JP4393268B2 - Drying method of fine structure - Google Patents

Description

  The present invention relates to a method for drying a microstructure surface using liquefied carbon dioxide or supercritical carbon dioxide for a structure having fine irregularities (microstructure surface) on a surface such as a semiconductor substrate, and more More specifically, the present invention relates to a drying method that can reduce the amount of particles adhering to the microstructure surface after drying without causing the fine pattern to swell or collapse.

  In the semiconductor manufacturing process, a pattern is formed on a substrate surface using a photoresist, developed, washed, and then immersed (rinsed) in an alcohol solvent such as ethanol, and then liquefied carbon dioxide and supercritical carbon dioxide are added. A method of using and drying is known (for example, see Patent Documents 1 and 2).

  Liquefied carbon dioxide or supercritical carbon dioxide is used to remove the rinsing liquid and dry the substrate when using normal organic solvents to dry the substrate due to the high surface tension and viscosity of the liquid. This is because there is a problem that the convex portion of the pattern collapses due to a capillary force generated at the liquid interface or volume expansion due to heating during drying.

  By the way, photoresists generally used in semiconductor manufacturing processes can be broadly classified into two types, alkali developed photoresists and organic developed photoresists. Among them, alkali developed photoresists are more widely used. . However, an alkali developed photoresist is dissolved in an alcohol solvent such as ethanol, so that the pattern collapses when the drying method is applied. Therefore, the processing target of the drying method is limited to the organic development photoresist.

Therefore, in order to realize a drying method that can be applied also to an alkali developed photoresist, the inventors have rinsed with an alcohol-based solvent and then rinsed with a liquefied carbon dioxide or a supercritical carbon dioxide. Studies have been made on a drying method in which displacement washing (or rinsing) is performed with a solvent containing a fluorine-containing compound. However, although the fine structure obtained by substitution cleaning (or rinsing) using a solvent containing a fluorine-containing compound has solved the problem of pattern collapse, many particles are present on the surface of the fine structure after drying. There was sometimes sticking. Since these particles have an adverse effect on the shape control of dry etching, which is the next process, it is required to reduce them as much as possible. In particular, in the next-generation ULSI device manufacturing process, the number of particles adhering to the surface of a φ8 inch silicon wafer is required to be 50 or less having a diameter of 0.16 μm or more.
JP 2000-223467 A (see [Claims], [0019], etc.) JP 2000-91180 A (see [Claims], [0040], etc.)

  The present invention has been made in view of such circumstances, and its purpose is to swell or collapse a pattern when drying a microstructure such as a semiconductor substrate after development with liquefied carbon dioxide or supercritical carbon dioxide. Another object of the present invention is to provide a drying method capable of reducing the amount of particles adhering to the microstructure surface after drying.

The fine structure cleaning method according to the present invention that has solved the above problems is a method of drying a fine structure with liquefied carbon dioxide or supercritical carbon dioxide, and the fine structure is obtained with a solvent A containing water. Cleaning the solvent A, replacing the solvent A with a solvent B containing a fluorine-containing compound a and a compound having a hydrophilic group and an affinity with the fluorine-containing compound a, and the solvent B containing the fluorine-containing compound a A step of substituting compound a and / or a solvent C containing a fluorine-containing compound b different from the fluorine-containing compound a, a step of substituting the solvent C with liquefied carbon dioxide or supercritical carbon dioxide, and a step of drying. In this case, the present invention has a gist in that the concentration of Na ⁺ contained in the solvent B and the solvent C is suppressed to 0.5 ng / ml or less.

  As the compound having affinity with the fluorine-containing compound a and having a hydrophilic group, a compound containing a fluorine-containing compound c different from the fluorine-containing compound a is preferable.

  According to the present invention, when a microstructure such as a semiconductor substrate after development is dried with liquefied carbon dioxide or supercritical carbon dioxide, the pattern does not swell or collapse, and adheres to the surface of the microstructure after drying. It is possible to provide a drying method that can reduce the amount of particles that are present.

