JPS63227026A - Gettering method for silicon crystal substrate - Google Patents

Abstract

PURPOSE:To improve the gettering efficiency of a silicon crystal substrate by intrinsically gettering a semiconductor device of the structure in which an epitaxial layer of film thickness replaced as a nondefect layer is formed on the substrate containing high carbon concentration. CONSTITUTION:After a crystal substrate 5 formed in thickness of approx. 5-50mum on which a silicon epitaxial layer 7 is formed by an epitaxial growing method on the surface of a high carbon concentration lifting silicon crystal 6 containing approx. 0.5-15ppma of carbon is first heat-treated to form a microdefect region in the crystal 6, and it is second heat-treated at higher temperature than that at the time of first heat treatment Since a heat treatment for forming the nondefect layer on the substrate surface is eliminated, total heat-treating time can be shortened to efficiently intrinsically getter it.

Description

[Detailed Description of the Invention] [Summary] The present invention provides intrinsic gettering (IG) in which micro defects are created inside a silicon crystal substrate on which an epitaxial layer is formed, and the silicon crystal substrate itself has gettering ability. In this method, gettering efficiency is improved by performing intrinsic gettering on a semiconductor device having a structure in which an epitaxial layer with a thickness that can be used as a defect-free layer is formed on a silicon crystal substrate with a high carbon concentration. This method is improved compared to the previous method.

[Industrial application field]

The present invention relates to a gettering method for a silicon crystal substrate,
In particular, the present invention relates to a gettering method for efficiently performing intrinsic gettering on a silicon crystal substrate (semiconductor device) having an epitaxial layer formed on its surface.

The pulling method (CZ method) is commonly used as a substrate for LSI devices.
The silicon crystal grown in step d) is contaminated with minute amounts of impurities during crystal production (internal contamination), and the silicon crystal substrate is also contaminated during the subsequent semiconductor device manufacturing process (external contamination). ,,These contaminants deteriorate the characteristics of semiconductor devices.

Gettering has traditionally been performed to remove and reduce contaminants (impurities, crystal defects) from the active region of silicon crystal substrates and obtain good characteristics, which can lead to problems such as a decrease in manufacturing yield. There is.

Intrinsic gettering (IG) is known as one of these gettering techniques, and it is required to improve gettering efficiency. .

(Prior Art) FIG. 3 shows an example of a conventional gettering method for a silicon crystal substrate. In the figure, thermal annealing of the silicon crystal substrate is started at time t1,
900 min in a mixed gas of 02 and 1-IC2
After thermal annealing is performed at a temperature of 0.degree. C., the temperature is increased at a rate of +10.degree. C. per minute.

Thereafter, from time t3 after S degree reaches 1100°C to t
For about 30 minutes up to 4, in a nitrogen (N2) gas atmosphere,
High temperature heat treatment at a temperature of 1100° C. is performed.

As a result, the impurity oxygen in the silicon crystal diffuses outward, and a defect-free layer is formed in the silicon crystal surface layer.

Next, from time t4, the heat treatment temperature was gradually lowered at a rate of 2°C per minute, and from time t5 to t6 when it reached 650°C.
Low-temperature heat treatment is performed while maintaining the temperature at 650°C. This low-temperature heat treatment generates microdefect regions (forms precipitation nuclei) inside the silicon crystal deeper than the defect-free layer.

Next, the temperature is increased at a rate of 2 degrees Celsius per minute from time t6, and when it reaches 1100 degrees Celsius at time t7, that time t7
For 30 minutes from t8 to t8, high-temperature heat treatment is performed while maintaining the temperature at 1100°C. This high-temperature heat treatment is intended to grow the minute defects formed by the low-temperature heat treatment of Nakedate to a B-magnification degree and provide gettering ability.

After that, the temperature is lowered at a rate of 4°C per minute from time t8, and the heat treatment ends at time t9 when it reaches 900°C (
(The silicon crystal substrate is taken out from the annealing device.)

