MXPA01005857A - High purity, siliconized silicon carbide having high thermal shock resistance - Google Patents

Abstract

This invention is a high strength, thermal shock resistant, high purity siliconized silicon carbide material made from siliconizing a converted graphite SiC body having at least 71 vol%silicon carbide therein.

Description

SILICON SILICON CARBIDE OF HIGH PURITY WHICH HAS HIGH RESISTANCE TO THE THERMAL IMPACT DESCRIPTIVE MEMORY The manufacture of devices such as integrated circuits almost always covers the heat treatment of silicon wafers in the presence of reactive gases at temperatures of approximately 250 ° C to more than 1200 ° C. The temperatures and gas concentrations to which the wafers are exposed should be carefully controlled, since the final devices often include circuitry elements smaller than 1 μm in size, which are sensitive to minute variations in the processing environment. wafers The semiconductor manufacturing industry has almost always used horizontal or vertical carriers made of silicon carbide or siliconized silicon carbide as dryer oven accessories for the wafers, and these carriers have been designed to hold up to 50 wafers. By employing such conventional carriers, processing steps generally encompass fairly slow ramp rates between about 10 ° C and 30 ° C / minute. However, due to the performance of the wafers and the increasingly stringent efficiency requirements, the industry has been considering the adoption of thermal processing wafer processing techniques. fast (RTP). In accordance with the patent of E.U.A. No. 4,978,567 ("Miller") under RTP conditions, the wafers are treated in an environment whose temperature rises from room temperature to about 1400 ° C in a period in the order of seconds. The RTP ramp rates that are typical are in the order of 600-6000 ° C / minute. Under these extreme processing conditions, the resistance to the thermal impact of the materials in this environment is of decisive importance. Miller describes carriers of RTP wafers made of CVD-independent silicon carbide, and carriers made of CVD-coated silicon carbide graphite. However, the cost of silicon carbide from independent CVD is often prohibitive, while the carriers made of CVD silicon carbide-coated graphite experience a significant inequality of thermal expansion coefficients ("OTE") that makes the mixed material susceptible to thermal impact. Silicon silicon carbide has been considered as a candidate material for drying oven accessories in RTP systems. In particular, the patent of E.U.A. No. 5,14,439 ("Sibley") discloses RTP's furnace accessories where the siliconized silicon carbide is chosen as the material. However, in a test involving a silicon carbide ("Si-SiC") material available on the market, commonly used as drying oven accessories in conventional wafer processing, it was found that this Si-SiC material lost 40% of its flexural strength (from 261 Mpa to 158 MPa) when subjected to a test of thermal desensitization, in which the temperature of the environment surrounding the material decreased from 500 ° C to 0 ° C almost in an instant. The discovery that the siliconized silicon carbide mentioned above does not have resistance to the relevant thermal impact in RTP environments is not surprising. Torti et al, ("High Performance Ceramics for Heat Engine Applications") "High Performance Ceramic Materials for Hot Engine Applications", ASME 84-GT-92, explains other siliconized silicon carbide material (NC-430) developed by a reaction bonding process that is said to have high resistance to thermal shock. However, Torti et al. Also discloses that this NC-430 material has a Te value of only 275 ° C, which seems to "signify that a significant resistance reduction occurs if this material is instantaneously subjected to a differential of temperature of only 275 ° C. Weaver et al., ("High Strength Silicon Carbide for Use in Severe Environments") "High Strength Silicon Carbide for Use in Intense Environments" (1973) reports that a heat-pressed SiC material comprising 95-99% of SiC has a poor thermal impact resistance. Therefore, there is an enormous need for a siliconized silicon carbide material that has a thermal impact resistance suitable for use in drying oven accessories that are designed for RTP applications.