  As described above, when a fine structure washed with a solvent containing water after development (including "rinse"; the same applies hereinafter) is substituted and dried using liquefied carbon dioxide or supercritical carbon dioxide, the pattern swells. Or collapse. This is presumably because water remaining on the surface of the fine structure causes volume expansion during drying. Therefore, the present inventors have repeatedly studied a measure for preventing water from remaining on the surface of the microstructure immediately before drying with liquefied carbon dioxide or supercritical carbon dioxide. As a result, when the fine structure washed with the solvent containing water is dried using liquefied carbon dioxide or supercritical carbon dioxide, the solvent A containing water is converted into the fluorine-containing compound a, the surfactant, and / or the surfactant. Substitution with a solvent B containing a compound having an affinity with the fluorine-containing compound a and having a hydrophilic group, and then the solvent B is replaced with the fluorine-containing compound a and / or a fluorine-containing compound different from the fluorine-containing compound a It has been found that after substitution with a solvent C containing b and subsequent substitution drying using liquefied carbon dioxide or supercritical carbon dioxide, the occurrence of pattern swelling and collapse can be suppressed.

However, when the surface of the fine structure obtained by adopting such a drying method was observed, a large number of particles were observed on the surface. Therefore, the present inventors also examined reducing the amount of particles adhering to the surface of the fine structure after drying. As a result, the inventors have found that the above problems can be solved by reducing the concentration of Na ⁺ contained in the solvent B and the solvent C used in the drying method, thereby completing the present invention.

That is, in the drying method of the present invention, it is important to include the following steps (1) to (5).
(1) a step of washing the microstructure with a solvent A containing water;
(2) The step of substituting the solvent A with a solvent B containing a compound having a hydrophilic group while having an affinity between the fluorine-containing compound a and a surfactant and / or the fluorine-containing compound a.
(3) replacing the solvent B with the solvent C containing the fluorine-containing compound a and / or a fluorine-containing compound b different from the fluorine-containing compound a;
(4) a step of replacing the solvent C with liquefied carbon dioxide or supercritical carbon dioxide (hereinafter sometimes referred to as “carbon dioxide fluid”);
(5) A step of drying.

  Hereinafter, it demonstrates in detail along each process.

  First, an object that can be dried using the drying method of the present invention is a fine structure, for example, fine irregularities (for example, wiring) such as a semiconductor substrate or a photomask substrate developed after pattern formation using a photoresist. The target object is not limited to a semiconductor substrate, and can be used as a drying method for forming a clean and dry surface on metal, plastic, glass, ceramics, or the like.

  In the step (1), the fine structure is washed with a solvent A containing water. This is because by using the solvent A containing water as the cleaning solvent, the developer component adhering to the surface of the microstructure after development can be efficiently removed (or rinsed).

  Here, the solvent A containing water is basically pure water or ultrapure water, but may contain a surfactant or the like as long as it is in a trace amount.

  Specific cleaning means using the solvent A containing water is not particularly limited. For example, the method of immersing the fine structure in the solvent A containing water or the solvent A containing water on the surface of the rotating fine structure is used. A method of dropping in the form of a shower can be employed.

  Next, in the step (2), the solvent A containing water is a solvent containing a compound having a hydrophilic group and an affinity between the fluorine-containing compound a and a surfactant and / or the fluorine-containing compound a. By substituting with B, the solvent A containing water is removed from the surface of the microstructure. The solvent B is a solvent obtained by mixing a surfactant or a compound having an affinity with the fluorine-containing compound a and a hydrophilic group into the solvent comprising the fluorine-containing compound a alone, if necessary, in combination. Point to. Further, a plurality of surfactants may be used in combination, or a plurality of compounds having an affinity with the fluorine-containing compound a and a hydrophilic group may be used in combination. The surfactant and the compound having an affinity for the fluorine-containing compound a and having a hydrophilic group may be collectively referred to as “draining agent” hereinafter.

  The fluorine-containing compound a is a compound containing at least one fluorine in the molecule. By containing fluorine, the solvent B becomes an incombustible or flame-retardant solvent, and the solvent C or liquefied carbon dioxide used in the next step Affinity with supercritical carbon dioxide can be increased. And it contains the said water by mixing at least 1 sort (s) among the compound which has affinity with this fluorine-containing compound a and surfactant or fluorine-containing compound a, and has a hydrophilic group, and it is set as the solvent B. The affinity of both the solvent A and the solvent C used in the next step can be increased. That is, the compound having an affinity with the surfactant or the fluorine-containing compound a and having a hydrophilic group increases the affinity with the solvent A containing water, and the fluorine-containing compound a is used in the next step. This is because the affinity with the solvent C containing a or the fluorine-containing compound b is increased. Accordingly, in the step (2), by using the solvent B, the solvent A containing water remaining on the surface of the fine structure is quickly replaced with the solvent B, and moisture is removed from the surface of the fine structure. In addition, since the solvent B has high affinity with the solvent C used in the next step, the step of replacing the solvent B with the solvent C can be performed smoothly.

