JPH08115919A - Method of processing semiconductor substrate - Google Patents

Abstract

PURPOSE: To improve electric property such as the breakdown strength of an oxide film made on a semiconductor substrate, and growing single-crystal silicon at a specified pull-up speed and slicing it, using CZ method or MCZ method, so as to form a semiconductor substrate, and performing heat treatment under specified conditions in reductive or inert atmosphere. CONSTITUTION: Single-crystal silicon is grown at a pull-up speed of 1.3mm/min. or over using either CZ method or MCZ method, and it is sliced into semiconductor substrates. The semiconductor substrates are heat-treated for 30 min. or more at a temperature of 1100 deg.C or over in either reductive or inert atmosphere. Single-crystal silicon of 150mmϕ, n-type, and about 15×10<17> atoms/cm<3> in concentration of interlattice oxygen is pulled up at a speed of 1.3mm/min, to provide substrates. Moreover, the atmosphere shall be mixed gas among H2 , He, Ne, Ar, Kr, and Xe, or inert atmosphere by any one among Ne, Ar, Kr, and Xe.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for processing a semiconductor substrate, and particularly to a silicon DZ (Denuded) having excellent crystallinity.
Zone) wafer manufacturing method.

[0002]

2. Description of the Related Art Conventionally, it is necessary to improve the electrical characteristics of a semiconductor substrate, particularly the electrical characteristics of a semiconductor substrate related to the oxide film breakdown voltage characteristics of an oxide film formed on a silicon semiconductor substrate and TDDB (Time Dependent Dielectric Breakdown) characteristics. The following two methods are mainly known as methods for achieving this.

(1) The first method is to grow a silicon single crystal such as Czochralski pulling method (CZ method).
This is a method of using a semiconductor substrate formed from a single crystal pulled at a lower speed (about 0.4 mm / min) than a normal pulling speed (about 1.0 mm / min).

(2) The second method is a method of heat-treating a silicon semiconductor substrate formed of a single crystal at a normal pulling rate at a high temperature (about 1100 to 1250 ° C.) in an inert gas or a reducing gas. is there.

[0005]

[Problems to be Solved by the Invention]
The two conventional methods have the following problems. That is, (1) In the first method, the crystal pulling capacity is remarkably reduced by the slow pulling (50% in the case of the normal pulling crystal).
%), And the cost of the semiconductor substrate manufactured from this crystal increases as compared with a normal semiconductor substrate.

(2) Further, in the second method, a step of subjecting a semiconductor substrate manufactured by a usual method to a high temperature heat treatment in an inert gas or a reducing gas is added. However, there is a problem in that the cost of the substrate increases (usually the cost increases by about 1.3 to 1.5 times that of the semiconductor substrate). Furthermore, the crystallographic characteristics of the semiconductor substrate and the electrical characteristics of the MOS diode and the like due to the oxide film formed thereon are not perfect and there is a problem that there is still room for improvement. For example, as shown in FIG. 4, the oxide film withstand voltage characteristic has a problem that the conventional product has a poor yield rate. This tendency becomes more remarkable as the oxide film thickness _tox increases,
FIG. 4 shows the case of _tox = 25 nm, but _tox = 55 nm.
Then, there was a problem that it would be 90% or less.

In view of the above problems, the present invention provides a semiconductor substrate capable of improving electrical characteristics such as breakdown voltage of an oxide film formed on the semiconductor substrate more than in the prior art.
It aims at providing at a lower cost than in the prior art.

[0008]

In order to solve the above problems, the present invention provides a CZ method or a magnetic-field-applied Czochralski method.
: Hereinafter, referred to as MCZ method), 1.3 mm / mi
A silicon single crystal is grown at a pulling rate of n or more, and the single crystal is sliced to form a semiconductor substrate (semiconductor wafer), and the semiconductor substrate is subjected to 1100 in either a reducing atmosphere or an inert atmosphere. The method is a method for heat treating a semiconductor substrate, in which heat treatment is performed for 30 minutes or more at a temperature of ℃ or more.

Preferably, as shown in FIG. 1, when plotting the density distribution of a precipitate or the like against the diameter of the precipitate or the like, the diameter of the precipitate or the like is divided in units of 1 nm, that is, the horizontal axis represents When viewed in units of 1 nm, the density of precipitates in each section having a diameter of 30 nm (critical diameter) or more is 2 ×
It is characterized in that a semiconductor substrate of 10 ⁵ pieces / cm ³ or less is selected, and then heat treatment is performed only on the selected specific semiconductor substrate. That is, diameter 30 to 31
nm, etc., such as those having a diameter of 31 to 32 nm, those having a diameter of 32 to 33 nm, etc.
A semiconductor substrate of x10 ⁵ / cm ³ or less is selected.

