JP7405070B2 - Epitaxial wafer defect evaluation method - Google Patents

Description

The present invention relates to a method for evaluating defects in epitaxial wafers.

In recent years, in addition to miniaturization, semiconductor devices are increasingly using different materials other than silicon. Examples include silicon germanium and germanium as high-mobility channel materials, silicon germanium as sacrificial layers in gate-all-around structures and nanosheet structures, and silicon carbide and gallium nitride as high-efficiency power device materials. Therefore, in device processes, it is thought that heteroepitaxial processes in which different materials are epitaxially grown will increase in the future. In heteroepitaxial structures, stress is generated due to lattice mismatch between the substrate and the epitaxial layer, which may cause stacking faults to occur in the epitaxial layer. Therefore, it can be said that evaluation technology for not only crystal defects in semiconductor substrates but also defects originating from epitaxial layers will become increasingly important in the future.

Patent Document 1 is a technique for exposing crystal defects in a semiconductor single crystal substrate by heat treatment at 800 to 1100° C. in a hydrogen atmosphere. Patent Document 2 is a technology for exposing crystal defects through a two-step heat treatment in which heat treatment is performed at 600 to 700° C. for 2 to 6 hours, followed by heat treatment at 1100 to 1150° C. for 1 to 2 hours, thereby exposing crystal defects. Patent Document 3 describes a technique for detecting defects by subjecting a heteroepitaxial wafer in which GaN is grown on a sapphire substrate to heat treatment at 500 to 900° C. in a hydrogen chloride + nitrogen atmosphere. There are techniques for detecting defects after they have become apparent, such as those described above, but these are techniques that are carried out in a hydrogen atmosphere at high temperatures of 800°C or higher for long periods of time requiring two-step heat treatment, or in an atmosphere containing hydrogen chloride and nitrogen. .

However, there are currently not many techniques for evaluating defects originating from epitaxial layers, and some dissimilar materials, such as germanium, are unstable to heat treatment at high temperatures and for long periods of time. There is a need for a defect evaluation method that can reveal and evaluate defects over time and under low temperature conditions.

JP2011-119528 JP2019-26537 JP2000-188285

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for evaluating defects in epitaxial wafers that allows defects in epitaxial wafers to become apparent in a shorter time and at lower temperatures and to be evaluated with high accuracy. .

In order to solve the above problems, in the present invention,
A method for evaluating defects in epitaxial wafers, the method comprising:
The epitaxial wafer is heated in a reducing atmosphere containing hydrogen halide and hydrogen,
The concentration of the hydrogen halide in the reducing atmosphere is 5% or more, and heat treatment is performed at a temperature of 300°C to 800°C for 3 seconds or more, or the concentration of the hydrogen halide in the reducing atmosphere is 1% or more. % or more and less than 5%, and by performing heat treatment at a temperature of 300°C to 800°C for 15 seconds or more,
A method for evaluating defects in epitaxial wafers is provided, in which defects are exposed on the surface of the epitaxial wafer, detected, and evaluated.

By performing such heat treatment, defects in the epitaxial wafer can be brought to light in a shorter time and at lower temperatures, making it easier to detect defects.

Further, it is preferable that the hydrogen halide is hydrogen chloride, and that the concentration of the hydrogen chloride in the reducing atmosphere is 30% or less.

Hydrogen chloride can reliably expose defects through its etching action. Further, by setting the concentration to 30% or less, it is possible to prevent the etching rate from becoming too high and completely etching the epitaxial film.

Further, it is preferable that the concentration of the hydrogen chloride in the reducing atmosphere is 10% or less.

If the concentration of hydrogen chloride is 10% or less, it is extremely easy to control the amount of etching with time.

Further, it is preferable that the epitaxial wafer is a heteroepitaxial wafer in which the substrate and the epitaxial layer have different compositions.

Furthermore, it is more preferable that the epitaxial wafer has a substrate made of silicon and an epitaxial layer made of silicon germanium or germanium.

The epitaxial wafer defect evaluation method of the present invention can be particularly suitably used for materials that are unstable to heat treatment at high temperatures and for long periods of time.

Further, it is preferable that the defects in the epitaxial wafer are stacking faults or threading dislocations originating from the epitaxial layer.

The epitaxial wafer defect evaluation method of the present invention can be suitably used to evaluate such defects.

Further, it is preferable that the revealed defects be detected and evaluated using a scanning electron microscope or a surface defect inspection device.

By using a scanning electron microscope, detailed analysis of defect shape, size, composition, defect density, etc. can be performed, and by using a surface defect inspection device, defect density and distribution can be accurately analyzed in a short time. can do.

