JPH07187899A - Silicon wafer having uniform oxygen density and its prduction - Google Patents

Abstract

PURPOSE:To obtain a uniform silicon wafer without variation in oxygen density in a wafer or among wafers by making the oxygen density in the silicon single crystal produced by Czochralski process uniform. CONSTITUTION:This silicon wafer is a silicon single crystal obtd. by Czochralski process and has uniform oxygen density. For example, a silicon single crystal grown by Czochralski process is heat treated to obtain >=0.1mm diffusion length [(Dt)<1/2>] of oxygen. The heat treatment is performed, for example, by high frequency heating in an inert gas atmosphere in a quartz tube. Or, even when oxygen condition in the growing interface varies during the crystal is grown by Czochralski process, high temp. thermal hysteresis can be given to the growing crystal rod and >=0.1mm diffusion length of oxygen is obtd. in the crystal by controlling the pulling rate as low as <=0.1mm/min. Thus, uniform oxygen density can be obtd. in the whole crystal rod.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for uniformizing the oxygen concentration in a silicon wafer, which plays an important role in manufacturing semiconductor devices.

[0002]

2. Description of the Related Art It is well known that when a silicon single crystal ingot is pulled by the Czochralski method (hereinafter referred to as the CZ method), oxygen eluted from a quartz crucible is incorporated as an interstitial impurity in the single crystal. Such interstitial oxygen impurities are nonuniformly incorporated into the single crystal due to nonuniform temperature fluctuations due to convection in the silicon melt, causing so-called growth fringes. This growth fringe is due to the uneven distribution in the crystal, but the fluctuation range (maximum concentration-minimum concentration) in the growth direction is usually 0.3 to 0.8 × 10 ¹⁷ atoms / cm ³ (1979 AST
M conversion, the same applies below), and the fluctuation cycle is 0.4 to 1.2 mm
It is about the degree (see FIGS. 1 and 2). A wafer manufactured from such a crystal rod has a thickness of about 6 "φ.
Since it is 0.6 mm, the above-mentioned fluctuation of oxygen concentration is caused within the wafer and between the wafers. Furthermore, C
In the growth of a silicon single crystal ingot by the Z method, the growth interface is not flat (convex upward), so that the fluctuation of oxygen distributed along the growth fringes is ultimately in the plane of the wafer cut out from the single crystal ingot. Will also occur in.

By the way, the oxygen taken in the silicon wafer forms an oxygen precipitate by the heat treatment in the IC manufacturing process and serves as a getter source of heavy metal impurities. Therefore, the oxygen concentration in the crystal often greatly affects the IC yield. Are known.

However, since the conventional silicon wafer has the above-mentioned growth fringes of oxygen, striped oxygen precipitation occurs in the heat treatment in the IC manufacturing process, and the getter effect of heavy metals is not uniform within the wafer or between the wafers. It was

To address this problem, Japanese Patent Laid-Open No. 5-97584 discloses that
In the first place, since the fluctuation of the oxygen concentration could not be measured accurately in the first place, it was manufactured by the conventional method using a so-called microscopic FTIR in which an infrared spectroscope with a Fourier transform calculation function capable of highly accurate measurement was equipped with a microscope. An invention is disclosed in which a wafer having a relatively small variation in oxygen concentration is selected from the produced wafers. However, with this method, only wafers with relatively small fluctuations can be selected from the wafers, and the fluctuation in oxygen concentration does not change, and the ratio of wafers with small oxygen fluctuations that can be obtained from the crystal rod is extremely low.

On the other hand, in the ordinary CZ method, it is extremely difficult to uniformly take in oxygen when growing a silicon single crystal ingot because the fluctuation of oxygen is due to the influence of melt convection during growth. is there. As a method of suppressing melt convection, there is a CZ method by applying a magnetic field (MCZ method).
Even with this method, the fluctuation of oxygen can be suppressed to some extent only when the crystal growth is performed under the condition that the oxygen concentration in the silicon crystal is extremely low. Except in the case of extremely low oxygen, oxygen fluctuations are similar to those in the conventional method.

[0007]

SUMMARY OF THE INVENTION In view of the above problems, the problem to be solved by the present invention is to obtain a uniform silicon wafer having no variation in oxygen concentration between wafers and within a wafer. More specifically, the purpose is to reduce the oxygen fluctuation range to half or less of the initial value.

[0008]

Since it is difficult for the present inventors to make oxygen taken in during crystal growth uniform, oxygen is diffused and made uniform by applying high temperature heat treatment after crystal growth. With this in mind, the present invention has been completed. That is, since the fluctuation period in the oxygen growth direction of the silicon crystal by the ordinary CZ method is about 0.4 to 1.2 mm, if the oxygen can be diffused by about 0.2 to 0.6 mm, which is half that length, the inside of the crystal can be diffused. Therefore, the oxygen concentration can be completely made uniform.

One aspect of the present invention is that the diffusion length of oxygen in the crystal (√ (D
t)) is added to heat treatment of 0.1 mm or more. It suffices to carry out the heat treatment according to a general method (for example, by high frequency heating or lamp heating in an inert gas atmosphere in a quartz tube), and in principle, the crystal form does not matter whether it is a wafer or an ingot. However, if a wafer is subjected to high temperature heat treatment for too long,
Since it easily slips, it is preferably performed in the form of an ingot. Another aspect of the present invention is that when a crystal is grown by the CZ method, even if oxygen changes at the growth interface, the pulling speed is set to a low speed of 0.1 mm / min or less, so that By applying a heat history and setting the diffusion length of oxygen in the crystal to 0.1 mm or more, oxygen is made uniform in the entire single crystal rod.

[0010]

First, as a guide, the conditions for setting the diffusion length L of oxygen in the silicon crystal to 0.2 mm = 0.02 cm or more were calculated by the following formula.

