CN116918041A

CN116918041A - Method for cleaning silicon wafer, method for manufacturing silicon wafer, and silicon wafer

Info

Publication number: CN116918041A
Application number: CN202280019373.6A
Authority: CN
Inventors: 藤井康太; 阿部达夫
Original assignee: Shin Etsu Handotai Co Ltd
Current assignee: Shin Etsu Handotai Co Ltd
Priority date: 2021-03-09
Filing date: 2022-02-21
Publication date: 2023-10-20

Abstract

The present invention relates to a method for cleaning a silicon wafer, which is a method for cleaning a silicon wafer by roughening the surface and the back of the silicon wafer, wherein an oxide film is formed on the silicon wafer by SC1 cleaning, SC2 cleaning, or ozone water cleaning, and the silicon wafer on which the oxide film is formed is cleaned with any one of an aqueous ammonium hydroxide diluted solution having an ammonium hydroxide concentration of 0.051 mass% or less, or an aqueous diluted solution containing ammonium hydroxide and an aqueous hydrogen peroxide solution, wherein the aqueous diluted solution containing ammonium hydroxide and the aqueous hydrogen peroxide has an ammonium hydroxide concentration of 0.051 mass% or less, the hydrogen peroxide concentration is 0.2 mass% or less, and the hydrogen peroxide concentration is 4 times or less the ammonium hydroxide concentration. Thus, a cleaning method capable of roughening the front and back surfaces of a silicon wafer can be provided.

Description

Method for cleaning silicon wafer, method for manufacturing silicon wafer, and silicon wafer

Technical Field

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

Background

The process for producing a silicon wafer for a semiconductor device includes a single crystal production process for growing a single crystal ingot by the Czochralski method (Czochralski method, CZ method) or the like and a wafer processing process for slicing and processing the single crystal ingot into a mirror surface shape, and may include an annealing process for performing a heat treatment or an epitaxial growth process for forming an epitaxial layer in order to increase the added value.

The mirror-surface processing step includes a DSP (double-sided polishing) step and a CMP (single-sided polishing) step after the DSP step. More specifically, from the standpoint of particle quality and handling, DSP-processed wafers may be transported to the CMP process after cleaning in a state of being kept in water, if necessary, without drying. Therefore, in the CMP process, the wafer stored in water needs to be gripped by a robot or the like and transported to the CMP apparatus. Further, after CMP polishing, it is also necessary to clamp a wet wafer such as a polishing agent or pure water and transport the wafer to a cleaning step as needed.

In such a wafer processing step, it is necessary to convey the wafer in a wet environment instead of in a dry environment, but in particular, when the wafer sucked by the chuck (chuck) is detached in such a wet environment, the wafer cannot be detached even if the chuck is released, and thus, a conveyance failure may occur. The reason for this is considered to be influenced by the roughness of the wafer surface to be clamped, and if the roughness of the wafer surface to be clamped is too good, the contact area with the chuck increases, and even if the chuck is released, the wafer becomes difficult to separate, whereas if the surface roughness of the wafer is poor, the contact area decreases, and therefore the wafer becomes easy to separate. In general, the quality of the wafer to be clamped is degraded due to the formation of a large number of chuck marks on the wafer surface, and therefore, the wafer surface is often the back surface of the silicon wafer. Therefore, from the viewpoint of reducing the handling failure, a method for manufacturing a wafer in which only the back surface of a silicon wafer is roughened is particularly desired.

As a general cleaning method of a silicon wafer, there is a method called RCA cleaning. The RCA cleaning is a method of performing cleaning by combining SC1 (Standard Cleaning1 ) cleaning, SC2 (Standard Cleaning2, standard cleaning 2) cleaning, and DHF (Diluted Hydrofluoric Acid ) cleaning according to purposes. The SC1 cleaning is a cleaning method in which ammonia water and an aqueous hydrogen peroxide solution are mixed at an arbitrary ratio, particles adhering to the surface of a silicon wafer due to etching are peeled off (lift-off) by an alkaline cleaning liquid, and particles are removed while preventing reattachment of the particles to the silicon wafer by electrostatic repulsion of the silicon wafer and the particles. The SC2 cleaning is a cleaning method for removing metallic impurities on the surface of a silicon wafer by dissolving the metal impurities in a cleaning solution obtained by mixing hydrochloric acid and an aqueous hydrogen peroxide solution in an arbitrary ratio. Further, DHF cleaning is a cleaning method for removing a chemical oxide film on the surface of a silicon wafer by dilute hydrofluoric acid. Further, ozone water having a strong oxidizing power is sometimes used for cleaning, so that removal of organic substances adhering to the surface of the silicon wafer and formation of a chemical oxide film on the surface of the silicon wafer after DHF cleaning are performed. The cleaning of the silicon wafer may be combined with these cleaning depending on the purpose. Since SC1 is a cleaning process accompanied by etching, it is generally known that the surface roughness of the wafer is deteriorated after SC1 cleaning.

As a method for evaluating the surface roughness of the wafer, a Sa (three-dimensional computed average height) value obtained by an atomic force microscope (AFM, atomic Force Microscope) or a Haze value obtained by a particle counter can be used as an index. Haze, expressed in terms of so-called Haze, is widely used as an indicator of the roughness of silicon surfaces, and a high level of Haze indicates a rough surface of the wafer.

Patent document 1 describes a method of forming natural oxide films having different thicknesses by cleaning a silicon wafer with a diluted aqueous solution having a composition of ammonium hydroxide, hydrogen peroxide, and water in the range of 1:1:5 to 1:1:2000. Patent document 2 describes that in SC1 cleaning, OH ionized by ammonium hydroxide ^－ If the concentration of Si is high, the direct etching of Si is preferentially initiated, and the surface roughness of the wafer is deteriorated.

Prior art literature

Patent literature

Patent document 1: japanese patent laid-open No. 7-66195

Patent document 2: japanese patent laid-open publication No. 2011-82372

Patent document 3: japanese patent laid-open No. 7-240394

Patent document 4: japanese patent laid-open No. 10-242107

Patent document 5: japanese patent laid-open No. 11-121419

Patent document 6: japanese patent application laid-open No. 2012-523706

Disclosure of Invention

Technical problem to be solved by the invention

As described above, in order to reduce the conveyance failure in the processing step, a silicon wafer having a rough surface to be clamped is required.

The present invention has been made to solve the above-described problems, and provides 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; a method for producing a silicon wafer capable of obtaining a silicon wafer having one surface roughened selectively; and a silicon wafer which is less likely to be carried in a processing step.

Technical means for solving the technical problems

In order to solve the above-mentioned problems, the present invention provides a cleaning method for roughening a silicon wafer, which is characterized in that,

an oxide film is formed on the silicon wafer by SC1 cleaning, SC2 cleaning or ozone water cleaning,

the silicon wafer on which the oxide film is formed is cleaned by any one of an ammonium hydroxide diluted aqueous solution having an ammonium hydroxide concentration of 0.051 mass% or less and a diluted aqueous solution containing an ammonium hydroxide and a hydrogen peroxide aqueous solution, thereby roughening the front surface and the back surface of the silicon wafer,

Wherein in the diluted aqueous solution comprising ammonium hydroxide and an aqueous hydrogen peroxide solution, the ammonium hydroxide concentration is 0.051 mass% or less, the hydrogen peroxide concentration is 0.2 mass% or less and the hydrogen peroxide concentration is 4 times or less the ammonium hydroxide concentration.

In such a cleaning method for a silicon wafer, roughening can be generated during etching of the natural oxide film, and the front surface and the back surface of the silicon wafer can be roughened.

Preferably, the ammonium hydroxide concentration or the relationship between the ammonium hydroxide concentration and the hydrogen peroxide concentration, the cleaning temperature, and the cleaning time and the surface roughness after the cleaning are obtained in advance for each oxide film forming method,

and selecting the ammonium hydroxide concentration or the ammonium hydroxide concentration and the hydrogen peroxide concentration, the cleaning temperature and the cleaning time according to the obtained relation, and cleaning.

