JPH11214322A - Method for manufacturing silicon semiconductor substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silicon semiconductor substrate with good characteristics by reducing dislocation density in an SOI structure. SOLUTION: After oxygen ions have been implanted in a silicon single crystal substrate, a heat treatment step is carried out to form an inner oxygen film in the silicon single crystal substrate, in a manufacturing method for forming a silicon semiconductor substrate. In this method, a heat treatment step is carried out prior to the ion implantation of oxygen. The previous heat treatment step is desirably carried out at 500 to 900 deg.C for 10 to 80 hours.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a silicon semiconductor substrate having an SOI structure, and more particularly to a method for manufacturing a silicon semiconductor substrate in which the dislocation density of a surface silicon layer of the substrate is reduced.

[0002]

2. Description of the Related Art In recent years, demands for higher integration, higher speed, and more functions in semiconductor devices have become more severe.
Accordingly, in manufacturing semiconductor substrates, SOI
The importance of (silicon-on-insulator) technology has been increasingly recognized. In other words, the above characteristics required for the device are inseparable from element isolation technology,
Various manufacturing techniques for semiconductor substrates having an SOI structure in which a single-crystal silicon layer is formed on an insulator have been studied in various ways. Practical applications have been attempted to reduce soft errors due to radiation, reduce power consumption, and reduce total process costs. I have. SIMOX (Separation by IMplanted)
Although the OXygen) method and the bonding method are widely used, the SIMOX technique is a promising manufacturing method because it is possible to manufacture a wafer having a very small variation in the thickness of the active layer.

In the SIMOX method, high-concentration oxygen ions are implanted into a single-crystal silicon substrate by an ion implanter.
Thereafter, a high-temperature heat treatment of 1200 ° C. or more is performed to react silicon and oxygen to form a buried oxide film layer in the substrate. At this time, oxygen ions are implanted at an acceleration voltage of 50 KeV to 200 KeV.

[0004] As an improved SIMOX method, SP
There is an IMOX (Separation by PlasmaIMplanted OXygen) method. In this method, at the time of oxygen ion implantation, oxygen ions are generated by plasma and accelerated and implanted by applying a bias to the silicon single crystal substrate.
The acceleration voltage at this time is about several tens KeV. For this reason,
The required equipment is inexpensive, and a large number of semiconductor substrates can be simultaneously processed over a large area, so that the manufacturing efficiency of a semiconductor substrate having an SOI structure can be improved. However, as for the heat treatment, as in the case of the SIMOX method, it is necessary to perform a high-temperature heat treatment at 1200 ° C. or higher after oxygen ion implantation.

In the SIMOX method and the SPIMOX method described above, the dislocation generated in the surface silicon layer due to the implantation of oxygen ions into the substrate is not sufficiently reduced even after the subsequent high-temperature heat treatment at 1200 ° C. or more. There is. For example, S. Nakasima and K. Izumi (Nuclear Instr
uments and Methods in Physics Research B55,1991847
According to -851), even if a high-temperature heat treatment at 1200 ° C. or more is performed for several hours after oxygen ion implantation, dislocations having a density of 10 ² cm ⁻² or more remain in the surface silicon layer.

[0006] Dislocations generated in the silicon layer on the substrate surface are classified into those caused by damage at the time of oxygen ion implantation and those caused by strain caused by interstitial silicon generated at the time of forming the buried oxide film layer. The former dislocation is
By keeping the substrate at a high temperature during oxygen ion implantation, damage due to implantation can be alleviated and reduced, but there is no effective method for suppressing dislocations by the latter, and a density of more than 10 ² cm ^{-2 is} inevitable. Dislocations remain in the surface silicon layer. Such dislocations degrade the electrical characteristics of the substrate, thereby deteriorating the yield of the substrate and significantly reducing the productivity of the SOI substrate.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in consideration of the problem of a semiconductor substrate having an SOI structure manufactured corresponding to a highly integrated device, and has been developed in consideration of a substrate manufactured by a SIMOX method or a SPIMOX method. It is an object of the present invention to provide a method for manufacturing a silicon semiconductor substrate that can sufficiently reduce the dislocation density in a surface silicon layer and has excellent substrate characteristics and productivity.

[0008]

In order to solve the above-mentioned problems, the present inventors have conducted various studies on the behavior of dislocations generated in the surface silicon layer of the substrate. The expected knowledge on interstitial silicon was obtained.

