JP2022138089A - Method of cleaning silicon wafer, method of manufacturing silicon wafer, and silicon wafer - Google Patents

Abstract

To provide a cleaning method capable of roughening front and rear faces of a silicon wafer, to provide a method of manufacturing a silicon wafer capable of obtaining a silicon wafer only whose one side face is selectively roughened, and to provide a silicon wafer capable of reducing conveyance failures during a processing step.SOLUTION: Provided is a cleaning method of roughening a silicon wafer. An oxide film is formed on the silicon wafer by SC1 cleaning, SC2 cleaning, or ozone water cleaning. Front and rear faces of the silicon wafer are roughened by cleaning the silicon wafer formed with the oxide film with any one of an ammonium hydroxide diluted water solution having an ammonium hydroxide concentration equal to or less than 0.051 mass% or a diluted water solution containing ammonium hydroxide and hydrogen peroxide water and having an ammonium hydroxide concentration equal to or less than 0.051 mass% and a hydrogen peroxide concentration equal to or less than 0.2 mass% and four times or less the ammonium hydroxide concentration.SELECTED DRAWING: Figure 1

Description

The present invention relates to a silicon wafer cleaning method capable of roughening the front and back surfaces of a semiconductor silicon wafer, a silicon wafer cleaning method capable of roughening the front and back surfaces or the back surface of a semiconductor silicon wafer, and a silicon wafer manufacturing method. A method and a silicon wafer.

The manufacturing process of silicon wafers for semiconductor devices consists of a single crystal manufacturing process in which a single crystal ingot is grown using the Czochralski (CZ) method, etc., and a wafer processing process in which the single crystal ingot is sliced and processed into a mirror surface. In order to further add value, it may include an annealing step for heat treatment and an epitaxial growth step for forming an epitaxial layer.

The process of mirror-finishing includes a DSP (double-sided polishing) process and a subsequent CMP (single-sided polishing) process. More specifically, from the viewpoint of particle quality and transportation, the DSP-processed wafers are not dried, but are washed as necessary and then stored in water and transported to the CMP process. Therefore, in the CMP process, it is necessary to chuck the wafer stored in water by a robot or the like and transport it to the CMP apparatus. Also, after CMP polishing, similarly, it is necessary to chuck a wafer wet with an abrasive or pure water and transport it to a cleaning process as necessary.

In this way, in the wafer processing process, it is essential to transport the wafer in a wet environment rather than a dry environment. Even if the chuck is released, the wafer is not detached, causing a transport failure. The reason for this is considered to be the roughness of the chucked wafer surface. On the other hand, if the surface roughness of the wafer is poor, the contact area is reduced and the wafer is likely to be detached. In general, the chucked surface is likely to form chuck marks in no small amount, degrading the quality, so the chucked surface is often the back surface of the silicon wafer. Therefore, from the viewpoint of reducing transportation defects, it is preferable that only the back surface of the silicon wafer is rough, and a method for manufacturing such a wafer is desired.

As a general silicon wafer cleaning method, there is a method called RCA cleaning. The RCA cleaning is a cleaning method in which SC1 (Standard Cleaning 1) cleaning, SC2 (Standard Cleaning 2) cleaning, and DHF (Diluted Hydrofluoric Acid) cleaning are combined according to the purpose. This SC1 cleaning involves mixing ammonia water and hydrogen peroxide water in an arbitrary ratio, etching the surface of the silicon wafer with an alkaline cleaning liquid to lift off adhering particles, and further utilizing electrostatic repulsion between the silicon wafer and the particles. It is a cleaning method that removes particles while suppressing redeposition to silicon wafers. SC2 cleaning is a cleaning method for dissolving and removing metal impurities on the surface of a silicon wafer with a cleaning liquid in which hydrochloric acid and hydrogen peroxide are mixed at an arbitrary ratio. DHF cleaning is a cleaning method for removing a chemical oxide film on the surface of a silicon wafer with dilute hydrofluoric acid. Furthermore, ozone water cleaning with strong oxidizing power is sometimes used to remove organic matter adhering to the silicon wafer surface and to form a chemical oxide film on the silicon wafer surface after DHF cleaning. Cleaning of silicon wafers is performed in combination with these cleaning methods depending on the purpose. Among them, SC1 cleaning involves etching, so it is generally known that the surface roughness of the wafer deteriorates after SC1 cleaning.

In addition, as a method for evaluating the surface roughness of the wafer, the Sa (three-dimensional calculated average height) value obtained by an atomic force microscope (AFM) and the Haze value obtained by a particle counter are used as indices. be able to. Haze is expressed as so-called cloudiness and is widely used as an index of silicon surface roughness, and a high haze level indicates that the wafer surface is rough.

In Patent Document 1, a silicon wafer is washed with a dilute aqueous solution containing ammonium hydroxide, hydrogen peroxide and water in a composition range of 1:1:5 to 1:1:2000 to form native oxide films of different thicknesses. method is described. Patent Document 2 describes that in SC1 cleaning, when the concentration of OH ⁻ ionized from ammonium hydroxide is high, Si is preferentially directly etched, resulting in deterioration of wafer surface roughness.

JP-A-7-66195 JP 2011-82372 A JP-A-7-240394 JP-A-10-242107 JP-A-11-121419 Japanese translation of PCT publication No. 2012-523706

As described above, there is a need for silicon wafers with rough surfaces to be chucked in order to reduce transport failures during processing.

The present invention has been made to solve the above-mentioned problems, and includes a cleaning method capable of roughening the front and back surfaces of a silicon wafer, a cleaning method capable of roughening the front and back surfaces or the back surface of a silicon wafer, and a cleaning method capable of roughening only one side surface. It is an object of the present invention to provide a silicon wafer manufacturing method capable of obtaining a silicon wafer which has been roughened to a high degree, and a silicon wafer capable of reducing transport failures during processing steps.

In order to solve the above problems, the present invention provides a cleaning method for roughening a silicon wafer, comprising:
forming an oxide film on the silicon wafer by SC1 cleaning, SC2 cleaning, or ozone water cleaning;
a silicon wafer having the oxide film formed thereon,
A diluted ammonium hydroxide aqueous solution having an ammonium hydroxide concentration of 0.051% by mass or less, or an ammonium hydroxide concentration of 0.051% by mass or less, a hydrogen peroxide concentration of 0.2% by mass or less, and the hydroxide A silicon wafer characterized in that the front and back surfaces of the silicon wafer are roughened by washing with an aqueous solution of either dilute aqueous solution containing ammonium hydroxide and hydrogen peroxide, which is four times or less the concentration of ammonium. Provide a cleaning method.

With such a silicon wafer cleaning method, roughening occurs during etching of the native oxide film, and the front and back surfaces of the silicon wafer can be roughened.

Obtaining in advance the relationship between the ammonium hydroxide concentration or the ammonium hydroxide concentration and the hydrogen peroxide concentration, the cleaning temperature and cleaning time, and the surface roughness after the cleaning for each method of forming the oxide film,
It is preferable to perform cleaning by selecting the ammonium hydroxide concentration or the ammonium hydroxide concentration and the hydrogen peroxide concentration, cleaning temperature, and cleaning time based on the obtained relationship.

The degree of roughening formed by the cleaning method of the present invention varies depending on the method of forming the oxide film, the concentration of ammonium hydroxide, or the concentration of ammonium hydroxide and hydrogen peroxide, the cleaning temperature, and the cleaning time. It is effective to determine the relationship between these conditions and the degree of roughening.

Further, in the present invention, one surface of the silicon wafer cleaned by the silicon wafer cleaning method of the present invention is subjected to CMP polishing, and only the surface opposite to the one surface is selectively roughened. Provided is a method for manufacturing a silicon wafer, characterized by obtaining a silicon wafer having a

After roughening by the cleaning method of the present invention, only one surface of the silicon wafer is polished, so that one surface is in a good surface condition and only the surface opposite to the one surface is selectively roughened. wafers can be produced.

Further, in the present invention, the silicon wafer is characterized by having a roughened surface having a roughness index Sa value of 0.3 nm or more and 5.5 nm or less measured with an atomic force microscope. Provide a silicon wafer for

With such a silicon wafer, the roughened surface exhibits roughness suitable for chucking by a chuck, so that it is possible to reduce transport failures during processing steps.

Further, the present invention provides a silicon wafer having a roughened surface with a roughness index Haze value of 50 ppm or more and 1900 ppm or less measured with a particle counter. .

With such a silicon wafer, the roughened surface exhibits roughness suitable for chucking by a chuck, so that it is possible to reduce transport failures during processing steps.

