JP7533100B2 - Wafer contamination detection method - Google Patents

Description

The present invention relates to a method for detecting contamination on a wafer.

In the field of electronics industries such as semiconductors, research and countermeasures against surface contamination of wafers (also called wafers, wafers, wafers, and wafers) have been actively pursued since the 1990s. The background to this is that as wafers become more and more sophisticated, contaminants originating from the wafer manufacturing environment have come to have a greater impact on product yield, quality, and reliability. In response to this, airborne particles such as dirt, dust, foreign matter, and other substances that were previously the biggest problem have been greatly improved through improvements in cleanroom technology. However, on the other hand, chemical contamination at the atomic and molecular level, especially organic contamination, has become more pronounced, and it is gradually becoming clear that this is deeply involved in device characteristics and manufacturing problems.

There are three main sources of organic matter that contaminate the wafer surface. The first is organic components from the outside air that is introduced into the clean room in large quantities. Outside air contains various hydrocarbon compounds emitted from factories and automobiles, as well as various organic components resulting from the spraying of pesticides and fertilizers. The second is organic components that are generated as outgassing from the polymer interior materials (floors, walls, partitions, filters), paints, adhesives, sealants, etc. that are the components of the clean room. In addition, outgassing from wafer carriers and cases, which are made of polymers, is also used in many parts of wafer manufacturing equipment, and the outgassing caused by these cannot be ignored. The third is organic components from various chemicals and medicines, such as cleaning solutions used in the wafer manufacturing process. Other sources of organic contamination include workers' breath, sweat, and clothing.

So far, various methods have been proposed for evaluating outgassing from polymers, such as the materials used to make clean rooms, as well as for evaluating surface contamination of the wafer itself.

For example, Patent Document 1 discloses _{a method} for evaluating organic compounds attached to a wafer surface _by measuring the increase or decrease in the thickness of a film of a deposit deposited on _the wafer surface and/or by measuring the change in the contact angle at a predetermined time after cleaning with a solution of NH 4 OH and H 2 O 2 diluted with H 2 O.

Patent Document 2 discloses a method of analyzing impurities by using an impurity collector that can move relatively at a fixed interval to the flat surface of a solid object to be measured, holding droplets of a decomposition liquid (HF, HCl, _NH4OH , _H2SO4 or _H2O ) between the collector and the surface of the object to be measured, heating the decomposition liquid while moving the collector relative to the surface of the object to collect impurities on the surface of the object with _the decomposition liquid, and measuring the decomposition liquid.

Patent document 3 discloses an evaluation device for evaluating organic contamination of a substrate surface originating from the atmosphere, characterized in that it includes a substrate having at least an insulating surface, a surface resistivity meter for measuring the electrical resistance between at least two points on the substrate surface, an isolated space for housing the substrate, a humidity control gas introduction means for introducing a humidity control gas having a substantially constant relative humidity into the isolated space, an evaluation target gas introduction means for introducing a gas to be evaluated into the isolated space, and an evaluation means for evaluating organic contamination of the substrate surface according to the surface resistivity measured by the surface resistivity meter.

Patent Document 4 discloses a method for evaluating contamination on a wafer surface, which is characterized by dropping dilute hydrofluoric acid or a hydrogen peroxide solution onto a wafer surface whose periphery is immersed in dilute hydrofluoric acid (HF aqueous solution), and quantifying the area of movement of the dropped liquid on the wafer surface.

Patent document 5 discloses a surface condition measuring device that includes a reflecting mirror disposed opposite the substrate to be measured, infrared incidence means for irradiating infrared rays so that the infrared rays are multiple-reflected between the substrate to be measured and the reflecting mirror, infrared detection means for detecting the infrared rays that pass through the substrate to be measured after multiple reflection between the substrate to be measured and the reflecting mirror, and infrared analysis means for analyzing the infrared rays detected by the infrared detection means and measuring contaminants attached to the substrate to be measured.

Patent Document 6 discloses an evaluation method for measuring the spectroscopic ellipsometric data of a clean GaAs wafer surface cleaned with an HF solution and an oxidized GaAs wafer surface, determining the refractive index and extinction coefficient as optical data for each from the spectroscopic ellipsometric data, calculating the spectroscopic ellipsometric data of a GaAs wafer on which organic contaminants have accumulated using the obtained optical data and the refractive index and extinction coefficient as optical data for polyethylene, and further using arbitrary film thickness data for the organic contaminants and the oxide film, and measuring the spectroscopic ellipsometric data of a GaAs wafer on which organic contaminants have accumulated, and determining the film thickness value of the organic contaminants and the oxide film that gives the calculated spectroscopic ellipsometric data that has the smallest difference from the actually measured spectroscopic ellipsometric data.

Patent document 7 discloses a method for evaluating organic contamination on the surface of a semiconductor substrate, which includes acquiring photoluminescence intensity information on the surface of a semiconductor substrate to be evaluated, and evaluating an evaluation item selected from the group consisting of the presence or absence, the degree, and the in-plane distribution of organic contamination on the surface of the semiconductor substrate to be evaluated based on the acquired photoluminescence intensity information.