  In addition, the fluorine-containing compound used as the solvent B and the fluorine-containing compound used as the solvent C in the next step may be the same type or different.

Examples of the fluorine-containing compound a include hydrofluoroethers, hydrofluorocarbons, a general formula; fluorinated alcohols represented by H- (CF ₂ ) _n —CH ₂ OH, “Fluorinert” (manufactured by Sumitomo 3M Limited) ( (Registered trademark) series and the like, and one of these can be used alone, or two or more arbitrarily selected can be mixed and used.

Specific examples of hydrofluoroethers include C ₄ F ₉ OCH ₃ (for example, “HFE7100” manufactured by Sumitomo 3M), C ₄ F ₉ OC ₂ H ₅ (for example, “HFE7200” manufactured by Sumitomo 3M), and the like. Is exemplified.

Specific examples of the hydrofluorocarbons include CF ₃ CHFCHFCF ₂ CF ₃ (for example, “Bertrel” series such as “Bertrel XF” (registered trademark) manufactured by DuPont).

As fluorinated alcohols, when n is 2 to 6 among those represented by the above general formula; H— (CF ₂ ) _n —CH ₂ OH, it is easy to become familiar with water remaining in the pattern, and water is efficiently used. This is preferable because it can be substituted.

  Examples of the “Fluorinert” series include “FC-40”, “FC-43”, “FC-70”, “FC-72”, “FC-75”, “FC-77”, “FC-84”. , “FC-87”, “FC-3283”, “FC-5312”, and the like.

  As the fluorine-containing compound a when used as the solvent B, it is particularly preferable to use a compound having an ether bond in the molecule (that is, hydrofluoroether). When a compound having an ether bond in the molecule is used as the fluorine-containing compound a, the reason is not clear, but dissolution of the resist can be suppressed.

  As the surfactant in the draining agent, a nonionic surfactant is preferable, and a sorbitan fatty acid ester-based surfactant is particularly preferable because of less dissolution of the resist.

  Specific examples of the sorbitan fatty acid ester surfactant include “Leodol SP-030”, “Leodol AO-15”, and “Leodol SP-L11” (both manufactured by Kao Corporation). It is done.

  The surfactant has an affinity for the fluorine-containing compound a described later and is less soluble in the fluorine-containing compound a than the compound having a hydrophilic group, but has a high affinity for water, and even in a relatively small amount, Considering that dissolution can occur, the amount used is preferably 0.05% by mass or less in the solvent B, and more preferably 0.02% by mass or less.

As a compound having affinity with fluorine-containing compound a in the draining agent and having a hydrophilic group, a compound having a hydrophilic group such as a hydroxyl group, a carboxyl group or a sulfonic acid group in the molecule and a fluorine atom It is. By containing a fluorine atom in the molecule, the affinity with the fluorine-containing compound a is increased, and by having a hydrophilic group, the affinity with the solvent A containing water is increased.

The compound having an affinity with the fluorine-containing compound a and having a hydrophilic group is specifically a fluorine atom-containing alcohol such as trifluoroethanol or perfluoroisopropanol, or a carbon number of 4 to 10 such as perfluorooctanoic acid. Fluorinated carboxylic acids having an alkyl group [for example, “C-5400” manufactured by Daikin Industries, Ltd .; C series such as H (CF ₂ ) ₄ COOH], alkyls of aliphatic sulfonic acids having an alkyl group having 4 to 10 carbon atoms Fluorinated sulfonic acids in which part or all of the hydrogen atoms in the group are substituted with fluorine, 1-carboxyperfluoroethylene oxide, and the like can be mentioned. These can be used alone or in admixture of two or more selected. Can be used.

  The compound having an affinity for the fluorine-containing compound a and having a hydrophilic group is preferably 0.1 to 10% by mass in the solvent B. If the amount is too large, the resist may be dissolved as described above. A more preferable upper limit is 8% by mass, and a further preferable upper limit is 5% by mass. On the other hand, if the amount is too small, the substitution with the solvent A containing water may be insufficient. A more preferred lower limit is 0.5% by mass, and a still more preferred lower limit is 1% by mass.

