JP2010245208A - Thermal treatment jig and thermal treatment method of semiconductor silicon substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal treatment jig of a semiconductor silicon substrate for reducing a slip that may be generated when a semiconductor silicon substrate having a diameter of 300 mm or more, particularly 450 mm is subjected to thermal treatment and for suppressing particles on the substrate, and a thermal treatment method using the jig. <P>SOLUTION: This thermal treatment jig is a jig formed with an oxide film converted into cristobalite having a thickness of 10 to 50 μm and a surface roughness Ra of 0.5 to 2 μm, and is used to support a silicon substrate for thermal treatment to conduct thermal treatment thereto. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a heat treatment jig for a semiconductor silicon substrate and a heat treatment method using the jig, and in particular, the occurrence of slip during heat treatment of a semiconductor silicon substrate having a diameter of 300 mm or more (hereinafter referred to as a large diameter). Is to effectively suppress

In general, a semiconductor silicon substrate is repeatedly subjected to high-temperature heat treatment in each step such as oxidation, diffusion, and film formation. Various heat treatment furnaces are used for the heat treatment of the semiconductor silicon substrate.
In addition, with the progress of silicon single crystal manufacturing technology, the diameter of the semiconductor silicon substrate is gradually increasing, and recently, a substrate having a diameter of 450 mm has been produced.

When high-temperature heat treatment of a semiconductor silicon substrate is performed using a heat treatment furnace, the temperature distribution of the semiconductor silicon substrate tends to become non-uniform as the diameter of the semiconductor silicon substrate increases, and this causes thermal stress (hereinafter simply referred to as thermal stress) to the semiconductor silicon substrate. Cause).
Further, when the semiconductor silicon substrate is mounted in the heat treatment furnace, the stress applied to the substrate (hereinafter simply referred to as stress) increases as the diameter of the semiconductor silicon substrate increases.
In particular, when heat-treating a large-diameter semiconductor silicon substrate, the method of supporting only the outer peripheral portion of a general substrate is greatly affected by the stress described above, and stable heat treatment becomes difficult.

  Thermal stress and stress cause crystal defects called slips (hereinafter simply referred to as slips) in the semiconductor silicon substrate. Since slip causes an increase in leakage current of LSI devices and deterioration of semiconductor silicon substrate flatness, proposals have been made to suppress these thermal stresses and stresses.

For example, Patent Document 1 proposes a heat treatment jig formed with a cristobalite-formed oxide film as a heat treatment jig for a vertical furnace.
In addition, along with the increase in diameter, process miniaturization technology has been applied to increase the device integration to achieve high speed, low power consumption, and low cost, and the demand for reducing the particle size and number of semiconductor substrate surfaces has increased. ing.

JP 2007-73923 A

However, in the above-mentioned Patent Document 1, the applicable range is limited to the vertical type, and the diameter of the target wafer is only described up to a maximum of 300 mm. Further, although there is a description of the cristobalite method, there is no description regarding the cristobalite layer thickness and surface roughness necessary for slip suppression.
On the other hand, large-diameter wafers, especially 450 mm diameter wafers that are being developed as next-generation wafers, have a significantly higher crevice rate of cristobalite grains into silicon wafers than conventional diameter wafers. Even if such a heat treatment jig having a cristobalite-formed oxide film is used repeatedly, there arises a problem that the slip suppression effect is not stable.
In other words, regarding the application of the above heat treatment jig to a wafer of 300 mm diameter or larger, which is a next generation semiconductor substrate, particularly a 450 mm diameter wafer, it relates to the heat treatment of the silicon substrate, such as the optimal cristobalite oxide film thickness, heat treatment atmosphere, etc. There was a problem with repeated use due to lack of information.

  Furthermore, for 300 mm diameter silicon wafers, quartz having a heat resistant temperature at 1000 ° C. which is cheaper than SiC has been used for heat treatment up to about 1000 ° C., but for large diameter wafers, even at 1000 ° C. There is a problem that slip occurs.