The surface opposite to the roughened surface is preferably a mirror surface.

Such a silicon wafer can exhibit excellent quality.

Further, in the present invention, there is provided a cleaning method for roughening a silicon wafer, comprising:
a first cleaning step of forming an oxide film on the silicon wafer by SC1 cleaning, SC2 cleaning, or ozone water cleaning;
a second cleaning step of roughening the front and back surfaces or the back surface of the silicon wafer by cleaning with either an aqueous solution containing ammonium hydroxide or an aqueous solution containing ammonium hydroxide and hydrogen peroxide;
There is provided a method for cleaning a silicon wafer, wherein the aqueous solution used in the second cleaning step has an etching selectivity of Si to SiO ₂ of 95 or more.

With such a silicon wafer cleaning method, the natural oxide film formed in the first cleaning step is roughened during etching in the second cleaning step, and a roughened wafer can be manufactured.

Further, the etching selectivity ratio of Si to the _SiO2 of the aqueous solution used in the second cleaning step is obtained from (etching amount of Si/etching amount of _SiO2 ),
As the wafer for calculating the etching amount of Si, using any one of a silicon wafer, an epitaxial wafer, or an SOI wafer with a bare surface without a native oxide film exposed,
As the wafer for calculating the etching amount of SiO ₂ , it is preferable to use a wafer with a silicon oxide film having a film thickness of 3 nm or more.

With such a method, the etching behavior for SiO ₂ and Si can be evaluated with high accuracy.

Further, in advance, for each method of forming the oxide film in the first cleaning step, an etching amount of SiO ₂ necessary for progress of roughening in the second cleaning step is calculated as a roughening etching amount,
The cleaning time of the second cleaning step is selected so that the etching amount of SiO ₂ in the second cleaning step is equal to or greater than the roughening etching amount, and/or the first cleaning is performed before the second cleaning step. An additional cleaning step is added to thin the oxide film so that a part of the oxide film formed in the process remains, and the etching amount of SiO ₂ in the additional cleaning step and the amount of SiO ₂ in the second cleaning step are calculated. It is preferable to adjust the cleaning time so that the total of the etching amount and the roughening etching amount is equal to or greater than the roughening etching amount.

_The roughening of the present invention is performed by etching _SiO2 by a predetermined amount during cleaning to expose Si to the surface. By calculating as, it is possible to advance the roughening more reliably.

Further, in advance, for each method of forming the oxide film in the first cleaning step, the relationship between the etching selectivity of Si to the SiO ₂ and the cleaning time and the surface roughness is obtained,
It is preferable to select the etching selectivity ratio of Si to SiO ₂ and the cleaning time based on the obtained relationship and perform the second cleaning step.

The degree of roughening formed by the cleaning method of the present invention varies depending on the method of forming the oxide film in the first cleaning step, the etching selectivity of Si to SiO ₂ and the cleaning time. It is effective to obtain the relationship with the degree.

Further, in the present invention, one surface of a silicon wafer which has been cleaned by the method for cleaning a silicon wafer of the present invention and whose front and back surfaces have been roughened is subjected to CMP polishing, and only the surface opposite to the one surface is subjected to CMP polishing. Provided is a method for producing a silicon wafer characterized by obtaining a silicon wafer in which is selectively roughened.

Thus, by polishing only the front surface after roughening the front and back surfaces, it is possible to produce a wafer having a good surface condition and having only the rear surface roughened.

Also, the removal amount of the CMP polishing can be set to be equal to or greater than the etching amount of Si in the second cleaning step.

As a result, it is possible to prevent LLS from remaining due to etching after CMP and maintain good LLS quality.

Also, the etching amount of Si in the second cleaning step can be set to be equal to or less than the removal amount of the CMP polishing.

As a result, it is possible to prevent LLS from remaining due to etching after CMP and maintain good LLS quality.

As described above, according to one aspect of the silicon wafer cleaning method of the present invention, the front and back surfaces of the silicon wafer can be roughened.

Further, according to the method for producing a silicon wafer of the present invention, it is possible to produce a wafer in which one surface is in a good surface condition and only the surface opposite to the one surface is selectively roughened. .

In addition, the silicon wafer of the present invention can reduce transport failures during processing steps.

In another aspect of the silicon wafer cleaning method of the present invention, the front and back surfaces or the back surface of the silicon wafer can be roughened.

BRIEF DESCRIPTION OF THE DRAWINGS It is a flowchart which shows an example of the 1st aspect of the cleaning method of the silicon wafer of this invention. After washing the bare surface and the O3 oxide film surface with _three levels of liquid composition NH ₄ OH:H ₂ O ₂ :H ₂ O=1:1:10, 1:1:100, and 1:1:1000 It is the figure which showed the SEM image and Haze value of this. It is the graph which showed the Si etching amount of three levels of liquid composition _NH4OH :H2O2: _{H2O = 1} :1:10, 1:1:100, and 1:1:1000. 1 is a graph showing the difference in Si etching amount between a bare surface and an O ₃ oxide film surface in a liquid composition of NH ₄ OH:H ₂ O ₂ :H ₂ O=1:1:1000 (45° C.). FIG. 10 is another graph showing the difference in Si etching amount on the O ₃ oxide film surface in the liquid composition NH ₄ OH:H ₂ O ₂ :H ₂ O=1:1:1000 (80° C.). It is the figure which showed the SEM image, Haze value, and Sa value of AFM after roughening by changing the oxide _- film formation method, _NH4OH density|concentration, H2O2 density _| concentration, cleaning temperature, and cleaning time. FIG. 10 is a graph showing variation of haze with respect to cleaning time when NH ₄ OH concentration, H ₂ O ₂ concentration, and cleaning time are changed. FIG. 4 is a flow chart showing an example of a second embodiment of the silicon wafer cleaning method of the present invention. Liquid composition _NH4OH :H2O2: _{H2O = 1} : ₁ :10, 1:1:100, 1:1:1000, 1:0.01: It is the figure which showed the SEM image and Haze value after wash|cleaning by 5 levels of 10 and 1:0.05:100. It is the graph which showed the Si etching amount of three levels of liquid composition _NH4OH :H2O2: _{H2O = 1} :1:10, 1:1:100, and 1:1:1000. 4 is a graph showing SiO ₂ etching amounts at three levels of liquid composition NH ₄ OH:H ₂ O ₂ :H ₂ O=1:1:10, 1:1:100, and 1:1:1000. 4 is a graph showing Si/SiO ₂ etching selectivity at three levels of liquid composition NH ₄ OH:H ₂ O ₂ :H ₂ O=1:1:10, 1:1:100, and 1:1:1000. FIG. 4 is a diagram showing SEM images, Haze values, and AFM Sa values after roughening with different oxide film types and Si/SiO ₂ etching selectivity ratios. 4 is a graph showing variation of Haze with respect to cleaning time when roughening is performed by changing Si/SiO ₂ etching selectivity and cleaning time. 5 is a graph showing the LLS quality after CMP polishing with a Si etching amount and a polishing allowance of 500 nm. It is a schematic side view showing a part of an example of the silicon wafer of the present invention.

As described above, a silicon wafer having a rough surface to be chucked has been required in order to reduce transport failures during processing.

In order to achieve the above object, the present inventors investigated the etching behavior of silicon wafers using a cleaning solution consisting of ammonium hydroxide, hydrogen peroxide solution, and water. (method of forming an oxide film), liquid composition (especially concentration of ammonium hydroxide and hydrogen peroxide), cleaning temperature, and cleaning time. As a result, for silicon wafers having natural oxide films on the front and back surfaces, the ammonium hydroxide diluted aqueous solution having an ammonium hydroxide concentration of 0.051% by mass or less, or the ammonium hydroxide concentration being 0.051% by mass or less, Oxidation by washing with any diluted aqueous solution containing ammonium hydroxide and hydrogen peroxide, in which the concentration of hydrogen peroxide is 0.2% by mass or less and the concentration of ammonium hydroxide is 4 times or less. The film is roughened without being etched uniformly, and the degree of roughening is determined by the type of natural oxide film (method of forming the oxide film), liquid composition (especially ammonium hydroxide concentration and hydrogen peroxide concentration), cleaning The inventors have found that the temperature and washing time can be controlled to complete the present invention.

In addition, in order to solve the above problems, the present inventors diligently studied the etching behavior using a cleaning solution consisting of ammonium hydroxide, hydrogen peroxide solution, and water, particularly the difference in etching behavior between SiO ₂ and Si. did. As a result, when a silicon wafer having a natural oxide film on its surface is cleaned with a cleaning solution having a high etching selectivity ratio of Si to _SiO2 , rapid etching occurs at places where Si is exposed, resulting in roughening, and The inventors have found that this roughening behavior can be adjusted by controlling the selectivity, and completed another aspect of the present invention.

