JP2023000110A - Evaluation method for washing step and drying step - Google Patents

Abstract

To provide a method capable of easily evaluating the flow of a chemical solution in a washing step of a single crystal silicon wafer and the drying unevenness in a drying step.SOLUTION: An evaluation method for a washing step and a drying step of a single crystal silicon wafer includes the step of cleaning a single crystal silicon wafer with hydrofluoric acid, drying the single crystal silicon wafer after the washing, forming a silicon film on the dried single crystal silicon wafer without hydrogen baking, and evaluating the wafer in-plane distribution of haze after the film formation.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to a method for evaluating a cleaning process and a drying process for a single crystal silicon wafer.

With the miniaturization of semiconductor devices, there is a demand for reducing particles on single crystal silicon wafers. Particles can be removed by cleaning the single-crystal silicon wafer, but the particle removal efficiency is poor in portions where the cleaning liquid flows slowly. In addition, in the drying process after washing, if there are portions that are difficult to dry due to uneven drying, particles in the gas phase may easily adhere or watermarks may occur. A watermark is a portion of a single crystal silicon wafer locally oxidized by water. As described above, in order to reduce particles, it is necessary to grasp the flow of the chemical liquid in the cleaning tank and the uneven drying, but it is difficult to investigate them. For example, by capturing and analyzing fine air bubbles introduced into the cleaning tank and videos of the drying process, it is possible to evaluate the flow of chemicals and uneven drying, but the problem is that special equipment and analysis software are required. There is In addition, since there are many wafers in a batch-type apparatus, there are blind spots for the camera, which may make evaluation difficult.

Reference is made to the prior art. In Patent Document 1, a semiconductor substrate is etched by anisotropic etching with a high selectivity, in which the etching rate for a watermark is lower than that of the substrate material, and the etching depth with respect to the semiconductor substrate is measured among the protruding etching residues exposed on the etching surface. is extracted, and based on the tip shape of the extracted etching residue, residues other than the etching residue formed with the watermark as the vertex are excluded, and the remaining etching residue in the extracted etching residue is A method for evaluating watermarks based on

JP 2009-147057 A

As described above, the method of evaluating the flow of the chemical solution in the cleaning process of single crystal silicon wafers and the drying unevenness in the drying process has been conventionally used. However, the conventional techniques have problems such as requiring special facilities, being unable to evaluate sufficiently, or requiring complicated evaluation.

For example, in the technique described in Patent Document 1, in order to exclude protrusions after dry etching formed due to reasons other than watermarks, the height of each protrusion is measured and the shape of the protrusion is discriminated. There was a problem that it was necessary to perform a complicated evaluation. In addition, there is no description of a method for evaluating the flow of the chemical solution in the washing process and the drying unevenness in the drying process.

As described above, conventional techniques can measure watermarks, but require complicated evaluations. Therefore, there is a need for a method that can easily evaluate the flow of the chemical solution in the washing process and the drying unevenness in the drying process.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and it is an object of the present invention to provide a method for easily evaluating the flow of a chemical solution in the washing process of a single crystal silicon wafer and the drying unevenness in the drying process. do.

In order to solve the above problems, the present invention provides a method for evaluating a cleaning process and a drying process of a single crystal silicon wafer, comprising:
a step of cleaning a single crystal silicon wafer with hydrofluoric acid;
drying the single crystal silicon wafer after the cleaning;
forming a silicon film on the dried single crystal silicon wafer without hydrogen baking;
A step of evaluating the wafer in-plane distribution of haze after the film formation;
To provide a method for evaluating a washing process and a drying process, comprising:

According to such an evaluation method, it is possible to easily evaluate the flow of the chemical solution in the washing process and the drying unevenness in the drying process.

Further, it is preferable to prepare a single crystal silicon wafer having a maximum haze value of 100 ppm or less as the single crystal silicon wafer to be cleaned.

By using such a wafer, it is possible to more reliably evaluate the haze caused by the chemical solution flow in the cleaning process and the drying unevenness in the drying process.

Further, the thickness of the silicon film layer in the film forming process can be set to 0.01 μm or more and 10 μm or less.

If the thickness of the film layer is 0.01 μm or more in this way, it is possible to more reliably evaluate the haze caused by the flow of the chemical solution in the washing process and the uneven drying in the drying process. Further, by setting the thickness to 10 μm or less, it is possible to prevent film formation from taking too much time.

Further, in the film formation step, the silicon film can be formed at a temperature of 450° C. or more and 800° C. or less.

