JPS6027678A - Method for growing single crystal - Google Patents

Abstract

PURPOSE:To grow a single crystal having uniform oxygen concentration by Czochralski process, by enlarging the diameter of the single crystal gradually in the course of the crystal pulling process, thereby decreasing the surface area of the molten liquid. CONSTITUTION:In the growing of a single crystal by Czochralski process using a crucible 1 made of an oxide such as quartz, the oxygen in the crucible material is diffused into the single crystal 4, and its amount decreases with the increase in the solidification ratio, because the convective stirring action of the molten liquid 2 decreases according to the decrease in the molten liquid 2 in the crucible 1 by the progress of solidification, resulting in the decrease of the oxygen supply from the crucible material 1. The decrease of the oxygen supply from the crucible material is compensated by enlarging the diameter of the pulling single crystal 4 gradually according to the progress of solidification, thereby decreasing the surface area of the molten liquid 2 and suppressing the dissipation of oxygen from the surface of the molten liquid. A single crystal having uniform oxygen concentration along the pulling direction can be produced by this process.

Description

[Detailed Description of the Invention] (81 Technical Field of the Invention The present invention relates to single crystal growth by the Czochralski method,
(Relates to a method for growing a single crystal with uniform oxygen concentration in the pulling direction.

(Background of 1+1 technology In the manufacturing of semiconductor integrated circuits, Intrinsic Getter, which effectively utilizes the properties of the semiconductor substrate itself,
A technique called -;ng (IG>) provides a defect-free layer on the surface of the substrate on which a semiconductor circuit is formed.

That is, in normal manufacturing processes, for example, copper (Cu
) or impurities such as nickel (Ni) are inevitably mixed in. As a result, the impurities may precipitate near the surface of the substrate, or the diffusion profile may change.
This has an undesirable effect on the characteristics of the formed semiconductor circuit. For this reason, the above-mentioned IG or Extrinsic Gette is used as a means to localize these impurities in positions where they do not affect the semiconductor circuit within the substrate.
An effect called "ring" is used.

In order to exhibit this IG effect, it is necessary that an appropriate concentration of oxygen be contained inside the substrate. This is because the above-mentioned impurity atoms are relatively easy to move within a substrate such as silicon and are easy to collect in a strained region around an oxygen precipitate or the like.

In other words, a substrate such as silicon containing an appropriate amount of oxygen,
A predetermined heat treatment is performed in advance to remove oxygen from the surface layer to form a defect-free region, and by forming oxygen precipitates only within the region, the impurities are confined within the substrate. In this way, a semiconductor circuit is formed on the surface layer of the substrate which has become defect-free.

tc+Prior Art and Problems The Czochralski method is usually used for industrial growth of silicon single crystals for conductive devices.

At this time, if a crucible made of an oxide such as quartz (Si02) is used as a crucible for melting the raw material silicon, a small amount of the quartz (Si02) will melt into the silicon melt. Most of the oxygen escapes into the atmospheric gas as lower silicon oxides such as silicon monoxide (SiO), but the remaining part of the oxygen is taken into the silicon single crystal.

Oxygen is contained in the silicon single crystal grown using an oxide layer crucible due to the above mechanism.
In single crystals obtained by conventional growth methods, the oxygen concentration in the pulling direction was not uniform, and generally had a distribution as shown in FIG. The solidification rate (%) in the figure is a value expressed as a percentage of the amount that has solidified into crystals out of the initial amount of raw silicon melt in the crucible.

As shown in the figure, the oxygen concentration in the single crystal decreases as the amount of silicon melt in the crucible decreases;・Viewed from the notched area), only about 10% of the grown single crystals meet this requirement. In other words, when using a wafer made from a single crystal with such an oxygen concentration distribution, the conditions of the semiconductor circuit formation process must be changed depending on the oxygen concentration, which means an increase in manufacturing costs. . Therefore, obtaining a high yield of wafers that have undergone mass processing is an essential requirement for reducing the cost of semiconductor integrated circuits, and for this reason, there is a need to develop a method that can grow single crystals with as uniform an oxygen concentration as possible. Ta.

(d1 Purpose of the Invention The object of the present invention is to enable the growth of a single crystal having a uniform oxygen concentration in a substantially arbitrary required concentration range.

(e) Structure of the Invention The present invention provides a uniform oxygen concentration in the single crystal by sequentially increasing the diameter of the single crystal during pulling to reduce the surface area of the melt during single crystal growth using the Czochralski method. It is characterized by making it.

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

As mentioned above, when an oxide layer crucible is used, it is believed that the rfJ of the crucible material serves as a source of oxygen for the single crystal. FIG. 2 is a schematic diagram explaining this mechanism, in which a crucible 1 made of quartz (Si02) is
Substitute of Si): For example, about 90% or more of the Si02 component 3 dissolved in the liquid 2 escapes from the free surface of the melt 11〉2 as a lower silicon oxide (SiOx) such as silicon monoxide (SiO), and the remaining Oxygen is incorporated into single crystal 1.

