JP2014076915A - Semiconductor crystal growth vessel and solar cell produced by using wafer obtained from crystal grown by the same - Google Patents

Abstract

When crystal growth is performed using a conventional crystal growth vessel, there is a problem that twins are likely to be generated in a crystal growth portion. Further, since the obtained ingot is cylindrical, a wafer obtained by slicing the ingot becomes a circular wafer, and there is a problem that the chip yield of the semiconductor chip having a quadrangular shape is poor.
As a semiconductor crystal growth vessel, a cross-sectional shape perpendicular to the crystal growth direction of the crystal growth portion and the crystal growth portion is a quadrangle, and the inner wall angle of the crystal growth portion is 35.3 ° with respect to the crystal growth direction. By doing so, it is possible to manufacture a prismatic ingot that suppresses the generation of twins, grows a semiconductor crystal having a zinc flash structure or the like, and obtains a rectangular wafer.
[Selection] Figure 1

Description

  The present invention relates to a container for crystal growth, and more particularly to a container for crystal growth of semiconductors such as GaAs, Si, and Ge.

Various semiconductor wafers can be obtained by growing a semiconductor seed crystal by a crystal growth method to produce an ingot and slicing the ingot.
As a method for growing a semiconductor crystal, a technique called a vertical boat method is widely used. In this method, a seed crystal is placed on the bottom of the crystal growth vessel having a cylindrical shape (hereinafter referred to as a narrow tube portion), and a crystal growth source as a raw material solution is gradually crystallized from the top surface of the seed crystal, thereby producing a crystal. Grow. During this crystal growth, a temperature gradient is applied so that the already crystallized portion has a temperature lower than the melting point of the crystal and the non-crystallized crystal growth source portion has a temperature higher than the melting point.

Various methods for controlling the temperature gradient have been proposed. As typical methods, a vertical temperature gradient solidification method (hereinafter referred to as VGF method) and a vertical Bridgman method (hereinafter referred to as VB method) are used. is there. In the former, a temperature gradient is given to the crystal growth direction, and the absolute value of the temperature is gradually lowered while keeping this temperature gradient constant.
On the other hand, in the latter, the crystal growth vessel is moved in the low temperature direction in a space having a predetermined temperature gradient.

Since this vertical boat method can reduce the temperature gradient in the crystal growth direction, it has an excellent feature that a crystal having a low dislocation density can be easily obtained especially in the crystal growth of a compound semiconductor such as InP or GaAs. Yes.
On the other hand, there is a defect that twins are easily generated in the crystal growth portion.

  The crystal increasing portion is a portion connecting the narrow tube portion and a cylindrical growth portion having a larger diameter, and has an inverted conical shape with a tip removed. It is known that a (111) facet plane appears in the growth process of a compound semiconductor crystal having a zinc flash structure such as InP or GaAs, and twins are generated from this facet plane in this crystal growth portion. Since the angle formed by the (100) plane and the (111) plane, which are the growth planes, is 54.7 °, the angle of the inner surface of the crystal growth portion should be sufficiently larger than 54.7 ° with respect to the horizontal direction. Thus, the occurrence of the (111) facet surface can be suppressed. However, in this case, the length of the crystal growth part becomes long, and the productivity is deteriorated.

  Therefore, it has been proposed to control the angle of the inner surface of the crystal growth portion from 0 ° to 10 ° with respect to the horizontal direction so that the temperature gradient in the crystal growth direction is 1 ° C./cm or more and less than 5 ° C./cm. (For example, Patent Document 1).

JP-A-10-87392

However, even in this method, even if the generation of twins in the crystal growth portion can be reduced to some extent, it has been difficult to sufficiently suppress it.
Moreover, since the obtained ingot is cylindrical, the wafer which sliced it becomes a circular wafer. Semiconductor chips such as ICs, LEDs, and solar cells all have a square shape, although their sizes are different. For this reason, when a rectangular semiconductor chip formed on a circular wafer is cut out by dicing or the like, the peripheral portion of the wafer becomes an unused area, resulting in a problem that chip yield from the wafer is poor. In particular, in the case of a device having a large chip size such as a solar cell, the peripheral loss becomes extremely large, and the chip yield is extremely deteriorated.