That is, the present invention is a cleaning method for roughening a silicon wafer,
forming an oxide film on the silicon wafer by SC1 cleaning, SC2 cleaning, or ozone water cleaning;
a silicon wafer having the oxide film formed thereon,
A diluted ammonium hydroxide aqueous solution having an ammonium hydroxide concentration of 0.051% by mass or less, or an ammonium hydroxide concentration of 0.051% by mass or less, a hydrogen peroxide concentration of 0.2% by mass or less, and the hydroxide A silicon wafer characterized in that the front and back surfaces of the silicon wafer are roughened by washing with an aqueous solution of either dilute aqueous solution containing ammonium hydroxide and hydrogen peroxide, which is four times or less the concentration of ammonium. cleaning method.

Further, according to the present invention, one surface of a silicon wafer cleaned by the method for cleaning a silicon wafer of the present invention is subjected to CMP polishing, and only the surface opposite to the one surface is selectively roughened. A method for producing a silicon wafer, characterized by obtaining a silicon wafer having a

Further, the present invention is characterized by a silicon wafer having a roughened surface with a roughness index Sa value of 0.3 nm or more and 5.5 nm or less measured with an atomic force microscope. It is a silicon wafer that

Further, the present invention is a silicon wafer characterized by having a roughened surface with a roughness index Haze value of 50 ppm or more and 1900 ppm or less measured with a particle counter.

The present invention also provides a cleaning method for roughening a silicon wafer, comprising:
a first cleaning step of forming an oxide film on the silicon wafer by SC1 cleaning, SC2 cleaning, or ozone water cleaning;
a second cleaning step of roughening the front and back surfaces or the back surface of the silicon wafer by cleaning with either an aqueous solution containing ammonium hydroxide or an aqueous solution containing ammonium hydroxide and hydrogen peroxide;
In the method of cleaning a silicon wafer, the aqueous solution used in the second cleaning step has an etching selectivity ratio of Si to SiO ₂ of 95 or more.

Further, according to the present invention, one surface of a silicon wafer which has been cleaned by the method for cleaning a silicon wafer of the present invention and whose front and back surfaces have been roughened is subjected to CMP polishing, and only the surface opposite to the one surface is subjected to CMP polishing. A method for producing a silicon wafer characterized by obtaining a silicon wafer in which is selectively roughened.

Incidentally, Patent Documents 1 and 2 refer only to the effect of surface roughness on the front and back surfaces of a wafer. Further, Patent Documents 3 to 6 also disclose techniques related to cleaning semiconductor substrates such as silicon wafers. No detailed study has been made on the type of oxide film, liquid composition, temperature and time.

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

(Silicon wafer cleaning method and silicon wafer manufacturing method)
[First aspect]
First, the first aspect of the method for cleaning a silicon wafer of the present invention will be described.
FIG. 1 is a flow chart showing an example of the first embodiment of the silicon wafer cleaning method of the present invention.
As shown in S1 of FIG. 1, a silicon wafer whose front and back surfaces are to be roughened is prepared. There are no restrictions on the conductivity type or diameter of the wafer, and examples thereof include wafers after DSP processing.

Next, as in S2, an oxide film is formed on the silicon wafer by SC1 cleaning, SC2 cleaning, or ozone cleaning. If a natural oxide film is formed on the wafer before cleaning, it is preferable to remove it by HF cleaning in advance, and then perform the cleaning described above. This is because, in the present invention, the etching behavior differs depending on the type of oxide film, that is, the method of forming the oxide film, and the formed roughness varies. For example, an oxide film can be formed as it is on a bare surface wafer after DSP processing without HF cleaning. The cleaning conditions at this time may be general conditions for SC1, SC2, and ozone water cleaning. For example, in SC1 cleaning, the mixing ratio of ammonium hydroxide, hydrogen peroxide, and water is NH ₄ OH:H ₂ O ₂ :H ₂ O=1:1:5 to 1:1:100, and the cleaning temperature is The washing time can be 1 minute to 30 minutes at 60° C. or higher. For example, in SC2 cleaning, the mixing ratio of HCl, hydrogen peroxide, and water is HCl:H ₂ O ₂ :H ₂ O=1:1:5 to 1:1:20, and the cleaning temperature is 60° C. or higher. The time can be from 1 minute to 30 minutes. For example, in the case of ozone water cleaning, the ozone concentration can be 3 ppm to 25 ppm, the cleaning temperature can be room temperature, and the cleaning time can be 1 minute to 30 minutes. As will be described later, the roughness formed in the present invention varies depending on the type of oxide film formed in S2 (method of forming the oxide film). Just do it.

Subsequently, as in S3, an ammonium hydroxide diluted aqueous solution having an ammonium hydroxide concentration of 0.051% by mass or less, or an ammonium hydroxide concentration of 0.051% by mass or less and a hydrogen peroxide concentration of 0.2% by mass % or less and not more than 4 times the ammonium hydroxide concentration, and washed with a dilute aqueous solution containing ammonium hydroxide and hydrogen peroxide. At this time, for example, in the case of washing with a batch-type washing machine in which chemical baths are continuous, the washing of the present invention can be efficiently performed in one batch by performing washing in S3 after washing in S2.

Here, the roughness formed by the present invention includes the presence or absence of an oxide film on the front and back surfaces of a silicon wafer, the type of oxide film (method of forming an oxide film), the liquid composition (concentration of ammonium hydroxide and hydrogen peroxide), cleaning temperature, and in terms of cleaning time.

In FIG. 2, SC1 liquid composition is NH ₄ OH:H ₂ O ₂ :H ₂ O=1:1:10, 1:1 for the bare surface of the DSP wafer and the O ₃ oxide film surface (formed in S2). : 100, 1: 1: 1000, and after washing at 80 ° C. / 10 minutes, the front and back surface observation results of a scanning electron microscope (SEM: Scanning Electron Microscopy) and the Haze value obtained with a particle counter were compared. Indicated. The chemicals used were 28% by mass of ammonia water (NH ₄ OH) and 30% by mass of hydrogen peroxide solution (H ₂ O ₂ ), each of which is also expressed in weight (wt) %. The mass % is the concentration expressed as a percentage by mass of the cleaning solution and the solute (ammonium hydroxide, hydrogen peroxide) contained therein, and is also expressed as wt %. Only the level washed with a liquid composition of 1: ₁ :1000 against the O3 oxide film surface has a large uneven shape in the SEM image, and the haze value is 470 ppm, which is larger than the other levels, indicating that the surface is roughened. I understand. The bare surface washed with a liquid composition of 1:1:1000 is also slightly roughened, but the degree of roughening is smaller than that of the _O3 oxide film surface. From these results, it can be seen that the deposition of oxide films on the front and back surfaces and the low composition of the SC1 solution are factors of roughening.

FIG. 3 shows the etching amount of Si in the SC1 solution composition NH ₄ OH:H ₂ O ₂ :H ₂ O=1:1:10, 1:1:100 and 1:1:1000. There is a tendency that the lower the liquid composition, the higher the etching amount, which indicates that the lower the liquid composition, the more dominant the etching reaction. 4 and 5 show the results of examining the amount of Si etched with two levels of surface conditions, bare surface and O ₃ oxide film surface, with a liquid composition of 1:1:1000. It can be seen that at 45° C., etching progresses only on the bare surface, and progresses only slightly on the O ₃ oxide film surface. Also, at 80° C., it can be seen that the progress of etching on the surface of the O ₃ oxide film is small at 80° C./3 minutes, but the etching progresses rapidly after 6 minutes. Although not shown in FIG. 5, at 80° C., the etching amount of the bare surface exceeded 55 nm after 3 minutes, and the etching amount of the O ₃ oxide film surface exceeded 55 nm after 12 minutes. Therefore, it can be seen that the etching behaviors of Si and _SiO2 are significantly different in a low-liquid composition environment, with Si being easily etched and _SiO2 being difficult to etch. Considering the results of FIG. 2 together with the etching amounts in FIGS. 4 and 5, it can be seen that roughening occurs not on the bare surface where the Si etching amount is large, but _on the O3 oxide film surface where the etching amount is small. It is considered that the roughening is caused by the etching behavior of the oxide film under the low liquid composition environment. In addition, since the same result as the liquid composition 1:1:1000 is obtained even with the liquid composition NH ₄ OH:H ₂ O ₂ :H ₂ O = 1:0:1000, the ammonia dilution containing no hydrogen peroxide solution Aqueous solutions can also be roughened.

