JP2003270167A - Method for evaluating grown-in defect density of silicon wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for evaluating a grown-in defect density of a silicon wafer for easily evaluating a volume density of the grown-in defect such as COP and the like existing in the silicon wafer without using special measurement equipment. <P>SOLUTION: A plurality of silicon wafers each taken from an adjacent area of identical silicon single crystals produced by the Czochralski method are mirror polished. After forming an oxide film having a respective film thickness on each surface of the plurality of the silicon wafers, a defect of each silicon wafer surface is detected as a light scattering body by a light scattering type surface inspection apparatus, and a number N of the light scanning bodies is measured. The volume density D (cm<SP>-3</SP>) of the grown-in defect existing in the silicon wafer is calculated by the equation (1): D=N/((R-E)<SP>2</SP>π(d/2+A)10<SP>-7</SP>), wherein R denotes a radius of the silicon wafer (cm), E denotes a edge cut (cm), d denotes a thickness of the oxide film (nm), and A denotes an apparatus coefficient (nm). <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating the grown-in defect density of a silicon wafer, and more specifically, it was obtained by the Czochralski (CZ) method using a light scattering type surface inspection device. The present invention relates to a method for evaluating the grown-in defect density of a silicon wafer, which evaluates the volume density of the grown-in defect existing in the silicon wafer.

[0002]

2. Description of the Related Art In recent years, with the highly integrated circuit elements,
Device processes such as gate oxide films are becoming finer and thinner. Therefore, even small defects existing on the surface of the silicon wafer on which the device is formed and on the surface layer have become factors that have a great influence on the device performance and the yield. In particular, COP (Crystal Originated Particl)
The very small defect called e) has come to be regarded as a problem from the viewpoint of device performance, and accurate and simple detection and evaluation of COPs existing on the surface of the silicon wafer and on the surface layer have been required.

This COP defect is formed during pulling of a single crystal by the CZ method, and is a so-called grain
It is a type of Grown-in defect. The formation of COP defects depends on the pulling conditions, and most of them are 0.1 to 0.
It has a defect size of about 2 μm and is considered to be a cluster of atomic vacancies.

Conventionally, as a method for obtaining the density of the grown-in defects such as COP existing inside the silicon wafer, a particle counter is used to detect the grown-in defects exposed on the mirror-finished wafer surface. However, a method of comparing in terms of surface density has been generally adopted.

[0005]

However, the above method is to evaluate the defect density two-dimensionally, that is, it is not possible to obtain the volume density conversion, that is, to obtain a three-dimensional evaluation value. Therefore, especially when three-dimensional defect density becomes a problem when analyzing the cause of device failure,
There was a problem that it was difficult to perform accurate analysis.

Therefore, in order to supply a high quality silicon wafer, the CO existing inside the silicon wafer is
There has been a strong demand for a method capable of easily evaluating a grown-in defect such as P.

The present invention has been made in order to solve the above technical problems, and the volume density of grown-in defects such as COP existing in a silicon wafer is not measured without using a special device. It is an object of the present invention to provide a method for evaluating the grown-in defect density of a silicon wafer, which can be easily evaluated.

[0008]

The method for evaluating the grown-in defect density of a silicon wafer according to the present invention comprises a plurality of mirror surfaces obtained from adjacent portions of the same silicon single crystal manufactured by the Czochralski method. With respect to the processed silicon wafer, after forming oxide films having different film thicknesses on the surface of the wafer, the surface defects of each silicon wafer are detected as a light scatterer by using a light scattering type surface inspection device, The number N is measured, and the volume density D of the grown-in defects existing in the silicon wafer is calculated by the equation (1).
It is characterized by calculating (cm ⁻³ ). D = N / ((R−E) ² π (d / 2 + A) × 10 ⁻⁷ ) ... (1) (where R is the radius of the silicon wafer (cm), E is the edge cut (cm), and d is The oxide film thickness (nm) and A are device constants (nm).) According to the above evaluation method, after forming an oxide film on the wafer surface, a special device is used only by measuring surface defects using a particle counter. Since the volume density of the grown-in defects can be calculated without performing measurement or the like by, it is possible to easily evaluate.

