JPWO2006080423A1 - MONITOR WAFER AND WAFER MONITORING METHOD - Google Patents

Abstract

A monitor wafer comprising a silicon carbide sintered body having a concave pocket for placing a test piece on a monitor portion on a wafer surface. A monitor wafer with good chemical resistance and reusability is provided.

Description

  The present invention relates to a monitor wafer and a wafer monitoring method. More particularly, the present invention relates to a monitor wafer made of a silicon carbide sintered body and a wafer monitoring method using the same.

  2. Description of the Related Art Conventionally, in a semiconductor manufacturing process such as LSI, a monitor wafer made of silicon is used to confirm the deposition state of a deposited film formed on a wafer surface during a wafer surface processing step such as a chemical vapor deposition (CVD) step. in use. Since such a monitor wafer is expensive, it is reused by washing and removing the surface film with nitric acid or the like after use.

  However, silicon is inferior in chemical resistance. Therefore, when reuse is repeated, silicon is eluted and the surface becomes rough and cannot be used as a monitor wafer. Further, since the wafer is thinned by re-polishing at the time of reuse, flatness is deteriorated, cracking occurs, and automatic conveyance is difficult. However, no means for improving the above problem has been found.

That is, the present invention relates to the following items:
(1) A monitor wafer comprising a silicon carbide sintered body having a concave pocket for mounting a test piece on a monitor portion on a wafer surface.

(2) a base wafer made of a silicon carbide sintered body;
A ring plate made of a silicon carbide sintered body that is detachably attached to the base wafer and forms a concave pocket for mounting a test piece on the monitor portion when attached to the base wafer. A monitor wafer characterized by

(3) The monitor wafer according to (1) or (2), further comprising a test piece that is detachably attached to the pocket.

(4) The test piece has at least one required flatness of 200 μm or less,
Surface roughness (Ra) 0.1 μm or less,
The monitor wafer according to (3) above, wherein

(5) A monitor wafer having a monitor wafer body made of a silicon carbide sintered body having a concave pocket for placing a test piece on the monitor portion on the wafer surface, and a test piece detachably attached to the pocket. A method for monitoring a wafer, wherein the deposited film deposited on the test piece is monitored using

1A is a top view of the monitor wafer according to the first embodiment, FIG. 1B is a cross-sectional view of the monitor wafer according to the first embodiment, and FIG. The cross-section partial enlarged view of the monitor wafer concerning the embodiment is shown. 2A is a top view of the monitor wafer according to the second embodiment, FIG. 2B is a cross-sectional view of the monitor wafer according to the second embodiment, and FIG. The cross-section partial enlarged view of the monitor wafer concerning the embodiment is shown. 3A to 3D show manufacturing process diagrams of the monitor wafer according to the first embodiment. 4A to 4E show manufacturing process diagrams of the monitor wafer according to the second embodiment. FIG. 5 is a partially enlarged view of a cross section of a monitor wafer according to a modification of the first embodiment.

  In order to improve the conventional problems, the use of a monitor wafer made of silicon carbide was studied from the viewpoint of good chemical resistance. Such monitor wafers have improved the chemical resistance problem. However, since silicon carbide has good chemical resistance, chemical mechanical polishing (CMP) treatment cannot be performed, and it has been extremely difficult to finish the surface flatness of a silicon wafer. Therefore, it is difficult to accurately grasp the deposition state of the deposited film deposited on the silicon from the deposited film deposited on the silicon carbide.

  As a result of further studies, the present inventors have found that the above problem can be solved by making it possible to place a test piece on a monitor wafer body made of a silicon carbide sintered body. The present invention will be described below with reference to embodiments, but the present invention is not limited to the following embodiments.

(First embodiment)
A monitor wafer 10 according to the first embodiment shown in FIGS. 1A to 1C is a monitor made of a silicon carbide sintered body having a concave pocket for placing a test piece on a monitor portion on the wafer surface. It has the wafer main body 2 and the test pieces 31-39 attached to the said pocket further detachably. The monitor wafer 10 has pockets 21 to 29 at positions where the test pieces 31 to 39 are attached.

  The monitor wafer main body 2 is not particularly limited, but is formed by a hot press method, a CVD method, and a reactive sintering method. A hot press method or a CVD method is preferable from the viewpoint of good chemical resistance. In addition, the monitor wafer body 2 formed by a hot press method is more preferable in that the flatness during high temperature processing is stable. The pockets formed in the form of dots on the wafer surface can be formed by a polishing method or the like.

  If the said pocket is arrange | positioned at the monitor part of the monitor wafer 10, it can provide without a restriction | limiting in particular. In addition to the arrangement in the form of scattered dots, the monitor wafer 10 may be provided concentrically. Although the depth of a pocket changes suitably with the thickness of the test pieces 31-39, if a test piece can be hold | maintained to the extent which does not shift | deviate at least in a CVD process, there will be no restriction | limiting in particular.

