JP2715832B2 - Single crystal silicon substrate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single crystal silicon substrate, and more particularly to a single crystal silicon substrate used as a substrate for an integrated circuit device such as an LSI.

[0002]

2. Description of the Related Art At present, most of single-crystal silicon substrates for forming substrates of integrated circuits such as LSIs use single-crystal silicon pulled up by the Czochralski method (hereinafter referred to as CZ method). It is manufactured. The CZ method uses a carbon heater in a quartz crucible for approximately 1500.
A seed crystal attached to the tip of a pull-up shaft is brought into contact with the silicon melt heated and melted at ℃, and the pull-up is performed while rotating the pull-up shaft to solidify the silicon melt as a single crystal and grow. It is a way to make it. When the CZ method is used, a part of the quartz crucible is dissolved in a silicon melt, and oxygen in quartz (SiO ₂ ) constituting the crucible is eluted. Contains about 10 ¹⁸ atoms / cm ³ of oxygen.

On the other hand, a typical temperature of thermal oxidation in an LSI manufacturing process is, for example, about 1000 ° C.
Oxygen solid solubility in single crystal silicon substrate at ℃ is about 3 ×
It is 10 ¹⁷ atoms / cm ³ . Therefore, the oxygen contained in the single-crystal silicon substrate is always in a supersaturated state, and the oxygen is easily precipitated.

[0004] The function of oxygen in single crystal silicon is complex and diversified. When the oxygen is present between silicon crystal lattices, it has the effect of fixing dislocations,
This has the effect of suppressing the warpage of the single crystal silicon substrate during the heat treatment. When the oxygen is precipitated and changed to SiO ₂ , silicon atoms are released due to volume expansion to cause stacking faults, or, when the strain is large, micro defects such as punch-out dislocations.

In the case where the minute defect exists only in the interior sufficiently separated from the surface of the single crystal silicon substrate, the minute defect adsorbs contaminants such as heavy metals attached to the surface of the single crystal silicon substrate. As a result, a so-called gettering action is performed which is excluded from the active region of the element. Therefore, the excess oxygen inside the single crystal silicon substrate is high quality L
It is extremely useful in manufacturing SI. On the other hand, if the minute defect exists in the active region of the element near the surface of the single crystal silicon substrate, it causes a leak current to increase. Therefore, excess oxygen on the surface of the single crystal silicon substrate is harmful in manufacturing a high quality LSI.

Therefore, as a pretreatment for manufacturing an LSI, a defect-free layer (Denuded Zone) is formed on the surface of the single-crystal silicon substrate, and a defect layer (Intrinsic Zone) is formed inside the single-crystal silicon substrate.
c Gettering Zone) is being performed.
That is, a single crystal silicon substrate obtained by slicing a single crystal silicon ingot is subjected to a heat treatment at a high temperature of, for example, about 1100 ° C. in a nitrogen atmosphere to diffuse oxygen outward and reduce the oxygen concentration near the surface. At the same time, the oxygen precipitate is dissolved again. Then for example 700
A heat treatment is performed at a low temperature of about ° C. to form a precipitate of oxygen inside a single crystal silicon substrate.

[0007]

In the single-crystal silicon produced by the above-mentioned CZ method, a high-temperature stable oxygen precipitate is often already formed at the time of crystal pulling. Therefore, even if a heat treatment at, for example, about 1100 ° C. is performed for the purpose of forming a defect-free layer on the surface of the single-crystal silicon substrate, the oxygen precipitates are unlikely to re-dissolve in single-crystal silicon. There is a problem that the precipitate becomes a minute defect and remains in the active region of the device, and it is difficult to improve the withstand voltage characteristics and the like of the oxide film formed on the single crystal substrate.

The present invention has been made in view of the above problems, and provides a single-crystal silicon substrate in which the formation of oxygen precipitates stable at high temperatures is suppressed and the percentage of minute defects in the active region of the device is extremely low. It is intended to be.

[0009]

Single crystal silicon substrate according to the present invention in order to achieve the above object, according to an aspect of, in a single crystal silicon substrate which is manufactured using the single-crystal silicon pulled by the CZ method or the like, at 6K it is characterized by the infrared absorption coefficient at 1104cm ^-1 vicinity of is 0.2 cm ^-1 or less.