In addition to the more stringent thermal impact requirements, another trend in the semiconductor manufacturing industry has been the steady decline in the level of acceptable metallic contamination in processed wafers. Consequently, the industry has concurrently needed that the drying oven accessories are made of increasingly high purity materials. As it is already known that the type of "converted graphite" of son carbide has very low levels of metallic contamination, the technique has considered making SiC drying oven accessories from converted graphite materialeei. The process for making such converted graphite materials involves exposure of a porous graphite body to SiO gas under carefully controlled conditions, which allow a 50% replacement of carbon atoms in the graphite matrix with son atoms and the final production of a stoichiometric beta-SiC body. The publication of JP Kokai No. 1-264969 (1989) ("Tanso") describes the sonization of 30% of porous SiC material made from graphite converted to essentially complete density, as well as the use of that sonized material as a trough for wafers in wafer processing operations for semiconductors. Tanso further describes that the non-porous sone product essentially made from its process can have a density of 2.9 g / cm3 at 3.2 g / cm3. Since son and son carbide have respective densities of 2.33 g / cm3 and 3.21 g / cm '!, respectively, it seems that Tanso describes SiC products sonadcs that have 64% by volume to 99% by volume of son carbide. However, the actual enabling technology described by Tanso seems to be limited to lower SiC fraction bodies only. In particular, Tanso describes that the reason for his successful conversion of graphite to SiC stoichiometric was his decision to limit the density of the starting graphite body to no more than 1.50 g / cm3 to provide sufficient porous vessels within the body of graphite to allow the complete infiltration of Siü gas. Since following these suggestions seems to limit the body density of 'SiC converted to only about 2.25 g / cm3, Tanso seems not to describe how to make a converted graphite SiC body that has a density of more than 2.25 g / cm3 (or 70.09 vol% SiC), and then no longer describes a sonized SiC body having more than 70.09% by volume of SiC. A known commercial producer of graphite converted for use in semiconductor wafer processing offers a porous beta-SiC material, made from converted graphite and having a density of 2.55 g / cm3, or about 80% by volume of SiC. However, the resistance to bending at room temperature that is reported for this material (around 175 MPa) is relatively low. Almost always, a resistance to bending at room temperature of less than about 230 MPa is much preferred for SiC diffusion components useful in the market. In addition, although it is known that the sonization of a body of porous SiC almost always improves its resistance, a brochure of the The aforementioned producer discourages the sonization of this porous converted graphite product having 80% by volume of SiC, for fear of the consequences of thermal expansion inequality. In particular, in accordance with the brochure of the producer, the difference in the coefficients of thermal expansion ("CTE") between son (CTE = 2.5-4.5x 10"6 / ° C) and son carbide (CTE = 4.8) x10"6 / ° C) is so high that, when cooled (from the son, SiC contracts much more than son), and this creates tensions of intragranular bonds in the SiC during the cooling of the son and the subsequent thermal cycles. Therefore, it seems that this leaf actively discourages the sonization of porous converted graphite products that have above 71% by volume of SiC for fear of producing cracks that degrade resistance in the mixed material., there is still another need for a silicon carbide silicon material having above 71% by volume of silicon carbide (preferably above 75% by volume SiC, more preferably at least 80% by volume SiC) ) having higher purity and adequate strength, which are necessary for conventional applications of wafer carriers, and preferably, the high thermal impact resistance needed for RTP applications of the future. The inventors ignored the descriptions of the aforementioned pamphlet and successfully siliconized the SiC converted porous graphite product having about 80 volume% SiC. It was discovered that the siliconized SiC body thus produced was essentially It was completely dense and had a resistance to ambient temperature (266 MPa), which in essence was equivalent to a commercial Si-SiC material that is routinely used as a drying oven accessory in the semiconductor processing industry. Therefore, this new silicon SiC body comprising converted graphite meets the desires of today's semiconductor manufacturers thanks to high purity and acceptable strength. Furthermore, the resistance to the suitable ambient temperature in the market of this material is surprising in light of the warnings provided by the manufacturer's brochure of the SiC converted porous graphite material. The inventors also examined the new siliconized material and discovered that the severe thermal impact test did not affect it in essence. In particular, when subjected to the thermal desensitization test, where the temperature of the environment surrounding the material dropped from 500 ° C to O'C almost in an instant, the subsequent MOR resistance of the material dropped by less than 10%. Therefore, this new siliconized SiC body comprising converted graphite meets the wishes of tomorrow's semiconductor manufacturers thanks to the high purity and high thermal impact resistance required for RTP applications. In addition, the superior thermal impact resistance of this new material is surprising in light of: a) the warnings provided by the manufacturer's brochure of SiC converted porous graphite material, in particular as they relate to the thermal stresses produced by the silicone; b) the failure of conventional Si-SiC products to adequately survive the thermal impact test at 500 ° C; c) the essential similarity in ambient temperature resistance and thermal impact test performance at 300 ° C between the commercial Si-SiC product and the new material. The material of this invention which exhibited a high temperature bending resistance (1300CC), which was superior to the commercial siliconized SiC material, was also discovered. Therefore, in accordance with the present invention, there is provided a process for making a silicon carbide material of high strength, resistant to thermal shock and of high purity comprising the steps of: a) providing a SiC body of porous converted graphite having at least 71% by volume of SiC, and b) silicone siliconized SiC body of porous graphite to a bulk density in essence to produce a body of mixed silicon carbide material. Preferably, step a) is achieved in the following manner: i) providing a body of porous graphite and ii) exposing the porous graphite body to a reagent sufficiently to produce a SiC body of graphite converted porous having at least 71% by volume SiC of converted graphite. Also, in accordance with the present invention, a silicon carbide mixed material of high strength, resistant to thermal shock and of high purity is provided; the material having at least about 71% by volume of converted graphite silicon carbide matrix having open porosity, wherein the open porosity of the SiC material is filled with silicon. Also, in accordance with the present invention, a drying oven accessories component for semiconductor manufacturing is provided, preferably in the form of a component suitable for the USD in RTP applications, wherein said component comprises the mixed material of siliconized silicon. of high resistance, resistant to the technical impact and of high purity that was mentioned previously. Also, in accordance with the present invention there is provided a method for using a drying oven accessory component to manufacture wafers for semiconductors, preferably in the form of a component suitable for use in RTP applications, wherein said component comprises the mixed material of silicon carbide of high resistance, resistant to thermal impact and of high purity mentioned above, which comprises the steps of: a) providing a component of drying accessories (preferably in the form of a component of RTP) of the new material of silicon carbide of high strength, resistant to thermal shock and of high purity as already mentioned, and b) exposing the component to a reactive gas used in the manufacture of semiconductors in an environment having a peak temperature of approximately 800 ° C a 1400 ° C (from approximately 1200 ° C to 1400 ° C in some modes). In some embodiments of RTP, the ambient temperature rises from about room temperature to the peak temperature at a rate of at least 100 ° C / minute (preferably at least 600 ° C / minute). Figure 1 is a photograph of a prior art microstructure of a converted, porous, non-siliconized graphite SiC body. Figure 2 is a photograph of a prior art microstructure of a siliconized SiC body comprising fine and coarse alpha-SiC grains. Figure 3 is a photograph of the present invention, a microstructure of a SiC body of siliconized graphite graphite. Figure 4 is a graph comparing the maximum lengths of silicon packs in the material of the present invention and a competitive prior art material. Figure 5 is a graph comparing the relative area sizes of silicon packs in the material of the present invention and a material of! the previous competitive technique. .

