartz crucible, 4 is a high-purity graphite crucible, 5, 6° 7.8 is a heating device,
F is the front line of the growth interface, BGI is the back line of the growth interface, B is the bank line of the ribbon crystal contact, and h is the distance between the growth interface and the heating surface of the heating device.

Claims (1)

[Claims] 1 In the horizontally drawn ribbon crystal growth method for crystalline substances, a ribbon-shaped seed crystal that contacts the surface of a melt supported in a crucible or a ribbon formed and/or maintained on all or part of the liquid contact surface of a growing crystal. A heating device having a heat generating surface approximately parallel to the growth interface is provided at a position of 30 degrees or less below the growth interface, and by adjusting the amount of heat generated by the heating device, the geometry of the growth interface can be adjusted. A horizontally drawn ribbon crystal growth method for crystalline materials, which is characterized by controlling the chemical shape to a predetermined position and size.