[0010]

In general, it is known that a nucleus for promoting precipitation (hereinafter referred to as a precipitation nucleus) is necessary to precipitate oxygen, which is dissolved in supersaturation between crystal lattices of single crystal silicon, as an oxygen precipitate. Have been.

As a result of cooling the single crystal silicon to 8K or less by the inventor and conducting an investigation by infrared spectroscopy, the carbon / oxygen complex at a high temperature stable at a wave number of about 1104 cm- ¹ mixed with other precipitation nuclei was obtained. Precipitation nuclei of the body were found, and it was found that reducing the infrared absorption coefficient of the carbon / oxygen composite to 0.2 cm- ¹ or less improved the oxide film breakdown voltage characteristics.

It is considered that the carbon / oxygen composite is formed by combining carbon decomposed by the above-described heater for heating and oxygen decomposed by the above-mentioned quartz crucible. In addition, an oxygen precipitate obtained by depositing a carbon / oxygen complex that is stable at a high temperature as a precipitation nucleus is more stable at a higher temperature than another oxygen precipitate, and it is difficult to form a solid solution in a heat treatment at about 1100 ° C. Conceivable. According to the single crystal silicon substrate of the present invention, the infrared absorption coefficient at around 1104 cm ^{-1 at} low temperature is 0.2 cm in a single crystal silicon substrate manufactured using single crystal silicon pulled up by the CZ method or the like. ⁻¹ or less, the formation of precipitation nuclei composed of a carbon-oxygen complex is suppressed, and the formation of oxygen precipitates stable at high temperatures is suppressed. And even if there are other oxygen precipitates that do not use the carbon / oxygen complex as precipitation nuclei, they can easily form a solid solution, and a single-crystal silicon substrate with extremely low abundance of micro defects in the active region of the device can be obtained. Becomes

[0013]

Examples and Comparative Examples Hereinafter, examples and comparative examples of a single crystal silicon substrate according to the present invention will be described with reference to the drawings.
In the production of the single crystal silicon substrate according to the example, the formation amount of the carbon / oxygen composite was controlled by pulling up by a CZ method at a pulling speed of about 1.3 mm / min, and the diameter was about 125 mm.
Was used. A wafer having a thickness of about 2 mm was cut out of the single crystal silicon, and both surfaces of the wafer were mirror-polished to prepare a measurement sample for spectral analysis. Next, the measurement sample was cooled to 6K, and an infrared absorption spectrum was measured using a Fourier transform infrared spectrometer (hereinafter, referred to as FT-IR).
^The concentration of the carbon-oxygen complex was evaluated based on the peak intensity near ^-1 . As a result, the absorption coefficient of the carbon-oxygen composite in the single-crystal silicon substrate according to the example was 0.15 cm ^-1 . The interstitial oxygen concentration (hereinafter referred to as [Oi]) in the single crystal silicon substrate evaluated by FT-IR was 1.5 × 10 ¹⁸ atoms /
cm ³ (conversion coefficient = 4.81 × 10 ¹⁷ atoms / c
m ² ) and the substitutional carbon concentration (hereinafter referred to as [Cs]) are at the detection limit (detection limit = 5.0 × 10 ¹⁵ atoms / cm).
³ ) It was the following.

Next, a thickness of about 0.1 mm is obtained from the single crystal silicon.
An 8 mm wafer is cut out, and one side of the wafer is mirror-polished and washed, and then subjected to a heat treatment at 950 ° C. in an oxygen atmosphere using a diffusion furnace. A film was formed. Next, LPCVD
(Low Pressure Chemical Vapor Deposition) 6% while flowing 20% He based SiH ₄ gas
Vapor deposition was performed at 30 ° C. to form a polycrystalline silicon layer having an electrode thickness of about 4000 ° on the oxide film of the wafer. Next, while flowing POCl ₃ , O ₂ , and N ₂ gas, 90
Heat treatment was performed at 0 ° C. to diffuse phosphorus into the polycrystalline silicon layer. Further, in order to remove an oxide film on the polycrystalline silicon formed on the back surface of the wafer, HF (50
%): Etching was performed for about 8 seconds using an aqueous hydrogen fluoride solution of H ₂ O = 1: 10. Thereafter, 254 electrodes were formed on the surface of the wafer by photolithography to produce a single crystal silicon substrate.