On the other hand, even in the conventional 300 mm diameter high-temperature heat treatment, when heat treatment was performed using a heat treatment jig whose surface was made cristobalite, the cristobalite peeled off when contacting the wafer, especially in the vertical furnace batch treatment, There was a problem that particles were deposited on the wafer directly below. To solve this problem, Patent Document 1 proposes placing a shielding plate having a diameter larger than the diameter under a cristobalite-treated jig, but it is difficult to completely shield the problem. Especially in batch processing heat treatment furnaces, the number of parts inside the furnace increases, so the heat capacity increases, it takes time to raise and lower the temperature, and the batch size (number of wafers processed at one time) decreases. Had.
In other words, as the device process becomes finer, particles that affect the device characteristics of a semiconductor silicon substrate having a large diameter of 300 mm or more, which is the maximum diameter of the conventional diameter, need to be more strictly controlled than before.

  The present invention has been developed in view of the above-mentioned present situation, and in particular, reduces the slip that may occur when heat-treating a large-diameter semiconductor silicon substrate having a diameter of 300 mm or more and suppresses particles on the substrate. An object of the present invention is to provide a heat treatment jig for a semiconductor silicon substrate and a heat treatment method using the jig.

As described in Patent Document 1, the cristobalite oxide film suppresses the occurrence of slip because the silicon wafer adhesion reaction does not proceed easily during high-temperature heat treatment at 900 ° C. or higher, and the occurrence of sticking is unlikely to occur. I know that
The inventors have studied to repeatedly use the above-described technology for suppressing the occurrence of slip even with large-diameter wafer heat treatment with high durability. For this purpose, various heat treatment experiments were conducted. As a result, the cristobalite film thickness and surface roughness optimum for heat treatment of large-diameter wafers were found. In addition, the present inventors have found an optimal post-heat treatment process that can reduce the increase in particles, which is a drawback of a cristobalite film having a high slip suppression effect.
The present invention has been made based on these findings.

That is, the gist configuration of the present invention is as follows.
(1) A heat treatment jig for supporting a semiconductor silicon substrate having a diameter of 300 mm or more during heat treatment, wherein a cristobalite-formed oxide film is formed in a thickness of 10 to 50 μm on a silicon substrate support region of the heat treatment jig, and A heat treatment jig for a semiconductor silicon substrate, wherein the surface roughness Ra of cristobalite is 0.5 to 2 μm.

  (2) The semiconductor silicon substrate heat treatment jig according to (1), wherein a material of the heat treatment jig is silicon or quartz.

  (3) After supporting a semiconductor silicon substrate having a diameter of 300 mm or more with the heat treatment jig described in (1) or (2) and performing heat treatment in a temperature range of 900 to 1350 ° C. in a non-reducing atmosphere. A method of manufacturing a semiconductor substrate, comprising: performing HF cleaning and then polishing the substrate surface.

  According to the present invention, during the heat treatment of a large-diameter silicon semiconductor substrate, the generation of slip can be effectively suppressed, and a silicon wafer with few crystal defects can be stably obtained.

It is the figure which showed an example of the boat made from quartz or silicon which has the oxide film made cristobalite.

Hereinafter, the present invention will be specifically described.
First, the reason why the thickness of the cristobalite-formed oxide film in the heat treatment jig for a semiconductor silicon substrate of the present invention is limited to the following numerical values will be described.
Cristobalite oxide thickness: 10-50μm
At the time of the heat treatment, a cristobalite oxide film having a thickness of 10 to 50 μm is formed in a region for supporting and supporting the semiconductor silicon substrate.
When the thickness of the cristobalite oxide film is less than 10 μm during the heat treatment of a large-diameter wafer, the cristobalite is likely to be detached due to the bite of the wafer, and it is difficult to obtain a stable effect.
On the other hand, when the thickness of the oxide film converted to cristobalite exceeds 50 μm, although a stable slip suppression effect can be obtained, it takes time to grow cristobalite, resulting in an increase in cost. Furthermore, since the difference in thermal expansion coefficient from the base material of the heat treatment jig becomes large, the cristobalite grains themselves are likely to be detached, and there is a disadvantage that it is likely to cause the generation of particles.

  The cristobalite surface roughness Ra is 0.5 μm to 2 μm. When Ra is 0.5 μm or less, the heat treatment jig and the wafer easily adhere to each other during the heat treatment, and stress is generated due to the difference in thermal expansion during the cooling from the starting point, and the probability of occurrence of slip increases. On the other hand, when Ra is 2 μm or more, cristobalite particles having a large particle size are pierced into the wafer, and slip is likely to occur starting from the scratches.