[0011]

[Equation 1] L = √ (Dt) ≧ 0.2 × 10 ⁻¹ (cm)

[Equation 2] D = 0.13exp (-Q / kT) (cm ² / s)

Here, D is a diffusion coefficient (cm ² / s), t is time (s), and Q is an experimentally obtained constant of 2.53 (e).
V) and k are Boltzmann constants 0.863 × 10 ^-4 (eV ・
K ^-1 ) and T are absolute temperatures (K). (The diffusivity and
solubility of oxygen in silicon, Materials Researc
h Society Symposium Proceeding vol.59 1986 p19-p30
Substituting numerical values into these formulas and calculating the relationship between temperature and time, it is about 59 hours or more at 1350 ° C and about 1250 ° C.
When the time is 195 hours or more, the oxygen diffusion length is calculated to be 0.2 mm or more. Of course, the temperature and time are not limited to these values, and various combinations can be made as long as the oxygen diffusion length is 0.2 mm or more. However, it is impossible to raise the melting point of silicon to about 1,420 ° C or higher, and if the temperature is too low, the processing time becomes long, resulting in low productivity.

On the other hand, by controlling the thermal history of high temperature in the cooling process from the melting point during crystal growth, the same effect as in the heat treatment can be obtained. The temperature range that is effective for oxygen diffusion is especially above 1,300 ℃, but in order to control the thermal history of such high temperature, it is most desirable to control the growth rate, and to control by the structure inside the furnace. Is very difficult. This is because Fig. 3 shows a simulation of the temperature distribution near the growth interface in the CZ method.
The height distribution is less than one-half the height (the length is shown in the relative ratio in FIG. 3), and the temperature distribution in the region just above the growth interface is
This is because heat conduction from the melt, direct radiation, and latent heat of solidification dominate. Based on this distribution, the diffusion length of oxygen is 0 when the growth rate is 1.0 mm / min or higher.
03 mm, 0.4 mm / min 0.04 mm, 0.1 mm / min 0.1
The crystal bears a thermal history of mm.

[0014]

EXAMPLES Next, examples of the present invention will be given. (Examples 1 and 2) CZ grown in the growth axis direction <100>
The heat treatment time was gradually extended to a silicon single crystal at 1,350 ° C., and the change in oxygen distribution was measured by microscopic FTIR (Example 1). The results are shown in Table 1 and FIG. Next, the heat treatment time was set to 48 hours and the treatment temperature was changed and the same measurement was performed (Example 2). The results are shown in Table 2 and FIG.

[0015]

[Table 1]

[Table 2]

As can be seen from Table 1 and FIG. 1, as the heat treatment time is lengthened, oxygen diffusion progresses and the oxygen concentration in the crystal becomes uniform. If the heat treatment condition is 1,350 ° C./60 hours, it will be possible to achieve almost complete homogenization, but even at 1,350 ° C./15 hours, oxygen fluctuations can be reduced to half of the initial value. In the treatment at 1,350 ° C./15 hours, the diffusion length of oxygen is 0.1 mm calculated from the above formula.

As can be seen from Table 2 and FIG. 2, if the treatment time is the same, the higher the heat treatment temperature, the faster the diffusion of oxygen, and the more uniform the oxygen concentration in the crystal. However, if the temperature is too high, the furnace and the sample will be damaged. Also in this case
By treating at 1,250 ° C for 48 hours (oxygen diffusion length is equivalent to 0.1 mm), the fluctuation of oxygen can be halved.

From Examples 1 and 2, it was found that if the diffusion length of oxygen is 0.1 mm or more, the fluctuation of oxygen can be reduced to half or less of the initial value. Of course, the temperature and time are not limited to these values, and various combinations can be made as long as the oxygen diffusion length is 0.1 mm or more. However, the melting point of silicon cannot be raised above 1,420 ° C, and if the temperature is too low, the processing time becomes long and the productivity becomes low.

(Example 3) Crystals having a diameter of 6 "and an orientation of <100> were grown at various pulling rates by the CZ method and the MCZ method.
It was measured by TIR. The results are shown in Table 3. As can be seen from Table 3, when the pulling speed is extremely reduced (0.1 mm / mi
(n or less), the diffusion time of oxygen progresses because the residence time of the crystal at high temperature is long, and the fluctuation range of oxygen concentration in the crystal is small.

[0020]

[Table 3]

[0021]

As described above, according to the present invention, it is possible to obtain a uniform silicon wafer having an oxygen concentration fluctuation of half or less as compared with the conventional one. Therefore, a silicon wafer having a uniform gettering effect is obtained over the entire surface of the wafer in the device process, which is extremely effective in improving device yield and device characteristics.

[Brief description of drawings]

FIG. 1 is a diagram showing how the oxygen concentration in crystals varies with heat treatment time.

FIG. 2 is a diagram showing how the oxygen concentration in the crystal varies with the heat treatment temperature.

FIG. 3 is a simulation of temperature distribution near the growth interface in the CZ method.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location H01L 21/324 Z (72) Inventor Hirotoshi Yamagishi 2-13-1 Isobe, Annaka-shi, Gunma Shin-Etsu Semiconductor Co., Ltd. Semiconductor Isobe Laboratory

Claims (3)

[Claims] 1. A silicon wafer which is a silicon single crystal produced by the Czochralski method and has a uniform oxygen concentration. 2. The silicon wafer according to claim 1, wherein the silicon single crystal produced by the Czochralski method is subjected to heat treatment so that the diffusion length (√ (Dt)) in the crystal is 0.1 mm or more. Manufacturing method. 3. The method for producing a silicon wafer according to claim 1, wherein the pulling speed of the silicon single crystal ingot by the Czochralski method is 0.1 mm / min or less.