  A preferred combination of the fluorine-containing compound a and the draining agent is that the fluorine-containing compound a (solvent) is a hydrofluoroether and / or hydrofluorocarbon, and the draining agent is an alcohol having a fluorine atom in the molecule (for example, perfluoroisopropanol) ) And / or a carboxylic acid having a fluorine atom in the molecule (fluorinated carboxylic acid).

  Specific means for substituting the solvent A containing water with the solvent B is not particularly limited as long as it is a method that does not break the fine structure such as a pattern, but for example, while rotating the fine structure, The spin coating method in which the solvent B is dropped from the nozzle is frequently used in the semiconductor substrate manufacturing field, and is preferable. Further, a dipping method in which the fine structure is immersed in the solvent B may be employed. In addition, the pressure in this substitution process is not specifically limited, What is necessary is just to carry out under atmospheric pressure. Also, the time for performing this step is not particularly limited, and a few seconds to several minutes is sufficient.

  Next, in the step (3), the solvent B is replaced with a solvent C containing the fluorine-containing compound a and / or a fluorine-containing compound b different from the fluorine-containing compound a, so that the surface of the microstructure is removed. The solvent B is removed. The solvent C is a solvent made of the fluorine-containing compound a or a solvent made of the fluorine-containing compound b different from the fluorine-containing compound a, but the fluorine-containing compound a is different from the fluorine-containing compound a. A solvent using b in combination may be used.

  As the fluorine-containing compound b different from the fluorine-containing compound a, specifically, the compounds exemplified as the fluorine-containing compound a can be used.

In the drying method of the present invention, it is important to suppress the Na ⁺ concentration contained in the solvent B and the solvent C to 0.5 ng / ml or less. That is, as described above, the surface of the fine structure obtained by washing (or rinsing) with a solvent containing a fluorine-containing compound and then drying with low-viscosity liquefied carbon dioxide or supercritical carbon dioxide. When observed with an electron microscope, a large number of particles adhered. Therefore, as shown in the examples described later, particles adhering to the surface of the fine structure are collected, and the constituent elements of the particles are energy dispersive X-ray detectors (EDX; attached to a scanning electron microscope (SEM)). energy dispersive X-ray spectrometer). As a result, the particles were found to be microcrystals made of NaF.

Therefore, the present inventors have conducted intensive studies to find out the cause of NaF formation. As a result, NaF is produced by the combination of F ⁻ and Na ⁺ contained in the solvent, and this F ⁻ is composed of (1) F ⁻ originally contained in the solvent and (2) a trace amount of water present in the solvent. but a fluorine-containing compound F which hydrolyze to release ^- it was found that from. Furthermore, Na ⁺ was found to be derived from the Na ⁺ contained originally in the solvent.

Therefore, the present inventors believe that if the Na ⁺ concentration contained in the solvent B and the solvent C is reduced as much as possible, the formation of NaF can be suppressed and a fine structure with almost no particles can be obtained. Considered along that line. As a result, as is clear from the examples described later, if the Na ⁺ concentration contained in the solvent is suppressed to 0.5 ng / ml or less, the maximum diameter attached to the surface of the φ8 inch silicon wafer is 0.16 μm or more. It was found that the number of particles can be reduced to 50 or less. Since the number of particles adhering to the silicon wafer surface should be reduced as much as possible, the Na ⁺ concentration contained in the solvent is preferably suppressed to 0.1 ng / ml or less from such a viewpoint.

A means for reducing the Na ⁺ concentration contained in the solvent B or the solvent C is not particularly limited, but the amount of Na ⁺ can be easily reduced by purifying the solvent by, for example, distillation.

  The specific means for substituting the solvent B with the solvent C can employ the same means as for substituting the solvent A with the solvent B. The replacement conditions such as pressure and time at this time are the same as described above.

  Next, in the step (4), the solvent C is replaced with a carbon dioxide fluid. That is, the fine structure covered with the solvent C is put into a chamber capable of high-pressure treatment as it is, and liquefied carbon dioxide or supercritical carbon dioxide is circulated in the chamber, so that the solvent C is fed into a carbon dioxide fluid. Replace with.