  The present invention has been made to solve the above-described problems, and provides an optimal crystal growth vessel that takes into consideration the specific phenomena and regularity of crystals.

  A semiconductor crystal growth vessel for growing a semiconductor crystal having a zinc flash structure or a diamond structure by a vertical boat method according to the present invention includes a narrow tube portion in which a seed crystal is installed, the seed crystal in the crystal growth axis direction, A crystal growth part that is increased in a plane perpendicular to the crystal growth axis direction, and a crystal growth part that is a straight body part for growing the crystal increased in the crystal growth part direction in the crystal growth axis direction. The cross-sectional shape orthogonal to the crystal growth axis direction of the growth part and the crystal growth part is a quadrangle, and the inner wall angle of the crystal growth part is 35.3 ° with respect to the crystal growth axis direction It is.

  The semiconductor crystal growth vessel according to the present invention has an optimal shape that takes into consideration the specific phenomena and regularity of crystals, thereby suppressing the occurrence of transition and twinning, and a rectangular wafer with a high wafer utilization rate. It is possible to produce a prismatic ingot that can be obtained.

1 is a perspective view of a semiconductor crystal growth vessel according to the present invention. 1 is a cross-sectional view of a semiconductor crystal growth apparatus according to the present invention. It is a figure which shows the surface orientation of the crystal | crystallization obtained using the semiconductor crystal growth container concerning this invention. It is a figure which shows the effect of the semiconductor crystal growth container concerning this invention.

Embodiment 1 FIG.
A semiconductor crystal growth apparatus according to the present invention, particularly a semiconductor crystal growth vessel, will be described below with reference to the drawings. In the following, a good example is shown, and the present invention is not limited to the following example with respect to a specific configuration such as the dimensions of the crystal vessel.

First, the structure of the semiconductor crystal growth vessel 1 according to the present invention will be described with reference to FIG.
A semiconductor crystal growth vessel 1 includes a narrow tube portion 2 for installing a seed crystal of a semiconductor crystal, a crystal increase portion 3 for gradually thickening the seed crystal, and a crystal growth portion 4 for growing the thickened crystal in a certain shape. have.

  The thin tube portion 2 is a part where a seed crystal is arranged, and has a square shape in cross section. Here, a square shape having a side of 10 mm is used, but the cross-sectional shape and depth are the size of the seed crystal to be arranged. Can be optimized.

  The crystal growth part 3 has a quadrilateral shape whose inner wall has an angle of 54.7 ° with respect to the horizontal direction. The small seed crystal grows into a crystal having a large cross section at the crystal growth portion.

  The crystal growth portion 4 has a quadrangular prism shape rising vertically from the crystal increase portion 3. Here, one piece has a square cross section of 55 mm and the length is 300 mm.

  FIG. 2 is a cross-sectional shape of a semiconductor crystal growth apparatus provided with the semiconductor crystal growth vessel 1, and has a plurality of annular heaters 5 a, 5 b and 5 c so as to surround the crystal growth vessel 1. The number of annular heaters is not limited to three, and may be two or four or more. Each heater can be controlled independently, and a plurality of heaters can give a desired temperature gradient to the semiconductor crystal growth vessel 1 along the crystal growth direction (a-axis direction).

Next, a specific operation when performing crystal growth by the vertical boat method using this semiconductor crystal growth apparatus will be described. As an example, an operation for growing a GaAs crystal by the VGF method and the VB method will be described below.
First, a GaAs seed crystal having a (100) plane as an upper surface is placed on the narrow tube portion 2 of the crystal growth vessel, and a GaAs crystal growth source is placed thereon. A plurality of annular heaters 5a, 5b, and 5c are placed in a crystal growth vessel provided with a seed crystal and a crystal growth source so that the seed crystal is at a temperature lower than the melting point of the GaAs crystal and the crystal growth source is at a temperature higher than the melting point. Gives a temperature gradient along the a-axis of FIG.