In this case, the reason why the oxygen concentration in the single crystal becomes a downward-sloping curve Xjl+ as shown in Figure 1 is that when the solidification rate increases and the melt in the crucible decreases, the convection of the melt This is explained by the fact that the stirring action of the crucible material decreases, and as a result, the amount of oxygen supplied from the crucible material decreases.

According to this consideration, if the amount of oxygen escaping from the melt surface (including the lower silicon oxide and gaseous oxygen) is suppressed to compensate for the decrease in the amount of oxygen supplied, the oxygen concentration in the single crystal can be made uniform. This means that it can be maintained at Therefore, in the present invention, the free surface area of the melt is reduced by increasing the diameter of the single crystal being pulled as the solidification rate increases.

Suppresses the amount of escaping oxygen.

As shown in FIG. 3, from the initial stage of pulling until the solidification rate reaches about 20%, the pulling speed or the power of the heater 5 for heating the melt 2 is controlled so that the diameter is 3 inches. . After that, until the solidification rate reaches about 60%, the diameter of 1yr becomes 4 inches, and then until the solidification rate reaches almost 100%, the diameter becomes 5 inches.
The pulling speed or the power of the heater 5 is controlled so that the pulling speed or the power of the heater 5 is adjusted to 1 inch.

This effect is shown in FIG. In the same figure, curves ■, ■, ■
are curves showing the relationship between solidification rate and oxygen concentration when the diameter of the single crystal is 3 inches, 4 inches, and 5 inches, respectively. In other words, when crucibles of the same diameter are used, the larger the diameter of the single crystal, the smaller the free surface flaw of the melt, which reduces the amount of escaping oxygen, resulting in a higher oxygen concentration in the single crystal. It is shown that 1'1. ing.

As mentioned above, the solidification rate is approximately 25% from the initial stage of pulling.
The oxygen concentration in the single crystal in this area is distributed along the solid line part of the curve (■), and the solidification rate is from approximately 25% to approximately 60%.
The oxygen concentration in the single crystal in this area is distributed along the solid line part of curve Ⅰ, and solidification Ⅰ is from about 60% to about 100% because the single crystal was pulled up to 4 inches in diameter.
Since the single crystal was pulled up to 3 inches in diameter, the oxygen concentration in the single crystal in this part is distributed along the solid line part of the curve (2).

As above, the solidification rate is almost 100% (!7
The oxygen concentration in the single crystal obtained could be kept within the concentration range required by the manufacturing process of semiconductor integrated circuits (the hatched range in FIG. 4).

If it is necessary to control the oxygen concentration to a concentration range different from that shown in the diagram, it is possible to use the curve in Figure 4 and change the solidification rate range in which the diameter is changed.If the concentration range is changed even more, it is possible. To do this, you can either draw similar curves for diameters other than those shown in the figure, or draw a similar group of curves when the diameter of the Ll pit is changed, and then change the diameter during pulling in the same way as above to create different curves. It is possible to produce a single crystal containing a range of concentrations of oxygen.

Note that, according to the principle of the present invention, it is clear that by continuously increasing the diameter, it is possible to control the oxygen concentration distribution to be completely constant.

Further, in the present invention, another advantage of °ζ is that single crystals of different diameters can be produced by one pulling process, and can be used for multiple purposes.

(g) Effect of the invention According to the invention, the oxygen concentration in the pulling axis direction is
It is possible to grow uniform single crystals within the concentration range required by the manufacturing process of semiconductor integrated circuits, and it has the advantage that webs suitable for mass processing can be economically supplied.

[Brief explanation of drawings]

Figure 1 shows the general relationship between the solidification rate of the melt and the oxygen concentration in the single crystal during single crystal growth using the Czochralski method, and Figure 2 shows the oxygen supply to the single crystal grown using the Czochralski method. Schematic diagram for explaining the mechanism, Part 3
The figure is a schematic diagram for explaining the details of the present invention for growing a single crystal with uniform oxygen concentration.
FIG. 2 is a diagram illustrating the principle of the single crystal growth method of the present invention in which the oxygen concentration in the single crystal is made uniform by using the solidification rate-oxygen concentration relationship shown in the figure. In the figure, 1 is a crucible, 2 is a melt, 3 is a 5i02 component,
4 is a single crystal, and 5 is a heater. % 1 Figure 4m

Claims (1)

[Claims] In single crystal growth using the Czochralski method, the diameter of the single crystal is gradually increased during pulling (by which the surface area of the melt is reduced, thereby making the oxygen concentration in the single crystal uniform). Crystal growth method.