As described above, with the method for evaluating defects in epitaxial wafers of the present invention, defects in epitaxial wafers can be exposed in a shorter time and at lower temperatures, and can be evaluated with high accuracy. Therefore, the epitaxial wafer defect evaluation method of the present invention can be suitably used for materials that are unstable to heat treatment at high temperatures and for long periods of time. Further, if the concentration of hydrogen halide (hydrogen chloride) in the reducing atmosphere is set to 10% or less, the amount of etching can be easily controlled in terms of time, which is also useful for detailed analysis.

FIG. 2 is a flow diagram illustrating a method for evaluating defects in epitaxial wafers according to the present invention.

As described above, there has been a need for the development of a method for evaluating defects in epitaxial wafers that allows defects in epitaxial wafers to become apparent in a shorter time and at lower temperatures and to be evaluated with high accuracy.

The present inventor prepared an epitaxial wafer in a reducing atmosphere containing a hydrogen halide gas etchant and hydrogen at a temperature of 300°C to 800°C, at a concentration of 5% or more of a hydrogen halide gas, for at least 3 seconds. It has been found that defects can be exposed and detected on the surface of the epitaxial wafer by performing a heat treatment of 1% or more and less than 5% of a gas consisting of hydrogen halide for 15 seconds or more. The present invention has been completed.

That is, the present invention provides a defect evaluation method for an epitaxial wafer, in which the epitaxial wafer is heated in a reducing atmosphere containing hydrogen halide and hydrogen, and the concentration of the hydrogen halide in the reducing atmosphere is 5% or more. and heat treatment for 3 seconds or more at a temperature of 300°C to 800°C, or the concentration of the hydrogen halide in the reducing atmosphere is set to 1% or more and less than 5%, and heat treatment is performed at a temperature of 300°C to 800°C for 15 seconds. This is a defect evaluation method for epitaxial wafers, in which defects are exposed on the surface of the epitaxial wafer and detected and evaluated by performing heat treatment for more than a second.

Hereinafter, the present invention will be explained in detail, but the present invention is not limited thereto.

FIG. 1 shows a flow diagram illustrating the epitaxial wafer defect evaluation method of the present invention. First, an epitaxial wafer is prepared (step (1) in the flow diagram). Next, this epitaxial wafer is heat-treated in a reducing atmosphere containing hydrogen halide and hydrogen to expose defects on the surface of the epitaxial wafer (step (2) in the flow diagram). The heat treatment at this time is heat treatment at a temperature of 300°C to 800°C for 3 seconds or more (heat treatment condition 1) at a concentration of hydrogen halide in a reducing atmosphere of 5% or more, or a heat treatment in a reducing atmosphere of hydrogen halide. Heat treatment is performed at a temperature of 300° C. to 800° C. for 15 seconds or more (heat treatment condition 2) at a concentration of 1% or more and less than 5%. Then, defects manifested on the wafer surface are detected and evaluated (step (3) in the flow diagram). Each step will be explained in more detail below.

<Step (1)>
Although the epitaxial wafer to be evaluated according to the present invention is not particularly limited, it is preferably a heteroepitaxial wafer in which the substrate and epitaxial layer have different compositions. For example, silicon germanium (SiGe) or germanium (Ge) is epitaxially grown on a silicon wafer. (a wafer in which the substrate is silicon and the epitaxial layer is silicon germanium or germanium).

For epitaxial growth conditions, when growing a SiGe film as a source gas, for example, monosilane (SiH ₄ ) gas and monogermane (GeH ₄ ) gas can be used. Moreover, when growing a Ge film, monogermane (GeH ₄ ) gas can be used. Note that the Ge film and the SiGe film may be non-doped films, or may be films doped with carbon (C), phosphorus (P), boron (B), or the like. The growth temperature can be, for example, 600 to 700°C, particularly 650°C. The atmospheric gas may be hydrogen, and the pressure may be, for example, 10 to 20 Torr (1333 to 2666 Pa), particularly 15 Torr (1999.5 Pa).

<Step (2)>
Next, this epitaxial wafer is grown using a reducing agent containing hydrogen halide (a gaseous etchant made of hydrogen halide) and hydrogen, either in the same epitaxial growth apparatus used to fabricate the epitaxial wafer or in another apparatus. Either heat treatment is performed at a temperature of 300°C to 800°C for 3 seconds or more (heat treatment condition 1) with the concentration of hydrogen halide in a reducing atmosphere of 5% or more, or in a reducing atmosphere of hydrogen halide. Heat treatment is performed at a temperature of 300° C. to 800° C. for 15 seconds or more (heat treatment condition 2) with a concentration of 1% or more and less than 5%.

In the present invention, the reducing atmosphere containing hydrogen halide and hydrogen is not particularly limited as long as it contains hydrogen halide and hydrogen at a concentration of 1% or more; for example, in addition to these, nitrogen, argon, etc. May contain. The reducing atmosphere in the present invention is preferably a reducing atmosphere consisting only of hydrogen halide and hydrogen. In the present invention, by performing heat treatment in a reducing atmosphere containing hydrogen halide and hydrogen, defects can be brought to light in a shorter time and at a lower temperature than in a hydrogen atmosphere.