From this state, in the case of the VGF method, the entire temperature is slowly lowered while maintaining the temperature gradient. In the case of the VB method, the crystal growth furnace is moved slowly. By doing so, the position of the melting point temperature of the GaAs crystal gradually rises along the a-axis, and the GaAs crystal is gradually grown along the inner wall in the crystal increasing portion 3.
Therefore, the crystal grown in the crystal growth vessel 1 according to the present invention expands in the shape of the crystal increase portion 3 in the crystal increase portion 3. And in the crystal growth part 4, it grows in the shape of a square pillar, ie, a fixed cross-sectional shape.

Next, the plane orientation at the time of crystal growth will be described with reference to FIG.
First, the seed crystal is placed in the thin tube portion 2 so that the (100) plane is perpendicular to the a-axis which is the crystal growth direction. This seed crystal grows in the shape of a quadrangular pyramid while forming the (−111) (−1-11) (−1-1-1) and (−1-1-1) planes at the crystal growth portion 3.

  When the crystallized portion reaches the boundary between the crystal growth portion 3 and the crystal growth portion 4, it rises vertically along the inner wall of the crystal growth portion 4. All four surfaces rising vertically from the {111} plane formed in the crystal growth portion 3 in the crystal growth portion 4 are {110} planes. That is, the (−111) plane is the (011) plane, the (−1-11) plane is the (0-11) plane, the (−1-1-1) plane is the (0-1-1) plane, The (-11-1) plane rises to the (01-1) plane. As described above, in the crystal growth portion 4, the {110} plane is set as the side surface, and the (100) plane of the seed crystal is maintained in a plane perpendicular to the a axis that is the growth direction, while the a axis that is the <100> direction. It grows in the shape of a square column along the direction.

  In a compound semiconductor crystal having a zinc flash structure such as GaAs, the (100) plane and the (111) plane have an angle of 54.7 °. Therefore, when the seed crystal is placed with the <100> direction facing upward and the crystal is grown in the <100> direction, the seed crystal increases while forming a {111} plane along the side surface of the crystal increase portion 3. This {111} plane has a feature that it is easier to form a surface in a compound semiconductor crystal having a zinc flash structure than in other planes.

  Thus, the {111} plane has the property of stably forming a crystal growth plane. Therefore, by setting the angle of the inner wall of the crystal growth portion 3 to 54.7 ° with respect to the horizontal direction, that is, 35.3 ° with respect to the a axis that is the crystal growth direction, The seed crystal can be thickened in the most natural form while forming a stable {111} plane. As a result, compared to a conventional vessel having a circular cross section, it is possible to suppress the occurrence of transition and twinning during crystal growth, the dislocation density (EPD) is small, and the single crystallization yield is reduced. Good crystals are obtained.

  Furthermore, the surface rising vertically from the {111} plane at an angle of 54.7 ° forms a {110} plane that is a cleavage plane of the crystal. Since these {110} planes intersect with other side surfaces at 90 °, the four sides of the quadrangular columnar crystal formed in the crystal growth portion 4 form {110} plane cleaved surfaces. That is, the wafer cut out from the square columnar crystal formed in this way has a quadrangular shape having a (100) surface and a {110} surface on the side surface. Therefore, even when a square chip is formed on the wafer and the chip is cut out, the chip can be cut along the cleavage direction of the crystal, so that there is an effect that the chip yield is low and the chip yield is high. .

  Here, the effect when a semiconductor device is manufactured using a rectangular wafer obtained by using the semiconductor crystal container 1 according to the present invention is specifically compared with the case where a circular wafer is used. explain.

  Although semiconductor chips such as integrated circuits, LEDs, and solar cells have different sizes, each semiconductor chip has a rectangular chip shape. Therefore, when a chip is cut out from a circular wafer, there is a problem that an unused area without a chip is generated around the wafer, and a chip yield from the wafer is reduced. In particular, in the case of a device having a large chip size such as a solar cell or a large integrated circuit, the ratio of the unused area in the peripheral portion of the wafer is increased, and the chip yield is extremely deteriorated.