Japanese Patent Application Publication No. 5-275410 Japanese Patent Application Publication No. 7-146220 Japanese Patent Application Publication No. 8-338822 JP 2001-221790 A JP 2001-311697 A JP 2004-271203 A JP 2016-018822 A

However, in Patent Document 1, the thickness of the organic matter adhering to the wafer surface after cleaning is measured, the wafer is stored for several hours, and the thickness is measured again to evaluate the degree of contamination by organic matter on the wafer surface by calculating the difference between the measured value after cleaning and the measured value after storage. This method is complicated and requires a long time to obtain the results. In Patent Documents 2, 4, and 6, hydrofluoric acid (HF), which is known as a dangerous poison that corrodes the human body when touched, is used as the decomposition liquid, dripping liquid, and cleaning liquid in the evaluation process, and this is by no means a clean method and has the disadvantage of compromising safety. Patent Document 3 describes that it provides a simple and inexpensive method for evaluating the surface contamination of a substrate by organic matter originating from the atmosphere, but it requires a surface resistivity meter, an isolated space, a means for introducing a humidity-controlling gas, a means for introducing a gas to be evaluated, an evaluation means, etc., and in reality, it is a large-scale evaluation device, so it must be said that both the initial and running costs are high. Patent Document 5 describes providing a method and device that realizes non-contact, non-destructive, and highly sensitive measurement of the local surface state of a substrate and can measure the distribution of organic contaminants on the substrate surface, but requires a reflector, infrared incidence means, infrared detection means, infrared analysis means, etc., and, like Patent Document 3, it is a large-scale evaluation device, which has the disadvantage of being high cost. Patent Document 7 introduces the photoluminescence method that has been used as a conventional technology to analyze defects and metal contamination in substrates, and as an extension of this, changes the detection conditions, etc., and converts it to the evaluation of organic contamination on the substrate surface, and, like Patent Documents 3 and 5, has the disadvantage of being high cost.

In addition, Patent Documents 1 to 7 list X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (ATR), gas chromatography-mass spectrometry (GC-MS), atmospheric pressure ionization mass spectrometry (APIMS), and secondary ion mass spectrometry (SIMS) as conventional techniques, and point out that these methods cannot directly observe large substrates, and that all of them require a form of destructive testing, and the wafer itself cannot be reused. The same can be said about time-of-flight secondary ion mass spectrometry (TOF-SIMS), in addition to the above analytical methods, and all of them require the introduction and ownership of expensive analytical equipment. If this is not possible, it is necessary to outsource the analysis to a specialized analytical institution, but this has the problem of paying high analysis fees and waiting a long time before the analysis results are reported.

Thus, it goes without saying that it is important to be able to safely, quickly, simply, and inexpensively evaluate the surface contamination of the wafer itself during the wafer manufacturing process, and this plays an extremely important role in process management and quality control, but currently a method that satisfies all of these requirements has not yet been developed or established.

The present invention was made in consideration of the above problems, and aims to provide a method for evaluating wafer surface contamination safely, quickly, simply, and inexpensively, and that is extremely effective in terms of process management and quality control.

The inventors have conducted extensive research to develop a new method for evaluating wafer surface contamination safely, quickly, simply, and inexpensively, and that is extremely effective in terms of process management and quality control. As a result, they have discovered a technology in which a color developer is adsorbed onto contaminants present on the wafer surface, and the contaminants are colored by the color developer.

That is, according to one aspect of the present invention completed by the inventor, a first aspect of the present invention is a method for detecting contamination on a wafer, which comprises adsorbing a coloring agent to contaminants present on a surface of a wafer in an exhaust environment, and causing the contaminants to develop a color with the coloring agent.

The second aspect of the present invention is a method for detecting contamination of a wafer, comprising the steps of: a preparation step of placing the coloring agent and the wafer in a sealed container and sealing the container; a pretreatment step of generating vapor of the coloring agent in the sealed container and bringing the vapor into contact with the surface of the wafer; a coloring step of adsorbing the coloring agent to the contaminants present on the surface of the wafer and causing the contaminants to develop a color with the coloring agent; and a detection step of visually detecting whether the contaminants have developed a color.

The third aspect of the present invention is a method for detecting contamination of a wafer, characterized in that the color developer generates the vapor at room temperature or by heating, in the invention described in the second aspect.

The fourth aspect of the present invention is a method for detecting contamination of a wafer, according to the second or third aspect of the invention, characterized in that the sealed container is transparent and made of glass.

The fifth aspect of the present invention is a method for detecting contamination of a wafer, characterized in that in the invention described in any one of the first to fourth aspects, the contaminant contains an organic compound, and the organic compound contains one or more compounds selected from aromatic hydrocarbons, aliphatic hydrocarbons, halogenated hydrocarbons, organic acids, alcohols, phthalates, adipic acid esters, phosphates, phenols, and siloxane compounds.

