JPS63112488A - Growth method for single crystal silicon - Google Patents

Abstract

PURPOSE:To readily obtain a single crystal silicon having an uniform density of defect occurrence, by controlling the thermal history which is applied to the single crystal silicon grown by the Czochralski process with oxygen concentration of the silicon. CONSTITUTION:A long crystal 21 of a single crystal silicon is pulled up from a melt 32 in a crucible 31 by the Czochralski process. In the process, the crucible 31 is rotated in the direction opposite to the rotational direction of the chuck 33 and the rotational speed (Rc) of the crucible 31 is set so to slowly increase in proportion to the growth of the long crystal 21, i.e. satisfy the condition of dRc/dt>0. Thereby oxygen is separated in the head part of the crystal 21 using latent nuclei as nuclei by utilizing the oxygen concentration of the long crystal 21 proportional to the rotational speed (Rc) of the crucible 31 and separation of the oxygen is promoted in the tail part by increasing the rotational speed of the crucible 31 for a few nuclei to provide a high oxygen concentration.

Description

[Detailed Description of the Invention] [Summary] The thermal history that single-crystal silicon, grown by the Czochralski (CZ) method, receives during the growth process is controlled by oxygen concentration.

[Industrial application field]

The present invention relates to a method for growing single-crystal silicon, and more specifically, to a method for making the density of defects uniform over the entire length of a long crystal of single-crystal silicon in the step of growing a long crystal of single-crystal silicon by the CZ method. .

[Conventional technology]

The yield of silicon crystals used as substrates for VLSIs is significantly increased by intrinsic gettering (IG) processing. To explain such an IG with reference to FIG. 3, 11 is a wafer processed (cut out) from a long crystal of single crystal silicon grown by the C2 method. In VLSI, devices 12 (such as impurity diffusion regions) are formed shallowly near the surface of wafer 11;
It is necessary that no crystal defects exist in the device forming layer 13 near the surface of the wafer 11 on which these devices 12 are formed.

In order to make the device forming layer 13 free from crystal defects, the above-mentioned IG treatment is carried out, but at the same time heat treatment is applied to the evaporator 11 to eliminate contamination sources such as the total bending layer 14 present in the device forming layer 13. While being emitted outside the wafer as indicated by the arrow in the figure, the oxygen 16 is aggregated in the internal region of the wafer, causing the oxygen 16, which is itself a defect, to getter the defects, thus causing the inside of the wafer where no devices are formed. Defects are taken into the region (gettered) so that the device forming layer 13 is free of defects. The wafer heat treatment described above is performed by simultaneously heating a large number of wafers processed from long crystals.

[Problem that the invention seeks to solve]

For the above-mentioned IG processing, when a large number of wafers serving as substrates are subjected to the same heat treatment, defects must be generated at the same density on all the wafers.

For this purpose, it was thought that it would be sufficient to make the oxygen concentrations the same before the heat treatment, but it has been experimentally known that this alone is not sufficient to control the generation of defects. The present invention
This idea was born from investigating the cause of this problem.

The diagram in FIG. 4 shows that even at the same oxygen concentration, the defect generation rate (that is, the oxygen reduction rate) differs depending on the wafer. Note that, to measure the oxygen concentration in the wafer, a known method of irradiating a laser beam of 1100 Kaiser (cm-'') is used.

The figure shows a location A approximately 1.50 (mm) away within a long crystal 21 made to have a uniform oxygen concentration (35 ppm).
The wafers processed from and B were heat-treated at 700°C ("C) and the decrease in oxygen concentration was investigated. The horizontal axis shows the length of this 700°C heat treatment in hours (hr), and the vertical axis shows The oxygen concentration is measured in ppm, and curves a and b show the oxygen concentrations of wafers processed from portions A and B of the long crystal 21, respectively.The difference in the rate of decrease between curves a and b is usually understood to be due to thermal history. However, after considering this in detail, we found the following.

During growth, the crystal is solidified at 1410 degrees Celsius (°C) and then cooled down, during which oxygen precipitates and forms micro-defects (or latent nuclei). It is understood that the tail (which is longer) is more prominent than the tail on the opposite side of the head.

FIG. 5 schematically shows the growth of a long crystal by the CZ method, and FIG. 5(a) shows the initial stage of growth, and FIG. First, the head portion 22 of the long crystal 21 is formed near the seed crystal 20 (FIG. 2(a)), and then, after a growth time of, for example, 10 hours (hr) has elapsed, the tail portion 23 shown in FIG. 2(b) is formed. However, it is understood that precipitation of oxygen occurs at the head 22 during the elapse of about 10 hours. In the figure, 31 indicates a crucible, 32 indicates a melt, and 33 indicates a chuck.

Figure 7 shows a sample processed from the head 22 and tail 23 of a crystal 21 with the same oxygen concentration at 1350 ("C") and 1 (h
r) Shows the increase in oxygen concentration after treatment, with the horizontal axis representing the position of the long crystal and the vertical axis representing the increased oxygen concentration in ppm. If the aforementioned latent nucleus is formed, 1350 ("
In C), this should dissolve and the oxygen concentration should increase. 7th
From the figure, it is understood that there are many latent nuclei in the head of the crystal. From the above, in order to make the defect generation density the same, it is necessary to make the potential nucleus density the same rather than making the oxygen concentration the same. However, when growing long crystals, the tail always has a shorter thermal history than the head, so it is impossible to make the potential nucleus density the same.

The present invention was created in view of these points, and C2
An object of the present invention is to provide a crystal growth method that makes the density of defects uniform over the entire length of the long crystal in the growth of long silicon crystals by the method.

