JPH09227291A - Silicon single crystal wafer and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of slip phenomenon at the time of heat treatment of a single crystal wafer by partially injecting carbon on an outer peripheral surface layer part of single crystal during or after pulling up thereof, at the time of growing the single crystal by CZ method. SOLUTION: Silicon melt is stored in a quartz crucible arranged within a chamber and a seed crystal is dipped in the melt and the silicon single crystal is pulled up at carbon concentration of <= lower limit of detection (1×10<15> atoms/ cm<3> ) according to an infrared absorption method by CZ method. A prescribed quantity of carbon is partially injected into the outer peripheral surface layer part of single crystal during or after pulling up and wafers are collected from thus obtained silicon single crystal. Thereby, the silicon single crystal wafers, wherein parts excluding the outer peripheral part have the concentration of <=the lower limit of detection (1×10<15> atoms/cm<3> ) according to an infrared absorption method and the carbon concentration at a part under the outer peripheral part within 5mm depth from an outer periphery surface has >=2×10<15> atoms/cm<3> , are obtained. Thereby, lowering of a mechanical strength due to lowering of oxygen concentration at the outer peripheral part of the wafers can be compensated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wafer made of a silicon single crystal manufactured by the CZ method and a manufacturing method thereof.

[0002]

2. Description of the Related Art A material for a silicon wafer used for a semiconductor device, that is, a silicon single crystal rod (this is simply referred to as a silicon single crystal in this specification) is often manufactured by a CZ method. In the production of a silicon single crystal by the CZ method, as shown in FIG. 1, a single crystal C is pulled from a melt B of silicon in a quartz crucible A while rotating with a wire D. At this time, oxygen is dissolved into the melt B from the inner surface of the quartz crucible A. Most of the melted oxygen is removed along with the evaporation of SiO 2 from the surface of the melt B, but part of the dissolved oxygen is taken into the crystal as an interstitial impurity through the solid-liquid interface.

Oxygen taken into the grown single crystal causes nonuniform concentration distribution in the pulling axis direction due to periodic fluctuations of crystal growth conditions at the solid-liquid interface. In addition to this, a phenomenon occurs in which the oxygen concentration in the outer peripheral portion in the radial direction of the single crystal becomes lower than that in other portions. The latter non-uniformity of oxygen concentration means that the low oxygen layer formed on the surface layer of the melt by the release of oxygen from the surface of the single crystal and the evaporation of SiO from the surface of the melt causes the outer peripheral part of the solid-liquid interface due to the convection of the melt. It is because it is supplied to.

[0004]

Conventionally, since the uneven oxygen concentration in the pulling axis direction causes variation in the oxygen concentration between wafers taken from a single crystal, various measures have been proposed. (Japanese Patent Laid-Open No. 6-
316483, 7-187899, etc.).
However, regarding the decrease in the oxygen concentration in the outer peripheral portion of the single crystal, the outer peripheral surface is cut to round the single crystal or remove the unevenness of the outer peripheral surface, and when the device is sampled from the wafer, the outer peripheral portion of the wafer is cut. However, it is inevitable because it will be a loss. Therefore, the oxygen concentration distribution in the radial direction of the wafer was extremely low in concentration in the outer peripheral portion as compared with other portions, as shown by the solid line in FIG.

The decrease in oxygen concentration in the outer peripheral portion of the wafer does not directly affect the quality because the outer peripheral portion causes an unavoidable loss. However, since the mechanical strength of this portion is inferior, radial cracks called slips are generated from the outer peripheral portion of the wafer during the heat treatment, resulting in a decrease in yield. Further, in order to prevent slippage from occurring in the heat treatment, work such as slowing down the loading speed into the heat treatment furnace and the removal speed from the heat treatment furnace, accommodating every other wafer in the boat, and ignoring the efficiency are also performed. . For these reasons, the manufacturing cost of wafers is currently high.

Although not a direct influence, oxygen in the crystal has a gettering action on heavy metals, so that a single crystal or a wafer having an extremely low oxygen concentration in the outer periphery is
Heavy metal may cause crystal defects on the outer periphery thereof.

An object of the present invention is to provide a silicon single crystal wafer which can effectively suppress the occurrence of slip during heat treatment and can be expected to have gettering ability equivalent to that of the central portion even in the outer peripheral portion, and a manufacturing method thereof. is there.

[0008]

A silicon single crystal wafer of the present invention is a wafer extracted from a silicon single crystal pulled from a silicon melt in a quartz crucible by a CZ method, and has a carbon concentration of a portion excluding an outer peripheral portion. Is less than the lower limit of detection by the infrared absorption method (1 × 10 ¹⁵ atoms / cm ³ ), and the carbon concentration in the outer peripheral portion up to 5 mm from the outer periphery of the wafer is 2 × 10 ¹⁵ atoms / cm ³ or more. And

In the wafer manufacturing method of the present invention, a single crystal having a carbon concentration lower than the detection limit (1 × 10 ¹⁵ atoms / cm ³ ) by the infrared absorption method is pulled from a silicon melt in a quartz crucible by the CZ method, 5 from the outer circumference of the wafer cut from the crystal
The carbon concentration in the outer peripheral part up to mm is 2 × 10 ¹⁵ atom
It is characterized in that carbon is partially injected into the surface layer portion of the outer peripheral surface of the single crystal during or after the pulling so as to be s / cm ³ or more.