With such a temperature range, it is possible to more reliably prevent the watermark from being removed during the film formation process.

As described above, according to the evaluation method of the cleaning process and the drying process of the present invention, it is possible to easily evaluate the flow of the chemical liquid in the cleaning process of a single crystal silicon wafer and the drying unevenness in the drying process.

Further, by adjusting the conditions of the cleaning process and the drying process based on the evaluation results of the evaluation method of the cleaning process and the drying process of the present invention, it is possible to easily and reliably reduce particles on the single crystal silicon wafer. can.

It is a figure which shows the flow of an example of the evaluation method of the washing process of this invention, and a drying process. 1 shows haze maps in Example 1-1, Example 1-2, Comparative Example 1 and Comparative Example 2. FIG.

As described above, there has been a demand for a method that can easily evaluate the flow of the chemical solution in the cleaning process of single crystal silicon wafers and the drying unevenness in the drying process.

As a result of intensive studies on the above problems, the inventors of the present invention have come up with a method for evaluating a cleaning process and a drying process of a single crystal silicon wafer, comprising a process of cleaning a single crystal silicon wafer with hydrofluoric acid and a process of drying after the cleaning. , a step of forming a silicon film on the dried single crystal silicon wafer without hydrogen baking, and a step of evaluating the distribution of haze in the wafer surface after the film formation. The inventors have found that the evaluation method can easily evaluate the flow of the chemical solution in the washing process of single crystal silicon wafers and the drying unevenness in the drying process, and have completed the present invention.

That is, the present invention is a method for evaluating a cleaning process and a drying process of a single crystal silicon wafer,
a step of cleaning a single crystal silicon wafer with hydrofluoric acid;
drying the single crystal silicon wafer after the cleaning;
forming a silicon film on the dried single crystal silicon wafer without hydrogen baking;
A step of evaluating the wafer in-plane distribution of haze after the film formation;
A method for evaluating a washing process and a drying process, comprising:

Hereinafter, the present invention will be described in detail with reference to the drawings, but the present invention is not limited thereto.

FIG. 1 shows a flow of an example of an evaluation method for a cleaning process and a drying process (flow of a chemical solution in the cleaning process and drying unevenness in the drying process) of a single crystal silicon wafer according to the present invention.

Step S11 in FIG. 1 is a step of preparing a single crystal silicon wafer.
Here, the manufacturing method of the substrate is not particularly limited. A substrate manufactured by the Czochralski method (hereinafter referred to as the CZ method) may be used, or a substrate manufactured by the Floating Zone method (hereinafter referred to as the FZ method) may be used. A substrate obtained by epitaxially growing single crystal silicon on a single crystal silicon substrate manufactured by the CZ method or the FZ method may also be used.

It is preferable to set the maximum haze value of the single crystal silicon wafer to be prepared to 100 ppm or less. With such a wafer on which haze is hardly formed at the beginning, it is possible to more reliably evaluate the haze caused by the flow of the chemical solution in the cleaning process and the drying unevenness in the drying process. There is no particular lower limit for haze.

Here, the haze is a low-frequency and low-amplitude component of scattered laser light incident on the surface of a single crystal silicon wafer, and is represented by the ratio of surface scattering intensity to incident laser light intensity.

The step S12 in FIG. 1 is a cleaning step using hydrofluoric acid. By making the single-crystal silicon wafer a hydrophobic surface, watermarks are easily formed, and it is possible to evaluate the cleaning process and the drying process. As hydrofluoric acid, a chemical solution containing other components such as buffered hydrofluoric acid may be used. The concentration of hydrofluoric acid is preferably such that the single crystal silicon wafer becomes a hydrophobic surface, and can be, for example, 0.1% or more and 60% or less. The temperature of hydrofluoric acid can be 10° C. or higher and 50° C. or lower. If the temperature is 10° C. or higher, the occurrence of dew condensation on the wafer after hydrofluoric acid treatment can be more effectively suppressed. Further, if the temperature is 50° C. or less, the amount of volatilized hydrofluoric acid can be set within an appropriate range, so safety can be enhanced.

The cleaning time with hydrofluoric acid can be set until the water repellency can be confirmed, and can be, for example, 1 second or more and 1 hour or less. If the time is 1 second or longer, water repellency can be ensured. Moreover, it is possible to prevent it from taking too much time by setting it to 1 hour or less.

For the hydrofluoric acid cleaning, a batch-type cleaning apparatus in which a plurality of wafers are immersed in a cleaning bath may be used, or a single wafer-type cleaning apparatus in which each wafer is spin-cleaned may be used.