The sixth aspect of the present invention is a method for detecting contamination on a wafer, characterized in that the color developer contains iodine in the invention described in any one of the first to fifth aspects.

The seventh aspect of the present invention is a method for detecting contamination of a wafer, according to any one of the first to sixth aspects of the invention, characterized in that the wafer contains one or more elements selected from silicon, carbon, aluminum, oxygen, gallium, phosphorus, arsenic, indium, nitrogen, tantalum, niobium, and lithium.

The eighth aspect of the present invention is a method for detecting contamination on a wafer, characterized in that the wafer has a diameter of 50 to 500 mm and a thickness of 0.1 to 1.0 mm, in the invention described in any one of the first to seventh aspects.

The present invention provides a method for evaluating wafer surface contamination safely, quickly, simply, and inexpensively, and is extremely effective in terms of process management and quality control.

FIG. 1 is an operational flow diagram showing an overall picture of a method for detecting contamination of a wafer according to an embodiment of the present invention. 1 is a front cross-sectional view of a sealed container in a preparation step of a method for detecting contamination of a wafer according to an embodiment of the present invention. 4 is a plan cross-sectional view of a sealed container in a detection step of a method for detecting contamination on a wafer according to an embodiment of the present invention. FIG.

[One embodiment of the present invention]
Hereinafter, an outline of a method for detecting contamination of a wafer (hereinafter, also simply referred to as a "coloring method") according to one embodiment of the present invention will be described. The present embodiment described below does not unduly limit the contents of the present invention described in the claims, and modifications are possible within the scope of the present invention. Note that not all of the configurations described in this embodiment are necessarily essential as a means for solving the problem of the present invention.

1. Overview A wafer is a material for IC chips (semiconductor integrated circuits) that refers to a thin, thick disk made of a single crystal semiconductor material, as well as a material for SAW (Surface Acoustic Wave) filters that refers to a thin, thick disk made of a single crystal lithium metal oxide.

The former is made by forming single crystals of semiconductor materials such as silicon (Si), silicon carbide (SiC), sapphire, gallium phosphide (GaP), gallium arsenide (GaAs), indium phosphide (InP), and gallium nitride (GaN), and processing the ingots into cylindrical shapes with a diameter of, for example, 300 mm, which are then thinly sliced to a thickness of about 0.75 mm. These are then subjected to surface polishing and terminal formation, and cut into small rectangular pieces to become pellets (chips).

The latter is made by crystallineing lithium metal oxides such as lithium tantalate (LT: _LiTaO3 ) and lithium niobate (LN: _LiNbO3 ) into single crystals, processing the ingots into cylindrical shapes with a diameter of, for example, 100 mm, and slicing these thinly to a thickness of about 0.5 mm. These are then cut into smaller pieces to become SAW filters that are used, for example, to cut noise in smartphones.

In the production (manufacturing process) of these wafers, there is always a risk of contamination by contaminants from manufacturing equipment, etc., and it plays an extremely important role in process management and quality control to evaluate (1) whether contaminants have been contaminated, (2) how much contaminants have been contaminated, and (3) what contaminants have been contaminated in intermediate products and finished products as safely, quickly, simply, and at low cost as possible. In addition, in the electronics industry, it is difficult to develop and manufacture advanced devices without measures against chemical contamination. In particular, in clean rooms, which are essential for the manufacture of electronic devices, the removal of chemical substances using chemical filters, as well as the reduction of outgassing from various components and building materials that make up the clean room itself, are important technologies for purifying air quality. In addition, in a wide range of fields, including the electronics industry, the construction industry, and the automobile industry, it is now very important to evaluate the degree of contamination by volatile chemical substances, known as outgassing and emitted gases, from various components and building materials.

The present invention has been made based on the above background. In the method for detecting contamination of a wafer according to one embodiment of the present invention, the specimen (hereinafter also referred to as "sample") refers to various types of wafer, and an example is a case in which contaminants present on the surface are evaluated. Each step in the method for detecting contamination of a wafer according to one embodiment of the present invention will be specifically described below.

2. Each step Fig. 1 is an operational flow diagram showing an overall picture of a method for detecting contamination of a wafer according to one embodiment of the present invention, and will be described in the order of the operational flow diagram. As shown in Fig. 1, the method for detecting contamination of a wafer according to one embodiment of the present invention includes a "preparation step S1", a "pretreatment step S2", a "coloring step S3", and a "detection step S4".

(1) Preparation step S1
The preparation step S1 is a step of placing a color developer and various wafers as samples in a sealed container and sealing the container.

1) Samples The various wafers used as samples are primarily those with a diameter of 50 to 500 mm and a thickness of 0.1 to 1.0 mm, which are used as materials for the IC chips and SAW filters described above, but are not limited thereto. Wafers that can be used include, but are not limited to, silicon (Si), silicon carbide (SiC), sapphire (Al ₂ O ₃ ), gallium phosphide (GaP), gallium arsenide (GaAs), indium phosphide (InP), gallium nitride (GaN), lithium tantalate (LiTaO ₃ ), and lithium niobate (LiNbO ₃ ).