[Means for solving problems]

FIG. 1 is a diagram of an embodiment of the present invention (a schematic diagram of an apparatus for carrying out the method of the present invention), in which 31 is a crucible, 32 is a melt, 33 is a chuck, and long crystals are being grown. is indicated by 21, and Rc and Rs are respectively the crucible 31 and the chuck 33.
It represents the rotational speed of Rc, l! : The rotation directions of Rs are opposite to each other.

In the present invention, Rc is raised while accelerating the rotation of the long crystal 21 under the condition that δRc/δ1>0 from the start of growth to the stage where growth ends.

[Effect]

The above method focuses on the fact that the oxygen concentration in long crystals is proportional to Rc, and as the growth progresses, the tail rotates faster, making the tail a higher oxygen concentration than the head. Precipitation is promoted as shown in FIG. In other words, in the head part, oxygen is precipitated from the latent nucleus, whereas in the tail part, oxygen is precipitated by distributing a large amount of oxygen around the small latent nucleus by increasing the rotation of the crucible as it approaches the end of growth. It is designed to encourage this.

〔Example〕

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

In the present invention, as described above, the oxygen concentration at the tail of the elongated crystal is made higher than the oxygen concentration at the head, so that the state of oxygen precipitation as shown in FIG. 2 is achieved. For this purpose, it is utilized that the oxygen concentration within the long crystal being grown is proportional to the rotation of the long crystal.

Referring again to FIG. 1, the long crystal being grown is rotated by the chuck 33 at 15 to 25 rpm in the direction of the arrow shown in the upper part of the figure.
rotates at a speed of Therefore, as shown in FIG. 5(b), until the tail portion 23 is grown, the crucible 31 is rotated in the direction indicated by the arrow drawn at the bottom of the figure, that is, in the opposite direction to the rotation direction of the chuck 33. let Further, the rotation of the crucible is set to gradually increase in proportion to the growth of the long crystal, that is, to satisfy the condition δRc/δ1>0.

The results of experiments conducted by the present inventor are shown in FIG. 2, which is an example of growing a long crystal with a crystal diameter of 4 inches (approximately 10 cm). Rotation Rs of the chuck 33 shown in FIG. 1 = -2
5 (rpm). The horizontal axis of the figure shows the crystal length of the grown crystal (mm), and the vertical axis shows the oxygen concentration (ppm).
) was taken. The diameter of the crucible 31 is 14 inches (approximately 36
cm), and the charge amount was 30 (Kg).

In the illustrated curve, the curve connecting the Δ marks is Rc −8+
0.75 (rpm/hr), the curve connecting the black circles is Rc = 8 + 0.62 (rpm/hr)
In the case of r), the curve connecting the white circles is Rc = 8 +
0.50 (rpm/hr), the curve connecting the X marks represents the result when Rc = 8 (rpm).

Here, Rc = 8 + 0.75 (rpm/h
r) means 0.75 (rpm) per hour from 8 (rpm)
) indicates that the rotational speed has increased at a rate of Rc =
8 (rpm) represents that the rotational speed of 8 (rpm) was maintained from the beginning to the end and there was no change in the rotational speed.

From Figure 2, Rc = 8 + 0.75 (rpm/
When a long crystal is pulled under the conditions of hr), when a wafer processed from the long crystal is heat-treated under the conditions shown in FIG. 4, no matter where on the long crystal the wafer is cut, It is predicted that the same amount of oxygen concentration reduction will be shown.

In addition, the above-mentioned numerical values are values under the above conditions,
When the dimensions of the crystal to be grown, the size of the crucible, and the amount of charge differ, Rc is set appropriately each time, and the scope of application of the present invention is not limited to the above-mentioned specific examples.

〔Effect of the invention〕

As described above, according to the present invention, wafers processed from any part of the crystal show the same heat treatment characteristics, which greatly contributes to improving the yield of semiconductor integrated circuit manufacturing.

[Brief explanation of the drawing]

Fig. 1 is a diagram of an embodiment of the present invention, Fig. 2 is a line diagram of an embodiment of the present invention, Fig. 3 is a cross-sectional view of a wafer to explain IG, and Fig. 4 shows the rate of oxygen reduction within the wafer. FIG. 5 is a diagram showing the growth of long crystals by the CZ method, and FIG. 6 is a diagram showing the increased oxygen concentration after wafer heat treatment. 1 to 6, 11 is a wafer, 12 is a device, 13 is a device forming layer, 14 is a metal, 15 is an internal region, 16 is oxygen, 20 is a seed crystal, 21 is a long crystal, and 22 is a long crystal. The head of the long crystal, 23 the tail of the long crystal, 31 the crucible, 32 the melt, and 33 the chuck. Agent Patent attorney: Hajime Kuki Agent: Yoshi Osuga Patent attorney: IGtvL1114 T4r=/+cf7xharat1
Menku Figure 3 Figure 2 70σ1% りIF'l (hrununihe4/l叡) 1 commandment and 1 degree of culm concave Figure 4 (a) (b) C7 Fan Jyu, non-length Diagram 5 showing the long color of the stream 1

Claims (2)

[Claims] (1) A method for growing single-crystal silicon, characterized in that the thermal history that single-crystal silicon, grown by the Czochralski method, receives during the growth process is controlled by the oxygen concentration of the silicon. (2) From the melt (32) in the crucible (31) to a long crystal (
21), the crucible (31) is rotated in the opposite direction to the rotational direction of the chuck (33) under the condition that dRc/dt>0 (where Rc is the rotational speed of the crucible). The method described in Scope 1.