  As shown in FIG. 5, a through hole 61 may be provided at the bottom of the pocket of the monitor wafer 6. In that case, it is preferable to provide support portions 62 a and 62 b for holding the test piece 39.

  The test pieces 31 to 39 are not particularly limited in thickness and shape as long as the state of the deposited film deposited on the surface can be monitored. From an economic point of view, the thickness is preferably thin. The shape may be a polygon such as a quadrangle in addition to a round shape. Examples of the material of the test piece include silicon, sapphire, graphite, and quartz. In the case of mirror polishing, the test pieces 31 to 39 have a flatness of 200 μm or less, preferably 100 μm or less, and a surface roughness (Ra) of 0.1 μm or less, preferably 0.05 μm or less, more preferably 0.02 μm or less. The test pieces 31 to 39 may be reused by performing a cleaning process after monitoring.

  Since the monitor wafer main body 2 according to the first embodiment is made of a silicon carbide sintered body, the monitor wafer main body 2 has high chemical resistance and is formed so that a test piece can be exchanged. Therefore, the monitor wafer body 2 can be reused any number of times by replacing the test pieces 31 to 39. That is, the life of the monitor wafer 10 according to the first embodiment is much longer than that of a conventional monitor wafer made of silicon that can be reused only about four times. Moreover, the state of the deposited film of the wafers of various materials can be accurately and economically known only by changing the material of the test piece without replacing the material of the entire monitor wafer. Furthermore, the monitor wafer 10 according to the first embodiment can be used in the same manner as a conventional monitor wafer. Therefore, it is possible to easily observe the state of the deposited film on the wafer without requiring a skilled technique.

(Second Embodiment)
A monitor wafer 60 according to the second embodiment shown in FIGS. 2A to 2C is detachably attached to the base wafer 3 made of a silicon carbide sintered body, and attached to the base wafer 3. A ring plate 5 made of a silicon carbide sintered body forming a concave pocket for placing the test piece on the monitor portion, and further, test pieces 41 to 49 detachably attached to the pocket, Have The ring plate 5 has pockets 51 to 59 at positions where the test pieces 41 to 49 are attached. The following description will focus on differences from the first embodiment.

  The base wafer 3 and the ring plate 5 are not particularly limited, but are formed by a hot press method, a CVD method, or a reactive sintering method. From the viewpoint of the stability of the flatness of the obtained monitor wafer, the hot press method is preferable. The wafer mounting surface of the base wafer 3 is preferably flat. This is because the stability of the test pieces 41 to 49 is improved by spreading the contact surface between the test pieces 41 to 49 and the base wafer 3 (the bottom of the pocket) when the wafer is placed. The flatness of the wafer mounting surface of the base wafer 3 is preferably about 10 μm to 50 μm. The holes formed in the ring plate 5 can be formed by an electric discharge machining method. The thickness of the ring plate 5, that is, the depth of the pocket is appropriately changed depending on the thickness of the test piece, but is not particularly limited as long as the test pieces 41 to 49 can be held so as not to be displaced at least in the CVD process.

  The monitor wafer 60 according to the second embodiment is configured so that the ring plate 5 can be detached from the base wafer 3, and thus the surface of the base wafer 3 can be easily polished. Therefore, the flatness of the wafer mounting surface of the base wafer 3 can be increased, and the stability of the test pieces 41 to 49 can be improved.

(Monitor method)
As another aspect of the present invention, a wafer monitoring method using the monitor wafers 10 and 60 according to the above-described embodiment is provided. That is, a monitor wafer having a monitor wafer body made of a silicon carbide sintered body having a concave pocket for placing a test piece on a monitor portion on the wafer surface, and a test piece detachably attached to the pocket. And a method for monitoring a wafer, characterized in that the deposited film deposited on the test piece is monitored.

(Monitor wafer manufacturing method)
As an embodiment of the monitor wafer manufacturing method, a manufacturing method using a hot press method will be described. First, the hot press method will be described.

(Hot press method)
Hereinafter, a method for producing silicon carbide used for producing a monitor wafer will be described. The silicon carbide sintered body having a free carbon content of 2 to 10% by weight is used in the method for manufacturing the monitor wafer of the present embodiment. Such a silicon carbide sintered body is obtained by firing a mixture of silicon carbide powder and a nonmetallic sintering aid.

  First, the silicon carbide powder will be described. As the silicon carbide powder, α-type, β-type, amorphous, or a mixture thereof can be widely used, and commercially available products may be used. Of these, β-type silicon carbide powder is preferably used. In order to increase the density of the silicon carbide sintered body, the silicon carbide powder used should have a smaller particle size. Preferably it is about 0.01-10 micrometers, More preferably, it is 0.05-2 micrometers. When the particle size is less than 0.01 μm, handling in processing steps such as weighing and mixing becomes difficult. On the other hand, when the particle size exceeds 10 μm, the specific surface area of the powder, that is, the contact area with the adjacent powder becomes small. This is not preferable because high density becomes difficult.