2) Coloring Agent There are no particular limitations on the coloring agent, so long as it is capable of coloring contaminants present on the surfaces of various wafers serving as samples.

By the way, molecular contaminants that cause device defects are roughly divided into four types: A: acidic substances (Acids), B: basic substances (Bases), C: condensable organic substances (Condensables), and D: dopants, and have the following characteristics:

A: Acidic substances are _mainly derived from the outside air, such as hydrogen chloride (HCl), nitric acid ( _HNO3 ), sulfuric acid ( _H2SO4 ), phosphoric acid ( _H3PO4 ), hydrofluoric acid ( _HF ), nitrogen oxides ( _NOx ), and sulfur oxides ( _SOx ). These are electron-pair acceptor compounds that are corrosive chemically and can cause corrosion of metal wiring during the manufacturing process.

B: Basic substances are mainly derived from manufacturing equipment (process materials), such as ammonia ( _NH3 ), organic amine compounds, etc. These are electron pair donor compounds, and in the manufacturing process, they cause the T-top phenomenon and clouding of lenses and mirrors in the chemically amplified lithography process.

C: Condensable organic substances are mainly derived from the materials that make up clean rooms, and include aromatic hydrocarbons such as toluene and xylene, aliphatic hydrocarbons such as dodecane and tetradecane, phthalates such as di-n-octyl phthalate (DOP) and di-n-butyl phthalate (DBP), adipic esters such as di-n-octyl adipate (DOA) and di-n-butyl adipate (DBA), phosphate esters such as tri-n-ethyl phosphate (TEP) and tri-n-butyl phosphate (TBP), as well as halogenated hydrocarbons, organic acids, alcohols, phenols, and siloxane compounds. During the manufacturing process, these substances can cause film formation abnormalities, deterioration of the voltage resistance of gate oxide films, and contamination of lenses and mirrors.

D: Dopants are mainly from the atmosphere, such as boron compounds, phosphorus compounds, and arsenic compounds. These can also have a negative effect on the electrical characteristics of devices during the manufacturing process.

Other metal components, mainly from workers and operators, such as sodium (Na), potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), and zinc (Zn), are also considered to be important chemical contaminants, and can cause junction leakage current abnormalities and increased interface states during the manufacturing process.

In particular, there are many types of condensable organic substances (C), which are dealt with from the perspective of chemical contamination, and phthalate esters such as di-n-octyl phthalate (DOP) and di-n-butyl phthalate (DBP), and phenols such as BHT, are considered to be substances that are highly likely to adsorb to the wafer surface. Among these, di-n-octyl phthalate (DOP) has the highest probability of being present, as it adsorbs to the wafer surface even pushing aside other low-boiling point molecules, and it can be said that it is essential to be able to evaluate this.

The coloring agent used for the above contaminants varies depending on the type of contaminant. For example, a phosphomolybdic acid solution (molybdenum blue reagent) is used to evaluate phosphorus compounds. This is sprayed onto the wafer surface and heated at about 200°C for about 30 minutes while open to the air, causing the areas contaminated with phosphorus compounds to turn blue. In addition, ninhydrin solution and basic potassium permanganate solution can also be used for a relatively large variety of contaminants, but of the many coloring agents available, it is preferable to use one that contains iodine, and it is even more preferable to use iodine.

Iodine is an excellent coloring agent that can be used to evaluate organic compounds in general, and can be applied to molecules containing unsaturated bonds such as double bonds, as well as polar compounds. In addition, it has advantages not found in other coloring agents, such as (1) no need for heating or heating equipment, making it possible to evaluate wafer surface contamination more safely, quickly, simply, and inexpensively, (2) coloring can be performed reversibly (after coloring, if the sample is left in the air and the iodine is removed, it can be evaluated in its original state using a different method), and (3) it can be used without being dissolved.

Coloring using iodine is achieved by sublimating iodine, and the vapor that is generated has the property of adsorbing to organic compounds and chemically reacting with organic compounds. Most of these reactions are physical adsorption (interactions) rather than chemical reactions, and interactions occur easily with unsaturated bonds in particular. For example, in the case of iodine and a benzene ring, electrons are transferred from the electron-rich benzene ring to the iodine, forming a charge transfer complex, which causes coloring, and a similar reversible bond occurs between iodine and carbonyls (such as amides).

Iodine is a substance that can exhibit a wide variety of colors; in its solid state it is blackish purple, in its gaseous (vapor) state it is reddish purple, and when it produces hypoiodous acid (HIO) it is yellow or green. Furthermore, when iodine is adsorbed into an organic solvent, for example, it is purple in hexane, brown in diethyl ether, and red in benzene. Because of these properties, the color will vary depending on the type of contaminant, but when visually observing whether or not there is contamination, it is sufficient to be able to determine the color, and this is not a major problem.

Iodine is the molecule with the weakest oxidizing effect compared to other halogen elements such as fluorine, chlorine, and bromine. Therefore, it does not have the strong toxicity of fluorine, chlorine, and bromine, and this weak oxidizing effect gives it a moderate bactericidal effect on the human body when used as a disinfectant or mouthwash, and it is also a safe and clean coloring agent.