The heat treatment from time t3 to t9 above was performed in a non-oxidizing atmosphere (in N2 gas here) to avoid forming an oxide film.
It will be held in

By such intrinsic gettering, minute defects are created inside the silicon crystal, and the silicon crystal substrate itself is given gettering ability. Therefore, in order to book into the minute defect region inside the silicon crystal substrate, the device active region on the surface of the silicon crystal substrate must be kept defect-free.

Conventionally, in order to keep the device active region on the surface of a silicon crystal substrate more defect-free, an epitaxial layer 2 with a thickness of 1 μm to 2 μm was formed on the surface of a silicon crystal substrate 1, as shown in the cross-sectional view of FIG. A method of subjecting a substrate to an intrinsic gettering heat treatment similar to that shown in FIG. 3 is also known.

In FIG. 4, a silicon crystal substrate 1 is grown by a pulling method,
and the carbon concentration is 0.1 ppHa or less and the oxygen concentration is 30
It is a pulled silicon crystal with a low carbon sm degree of about ppm 1a.

According to this conventional method, the epitaxial layer 2 with fewer defects than the silicon crystal substrate 1 is used in the element active region of the substrate 3, and the epitaxial layer contamination caused by external and internal causes is prevented from forming on the silicon crystal substrate 1. It is reduced by internal gettering action.

[Problem that the invention seeks to solve]

However, in the conventional gettering methods described above, the impurity oxygen necessary for the gettering action is not sufficiently precipitated. If sufficient precipitation is to be obtained, the gettering heat treatment will take a long time, or a heat treatment at a higher temperature than III will be required.

Due to this long-time and high-temperature heat treatment, there was a problem in that dopants (phosphorous and boron) in the silicon crystal substrate crawled up near the surface or into the epitaxial layer 1112 in FIG. 4.

The present invention was created in view of the above points, and an object of the present invention is to provide a gettering method for a silicon crystal substrate that can improve gettering efficiency.

Means for Solving Problem C] The gettering method for a silicon crystal substrate of the present invention includes forming an epitaxial layer of silicon on the surface of a pulled silicon crystal with a high carbon concentration containing approximately 0.5 to 15 ρ pla of carbon.
A crystal substrate formed with a film thickness of ~50 μm is sequentially subjected to a first heat treatment to form a microdefect region inside the silicon crystal and a second heat treatment at a higher temperature than the first heat treatment. It is something that is done.

[Effect]

In a pulled silicon crystal with an impurity oxygen concentration of about 20 to 30 ppma, if carbon is included as an impurity, the carbon becomes a precipitation nucleus during impurity oxygen precipitation and has the effect of promoting precipitation. It is known that.

This is because the covalent bond radius of carbon atoms is 30% to 40% smaller than that of silicon, and therefore the crystal lattice of silicon has larger gaps around carbon, which is a substitutional impurity atom, than in the case of a perfect crystal. (the distance between silicon atoms has become longer), impurity oxygen is likely to collect there, and a precipitation reaction (release of interstitial silicon)
This is thought to be due to the fact that it becomes more likely to occur.

In fact, two types of pulled silicon crystals with the same oxygen concentration (about (301) l) ma) but different carbon concentrations were subjected to nucleation annealing at 750° C. for 64 hours as the first heat treatment, and then When performing a nucleus growth annealing at 1000°C as the second heat treatment, it was found that the period of oxygen precipitation obtained by 64 hours of nucleus growth annealing in a silicon crystal with a normal low carbon concentration (1 ppma or less) was at a high carbon concentration (5 ppma or less). It is known that a silicon crystal of ~7 ppma) can be obtained by 2 hours of nuclear growth annealing.

In this way, increasing the carbon concentration in the pulled silicon crystal can promote the precipitation of impurity oxygen, but if it is too high, it will reduce the crystallinity of the silicon substrate, so it is not recommended to increase the concentration above a certain value. Can not.

Therefore, in the present invention, the silicon crystal contains 0.5 to 15 carbon atoms.
p1) Selected to have a high carbon concentration containing about la.

In addition, the thickness of the silicon epitaxial layer, which has fewer defects than silicon crystal, is 5 to 50 μm so that it can be used as a defect-free layer on the surface of the silicon crystal.
It is formed to a certain extent and thickly. Therefore, heat treatment for outward diffusion of impurity oxygen to form a defect-free layer in the element active region on the surface of the silicon crystal substrate is unnecessary.