Next, FIG. 6 shows the results of investigating the effects of the type of natural oxide film (method of forming the oxide film), liquid composition (concentration of ammonium hydroxide and hydrogen peroxide), cleaning temperature, and cleaning time. . From the SEM image, the type of oxide film _, SC1 liquid composition, cleaning temperature, , and the washing time, various roughnesses are formed. Furthermore, the Sa value obtained from AFM also varies widely from 0.31 to 5.5 nm, and the Haze value also varies from 104 to 1871 ppm. That is, the method of forming the oxide film, the concentration of ammonium hydroxide, or the concentration of ammonium hydroxide and hydrogen peroxide, the cleaning temperature, and the cleaning time are evaluated in advance to evaluate the roughness after cleaning, and these conditions and the roughness after cleaning are evaluated. By obtaining the relationship between , the cleaning conditions can be determined according to the desired roughness.

When the temperature was fixed at 80° C. in more detail and the liquid composition was investigated, as shown in FIG. However, with the cleaning liquid having a liquid composition of 1:5:1000, the haze value did not increase even after cleaning for 15 minutes, and the silicon wafer was not roughened. Therefore, hydrogen peroxide has the effect of inhibiting the progress of etching, and the weight concentration of the liquid composition 1:3:1000 is 0.025% by mass for NH ₄ OH and 0.099% by mass for H ₂ O ₂ . Therefore, the H ₂ O ₂ weight concentration should be less than four times the NH ₄ OH weight concentration. Since the cleaning method of the present invention is based on the etching action of ammonium hydroxide and the oxidizing action of aqueous hydrogen peroxide, the cleaning method for silicon wafers of the present invention is effective in such cases. In addition, since the NH ₄ OH weight concentration of the liquid composition 1:1:500 is 0.051% by mass, the NH ₄ OH must be 0.051% by mass or less, and the liquid composition is changed within this range. It becomes possible to

Next, the oxide film type (oxide film forming method) was also investigated. A thermal oxide film with a thickness of 5 nm was produced in a dry oxygen atmosphere using a resistance heating furnace, and was washed under the conditions of 80° C./10 minutes using a liquid composition of 1:1:1000, but the haze value did not increase, and the SEM No roughened image was observed from the images. From this result, it is considered that the oxide film formed by SC1, SC2, or ozone water cleaning is optimal for roughening within the time when actual operation is possible.

In general, the thickness of the oxide film formed by cleaning is about 1 nm, the presence of an uneven and unstable layer called a structural transition layer at the interface between the silicon oxide film and silicon, and the oxide film thickness. Combined with the fact that no roughening occurs with a thermal oxide film of as little as 5 nm, it is considered that the roughening that occurs during etching of the oxide film occurs from the vicinity of the structural transition layer at the interface between the silicon oxide film and silicon. In the case of a thermally oxidized film with a thickness of 5 nm, it is considered that etching of the oxide film did not proceed to the vicinity of the structural transition layer in the cleaning time of 10 minutes, and therefore roughening did not occur. As a result, it is thought that the roughness changed depending on the type of natural oxide film.

Therefore, as described above, for each oxide film type (oxide film forming method), the ammonium hydroxide concentration or the ammonium hydroxide concentration and hydrogen peroxide concentration, the cleaning temperature and cleaning time, and the surface roughness after cleaning are determined in advance. It is more preferable to determine the relationship, select the ammonium hydroxide concentration or the ammonium hydroxide concentration and the hydrogen peroxide concentration, the cleaning temperature, and the cleaning time based on the determined relationship, and perform the cleaning. As a result of intensive investigation by the present inventors, as shown in FIGS. 6 and 7, for example, the AFM roughness index Sa value is 0.3 to 5.5 nm, and the particle counter Haze is 50 to 1871 ppm. can be changed.

Finally, it is often preferable that the surface roughness of the front surface of the silicon wafer, which serves as the device fabrication surface, is good. For example, if the cleaning method of the present invention is performed with a batch-type cleaning machine, both the front and back surfaces will be roughened. It is possible to produce wafers that are selectively roughened only on the surface of the With such a wafer, chuck failure does not occur even in a wet environment, and stable production is possible.

[Second aspect]
Next, a second embodiment of the method for cleaning silicon wafers of the present invention will be described.
FIG. 8 is a flow chart showing an example of the second embodiment of the silicon wafer cleaning method of the present invention.

First, prepare a silicon wafer whose back surface is to be roughened. There are no restrictions on the conductivity type or diameter of the wafer, and examples thereof include wafers after DSP processing.

Next, as in SA1, an oxide film is formed on the silicon wafer by SC1 cleaning, SC2 cleaning or ozone cleaning (first cleaning step). If a natural oxide film is formed on the wafer before cleaning, it is preferable to perform the above first cleaning step after removing it by HF cleaning in advance. This is because, in the present invention, the etching behavior differs depending on the type of oxide film, that is, the method of forming the oxide film in the first cleaning step, and the formed roughness varies. For example, an oxide film can be formed as it is on a bare surface wafer after DSP processing without HF cleaning. The cleaning conditions at this time may be general conditions for SC1, SC2, and ozone water cleaning. This general condition can be, for example, the condition described in the first aspect.

SA3 shown in FIG. 8 is an optional step that can be performed after the first cleaning step SA1 and before the second cleaning step SA2 described below. Step SA3 will be described later.

Subsequently, as in SA2, the silicon wafer on which the oxide film was formed was treated with an aqueous solution containing ammonium hydroxide or a hydroxide with an etching selectivity ratio of Si to _SiO2 (Si/ _SiO2 etching selectivity) of 95 or more. Wash with any one of aqueous solutions containing ammonium and hydrogen peroxide (second washing step).

Here, the roughening phenomenon of the present invention is described in detail in terms of the etching behavior of Si and _SiO2 . Details of the method for calculating the etching amounts of Si and SiO ₂ will be described later.

_FIG . 9 shows SC1 composition (liquid composition NH ₄ OH:H ₂ O ₂ :H ₂ O), cleaning temperature and SEM (Scanning Electron Microscope) surface observation results and Haze values obtained with a particle counter after washing for different washing times are shown.

The chemicals used were 28% by mass ammonia water (NH ₄ OH) and 30% by mass hydrogen peroxide solution (H ₂ O ₂ ), each of which is also expressed in mass (wt) %. The mass % is the concentration expressed as a percentage by mass of the cleaning solution and the solute (ammonium hydroxide, hydrogen peroxide) contained therein, and is also expressed as wt %. FIG. 9 also shows the etching selectivity ratio of Si to SiO ₂ obtained by a calculation method to be described later.

Only the levels washed with aqueous solutions of 1:1:1000, 1:0.01:10, and 1:0.05:100, which have a very high selectivity with respect to the O3 oxide film surface _, have large irregularities in the SEM image. is observed, and the haze value is also 275 to 470 ppm, which is much higher than other levels, indicating that the surface is roughened. The bare surface is also slightly roughened by washing with aqueous solutions of 1:1:1000, 1:0.01:10, and 1:0.05:100 liquid compositions with very high selection ratios. However, the degree of roughening is smaller than that of the O3 oxide film surface _, and the oxide film is deposited on the surface and the Si/ _SiO2 etching selectivity of the cleaning solution used in the second cleaning step SA2 is high. I understand. This is because the oxide film formed in the first cleaning step SA1 is etched during the second cleaning step SA2, causing rapid etching of Si at locations where Si is locally exposed, resulting in roughening. In order to advance the etching, it is necessary to wash with a cleaning solution having a high Si/SiO ₂ etching selectivity, specifically 95 or more.

Next, a method for calculating the Si/SiO ₂ etching selectivity, which is used as an index in the present invention, will be described in detail.

The etching selectivity ratio of Si to SiO ₂ of the aqueous solution used in the second cleaning step SA2 can be obtained from (etching amount of Si/etching amount of SiO ₂ ).

The etching amount of Si is determined by preparing a silicon wafer, an epitaxial wafer, or an SOI (Silicon on Insulator) wafer having no natural oxide film, that is, a bare surface without a natural oxide film, or an SOI (Silicon on Insulator) wafer. (an aqueous solution for calculating the Si/SiO ₂ etching selectivity), the difference in film thickness before and after cleaning is measured, and this can be used as the etching amount.