  The liquefied carbon dioxide that can be used in the drying method of the present invention is pressurized carbon dioxide of 5 MPa or more. To obtain supercritical carbon dioxide, it should be 31.2 ° C. or more and 7.4 MPa or more. The pressure in the step (4) is preferably in the range of 5 to 30 MPa, more preferably 7.4 to 20 MPa. The temperature in this step is preferably 31.2 to 120 ° C. When the temperature is lower than 31.2 ° C., a gas-liquid interface of carbon dioxide is generated, and the resist pattern may collapse. On the other hand, if no improvement in drying efficiency is observed even when the temperature exceeds 120 ° C., energy is wasted. The time required for the step (4) may be appropriately changed according to the size of the object, but a few minutes to several tens of minutes is sufficient.

  Next, after the high-pressure treatment is completed, the carbon dioxide fluid quickly becomes a gas and evaporates by making the pressure in the chamber normal, so that the fine pattern of the fine structure is not destroyed. Then, the drying is completed [Step (5)]. The carbon dioxide fluid in the chamber before decompression is preferably in a supercritical state. Since the pressure can be reduced to atmospheric pressure only through the gas phase, pattern collapse can be prevented.

  The present invention will be described in further detail with reference to the following examples. However, the following examples are not intended to limit the present invention, and all modifications that are made without departing from the spirit of the preceding and following description are all included in the technical scope of the present invention. The Unless otherwise specified, “%” indicates “mass%”.

Experimental example 1
As a solvent comprising the fluorine-containing compound a, hydrofluoroether (“HFE7200” manufactured by Sumitomo 3M) or “FC-40” [“Fluorinert” (registered trademark) series manufactured by Sumitomo 3M] is used, and a draining agent (fluorine) Perfluoroisopropanol [manufactured by Central Glass Co., Ltd., (CF ₃ ) ₂ CHOH] is used as a solvent comprising a compound having an affinity for the contained compound and a hydrophilic group), and a cation (metal) contained as an impurity in these solvents The amount of ions) was quantitatively analyzed with an inductively coupled plasma mass spectrometer (ICP-MS). Some impurity elements were quantitatively analyzed by flameless atomic absorption spectrometry. The analysis results are shown in Table 1 below.

As is apparent from Table 1, “HFE7200” and “FC-40” contained almost no cations (impurities). On the other hand, perfluoroisopropanol (hereinafter sometimes referred to as “unpurified perfluoroisopropanol”) contained a large amount of cations (impurities) such as Na and K. In particular, the amount of Na ⁺ was 150 ng / ml.

  Next, after the perfluoroisopropanol was supplied to the bottom (bottom) of the fully packed distillation column, the bottom was heated to about 60 ° C. and distilled. After the first fraction generated in the initial stage of heating was discharged from the top (top part) of the distillation column, the top part was reflux-cooled with water to recover purified perfluoroisopropanol. In addition, a part of perfluoroisopropanol was left in the bottom part as a post-treatment.

  The amount of cations contained as impurities in the recovered perfluoroisopropanol was quantitatively analyzed in the same manner as described above. The analysis results are also shown in Table 1 below.

As is clear from Table 1, the purified perfluoroisopropanol contained almost no cations (impurities), and in particular, the amount of Na ⁺ could be reduced to 0.9 ng / ml. The amount of Al contained in perfluoroisopropanol after purification was 0.1 ng / ml. However, the amount of Al is not increased compared with that before purification, but is within the range of measurement error, and the amount of Al is increased. Absent.

Experimental example 2
As a solvent comprising the fluorine-containing compound a, hydrofluoroether (“HFE7200” manufactured by Sumitomo 3M) or “FC-40” (“Fluorinert” (registered trademark) series manufactured by Sumitomo 3M) is used, and a draining agent (fluorine) Perfluoroisopropanol [manufactured by Central Glass Co., Ltd., (CF ₃ ) ₂ CHOH] as a solvent comprising a compound having an affinity with a contained compound and a hydrophilic group), and the amount of anion contained as an impurity in these solvents Quantitative analysis was performed by ion chromatography. The analysis results are shown in Table 2 below. In Table 2, “0” indicates that the value is below the detection limit, and “−” indicates that no measurement is performed.

As is apparent from Table 2, “HFE7200” and “FC-40” contained a large amount of F ⁻ (anions). On the other hand, unpurified perfluoroisopropanol contained almost no F ⁻ (anion).