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

The present invention also provides a method for producing a silicon wafer, wherein one surface of a silicon wafer cleaned by the cleaning method of the present invention is subjected to CMP polishing, and a silicon wafer having selectively roughened surfaces on the opposite side of the one surface is obtained.

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

The present invention also provides a silicon wafer having a roughened surface, the roughened surface having a roughness index Sa value of 0.3nm or more and 5.5nm or less, as measured by an atomic force microscope.

In such a silicon wafer, the roughened surface exhibits a roughness suitable for suction by the chuck, and thus, defective conveyance in the processing step can be reduced.

The present invention also provides a silicon wafer having a roughened surface, the roughened surface having a Haze value of 50ppm to 1900ppm as measured by a particle counter.

Preferably, the surface opposite to the roughened surface is a mirror surface.

Such a silicon wafer can exhibit excellent quality.

The present invention also provides a method for cleaning a silicon wafer, comprising the steps of:

a first cleaning step of forming an oxide film on the silicon wafer by SC1 cleaning, SC2 cleaning, or ozone water cleaning; the method comprises the steps of,

a second cleaning step of cleaning the silicon wafer on which the oxide film is formed with at least one aqueous solution of an aqueous solution containing ammonium hydroxide or an aqueous solution containing ammonium hydroxide and an aqueous solution of hydrogen peroxide, thereby roughening the front and back surfaces or the back surface of the silicon wafer;

wherein Si relative to SiO is used as the aqueous solution used in the second cleaning step ₂ An etching selectivity of 95 or more.

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

Furthermore, it is preferable that the etching amount based on (Si/SiO ₂ Etching amount) of the aqueous solution used in the second cleaning step, the Si to SiO ratio is determined ₂ Is used for the etching selection ratio of (a),

as a wafer for calculating the etching amount of Si, any one of a silicon wafer, an epitaxial wafer, or an SOI wafer having no natural oxide film exposed to the bare surface is used,

as a method for calculating the SiO ₂ The wafer with silicon oxide film having a film thickness of 3nm or more was used.

With such a method, the SiO can be evaluated with high accuracy ₂ And Si.

Further, it is preferable that SiO necessary for roughening in the second cleaning step is calculated in advance for each oxide film forming method in the first cleaning step ₂ As the etching amount of the roughening etching amount,

so that SiO in the second cleaning process ₂ The cleaning time of the second cleaning procedure is selected in a mode that the etching amount is more than or equal to the roughening etching amount, and/or

An additional cleaning step of thinning the oxide film so as to leave a part of the oxide film formed in the first cleaning step, is added before the second cleaning step, so that SiO in the additional cleaning step is removed ₂ And the etching amount of SiO in the second cleaning process ₂ The cleaning time is adjusted so that the total of the etching amounts of the roughening etching amounts is equal to or larger than the total of the roughening etching amounts.

The roughening of the invention is achieved by washing SiO ₂ Since the etching is performed by a predetermined amount to expose Si on the surface, the SiO required for roughening is calculated in advance by such a method ₂ And the etching amount is used as the roughening etching amount, the roughening can be performed more reliably.

Further, it is preferable that the Si relative to SiO be obtained in advance for each oxide film forming method in the first cleaning step ₂ The relation between the etching selectivity and the cleaning time and the surface roughness is selected according to the relation obtained ₂ The etching selectivity and the cleaning time of the substrate are used for performing the second cleaning process.

The roughening degree formed by the cleaning method of the present invention depends on the method for forming the oxide film in the first cleaning step, and the Si to SiO ratio ₂ It is effective to obtain the relation between these conditions and the roughening degree in advance because the etching selectivity and the cleaning time are changed.

The present invention also provides a method for producing a silicon wafer, characterized in that one surface of a silicon wafer, the surface and the back surface of which have been roughened by the cleaning method of the present invention, is subjected to CMP polishing, and a silicon wafer, the surface of which is selectively roughened only on the side opposite to the one surface, is obtained.

Thus, by roughening the front and back surfaces and polishing only the front surface side, a wafer having a good front surface and roughened only the back surface can be produced.

Further, the process margin of the CMP polishing can be set to be equal to or larger than the etching amount of Si in the second cleaning step.

This can prevent LLS (Localized Light Scatter, local light scattering material) from remaining after CMP due to etching, and can ensure good LLS quality.

In addition, the etching amount of Si in the second cleaning step may be set to be equal to or less than the processing margin of the CMP polishing.

This can prevent LLS residues caused by etching after CMP, and can ensure good LLS quality.

Effects of the invention

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

Further, according to the method for manufacturing a silicon wafer of the present invention, a wafer in which one surface is a good surface and only the surface opposite to the one surface is selectively roughened can be manufactured.

In addition, the silicon wafer of the present invention can reduce defective conveyance in the processing step.

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

Drawings

Fig. 1 is a flowchart showing an example of a first embodiment of a method for cleaning a silicon wafer according to the present invention.

FIG. 2 shows the NH composition of the liquid at three levels ₄ OH:H ₂ O ₂ :H ₂ O=1:1:10, 1:1:100, 1:1:1000 pairs of bare surfaces and O ₃ SEM image and Haze value of the oxide film surface after cleaning.

FIG. 3 is a schematic diagram showing the liquid composition NH ₄ OH:H ₂ O ₂ :H ₂ Graph of three levels of Si etch amounts o=1:1:10, 1:1:100, 1:1:1000.

FIG. 4 shows the NH composition in a liquid ₄ OH:H ₂ O ₂ :H ₂ Bare surface at o=1:1:1000 (45 ℃) and O ₃ A graph of the difference in the Si etching amount of the oxide film surface.

FIG. 5 shows the liquid composition NH ₄ OH:H ₂ O ₂ :H ₂ O=1:1:1000 (80 ℃) ₃ Another graph of the difference in the Si etching amount of the oxide film face.

FIG. 6 shows a modified oxide film formation method, NH ₄ OH concentration, H ₂ O ₂ SEM images after roughening, haze value, and Sa value of AFM.

FIG. 7 shows the change of NH ₄ OH concentration, H ₂ O ₂ A graph of the change in Haze with respect to the cleaning time when the cleaning is performed for the concentration and the cleaning time.

Fig. 8 is a flowchart showing an example of a second embodiment of the method for cleaning a silicon wafer according to the present invention.

FIG. 9 shows NH in liquid composition ₄ OH:H ₂ O ₂ :H ₂ Five horizontal pairs of bare faces o=1:1:10, 1:1:100, 1:1:1000, 1:0.01:10, 1:0.05:100, O ₃ SEM image and Haze value of the oxide film surface after cleaning.

FIG. 10 is a schematic diagram showing the liquid composition NH ₄ OH:H ₂ O ₂ :H ₂ Graph of three levels of Si etch amounts o=1:1:10, 1:1:100, 1:1:1000.

FIG. 11 is a schematic diagram showing the liquid composition NH ₄ OH:H ₂ O ₂ :H ₂ Three levels of SiO at o=1:1:10, 1:1:100, 1:1:1000 ₂ Graph of etching amount.

FIG. 12 is a schematic diagram showing the liquid composition NH ₄ OH:H ₂ O ₂ :H ₂ Three levels of Si/SiO with o=1:1:10, 1:1:100, 1:1:1000 ₂ Is a graph of etch selectivity ratio.

FIG. 13 shows the change of oxide film type and Si/SiO ₂ Graph of SEM image, haze value, sa value of AFM after roughening etching selection ratio.

FIG. 14 shows a modification of Si/SiO ₂ A graph of the change in Haze with respect to the cleaning time when roughening is performed in terms of etching selectivity and cleaning time.

FIG. 15 is a graph showing the LLS quality after CMP polishing at a Si etching amount and a polishing process margin of 500 nm.

Fig. 16 is a schematic side view showing a part of one example of a silicon wafer of the present invention.