In one embodiment of the present invention, a porous converted graphite material commercially available having at least 71 volume% SiC is subjected to siliconization. A porous converted graphite SiC material commercially available and suitable is SUPERSiCR, marketed by Poco Graphite, Inc, of Decatur, TX. This material is a porous SiC made from converted graphite comprising about 80% by volume of beta-SiC. The SiC microstructure of a converted graphite body retains the general appearance of a graphite microstructure and is also unique among the SiC microstructures and are well known to those skilled in the art. A photomicrograph of this material is illustrated in Figure 1. The microstructure is characterized by the essential absence of discrete particles. It also has more substantial lowering than conventional porous SiC bodies which can be comparable made from a bimodal blend of SiC powders. It also has some large deposits of silicon packs that bimodal SiC bodies that are comparable. In general, the absence of coarse SiC particles, the higher degree of lowering, and the relative absence of large silicon packs makes the graphite body structure much more homogenous than the recrystallized bimodal SiC bodies that can be compared. Preferably, the porous graphite starting material has a total metal impurity content of less than 10 ppm.

It is believed that any converted graphite material having an acceptable amount of continuous porosity to allow the infiltration of adhered silicon can also be used as a starting material for the silicone. The porosity of the converted graphite material needs to be in the range of 5% by volume and 29% by volume. If the material has less than 5% by volume of porosity, then it is considered that the porosity is closed and in essence no infiltration is expected. More preferably, the material has between 5% by volume and 25% by volume of porosity, and 75-95% by volume of SiC. In this scale, the degree of porosity almost always allows the complete infiltration in essence of the porosity by the silicon with ease, and the percentage in volume of SiC has the sufficient level to produce a strong mixed material. More preferably, the material has between 15% by volume and 25% by volume of porosity. Typical converted graphite materials contain less than 10 ppm of total metallic impurity and less than 0.1 ppm of iron impurity. In another embodiment to elaborate the present invention, first the body of porous converted graphite is produced. In this embodiment, the porous graphite body is then converted to a porous stoichiometric SiC body having at least 71 volume% SiC. The conventional procedures for making converted graphite can be followed. A known method for making converted graphite is described in the U.S.A. No. 4,900,531, whose specification is incorporated by reference.