For example, HF cleaning or the like is used to remove the natural oxide film. If a natural oxide film exists on the wafer, etching of Si does not occur until the natural oxide film is etched, and the etching amount of Si cannot be evaluated with high accuracy. In addition, the presence of the natural oxide film advances the above-described roughening phenomenon, roughening the wafer surface, which may affect the measurement value. , the wafer must have no native oxide film.

The wafer to be used may be appropriately selected according to the amount of etching. Since the thickness of a silicon wafer is generally about 775 μm, if the etching amount is at least 1 μm or more, the amount of change in thickness can be captured. For example, the thickness of the wafer measured by a general flatness measuring device can be used as an index, and the thickness of the wafer before and after cleaning can be used as the etching amount. Note that the measuring instrument is not particularly limited as long as it can measure the thickness of the wafer. For example, if the etching amount is several tens of nanometers, the amount of change in thickness is very small and it is difficult to grasp the amount of change, and it is not preferable to use the wafer thickness as an index.

When the etching amount is several tens of nm to several hundreds of nm, an epitaxial wafer having an epitaxial thickness of several μm or an SOI wafer having a Si layer thickness of several tens of nm to several hundreds of nm on the surface side of the Si/SiO ₂ /Si structure is used. It may be selected according to the necessary etching amount. Regarding film thickness measurement, for example, in the case of an epitaxial wafer, the difference in film thickness is calculated by measuring the epitaxial thickness after washing by measuring the spreading resistance, using the difference in resistivity between the epilayer and sublayers. be able to. For example, spectroscopic ellipsometry can be used to measure the film thickness of an SOI wafer. For example, if an SOI wafer with a Si layer of 100 nm or less is used when the etching amount is several nn, accurate evaluation can be performed. The evaluation method is not particularly limited as long as the thickness of the epi layer and Si layer can be evaluated for both the epitaxial wafer and the SOI wafer.

Subsequently, as a wafer for calculating the etching amount of SiO ₂ , it is desirable to prepare a wafer having a silicon oxide film of 3 nm or more.

In general, when a silicon wafer having a natural oxide film is subjected to SC1 cleaning, in which the etching of the oxide film and the oxidation reaction of silicon compete, when the silicon oxide film is etched and becomes thin, the oxidation species diffuses through the silicon oxide film. Since the oxidation reaction of silicon proceeds, the natural oxide film thickness becomes a constant value regardless of the cleaning time. In this case, even if the film thickness difference before and after cleaning is calculated, the etching amount of SiO ₂ cannot be obtained accurately due to the presence of the silicon oxide film formed by the oxidation reaction of silicon. Furthermore, the normal native oxide film thickness is about 1 nm, and it is difficult to accurately measure a change of 1 nm.

Therefore, by preparing a silicon oxide film having a thickness of 3 nm or more by thermal oxidation, for example, and measuring the thickness of the oxide film before and after cleaning, the etching amount of SiO ₂ can be calculated with high accuracy. If the film thickness is 3 nm or more, oxidizing species cannot diffuse in the oxide film and oxidation of silicon does not occur. Therefore, since only the etching of SiO ₂ proceeds, the etching amount of SiO ₂ can be calculated with high accuracy. Furthermore, the film thickness can also be measured with high accuracy.

The film thickness of the silicon oxide film can be appropriately selected from the amount of etching, and the prepared wafer with the silicon oxide film is washed with an aqueous solution for calculating the Si/SiO ₂ etching selectivity, and the film thickness difference before and after washing is calculated. For example, spectroscopic ellipsometry can be used as a measurement method.

After obtaining the etching amount of Si and the etching amount of _SiO2 at the same liquid composition and cleaning temperature in this manner, the etching selectivity ratio of Si to _SiO2 is calculated from (etching amount of Si/etching amount of _SiO2 ). Just calculate. Alternatively, the etching rate per unit time may be calculated, and the etching selectivity ratio of Si to SiO ₂ may be calculated from (etching rate of Si/etching rate of SiO ₂ ).

If this index is equal to or higher than a certain value, only Si is preferentially etched at a location where SiO ₂ is etched and Si is exposed, so roughening progresses. Since the etching behavior of Si and SiO ₂ changes depending on the cleaning temperature, the Si/SiO ₂ selection ratio is obtained for each composition and cleaning temperature to ensure that the roughening proceeds under various conditions. can be done. As a result of investigation by the present inventors, it was found that the etching selectivity of Si/ _SiO2 was 95 or more because the roughening progressed with a cleaning liquid having a selectivity of 95 (for example, a liquid composition of 1:1:1000 and a cleaning condition of 45°C). must be.

10 to 12 show the etching amounts of Si and SiO ₂ and the calculated Si/SiO ₂ etching selectivity when cleaning was performed with a cleaning time of 3 minutes, three levels of liquid composition, and three levels of cleaning temperature. indicates From FIGS. 10 to 12, the Si etching amount is the largest in the aqueous solution with a liquid composition of 1:1:1000, and the _SiO2 etching amount is small in the aqueous solution with a liquid composition of 1:1:1000. It can be seen that the Si/SiO ₂ etching selectivity ratio is high in the aqueous solution with a composition of 1:1:1000.

Next, the details of the SiO ₂ etching amount required to advance the roughening are described. As described above, the roughening of the present invention progresses by etching the native oxide film during cleaning and causing rapid etching of Si at locations where Si is exposed. In other words, roughening can be promoted by etching the amount of SiO ₂ necessary for exposing Si when cleaning with a cleaning solution having a selection ratio of 95 or more. Therefore, the etching amount of SiO ₂ required for roughening in the second cleaning step SA2 is obtained as a roughening etching amount for each method of forming an oxide film in the first cleaning step SA1. By setting the cleaning time of the second cleaning step SA2 so that the etching amount of SiO ₂ of is equal to or greater than the roughening etching amount, roughening can be more reliably performed, and the cleaning of the second cleaning step SA2 can be performed. Selection of conditions is also facilitated.

It is known that the etching behavior of an oxide film depends on the quality of the oxide film, and that the denser the film structure, the more difficult it is to be etched. Table 1 below shows the result of cleaning the oxide film formed by SC1 cleaning or ozone cleaning in the first cleaning step SA1 with a cleaning solution having a high Si/SiO ₂ etching selectivity (95 or more).

In the case where an oxide film was formed by SC1 cleaning in the first cleaning step SA1 of the first tank (levels 1 and 2), the etching amount of SiO ₂ was 0.14 nm or more in the second cleaning step SA2 of the second tank. However, when an oxide film was formed by ozone cleaning in the first cleaning step SA1 of the first tank (levels 3 to 8), the etching amount of SiO ₂ was 0 in the second cleaning step SA2 of the second tank. Roughening progressed at 2 nm or more. Thus, by calculating the SiO ₂ etching amount required for roughening as the roughening etching amount for each oxide film forming method in the first cleaning step SA1, the roughening can be progressed reliably. . It should be noted that the natural oxide film thickness is generally known to be 1 nm, and the reason why the etching amount, which is an index, is less than 1 nm is that the present invention uses a thermal oxide film that is very dense in the etching amount of SiO ₂ and is difficult to etch. It's for. By using the etching amount of the thermal oxide film as an index, the etching amount required for roughening can be grasped in advance as the roughening etching amount even when the oxide film type is different for each oxide film forming method in the first cleaning step SA1. Therefore, it is not necessary to calculate the etching amount for each type of oxide film, and cleaning conditions can be quickly selected.

Further, in the cleaning method of this aspect, as shown in FIG. 8, the oxide film formed in the first cleaning step SA1 is partially removed before the cleaning step of the second cleaning step SA2. An additional cleaning step SA3 for thinning is added, and the cleaning time is adjusted so that the sum of the etching amount of SiO ₂ in the additional cleaning step and the etching amount of SiO ₂ in the second cleaning step is greater than or equal to the roughening etching amount. can also

In Table 2 below, an oxide film is formed in the first cleaning step SA1 of the first tank, an additional cleaning step SA3 for thinning the oxide film is performed in the second tank, and Si/SiO is formed in the second cleaning step SA2 of the third tank. ₂ shows the results of determining the haze value and the degree of roughening of a wafer cleaned with a cleaning liquid having an etching selectivity of 95.

In Levels 2, 4 and 5, after the first cleaning step SA1 in the first tank, cleaning by SC1 was performed as an additional cleaning step SA3 in the second tank, and then the second cleaning step SA2 in the third tank was performed. . On the other hand, in Levels 1 and 3, the additional cleaning step SA3 was not performed.