As described above, the SIMOX method and the SPIM method
In the manufacture of a substrate by the OX method, a heat treatment is performed on the substrate at a high temperature of 1200 ° C. or more to promote the formation of a buried oxide film after oxygen ion implantation and to recover and improve the crystallinity of the surface silicon single crystal region. You. At this time, oxygen precipitates are formed in the silicon substrate, and the reaction is represented by the following equation.

(L + y) Si + 2Oi + xV → SiO ₂ + yI where Oi: interstitial oxygen, V: vacancy I: interstitial silicon, x, y: coefficients As shown in the above formula, oxygen With the formation of the buried oxide film by ion implantation, oxygen precipitates (SiO 2
₂ ) is generated and interstitial silicon is generated accompanying it.

FIG. 1 shows a SIMOX method and a SIMOX method.
FIG. 4 is a diagram schematically showing a situation where dislocations occur in a surface silicon layer as a buried oxide film is formed in a substrate by a method. As shown in FIG. 1, along with the formation of the buried oxide film, oxygen precipitates 2 are formed in the substrate 1 and interstitial silicon I is generated. Due to the generation of the interstitial silicon I, the strain 3 in the substrate 1 becomes remarkable, and due to the strain 3, dislocations 4 occur in the surface silicon layer.

Since the dislocation density generated at this time depends on the amount of interstitial silicon I, as will be described later, by reducing the amount of interstitial silicon generated in the heat treatment after oxygen ion implantation, strain in the substrate is reduced. And the dislocation density can be sufficiently reduced.

The present invention has been completed on the basis of the above findings, and has the following method of manufacturing a silicon semiconductor substrate.

That is, a method for manufacturing a silicon single crystal substrate in which an internal oxide film is formed in the silicon single crystal substrate by implanting oxygen ions into the silicon single crystal substrate and then performing a heat treatment. A method of manufacturing a silicon single crystal substrate, which comprises subjecting the substrate to a heat treatment before the step (a).

In this manufacturing method, the conditions of the heat treatment to be performed on the substrate before the oxygen ion implantation are performed at 500 ° C. to 900 ° C. for 10 to 10 hours.
Preferably 80 hours.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a method of manufacturing a semiconductor substrate having an SOI structure according to the present invention, a silicon substrate is subjected to a predetermined heat treatment to form oxygen precipitates, and then oxygen ions are accelerated and implanted into the substrate. After that, high-temperature heat treatment is performed for the purpose of forming a buried oxide film and restoring the crystallinity of the surface silicon single crystal region. Hereinafter, in the description of the manufacturing method of the present invention, the heat treatment applied to the silicon substrate in advance is referred to as “first heat treatment”, and the heat treatment performed after oxygen ion implantation is referred to as “second heat treatment”. Then, in order to clarify the effects of the respective heat treatments, those generated as a result of the “first heat treatment” are given the suffix “a” and “second heat treatment”.
Generated by the “heat treatment” is given a subscript “b”.

FIG. 2 is a view for explaining the behavior of oxygen precipitates generated by the first heat treatment in the production method of the present invention. FIG. 2 (a) shows the oxygen precipitates 2a by the first heat treatment.
(B) shows the first heat-treated state by the second heat treatment.
2 shows a state in which the oxygen precipitate 2a generated by the heat treatment is dissolved.

When the silicon substrate is subjected to the first heat treatment, as shown in the above formula, the silicon in the substrate 1 and the interstitial oxygen (Oi) originally present in the silicon substrate are combined to form a silicon oxygen precipitate 2a. Is done. At this time, volume expansion occurs with the formation of the oxygen precipitate 2a, and interstitial silicon Ia is generated. After that, the generated interstitial silicon Ia diffuses,
It disappears on the surface of the substrate 1 and the like, and interstitial silicon decreases (see FIG. 2A).

After the first heat treatment, oxygen ions are implanted while the temperature of the substrate is kept at 400 ° C. or higher in order to minimize damage due to ion implantation. After that, a second heat treatment is performed at a high temperature of 1200 ° C. or more to form a buried oxide film. Also in this second heat treatment,
As shown in the above equation, Si in the substrate 1 and the implanted interstitial oxygen (Oi) combine to form a silicon oxygen precipitate 2b in a high-concentration oxygen region in the substrate.