The use of high-purity silicon carbide powder is preferable because the resulting silicon carbide sintered body also has high purity. The high-purity silicon carbide powder is obtained, for example, by mixing a silicon compound (hereinafter sometimes referred to as “silicon source”), an organic material that generates carbon by heating, and a polymerization catalyst or a crosslinking catalyst. It can be produced by firing the product in a non-oxidizing atmosphere. As the silicon source, liquid and solid compounds can be widely used, but at least one liquid compound is used. Examples of the liquid silicon source include polymers of alkoxysilanes (mono-, di-, tri-, tetra-). Among the alkoxysilane polymers, tetraalkoxysilane polymers are preferably used. Specific examples include methoxysilane, ethoxysilane, propyloxysilane, butoxysilane, and the like. From the viewpoint of handling, ethoxysilane is preferable. When the degree of polymerization of the tetraalkoxysilane polymer is about 2 to 15, a liquid low molecular weight polymer (oligomer) is obtained. In addition, there is a liquid silicate polymer having a high degree of polymerization. Examples of the solid silicon source that can be used in combination with the liquid silicon source include silicon carbide. In addition to silicon monoxide (SiO) and silicon dioxide (SiO ₂ ), the silicon carbide referred to here is a silica sol (a colloidal ultrafine silica-containing liquid containing colloidal molecules containing OH groups or alkoxy groups. ), Fine silica, quartz powder and the like. Among these silicon sources, an oligomer of tetraalkoxysilane or a mixture of an oligomer of tetraalkoxysilane and fine powder silica, which has good homogeneity and handling properties, are preferable. Further, these silicon sources are preferably highly pure. Specifically, the initial impurity content is preferably 20 ppm or less, and more preferably 5 ppm or less.

  As an organic material that generates carbon by heating, in addition to a liquid material, a liquid material and a solid material can be used in combination. An organic material that has a high residual carbon ratio and is polymerized or crosslinked by a catalyst or heating is preferable. Specifically, monomers such as phenol resin, furan resin, polyimide, polyurethane, polyvinyl alcohol, and prepolymer are preferable. In addition, liquid materials such as cellulose, sucrose, pitch, and tar are also used. Among them, a resol type phenol resin is preferable in terms of thermal decomposability and purity. The purity of the organic material may be appropriately controlled according to the purpose. In particular, when high-purity silicon carbide powder is required, it is preferable to use an organic material having an impurity element content of less than 5 ppm each.

  The blending ratio of the silicon source and the organic material can be determined in advance by using a molar ratio of carbon to silicon (hereinafter abbreviated as “C / Si”) as a guide. Here, C / Si is C / Si obtained from elemental analysis of a silicon carbide intermediate obtained by carbonizing a mixture of a silicon source and an organic material at 1000 ° C., and analyzing the result. As represented by the following reaction formula, carbon reacts with silicon oxide and changes to silicon carbide.

Formula (I) SiO ₂ + 3C → SiC + 2CO Therefore, in terms of stoichiometry, when C / Si is 3.0, the free carbon in the silicon carbide intermediate is 0%. Volatilizes, and free carbon is generated even if C / Si is a lower value. Since free carbon has an effect of suppressing grain growth, C / Si may be determined according to the particle size of the target powder particles, and the silicon source and the organic material may be blended so as to obtain the ratio. For example, when firing a mixture of a silicon source and an organic material at about 1 atm and 1600 ° C. or higher, the generation of free carbon is suppressed by blending so that C / Si is in the range of 2.0 to 2.5. can do. When C / Si is blended so as to exceed 2.5 under the same conditions, the generation of free carbon becomes remarkable and a silicon carbide powder with small particles can be obtained. Thus, the blending ratio can be appropriately determined according to the purpose. In addition, since the action and effect of free carbon resulting from the silicon carbide powder are very weak compared with the action and effect of free carbon generated from the sintering aid, the free carbon resulting from the silicon carbide powder is the present embodiment. The effect of is essentially unaffected.

  A mixture of a silicon source and an organic material can be cured to form a solid. Examples of the curing method include a method using a crosslinking reaction by heating, a method using a curing catalyst, a method using an electron beam and radiation. The curing catalyst to be used can be appropriately selected according to the organic material to be used. However, when phenol resin or furan resin is used as the organic material, acids such as toluenesulfonic acid, toluenecarboxylic acid, acetic acid, oxalic acid, hydrochloric acid, sulfuric acid, hexamine, etc. And the like. The solid containing the silicon source and the organic material is heated and carbonized as necessary. Carbonization is performed by heating at 800 ° C. to 1000 ° C. for 30 to 120 minutes in a non-oxidizing atmosphere such as nitrogen or argon. Furthermore, silicon carbide is produced when heated at 1350 ° C. to 2000 ° C. in a non-oxidizing atmosphere. The firing temperature and firing time affect the particle size and the like of the resulting silicon carbide powder, and may be appropriately determined. However, firing at 1600 to 1900 ° C. is efficient and preferable. The method for obtaining the high-purity silicon carbide powder described above is described in detail in JP-A-9-48605.