〔Example〕

FIG. 1 is an explanatory diagram of an embodiment of the method of the present invention.

In this embodiment, the silicon crystal substrate to be gettered has a cross-sectional structure as shown in FIG. In FIG. 2, a silicon crystal substrate 5 consists of a pulled silicon crystal 6 in the shape of a disk with a diameter of 4 inches, and a silicon epitaxial layer 7 formed on the surface of the silicon crystal 6 by an epitaxial method.

The silicon crystal 6 has a carbon concentration of 7 to 1 Qppma.

It is a high carbon concentration silicon crystal with an oxygen concentration of 30 ppma. Further, the epitaxial layer 7 has a thickness of 10 to 15 μm.
As shown in FIG. 1, for the silicon crystal substrate 5 having the structure shown in FIG. Thermal annealing (low-temperature heat treatment) is performed at a temperature of 750° C. for an hour in an N2 gas atmosphere. By this low-temperature heat treatment, microdefect regions are formed inside the silicon crystal 6.

Next, as shown in Fig. 1, the temperature is gradually increased at a rate of 5°C per minute from time tb, and at time tc when it reaches 1000'C.
For four hours until time td, thermal annealing (high-temperature heat treatment) is performed in an N2 gas atmosphere while keeping the temperature at 1000°C. By this high-temperature heat treatment, minute defects inside the silicon crystal 6 grow, and a high-density minute defect region is pierced.

Next, the temperature is lowered at a rate of 4° C. per minute from time td, and at time e when it reaches 850° C., the thermal annealing of the silicon crystal substrate 5 is completed.

As described above, according to this embodiment, the heat treatment for outward diffusion of oxygen, which was conventionally necessary, can be omitted, and only the heat treatment for the formation and growth of micro-defect regions is required.
As shown in the figure, the total processing time is 8 hours and 30 minutes, and compared to the conventional method shown in FIG. 3, which takes a total processing time of 13 minutes and 30 minutes, gettering can be accomplished in a shorter time.

Further, the R high temperature in this example is 1000°C, which is lower than the maximum temperature of 1100°C in the conventional method.
The creeping up of dopants from silicon crystal 6 to epitaxial layer 7 can be reduced.

(Effects of the Invention) As described above, according to the present invention, a pulled silicon crystal with a high carbon S degree is used to promote the precipitation of impurity acid wood, so it can be produced in a shorter time (or at a lower temperature) than in the past. ) equivalent oxygen precipitation m can be obtained. In addition, an epitaxial layer that becomes a defect-free layer is formed on the surface of the silicon crystal, eliminating the need for heat treatment to form a defect-free layer on the substrate surface. The total heat treatment time can be significantly shortened compared to the conventional method.
The present invention has the advantage that it is possible to reduce the amount of noise compared to the conventional method, and to perform intrinsic gettering more efficiently than the conventional method.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of an embodiment of the method of the present invention, FIG. 2 is a vertical cross-sectional view of an embodiment of a silicon crystal substrate to be gettered in the method of the present invention, and FIG. 3 is an explanatory diagram of an example of the conventional method. FIG. 4 is a vertical cross-sectional view showing an example of a silicon crystal substrate that is gettered in a conventional method. In the figure, 5 is a silicon crystal substrate, 6 is a pulled silicon crystal, and 7 is a silicon epitaxial layer. An explanatory diagram of an embodiment of the method of the present invention. Figure 1. A sectional view of an embodiment of a silicon crystal substrate. Figure 2.

Claims (1)

[Claims] A silicon epitaxial layer (7) with a thickness of 5 to 50% is formed by an epitaxial growth method on the surface of a pulled silicon crystal (6) with a high carbon concentration containing about 0.5 to 15 ppma of carbon.
After performing a first heat treatment for forming a micro defect region inside the silicon crystal (6) on a crystal substrate (5) formed with a thickness of about μm, the first heat treatment 1. A method for gettering a silicon crystal substrate, the method comprising performing a second heat treatment at a temperature higher than the temperature at which the silicon crystal substrate is heated.