Detailed Description

The inventors of the present application have studied the etching method of a silicon wafer using a cleaning solution comprising ammonium hydroxide, an aqueous hydrogen peroxide solution and water, in view of the presence or absence of an oxide film on the front and back surfaces of the silicon wafer, the type of oxide film (method of forming an oxide film), the liquid composition (in particular, ammonium hydroxide concentration and hydrogen peroxide concentration), the cleaning temperature and the cleaning time, in order to solve the above-mentioned problems. As a result, they have found that the oxide film can be roughened so as not to be uniformly etched by cleaning a silicon wafer having a natural oxide film on the front and rear surfaces with either an aqueous ammonium hydroxide solution having an ammonium hydroxide concentration of 0.051 mass% or less or a diluted aqueous solution containing an aqueous ammonium hydroxide and an aqueous hydrogen peroxide solution having an ammonium hydroxide concentration of 0.051 mass% or less, a hydrogen peroxide concentration of 0.2 mass% or less and a hydrogen peroxide concentration of 4 times or less, and that the roughness can be adjusted by controlling the type of the natural oxide film (oxide film forming method), the liquid composition (in particular, the ammonium hydroxide concentration and the hydrogen peroxide concentration), the cleaning temperature and the cleaning time, and have completed the present application based on the above-mentioned findings.

In order to solve the above problems, the inventors of the present application have found that, in an etching method using a cleaning solution comprising ammonium hydroxide, an aqueous hydrogen peroxide solution and water, siO is particularly useful for ₂ The difference from the etching mode of Si was studied. As a result, it was found that if Si is used relative to SiO ₂ The applicant has completed another embodiment of the present application based on the above finding, by cleaning a silicon wafer having a natural oxide film on the surface thereof, which is roughened by rapid etching at a portion where Si is exposed, and by adjusting the roughening method by controlling the selection ratio.

That is, the present application is a cleaning method for roughening a silicon wafer, characterized in that,

cleaning the silicon wafer on which the oxide film is formed by using any one of an ammonium hydroxide diluted aqueous solution with an ammonium hydroxide concentration of 0.051 mass% or less or a diluted aqueous solution containing an ammonium hydroxide and a hydrogen peroxide aqueous solution, thereby roughening the front surface and the back surface of the silicon wafer,

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

The present invention is a silicon wafer having a roughened surface, the roughened surface having a Haze value of 50ppm to 1900ppm as measured by a particle counter.

si to SiO solution is used as the aqueous solution used in the second cleaning step ₂ An etching selectivity of 95 or more.

Patent documents 1 and 2 only mention the influence on the surface roughness of the front and rear surfaces of the wafer. Although patent documents 3 to 6 disclose techniques related to cleaning of semiconductor substrates such as silicon wafers, patent documents 1 to 6 do not make detailed studies on the presence or absence of an oxide film on a silicon wafer before cleaning, and the type, liquid composition, temperature, and time of a natural oxide film.

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

(method for cleaning silicon wafer and method for manufacturing silicon wafer)

First scheme

First, a first aspect of the cleaning method for a silicon wafer according to the present invention will be described.

Fig. 1 is a flowchart showing an example of a first aspect of the cleaning method of a silicon wafer 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. The conductivity type and caliber of the wafer are not limited, and examples thereof include a wafer after DSP processing.

Next, as shown in S2, an oxide film is formed on the silicon wafer by SC1 cleaning, SC2 cleaning, or ozone water cleaning. When a natural oxide film is formed on a wafer before cleaning, it is preferable to perform the above cleaning after removing the natural oxide film by HF cleaning in advance. This is because, in the present invention, the etching method varies depending on the kind of oxide film, that is, the method of forming the oxide film, and the roughness to be formed varies. For example, an oxide film can be directly formed on a wafer having an exposed surface such as after DSP processing without HF cleaning. The cleaning conditions in this case may be the same general conditions as those of the SC1, SC2, and ozone water cleaning. For example, if SC1 cleaning is used, the mixing ratio of ammonium hydroxide, hydrogen peroxide and water is NH ₄ OH:H ₂ O ₂ :H ₂ When the cleaning temperature is 60 ℃ or higher in the range of o=1:1:5 to 1:1:100, the cleaning time can be set to 1 to 30 minutes. For example, in the case of SC2 cleaning, the mixture ratio of HCl, hydrogen peroxide and water is in the range of HCl:H ₂ O ₂ :H ₂ When the cleaning temperature is 60 ℃ or higher in the range of o=1:1:5 to 1:1:20, the cleaning time can be set to 1 to 30 minutes. For example, in the case of ozone water washing, the ozone concentration can be 3ppm to 25ppm, the washing temperature can be room temperature, and the washing time can be 1 minute to 30 minutes. As described later, since the roughness formed in the present invention varies depending on the kind of oxide film formed in S2 (oxide film forming method), an appropriate cleaning liquid may be selected according to the target roughness.

Next, as shown in S3, the aqueous solution is washed with an aqueous ammonium hydroxide diluted solution having an ammonium hydroxide concentration of 0.051 mass% or less or an aqueous ammonium hydroxide-hydrogen peroxide diluted solution in which the ammonium hydroxide concentration is 0.051 mass% or less, the hydrogen peroxide concentration is 0.2 mass% or less and the hydrogen peroxide concentration is 4 times or less the ammonium hydroxide concentration. In this case, for example, when cleaning is performed by a batch type cleaning machine in which a chemical solution tank is continuous, cleaning according to the present invention can be efficiently performed in a single batch by performing cleaning of S3 after cleaning in S2.

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

FIG. 2 shows the SC1 liquid composition set to NH ₄ OH:H ₂ O ₂ :H ₂ O=1:1:10, 1:1:100, 1:1:1000 and at 80 ℃/10 minutes to the exposed face of the DSP wafer and O ₃ The observation results of the front and back surfaces of the oxide film surface (formed in S2) after cleaning by a scanning electron microscope (SEM: scanning Electron Microscopy) and the Haze value obtained by the particle counter. The chemical solution used was 28 mass% aqueous ammonia (NH ₄ OH), 30% by mass aqueous hydrogen peroxide solution (H ₂ O ₂ ) The labels are also each given in weight (wt%). In addition, the mass% is expressed as a percentageThe concentration of the mass ratio of the wash solution to the solutes contained therein (ammonium hydroxide, hydrogen peroxide) is also labeled wt%. Only when the liquid composition is 1:1:1000 to O ₃ In the SEM image of the oxide film surface cleaning level, a large roughness was observed, and the Haze value was also greatly increased from other levels to 470ppm, indicating roughening. And it was found that the bare surface cleaned at a liquid composition level of 1:1:1000 was also slightly roughened, but to a lesser extent than O ₃ And oxidizing the film surface. From these results, it was found that the roughening factor was that oxide films were deposited on the front and back surfaces and that the SC1 liquid composition was low.

FIG. 3 shows the SC1 liquid composition NH ₄ OH:H ₂ O ₂ :H ₂ The etching amount of Si at o=1:1:10, 1:1:100, 1:1:1000. It can be found that there is a tendency that the lower the liquid composition is, the more the etching amount is increased, which means that the lower the liquid composition is, the more etching-advantageous the reaction is. Further, for a liquid composition of 1:1:1000, the facing states were bare surface and O ₃ The Si etching amounts were examined at two levels of the oxide film surface, and the results are shown in fig. 4 and 5. It was found that only the exposed surface was etched at 45℃and at O ₃ The oxide film surface is only slightly etched. It was found that O was present at 80℃and 80℃for 3 minutes ₃ The oxide film surface was etched slightly, but after 6 minutes, the etching was performed sharply. Although not shown in FIG. 5, the etching amount of the exposed surface after 3 minutes at 80℃is more than 55nm, O ₃ The etching amount of the oxide film surface after 12 minutes is also larger than 55nm. Therefore, it is known that Si and SiO are contained in a low liquid composition environment ₂ The etching mode difference is large, si is easy to be etched, and SiO ₂ Is not easy to etch. When the result of FIG. 2 is taken into consideration together with the etching amounts of FIGS. 4 and 5, it is considered that roughening occurs at O with a small etching amount ₃ Since the oxide film surface is not a bare surface with a large amount of Si etching, the roughening is considered to be caused by the etching method of the oxide film in the low liquid composition environment. In addition, in the liquid composition NH ₄ OH:H ₂ O ₂ :H ₂ In o=1:0:1000, the same results as for the liquid composition 1:1:1000 were obtained, and therefore water-soluble even without hydrogen peroxideThe aqueous ammonium dilution of the liquor can also be roughened.