The properties, manufacturing method, thermal history, etc. of the cristobalite oxide film will be described.
Here, cristobalite formation means a state in which the oxide film is crystallized from an amorphous state. The cristobalite oxide film preferably has some cracks on the surface.

  In the present invention, the cristobalite-formed oxide film having such cracks is obtained by applying a cristobalite formation accelerator to the surface of the heat treatment jig and then performing heat treatment. By the action of the cristobalite accelerator, an oxide film having a large number of cracks can be formed on the surface of the heat treatment jig by a relatively simple operation.

  When heat treatment is performed by introducing a cristobalite accelerator, an oxide film may be formed in advance on the surface of the heat treatment jig. Due to the action of the cristobalite forming accelerator introduced on the surface of the oxide film or in the vicinity of the surface, the oxide film is converted to cristobalite to generate a large number of cracks, or at the same time, the oxide film having a large number of cracks becomes the oxide film. Newly formed on the surface.

  There are no particular limitations on the type of cristobalite accelerator, but for example, alkali metals such as sodium and potassium well known as components that cause devitrification of quartz, alkaline earth metals such as calcium, barium, and magnesium, tungsten It is desirable to use transition metals such as zirconium and molybdenum, and aluminum. This is because these metals have a remarkable effect of promoting cristobalite formation and have little contamination action on the silicon substrate.

The heat treatment for obtaining the cristobalite oxide film is not limited to a specific condition. Depending on the type of cristobalite accelerator used and its concentration (area equivalent concentration), for example, when calcium forming a cristobalite film having a thickness of 10 to 50 μm on a silicon material is used, in an oxidizing atmosphere, Heat treatment for about 10 to 50 hours in the range of 1100 to 1350 ° C. is a desirable condition.
In the cristobalite film, the higher the heat treatment and the longer the heating, the larger the particle size constituting the film, which affects the surface roughness. Ra: In order to control to 0.5 to 2.0 μm, it is preferable to heat in an oxidizing atmosphere in the range of 1100 to 1350 ° C. for about 10 to 100 hours.
To achieve both film thickness and surface roughness, use heat treatment conditions that satisfy both conditions simultaneously, or if a thick cristobalite film is formed and the surface roughness is large, the surface contains CeO ₂ -based abrasive grains. It is only necessary to polish using a polishing material, etc. If the surface roughness is small, using HF solution, etc., using the phenomenon that the SiO ₂ grain boundary or cristobalite cracks are selectively etched The surface should be roughened.

There is no particular limitation on the method for introducing the above-described cristobalite accelerator to the surface of the heat treatment jig or the surface of the heat treatment jig that has been previously oxidized. For example, by applying a method of immersing the heat treatment jig in an aqueous sodium solution, a method of dropping a sodium aqueous solution onto the surface of the heat treatment jig (that is, the surface to be cristobaliteized), etc., It can be easily introduced on or near the surface of a heat treatment jig or a heat treatment jig that has been previously oxidized.
Note that “near the surface” as used herein means that a part of the cristobalite accelerator applied to the surface of the jig may slightly enter from the surface to the inside due to thermal diffusion during the introduction treatment. This refers to the range.

The concentration of the cristobalite accelerator introduced on or near the surface of the heat treatment jig is 1 × 10 ¹⁰ atoms / cm ² or more in terms of area, that is, sodium and potassium existing on the surface (1 cm ² ) of the heat treatment jig. It is desirable that the number of metal atoms is 10 ¹⁰ or more.
When the concentration is higher than this concentration, cristobalite formation of the oxide film to be formed is promoted, and an oxide film having a large number of cracks formed on the surface of the silicon material can be formed.

  FIG. 1 shows an example of a quartz or silicon boat having an oxide film converted to cristobalite according to the present invention. In the present invention, it is possible to change only the material without changing the structure. In the figure, 1 is a heat treatment boat, 2 is an opening, 3 is a column, 4 is a substrate support, 5 is an upper top plate, and 6 is a lower top plate.

As a material for a heat treatment jig for forming a cristobalite-formed oxide film, silicon (described in Patent Document 1) is generally used. However, when the heat treatment temperature is 1000 ° C. or less, quartz is also preferably used. it can.
Even when the silicon substrate is heat-treated even at 1000 ° C. or lower, slip occurs in the large-diameter silicon substrate. Therefore, even in the quartz boat used for the heat treatment, a cristobalite-formed oxide film is formed on the surface. There is a need.