Further, the hydrogen halide is preferably hydrogen chloride. Further, the concentration of hydrogen chloride in the reducing atmosphere is preferably 30% or less. Hydrogen chloride can reliably expose defects through its etching action. Further, by setting the amount to 30% or less, it is possible to prevent the etching rate from becoming too high and completely etching the epitaxial film. Further, it is more preferable that the concentration of hydrogen chloride is 10% or less because the etching amount can be extremely easily controlled by time. In the present invention, the concentration of hydrogen halide in the reducing atmosphere is a volume ratio.

<Heat treatment conditions 1>
In heat treatment condition 1, heat treatment is performed at a concentration of hydrogen halide in a reducing atmosphere of 5% or more and at a temperature of 300° C. to 800° C. for 3 seconds or more.

The concentration of hydrogen halide in the reducing atmosphere is not particularly limited as long as it is 5% or more, but from the viewpoint of ease of controlling the etching amount, it is preferably 30% or less, more preferably 20% or less, and even more preferably It is 10% or less.

The heat treatment temperature is 300°C to 800°C. From the viewpoint of more reliably ensuring thermal stability of the epitaxial wafer, the heat treatment temperature is preferably 700°C or lower, more preferably 600°C or lower, still more preferably 500°C or lower, and extremely preferably 400°C or lower. In addition, from the viewpoint of making defects more reliable, the heat treatment temperature is preferably 400°C or higher, more preferably 500°C or higher, still more preferably 600°C or higher, and extremely preferably 700°C or higher.

If the heat treatment temperature is less than 300° C., it will be outside the temperature control range of the apparatus and is not practical. A heat treatment temperature higher than 800° C. is not practical due to thermal stability problems such as worsening of the roughness of silicon germanium and generation of dislocations due to lattice relaxation.

Further, the heat treatment time is not particularly limited as long as it is 3 seconds or more, but is preferably 300 seconds or less, more preferably 60 seconds or less, still more preferably 45 seconds or less, and extremely preferably 30 seconds or less. The heat treatment time is preferably longer from the viewpoint of more reliably making defects visible, and is preferably shorter from the viewpoint of more reliably ensuring the thermal stability of the epitaxial wafer.

<Heat treatment conditions 2>
In heat treatment condition 2, the heat treatment is performed at a concentration of hydrogen halide in a reducing atmosphere of 1% or more and less than 5% at a temperature of 300° C. to 800° C. for 15 seconds or more.

The upper limit, lower limit, and preferred range of the heat treatment temperature are the same as in the case of heat treatment condition 1. Further, the heat treatment time is not particularly limited as long as it is 15 seconds or more, but is preferably 300 seconds or less, more preferably 60 seconds or less, still more preferably 45 seconds or less, and extremely preferably 30 seconds or less. The heat treatment time is preferably longer from the viewpoint of more reliably making defects visible, and is preferably shorter from the viewpoint of more reliably ensuring the thermal stability of the epitaxial wafer.

By performing heat treatment under heat treatment conditions 1 or 2 as described above, the difference in etching rate between the defective part and other parts is utilized to form pits in the defective part, thereby exposing the defect with high sensitivity. I can do it.

By performing such heat treatment, defects such as stacking faults or threading dislocations originating from the epitaxial layer can be brought to light in a shorter time and at lower temperatures.

<Step (3)>
The method for detecting and evaluating defects that have become apparent on the surface due to the above-described heat treatment is not particularly limited, but can be performed using, for example, a scanning electron microscope, a surface defect inspection device, or the like. By using a scanning electron microscope, detailed analysis of the shape, size, composition, defect density, etc. of defects in the epitaxial layer can be performed. Further, by using a surface defect inspection device, the defect density and distribution of the epitaxial layer can be accurately analyzed in a short time.

Hereinafter, the present invention will be specifically explained using Examples and Comparative Examples, but the present invention is not limited thereto.

(Example 1)
As the epitaxial wafer to be evaluated, a wafer in which silicon germanium was epitaxially grown on a silicon wafer having a diameter of 300 mm was used. This epitaxial wafer was grown in a single-wafer type epitaxial growth apparatus in a hydrogen + hydrogen chloride atmosphere with hydrogen chloride mixing ratios of 1%, 5%, 10%, and 30%, at 600°C for 15 seconds and 30 seconds. Heat treatment was performed. Further, the mixture ratios were set to 5%, 10%, and 30%, and heat treatment was performed at 600° C. for 3 seconds. The number of defects after heat treatment was measured using SP3 (manufactured by KLA-Tencor) in DCO (Darkfield Composite Oblique) mode 60 nmup. The increase rate of detected defects was more than twice as high as the number of defects when the epitaxial wafer was not heat-treated.