Next, fig. 6 shows the results of examining the influence of the type of natural oxide film (oxide film formation method), the liquid composition (ammonium hydroxide concentration and hydrogen peroxide concentration), the cleaning temperature, and the cleaning time. From SEM images, the oxide film was cleaned to O by a liquid composition of 1:2:1000 at 80 ℃ C./4 min ₃ The wafer of the oxide film has various roughness in the levels other than the above level according to the kind of the oxide film, the SC1 liquid composition, the cleaning temperature, and the cleaning time. Further, the Sa value obtained by AFM also varied significantly from 0.31 to 5.5nm, and similarly, the Haze value varied from 104 to 1871 ppm. That is, the post-cleaning roughness is evaluated in advance for the oxide film formation method, ammonium hydroxide concentration, or ammonium hydroxide concentration, hydrogen peroxide concentration, cleaning temperature, and cleaning time, and the relationship between these conditions and post-cleaning roughness is obtained in advance, whereby the cleaning conditions can be determined from the target roughness.

More specifically, the liquid composition was examined by fixing the temperature at 80 ℃, and as a result, as shown in fig. 7, the Haze value was increased in the cleaning liquid having the liquid compositions of 1:1:500, 1:1:1000, and 1:3:1000, but the Haze value was not increased even in the cleaning liquid having the liquid composition of 1:5:1000 for 15 minutes, and the silicon wafer was not roughened. Thus, hydrogen peroxide has the effect of hindering the progress of etching, NH in weight concentration from the liquid composition 1:3:1000 ₄ OH is 0.025 mass%, H ₂ O ₂ This point was found to be 0.099 mass%, H ₂ O ₂ Is required to be NH ₄ The weight concentration of OH is less than 4 times. The cleaning method of the present invention is caused by etching action by ammonium hydroxide and oxidation action by aqueous hydrogen peroxide, and thus the cleaning method of the present invention for silicon wafer is effective in such a case. Furthermore, NH in 1:1:500 from liquid composition ₄ NH based on the OH weight concentration of 0.051 mass% ₄ The OH content is required to be 0.051 mass% or less, and the liquid composition can be changed within this range.

In aqueous ammonium hydroxide dilutionAmmonium NH ₄ The OH concentration is preferably 0.0051 mass% or more and 0.051 mass% or less. In addition, in a diluted aqueous solution comprising ammonium hydroxide and an aqueous hydrogen peroxide solution, ammonium hydroxide NH ₄ The OH concentration is preferably 0.0051 mass% or more and 0.051 mass% or less, hydrogen peroxide H ₂ O ₂ The concentration is preferably 0.0067 mass% or more and 0.2 mass% or less, and hydrogen peroxide H ₂ O ₂ The concentration is more than 0.1 times and less than 4 times of the concentration of ammonium hydroxide.

Next, the kind of oxide film (oxide film formation method) was examined. A thermal oxide film having a thickness of 5nm was produced in a dry oxygen atmosphere using a resistance heating furnace, and the film was cleaned at 80 ℃/10 minutes using a liquid composition of 1:1:1000, but the Haze value was not increased, and a roughened image was not observed by SEM imaging. From the results, it is considered that, in order to perform roughening in a practically operable time, an oxide film formed by SC1, SC2 or ozone water cleaning is most suitable.

In general, if the following are combined: it is considered that the roughening that occurs when etching the oxide film starts from the vicinity of the structure transition layer at the interface between the silicon oxide film and silicon, if the oxide film formed by the cleaning has a thickness of about 1nm, an uneven and unstable layer called a structure transition layer exists at the interface between the silicon oxide film and silicon, and roughening does not occur at the thermal oxide film having a thickness of 5 nm. In the case of a thermal oxide film having a thickness of 5nm, the etching of the oxide film had not been performed to the vicinity of the structural transition layer at a cleaning time of 10 minutes, and therefore, it was considered that roughening did not occur, and since only the film thickness and film quality of the structural transition layer slightly changed even in the SC1 and ozone water cleaning, it was considered that the roughness changed depending on the kind of natural oxide film.

Therefore, it is preferable to calculate the relationship between the ammonium hydroxide concentration and the hydrogen peroxide concentration, the cleaning temperature, and the cleaning time and the surface roughness after cleaning for each oxide film type (oxide film forming method) in advance as described above, and to 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 calculated relationship, and to clean. The inventors of the present application examined, as shown in fig. 6 and 7, that the roughness was widely varied, for example, between 0.3 and 5.5nm for the roughness index Sa of AFM and between 50 and 1871ppm for the Haze of the particle counter.

Finally, in general, it is often preferable that the roughness of the surface side of the silicon wafer as the device fabrication surface is good. For example, if the cleaning method of the present application is carried out by a batch type cleaning machine, both the front and rear surfaces are roughened, and therefore, one surface thereof may be subjected to single-sided polishing such as CMP polishing thereafter, whereby a wafer having only the surface on the opposite side to the one surface thereof selectively roughened can be manufactured. In such a wafer, the wafer can be stably manufactured without causing a problem of barred wire even in a wet environment.

Second scheme

Next, a second aspect of the cleaning method for a silicon wafer according to the present invention will be described.

Fig. 8 is a flowchart showing an example of a second aspect of the cleaning method of a silicon wafer of the present invention.

First, a silicon wafer whose back surface is to be roughened is prepared. The conductivity type and caliber of the wafer are not limited, and examples thereof include a wafer after DSP processing.

Next, as shown in SA1, an oxide film is formed on the silicon wafer by SC1 cleaning, SC2 cleaning, or ozone water cleaning (first cleaning step). When a natural oxide film is formed on the wafer before cleaning, it is preferable to perform the first cleaning step after removing the natural oxide film by HF cleaning in advance. This is because, in the present invention, the etching method is different depending on the kind of oxide film, that is, the method of forming the oxide film in the first cleaning step, and the roughness to be formed is also changed. For example, an oxide film can be directly formed on a wafer having an exposed surface such as after DSP processing without HF cleaning. The cleaning conditions in this case may be the same general conditions as those of the SC1, SC2, and ozone water cleaning. The general conditions may be, for example, the conditions as described in the first scheme.

SA3 shown in fig. 8 is an arbitrary step that can be performed after the first cleaning step SA1 and before the second cleaning step SA2 described below. The step SA3 will be described in the following paragraphs.

Next, as shown in SA2, si is used for SiO ₂ Etching selectivity (Si/SiO) ₂ The etching selectivity of (a) is 95 or more and an aqueous solution containing ammonium hydroxide or an aqueous solution containing ammonium hydroxide and an aqueous solution of hydrogen peroxide is used to clean the silicon wafer on which the oxide film is formed (a second cleaning step).

Wherein Si and SiO are used as ₂ The roughening phenomenon of the present invention will be described in detail in terms of the etching mode. In addition, si and SiO ₂ The details of the method for calculating the etching amount of (c) will be described later.

FIG. 9 shows the bare surface and O for a DSP wafer ₃ Oxide film surface (formed in the first cleaning step SA 1) is changed to change SC1 composition (liquid composition NH ₄ OH:H ₂ O ₂ :H ₂ O), cleaning temperature and cleaning time, and Haze values obtained by a particle counter.

The chemical solution used was 28 mass% aqueous ammonia (NH ₄ OH), 30% by mass aqueous hydrogen peroxide solution (H ₂ O ₂ ) The labels are also each given in weight (wt%). The mass% is a concentration expressed as a percentage of the mass ratio of the cleaning solution to the solute (ammonium hydroxide, hydrogen peroxide) contained therein, and may be also denoted as wt%. Fig. 9 also shows Si relative to SiO obtained by a calculation method described later ₂ Is used for etching the substrate.