FIG. 1 is a schematic plan view showing an in-plane distribution of an oxide film breakdown voltage characteristic in a single crystal silicon substrate according to an embodiment. The oxide film breakdown voltage characteristics are defined as breakdown when a current of 1 mA flows between the electrodes, and black squares and 2-5 MV when the electric field strength at the time of the breakdown is 0-2 MV / cm 2.
/ cm, × mark for 5-8 MV / cm, 8 MV / c
The evaluation was performed by representing the cases of m or more with □ marks.

As is clear from FIG. 1, in the single crystal silicon substrate according to the embodiment, the number of elements that did not break down at an electric field strength of 8 MV / cm was 206 out of 254 elements, and the yield rate was about 81%. Met.

As a comparative example, approximately 1.1 mm / min was used to control the amount of carbon / oxygen complex formed by the CZ method.
A single-crystal silicon substrate was produced in the same manner as in the above-described embodiment, using single-crystal silicon formed to have a diameter of about 125 mm by using the above-mentioned pull-up speed. The absorption coefficient of the carbon / oxygen composite in this single crystal silicon substrate is 0.1.
25 cm ⁻¹ , and [Oi] is 1.5 × 10 ¹⁸ at
oms / cm ³ (conversion coefficient = 4.81 × 10 ¹⁷ atom
ms / cm ² ), [Cs] is the detection limit (detection limit = 5.
0 × 10 ¹⁵ atoms / cm ³ ) or less.

FIG. 2 is a schematic plan view showing an in-plane distribution of breakdown voltage characteristics of an oxide film in a single crystal silicon substrate according to a comparative example. The display method of evaluation is the same as that of the embodiment. As is clear from FIG. 2, in the single crystal silicon substrate according to the comparative example, 97 out of 254 devices did not break down at an electric field strength of 8 MV / cm 2, and the yield rate was about 38%. .

As is apparent from the results, the infrared absorption coefficient of the carbon-oxygen complex near 1104 cm ^{-1 at} 6K on a single-crystal silicon substrate manufactured using single-crystal silicon pulled up by the CZ method. Is 0.25cm
^In the case of ^-1 , the pressure resistance of the oxide film is poor, but in the case of 0.15 cm ^-1 , the formation of precipitate nuclei composed of a carbon-oxygen complex is suppressed, and the formation of stable oxygen precipitates at high temperatures is suppressed. Can be. Therefore, formation of minute defects in the active region of the element can be suppressed, and a single-crystal silicon substrate having an excellent withstand voltage characteristic of the oxide film can be obtained.

FIG. 3 is a graph showing the relationship between the infrared absorption coefficient near 1104 cm ^-1 at a low temperature and the yield rate of the oxide film withstand voltage characteristics, and the infrared absorption of the carbon / oxygen composite in single crystal silicon. It was found that when the coefficient was 0.2 cm ^-1 or less, the yield rate of the oxide film breakdown voltage characteristics of the single crystal silicon substrate was 49% or more.

Although the embodiment has been described with reference to the case of the CZ method, the same result can be obtained by the molten layer method.

[0022]

As described above in detail, in the single crystal silicon substrate according to the present invention, a single crystal silicon substrate manufactured by using a single crystal silicon pulled up by a CZ method or the like is 1104 cm at 6K. ^Since the infrared absorption coefficient in the vicinity of ^-1 is 0.2 cm ^-1 or less, it is possible to suppress the formation of the precipitation nucleus composed of the carbon-oxygen complex,
The formation of oxygen precipitates stable at high temperatures can be suppressed. Therefore, the abundance of minute defects in the active region of the element can be suppressed low, and a single crystal silicon substrate having an oxide film with excellent withstand voltage characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic plan view showing an in-plane distribution of an oxide film breakdown voltage characteristic in a single crystal silicon substrate according to an example of the present invention.

FIG. 2 is a schematic plan view showing an in-plane distribution of an oxide film breakdown voltage characteristic in a single crystal silicon substrate according to a comparative example.

FIG. 3 is a graph showing the relationship between the infrared absorption coefficient near 1104 cm ^{−1 at} 6K and the yield rate of oxide film breakdown voltage characteristics.

Claims (1)

(57) [Claims] 1. A single crystal silicon substrate which is manufactured using the single-crystal silicon pulled by Czochralski (CZ) method or the like, infrared absorption coefficient at 1104cm ^-1 vicinity of at 6K is 0.2 cm ^-1 A single crystal silicon substrate characterized by the following.