Since the first heat treatment is performed at a relatively low temperature and the heat treatment time is short, the oxygen precipitate 2a formed in the silicon active layer on the substrate surface by the first heat treatment is subjected to the second heat treatment under a high temperature condition. Is smaller than the critical nuclear radius. This critical nucleus radius is determined by the interstitial oxygen concentration, the vacancy concentration, the interfacial energy and the strain energy of the precipitate at a certain temperature, and the precipitate smaller than the critical nucleus radius is unstable and does not grow. Eventually dissolved. That is, the oxygen precipitate 2a formed by the first heat treatment becomes unstable and is dissolved by the heat treatment at 1200 ° C. or higher, which is the second heat treatment condition. The reaction in the substrate at this time is in accordance with the following equation, and vacancies Va are released as the oxygen precipitate 2a dissolves (FIG. 2).
(b)).

[0021] (l + y) Si + 2Oi + xV ← SiO 2 + yI ··· However, Oi: interstitial oxygen, V: vacancy I: interstitial silicon, x, y: coefficient Figure 3, the second heat treatment FIG. 5 is a diagram for explaining a situation in which interstitial silicon formed by the above process disappears to suppress generation of dislocations in the surface silicon layer. As described above, the silicon oxide precipitate 2b is formed in the substrate 1 by the second heat treatment, and the interstitial silicon Ib is thereby generated. Meanwhile, the first
When the oxygen precipitates 2a formed by the heat treatment are dissolved, the vacancies Va are released into the substrate 1. And the void Va
Couples with the newly generated interstitial silicon Ib and annihilates. As a result of the annihilation of the vacancies Va and the interstitial silicon Ib, the interstitial silicon Ib generated in the substrate 1 is suppressed, and the distortion due to the generation of the interstitial silicon Ib is reduced. . Thereby, the dislocation density in the substrate can be sufficiently reduced.

In the manufacturing method of the present invention, the condition of the first heat treatment is desirably 500 to 900 ° C. for 10 to 80 hours. When the heat treatment temperature is lower than 500 ° C., oxygen precipitates are less likely to be generated, and the generated interstitial silicon is not sufficiently diffused and disappeared, and the effect of suppressing dislocation by reducing the strain by the second heat treatment is obtained. Absent. On the other hand, if the heat treatment temperature is 90
If the temperature exceeds 0 ° C., it becomes difficult to generate oxygen precipitates.

Further, in the first heat treatment, various atmospheres are adopted without being limited to the oxygen-containing atmosphere. That is, in addition to the atmosphere containing oxygen, nitrogen, argon, and a mixed gas thereof, for example, Ar + O ₂ , N ₂ +
An atmosphere containing O ₂ , O ₂ + HCl or the like can be employed. Depending on the employed atmosphere, the precipitation reaction of oxygen precipitates may be affected. For example, in an oxygen-containing atmosphere, interstitial silicon is introduced from the surface of the substrate along with oxidation, so that precipitation is suppressed. Vacancies are introduced, and precipitation is promoted.

The accelerated implantation of oxygen ions in the production method of the present invention may be performed by a known method employed in the conventional SIMOX method and SPIMOX method, and an ion implanter, a plasma ion generator, or the like is used. Is 50 KeV
To 200 KeV. Further, the second aspect of the present invention
Is performed to promote the formation of a buried oxide film after oxygen ion implantation and to restore the crystallinity of the surface silicon single crystal region. Therefore, the second
The conditions of the heat treatment of the conventional SIMOX method and S
A high temperature condition of 1200 ° C. or higher employed in the PIMOX method may be used.

[0025]

EXAMPLES The effect of reducing the dislocation density by the manufacturing method of the present invention will be described based on specific examples.

(Example 1) A semiconductor substrate used in an example was processed from a single crystal ingot grown by the Czochralski method, and had a resistivity of 20 Ωcm and an initial interstitial oxygen concentration.
A 6-inch silicon substrate of 13 × 10 ¹⁷ atoms / cm ³ with a crystal face (100) is prepared, and oxygen ions are implanted by the above-described SI.
This was performed by the MOX method and the SPIMOX method.

In the first embodiment, the first heat treatment is performed in a nitrogen-containing atmosphere (oxygen concentration 10%) as an example of the present invention.
24 at 500 ℃, 600 ℃, 700 ℃, 800 ℃ and 900 ℃
This was performed under the condition of time, and oxygen precipitates were formed in the substrate.