More preferably, the reducing atmosphere is about 1.
00% H ₂ , or H ₂ and He, Ne, Ar, K
It is a mixed gas with at least one of r and Xe, or the inert atmosphere is one of He, Ne, Ar, Kr, and Xe alone, or a mixed gas including at least two of these. Is.

[0011]

According to the features of the present invention, by pulling a single crystal at a higher speed than in the prior art and growing it in a short time, it is possible to reduce costs such as light heat and labor costs. Further, the density distribution can be such that the diameter of the precipitate or the like in the pulled single crystal (ingot) is high with a predetermined size (critical diameter) or less. By selecting and heat-treating a semiconductor substrate having a high density distribution of precipitates or the like having a predetermined size or less, the scatterer density in the semiconductor substrate is efficiently reduced, and the crystallinity is improved.

FIG. 2 shows a precipitate or a precipitation nucleus from any size (diameter), which is obtained by performing heat treatment at 1200 ° C. for 1 hour in a 100% H ₂ atmosphere using a conventional substrate at a normal pulling rate. Is a result of an examination using an IR tomography method before and after heat treatment on the same substrate. It is understood that the precipitates or the precipitation nuclei having a size smaller than the size of about 30 nm suddenly shrink due to the heat treatment under the above conditions. It is considered that this is because the critical diameter for the heat treatment at 1200 ° C. is about 30 nm. The higher the heat treatment temperature, the larger the critical diameter, and the lower the heat treatment temperature, the smaller the critical diameter. Therefore, paying attention to the critical diameter that is determined by the heat treatment temperature, select a semiconductor substrate that has a density distribution that contains a high density of precipitates and the like having a critical diameter or less before the heat treatment, and heat-treat this semiconductor substrate to crystallize the semiconductor substrate. It has high efficiency, high efficiency, and high yield.

In the CZ method, 1.3 mm / min
If the pulling speed is higher than the above, the density distribution of precipitates with a critical diameter of 30 nm or less in the single crystal (ingot) increases, so this selection becomes easy.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In this embodiment, 150 mm
φ, n-type, interstitial oxygen concentration 15 × 10 ¹⁷ atoms / c
A single crystal of about m ³ was pulled at a pulling rate of 1.3 mm / min, and a substrate was produced from this CZ crystal. Since the pulling speed is usually 1.0 mm / min, the pulling speed is 1.3 times higher.

First, As grow (As grow)
n) FIG. 1 shows the results of examination using an electron microscope (TEM) to find out how the size and density of precipitates or precipitation nuclei in the crystal change due to the difference in crystal pulling rate. In FIG. 1, the normal pulling speed of the conventional example is 150.
mmφ, n-type, interstitial oxygen concentration 15 × 10 ¹⁷ atoms
The results of the substrate made of CZ crystal of about / cm ³ are also shown at the same time. When the precipitate or the precipitation nucleus is regarded as a sphere, the density of the precipitate or the precipitation nucleus is higher in the high speed pulling product than in the normal pulling product in the diameter range of 5 to 20 nm, and when the diameter is 30 nm or more. On the contrary, it can be seen that the density of the precipitates or precipitation nuclei is higher in the normally pulled product.

Next, using these substrates, H ₂ 100%
Heat treatment is performed in an atmosphere at 1200 ° C. for 1 hour. FIG.
Is the result of evaluation of the infrared scatterer density in the depth direction profile using the IR tomography method. For reference, the results of the conventional substrate are also shown in FIG. Although the scatterer density of the high speed pulling product (this example) and the normal pulling product (conventional example) is the same at a deep place from the surface, the scatterer density of the high speed pulling product is lower in the surface layer part. Recognize.

