JPS5932436B2 - Band-shaped silicon crystal growth device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for growing band-shaped silicon crystals using capillary action.

2. Description of the Related Art Conventionally, an apparatus shown in FIG. 1 is known as an apparatus for growing band-shaped silicon crystals from a silicon melt.

That is, in a crucible 12 made of quartz glass that accommodates a silicon melt 11, dies 13a and 13b having slits (gaps) made of carbon are attached to support rods 14a,
14b.

The tips of the dies 13a and 13b are sharply machined into a knife shape.

A pair of plate-shaped main heaks 15a are located outside the crucible 12.
y 15 b is provided.

With this configuration, when polycrystalline silicon as a raw material is put into the crucible 12 and power is supplied to the main heak 15 a 515 b, the polycrystalline silicon becomes a silicon melt 11 .

Then, this silicon melt 11 rises in the slit between the dies 13a and 13b due to capillary action and reaches the tip.

By bringing a seed crystal into contact with the silicon melt 11 that has reached the tip and gradually pulling up the seed crystal, a band-shaped silicon crystal 16 grows.

By the way, in this growth apparatus, the shape of the solid-liquid interface in the thickness direction of the band-shaped silicon crystal 16 during growth is a convex shape as shown at 21 in FIG.

This is because the temperature of the tips 23a and 23b of the dies 13a and 13b made of carbon is lower than the temperature of the portion 22 of the silicon melt 11 near the die tips, so the temperature distribution of the portion 22 of the silicon melt 11 is This is because the temperature is low near the sides 13a and 13b, and the temperature is high in the center.

When growth is performed with the solid-liquid interface 21 in this shape,
Since crystal nuclei are generated from the surface of the band-shaped silicon crystal 16, a crystal irregularity 31 occurs at the center of the band-shaped silicon crystal 16 in the thickness direction as shown in FIG.

Note that 32 is a twin grain boundary.

If such crystal irregularity 31 exists in the crystal, the distribution of resistivity in the bulk crystal becomes non-uniform.

Moreover, the minority carrier lifetime in the crystal becomes extremely short, and when it is made into a solar cell, the electrical conversion efficiency becomes extremely low.

The present invention has been made in view of these points, and its object is to provide an apparatus for growing band-shaped silicon crystals that does not cause crystal irregularity in the central portion in the thickness direction.

The present invention includes a temperature control device that controls the temperature of the die tip to a state higher than the temperature of the silicon melt rising in the slit of the die near the die tip.
The temperature distribution of the silicon melt in the vicinity of the die tip is reversed from the conventional technique, with a high temperature on the die side and a low temperature at the center of the slit.

In this way, the shape of the solid-liquid interface in the thickness direction of the band-shaped silicon crystal becomes concave, so that it is possible to eliminate the crystal irregularity in the central part in the thickness direction, which has been a problem in the past.

Note that the above temperature control can be specifically achieved by cooling the central portion of the silicon melt rising inside the slit.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 4 is a diagram showing a main part of an embodiment of the present invention, in which a is a perspective view and b is a sectional view.

Die 13a. A thin cooling plate 41 is installed in the center of the slit between the holes 13b.

This cooling plate 41 is made of, for example, a carbon plate, and the die 13
It is provided parallel to the dies 13a and 13b, and its tip position is set lower than the tip edge of the dies 13a and 13b.

Further, the tips of the cooling plate 41 are formed to be wider than the widths of the dies 13a and 13b in the form of protruding from both sides as 42a and 42b, and these protrusions 42a and 42b are connected to a cooling gas 43a such as argon gas. , 43b are sprayed onto the surface of the substrate.

And, gas 43a. The temperature of at least the tip of the cooling plate 41 is controlled by controlling the flow rate of the die 13a, 13b.
Set it to a temperature lower than that of the tip.

Under such temperature conditions, the die 1 of the silicon melt 11
The temperature distribution in the vicinity of the tips of 3a and 13b is low at the center of the slit, that is, near the cooling plate 41, and high at the dies 13a and 13b.

Therefore, when a band-shaped silicon crystal is pulled under these temperature conditions, the shape of the solid-liquid interface in the thickness direction of the crystal becomes concave as shown at 51 in FIG.

The cross section in the thickness direction of the band-shaped silicon crystal 16 grown with the solid-liquid interface 51 having such a shape is shown in FIG.

That is, crystal nuclei are generated from the center in the thickness direction and proceed to the ribbon surface, so that the crystal irregularity in the center is removed and the ribbon is composed only of twin grain boundaries 61.

The band-shaped silicon crystal obtained in this way not only has a uniform distribution of resistivity, but also has a significantly longer minority carrier lifetime, and when made into a solar cell, its electrical conversion efficiency is 10% on average. A significant improvement was seen.

As explained above, according to the present invention, the temperature condition is such that the temperature at the die tip is higher than the silicon melt near the die tip, and the shape of the solid-liquid interface in the thickness direction is made concave. By doing so, it is possible to prevent the occurrence of crystal irregularities in the central part of the band-shaped silicon crystal in the thickness direction and improve the quality of the crystal, and it is possible to significantly improve the electrical conversion efficiency when used as a solar cell. becomes.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing the basic configuration of a band-shaped silicon crystal growth apparatus, Fig. 2 is a sectional view illustrating the shape of the solid-liquid interface in the conventional apparatus, and Fig. 3 is a sectional view of the band-shaped silicon crystal grown in the conventional apparatus. A sectional view in the thickness direction, FIGS. 4a and 4b are a perspective view and a sectional view showing the configuration of essential parts of an embodiment of the present invention, and FIG. 5 illustrates the shape of the solid-liquid interface in the device of the embodiment. FIG. 6 is a cross-sectional view in the thickness direction of a band-shaped silicon crystal obtained by the apparatus of the same example. 11... Silicon melt, 12... Crucible, 1'z a t i 3b... Die, 14
a, 14b... Support rod, 15 a, 15 b
"" Main heater, 16... Band-shaped silicon crystal, 21... Solid-liquid interface, 31... Crystal irregularity, 32... Twin grain boundary, 41 ......Cooling plate, 43a, 43b...Cooling gas, 51...
...Solid-liquid interface, 61...Twin grain boundary.

Claims (1)

[Claims] 1. A die having a slit is set up in a crucible containing a silicon melt, a seed crystal is brought into contact with the silicon melt rising inside the slit, and the seed crystal is pulled up to form a silicon band. The apparatus for growing a crystal is characterized in that a cooling plate is provided at the center of the slit of the die, and the temperature of the silicon melt at the tip of the die is controlled to be lower at the center of the slit than at the die side. A device for growing band-shaped silicon crystals. 2. The apparatus for growing a band-shaped silicon crystal according to claim 1, wherein the cooling plate is cooled by gas.