O is only in the case of aqueous solutions with very high liquid compositions of 1:1:1000, 1:0.01:10, 1:0.05:100 by means of the stated selectivity ratio ₃ In the SEM image of the level at which the oxide film surface was cleaned, a large uneven shape was observed, and the Haze value was greatly increased from that of the other levels, and it was found that the oxide film surface was roughened. By washing with an aqueous solution of the very high-selectivity liquid composition 1:1:1000, 1:0.01:10, 1:0.05:100, the bare surface is also only slightly roughened, but to a degree that is comparable to O ₃ The oxide film surface was small, and it was found that the roughening factor was Si/SiO, on which the oxide film was deposited on the surface, and the cleaning liquid used in the second cleaning step SA2 ₂ Is high in etching selectivity ratio. This is caused by rapid etching of Si at the portion where Si is exposed locally by etching the oxide film formed in the first cleaning step SA1 in the second cleaning step SA2, and therefore it is necessary to use Si/SiO for roughening ₂ High etching selectivity ratio, in particular Si/SiO ₂ The etching selectivity ratio is more than 95. Si/SiO of the aqueous solution used in the second cleaning step SA2 ₂ The upper limit of the etching selectivity of (c) is not particularly limited, and may be 10000, for example.

Next, the Si/SiO used as an index in the present invention is subjected to ₂ The method for calculating the etching selectivity of (c) is described in detail.

Si in the aqueous solution used in the second cleaning step SA2 is relative to SiO ₂ The etching selectivity of (a) can be determined according to (etching amount of Si/SiO ₂ Etching amount of (a) is determined.

The etching amount of Si is as follows: preparing any one of a silicon wafer, an epitaxial wafer or a SOI (Silicon on Insulator) wafer which is free of natural oxide film, i.e. free of natural oxide film and has exposed surface, and using an aqueous solution (Si/SiO to be calculated) ₂ An aqueous solution of etching selectivity of (a)), and then the difference between the film thicknesses before and after the cleaning was measured as the etching amount.

For example, an HF cleaning or the like may be used to remove the natural oxide film. If the natural oxide film is present on the wafer, si etching does not occur until the natural oxide film is etched, and the etching amount of Si cannot be evaluated with good accuracy. Further, since the roughening phenomenon is performed by the presence of the natural oxide film, the wafer surface is roughened, and thus the measured value may be affected, and therefore, the wafer for calculating the etching amount of Si needs to be a wafer without the presence of the natural oxide film.

The wafer to be used may be selected appropriately according to the etching amount. In general, the thickness of a silicon wafer is about 775 μm, and thus the etching amount is at least 1 μm or more, and the thickness variation thereof can be obtained. For example, the wafer thickness before and after cleaning may be used as the etching amount using the wafer thickness measured by a general flatness measuring machine or the like as an index. The measuring machine is not particularly limited as long as the thickness of the wafer can be measured. For example, when the etching amount is several tens of nanometers, the variation in thickness is very small and it is difficult to obtain the variation, so that it is not preferable to use the wafer thickness as an index.

When the etching amount is tens to hundreds of nanometers, an epitaxial wafer having an epitaxial thickness of several micrometers, or Si/SiO, is used ₂ The thickness of the Si layer on the surface side of the Si structure may be several tens nm to several hundreds nm, and may be appropriately selected according to the etching amount required. In the case of an epitaxial wafer, for example, the difference in film thickness can be calculated by measuring the epitaxial thickness after cleaning by using the extension resistance measurement using the difference in resistivity between the epitaxial layer and the underlying layer (subelayer). For film thickness measurement of an SOI wafer, for example, an ellipsometer can be used, and for example, when the etching amount is several nanometers, an SOI wafer having an Si layer of 100nm or less can be used to evaluate the film with high accuracy. The evaluation method is not particularly limited as long as the thicknesses of the epitaxial layer and the Si layer can be evaluated for both the epitaxial wafer and the SOI wafer.

Next, as a method for calculating SiO ₂ It is desirable to prepare a wafer having a silicon oxide film of 3nm or more.

In general, when SC1 cleaning is performed in which etching of an oxide film and oxidation reaction of silicon compete with each other on a silicon wafer having a natural oxide film, the silicon oxide film is etched to be thin, and an oxide species (oxidative species) easily diffuses into the silicon oxide film to perform oxidation reaction of silicon, so that the natural oxide film thickness becomes a fixed value regardless of cleaning time. In this case, even if the difference between the film thicknesses before and after the cleaning is calculated, since there is a silicon oxide film formed by the oxidation reaction of silicon, siO cannot be accurately obtained ₂ Is used for etching. Further, the thickness of a typical natural oxide film is about 1nm, and it is difficult to measure the change at 1nm with high accuracy.

Thus, for exampleA silicon oxide film of 3nm or more formed by thermal oxidation is prepared, and the thickness of the oxide film before and after cleaning is measured, whereby SiO can be calculated with high accuracy ₂ Is used for etching. When the film thickness is 3nm or more, the oxide species does not diffuse in the oxide film, and oxidation of silicon does not occur. Therefore, siO is performed only ₂ Therefore, siO can be calculated with good accuracy ₂ Is used for etching. Further, the film thickness can be measured with good accuracy.

The thickness of the silicon oxide film may be appropriately selected depending on the etching amount, so long as the Si/SiO film to be calculated is used ₂ The wafer with the silicon oxide film prepared is cleaned with the aqueous solution of the etching selectivity of (a), and the difference between the film thickness before and after cleaning is calculated, and for example, an ellipsometer or the like may be used as a measurement means.

Thus, the etching amount of Si and SiO can be obtained at the same liquid composition and the same cleaning temperature ₂ After the etching amount according to (etching amount of Si/SiO) ₂ Etching amount) of Si relative to SiO was calculated ₂ The etching selection ratio of (2) is sufficient. In addition, the etching rate per unit time can be calculated based on (etching rate of Si/SiO ₂ Etch rate of (c) to calculate Si versus SiO ₂ Is used for etching the substrate.

If the index is a certain value or more, siO ₂ The Si is etched, and only the Si is etched preferentially at the exposed portion, and therefore roughening is performed. In addition, si and SiO ₂ The etching mode of (2) is changed depending on the cleaning temperature, so that Si/SiO can be obtained in advance according to the composition and the cleaning temperature ₂ And thereby roughening can be reliably performed under various conditions. As a result of examination by the inventors of the present application, it was found that roughening was performed in the cleaning liquid (for example, the liquid composition was 1:1:1000, and the cleaning condition was 45 ℃) at the selection ratio of 95, and therefore Si/SiO was required ₂ The etching selectivity of (2) is 95 or more.

FIGS. 10 to 12 show Si and SiO when cleaning is performed at three levels of cleaning time of 3 minutes, three levels of liquid composition, and three levels of cleaning temperature ₂ Is calculated and the etching amount of Si/SiO is calculated ₂ Etching selectivity ratio of (a). As can be seen from fig. 10 to 12, the Si etching amount is the largest in the aqueous solution having a liquid composition of 1:1:1000, siO ₂ Instead, the etching amount of (C) is smaller in the aqueous solution with the liquid composition of 1:1:1000, and the result also reflects Si/SiO in the aqueous solution with the liquid composition of 1:1:1000 ₂ The etching selectivity of (c) becomes high.

Next, siO required for roughening is treated ₂ Is described in detail. As described above, the roughening according to the present invention is performed by etching the natural oxide film during cleaning and performing rapid etching of Si at the portion where Si is exposed. In other words, when cleaning is performed with a cleaning liquid having a selectivity of 95 or more, the amount of SiO required for exposing Si is etched ₂ The roughening can be promoted by etching. Therefore, for each of the oxide film forming methods in the first cleaning step SA1, siO necessary for roughening in the second cleaning step SA2 is obtained in advance ₂ As the roughening etching amount, so that SiO in the second cleaning step SA2 ₂ The cleaning time of the second cleaning step SA2 is selected in advance so that the etching amount is equal to or larger than the roughening etching amount, whereby roughening can be performed more reliably, and the cleaning conditions of the second cleaning step SA2 can be easily selected.

It is known that the etching method of an oxide film depends on the film quality of the oxide film, and the denser the film structure is, the less likely the oxide film is etched. By Si/SiO ₂ The results of cleaning the oxide film formed by SC1 cleaning or ozone cleaning in the first cleaning step SA1 with the cleaning liquid having a high etching selectivity ratio (95 or more) are shown in table 1.