Experimental example 3
“HFE7200” used in Example 1 above was used as a solvent comprising the fluorine-containing compound a, and this solvent was used in Example 1 as a draining agent (a compound having affinity with the fluorine-containing compound and having a hydrophilic group). 5% by mass of “unpurified perfluoroisopropanol” or “purified perfluoroisopropanol” was added to prepare a mixed solution (solvent B). The solvent B was poured into glass bottles in a clean environment, and the number of particles present in the liquid was measured with a NALOLYZER PC500 type particle counter manufactured by Kowa. The results are shown in Table 3 below.

  Next, after the solvent B was stored in a glass bottle for 100 hours, 200 hours or 300 hours, the number of particles present in the solvent was measured in the same manner as described above.

  Note that the glass bottle is a container with a lid and is allowed to stand during storage. Further, the number of particles having a maximum diameter of 0.1 μm or more was measured.

  As is apparent from Table 3, many particles exist in the solvent B to which unpurified perfluoroisopropanol is added, and the number of particles increases as the storage time increases. On the other hand, particles are also present in the solvent B to which purified perfluoroisopropanol has been added, but the number is much smaller than the number in solvent B to which unpurified perfluoroisopropanol has been added. It was.

That is, it is considered that perfluoroisopropanol is gradually hydrolyzed by water slightly contained in the solvent when stored for a long time to produce F ⁻ , but Na ⁺ is almost present in the purified perfluoroisopropanol. Therefore, it is considered that the amount of particles does not increase even if the amount of F ⁻ increases.

  Next, the solvent B added with unpurified perfluoroisopropanol was stored for 360 hours in a clean room through a PTFE filter with a mesh size of 0.1 μm, and the filtered filter surface was observed at 30000 times with SEM. did. As a result, particles were collected on the filter. An electron micrograph of this particle is shown in FIG. As is clear from FIG. 1, the particles collected on the filter were single crystals (equal axis crystals).

  In addition, after purifying solvent B to which perfluoroisopropanol was added for 360 hours, it was filtered in a clean room through a PTFE filter having a mesh size of 0.1 μm, and the filtered filter surface was observed by SEM at 30000 times. . As a result, particles could be collected on the filter, and the particles were single crystals (equal axis crystals).

  The constituent elements of each particle collected on the filter were analyzed by EDX attached to the SEM. As a result, only peaks indicating Na and F were detected, and it was found that the particles consisted of NaF.

  Further, as a result of analyzing this particle by μ-AES, only peaks indicating Na and F were detected, and it became clear that the particle was composed of Na and F.

Experimental Example 4
The surface of the rotating silicon wafer (bare wafer) was cleaned by supplying ultrapure water as a solvent A containing water. The silicon wafer has a disk shape of φ8 inches.

Next, a solvent B (Na ⁺ concentration exceeds 0.5 ng / ml) is prepared by adding 5% by mass of “unpurified perfluoroisopropanol” to the solvent consisting of “HFE7200” used in Example 1 above. did. The solvent B was supplied to the surface of the rotating wafer, and the ultrapure water (solvent A) on the wafer surface was replaced with the solvent B. Subsequently, the surface of the wafer is covered with the solvent B, and the solvent C (Na ⁺ concentration of 0.5 ng / ml or less) made of “FC-40” (manufactured by Sumitomo 3M) is applied to the rotating wafer surface without drying. And solvent B was completely replaced with solvent C. The wafer rotation was stopped, "FC-40" was supplied to the surface of the wafer about 10cc so that the wafer surface did not dry, and the wafer was loaded into a chamber capable of high pressure processing while covered with the "FC-40". . The carbon dioxide fluid was brought into a supercritical state by adjusting the inside of the chamber to 8 MPa with a pressure adjusting valve while feeding carbon dioxide heated in advance to 60 ° C. under pressure to the chamber held at 60 ° C. by a liquid feed pump. By circulating this supercritical carbon dioxide in the chamber, “FC-40” was replaced with supercritical carbon dioxide, “FC-40” was removed from the chamber, and the inside of the chamber was made only supercritical carbon dioxide. . Thereafter, while the chamber was kept at 60 ° C., the pressure in the chamber was reduced to atmospheric pressure to obtain a dry silicon wafer.