If the converted graphite body is made at a low temperature, it may be desirable to recrystallize the porous SiC body at a temperature of at least 1600 ° C prior to siliconizing to provide for greater recessing in the body. The siliconization of the converted graphite material can be guided in accordance with the siliconization typical of recrystallized and porous silicon carbide bodies. Conventional procedures are described in the US patent. No. 3,951, 587, whose specification is incorporated by reference. For example, in one case, pieces of solid semiconductor grade silicon are placed in an oven near the porous converted graphite body, and the temperature of the furnace rises beyond the melting point of the silicon. The molten silicon then passes through the porous SiC body and produces the complete silicone. In other embodiments, the method for siliconization described in the US patent is used. No. 4,795,673 ("Frechette"). Without wanting to stick to the theory, it is hypothesized that certain recrystallization of the SiC microstructure of converted graphite can occur during siliconization (thereby improving the degree of interparticle SiC bonding (or debonding) and producing a stronger material ) if the silicone continues at temperatures above 1600 ° C. Therefore, in preferred embodiments, the converted graphite comes into contact with the molten silicon at a temperature of at least 1600 ° C (preferably at least 1700 ° C, and more preferably at least 1800 ° C) to stimulate the lowering. Preferably, the body of the mixed silicon carbide composite material produced in accordance with the present invention comprises a SiC matrix of converted graphite having a porosity that is essentially filled with silicon, wherein at least 71% by volume of the body is SiC. Preferably, at least 75% by volume of the body is SiC, more preferably at least 80%. Since the porous converted graphite starting materials must also have adequate porosity to allow complete siliconization, in preferred embodiments, the mixed material has between 75% by volume and 95% by volume of SiC and between 5% by volume and 25% in volume and silicon. A particularly preferred embodiment has about 80% by volume SiC of converted graphite. Almost always, the silicon essentially fills the porosity of the SiC matrix of converted graphite, which preferably results in a mixed material having no more than 4% by volume of final porosity, more preferably less than 2% by volume of final porosity, more preferably less than 1% by volume of final porosity. In other words, the mixed material has a density that is at least 96%, preferably at least 98% theoretical density, more preferably at least 99% theoretical density. The SiC microstructure of the mixed material retains the overall appearance of the converted SiC graphite SiC starting material and is therefore once again unique among the SiC microstructures, and the experts in the technique they recognize it well. A photomicrograph of the siliconized graphite converted structure is illustrated in Figure 3. Since typical graphite conversion produces essentially beta-silicon carbide, (i.e., at least 90%) of all SiC in this mixed material almost It is always beta-silicon carbide. It is known that beta-SiC is a cubic phase, and that a cubic phase material will generally produce an isotropic response. In contrast, alpha-SiC is a hexagonal phase and therefore it is expected to produce responses that are more anisotropic. Since it is known that there is an inequality of thermal expansion between silicon and SiC, the isotropic response of the material of the present invention to this inequality can moderate the stresses produced therefrom, thereby producing greater strength. Therefore, in preferred modalities, SiC is at least 90% by volume of beta-SiC. Accordingly, in some embodiments, the converted graphite SiC comprises at least 90% by weight of beta-SiC and the step for silicone is performed at a low enough temperature to prevent substantial conversion of the converted graphite beta-SiC and the body of the mixed material comprises at least 90% by volume of beta-SiC. However, it is contemplated that the conversion of graphite at higher temperature or silicone processes may be employed, whereby beta-SiC to alpha-SiC is partially or completely converted. Preferably, less than 10% by weight of SiC is characterized as a SiC particle having a size greater than 30 microns (more preferably less than 5% by weight). Without wishing to stick to the theory, it is believed that a reason for the superior thermal impact resistance of this new material may lie in that it essentially does not have a thick SiC particle. In particular, while the SiC fractions of the aforementioned NT-430 and the commercial Si-SiC materials possess about 50% by weight grains of; Silicon carbide having a grain size between 10 and 150 μm, the new material essentially does not have thicker SiC grains at 30 microns. It is believed that the important difference in the thermal expansion coefficients of silicon and SiC grains in these prior art materials causes the stress concentrations around the SiC grains during the cooling of the mixed material after siliconization. However, it is also believed that the spheres of influence of the stress produced by the thicker SiC grains is much larger than the spheres produced by the smaller SiC grains. Simply, the grains of; SiC thicker are more important in situations of thermal stress. The elimination of the most dangerous and potentially dangerous SiC grains of the siliconized material can reduce the critical sphere of stress concentration influence that occurs through cooling (thus increasing the mechanical properties of the siliconized material) and can be decisive for the present invention. If the removal of coarse SiC grains is the reason for the improved thermal impact resistance of the new material, this discovery is surprising in light of the essential similarity in the ambient temperature resistances of the silicon carbide material. siliconadc commercial and the new material, and the apparent resistance of the conventional material for thermal impact test at 300 ° C. In particular, if the thick SiC particles have a strong effect on MOR at room temperature and thermal impact characteristics, then there should also be significant differential stresses in the silicone bodies produced in their cooling after siliconizing, and these stresses could have been reflected in difference results in the tests of ambient temperature and thermal impact at 300 ° C. The fact that a difference in performance between these materials only appears in the thermal impact test at 500 ° C is testimony that the effect is quite subtle. Likewise, if the removal of SiC grains is the reason for the improved thermal impact resistance of the new material, this discovery is surprising in light of the well-known fact that coarse grains often act as breaking deflectors that increase stiffness. of the ceramic body. Since it is known that the thermal impact resistance is improved by increasing the stiffness of the material, it was considered that the removal of the coarse grains could have reduced the stiffness of the material and consequently reduced its thermal impact resistance. Although not desired in particular, the mixed material may contain additional SiC particles (eg, present in an amount between 1 and 33% by volume) that were infiltrated in the beta-body.