It is preferable that the device constant A be a value at which the standard deviation of the volume density D (cm ^-3 ) of the grown-in defects obtained from the equation (1) becomes minimum at different oxide film thicknesses. The device constant A is determined by the defect size distribution, the absorption of the laser light used in the device (particle counter) in the Si layer, the surface condition of the wafer, the detection limit of the device, etc., and this constant is calculated arithmetically. Since it is very difficult to do so, it was decided to simply obtain it from the measured value.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail below. A method for evaluating a grown-in defect density of a silicon wafer according to the present invention is a method of evaluating a plurality of mirror-finished silicon wafers obtained from adjacent portions of the same CZ silicon single crystal, in which the film thickness is After forming different oxide films, the surface defects of each silicon wafer are detected as light scatterers by using a light scattering type surface inspection device, and the number N thereof is measured. Volume density of existing grown-in defects D
It is characterized by calculating (cm ⁻³ ). D = N / ((R−E) ² π (d / 2 + A) × 10 ⁻⁷ ) ... (1) (where R is the radius of the silicon wafer (cm), E is the edge cut (cm), and d is The oxide film thickness (nm) and A are device constants (nm).) In the evaluation method according to the present invention, since the distribution of the grown-in defects existing in the CZ silicon wafer is uniform in the thickness direction, After forming an oxide film on the wafer surface, surface defects are measured by a particle counter, and the volume density of grown-in defects can be easily calculated from each oxide film thickness and the number of detected surface defects. is there.

Usually, when the surface of a silicon wafer is analyzed and measured using a light scattering type surface inspection device such as a particle counter, foreign matter existing on the surface and in the range of several nm of surface layer is regarded as a light scattering body (LPD). To be detected. Therefore, the grown-in defect, which is a cavity defect, becomes a pit-shaped concave defect when exposed on the surface, and this is detected as LPD by the particle counter.

When the silicon wafer is oxidized to form an oxide film (SiO ₂ ) on the surface, pit-shaped concave defects existing on the surface of the silicon wafer and silicon (Si) which has become an oxide film The grown-in defects existing inside the surface layer are transferred to the SiO ₂ / Si interface and appear as pits at this interface. Since the laser light used in the particle counter is hardly attenuated in SiO ₂ , the laser light is scattered by the pit-like defects existing at the SiO ₂ / Si interface and detected as LPD.

At this time, the volume ratio of Si to SiO ₂ is 1:
Since it is 2, the silicon (Si) layer having a thickness of ½ of the thickness of the formed oxide film is changed to SiO ₂ by oxidation. Therefore, after forming an oxide film on the surface of a silicon wafer, the particle counter detects and measures the LPD on the oxide film surface, and calculates the number by multiplying the sum of 1/2 of the oxide film thickness and the device constant by the effective measurement surface area. The volume density of the grown-in defects can be easily calculated by dividing by the divided volume.

The detailed procedure of the evaluation method according to the present invention will be described below. First, a plurality of silicon wafers obtained from adjacent portions of the same CZ silicon single crystal are mirror-polished to be sufficiently clean, and then oxide films having different film thicknesses are formed on the surfaces of these silicon wafers. Form. Then, using a particle counter, the surface defects of each wafer having an oxide film formed thereon are detected as LPD, and the number N thereof is measured. Then, according to the equation (1), the volume density D (c of the grown-in defects existing in the silicon wafer
m ^-3 ) is calculated. D = N / ((R−E) ² π (d / 2 + A) × 10 ⁻⁷ ) ... (1) (where R is the radius of the silicon wafer (cm), E is the edge cut (cm), and d is The oxide film thickness (nm) and A are device constants (nm).)

Here, the device constant A is determined by the size distribution of defects, absorption of laser light used in the device (particle counter) in the Si layer, surface condition of the wafer, detection limit of the device, etc. It is very difficult to calculate the constant arithmetically. Therefore, in the present invention, this device constant A is
Volume density D of grown-in defects obtained from equation (1)
It is preferable that the standard deviation of (cm ⁻³ ) is a minimum value. To more easily obtain this device constant A, C
Utilizing the fact that the distribution of grown-in defects existing in the Z silicon wafer is uniform in the thickness direction, specifically, the following method can be adopted.

First, assuming that the device constant A is A ′ in advance, the number N of surface defects (light scatterers) measured for each different oxide film thickness is substituted into the equation (1), and the defect density is provisionally determined. The value D ′ is obtained for each oxide film thickness. Then, while changing the assumed value A ′ of the device constant, a temporary value D ′ of the defect density with respect to the assumed value is obtained for each oxide film thickness in the same manner as described above. Then, the defect density becomes almost equal in all the oxide film thicknesses, that is, A ′ when the standard deviation becomes minimum.
Is determined as a device constant A. Also, the average value of the defect densities in each oxide film thickness calculated using the determined device constant A is determined as the volume density D of the grown-in defects in the silicon ingot of this lot.

In the evaluation method according to the present invention, the target silicon wafer is a silicon wafer obtained from adjacent portions of the same silicon single crystal pulled by the CZ method. Further, as the silicon wafer, a clean silicon wafer whose surface is mirror-finished, is sufficiently washed, and has almost no dust or other foreign matter on the surface is used.
Since the lower limit detection size of the LPD such as a particle counter which is a laser light scattering type surface inspection device depends on the smoothness and cleanliness of the wafer surface, the surface is smoothed and cleaned by mirror finishing. It is preferable.
This mirror surface processing can be performed by mechanochemical polishing or the like in addition to ordinary mechanical polishing.