Next, the reason why the processing temperature and atmosphere are limited to the above ranges in the heat treatment method using the heat treatment jig described above will be described.
Heat treatment temperature of silicon: 900-1350 ° C
When the heat treatment temperature is less than 900 ° C., heat treatment of a large-diameter wafer can be performed without causing slip even if there is no cristobalite oxide film on the jig surface. However, since the processing time becomes very long, it is not realistic. On the other hand, heat treatment exceeding 1350 ° C. is not performed because silicon softens.

  In order to maintain the slip-free effect even by repeated heat treatment, it is necessary to have a non-reducing atmosphere that suppresses the decomposition of cristobalite. In particular, an oxidizing atmosphere or a nitrogen atmosphere is suitable.

This is because the heat treatment in a reducing atmosphere reduces the slip suppression effect due to the decomposition of cristobalite, and the SiOx (gas) generated by the decomposition reacts with the surface silicon to form pits, resulting in deterioration of the surface quality. is there.
In contrast, if the atmosphere is a non-reducing atmosphere (for example, a mixed atmosphere of O ₂ , N ₂ -O ₂ , Ar-O _2, etc.), the degradation of the cristobalite-formed oxide film is hardly observed. In addition, even in a nitrogen atmosphere, there is a possibility that the oxynitride is partially changed depending on the heat treatment temperature / time / number of times.

  Examples of the type of heat treatment described above include donor killer annealing (˜1000 ° C.) for eliminating oxygen donors in a silicon wafer manufacturing process, and precipitation promotion annealing for promoting intrinsic gettering formation before epitaxial growth ( 900 to 1000 ° C.), bonding strengthening heat treatment (1000 to 1200 ° C.), SIMOX annealing (1300 to 1350 ° C.) for SOI production, and the like.

Usually, when processing at 900-1000 degreeC, it is common to support the wafer outer peripheral part 3 or 4 points | pieces. At a high temperature of 1000 to 1350 ° C., for example, a ring-shaped silicon boat having an inner diameter of 1/2 (50%) to 2/3 (67%) of the wafer diameter and a width of about 30 to 70 mm is used. In the case of a ring-shaped silicon boat, it is used by being loaded on a SiC boat.
In addition, even in the conventional high-temperature heat treatment with a diameter of 300 mm, when heat treatment is performed using a heat treatment jig whose surface is made cristobalite, the cristobalite comes off when it comes into contact with the wafer. Particles accumulate on the surface. These particles react with and adhere to the wafer during heat treatment, and are difficult to remove by SC1 / SC2 cleaning used in normal semiconductor processes.

Here, in the present invention, since the cristobalite is composed of SiO ₂ , the melt is removed by HF cleaning. However, it is preferable to remove the cristobalite particles or the fixed traces by polishing after removing the oxide film formed by the heat treatment in the oxidizing atmosphere with HF because the fixed traces remain.
From the above, the present invention can suitably use a semiconductor silicon substrate having a diameter of 300 mm or more for heat treatment.
The polishing allowance is preferably from 0.01 μm to 1.0 μm, and more preferably from 0.01 to 0.05 μm when the device characteristics deteriorate due to loss of wafer flatness by polishing.

<Basic conditions>
300mm, 450mm silicon wafer: P type (100) substrate Silicon ring:
Inner diameter: 200 mm, width: 50 mm, flatness: 20 μm, surface roughness: 2 μm
(Supports 50 to 55% of wafer diameter for 450 mm)
Quartz boat: 4 points on the outer periphery

-Conditions for cristobalite treatment The silicon ring was dipped in an aqueous solution having a sodium concentration of 20 ppm for 10 minutes, pulled up, and allowed to dry naturally. Next, this silicon ring was subjected to an oxidation heat treatment at 1320 ° C. for 5 to 60 hours. As a result of observing the obtained silicon ring with a microscope, it was confirmed that cracks occurred in various portions of the formed oxide film. Further, when the oxide film was examined by X-ray diffraction, it was confirmed that the oxide film was converted to cristobalite. Furthermore, the thickness of the oxide film was measured by SEM observation. The surface roughness was measured with an AFM (atomic force microscope), and the roughness was adjusted by dipping in a polishing or HF solution.