TABLE 1

When the oxide film is formed by SC1 cleaning in the first cleaning step SA1 of the first tank (levels 1, 2), siO is used in the second cleaning step SA2 of the second tank ₂ Roughening is performed under the condition that the etching amount is 0.14nm or more, but when the oxide film is formed by ozone cleaning in the first cleaning step SA1 of the first trench(level 3-8), in the second cleaning step SA2 of the second tank, siO ₂ Roughening is performed under the condition that the etching amount is more than 0.2 nm. Thus, for each of the oxide film forming methods in the first cleaning step SA1, siO required for roughening is calculated in advance ₂ As the roughening etching amount, roughening can be performed reliably. In addition, in general, it is known that the natural oxide film thickness is 1nm, and the etching amount as an index is less than 1nm because SiO is used in the present invention ₂ Is very dense and is not easy to etch. By using the etching amount of the thermal oxide film as an index, even in the case where the oxide film types are different for each of the oxide film forming methods in the first cleaning step SA1, by grasping the etching amount required for roughening in advance as the roughened etching amount, it is not necessary to calculate the etching amount for each oxide film type, and the cleaning conditions can be quickly selected.

In the cleaning method of this embodiment, as shown in fig. 8, an additional cleaning step SA3 for thinning the oxide film formed in the first cleaning step SA1 may be added so as to leave a part of the oxide film remaining before the cleaning step of the second cleaning step SA2, and SiO in the additional cleaning step may be added as well ₂ And the etching amount of SiO in the second cleaning process ₂ The cleaning time is adjusted so that the total of the etching amounts is equal to or larger than the roughening etching amount.

Table 2 below shows that the oxide film formation in the first cleaning step SA1 is performed in the first tank, the additional cleaning step SA3 for thinning the oxide film is performed in the second tank, and the Si/SiO treatment in the second cleaning step SA2 is performed in the third tank ₂ The Haze value of the wafer cleaned by the cleaning liquid with the etching selection ratio of 95 and the result of determining the roughening degree.

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

Even with Si/SiO ₂ The oxide film formed by SC1 cleaning in the first cleaning step SA1 was cleaned with a cleaning solution (liquid composition 1:1:1000, 45 ℃) having an etching selectivity of 95 for 3 minutes, siO ₂ The etching amount of (2) was 0.12nm, which was 0.14nm or less as an index of roughening, and therefore roughening was not performed (level 1). On the other hand, before the second cleaning step SA2, additional cleaning was performed in the additional cleaning step SA3 with an aqueous solution containing ammonium hydroxide having a liquid composition of 1:0:100 for 1 minute, and then the same cleaning as level 1 was performed, and as a result, roughening was performed. The etching amount in the additional cleaning step was 0.06nm, whereby SiO ₂ The total etching amount of (a) was 0.06nm+0.12 nm=0.18 nm, which is 0.14nm or more as an index, and thus it was considered that roughening was performed. For the ozone oxidation film of level 3 to 5, only level 5 having an index of 0.2nm or more was roughened. Thus, the additional cleaning step SA3, which is easy to roughen, can be added before the second cleaning step SA2.

Thereby, the SiO can be adjusted by the cleaning temperature, the cleaning time and the liquid composition in the second cleaning step SA2 ₂ The etching amount of (2) may be adjusted by adjusting SiO in the additional cleaning step SA3 ₂ Is used for etching. The chemical solution in the additional cleaning step SA3 is not particularly limited as long as it is a cleaning solution capable of thinning the silicon oxide film, and examples thereof include an aqueous solution containing ammonium hydroxide, hydrofluoric acid, and the like.

Next, a method for forming a natural oxide film (type of natural oxide film) and Si/SiO will be examined ₂ The result of the influence of the etching selectivity of (c) is shown in fig. 13. Comparing SEM images, it was found that the Si/SiO ratio was determined according to the type of natural oxide film ₂ The etching selectivity and the cleaning time of the substrate are used for forming various roughness. The Haze value obtained by particle counter SP manufactured by KLA company was in the range of 88 to 1871ppm, and the Sa value obtained by AFM was varied between 0.31 and 5.5 nm. That is, the first cleaning is performed in advanceMethod for forming oxide film (oxide film type) in washing step, si/SiO ₂ The etching selectivity of (a) is evaluated after the second cleaning step, and the relation between these conditions and the surface roughness after the second cleaning step is obtained in advance, whereby the cleaning conditions can be determined from the target roughness. For example, si to SiO is preferably obtained in advance for each oxide film forming method in the first cleaning step SA1 ₂ The relation between the etching selectivity and the cleaning time and the surface roughness, and Si to SiO is selected according to the relation ₂ The etching selectivity and the cleaning time of the substrate are used for the second cleaning step. The discrepancy between the size of the Haze value and the Sa value is caused by the detection methods of both, and the proper required index is used flexibly. As to the influence of the cleaning time, as shown in FIG. 14, in Si/SiO ₂ In the etching selectivity of (c) is different from that of the other, the Haze value is greatly changed depending on the cleaning time, and thus it is found that the target roughness is easily formed by adjusting the cleaning time. Thus, the roughening method of the present application can utilize the type of oxide film formed in the first cleaning step (oxide film forming method in the first cleaning step), si/SiO ₂ It is advantageous to flexibly vary the roughness to be formed by the etching selectivity and the cleaning time.

Next, a cleaning method in the cleaning according to the present application will be described. Currently, most of the wafer cleaning methods are performed using a liquid such as a chemical solution or pure water, and are called wet cleaning. The main methods include batch type in which a plurality of wafers are collectively cleaned at one time, and single-wafer type in which wafers are processed one by one. Since both the front and back surfaces of the wafer are immersed in the chemical solution in the device configuration in a batch manner, the front and back surfaces are roughened when the cleaning of the present application is performed. In contrast, the single wafer is rotated while the chemical solution is sprayed, so that only one surface of the wafer can be cleaned. As a result of examination by the inventors of the present application, it was found that when SiO is used in the present application ₂ Is a certain value or more and Si/SiO ₂ The second cleaning step is performed with an aqueous solution having an etching selectivity of 95 or more, and the cleaning is performed in batchAnd any of the single-piece type can be roughened. It is known that an appropriate method can be selected in consideration of the wafer manufacturing process.

As described above, in order to produce a wafer having only a rough back surface, only the back surface needs to be cleaned in the case of a single wafer, and in the case of a batch, both the front surface and the back surface are roughened, so that it is desired that the quality of the front surface side be improved by a polishing step described later.

For example, when the cleaning method of the silicon wafer of the present invention is performed by using a batch type cleaning machine, the surface and the back surface of the silicon wafer are roughened at the same time, and then by performing single-sided polishing such as CMP polishing on one side (i.e., the front surface), a wafer in which only the surface opposite to the one side (i.e., the back surface) is selectively roughened can be manufactured.

Therefore, the polishing process which can be performed after the cleaning method of a silicon wafer according to the present invention will be described in detail. The utilized Si/SiO is aimed at the polishing allowance of 500nm ₂ The wafer roughened with the cleaning solution having an etching selectivity of 95 or more was subjected to CMP polishing, and the LLS number of more than 19nm was evaluated with 19nmUP by particle counter SP manufactured by KLA, and as a result, as shown in fig. 15, the LLS number increased in the level where the etching amount of Si was large. This is because a large etching amount cannot remove defects caused by etching by polishing. In contrast, the LLS number is very small and good at the level where the etching amount of Si is small. Therefore, by using the etching amount of Si as an index, the LLS quality after CMP can be estimated. Further, for the level at which the number of LLS increases, the LLS quality can be made good by increasing the process margin of CMP, and it is preferable to select the process margin of CMP polishing according to the Si etching amount. As described above, in SiO ₂ Since roughening occurs after etching to expose Si, for example, when the start time of roughening is estimated to be 2 minutes when the cleaning time of the second cleaning step SA2 is set to 3 minutes, the process margin can be adjusted so that the etching amount of Si is equal to or greater than the cleaning time of 1 minute. Thus, a minimum machining allowance can be formed. In addition, from the viewpoint of the throughput (throughput), in the case where the polishing process margin is to be controlled to be small,the second cleaning step SA2 may be performed under the condition that the etching amount of Si is small, and the etching amount or the polishing margin may be appropriately selected and controlled. By polishing under such conditions, even when the front and rear surfaces are roughened in a batch manner, a wafer having a good surface LLS quality and selectively roughened only the rear surface can be manufactured. Such a wafer can be stably manufactured without causing a problem of barred hair even in a wet environment.