Even if the oxide film formed by the SC1 cleaning in the first cleaning step SA1 is cleaned for 3 minutes with a cleaning liquid having a Si/ _SiO2 etching selectivity of 95 (liquid composition: 1:1:1000, 45° C.), no SiO ₂ remains. Since the etching amount was 0.12 nm, which was 0.14 nm or less, which is an index of the progress of roughening, the roughening did not progress (Level 1). On the other hand, in the additional cleaning step SA3 before the second cleaning step SA2, after additional cleaning for 1 minute with an aqueous solution containing ammonium hydroxide with a liquid composition of 1:0:100, the same cleaning as in Level 1 was performed, and roughening progressed. Was. Since the etching amount in this additional cleaning step was 0.06 nm, the total etching amount of _SiO2 was 0.06 nm + 0.12 nm = 0.18 nm. Conceivable. As for the ozone oxide films of levels 3 to 5, only level 5 where the index is 0.2 nm or more was roughened. In this way, an additional cleaning step SA3 that facilitates the progress of roughening can be added before the second cleaning step SA2.

Thus, the etching amount of SiO ₂ may be adjusted by the cleaning temperature, cleaning time, and liquid composition in the second cleaning step SA2, or the etching amount of SiO ₂ may be adjusted in the additional cleaning step SA3. . The chemical solution used in the additional cleaning step SA3 is not particularly limited as long as it is a cleaning solution that thins the silicon oxide film, and examples thereof include an aqueous solution containing ammonium hydroxide and hydrofluoric acid.

Next, FIG. 13 shows the results of investigating the influence of the method of forming a natural oxide film (type of natural oxide film) and the Si/SiO ₂ etching selectivity. Comparing the SEM images, it can be seen that various roughnesses are formed depending on the type of native oxide film, the Si/ _SiO2 etching selectivity, and the cleaning time. The Haze value with a KLA particle counter SP3 is in the range of 88 to 1871 ppm, and the Sa value obtained by AFM varies from 0.31 to 5.5 nm. That is, the method of forming an oxide film (kind of oxide film) in the first cleaning step and the roughening (surface roughness) after the second cleaning step with respect to the Si/ _SiO2 etching selectivity were evaluated in advance, and these conditions and By determining the relationship with the surface roughness after the second cleaning process, the cleaning conditions can be determined according to the target roughness. For example, for each method of forming an oxide film in the first cleaning step SA1, the relationship between the etching selectivity of Si to SiO ₂ , the cleaning time, and the surface roughness is obtained, and based on the obtained relationship, the etching of Si to SiO ₂ is performed. It is preferable to select the selection ratio and the washing time and perform the second washing step. The reason why the magnitude relationship between the Haze value and the Sa value does not match is due to the method of detection of both, and it is possible to appropriately use necessary indices. Regarding the effect of the cleaning time, as shown in FIG. 14, at two levels with different Si/SiO ₂ etching selectivity ratios, the Haze value varies greatly depending on the cleaning time. It is also easy to form roughness. As described above, the roughening method of the present invention can be flexibly formed according to the type of oxide film formed in the first cleaning process (method of forming the oxide film in the first cleaning process), the Si/ _SiO2 etching selectivity, and the cleaning time. The roughness can be varied, which is useful.

Next, a cleaning method for carrying out the cleaning of the present invention will be described. Currently, most wafer cleaning methods use chemicals, pure water, and other liquids, and are called wet cleaning. Among them, the main methods are divided into a batch method in which many wafers are cleaned at once and a single wafer method in which wafers are processed one by one. In the batch method, both the front and back surfaces of the wafer are immersed in the chemical liquid due to the equipment configuration, so that the front and back surfaces are roughened when the cleaning of the present invention is performed. On the other hand, in the single-wafer method, the chemical solution is sprayed while rotating the wafer, so only one side of the wafer can be cleaned. As a result of investigations by the present inventors, in the present invention, if the second cleaning step is performed using an aqueous solution having a SiO ₂ etching amount of a predetermined value or more and a Si/SiO ₂ etching selection ratio of 95 or more, batch method and Roughening can be performed by either the single-wafer method or the method. It was found that the method can be appropriately selected in consideration of the wafer manufacturing process.

As described above, in order to produce a wafer with only a rough back surface, only the back surface needs to be cleaned in the case of the single-wafer method, and in the case of the batch method, both the front and back surfaces are roughened. It is desirable to improve the quality of the surface side by

For example, the silicon wafer cleaning method of the present invention is performed in a batch type cleaning machine to roughen both the front and back surfaces of the silicon wafer, and then one side polishing such as CMP polishing is performed on one side (that is, the front side). , it is possible to produce wafers that are selectively roughened only on the side opposite to the one side (ie the back side).

Therefore, the polishing step that can be performed after the silicon wafer cleaning method of the present invention will be described in detail. A wafer roughened with a cleaning solution having a Si/SiO ₂ etching selectivity of 95 or more was subjected to CMP polishing with a polishing allowance of 500 nm, and a KLA particle counter SP5 was used to evaluate the LLS number greater than 19 nm at 19 nmUP. , as shown in FIG. 15, the number of LLS increased at a level where the etching amount of Si was large. This is because the amount of etching was large and the defects caused by the etching could not be removed by polishing. On the other hand, when the amount of etching of Si was small, the number of LLS was very small and favorable. Therefore, the LLS quality after CMP can be estimated by using the etching amount of Si as an index. Also, the LLS quality can be improved by increasing the removal amount of CMP at the level where the number of LLS is increased, and it is preferable to select the removal amount by CMP polishing based on the Si etching amount. As described above, since roughening occurs after SiO ₂ is etched and Si is exposed, for example, when the cleaning time of the second cleaning step SA2 is set to 3 minutes, the time to start the progress of roughening is estimated to be 2 minutes. In some cases, the removal amount can be adjusted so as to be equal to or greater than the Si etching amount corresponding to one minute of cleaning time. With this, it is possible to reduce the machining allowance to the minimum required. Further, if it is desired to reduce the removal amount by polishing from the viewpoint of manufacturing throughput, the second cleaning step SA2 can be performed under the condition that the Si etching amount is small. can be selected as appropriate. By polishing under such conditions, even when the front and back surfaces are roughened by a batch method, it is possible to manufacture wafers having good surface LLS quality and having only the back surface selectively roughened. With such a wafer, chuck failure does not occur even in a wet environment, and stable production is possible.

(silicon wafer)
FIG. 16 is a schematic side view showing part of an example of the silicon wafer of the present invention.

A silicon wafer 1 shown in FIG. 16 has a roughened surface 2 . The roughness index Sa value of the roughened surface 2 measured with an atomic force microscope is 0.3 nm or more and 5.5 nm or less. Moreover, the roughness index Haze value of the roughened surface 2 measured with a particle counter is 50 ppm or more and 1900 ppm or less.

With such a silicon wafer 1, since the roughened surface 2 exhibits roughness suitable for chucking by a chuck, it is possible to reduce transport failures during processing steps.

The silicon wafer 1 having such a roughened surface 2 can be obtained by roughening the front and back surfaces of the silicon wafer by the silicon wafer cleaning method of the present invention.

A silicon wafer 1 shown in FIG. 16 has a mirror surface 3 as the surface opposite to the roughened surface 2 . Such a mirror surface 3 can be obtained by subjecting one side of the silicon wafer cleaned by the silicon wafer cleaning method of the present invention to one side polishing such as CMP polishing.

Since the silicon wafer 1 shown in FIG. 16 has a mirror surface 3 in addition to the roughened surface 2, it can exhibit excellent quality.

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

(Examples 1 to 8)
A silicon wafer with a bare surface after DSP processing was prepared, and the following cleaning was performed with a batch-type cleaning machine. 28% by mass of ammonia water (NH ₄ OH) and 30% by mass of hydrogen peroxide solution (H ₂ O ₂ ) were used as chemical solutions for SC1 cleaning. In the first tank, ozone water cleaning (25 ppm, 25°C/3 minutes) or SC1 cleaning (NH ₄ OH:H ₂ O ₂ :H ₂ O = 1:1:10, 60°C/3) was performed for the purpose of forming an oxide film. In the second tank, SC1 cleaning was performed by varying the liquid composition, temperature and time for the purpose of roughening. More specific conditions are shown in Table 3. After that, Haze evaluation was performed using a particle counter SP3 manufactured by KLA. Since the haze value of the non-roughened wafers was 20 to 30 ppm, it was determined that the wafers with a haze value of 50 ppm or more were roughened. The results are shown in Table 3 below. In addition, as described in claim 1, the present invention roughens a silicon wafer, so the final example of roughening is the original example, but for reference, The level at which roughening did not finally occur is also shown in the Example column of Table 3 below for reference.