(Example 2)
As the epitaxial wafer to be evaluated, a silicon germanium epitaxial wafer similar to that in Example 1 was used, and in a single-wafer epitaxial growth apparatus, the mixture ratio of hydrogen chloride was 5% in a hydrogen + hydrogen chloride atmosphere, and 300, 400, 600, 800 Heat treatment was performed at ℃ for 3 seconds. The number of defects after heat treatment was measured using SP3 DCO (Darkfield Composite Oblique) mode 60 nmup. The increase rate of detected defects was more than twice as high as the number of defects when the epitaxial wafer was not heat-treated.

(Comparative example 1)
As the epitaxial wafer to be evaluated, a silicon germanium epitaxial wafer similar to that in Example 1 was used. In a single-wafer epitaxial growth apparatus, the mixture ratio of hydrogen chloride was 1% in a hydrogen + hydrogen chloride atmosphere, and the mixture was heated at 600°C for 3 seconds. Heat treatment was performed. The increase rate of detected defects was 0.99 times the number of defects when the epitaxial wafer was not heat-treated.

(Comparative example 2)
As the epitaxial wafer to be evaluated, a silicon germanium epitaxial wafer similar to that in Example 1 was used, and heat treatment was performed at 600° C. for 3 seconds, 15 seconds, and 30 seconds in a hydrogen atmosphere in a single-wafer epitaxial growth apparatus. The number of defects after heat treatment was measured using SP3 DCO (Darkfield Composite Oblique) mode 60 nmup. The increase rate of detected defects was less than 1.1 times the number of defects when the epitaxial wafer was not heat-treated.

(Comparative example 3)
As the epitaxial wafer to be evaluated, a silicon germanium epitaxial wafer similar to that in Example 1 was used, and heat treatment was performed for 3 seconds at 300, 400, 600, and 800° C. in a hydrogen atmosphere in a single-wafer epitaxial growth apparatus. The number of defects after heat treatment was measured using SP3 DCO (Darkfield Composite Oblique) mode 60 nmup. The increase rate of detected defects was less than 1.1 times the number of defects when the epitaxial wafer was not heat-treated.

Table 1 shows a summary of Example 1 and Comparative Examples 1 and 2. In the range of a hydrogen chloride mixing ratio of 1% to 30%, the increase rate of detected defects is more than double, except when the hydrogen chloride mixing ratio is 1% and the heat treatment time is 3 seconds, which makes the defects of epitaxial wafers obvious and increases the Sensitively detectable.

Table 2 shows a summary of Example 2 and Comparative Example 3. In a heat treatment temperature range of 300° C. or more and 800° C. or less, the increase rate of detected defects is more than double in a hydrogen + hydrogen chloride atmosphere, and defects in the epitaxial wafer are exposed and can be detected with higher sensitivity.

Note that the present invention is not limited to the above embodiments. The above-mentioned embodiments are illustrative, and any embodiment that has substantially the same configuration as the technical idea stated in the claims of the present invention and has similar effects is the present invention. covered within the technical scope of

Claims (7)

A method for evaluating defects in epitaxial wafers, the method comprising:
The epitaxial wafer is heated in a reducing atmosphere containing hydrogen halide and hydrogen,
The concentration of the hydrogen halide in the reducing atmosphere is 5% or more, and heat treatment is performed at a temperature of 300°C to 800°C for 3 seconds or more, or the concentration of the hydrogen halide in the reducing atmosphere is 1% or more. % or more and less than 5%, and by performing heat treatment at a temperature of 300°C to 800°C for 15 seconds or more,
A method for evaluating defects in epitaxial wafers, characterized in that defects are exposed on the surface of the epitaxial wafer, detected, and evaluated. 2. The epitaxial wafer defect evaluation method according to claim 1, wherein the hydrogen halide is hydrogen chloride, and the concentration of the hydrogen chloride in the reducing atmosphere is 30% or less. 3. The epitaxial wafer defect evaluation method according to claim 2, wherein the concentration of the hydrogen chloride in the reducing atmosphere is 10% or less. 4. The epitaxial wafer defect evaluation method according to claim 1, wherein the epitaxial wafer is a heteroepitaxial wafer in which a substrate and an epitaxial layer have different compositions. Defect evaluation of an epitaxial wafer according to any one of claims 1 to 4, wherein the epitaxial wafer has a substrate made of silicon and an epitaxial layer made of silicon germanium or germanium. Method. 6. The method for evaluating defects in an epitaxial wafer according to claim 1, wherein the defects in the epitaxial wafer are stacking faults or threading dislocations originating from the epitaxial layer. The epitaxial wafer defect evaluation method according to any one of claims 1 to 6, wherein the revealed defects are detected and evaluated using a scanning electron microscope or a surface defect inspection device. .

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