Carbon existing in a silicon single crystal promotes precipitation of interstitial oxygen and causes crystal defects due to oxygen precipitation. Therefore, it is generally treated as an impurity and its concentration is excluded except in special cases. Is controlled below the lower limit of detection by the infrared absorption method (1 × 10 ¹⁵ atoms / cm ³ ). However, the carbon can, on the one hand, fix dislocations and increase the mechanical strength of the wafer. Further, since it becomes an oxygen precipitation nucleus, it is possible to promote oxygen precipitation and enhance the gettering ability of heavy metals.

In the silicon single crystal wafer of the present invention, as shown by the broken line in FIG. 2, the carbon concentration in the outer peripheral edge portion is 2 × 10 ¹⁵ atoms / cm ³ or more,
Since the outer peripheral portion is reinforced and the strength reduction due to the lower oxygen concentration in this portion is compensated for, the occurrence of slip during heat treatment can be suppressed. Further, the carbon promotes the precipitation of oxygen in the outer peripheral portion of the wafer, so that the gettering ability of this portion is improved. Carbon concentration at the outer peripheral edge is 2 × 10 ¹⁵
If the amount is less than atoms / cm ³ , these effects cannot be sufficiently obtained.

By increasing the carbon concentration in the outer peripheral portion, the generation of crystal defects due to oxygen precipitation becomes a problem in this portion, but since the outer peripheral portion of the wafer is a region that does not become a device, the generation of crystal defects in this portion occurs. Does not really matter.

Regarding the upper limit of the carbon concentration at the outer peripheral edge, when the carbon concentration at this portion is extremely increased, the high concentration region extends inside the wafer and oxygen precipitates are generated in the active layer (wafer surface layer) of the device. However, the characteristic of the device becomes poor, so 1 × 10 ¹⁶ atoms / cm ³ or less is desirable.

In the wafer manufacturing method of the present invention, the operation of partially injecting carbon into the outer surface of the single crystal is
It may be performed during the pulling of the single crystal or after pulling the single crystal. An operation performed during pulling includes heating the single crystal being pulled from the outer surface side with a carbon heater. Examples of the operation performed after the pulling include heating the single crystal in a carbon atmosphere and heating by attaching carbon to the outer peripheral surface of the single crystal. The operation performed during pulling is more advantageous in terms of man-hours.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 is a vertical cross-sectional view showing an example of a single crystal manufacturing apparatus suitable for carrying out the present invention.

This apparatus pulls a single crystal 11 from a silicon melt 10 by a CZ method in a chamber,
A main chamber 1 and a pull chamber 2 are provided as chambers. A crucible 3 is arranged in the main chamber 1. The crucible 3 comprises an inner quartz crucible 3 a and an outer support crucible 3 b, and is mounted on the rotary support shaft 4. A heater 5 is arranged outside the crucible 3, and a heat insulating material 6 is arranged further outside the heater 5.

In the crucible 3, a carbon heater 7 for carbon injection is arranged on the surface of the melt 10. The carbon heater 7 has an annular shape and is located near the outer peripheral surface of the single crystal 11 passing through the inside thereof. Regarding the output of the carbon heater 7, it is considered that carbon is mixed in the silicon melt if it is too large, and the carbon concentration in the central portion as well as the outer peripheral portion of the single crystal becomes high. If the distance from the outer peripheral surface of the single crystal 11 to the carbon heater 7 is too large, carbon cannot be efficiently adhered, so 10 mm to 30 mm is appropriate. Regarding the arrangement level of the carbon heater 7, it is taken into consideration that it does not interfere with the diameter measurement of the single crystal 11.

In pulling the single crystal 10, the chamber is evacuated and the heater 5 is controlled to generate the silicon melt 10 in the crucible 3. The seed crystal at the lower end of the wire 8 hanging down into the main chamber through the pull chamber 2 is immersed in the melt 10, and the wire 8 is raised from this state while rotating to raise the single crystal 11 from the melt 10. . At this time, an inert gas is introduced from the pull chamber 2 into the main chamber 1 for scavenging.

The single crystal 11 pulled from the melt 10 is
Detection limit of carbon concentration by infrared absorption method (1 × 10 ¹⁵ atom
s / cm ³ ) or less. The single crystal 11 passes through the inside of the carbon heater 7 and is drawn into the pull chamber 2 while being gradually cooled. By operating the carbon heater 7, the single crystal 11 that is being pulled is injected with carbon in the outer peripheral surface layer portion while passing through the inside of the heater. The implantation amount can be changed by the output of the heater and the distance from the outer peripheral surface of the single crystal 11 to the heater.