  On the other hand, the quartz boat, like the silicon ring, is immersed in an aqueous solution with a sodium concentration of 20 ppm for 10 minutes, pulled up and naturally dried, and then subjected to oxidation heat treatment at 1100 ° C. for 1 to 20 hours using the same furnace. Carried out. To evaluate cristobalite, a sample piece (10 mm x 10 mm) was processed simultaneously with the boat body and evaluated. As in the case of the silicon ring, as a result of observing under a microscope, it was confirmed that cracks occurred in various portions of the formed oxide film. Further, when the oxide film was examined by X-ray diffraction, it was confirmed that the oxide film was converted to cristobalite. Furthermore, the thickness of the oxide film was measured by SEM observation. The surface roughness was measured by AFM, and the roughness was adjusted by polishing or immersing in HF solution.

Heat treatment conditions for silicon ring Atmosphere: oxygen, argon, temperature: 1200-1350 ° C., time: supported for 2 hours After 10 repeated treatments, an evaluation wafer was loaded.
Wafer diameter: 300mm
After the heat treatment, the substrate was immersed in a HF: 5% solution for 30 minutes, and then washed with SC1 cleaning + hydrofluoric acid ozone mixed solution. Then, a part of the surface was polished by about 0.2 μm and further washed with SC1 cleaning + hydrofluoric acid ozone mixed solution.

・ Heat treatment conditions for quartz boats Atmosphere: Oxygen, Argon, Temperature: 1000 ° C, Time: Support for 2 hours Inner diameter: A SiC boat is installed in a vertical heat treatment furnace with a diameter of 600mm, and the above silicon ring is prepared there and processed 10 times repeatedly. Thereafter, an evaluation wafer was loaded.
Wafer diameter: 450mm

<Evaluation>
The 300 mm wafer was left as it was, and the 450 mm wafer was cleaved into four parts with a diamond pen.
As a result of the investigation, when a slip having a length of 10 mm or more was observed, it was evaluated as x, and when the slip was observed, it was evaluated as ◯.
The obtained results are shown in Table 1.

Next, particles detected as LPD (Laser Particle Defect) having a size of 60 nm or more were measured for a sample with and without polishing using a particle measuring device using a laser, and the number of particles of> 0.065 μm was counted.
・ Production conditions for particle measurement defect samples with and without polishing
300m wafer, silicon ring, cristobalite thickness 30μm, surface roughness 1μm, heat treatment temperature 1350 ℃ (oxidizing atmosphere)
The obtained results are shown in Table 2.

As shown in Table 1, no slip was observed on the evaluation wafer having the cristobalite oxide film according to the present invention. On the other hand, the cristobalite-thick oxide film having a thickness outside the present invention and the one treated in a reducing atmosphere produced slip on the evaluation wafer. Furthermore, it can be seen that the presence or absence of slip changes depending on the surface roughness of the cristobalite.
In addition, as shown in Table 2, it was confirmed that the LPD caused by cristobalite decreased and the number of polished particles decreased to a finite number even> 0.065 μm as shown in Table 2.

  According to the present invention, it is possible to prevent the occurrence of slip during the heat treatment of a large-diameter silicon substrate, thereby suppressing the adhesion of particles to the surface of the silicon substrate, maintaining a high quality characteristic of the device, and improving the yield of device manufacturing. Is possible. As a result, a low-cost high-quality large-diameter silicon substrate can be provided.

1: Heat treatment boat 2: Opening
3: Support column 4: Substrate support part 5: Upper top plate 6: Lower top plate

Claims (3)

  A heat treatment jig for supporting a semiconductor silicon substrate having a diameter of 300 mm or more during heat treatment, wherein a cristobalite-formed oxide film is formed with a thickness of 10 to 50 μm on a silicon substrate support region of the heat treatment jig, and the surface of the cristobalite A heat treatment jig for a semiconductor silicon substrate, having a roughness Ra of 0.5 to 2 μm.   2. The heat treatment jig for a semiconductor silicon substrate according to claim 1, wherein a material of the heat treatment jig is silicon or quartz.   A semiconductor silicon substrate having a diameter of 300 mm or more is supported by the heat treatment jig according to claim 1 or 2, subjected to heat treatment in a temperature range of 900 to 1350 ° C. in a non-reductive atmosphere, and then subjected to HF cleaning. Then, a method for manufacturing a semiconductor substrate comprising a step of polishing the substrate surface.

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