On the other hand, in place of the above-mentioned “unpurified perfluoroisopropanol”, 5% by mass of “purified perfluoroisopropanol” obtained in Example 1 was added to add solvent B (Na ⁺ concentration is 0.5 ng / ml or less). A dry silicon wafer was obtained using the solvent B in the same manner as described above.

  The number of particles adhering to the surface of each of the obtained dry silicon wafers was measured using an LS6300 type particle counter manufactured by Hitachi Electronics Engineering. The measurement results are shown in Table 4 below. Since the detection limit of this apparatus was 0.14 μm, the number of particles having a maximum diameter of 0.14 μm or more was measured.

  As is clear from Table 4, when the solvent B mixed with unpurified perfluoroisopropanol was used, many particles were observed on the surface of the silicon wafer. Most of the particles had a maximum diameter of 0.14 to 0.18 μm. On the other hand, when solvent B mixed with purified perfluoroisopropanol was used, almost no particles were observed on the surface of the silicon wafer.

Experimental Example 5
Perfluoroisopropanol having different Na ⁺ concentrations was prepared by mixing the unpurified perfluoroisopropanol used in Example 1 and the purified perfluoroisopropanol at an arbitrary ratio. The amount of Na ⁺ was analyzed using ICP-MS.

  In the above Example 4, a dry silicon wafer was obtained in the same procedure as in Example 4 using the perfluoroisopropanol prepared above instead of unpurified perfluoroisopropanol.

  The number of particles adhering to the surface of the obtained dry silicon wafer was measured using an LS6300 type particle counter manufactured by Hitachi Electronics Engineering. The number of particles was measured with a maximum diameter of 0.14 μm or more.

FIG. 2 shows the relationship between the Na ⁺ concentration in the solvent B and the number of particles adhering to the surface of the silicon wafer.

As is clear from FIG. 2, there is a correlation between the Na ⁺ concentration in perfluoroisopropanol and the number of particles adhering to the surface of the silicon wafer, and the higher the amount of Na ⁺ contained in the solvent B, It can be seen that the number of particles increases, and that the number of particles having a maximum diameter of 0.14 μm or more exceeds 50 when the amount of Na ⁺ exceeds 0.5 ng / ml. Therefore, among the particles adhering to the surface of φ8 inch silicon wafer, in order to keep the number of particles having a maximum diameter of 0.14 μm or more to 50 or less, the amount of Na ⁺ needs to be suppressed to 0.5 ng / ml or less. .

It is an electron micrograph (drawing substitute photograph) of particles. It is a graph which shows the relationship between the Na ^<+> density | concentration in the solvent B, and the number of the particles adhering to the surface of a silicon wafer.

Claims (1)

A method of drying a microstructure with liquefied carbon dioxide or supercritical carbon dioxide,
Washing the microstructure with a solvent A containing water;
The solvent A is one or two or more fluorine-containing compounds a selected from the following compound group I and a fluorine-containing compound c different from the fluorine-containing compound a, and the affinity for the fluorine-containing compound a step have a hydrophilic group is replaced with a solvent B comprising one or more compounds selected from the following group of compounds II and having sex,
Said solvent B, a the fluorine-containing compound a and / or, Unlike the fluorine-containing compound a and the fluorine-containing compound c, 1 or more kinds of the fluorine-containing compound b is selected from the following group of compounds I Substituting with the solvent C containing,
Replacing the solvent C with liquefied carbon dioxide or supercritical carbon dioxide;
And then drying.
At this time, the method for drying a microstructure is characterized in that the concentration of Na ⁺ contained in the solvent B and the solvent C is suppressed to 0.5 ng / ml or less.
(Compound group I)
Hydrofluoroethers,
Hydrofluorocarbons,
Fluorinated alcohols represented by the general formula: H— (CF ₂ ) _n —CH ₂ OH;
"Fluorinert" (registered trademark) series manufactured by Sumitomo 3M Limited.
(Compound group II)
Fluorine atom-containing alcohols,
Fluorinated carboxylic acids having an alkyl group having 4 to 10 carbon atoms,
Fluorinated sulfonic acids in which part or all of the hydrogen of the alkyl group of the aliphatic sulfonic acid having an alkyl group having 4 to 10 carbon atoms is substituted with fluorine,
1-carboxyperfluoroethylene oxide.

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