3) Airtight container As mentioned above, depending on the contaminant to be evaluated and the coloring agent used, it is possible to treat the sample in an open air state, but it is preferable to use an airtight container because the use of iodine as the coloring agent can broaden the range of application to contaminants. The airtight container is not particularly limited as long as it can accommodate at least the coloring agent and various wafers as samples. In addition, the airtight container is preferably made of glass, which is less likely to be contaminated by outgassing, and is preferably transparent so that the presence or absence of contamination can be observed from outside the container.

4) Arrangement of Colorant and Sample The arrangement of the colorant and sample will be described with reference to Fig. 2. Fig. 2 is a front cross-sectional view of a sealed container in a preparation step of a method for detecting contamination on a wafer according to an embodiment of the present invention.

As shown in FIG. 2, the sealed container 10 is composed of a sealed container body 1 and a sealed container lid 2. The lower part of the sealed container body 1 is provided with a narrowed portion for placing the middle plate 3, and the upper part is provided with a mating surface 1a that forms an opening for inserting and removing the coloring agent and sample (wafer). The sealed container lid 2 is provided with a mating surface 2a that abuts against the mating surface 1a of the sealed container body 1 and has the same diameter as the opening 1a of the sealed container body 1. The middle plate 3 is also provided with an air vent 4.

In the preparation step S1, first, the color developer 6 is placed on the bottom of the sealed container body 1, and the middle plate 3 is placed above it. At this time, a placement stand 5 may be placed on the middle plate 3, taking into consideration the ease of operation when placing the various wafers that are samples.

Next, samples 7, which are various types of wafers, are placed on the placement stage 5 with the surface of the samples 7 facing up. As shown in FIG. 2, contaminants 8 are present on the surface of the samples 7. There is no particular limit to the number of samples 7 placed on the placement stage 5, and the number is set appropriately depending on the size of the sealed container 10 and the samples 7.

Next, the mating surface 1a of the sealed container body 1 and the mating surface 2a of the sealed container lid 2 are brought into contact with each other to create a sealed state inside the sealed container 10.

(2) Pretreatment step S2
The pretreatment step S2 is a step of generating vapor of the color developer 6 in a closed container 10 and bringing the vapor into contact with the surface of various wafers, which are samples 7.

As mentioned above, depending on the contaminant 8 to be evaluated and the coloring agent 6 used, spraying or heating of the coloring agent may be necessary. When iodine is used as the coloring agent, since iodine has sublimation properties even at room temperature, simply placing it in the sealed container 10 causes the container to fill (saturate) with its vapor, and it preferentially adsorbs and colors the contaminant 8 present on the surface of the various wafers that are the sample 7. In this application, room temperature refers to a temperature between 5°C and 35°C. It is more preferable that the temperature is between 20°C and 35°C. The amount of iodine added is preferably adjusted appropriately depending on the size of the sealed container used so that the vapor is sufficiently filled, and is not particularly limited.

(3) Coloring step S3
The color development step S3 is a step of adsorbing a color developer 6 onto contaminants 8 present on the surfaces of various wafers serving as samples 7, and causing the contaminants 8 to develop a color with the color developer 6.

As mentioned above, depending on the contaminant to be evaluated and the coloring agent used, heating may be necessary to promote coloration. When iodine is used as the coloring agent, heating is not necessary, but this does not limit heating. The time required for coloration may vary depending on the temperature, the amount of coloring agent added, the amount of contaminant present, the size and shape of the sealed container, etc. Therefore, the observation time for detecting the presence or absence of contamination should preferably be at least one hour after the sealed container 10 is sealed, taking into account cases where there is no contamination. If no coloration is confirmed after one hour or more has passed, it can be determined that there is no contamination.

(4) Detection step S4
The detection step S4 is a step of visually detecting the presence or absence of coloration of the contaminant.

Figure 3 shows a planar cross-sectional view of a sealed container in a detection step of a wafer contamination detection method according to one embodiment of the present invention. As shown in Figure 3, contaminant 8 present on the surface of sample 7 is colored by a coloring agent adsorbed to contaminant 8 in coloring step S3. In detection step S4, sample 7 is visually observed from above sealed container 10 to confirm the presence or absence of coloring on the surface of sample 7. If coloring is present, it is detected that contaminant 8 is present on the surface of sample 7 and that sample 7 is contaminated. If coloring cannot be confirmed on the surface of sample 7 even after one hour or more has passed since sealed container 10 was put into a sealed state, it is detected that contaminant 8 is not present on the surface of sample 7 and sample 7 is not contaminated.

As mentioned above, depending on the contaminant to be evaluated and the coloring agent used, it may be possible to detect the contaminant while it is open to the atmosphere. When iodine is used as the coloring agent, it may be possible to observe from outside the sealed container 10, and if observation from outside the container is difficult due to steam filling, the sealed container lid 2 of the sealed container 10 may be removed for observation, or various wafers, which are the sample 7, may be removed from the sealed container 10 for observation.