Porous SiC before the silicone, or infiltrated in the porous SiC body at the time of siliconization. The chemical properties of the mixed material body were measured and are as follows: the total metallic impurity content of the mixed material (as measured by any conventional method, such as suspension GDMS or ICP) is almost never greater than 10 ppm, preference not greater than 5 ppm, more preferably not more than 1 ppm. The iron impurity content of the mixed material (as measured by GDMS or suspension ICP) is almost never greater than 1 ppm, preferably not greater than 0.5 ppm, more preferably not greater than 0.1 ppm. The titanium impurity content of the mixed material (as measured by GDMS or suspension ICP) is almost never greater than 3 ppm, preferably not greater than 1 ppm. The aluminum impurity content of the mixed material (as measured by GDMS or suspension ICP) is almost never greater than 5 ppm, preferably not greater than 1 ppm, more preferably not greater than 0.5 ppm. In comparison, the conventional siliconized SiC material has about 80-100 ppm of total metallic impurity and about 1 ppm of iron impurity. Preferably, the mixed material of the present invention has a thermal conductivity of at least 85 W / mK at 400 ° C, and at least 50 W / mK at 800 ° C. The upper thermal conductivity of the material of this invention at elevated temperatures is demonstrated in Table II below which reveals values that are almost 10-15% higher than those of the material of SiC sil conado comercial. It is possible that the thermal conductivity in some way evades the siliconized graphite converted material is the cause of its resistance to thermal impact higher than 500 ° C. When the material receives a thermal impact, its survival depends in part on its ability to dissipate heat rapidly, thus minimizing its internal temperature gradients. It is that the greater thermal conductivity of the material of the present invention allows it to dissipate heat more quickly and uniformly, so that the voltage induced temperature gradient is almost always reduced, almost always related to the failure of the thermal impact. However, it is also well known that although the thermal conductivity of the material of this invention is greater than the silicone material available in the market, it is only about 10-15% higher. Therefore, we hypothesize that the practical effect of this moderate increase in thermal conduction is adequate and is only revealed under certain conditions in which the difference of 10-15% is decisive. For example, while the difference of 10-15% does not seem to produce any difference in the thermal impact test at 300 ° C (shown in Table 1 below), it seems to produce a large difference in the thermal impact test at 500 ° C. To the extent that the similar performance in appearance of these materials in a 300 ° C thermal impact test provides similar hope for results in high temperature tests, the thermal impact strength exceeds 500 ° C of the material of the present invention. it's amazing.

As mentioned above, the superior thermal conductivity of the material of this invention is demonstrated in Table 2 below as being about 10-15% greater than that of siliconized SiC available in the market. Since SiC has a significantly higher thermal conductivity than silicon (by almost an order of magnitude), it is clear that heat dissipation in these bodies is most likely carried out mainly by conducting it through the SiC phase. However, since each of these materials contains about 80% by volume of SiC, the difference in thermal conductivity between these two. Materials can not be explained solely on the basis of any difference in SiC content. Instead, it is believed that the upper thermal conductivity of the material of the present invention may be due to the superior connectivity of its SiC phase (as compared to the conventional SiC material). The analysis of the material of the present invention revealed that its SiC phase is quite continuous throughout its microstructure. In other words, the "veins" of the SiC phase are of relative and uniform thickness. In contrast, the SiC silicon material available on the market is essentially characterized by thick SiC particles which are partly connected to each other by smaller recrystallized SiC particles which do not have the same width as the vein thickness of the material. of graphite converted of the present invention. In other words, commercial material has a low degree of debasement. In this way, it is possible for the heat to be conducted more easily through the material of the present invention thanks to the fact that its SiC veins of uniform thickness do not have as many low resistance levels as the material available in the market. The limited quantitative analysis of the microstructures of these two materials provides information that is quite consistent with this hypothesis. In an analytical exercise, the maximum length of discrete silicon packages was characterized by a 2-D analysis of a polished microstructure. It is believed that high maximum length values are characteristic of increased silicon