The samples used in this example are n-type and 15-type.
Although it is 0 mmφ, it can be applied to p-type and 200 mmφ. As described above, the type of single crystal used, the pulling rate, the heat treatment atmosphere, the heat treatment temperature, the heat treatment time, and the like can be modified without departing from the technical scope of the present invention. The type of the single crystal may be the MCZ method or the continuous pulling method, and the pulling rate is 1.3 mm / min to 1.
Any value between 7 mm / min may be used. 2 mm / m
In may be used, and a higher pulling rate is preferable. The heat treatment temperature may be 1200 ° C. for 1 hour, 1100 ° C. for 8 hours, 1150 ° C. for 3 hours, or 1250 ° C. for 40 minutes. The atmosphere is H ₂ , He, Ne, A
Mixed gas of r, Kr, Xe, Ne, Ar, Kr, X
An inert atmosphere of any one of e may be used. A mixed gas composed of two or more of these, such as a combination of He and Ne, may be used. More preferably, the temperature rising process up to the predetermined heat treatment temperature is performed with an inert gas such as Ar, and the heat treatment at the predetermined heat treatment temperature is preferably performed in a reducing atmosphere such as 100% H ₂ .

[0018]

By using the substrate according to the embodiment of the present invention, M
FIG. 4 compares the non-defective rate when the OS capacitor is manufactured with the conventional technique. FIG. 4 plots the results according to the example of the present invention and the cases where the normal pulling product is heat-treated in an H ₂ atmosphere and the high-speed pulling crystal and the normal pulling crystal are not heat-treated. The conditions of the sample shown in FIG. 4 are as follows: oxide film thickness 25 nm, polysilicon gate, area 10
It is a MOS capacitor of mm ² . In the determination of the defect in FIG. 4, when the electric field applied to the oxide film was 8.0 MV / cm, the gate current was 1.0 × 10 ⁻⁵ [A] or more, and the defect was determined. When the heat treatment is performed in the H ₂ atmosphere, the yield rate of both samples is 90% or more regardless of the pulling rate, and it is understood that the product of this example is better among them.

As described above, according to the present invention, the scatterer density in the semiconductor substrate is reduced and the characteristics of the MOS capacitor formed on the semiconductor substrate are improved.

Further, according to the present invention, the high-speed pulling crystal has a higher pulling speed than the normal pulling crystal and thus has higher production efficiency, and has a lower cost than the normal pulling crystal. Therefore, by using this point, even if a high temperature heat treatment step is added after the pulling, it is possible to provide the product of the present invention at a cost equal to or lower than that of a substrate (without heat treatment) usually manufactured from a pulled crystal.

[Brief description of drawings]

FIG. 1 is a change diagram showing a difference in a density distribution of a precipitate or the like in a crystal as-grown (As grown) depending on a crystal pulling rate.

FIG. 2 is a diagram showing the size dependence of precipitates or precipitation nuclei shrinkable by heat treatment at 1200 ° C. in a H ₂ 100% atmosphere.

FIG. 3 This example (high speed pulling + heat treatment in H ₂ atmosphere) and conventional example (normal pulling + heat treatment in H ₂ atmosphere)
Depth profile of infrared light scatterer density at.

[FIG. 4] This example (high speed pulling + heat treatment in H ₂ atmosphere), conventional example (normal pulling + heat treatment in H ₂ atmosphere),
FIG. 8 is a diagram showing the results of evaluation of the oxide film breakdown voltage of a MOS capacitor using a high speed pulling product without heat treatment and a normal pulling product without heat treatment.

Claims (5)

[Claims] 1. Using either the CZ method or the MCZ method,
A silicon single crystal is grown at a pulling rate of 1.3 mm / min or more, a semiconductor substrate is formed by slicing the single crystal, and the semiconductor substrate is subjected to 1100 in either a reducing atmosphere or an inert atmosphere. 30 at temperatures above ℃
A method for treating a semiconductor substrate, characterized by performing heat treatment for not less than a minute. 2. In the semiconductor substrate, the diameters of precipitates and precipitation nuclei (hereinafter referred to as “precipitates, etc.”) are divided in units of 1 nm, and the density of the precipitates, etc. in each division having a predetermined diameter or more is a predetermined density. The semiconductor substrate processing method according to claim 1, wherein the following semiconductor substrate is selected and the heat treatment is performed. 3. The reducing atmosphere is substantially 100% H ₂ or a mixed gas of H ₂ and at least one of He, Ne, Ar, Kr and Xe. A method for processing a semiconductor substrate as described above. 4. The inert atmosphere is He, Ne, Ar,
The method for processing a semiconductor substrate according to claim 1 or 2, wherein the method comprises at least one of Kr and Xe. 5. The predetermined diameter is 30 nm, the predetermined density is 2 × 10 ⁵ pieces / cm ³ , and the substrate temperature is 120.
The method for treating a semiconductor substrate according to claim 2, wherein the heat treatment is performed at 0 ° C.