(Comparative example 1)
Wafers were cleaned in the same manner as in Example 2, except that SC1 cleaning was performed in the second tank with a liquid composition of NH ₄ OH:H ₂ O ₂ :H ₂ O=1:5:1000. The results are shown in Table 3 below.

With respect to the ozone (O ₃ ) oxide film surface, the liquid composition NH ₄ OH:H ₂ O ₂ :H ₂ O=1:1:1000 (NH ₄ OH concentration: 0.025% by mass, H ₂ O ₂ concentration: 0 .033% by mass) or liquid composition NH ₄ OH:H ₂ O ₂ :H ₂ O=1:1:500 (NH ₄ OH concentration: 0.051% by mass; H ₂ O ₂ concentration: 0.066% by mass) (Examples 1 to 3), with a liquid composition of 1:1:1000, it took 4 minutes at a cleaning temperature of 70°C (Example 1) and 4 minutes at a cleaning temperature of 80°C (Example 2). ), the haze value increased from 3 minutes, and roughening progressed. It is considered that the etching of the oxide film progressed faster at 80° C., and thus the roughening was easier at 80° C. In the case of the liquid composition of 1:1:500 and the cleaning temperature of 80° C. (Example 3), the haze value increased from 4 minutes and the roughening progressed.

Subsequently, the surface of the ozone (O ₃ ) oxide film was washed at a cleaning temperature of 80° C., and the liquid composition was NH ₄ OH:H ₂ O ₂ :H ₂ O=1:2:1000 (NH ₄ OH concentration: 0.025). mass %, H ₂ O ₂ concentration: 0.066 mass %), liquid composition NH ₄ OH:H ₂ O ₂ :H ₂ O=1:3:1000 (NH ₄ OH concentration: 0.025 mass %, H ₂ O ₂ concentration: 0.099% by mass), liquid composition NH ₄ OH:H ₂ O ₂ :H ₂ O=1:5:1000 (NH ₄ OH concentration: 0.025% by mass, H ₂ O ₂ concentration: 0 .165% by weight), the levels (Examples 4 and 5, and Comparative Example 1) show 10 An increase in Haze value was observed only at 3 minutes and no roughening occurred at 3 minutes and 5 minutes. With the liquid composition of 1:5:1000 (Comparative Example 1), no increase in haze value was observed even after 10 minutes, and no roughening occurred. This is probably because etching was suppressed by increasing only hydrogen peroxide.

Next, for the SC1 oxide film surface formed by SC1 cleaning, the liquid composition NH ₄ OH:H ₂ O ₂ :H ₂ O=1:2:1000 (NH ₄ OH concentration: 0.025% by mass, H ₂ O ₂ concentration: 0.066% by mass), liquid composition NH ₄ OH:H ₂ O ₂ :H ₂ O=1:3:1000 (NH ₄ OH concentration: 0.025% by mass, H ₂ O ₂ concentration: 0.025% by mass). 099% by mass), or liquid composition NH ₄ OH:H ₂ O ₂ :H ₂ O=1:1:500 (NH ₄ OH concentration: 0.051% by mass, H ₂ O ₂ concentration: 0.066% by mass) In the level washed with (Examples 6 to 8), the liquid composition 1:2:1000 (Example 6) and 1:1:500 (Example 8) roughened after 1.5 minutes of washing time. , and roughening progressed more easily than the ozone (O ₃ ) oxide film surface. This is probably because the ozone (O ₃ ) oxide film and the SC1 oxide film are different in film thickness and film quality. If the relationship between the ammonium hydroxide concentration, the hydrogen peroxide concentration, the cleaning temperature and cleaning time, and the surface roughness is obtained for each oxide film type (oxide film forming method), the cleaning conditions can be determined based on this relationship. By selecting and cleaning, it is possible to manufacture wafers with the target roughness. In Example 7 as well, it was confirmed that the front and back surfaces of the wafer were roughened after 6 minutes of cleaning.

After performing CMP processing on one side surface of the silicon wafer which was cleaned at the level of 1.5 minutes for the second tank cleaning time of Example 6, a chuck test was performed by a CMP polishing machine. A test was repeated 200 times in which the roughened surface (back surface) of the wafer stored in water opposite to the side subjected to CMP processing was chucked and the wafer was unchucked on the stage of the polishing machine. It was able to be transported without any defects.

(Comparative Examples 2 to 6)
A silicon wafer having a bare surface after DSP processing equivalent to that of the example was prepared, and the following cleaning was performed using a batch type cleaning machine. In the first tank, an oxide film was formed by washing with ozone water (Comparative Examples 2 and 3), or the bare surface was left without washing (Comparative Examples 4 to 6). The second tank had a liquid composition of NH ₄ OH:H ₂ O ₂ :H ₂ O=1:1:10 (NH ₄ OH concentration: 2.12% by mass, H ₂ O ₂ concentration: 2.77% by mass), Alternatively, NH ₄ OH:H ₂ O ₂ :H ₂ O=1:1:100 (NH ₄ OH concentration: 0.25% by mass, H ₂ O ₂ concentration: 0.33% by mass), and only the bare surface, these In addition, the liquid composition NH ₄ OH:H ₂ O ₂ :H ₂ O = 1:1:1000 (NH ₄ OH concentration: 0.025% by mass, H ₂ O ₂ concentration: 0.033% by mass) I also washed. The cleaning conditions and results for Comparative Examples 2-6 are shown in Table 4 below.

In all of Comparative Examples 2 to 6, there was no level exceeding the haze value of 50 ppm. In Comparative Example 6, when the second tank was washed for 10 minutes, the haze value was slightly increased to 42 ppm, but it did not exceed 50 ppm, so it was judged that the surface was not roughened.

After performing CMP processing on one side surface of the silicon wafer which was cleaned in the level of 10 minutes for the second tank cleaning time of Comparative Example 2, the same chuck test as in the example was performed 200 times with a CMP polisher. As a result, 4 out of 200 times, the wafer was not detached from the chuck.

(Examples A1 to A12, A19 to A33)
A wafer having a bare surface after DSP polishing was prepared, and the following cleaning was performed using a batch-type cleaning machine. 28% by mass of ammonia water (NH ₄ OH) and 30% by mass of hydrogen peroxide solution (H ₂ O ₂ ) were used as chemical solutions for SC1 cleaning. In the first tank, ozone water cleaning (25 ppm, 25° C./3 minutes) or SC1 cleaning (NH ₄ OH:H ₂ O ₂ :H ₂ O=1:1:10) is performed for the purpose of forming an oxide film as the first cleaning step. , 45° C./3 minutes), and in the second tank, as the second cleaning process, SC1 cleaning was performed with the composition, temperature, and time varied as shown in Tables 5 and 6 below for the purpose of roughening formation. . After that, Haze evaluation was performed using a particle counter SP3 manufactured by KLA. At the same time, for each aqueous solution used in the second tank, the etching amount of Si and the etching amount of SiO ₂ were calculated from the film thickness difference before and after cleaning by the method described above, and the Si/SiO ₂ etching selection ratio was calculated. was calculated. The amount of Si etched was calculated using a silicon wafer having an exposed bare surface without a natural oxide film after HF cleaning, and the amount of Si etched was obtained from the thickness of the wafer before and after cleaning with a flatness measuring machine. The etching amount of SiO ₂ was calculated using a wafer with a 5 nm oxide film formed by thermal oxidation. A. The etching amount of SiO ₂ was obtained from the thickness of the oxide film before and after cleaning with a spectroscopic ellipsometry M-2000V manufactured by Woolam.

Since the haze value of the wafer before roughening was about 20 ppm, it was determined that all of Examples A1 to A12 and A19 to A33 were roughened.

(Examples A13 to A18, and A34)
A wafer having a bare surface after DSP polishing was prepared, and the following cleaning was performed using a batch-type cleaning machine. 28% by mass of ammonia water (NH ₄ OH) and 30% by mass of hydrogen peroxide solution (H ₂ O ₂ ) were used as chemical solutions for SC1 cleaning. In the first tank, ozone water cleaning (25 ppm, 25° C./3 minutes) or SC1 cleaning (NH ₄ OH:H ₂ O ₂ :H ₂ O=1:1:10) is performed for the purpose of forming an oxide film as the first cleaning step. , 45° C./3 minutes), and in the second tank, as an additional cleaning process for thinning the oxide film, ammonia water with a composition of 1:0:100 or 0.05 wt % HF is used so that the bare surface is not exposed. , Part of the oxide film formed in the first bath is removed, and the third bath is the second cleaning step for the purpose of roughening. A shaken SC1 wash was performed. At the same time, for each aqueous solution used in the third tank, the etching amount of Si and the etching amount of SiO ₂ were calculated from the film thickness difference before and after cleaning by the method described above, and the Si/SiO ₂ etching selectivity was calculated. Calculated. In addition, in the additional cleaning process of the second tank, a wafer with a 5 nm oxide film was used in advance to calculate the etching amount of SiO ₂ . When the oxide film species in the first tank is the SC1 oxide film, the total etching amount of SiO2 in the _second tank and the third tank is set so that the total etching amount of SiO ₂ is 0.2 nm or more. Cleaning conditions were adjusted so that the thickness was 1.4 nm or more. From the Haze value of SP3 after washing, it was determined that all were roughened.