packet connectivity, and consequently lower connectivity of the SiC phase (which is important for heat conduction). The value is of maximum length in the material of the present invention (in comparison with the commercial material) appear in Figure 4. Figure 4 illustrates that: between 65 -75% of the silicon packs in the present invention have a length maximum less than 10 μm. By contrast, no more than 55% of the silicon packages in the conventional material have a maximum length of less than 10 μm. Therefore, in preferred embodiments of the present invention, at least 60% of the silicon packs in the material of the present invention have a maximum length of less than 10 μm. The mechanical properties of the mixed material body are as follows: almost always, the mixed material has a bending strength of 4 points at room temperature less than about 230 MPa, preferably at least about 250 MPa. It has a four-point fold resistance at 1300 ° C of at least almost 200 MPa, of preference at least almost 220 MPa. Their resistance to thermal shock at 500 ° C (as they are characterized by their resistance to ambient temperature measured after being desensitized in ice water of a temperature of approximately 500 ° C) is almost always at least 80% of their resistance before the test (preferably at least 90%) and almost always is at least about 230 MPa (preferably at least 250 MPa). Since the porous converted graphite matrix is characterized by a relatively homogeneous microstructure (ie, absence of discrete particles, essentially non-coarse particles and some large silicon packs), the SiC matrix of "converted graphite" resulting also it is similarly characterized as homogeneous. Another reason for the superior thermal impact property of the material of the present invention may reside in its high degree of homogeneity. In a simple way, a mixed material that has a more homogeneous structure can conduct heat and respond to stress better than materials with less homogeneity. In this regard, it has been found that the material of the present invention has SiC veins of uniform thickness and small silicon packs. In contrast, commercial silicone material has thin SiC debonders and large silicon packs. In addition, the quantitative analysis of the microstructures of these two materials provides information that once again is quite consistent with this hypothesis. In another analytical exercise, the area of each individual silicon package is measured. It is believed that a fair unimodal distribution of areas relatively small is characteristic of a good dispersed silicon phase. As illustrated in Figure 5 below, the area of the average package in the material of the present invention is less than that of the commercially available silicone material. The figure shows that between 55-65% of the silicon packs in the present invention have an area smaller than 20 μm2. In contrast, about 45% of the silicon packages in the conventional material have an area smaller than 20 μm2. Therefore, in preferred embodiments of the present invention, at least 50% of the silicon packages have an area of less than 20 μm2. In addition, the distribution of the packages seems to be narrower (the initial slope is more inclined), so it indicates a greater degree of homogeneity in the material of the present invention. Preferably, the mixed material of the present invention has a coefficient of thermal expansion not greater than 5 x 10"6 / ° C, preferably not greater than 4 5 x 10" 6 / ° C. The overall thermal expansion coefficient of the material of this invention is much lower than that of the commercially available silicone material. See table 2. Since a lower coefficient of thermal expansion would appear to produce less stress during thermal cycling, it is believed that the lower thermal expansion coefficient of the material of the present invention intervenes in its performance properties at apparently higher elevated temperature. Since the mixed material of the present invention has high purity and resistance to the optimum ambient temperature and optimum resistance to the elevated temperature, it can be suitably used as a material of drying oven accessories for the manufacture of wafers for conventional semiconductors. Such components almost always include troughs for horizontal wafers, vertical supports, procedure tubes, and pallets. Since the mixed material of the present invention also has superior thermal impact resistance, it appears to be the ideal candidate for use in fast thermal processing applications. In such applications, the mixed material can be the building material for RTP processing, such as bell chambers and wafer susceptors. In some preferred RTP applications, the processing environment increases at a rate of at least 150 ° C / minute, preferably at least about 600 ° C / minute. In some RTP applications, the processing environment is cooled at a rate of at least 100 ° C / minute. In some preferred applications involving fast ramp furnaces, the processing environment increases at a speed between 40 and 100 ° C / minute, preferably between 60 and 100 ° C / minute.