(silicon wafer)

The silicon wafer 1 shown in fig. 16 has a roughened surface 2. The roughened surface 2 has a roughness index Sa value of 0.3nm to 5.5nm as measured by an atomic force microscope. The roughened surface 2 has a roughness index Haze value of 50ppm to 1900ppm as measured by a particle counter.

In the case of such a silicon wafer 1, the roughened surface 2 exhibits a roughness suitable for suction by a chuck, and thus, defective conveyance in the processing step can be reduced.

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

The silicon wafer 1 shown in fig. 16 has a mirror surface 3 as a surface opposite to the roughened surface 2. Such a mirror surface 3 can be obtained by performing single-sided polishing such as CMP polishing on one surface of a silicon wafer cleaned by the cleaning method of a silicon wafer of the present invention.

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

Examples (example)

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

Examples 1 to 8

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

Comparative example 1

Liquid composition of NH ₄ OH:H ₂ O ₂ :H ₂ The cleaning of the wafer was performed in the same manner as in example 2 except that the SC1 cleaning in the second tank was performed at o=1:5:1000. The results are shown in table 3 below.

TABLE 3

Liquid composition of NH ₄ OH:H ₂ O ₂ :H ₂ O＝1:1:1000(NH ₄ OH concentration 0.025 mass%, H ₂ O ₂ Concentration 0.033 mass%) or liquid composition NH ₄ OH:H ₂ O ₂ :H ₂ O＝1:1:500(NH ₄ OH concentration 0.051 mass%, H ₂ O ₂ Concentration 0.066 mass%) to ozone (O) ₃ ) Oxide films were cleaned, and the cleaning levels were examined (examples 1 to 3) and NH was formed in the liquid composition ₄ OH:H ₂ O ₂ :H ₂ The roughening was performed by increasing the Haze value from 4 minutes at a washing temperature of 70 c (example 1) at o=1:1:1000, and by increasing the Haze value from 3 minutes at a washing temperature of 80 c (example 2). The etching of the oxide film proceeds faster at 80 c, and thus it is considered that roughening is easy at 80 c. In liquid composition NH ₄ OH:H ₂ O ₂ :H ₂ At o=1:1:500 and a cleaning temperature of 80 ℃ (example 3) the Haze value increased from 4 minutes, and roughening was performed.

Next, the cleaning temperature is 80 ℃ and the liquid is composed of 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 mass%) or liquid composition NH ₄ OH:H ₂ O ₂ :H2O＝1:5:1000(NH ₄ OH concentration 0.025 mass%, H ₂ O ₂ Concentration 0.165 mass%) to ozone (O) ₃ ) Oxide films were cleaned, and the cleaning levels were examined (examples 4 and 5 and comparative example 1) and NH was formed in the liquid composition ₄ OH:H ₂ O ₂ :H ₂ The increase in Haze value was observed only at 10 minutes in o=1:2:1000 (example 4) and 1:3:1000 (example 5), no roughening occurred at 3 minutes and 5 minutes. In the liquid composition 1:5:1000 (comparative example 1), no increase in Haze value was observed even after 10 minutes, and no roughening occurred. This is thought to be because merely adding hydrogen peroxide inhibits etching.

Next, NH is composed of liquid 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 mass%) or liquid composition NH ₄ OH:H ₂ O ₂ :H ₂ O＝1:1:500(NH ₄ OH concentration 0.051 mass%, H ₂ O ₂ Concentration 0.066 mass%) the surface of the SC1 oxide film formed by the SC1 cleaning was cleaned, and at these cleaning levels (examples 6 to 8), the liquid compositions 1:2:1000 (example 6) and 1:1:500 (example 8) were roughened at a cleaning time of 1.5 minutes, compared with ozone (O) ₃ ) The oxide film surface is more easily roughened. This is considered to be because ozone (O) ₃ ) The oxide film has a different film thickness and film quality from those of the SC1 oxide film. Thus, if the relationship between the ammonium hydroxide concentration, the hydrogen peroxide concentration, the cleaning temperature, and the cleaning time and the surface roughness is obtained in advance for each oxide film type (oxide film forming method), the wafer having the target roughness can be manufactured by selecting the cleaning conditions based on the relationship and cleaning. In example 7, it was confirmed that the front and back surfaces of the wafer were roughened at a cleaning time of 6 minutes.

After performing CMP processing on one surface of the silicon wafer cleaned horizontally with the second bath cleaning time of 1.5 minutes in example 6, a chucking test was performed in a CMP polisher. The roughened surface (back surface) of the wafer stored in water on the opposite side to the CMP processing side was clamped, and the wafer was removed from the chuck (unchuck) and conveyed on the table of the polisher, and the conveyance test was repeated 200 times, with the result that 200 times of no defective conveyance was possible.

Comparative examples 2 to 6

A silicon wafer having a bare surface after DSP processing as in the example was prepared, and the following cleaning was performed in a batch type cleaning machine. The first tank was cleaned with ozone water to form an oxide film (comparative examples 2 and 3) or was directly exposed (comparative examples 4 to 6). A second tank for containing NH in liquid form ₄ OH:H ₂ O ₂ :H ₂ O＝1:1:10(NH ₄ OH concentration 2.12 mass%, H ₂ O ₂ Concentration: 2.77 mass%) or NH ₄ OH:H ₂ O ₂ :H ₂ O＝1:1:100(NH ₄ OH concentration 0.25 mass%, H ₂ O ₂ Concentration 0.33 mass%) and cleaning only the bare surface, except for NH in liquid composition ₄ OH:H ₂ O ₂ :H ₂ O＝1:1:1000(NH ₄ OH concentration 0.025 mass%, H ₂ O ₂ Concentration 0.033 mass%) was washed. The cleaning conditions and the results of comparative examples 2 to 6 are shown in table 4 below.

TABLE 4

It was found that in comparative examples 2 to 6, the Haze value was not higher than 50 ppm. It was found that the Haze value of the second tank of comparative example 6 was slightly raised to 42ppm at a cleaning time of 10 minutes, but was judged not to be roughened since it did not exceed 50 ppm.

One surface of the silicon wafer cleaned horizontally with the second bath for 10 minutes in comparative example 2 was subjected to CMP processing, and then, the same chucking test as in example was performed 200 times in a CMP polisher. As a result, the wafer was not detached from the chuck for 4 times out of 200 times.

Examples A1 to A12 and A19 to A33

The silicon wafer having the exposed surface after DSP polishing was prepared, and the following cleaning was performed in a batch type cleaning machine. As the chemical solution for SC1 cleaning, 28 mass% aqueous ammonia (NH) ₄ OH), 30% by mass aqueous hydrogen peroxide solution (H ₂ O ₂ ). The first tank, as a first cleaning step, was subjected to 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, 45 ℃/3 minutes), the second tank, as a second cleaning step, was subjected to SC1 cleaning with the composition, temperature, and time changed as shown in tables 5 and 6 below for the purpose of forming roughening. Then, haze evaluation was performed using particle counter SP3 manufactured by KLA corporation. Further, the etching amount of Si and SiO were calculated from the difference between the film thicknesses before and after the cleaning by the method described above for each aqueous solution used in the second tank ₂ And calculates Si/SiO ₂ Is used for etching the substrate. In addition, utilize HAnd F, calculating the etching quantity of Si on the silicon wafer with the exposed surface and without the natural oxide film after cleaning, and calculating the etching quantity of Si according to the thicknesses of the wafers before and after cleaning by using a flatness measuring machine. SiO Using wafer with 5nm oxide film formed by thermal oxidation ₂ Is used to determine SiO from the thickness of oxide film before and after cleaning by using an ellipsometer M-2000V manufactured by J.A. Woolam company ₂ Is used for etching.

The wafers before roughening had a Haze value of about 20ppm, and it was determined that examples A1 to A12 and A19 to A33 were roughened.