The implantation of oxygen ions into the substrate reduces the temperature of the substrate.
The temperature is maintained at 400 ° C. or higher. In the SIMOX method, an ion implanter is used, the acceleration voltage is 180 KeV, and the dose amount is 4 × 10 ¹⁷ c.
m ⁻² oxygen ions were implanted. On the other hand, in the SIMOX method, oxygen ions are generated by ECR plasma,
The substrate was biased at -60 KeV and oxygen ions with a dose of 4 × 10 ¹⁷ cm ⁻² were implanted. At this time, in oxygen plasma,
About 95% of the oxygen ions were O ₂ ⁺ and the remaining about 5% of the oxygen ions were O ⁺ .

Further, the SIMOX method and the SPIMOX method
The substrate into which oxygen ions were implanted by the method was subjected to a second heat treatment in an atmosphere containing argon (oxygen concentration: 2%) at a temperature of 1300 ° C. for 4 hours.

As a comparative example, oxygen ions were implanted by the SIMOX method and the SPIMOX method using the same silicon substrate without performing the first heat treatment. A sample was prepared. However, the conditions for the implantation of oxygen ions and the second heat treatment in the comparative example are the same as those in the example of the present invention.

FIG. 4 is a view showing the result of observing the dislocation density in the surface silicon layer from the cross section of the substrate in Example 1. As shown in the figure, in the comparative example in which the first heat treatment was not performed, dislocations of 2 × 10 ² cm ⁻² or more remained in the surface silicon layer of the substrate. On the other hand, in the example of the present invention, it can be seen that a substrate having a dislocation density of 10 ² cm ⁻² or less and a reduction of one digit or more can be obtained.

Example 2 In Example 2, in order to investigate the influence of the holding time in the first heat treatment, the time of the first heat treatment at 600 ° C., 700 ° C. and 800 ° C. in Example 1 was changed. After the oxygen ion implantation by SIMOX method, a second heat treatment was performed to measure the dislocation density in the surface silicon layer. Also in Example 2, the conditions of the oxygen ion implantation by the SIMOX method and the conditions of the second heat treatment were the same as those in Example 1.

FIG. 5 is a diagram showing the relationship between the first heat treatment time and the dislocation density in the surface silicon layer in the second embodiment. At a temperature of 600 ° C. for the first heat treatment, the dislocation density in the surface silicon layer of the substrate becomes the lower limit of detection (approximately 0 cm ⁻² ) during the heat treatment time of 60 to 80 hours. Similarly, the temperature 700 ℃
The dislocation density is the lower limit of detection between 20 hours and 60 hours, and between 10 hours and 60 hours at a temperature of 800 ° C. From this, it is clear that it is desirable to maintain the dislocation density in the surface silicon layer at 600 ° C. to 800 ° C. for 10 to 80 hours.

[0034]

According to the method for manufacturing a silicon semiconductor substrate of the present invention, even if the substrate is manufactured by the SIMOX method or the SPIMOX method, the dislocation density in the surface silicon layer is 10%.
The generation of dislocations can be sufficiently suppressed so as to be ² cm ⁻² or less, and a semiconductor substrate having excellent characteristics can be manufactured. In addition, the present invention is suitable for efficient production of a semiconductor substrate having an SOI structure corresponding to a low-cost and highly integrated device.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a situation where dislocations occur in a surface silicon layer as a buried oxide film is formed in a substrate by a SIMOX method and a SPIMOX method.

FIG. 2 is a diagram illustrating the behavior of oxygen precipitates generated by a first heat treatment in the production method of the present invention.

FIG. 3 is a diagram illustrating a situation in which interstitial silicon formed by a second heat treatment disappears to suppress generation of dislocations in a surface silicon layer.

FIG. 4 is a diagram showing the results of observing the dislocation density in the surface silicon layer from the cross section of the substrate in Example 1.

FIG. 5 is a diagram showing a relationship between a first heat treatment time and a dislocation density in a surface silicon layer in Example 2.

[Explanation of symbols]

 1: substrate, 2, 2a, 2b: oxygen precipitate 3: strain, 4: dislocation I, Ia, Ib: interstitial silicon V, Va, Vb: vacancy

Claims (2)

[Claims] 1. A method for manufacturing a silicon single crystal substrate, comprising forming an internal oxide film in the silicon single crystal substrate by implanting oxygen ions into the silicon single crystal substrate and then performing a heat treatment. A method of producing a silicon single crystal substrate, wherein the substrate is subjected to a heat treatment before the step (a). 2. The method for producing a silicon single crystal substrate according to claim 1, wherein the condition of the heat treatment performed beforehand on the substrate before oxygen ion implantation is at 500 ° C. to 900 ° C. for 10 to 80 hours.