  Next, the nonmetallic sintering aid will be described. The silicon carbide sintered body used in the present embodiment has a free carbon content of 2 to 10% by weight. This free carbon is attributed to the organic material used for the nonmetallic sintering aid, and the amount of free carbon is adjusted to the above-mentioned range by adjusting the addition conditions such as the addition amount of the nonmetallic sintering aid. Can be.

  As the non-metallic sintering aid, those containing an organic material that can be a free carbon source as described above, that is, carbon that is generated by heating (hereinafter sometimes referred to as “carbon source”) are used. The above-mentioned organic material alone or a material obtained by coating the above-mentioned organic material on the surface of silicon carbide powder (particle size: about 0.01 to 1 micron) may be used as a sintering aid. Therefore, it is preferable to use an organic material alone. Specific examples of organic materials that generate carbon by heating include coal tar pitch, pitch tar, phenol resin, furan resin, epoxy resin, phenoxy resin, and various sugars such as glucose, which have a high residual carbonization rate. Examples thereof include small sugars such as monosaccharides and sucrose, and polysaccharides such as cellulose and starch. In order to uniformly mix the organic material with the silicon carbide powder, the organic material is preferably liquid at room temperature, dissolved in a solvent, or softened by heating such as thermoplasticity and heat melting. Among these, the use of a phenol resin is preferable because the strength of the silicon carbide sintered body is improved, and a resol type phenol resin is more preferable. Although the action mechanism of these organic materials is not clear, when the organic materials are heated, inorganic carbon compounds such as carbon black and graphite are produced in the system. It is considered that this inorganic carbon-based compound acts effectively as a sintering aid. However, the same effect cannot be obtained even if carbon black or the like is used as a sintering aid.

  The nonmetallic sintering aid may be dissolved in an organic solvent if desired, and the solution and silicon carbide powder may be mixed. The organic solvent to be used varies depending on the nonmetallic sintering aid. For example, when a phenol resin is used as the sintering aid, lower alcohols such as ethyl alcohol, ethyl ether, acetone, or the like can be selected. When producing a high-purity silicon carbide sintered body, it is preferable to use not only a high-purity silicon carbide powder but also a sintering aid and an organic solvent having a low impurity content.

The addition amount of the nonmetallic sintering aid to the silicon carbide powder is determined so that the free carbon of the silicon carbide sintered body is 2 to 10% by weight. If the free carbon is outside this range, the chemical change to SiC that progresses during the bonding process, and the bonding between the silicon carbide sintered bodies becomes insufficient. Here, the content (% by weight) of free carbon is determined by heating the silicon carbide sintered body at 800 ° C. for 8 minutes in an oxygen atmosphere, and measuring the amount of generated CO ₂ and CO with a carbon analyzer. It can be calculated from the measured value. The amount of sintering aid added varies depending on the type of sintering aid used and the amount of surface silica (silicon oxide) in the silicon carbide powder. As a guideline for determining the addition amount, the surface silica (silicon oxide) content of the silicon carbide powder is quantified in advance using hydrogen fluoride water, and the stoichiometry sufficient to reduce the silicon oxide (formula (I)) The stoichiometry calculated in (1) is calculated. In consideration of this and the ratio of the nonmetallic sintering aid to generate carbon by heating, the amount added can be determined so that the free carbon falls within the above-mentioned suitable range. The description of the non-metallic sintering aid for the silicon carbide sintered body described above is described in more detail in the specification of Japanese Patent Application No. 9-041048.

  Next, a method for sintering a mixture of silicon carbide powder and a nonmetallic sintering aid will be described. The silicon carbide powder and the nonmetallic sintering aid are mixed homogeneously. In order to obtain a homogeneous mixture, a solution obtained by dissolving a sintering aid in an organic solvent as described above may be used. Examples of the mixing method include known methods such as a method using a mixer, a planetary ball mill, and the like. The instrument used for mixing is preferably made of a synthetic resin material in order to prevent mixing of metal element impurities. Mixing is preferably performed for about 10 to 30 hours, particularly about 16 to 24 hours, and mixed sufficiently. After thorough mixing, the solvent is removed and the mixture is evaporated to dryness. Thereafter, the mixture is sieved to obtain a raw material powder of the mixture. For drying, a granulating apparatus such as a spray dryer may be used.