Examples A13 to A18 and A34

The wafers having the exposed surfaces after DSP polishing were prepared and were cleaned in a batch type cleaning machine as follows. As the chemical solution for SC1 cleaning, 28 mass% aqueous ammonia (NH) ₄ OH), 30% by mass aqueous hydrogen peroxide solution (H ₂ O ₂ ). The first tank, as a first cleaning step, was subjected to ozone water cleaning (25 ppm,25 ℃/3 minutes) or SC1 cleaning (NH ₄ OH:H ₂ O ₂ :H ₂ O=1:1:10, 45 ℃/3 minutes), a second tank, as an additional cleaning step for thinning the oxide film, a part of the oxide film formed in the first tank was removed with ammonia water or 0.05wt% HF having a composition of 1:0:100 so as not to expose the exposed surface, and a third tank, as a second cleaning step, was subjected to SC1 cleaning with the composition, temperature, and time changed as shown in tables 5 and 6 below for the purpose of forming roughness. Meanwhile, for each aqueous solution used in the third tank, the etching amount of Si and SiO were calculated from the difference between the film thicknesses before and after the cleaning by the method described above ₂ And calculates Si/SiO ₂ Is used for etching the substrate. In addition, in the additional cleaning step of the second trench, siO was calculated using a wafer with a 5nm oxide film formed in advance ₂ When the oxide film of the first trench is ozone oxide film, the etching amount of the second trench and the third trench is such that SiO ₂ The cleaning conditions are adjusted so that the total etching amount is 0.2nm or more; oxide film of the first grooveWhen the species is SC1 oxide film, the second and third grooves are formed by SiO ₂ The cleaning conditions were adjusted so that the total etching amount was 1.4nm or more. All coarsened were judged from the Haze value of SP3 after washing.

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Next, since the Si etching amount of example a19 was 820nm and the Si etching amount of example a22 was 230nm, the surface of the silicon wafer of example a19 was subjected to CMP polishing with a polishing margin of 1000nm, and the silicon wafer of example a22 was subjected to CMP polishing with a polishing margin of 500 nm. The LLS of each wafer after CMP was evaluated by SP5/19nmUP manufactured by KLA company, and as a result, it was 12pcs and 19pcs, respectively, to obtain good LLS quality. Then, the back side of the wafer stored in the water was clamped, and the wafer was carried by removing the chuck (unchuck) on the platen of the polisher, and the carrying test was repeated 200 times, so that it was possible to carry 200 times without any trouble.

Comparative examples A1 to A13

The silicon wafer having the exposed surface after DSP polishing was prepared, and the following cleaning was performed in a batch type cleaning machine. As the chemical solution for SC1 cleaning, 28 mass% aqueous ammonia (NH) ₄ OH), 30% by mass aqueous hydrogen peroxide solution (H ₂ O ₂ ). The first tank was subjected to ozone water cleaning (25 ppm,25 ℃/3 minutes) for the purpose of forming an oxide film as the first cleaning step, and the second tank was subjected to SC1 cleaning with the composition, temperature and time changed as shown in table 7 below for the purpose of forming roughening as the second cleaning step. Then, haze evaluation was performed using particle counter SP3 manufactured by KLA corporation. Meanwhile, for each aqueous solution used in the second tank, the etching amount of Si and SiO were calculated from the difference between the film thicknesses before and after the cleaning by the method described above ₂ And calculates Si/SiO ₂ Is used for etching the substrate. Furthermore, the etching amount of Si was calculated using a silicon wafer having no natural oxide film exposed to the exposed surface after HF cleaning, and the etching amount of Si was obtained from the wafer thicknesses before and after the wafer cleaning using a flatness measuring machine. SiO using wafer with 5nm oxide film formed by thermal oxidation ₂ Is used for calculating the SiO according to the thickness of the oxide film before and after cleaning by using an ellipsometer ₂ Is used for etching.

As shown in table 7, in comparative examples A1 to a13, SP3 had Haze values of about 20ppm, which were equivalent to those of the non-roughened wafers, and were determined to be non-roughened.

After the CMP polishing with a polishing margin of 500nm was performed on the level of comparative example A1, the same gripping test as in example a19 was performed 200 times in the CMP polisher. The wafer was not detached from the chuck for 4 times among 200 times.

From the above results, it is understood that in examples A1 to A34 of the present invention, si is used for SiO in the second cleaning step ₂ The etching selectivity of 95 or more can be sufficiently roughened on the front and back surfaces of the silicon wafer, particularly on the back surface, to exhibit a roughness suitable for adsorption by the chuck.

On the other hand, in comparative examples A1 to A13, si to SiO was not used in the second cleaning step ₂ Since the etching selectivity of (a) is 95 or more, the front surface and the back surface of the silicon wafer, particularly the back surface, cannot be sufficiently roughened, and the surface exhibits a roughness suitable for the chuck to adsorb.

In addition, the present invention is not limited to the above embodiments. The above embodiments are exemplary, and embodiments having substantially the same composition and exhibiting the same effects as the technical idea described in the claims of the present invention are included in the technical scope of the present invention.

Claims

1. A cleaning method for a silicon wafer is provided, which is a cleaning method for roughening the silicon wafer, and is characterized in that,

2. The method of cleaning a silicon wafer according to claim 1, wherein a relationship between the ammonium hydroxide concentration or the relationship between the ammonium hydroxide concentration and the hydrogen peroxide concentration, the cleaning temperature, and the cleaning time and the surface roughness after cleaning is obtained for each oxide film forming method in advance,

3. A method for manufacturing a silicon wafer, characterized in that one surface of a silicon wafer cleaned by the cleaning method for a silicon wafer according to claim 1 or 2 is subjected to CMP polishing, and a silicon wafer in which only the surface opposite to the one surface is selectively roughened is obtained.

4. A silicon wafer is characterized by having a roughened surface with a roughness index Sa value of 0.3-5.5 nm as measured by an atomic force microscope.

5. A silicon wafer is characterized by having a roughened surface with a roughness index Haze value of 50ppm to 1900ppm as measured by a particle counter.

6. The silicon wafer according to claim 4 or 5, wherein a surface opposite to the roughened surface is a mirror surface.

7. A cleaning method for a silicon wafer, which is a cleaning method for roughening a silicon wafer, the cleaning method characterized by comprising the steps of:

A first cleaning step of forming an oxide film on the silicon wafer by SC1 cleaning, SC2 cleaning, or ozone water cleaning; a kind of electronic device with high-pressure air-conditioning system

8. The method for cleaning a silicon wafer according to claim 7, wherein the etching amount of Si/SiO ₂ Etching amount) of the aqueous solution used in the second cleaning step, the Si to SiO ratio is determined ₂ Is used for the etching selection ratio of (a),

9. The method for cleaning a silicon wafer according to claim 7 or 8, wherein the SiO required for roughening in the second cleaning step is calculated in advance for each of the oxide film forming methods in the first cleaning step ₂ As the etching amount of the roughening etching amount,

with SiO in the second cleaning process ₂ The cleaning time of the second cleaning procedure is selected in a mode that the etching amount is more than or equal to the roughening etching amount, and/or

10. The method for cleaning a silicon wafer according to any one of claims 7 to 9, wherein the Si relative to the SiO is obtained in advance for each of the oxide film forming methods in the first cleaning step ₂ The relation between the etching selectivity and the cleaning time and the surface roughness,

selecting the Si relative to SiO according to the obtained relation ₂ The etching selectivity and the cleaning time of the substrate are used for performing the second cleaning process.

11. A method for producing a silicon wafer, characterized in that one of the surfaces of a silicon wafer, which has been cleaned by the cleaning method for a silicon wafer according to any one of claims 7 to 10 and has been roughened on the front and back surfaces, is subjected to CMP polishing, and a silicon wafer having only the surface on the opposite side from the one surface selectively roughened is obtained.

12. The method of manufacturing a silicon wafer according to claim 11, wherein a process margin of the CMP polishing is set to be equal to or larger than an etching amount of Si in the second cleaning step.

13. The method according to claim 11, wherein an etching amount of Si in the second cleaning step is set to be equal to or less than a machining allowance of the CMP polishing.