Furthermore, after the detection step S4, the sealed container lid 2 may be removed from the sealed container body 1, and the sealed state may be changed to an open-to-air state. When iodine is used as the coloring agent, the iodine adsorbed to the contaminant escapes from the contaminant as vapor, so that the contaminant can be identified by a physical property analysis method such as time-of-flight secondary ion mass spectrometry (TOF-SIMS) on the same sample.

It is also preferable to use the above-described wafer contamination detection method during wafer production (manufacturing process). In actual wafer production (manufacturing process), in order to minimize the number of defective products, it is more important to be able to test for the presence or absence of contamination as quickly as possible, rather than identifying the type of contaminant. The wafer contamination detection method according to one embodiment of the present invention can quickly and easily evaluate wafer surface contamination, and after contamination is confirmed, improvement measures can be quickly implemented in the wafer production (manufacturing process).

The method for detecting contamination of a wafer according to one embodiment of the present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. In addition, all reagents used in these examples were manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

(Reference Example 1)
First, a glass desiccator (custom-made product with inner diameter of 350 mm, manufactured by AS ONE Corporation) was placed on the workbench of the activated draft chamber, and after removing the top lid, iodine (special reagent grade) was added to the bottom as a coloring agent, and an inner plate (made of porcelain, with air holes) that is an accessory of the glass desiccator was attached, and a placement stand (made of porcelain) was placed on top of that. Furthermore, a silicon (Si) wafer (diameter 300 mm, thickness 0.8 mm) was placed on the placement stand, and finally the top lid was attached to create an airtight state.

Next, iodine was evaporated in a glass desiccator at room temperature and the chamber was left to stand until it was filled with iodine vapor (reddish purple).

Then, from outside the glass desiccator, the presence or absence of colored areas on the wafer surface was visually observed. As a result, no colored areas were found, even though observation was continued for one hour after the sealed state (start of detection).

(Reference Example 2)
Except for placing a silicon carbide (SiC) wafer (diameter 150 mm, thickness 0.8 mm) on the placement table, the same operation as in Reference Example 1 was carried out. As a result, no colored areas were observed.

(Reference Example 3)
Except for placing a sapphire wafer (diameter 150 mm, thickness 0.8 mm) on the placement table, the same operation as in Reference Example 1 was carried out. As a result, no colored areas were observed.

(Reference Example 4)
Except for placing a gallium phosphide (GaP) wafer (diameter 150 mm, thickness 0.8 mm) on the placement stage, the same operation as in Reference Example 1 was carried out. As a result, no colored areas were observed.

(Reference Example 5)
Except for placing a gallium arsenide (GaAs) wafer (diameter 150 mm, thickness 0.8 mm) on the placement table, the same operation as in Reference Example 1 was carried out. As a result, no colored areas were observed.

(Reference Example 6)
Except for placing an indium phosphide (InP) wafer (diameter 150 mm, thickness 0.8 mm) on the placement stage, the same operation as in Reference Example 1 was carried out. As a result, no colored areas were observed.

(Reference Example 7)
Except for placing a gallium nitride (GaN) wafer (diameter 150 mm, thickness 0.8 mm) on the placement stage, the same operation as in Reference Example 1 was carried out. As a result, no colored areas were observed.

(Reference Example 8)
Except for placing a lithium tantalate (LT: LiTaO ₃ ) wafer (diameter 150 mm, thickness 0.5 mm) on the placement stage, the same operation as in Reference Example 1 was carried out. As a result, no colored areas were observed.

(Reference Example 9)
Except for placing a lithium niobate (LN:LiNbO ₃ ) wafer (diameter 150 mm, thickness 0.5 mm) on the placement stage, the same operation as in Reference Example 1 was carried out. As a result, no colored areas were observed.

Example 1
The same operations as in Reference Example 1 were carried out except that di-n-octyl phthalate (DOP) (special grade reagent) was applied (thinly coated) to the surface of the silicon wafer used in Reference Example 1 in anticipation of contamination by organic matter, and then the wafer was placed on a placement table. As a result, it was confirmed that the area where di-n-octyl phthalate was applied was colored.

Example 2
The same operation as in Reference Example 1 was carried out except that di-n-octyl phthalate (DOP) (special grade reagent) was thinly applied to the surface of the silicon carbide wafer used in Reference Example 2 and then the wafer was placed on a placement table. As a result, it was confirmed that the area where di-n-octyl phthalate was applied was colored.

Example 3
The same operation as in Reference Example 1 was carried out except that a thin layer of di-n-octyl phthalate (DOP) (special grade reagent) was applied to the surface of the sapphire wafer used in Reference Example 3 and then the wafer was placed on a placement table. As a result, it was confirmed that the area where di-n-octyl phthalate was applied was colored.