  The raw material powder thus obtained is placed in a molding die. It is preferable that the molding die to be used is made of graphite because metal impurities are not mixed in the silicon carbide sintered body. In order to prevent direct contact between the raw material powder and the metal part of the mold, even if it is a metal mold, the contact part is made of graphite, or a polytetrafluoroethylene sheet (Teflon (registered (Trademark) sheet) can be used preferably. In particular, when it is desired to produce a high-purity silicon carbide sintered body, it is preferable to use a high-purity graphite material for the mold and the heat insulating material in the furnace. Specifically, a graphite material or the like that is sufficiently baked in advance at a temperature of 2500 ° C. or higher and does not generate impurities even when used at a high temperature.

The raw material powder placed in the molding die is subjected to hot pressing. There is no restriction | limiting in particular about the pressure of a hot press, It can carry out by the pressure of the wide range of 300-700 kgf / cm < ² >. However, when pressurizing at 400 kgf / cm ² or more, it is necessary to use a hot press component, for example, a die, a punch or the like having excellent pressure resistance.
The hot pressing is performed at 2000 ° C. to 2400 ° C., and it is preferable to raise the temperature up to the hot pressing temperature gently and stepwise. When the temperature is increased in this way, chemical changes, state changes, and the like that occur at each temperature can be sufficiently advanced. As a result, it is possible to prevent impurities from being mixed, cracks and vacancies. An example of a preferred temperature raising step is shown below. First, a molding die containing raw material powder is placed in a furnace, and the inside of the furnace is brought to a vacuum state of 10 ⁻⁴ torr. Gently raise the temperature from room temperature to 200 ° C. and keep it at 200 ° C. for about 30 minutes. Thereafter, the temperature is raised to 700 ° C. in 6 to 10 hours and maintained at 700 ° C. for 2 to 5 hours. In the temperature raising process from room temperature to 700 ° C., desorption of adsorbed moisture and organic solvent occurs, and carbonization of the nonmetallic sintering aid proceeds. The holding time at the constant temperature varies depending on the size of the silicon carbide sintered body, and may be set to a suitable time as appropriate. In addition, the determination of whether the holding time is sufficient can be based on the time point when the decrease in the degree of vacuum is reduced to some extent. Next, the temperature is raised from 700 ° C. to 1500 ° C. in 6 to 9 hours, and held at 1500 ° C. for about 1 to 5 hours. While the temperature is maintained at 1500 ° C., a reaction in which silicon oxide is reduced and converted into silicon carbide proceeds (formula (I)). Insufficient holding time is not preferable because silicon dioxide remains and adheres to the surface of the silicon carbide powder, preventing densification of the particles and causing large grains to grow. The determination as to whether or not the holding time is sufficient is based on whether or not the generation of carbon monoxide as a by-product is stopped, that is, the reduction of the vacuum degree is stopped, and the reduction reaction start temperature is 1300 ° C. It can be used as a guide whether the vacuum has been recovered.
The hot pressing is preferably performed after the inside of the furnace is heated to about 1500 ° C. at which the sintering starts, and then filled with an inert gas in order to make the inside of the furnace a non-oxidizing atmosphere. Nitrogen gas or argon gas is used as the inert gas, but it is preferable to use argon gas that is non-reactive even at high temperatures. When it is desired to produce a high purity silicon carbide sintered body, an inert gas having a high purity is used. After making the inside of the furnace a non-oxidizing atmosphere, the inside of the furnace is heated and pressurized so that the temperature becomes 2000 ° C. to 2400 ° C. and the pressure becomes 300 to 700 kgf / cm ² . If the maximum temperature is less than 2000 ° C., densification is insufficient. On the other hand, if the maximum temperature exceeds 2400 ° C., there is a possibility that the powder or the molded body raw material may be sublimated (decomposed). It is preferable to raise the temperature from about 1500 ° C. to the maximum temperature over 2 to 4 hours and hold at the maximum temperature for 1 to 8 hours. Sintering proceeds rapidly at 1850-1900 ° C. and is completed during the maximum temperature holding time. The pressurization condition, insufficient is the density is less than 300 kgf / cm ^2, sometimes graphite of the mold exceeds 700 kgf / cm ² is damaged, the manufacturing efficiency is not preferable. The surface roughness (Ra) is preferably 0.5 μm or less, and more preferably 0.2 μm or less. In order to suppress the pressure grows abnormal ^grain, preferably pressurized with 300kgf / cm ² ~700kgf / cm 2 approximately.

The silicon carbide sintered body to be used is densified, preferably has a density of 2.9 g / cm ³ or more and a porosity of 1% or less, has a density of 3.0 g / cm ³ or more, and has a porosity of 0. .8% or less is particularly preferable. Use of a densified silicon carbide sintered body improves mechanical properties such as bending strength and fracture strength, and electrical physical properties of the resulting silicon carbide bonded body. In addition, when a silicon carbide sintered body having a high density is used, the constituent particles are reduced in size, which is preferable in terms of contamination. On the other hand, when a low-density, for example, porous silicon carbide sintered body is used, the heat resistance, oxidation resistance, chemical resistance, and mechanical strength of the silicon carbide bonded body are inferior and the bonding strength is insufficient. In some cases.