EXAMPLE 1 A portion of a commercial wafer trough made of "converted graphite" SiC material having about 20 volume percent porosity was placed in a siliconized SiC channel, and the channel was filled with pieces of electronic grade silicon. The tundish, the silicon and the channel were placed in an induction furnace and heated to approximately 1850 ° C. After cooling the siliconized article then they were cleaned by sandblasting to remove excess silicon. The siliconized article was then subjected to several conventional mechanical tests, including resistance to bending of four points at room temperature, resistance to bending of four points at 1300 ° C, thermal impact of 300 ° C, thermal impact of 500 ° C . The thermal impact tests were performed by heating the article to the test temperature in an oven and taking it out to desensitize it immediately in a bucket of water at approximately 0 ° C for almost one second after it had been removed from the oven. Other characteristics of these articles were also measured, including thermal diffusion capacity, coefficient of thermal expansion. The coefficient of thermal expansion was obtained by conventional dilatometry. The values of thermal diffusion capacity were measured by an instantaneous laser technique. The specific heat of the materials was measured by differential scanning calorimetry. The thermal conductivity of the materials was then determined through the thermal diffusion capacity obtained in that way, as well as specific heat values. Finally, the microstructure of the siliconized material was prepared for a quantitative analysis by assembling and polishing small sections. A series of image analysis measurements were made in two separate sections.

The results of these tests appear in Tables I and II below, in Figures 3-5 and in the previous text.