Also, after cleaning with hydrofluoric acid, the substrate may be rinsed with pure water. That is, the cleaning step in the present invention can also include rinsing.

The temperature of the pure water can be 10°C or higher and 100°C or lower. If the temperature is 10° C. or higher, it is possible to more effectively suppress dew condensation on the wafer after rinsing with pure water. Also, the temperature can be 100° C. or lower, which is the boiling point of water.

The time for rinsing with pure water can be 1 second or more and 1 hour or less. If it is 1 second or more, the hydrofluoric acid adhering to the single crystal silicon wafer can be removed more reliably. Moreover, it is possible to prevent it from taking too much time by setting it to 1 hour or less.

Pure water rinsing may be performed using a batch-type cleaning apparatus or a single wafer-type cleaning apparatus.

S13 in FIG. 1 is a step of drying the single crystal silicon wafer after the cleaning.
Drying may be performed in air or in an inert gas atmosphere. Moreover, the temperature at the time of drying can be, for example, room temperature or higher and 300° C. or lower. Dry at room temperature or higher. Further, by setting the temperature to 300° C. or less, a general-purpose heating device can be used.

The environment for transporting the dried wafer to the film forming process can be an atmosphere of an inert gas such as nitrogen or a rare gas or a vacuum to prevent oxidation during transport. No problem. Oxidation in the air progresses more slowly the slower the air flow, so if the environment is closed, the progress of oxidation can be prevented. For example, the dried wafers can be transported in a FOUP (Front Opening Unified Pod) or FOSB (Front Opening Shipping Box) generally used for transporting single crystal silicon wafers.

Moreover, the humidity of the environment during which the wafer is transferred is preferably such that dew condensation does not occur, and can be, for example, 70% or less. There is no lower limit for humidity.

Moreover, the temperature of the environment when the wafer is transferred is preferably about room temperature, and can be, for example, 10° C. or higher and 40° C. or lower. A general-purpose wafer transfer container can be used within such a temperature range.

The time until the wafer after drying is transported to the film forming process can be within one day. Within one day, there is no influence of oxidation in the transportation process. Also, there is no particular lower limit for the transport time.

Step S14 in FIG. 1 is a step of forming a silicon film on a single crystal silicon wafer without hydrogen baking.

For example, silicon can be deposited on a single crystal silicon wafer by epitaxial growth, but the method for depositing silicon is not limited to this.

The film formation conditions are preferably conditions under which a single crystal silicon film can be formed on a bare silicon surface without watermarks. Monosilane or disilane can be used as the gas used for growth. Nitrogen or hydrogen may be used as a carrier gas. Moreover, it is preferable that the pressure of the chamber for epitaxial growth is a pressure at which silicon microcrystals are not generated in the gas phase. For example, the pressure can be 133 Pa or more and 13300 Pa or less. As an epitaxial growth apparatus, a batch type may be used, or a single wafer type may be used.

Also, the film formation temperature can be set to 450° C. or higher and 800° C. or lower. By forming the film at such a temperature, it is possible to prevent watermarks from being removed by hydrogen generated by decomposition of the film forming gas or hydrogen used in the carrier gas.

The thickness of the deposited layer can be 0.01 μm or more and 10 μm or less. By setting the thickness of the film layer to 0.01 μm or more, it is possible to more reliably evaluate the flow of the chemical solution in the cleaning process and the drying unevenness in the drying process. Further, by setting the thickness to 10 μm or less, it is possible to prevent film formation from taking too much time.

In the case of forming a single crystal silicon film, hydrogen baking is usually performed immediately before the film formation to remove the natural oxide film on the substrate surface and to clean the film. In the process, it is preferable to start film formation when a predetermined growth temperature is reached without hydrogen baking. This is to prevent the watermark from being removed by hydrogen. The term "hydrogen baking" as used herein means holding a single crystal silicon wafer at 800° C. or higher in a hydrogen atmosphere for a certain period of time. Since watermarks are not removed at temperatures below 800° C., there is no problem in flowing hydrogen as a carrier gas before film formation at temperatures below 800° C. FIG.

It can be considered that the reason why the watermark becomes conspicuous due to the film formation is that the difference in the film formation speed between the bare silicon surface and the watermark causes a difference in the film thickness, resulting in unevenness. .

S15 in FIG. 1 is a step of evaluating the wafer in-plane distribution of haze.
Haze can be evaluated by a general-purpose defect inspection apparatus that detects defects using scattered laser light. For example, the SurfScan series manufactured by KLA-Tencor can be used for evaluation.