As a method for increasing the density of a silicon carbide sintered body, there is a method in which a forming step is performed in advance prior to the sintering step. This molding process is performed at a lower temperature and lower pressure than the sintering process. By carrying out this sintering step, the bulky powder can be made compact (small volume) in advance, and by repeating this step many times, it becomes easy to produce a large compact. An example of various conditions of the molding process performed in advance prior to the sintering process is shown below. The raw material powder obtained by homogeneously mixing the silicon carbide powder and the nonmetallic sintering aid is placed in a molding die, and the temperature is 80 ° C. to 300 ° C., preferably 120 ° C. to 140 ° C., pressure 50kgf ^/ cm ² ~100kgf ^/ cm 2 in 5 to 60 minutes, preferably to obtain a molded body and pressed 20-40 minutes. The heating temperature may be appropriately determined according to the characteristics of the nonmetallic sintering aid. The density of the obtained molded body is 1.8 g / cm ² or more when a powder having an average particle size of about 1 μm is used, and 1. 1 when a powder having an average particle size of 0.5 μm is used. It is preferable to press so that it may become 5 g / cm < ² >. It is preferable for the density of the molded body to be used to be within this range because the silicon carbide sintered body can be easily densified. The molded body may be cut so that the obtained molded body is compatible with a molding die used in the sintering process.

  Total content of impurity elements (elements with atomic number of 3 or more excluding C, N, O, Si in the periodic table of the 1989 IUPAC inorganic chemical nomenclature revised edition) in the sintered silicon carbide used in this embodiment The amount of 5 ppm or less is preferable because it can be used for a process requiring high cleanliness, for example, a semiconductor manufacturing process. More preferably, it is 3 ppm or less, Especially preferably, it is 1 ppm or less. However, the impurity content by chemical analysis has only a meaning as a reference value in actual use. For example, even if the impurity content is the same, the evaluation of the contamination with respect to the silicon carbide bonded body may differ depending on whether the impurities are uniformly distributed or locally distributed. If the materials specifically exemplified above and the exemplified sintering method are used, a silicon carbide sintered body having an impurity content of 1 ppm or less can be obtained. Moreover, in order to reduce the impurity element content of the silicon carbide sintered body, the content of impurity elements contained in the raw materials used (for example, silicon carbide powder and nonmetallic sintering aid) and the inert gas is 1 ppm or less. Or a method of removing impurities by adjusting various sintering conditions such as sintering time and temperature. The impurity element here is the same as described above, and has an atomic number of 3 or more (except for C, N, O, Si) in the periodic table of the 1989 IUPAC inorganic chemical nomenclature revised edition. This element.

Other physical property values of the silicon carbide sintered body used in the present embodiment are bending strength at room temperature of 200 to 800 kgf / mm ² , Young's modulus 250 GPa to 500 GPa, Vickers hardness 2000 to 3500 kgf / mm ² , Poisson's ratio 0.14 to When the thermal expansion coefficient is 0.21, the thermal expansion coefficient is 3.8 × 10 ^{−6 to} 4.5 × 10 ⁻⁶ l / ° C., and the volume resistivity is 0.1 Ω · cm or less, the characteristics of the obtained silicon carbide joined body are good Therefore, it is preferable. As the silicon carbide sintered body of the present embodiment, a silicon carbide sintered body described in Japanese Patent Application No. 9-041048 can be suitably used.

Further, the surfaces to be joined of the silicon carbide sintered body are preferably smooth from the viewpoint of adhesion, and specifically, the surface roughness (Ra) of the surfaces to be joined is preferably 0.5 μm or less, and 0.2 μm. The following is more preferable. The surface roughness (Ra) of the silicon carbide sintered body can be adjusted to the above-mentioned range by performing grinding or buffing with a 200th to 800th grindstone.
Next, silicon metal used as a bonding material will be described. The silicon metal used in this embodiment preferably has a purity of 98% or more, more preferably has a purity of 99% or more, and particularly preferably has a purity of 99.9%. When silicon metal with low purity is used, a shared compound due to an impurity element is generated in the silicon carbide bonded body, and the fire resistance is lowered. In particular, when used in connection with a semiconductor process such as a wafer jig, it is preferable to use one having a purity of 99.999% or more. When the silicon metal to be used is powder, the powder is preferably 100 mesh or more. If the size of the silicon metal is less than 100 mesh, the surfaces to be joined are likely to be displaced, and dimensional accuracy cannot be obtained. Although there is no restriction | limiting in particular about an upper limit, What is actually obtained is a thing of 350 mesh or less.
The amount of silicon metal used for bonding affects the bonding strength and the like of the resulting silicon carbide bonded body. As a result of intensive studies by the present inventors, when an amount of silicon metal calculated according to the following formula (1) is used, the resulting silicon carbide bonded body has a good bonding strength and is due to the remaining silicon metal. It has been found that there is no reduction in bonding strength or contamination. Formula (1) k × {bonding surface area of silicon carbide bonded body (cm ² )} × {free carbon amount of sintered silicon carbide (%)} (g) In the formula, the bonded surface area of silicon carbide bonded body is The surface area seen from the projection surface of the joint surface is shown. For example, in the case of joining two sintered bodies having the same surface, the surface area of the surface of one silicon carbide sintered body as viewed from the projected surface is shown. Further, when three or more silicon carbide sintered bodies are joined, the total surface areas seen from the projection surfaces of all the surfaces to be joined of the silicon carbide sintered body are summed, and the half of the area is shown. In the formula, k is 0.08 to 0.12, and is a coefficient obtained experimentally. Its dimension is g / cm ² .