Example 4
The same operation as in Reference Example 1 was carried out except that di-n-octyl phthalate (DOP) (special grade reagent) was thinly applied to the surface of the gallium phosphide wafer used in Reference Example 4 and then placed on the placement table. As a result, it was confirmed that the area where di-n-octyl phthalate was applied was colored.

Example 5
The same operation as in Reference Example 1 was carried out except that di-n-octyl phthalate (DOP) (special grade reagent) was thinly applied to the surface of the gallium arsenide wafer used in Reference Example 5 and then the wafer was placed on a placement table. As a result, it was confirmed that the area where di-n-octyl phthalate was applied was colored.

Example 6
The same operation as in Reference Example 1 was carried out except that di-n-octyl phthalate (DOP) (special grade reagent) was thinly applied to the surface of the indium phosphide wafer used in Reference Example 6 and then placed on the placement table. As a result, it was confirmed that the area where di-n-octyl phthalate was applied was colored.

(Example 7)
The same operation as in Reference Example 1 was carried out except that di-n-octyl phthalate (DOP) (special grade reagent) was thinly applied to the surface of the gallium nitride wafer used in Reference Example 7 and then the wafer was placed on a placement table. As a result, it was confirmed that the area where di-n-octyl phthalate was applied was colored.

(Example 8)
The same operation as in Reference Example 1 was carried out except that di-n-octyl phthalate (DOP) (special grade reagent) was thinly applied to the surface of the lithium tantalate wafer used in Reference Example 8 and then the wafer was placed on a placement table. As a result, it was confirmed that the area where di-n-octyl phthalate was applied was colored.

Example 9
The same operation as in Reference Example 1 was carried out except that di-n-octyl phthalate (DOP) (special grade reagent) was thinly applied to the surface of the lithium niobate wafer used in Reference Example 9 and then the wafer was placed on a placement table. As a result, it was confirmed that the area where di-n-octyl phthalate was applied was colored.

(Comparative Example 1)
We requested an external analysis agency A to evaluate the silicon wafer (coated with di-n-octyl phthalate) used in Example 1 by time-of-flight secondary ion mass spectrometry (TOF-SIMS). As a result of the evaluation using a time-of-flight secondary ion mass spectrometer (TOF-SIMS device) TOFSIMS5 (manufactured by IONTOF, Germany) owned by the external analysis agency A, di-n-octyl phthalate was detected on the wafer surface. It took about two weeks for the external analysis agency A to report the evaluation results.

(Comparative Example 2)
The same operations as in Comparative Example 1 were carried out, except that the silicon carbide wafer (already coated with di-n-octyl phthalate) used in Example 2 was used as the evaluation sample. As a result, di-n-octyl phthalate was detected on the wafer surface. It took about two weeks for the evaluation results to be reported by external analysis organization A.

(Comparative Example 3)
The same operations as in Comparative Example 1 were carried out, except that the sapphire wafer (already coated with di-n-octyl phthalate) used in Example 3 was used as the evaluation sample. As a result, di-n-octyl phthalate was detected on the wafer surface. It took about two weeks for the evaluation results to be reported by external analysis agency A.

(Comparative Example 4)
The same operations as in Comparative Example 1 were carried out, except that the gallium phosphide wafer (already coated with di-n-octyl phthalate) used in Example 4 was used as the evaluation sample. As a result, di-n-octyl phthalate was detected on the wafer surface. It took about two weeks for the evaluation results to be reported by external analysis organization A.

(Comparative Example 5)
The same operations as in Comparative Example 1 were carried out, except that the gallium arsenide wafer (already coated with di-n-octyl phthalate) used in Example 5 was used as the evaluation sample. As a result, di-n-octyl phthalate was detected on the wafer surface. It took about two weeks for the evaluation results to be reported by external analysis agency A.

(Comparative Example 6)
The same operations as in Comparative Example 1 were carried out, except that the indium phosphide wafer (already coated with di-n-octyl phthalate) used in Example 6 was used as the evaluation sample. As a result, di-n-octyl phthalate was detected on the wafer surface. It took about two weeks for the evaluation results to be reported by external analysis organization A.

(Comparative Example 7)
The same operations as in Comparative Example 1 were carried out, except that the gallium nitride wafer (already coated with di-n-octyl phthalate) used in Example 7 was used as the evaluation sample. As a result, di-n-octyl phthalate was detected on the wafer surface. It took about two weeks for the evaluation results to be reported by external analysis organization A.

(Comparative Example 8)
The same operations as in Comparative Example 1 were carried out, except that the lithium tantalate wafer (already coated with di-n-octyl phthalate) used in Example 8 was used as the evaluation sample. As a result, di-n-octyl phthalate was detected on the wafer surface. It took about two weeks for the evaluation results to be reported by external analysis organization A.

(Comparative Example 9)
The same operation as in Comparative Example 1 was carried out, except that the lithium niobate wafer (already coated with di-n-octyl phthalate) used in Example 9 was used as the evaluation sample. As a result, di-n-octyl phthalate was detected on the wafer surface. It took about two weeks for the evaluation results to be reported by external analysis organization A.