FIG. 4 is an explanatory diagram for quantitatively comparing (a) the case of using a rectangular wafer and (b) the case of using a circular wafer regarding the chip yield.
The size of the wafer obtained using the semiconductor crystal growth vessel 1 according to the present invention is a square having a side of 55 mm. When 50 mm square solar cells 11 are formed on the wafer 10, the chip yield is 82.6% from the area ratio. The unused area 12 is only 17.4% of the area of the wafer 10.

On the other hand, when a 50 mm square solar cell 21 is formed on a 3-inch diameter circular wafer 20 cut out from an ingot crystal-grown in a columnar shape in a conventional crystal growth vessel, the chip yield is calculated from the area ratio. 54.8%. The unused area 22 reaches 45.2% of the area of the wafer 20.
Thus, when producing a semiconductor chip having a large chip size such as a solar cell, the chip yield can be greatly improved by performing crystal growth using the semiconductor crystal growth vessel 1 according to the present invention. This makes it possible to effectively use an expensive substrate such as GaAs, thereby significantly reducing the cost of the device.

The crystal growth container of the present invention is not rounded at the corners of the container as shown in FIG. 1 and the like, but may be rounded (R) depending on the size of the container.
In the present embodiment, GaAs crystal has been described as an example. However, the crystal growth vessel 1 according to the present invention can be similarly applied to the growth of a crystal having a zinc flash structure such as InP or GaP. .

Furthermore, although there are differences in the number of constituent elements, the same effect can be obtained when the crystal growth vessel 1 is used for growing a crystal having a diamond structure such as Si or Ge having the same structure as the zinc flash structure.
In addition, although the square polycrystal substrate widely used for Si solar cells is made by the casting method, there are problems that the purity of the crystal is poor and the grain size of the polycrystal is small. If crystal growth is performed at a relatively high growth rate using the semiconductor crystal growth vessel 1 according to the present invention, it is possible to produce a polycrystalline square wafer that is inexpensive and has better crystallinity than the casting method.

  Thus, regardless of the feature of the present invention that a crystal with a high yield of single crystallization can be obtained, a polycrystalline square wafer suitable for Si solar cells can be obtained by a method such as increasing the crystal growth rate. It is also possible to provide it at low cost.

As disclosed above, the semiconductor crystal growth vessel according to the present invention has the following effects by having a shape that takes into account the crystal structure of the crystal having the zinc flash structure and the diamond structure and the characteristics during crystal growth. .
First, it is possible to suppress the generation of twins during crystal growth, to obtain a crystal having a low dislocation density and a good single crystallization yield.

Second, since a quadrilateral wafer is obtained, the chip yield of semiconductor chips can be greatly improved as compared to the case of using a circular wafer. In particular, in a device having a large chip size such as a solar cell, the chip yield can be remarkably improved.
In addition, the ability to cut the chip along the cleavage direction of the crystal when cutting the chip contributes to the improvement of the chip yield.
In particular, compound semiconductor wafers such as GaAs are expensive, and improvement in chip yield results in a significant cost reduction effect of the device.

  Thirdly, regardless of the first effect, it is possible to provide a polycrystalline square wafer suitable for Si solar cells and the like at a low cost by a method such as increasing the crystal growth rate.

DESCRIPTION OF SYMBOLS 1 Crystal growth container 2 Narrow tube part 3 Crystal increase part 4 Crystal growth part 5a, 5b, 5c Heater

Claims (2)

A semiconductor crystal growth vessel for growing a semiconductor crystal having a zinc flash structure or a diamond structure by a vertical boat method,
A narrow tube section for installing a seed crystal;
A crystal increase part for increasing the seed crystal in a crystal growth axis direction and in a plane perpendicular to the crystal growth axis direction;
A crystal growth part which is a straight body part for growing the crystal increased in the crystal growth part in the crystal growth axis direction;
With
The cross-sectional shape orthogonal to the crystal growth axis direction of the crystal growth part and the crystal growth part is a quadrangle,
The semiconductor crystal growth container, wherein an inner wall angle of the crystal growth part is 35.3 ° with respect to a crystal growth axis direction.   A solar cell produced by using a wafer obtained from a semiconductor crystal having a zinc flash structure or a diamond structure grown by the semiconductor crystal growth vessel according to claim 1.