Silicon metal is sandwiched between the surfaces of two or more silicon carbide sintered bodies to be joined. For example, a silicon metal powder is spread on the surface of one silicon carbide sintered body, and then the surface to which the other silicon carbide sintered body is joined is overlapped on the surface on which the silicon metal is dispersed, The silicon sintered body may be disposed close to each other so as to obtain a predetermined space (arranged so that the bonding surfaces face each other), and the space may be filled with metal silicon powder. At this time, it is not necessary to pressurize in particular. For example, in the case where the silicon carbide sintered bodies are joined in a stacked state, the surface may not be displaced even if the weight of the silicon carbide sintered body is loaded. You may fix with a fixing tool or pressurize so that a surface may not slip | deviate. As a method of spraying silicon metal on the surface of the silicon carbide sintered body, for example, there is a method of spraying using a funnel or the like so that the surface of the silicon carbide sintered body is entirely covered with silicon metal.
Next, the silicon carbide sintered body sandwiching the silicon metal is subjected to a high-temperature heat treatment. The heat treatment is preferably performed in a non-oxidizing atmosphere, and is preferably performed in a vacuum or an inert gas atmosphere other than nitrogen gas. As the inert gas used, argon gas and helium gas are preferable. When nitrogen gas is used as the inert gas, it reacts with silicon metal at a high temperature to produce silicon nitride, and the bonded surface may be peeled off or broken due to a difference in thermal expansion. On the other hand, since argon gas and helium gas are non-reactive even at high temperatures, such problems do not occur and are preferable. In addition, when manufacturing a high purity silicon carbide joined body, it is preferable to use a high purity inert gas.

  The heating temperature should just be more than melting | fusing point of a silicon metal, and 1450 to 2200 degreeC is preferable. When the temperature is lower than 1450 ° C., the silicon metal does not melt, and when the temperature is 2200 ° C., the silicon metal partially sublimates. When β-type silicon carbide is used as a raw material, the upper limit is preferably 2000 ° C., and when α-type is used, the upper limit is preferably 1800 ° C. In particular, bonding at about 1600 ° C. is preferable because a high-strength bonded body can be efficiently manufactured. Moreover, it is preferable to raise the temperature gently because the reaction between silicon metal and free carbon in the silicon carbide sintered body proceeds sufficiently. Specifically, it is preferable to raise the temperature at 5 ° C./min to 15 ° C./min, and particularly preferably at about 10 ° C./min.

(Monitor wafer manufacturing process)
The monitor wafer 10 according to the first embodiment is manufactured by the following process.
(A) The monitor wafer body 2 shown in FIG. 3A is manufactured according to the hot press method.
(B) Next, as shown in FIG. 3B, pockets 24, 28, 29, 26, and 22 having a concave cross section are formed in the monitor portion of the monitor wafer body 2 by using a polishing method.
(C) Subsequently, the test pieces 34, 38, 39, 36, 32 are embedded in the pockets 24, 28, 29, 26, 22 as shown in FIG. Thus, the monitor wafer 10 according to the first embodiment is manufactured.

The monitor wafer 60 according to the second embodiment is manufactured by the following process.
(A) The base wafer 3 and the ring plate 5 constituting the monitor wafer 60 shown in FIG. 4A are manufactured according to the hot press method.

(B) Next, the wafer mounting surface of the base wafer 3 is polished so as to be flat.

(C) Subsequently, as shown in FIG. 4 (b), holes (pockets) 54, 58, and the like are formed in the ring plate 5 by using an electric discharge machining method so as to form pockets when attached to the base wafer 3. 59, 56 and 52 are provided.

(D) Next, the ring plate 5 is fixed to the base wafer 3 using bolts.

(E) Subsequently, the test pieces 44, 48, 49, 46, 42 are embedded in the pockets 54, 58, 59, 56, 52 as shown in FIG. As described above, the monitor wafer 60 according to the second embodiment is manufactured.