The single crystal 11 that has been pulled is finished to have a predetermined outer diameter by cutting the outer surface for rounding and smoothing the outer surface. Then, the wafer is cut out from the single crystal 11.
The cut-out wafer has only a high carbon concentration in the outer peripheral portion. The carbon implantation amount in the pulling stage is controlled so that the diameter of the wafer is D and the carbon concentration in the region from the outer periphery to 5 mm is 2 × 10 ¹⁵ atoms / cm ³ or more. The carbon concentration in the portion other than the outer peripheral portion is below the detection limit (1 × 10 ¹⁵ atoms / cm ³ ) by the infrared absorption method.

The region where the carbon concentration is 2 × 10 ¹⁵ atoms / cm ³ or more is set to the region from the outer periphery of the wafer to 5 mm, because the carbon concentration in this region has a great influence on the occurrence of slip.

As described above, the operation of injecting carbon into the single crystal after pulling can be performed not only during pulling.

[0023]

[Example] Outer diameter after finishing cutting 12 inches, lower limit of carbon concentration detection by infrared absorption method (1 x 10 ¹⁵ atoms / cm ³ )
The following pulled silicon single crystal was heat-treated in a vacuum using a carbon heater to inject carbon into the surface layer portion of the outer peripheral surface.

The wafer cut out from the single crystal after carbon implantation was subjected to heat treatment under the two conditions A and B shown in Table 1 for the purpose of thermal oxidation. A is a conventional processing condition in which the occurrence of slip in the outer peripheral portion of the wafer is taken into consideration, and B is a processing condition in which efficiency is prioritized. Table 2 shows the results of investigating the slip occurrence rate of the wafer in each heat treatment and the carbon concentration in the region from the wafer outer periphery to 5 mm by the infrared absorption method.

[0025]

[Table 1]

[0026]

[Table 2]

The carbon concentration in the outer peripheral portion is 2 × 10 ¹⁵ atoms / cm
^For a wafer having a size of ³ or more, not only the occurrence of slips was suppressed by the method A, but also the occurrence of slips was suppressed by the method B, which has a high efficiency, so that the high efficiency heat treatment by the method B is possible.
On the other hand, in the conventional wafers whose carbon concentration in the outer peripheral edge portion was less than the detection limit, the occurrence of slip was not sufficiently suppressed even in the method A, and most of the conventional wafers were slipped in the method B, and were defective.

[0028]

As described above, the silicon single crystal wafer of the present invention partially increases the carbon concentration in the outer peripheral portion,
Since the decrease in mechanical strength due to the decrease in oxygen concentration in that portion is compensated for, slip is less likely to occur even in rough heat treatment that prioritizes efficiency, and it is possible to significantly reduce manufacturing costs from both aspects of yield improvement and efficiency improvement. Further, the carbon can be expected to improve the gettering ability of the outer peripheral portion.

In the wafer manufacturing method of the present invention, since the carbon concentration in the outer peripheral portion is increased by the carbon injection from the outside, the above-mentioned low-priced wafer of the present invention can be easily manufactured without depending on the complicated operation of pulling conditions. It is possible to reduce the manufacturing cost of the wafer.

[Brief description of drawings]

FIG. 1 is a schematic view showing pulling of a single crystal by a CZ method.

FIG. 2 is a graph showing an oxygen concentration distribution and a carbon concentration distribution in a radial direction of a wafer.

FIG. 3 is a vertical sectional view showing the structure of an example of a single crystal manufacturing apparatus suitable for carrying out the present invention.

[Explanation of symbols]

 1 Main Chamber 2 Pull Chamber 3 Crucible 3a Quartz Crucible 5 Heater 7 Carbon heater for carbon injection

Claims (2)

[Claims] 1. A wafer sampled from a silicon single crystal pulled from a silicon melt in a quartz crucible by the CZ method, wherein the carbon concentration of the portion excluding the outer peripheral portion is the lower limit of detection by the infrared absorption method (1 × 10 ¹⁵ A silicon single crystal wafer having a concentration of atoms / cm ³ ) or less and a carbon concentration of 2 × 10 ¹⁵ atoms / cm ³ or more in an outer peripheral edge portion up to 5 mm from the outer periphery of the wafer. 2. The lower limit of detection of carbon concentration from the silicon melt in the quartz crucible by the CZ method (1 × 10 6) by the infrared absorption method.
A single crystal of ¹⁵ atoms / cm ³ ) or less is pulled up, and is being pulled up or pulled up so that the carbon concentration in the outer peripheral portion up to 5 mm from the outer periphery of the wafer cut from the single crystal is 2 × 10 ¹⁵ atoms / cm ³ or more. A method for producing a silicon single crystal wafer, which comprises partially injecting carbon into the outer peripheral surface layer portion of a single crystal thereafter.