Since oxidation during rinsing progresses faster as the flow velocity increases, a map of the entire wafer surface reflecting the flow velocity distribution can be obtained. In addition, since watermarks are formed at locations where drying is slow, unevenness in drying can also be evaluated.

The in-plane distribution of defects can also be used to evaluate the flow of chemicals in the cleaning process and uneven drying in the drying process, but the in-plane distribution of haze has higher resolution.

As described above with the examples, according to the method for evaluating the cleaning process and the drying process of the present invention, the haze caused by the chemical solution flow in the cleaning process and the drying unevenness in the drying process can be easily evaluated. By adjusting the conditions of the cleaning process and the drying process based on this evaluation result, it is possible to easily and reliably reduce particles on the single crystal silicon wafer.

EXAMPLES The present invention will be specifically described below using Examples and Comparative Examples, but the present invention is not limited to these.

[Example 1-1 and Example 1-2]
The conductivity type, diameter, crystal plane orientation and maximum haze of the prepared single crystal silicon wafer are as follows.
Wafer conductivity type: p-type Diameter: 300 mm
Crystal plane orientation: (100)
Maximum haze: 0.5 ppm

Next, the prepared single crystal silicon wafers were treated with hydrofluoric acid in a batch type (Example 1-1) in which a plurality of wafers were immersed or in a single wafer type (Example 1-2) in which each wafer was spin-washed. washed. After washing, it was rinsed with pure water. Thereafter, in Examples 1-1 and 1-2, a silicon film was formed on the single crystal silicon wafer without hydrogen baking. At this time, the pressure was 4000 Pa, the film formation temperature was 580° C., and the film thickness was 100 nm. Thus, single crystal silicon wafers to be evaluated in Examples 1-1 and 1-2 were obtained.

[Comparative Example 1 and Comparative Example 2]
In Comparative Example 1, a single crystal silicon wafer to be evaluated in Comparative Example 1 was obtained in the same procedure as in Example 1-1 except that silicon film formation was not performed after cleaning with a batch-type apparatus.

In Comparative Example 2, the evaluation target of Comparative Example 2 was performed in the same procedure as in Example 1-1 except that after cleaning with a batch type apparatus, hydrogen baking treatment was performed and then silicon film formation was performed. A single crystal silicon wafer was obtained.

In Comparative Example 2, the hydrogen baking temperature was 1150° C. and the time was 1 minute.

[Evaluation of wafer in-plane distribution of haze]
For the single crystal silicon wafers to be evaluated in Example 1-1, Example 1-2, Comparative Example 1 and Comparative Example 2, the haze was then measured in the DW2 (Darkfield Wide) mode of SurfScan SP5 manufactured by KLA-Tencor. did. The results are shown in FIG.

As shown in FIG. 2, in Comparative Examples 1 and 2, no distribution derived from the washing process and the drying process was observed. In Examples 1-1 and 1-2, a distribution resulting from the washing process or the drying process was observed. A pattern of convection was observed in Example 1-1, which is the case of the batch type apparatus, and a concentric pattern was observed in Example 1-2, which is the case of the single wafer type apparatus. Note that the concentric circular distribution seen in Comparative Example 1 is a distribution derived from the measuring apparatus.

It should be noted that the present invention is not limited to the above embodiments. The above-described embodiment is an example, and any device having substantially the same configuration as the technical idea described in the claims of the present invention and exhibiting the same effect is the present invention. included in the technical scope of

Claims (4)

A method for evaluating a cleaning process and a drying process of a single crystal silicon wafer,
a step of cleaning a single crystal silicon wafer with hydrofluoric acid;
drying the single crystal silicon wafer after the cleaning;
forming a silicon film on the dried single crystal silicon wafer without hydrogen baking;
A step of evaluating the wafer in-plane distribution of haze after the film formation;
A method for evaluating a washing process and a drying process, comprising: 2. The method for evaluating a cleaning process and a drying process according to claim 1, wherein the single crystal silicon wafer to be cleaned has a maximum haze value of 100 ppm or less. 3. The evaluation method of the cleaning process and the drying process according to claim 1, wherein the thickness of the silicon film layer in the film forming process is 0.01 [mu]m or more and 10 [mu]m or less. 4. The evaluation method of the cleaning process and the drying process according to claim 1, wherein in the film forming process, the silicon film is formed at a temperature of 450[deg.] C. or more and 800[deg.] C. or less. .

Images