  A silicon carbide sintered body (monitor wafer) having high purity, high density, and high toughness can be obtained by the above manufacturing method. In the said hot press method, if the above-mentioned heating conditions of this embodiment are satisfy | filled, there will be no restriction | limiting in particular in a manufacturing apparatus etc., A well-known heating furnace and reaction apparatus can be used.

The obtained monitor wafers 10 and 60 have a structure in which the amount of residual silicon is small and silicon carbide particles are uniformly dispersed. The monitor wafers 10 and 60 obtained according to the present embodiment have a structure in which mainly isotropic silicon particles having a density of 2.9 g / cm ³ or more and an average particle diameter of 2 μm to 10 μm are uniformly dispersed. . Therefore, it can be used as a structural member with small variations in density and the like. In general, when the density of the sintered body is less than 2.9 g / cm ³ , mechanical properties such as bending strength and fracture strength and electrical properties are deteriorated, and further, particles are increased and contamination is deteriorated. Therefore, it can be said that the monitor wafer of this embodiment has good mechanical characteristics and electrical characteristics. The density of the monitor wafers 10 and 60 in a preferred embodiment is 3.0 g / cm ³ or more.

  The total content of impurities in the monitor wafers 10 and 60 obtained in this embodiment is less than 10 ppm, preferably less than 5 ppm, more preferably less than 3 ppm, and even more preferably less than 1 ppm. A solid material obtained by homogeneously mixing a liquid silicon compound, a nonmetallic sintering aid, and a polymerization or crosslinking catalyst is heated and carbonized in a nonoxidizing atmosphere, and then further nonoxidized. According to the manufacturing method including the firing step of firing in a neutral atmosphere, the total content of impurities other than silicon, carbon, and oxygen contained in the monitor wafers 10 and 60 can be less than 1 ppm. The nitrogen content of the monitor wafers 10 and 60 obtained in this embodiment is 150 ppm or more.

In addition, when examining preferable physical properties of the monitor wafers 10 and 60 obtained in the present embodiment, for example, the bending strength at room temperature is 400 MPa to 700 MPa, the Vickers hardness is 1500 kgf / mm ² or more, and the Poisson's ratio is 0.14 to 0.00. 21, Thermal expansion coefficient is 3.8 × 10 ^{−6 to} 4.5 × 10 ⁻⁶ (° C. ⁻¹ ), thermal conductivity is 150 W / m · k or more, specific heat is 0.60 to 0.70 J / g · K and specific resistance are 1 × 10 ⁻¹ Ωcm or less.

The monitor wafers 10 and 60 of the present embodiment obtained as described above preferably have the following physical properties:
The monitor wafers 10 and 60 have a volume resistance of 1 Ωcm or less, and more preferably 0.5 Ωcm to 0.05 Ωcm. The monitor wafers 10 and 60 have a total content of inevitable elements other than silicon and carbon, that is, impurity elements, of the monitor wafers 10 and 60 is less than 5 ppm. Monitor wafers 10, 60 has a density of 2.9 g / cm ³ or more, 3.00~3.15g / cm ³ in a further preferred embodiment. The monitor wafers 10 and 60 have a bending strength of 400 MPa or more, and in a more preferred embodiment, 500 to 700 MPa.

  The silicon carbide powder that is the raw material powder of the present embodiment, the silicon source and the nonmetallic sintering aid for producing the raw material powder, and the inert gas used to make the nonoxidizing atmosphere, respectively The content of each impurity element is preferably 1 ppm or less in each impurity element, but is not necessarily limited to this as long as it is within the allowable range of purification in the heating and sintering processes. Further, the base plate and the ring plate are not limited to the hot press method, and may be manufactured using, for example, a reactive sintering method.

  This application is accompanied by a priority claim based on a Japanese patent application previously filed by the same applicant, ie, Japanese Patent Application No. 2005-23583 (filing date: January 31, 2005). Are hereby incorporated by reference.

  According to the present invention, a reusable monitor wafer having good chemical resistance is provided.

Claims (5)

  A monitor wafer comprising a silicon carbide sintered body having a concave pocket for placing a test piece on a monitor portion on a wafer surface. A base wafer made of a sintered silicon carbide;
A ring plate made of a silicon carbide sintered body that is detachably attached to the base wafer and forms a concave pocket for placing a test piece on a monitor portion when attached to the base wafer;
A monitor wafer characterized by comprising:   The monitor wafer according to claim 1, further comprising a test piece detachably attached to the pocket. The test piece has at least one required flatness of 200 μm or less,
Surface roughness (Ra) 0.1 μm or less,
The monitor wafer according to claim 3, wherein:   Using a monitor wafer having a monitor wafer body made of a silicon carbide sintered body having a concave pocket for mounting a test piece on a monitor portion on the wafer surface, and a test piece detachably attached to the pocket A method for monitoring a wafer, comprising monitoring a deposited film deposited on the test piece.

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