Next, since the Si etching amount of Example A19 was 820 nm and the Si etching amount of Example A22 was 230 nm, the surface of the silicon wafer of Example A19 was subjected to CMP polishing with a polishing allowance of 1000 nm. The silicon wafer of Example A22 was subjected to CMP polishing with a polishing stock removal of 500 nm. When the LLS of each wafer after CMP processing was evaluated by SP5/19 nmUp manufactured by KLA, the results were 12 pcs and 19 pcs, respectively, indicating good LLS quality. After that, when a test was repeated 200 times in which the rear side of the wafer stored in water was chucked and the wafer was unchucked to the stage of the polishing machine, the wafer could be transported without defects for all 200 times.

(Comparative Examples A1 to A13)
A wafer having a bare surface after DSP polishing was prepared, and the following cleaning was performed using a batch-type cleaning machine. 28% by mass of ammonia water (NH ₄ OH) and 30% by mass of hydrogen peroxide solution (H ₂ O ₂ ) were used as chemical solutions for SC1 cleaning. In the first tank, ozone water washing (25 ppm, 25° C./3 minutes) is used as the first washing process for the purpose of forming an oxide film, and in the second tank, as the second washing process, for the purpose of forming a roughening, Table 7 below is used. , SC1 cleaning was performed with different compositions, temperatures, and times. After that, Haze evaluation was performed using a particle counter SP3 manufactured by KLA. At the same time, for each of the aqueous solutions used in the second tank, the Si etching amount and the SiO ₂ etching amount were calculated from the film thickness difference before and after cleaning by the method described above, and the Si/SiO ₂ selection ratio was calculated. The amount of Si etched was calculated using a silicon wafer having an exposed bare surface without a natural oxide film after HF cleaning, and the amount of Si etched was obtained from the thickness of the wafer before and after cleaning with a flatness measuring machine. The etching amount of SiO ₂ was calculated using a wafer with a 5 nm oxide film formed by thermal oxidation, and the etching amount of SiO ₂ was obtained from the thickness of the oxide film before and after cleaning by spectroscopic ellipsometry.

As shown in Table 7, in Comparative Examples A1 to A13, the haze values of SP3 were all around 20 ppm, which was equivalent to that of the non-roughened wafer, and it was determined that the wafer was not roughened.

After performing CMP polishing processing with a polishing allowance of 500 nm for the level of Comparative Example A1, the same chuck test as in Example A19 was performed 200 times with a CMP polishing machine. Four out of 200 times, a defect occurred in which the wafer did not come off from the chuck.

From the above results, in Examples A1 to A34 of the present invention, the etching selectivity of Si to SiO ₂ was 95 or more in the second cleaning step, so that the front and back surfaces of the silicon wafer, particularly the back surface, were chucked. It can be seen that it was possible to roughen sufficiently to exhibit a roughness suitable for adsorption by .

On the other hand, in Comparative Examples A1 to A13, since the etching selectivity ratio of Si to SiO ₂ was 95 or more in the second cleaning step, the front and back surfaces of the silicon wafer, particularly the back surface, were treated with a rough surface suitable for chucking by a chuck. could not be sufficiently roughened to exhibit roughness.

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

1... Silicon wafer, 2... Roughened surface, 3... Mirror surface.

Claims (13)

A cleaning method for roughening a silicon wafer, comprising:
forming an oxide film on the silicon wafer by SC1 cleaning, SC2 cleaning, or ozone water cleaning;
a silicon wafer having the oxide film formed thereon,
A diluted ammonium hydroxide aqueous solution having an ammonium hydroxide concentration of 0.051% by mass or less, or an ammonium hydroxide concentration of 0.051% by mass or less, a hydrogen peroxide concentration of 0.2% by mass or less, and the hydroxide A silicon wafer characterized in that the front and back surfaces of the silicon wafer are roughened by washing with an aqueous solution of either dilute aqueous solution containing ammonium hydroxide and hydrogen peroxide, which is four times or less the concentration of ammonium. cleaning method. Obtaining in advance the relationship between the ammonium hydroxide concentration or the ammonium hydroxide concentration and the hydrogen peroxide concentration, the cleaning temperature and cleaning time, and the surface roughness after the cleaning for each method of forming the oxide film,
2. The method according to claim 1, wherein the cleaning is performed by selecting the ammonium hydroxide concentration or the ammonium hydroxide concentration and the hydrogen peroxide concentration, cleaning temperature, and cleaning time based on the obtained relationship. A method for cleaning a silicon wafer. CMP polishing is performed on one surface of the silicon wafer cleaned by the silicon wafer cleaning method according to claim 1 or 2, and only the surface opposite to the one surface is selectively roughened. A method for producing a silicon wafer, comprising obtaining a silicon wafer. A silicon wafer having a roughened surface with a roughness index Sa value of 0.3 nm or more and 5.5 nm or less as measured by an atomic force microscope. A silicon wafer having a roughened surface with a roughness index Haze value of 50 ppm or more and 1900 ppm or less measured by a particle counter. 6. The silicon wafer according to claim 4, wherein the surface opposite to the roughened surface is a mirror surface. A cleaning method for roughening a silicon wafer, comprising:
a first cleaning step of forming an oxide film on the silicon wafer by SC1 cleaning, SC2 cleaning, or ozone water cleaning;
a second cleaning step of roughening the front and back surfaces or the back surface of the silicon wafer by cleaning with either an aqueous solution containing ammonium hydroxide or an aqueous solution containing ammonium hydroxide and hydrogen peroxide;
A method of cleaning a silicon wafer, wherein the aqueous solution used in the second cleaning step has an etching selectivity of Si to SiO ₂ of 95 or more. The etching selectivity ratio of Si to _SiO2 of the aqueous solution used in the second cleaning step is obtained from (etching amount of Si/etching amount of _SiO2 ),
As the wafer for calculating the etching amount of Si, using any one of a silicon wafer, an epitaxial wafer, or an SOI wafer with a bare surface without a native oxide film exposed,
8. The method of cleaning a silicon wafer according to claim 7, wherein a wafer with a silicon oxide film having a film thickness of 3 nm or more is used as the wafer for calculating the etching amount of _SiO2 . The etching amount of SiO ₂ necessary for progressing roughening in the second cleaning step is calculated in advance as a roughening etching amount for each method of forming the oxide film in the first cleaning step,
The cleaning time of the second cleaning step is selected so that the etching amount of SiO ₂ in the second cleaning step is equal to or greater than the roughening etching amount, and/or the first cleaning is performed before the second cleaning step. An additional cleaning step is added to thin the oxide film so that a part of the oxide film formed in the process remains, and the etching amount of SiO ₂ in the additional cleaning step and the amount of SiO ₂ in the second cleaning step are calculated. 9. The method of cleaning a silicon wafer according to claim 7, wherein the cleaning time is adjusted so that the total amount of etching is equal to or greater than the amount of roughening etching. Obtaining in advance the relationship between the etching selectivity of Si to _SiO2 , the cleaning time, and the surface roughness for each method of forming the oxide film in the first cleaning step,
The silicon wafer according to any one of claims 7 to 9, wherein the second cleaning step is performed by selecting the etching selectivity of Si to SiO ₂ and the cleaning time based on the obtained relationship. cleaning method. CMP polishing is performed on one side of the silicon wafer, which has been cleaned by the silicon wafer cleaning method according to any one of claims 7 to 10 and whose front and back surfaces have been roughened, and the opposite side of the one side. A method for producing a silicon wafer, characterized by obtaining a silicon wafer in which only the surface of the surface is selectively roughened. 12. The method of manufacturing a silicon wafer according to claim 11, wherein the removal amount of said CMP polishing is set to be equal to or greater than the etching amount of Si in said second cleaning step. 12. The method of manufacturing a silicon wafer according to claim 11, wherein the etching amount of Si in said second cleaning step is set to be equal to or less than the removal amount of said CMP polishing.

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