Table 1 shows the type, diameter, and thickness of the wafers in Reference Examples 1 to 9, Examples 1 to 9, and Comparative Examples 1 to 9. It also shows whether di-n-octyl phthalate was applied and whether di-n-octyl phthalate was detectable in the above Reference Examples, Examples, and Comparative Examples.

"DOP added" in Table 1 indicates whether di-n-octyl phthalate (DOP) was added (thinly applied) to the wafer surface. "Coloration" in Table 1 indicates the presence or absence of colored areas on the wafer surface as determined by visual observation, with "◯" indicating that coloration was confirmed, "×" indicating that no colored areas were confirmed, and "-" indicating that no visual observation was performed. "TOF-SIMS" in Table 1 indicates the results of evaluation using TOF-SIMS, with "◯" indicating that di-n-octyl phthalate was detected on the wafer surface and "-" indicating that evaluation using TOF-SIMS was not performed.

As shown in Table 1, in the wafer contamination detection method (colorization method) of the present invention, coloration indicating organic contamination was confirmed in each example in which di-n-octyl phthalate was added. In addition, in conjunction with the results of each reference example in which di-n-octyl phthalate was not added, it was possible to confirm the presence or absence of contamination within about one hour from the start of detection.

In contrast, in the comparative examples where evaluation was outsourced to external analysis organization A, the advantage of evaluation using time-of-flight secondary ion mass spectrometry (TOF-SIMS) was that the contaminant was identified as di-n-octyl phthalate, but it took about two weeks for the evaluation results to be reported, and a high analysis fee of about 120,000 yen per sample had to be paid.

In the actual production (manufacturing process) of wafers, it goes without saying that it is more important to be able to test for the presence or absence of contamination as quickly as possible than to identify what the contaminants are. The wafer contamination detection method of the present invention is not only simple, requiring only an airtight container and a coloring agent for evaluation, but also far surpasses conventional technologies in terms of safety and initial running cost performance, as it only requires adding a coloring agent to an airtight container, placing the wafer in it, and visually observing whether coloration occurs or not. For example, it can be said that this technology is comparable to test kits that are safe, quick, simple, and cost-effective, such as Pack Test (registered trademark) (manufactured by Kyoritsu Rika Kenkyusho Co., Ltd.), which tests for regulated substances contained in factory wastewater, and gas detector tubes (manufactured by Gastec Co., Ltd.), which test for gas components such as harmful gases and foul-smelling gases.

In other words, the present invention provides a method for evaluating wafer surface contamination safely, quickly, simply, and inexpensively, and is extremely effective in terms of process management and quality control, and it is clear that the above evaluation results are sufficient to support this.

The technical scope of the present invention is not limited to the aspects described in the above embodiment. One or more of the requirements described in the above embodiment may be omitted. The requirements described in the above embodiment may be combined as appropriate. Furthermore, to the extent permitted by law, the contents of all documents cited in this specification are incorporated by reference and are included as part of the description in this text.

1 Sealed container body, 2 Sealed container lid, 3 Middle plate, 4 Vent, 5 Placement stand, 6 Coloring agent, 7 Sample, 8 Contaminant, 10 Sealed container, S1 Preparation process, S2 Pretreatment process, S3 Coloring process, S4 Detection process

Claims (8)

A method for detecting contamination on a wafer, comprising the steps of: adsorbing a coloring agent to contaminants present on a surface of a wafer in an exhaust environment; and causing the contaminants to develop a color with the coloring agent. a preparation step of placing the color developer and the wafer in a sealed container and sealing the container;
a pretreatment step of generating vapor of the color developer in the sealed container and bringing the vapor into contact with the surface of the wafer;
a coloring step of adsorbing the color developer onto the contaminants present on the surface of the wafer and causing the contaminants to develop a color with the color developer;
A detection step of visually detecting the presence or absence of coloration of the contaminant;
2. The method for detecting contamination of a wafer according to claim 1, further comprising: The method for detecting contamination on a wafer according to claim 2, characterized in that the color developer generates the vapor at room temperature or by heating. The method for detecting contamination of a wafer according to claim 2 or 3, characterized in that the sealed container is transparent and made of glass. The method for detecting contamination of a wafer according to any one of claims 1 to 4, characterized in that the contaminant contains an organic compound, and the organic compound contains one or more compounds selected from aromatic hydrocarbons, aliphatic hydrocarbons, halogenated hydrocarbons, organic acids, alcohols, phthalates, adipic acid esters, phosphates, phenols, and siloxane compounds. The method for detecting contamination on a wafer according to any one of claims 1 to 5, characterized in that the coloring agent contains iodine. The method for detecting contamination of a wafer according to any one of claims 1 to 6, characterized in that the wafer contains one or more elements selected from silicon, carbon, aluminum, oxygen, gallium, phosphorus, arsenic, indium, nitrogen, tantalum, niobium, and lithium. The method for detecting contamination of a wafer according to any one of claims 1 to 7, characterized in that the wafer has a diameter of 50 to 500 mm and a thickness of 0.1 to 1.0 mm.

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