In the present invention, the plurality of mirror-finished silicon wafers are subjected to oxidation heat treatment to form oxide films having different film thicknesses. The thickness of the oxide film is 20 to 30.
The range of 0 nm is preferable from the viewpoints of ensuring the uniformity of the oxide film to be formed, the accuracy of LPD detection and measurement by transmitting laser light, and the like.

The oxide film is formed, for example, by arranging the wafer in a batch furnace such as a resistance heating type heat treatment furnace or a furnace such as a rapid heating / rapid cooling apparatus and mixing oxygen gas, water vapor, and oxygen gas with hydrogen gas. It is performed by heating and oxidizing treatment in an atmosphere such as a combustion gas. The heating temperature, processing time, etc. at this time are appropriately set according to the type and state of the atmospheric gas, the film thickness of the oxide film to be formed, and the like.

In the present invention, for each silicon wafer having an oxide film formed as described above, LPD is detected using a light scattering type surface inspection device and the number thereof is measured. As a particle counter, which is a light-scattering surface inspection device, the lower detection limit of the LPD size is 0.0.
A laser light scattering type surface inspection device of about 9 μm is preferably used from the viewpoint of detection accuracy and the like.

As described above, according to the evaluation method of the present invention, the grown-in defects existing on the mirror-finished CZ silicon wafer can be measured only by the particle counter without performing the measurement using the special device. The volume density of can be easily obtained. Therefore, it is useful for a simple inspection for quality control of a silicon wafer in a semiconductor manufacturing process.

[0022]

EXAMPLES The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited by the following examples. [Examples] Oxide film thicknesses d = 0, 15, 24, 38, 21 on the surfaces of a plurality of mirror-polished silicon wafers having a diameter of 20 cm obtained from the same CZ silicon single crystal, respectively.
An oxide film of 0 nm was formed. A laser light scattering particle counter (SFS6200: Tencor
LPD of 0.108 μm or more was detected with the edge cut E = 0.6 cm, and the number N thereof was measured. The results are shown in Table 1.

[0023]

[Table 1]

Here, the volume density D of the grown-in defect
(Cm ⁻³ ) is represented by the following formula. D = N / {(10−0.6) ² π (d / 2 + A) × 10
^-7 } At this time, the device constant A = 20, 30, 40, 60, 10
The volume density D in each oxide film thickness when changed to 0 was calculated. The results are shown in Table 2.

[0025]

[Table 2]

As shown in Table 2, when A = 40, the average value of D in each oxide film thickness is about 1.2 × 10 ⁶ cm ^-3.
It was confirmed that the standard deviation / average value was the smallest and was almost constant. Therefore, the volume density of grown-in defects in this silicon wafer is 1.2 × 10 ⁶ cm.
^-3 is obtained.

[0027]

As described above, by using the evaluation method according to the present invention, the volume density of the grown-in defects such as COP existing in the silicon wafer can be measured without using a special device. It can be easily obtained only by the measurement by the counter. Therefore, the evaluation method according to the present invention is useful for a simple inspection for quality control of a silicon wafer in a semiconductor manufacturing process, and eventually contributes to providing a high-quality silicon wafer.

Continued front page    F-term (reference) 2G051 AA51 AB02 AB06 AB07 BA10                       CB05 EA16 EC03                 2G059 AA05 BB10 BB16 EE02 GG01                       MM01 MM02

Claims (2)

[Claims] 1. A plurality of mirror-finished silicon wafers obtained from adjacent portions of the same silicon single crystal manufactured by the Czochralski method, wherein an oxide film having a different film thickness is formed on the surface of the wafer. After the formation, the surface defect of each silicon wafer is detected as a light scatterer by using a light scattering type surface inspection device, and the number N
Is calculated, and the volume density D (cm ⁻³ ) of the grown-in defects existing in the silicon wafer is calculated by the formula (1), the method for evaluating the grown-in defect density of a silicon wafer. D = N / ((R−E) ² π (d / 2 + A) × 10 ⁻⁷ ) ... (1) (where R is the radius of the silicon wafer (cm), E is the edge cut (cm), and d is The oxide film thickness (nm) and A are device constants (nm).) 2. The apparatus constant A is set to a value at which the standard deviation of the volume density D (cm ⁻³ ) of the grown-in defects obtained from the equation (1) becomes minimum in different oxide film thicknesses. The silicon wafer clone according to claim 1.
In-defect density evaluation method.