COMPARATIVE EXAMPLE 1 A sample of siliconized CRYSTAR, a siliconized silicon carbide material having about 80 volume% SiC and commercially available from Norton Electronics Worcester, Massachusetts, was obtained.

This sample was subjected to the same tests as in Example 1. The results of the analysis are reported in a similar manner. As seen in Table 1, this comparative example has in essence the same density and resistance of room temperature, and the thermal impact resistance of 300 ° C as the present invention, but has a much worse resistance to the thermal impact of 500 °. C and a lower resistance to bending of 1300 ° C.

COMPARATIVE EXAMPLE 2 A sample of porous SUPERSICR was obtained, a converted graphite silicon carbide material having about 80 volume% SiC and available on the market by Poco Graphite, Inc. of Decatur, Texas.

This sample was subjected to the same tests as Example 1. The results of the analyzes appear later in Table 1.

Resistance to the weakness of this material is evident almost in all mechanical tests. TABLE 1 Density Resistance to Impact Resistance Impact 500 ° C bending 4 fold from 4 thermal to thermal to material points at 22 ° C points at 1300 ° C 300 ° C 300 ° C (MPa) (q / cm3) (MPa) (MPa) (MPa) Example (graphite 3.04 266 221 294 269 converted silicone) Example 3.02 261 194 260 158 comparative 1 (commercial siliconised SiC material) Example 2.63 208 180 195 11 comparative 2 (non-siliconized converted graphite) TABLE 2 Material Coefficient Thermal conductivity (W / mK) expansion thermal a a a a a 22 ° C 400 ° C 800 ° C 1300 ° C Example 1 (graphite 4.6x10"6 / ° C 223 88 53 36 converted silicone) Comparative example 1 5.1x10" ß / ßC 222 80 46 31 (commercial siliconised SiC material) Comparative example 2 4.6x10"6 / ° C 172 69 42 30 (non-siliconized converted graphite)

Claims (30)

NOVELTY OF THE INVENTION CLAIMS

1. - A mixed material based on siliconized silicon carbide comprising at least about 71% by volume of converted graphite SiC matrix having open porosity, characterized in that the open porosity of the matrix is essentially filled with silicon.

2. The mixed material according to claim 1, further characterized in that it comprises at least 75% by volume of SiC.

3. The mixed material according to claim 2, further characterized in that it comprises between 75% by volume and 95% by volume of SiC.

4. The mixed material according to claim 1, further characterized in that it has a density of at least 96% theoretical density.

5. The mixed material according to claim 1, further characterized in that the SiC matrix is at least 90% by weight of beta-silicon carbide.

6. The mixed material according to claim 1, further characterized in that less than 10% by weight of the SiC matrix comprises SiC particles greater than 30 microns.

7. - The mixed material according to claim 1, further characterized in that it has a content of metallic purity not greater than 10 ppm.

8. The mixed material according to claim 1, further characterized in that the silicon is present as packages, and at least 60% of the silicon packages have a maximum length of less than 10 μm.

9. The mixed material according to claim 1, further characterized in that the silicon is present as packages, and at least 50% of the silicon packages have an area smaller than 20 μm2.

10. The wafer fabrication component for semiconductors comprising the mixed material according to claim 1.

11. The semiconductor wafer manufacturing component according to claim 10, further characterized in that it is selected from the group consisting of in a horizontal trough for wafers, a vertical support, a processing tube and a pallet.

12. The manufacturing component for semiconductor wafers according to claim 10, further characterized in that it is selected from the group consisting of a bell chamber and a wafer susceptor.

13. The method for using a component of drying oven accessories to manufacture semiconductors, comprising the steps of: a) providing a component of drying oven accessories, wherein the component comprises the mixed material according to claim 1, and b) exposing the component to a reactive gas used in the manufacture of semiconductors in an environment having a peak temperature from approximately 800 ° C to 1400 ° C.

14. The method according to claim 13, further characterized in that the component has a resistance to bending at room temperature of at least 230 MPa.

15. The method according to claim 13, further characterized in that the peak temperature is from about 1200 ° C to 1400 ° C.

16. The method according to claim 15, further characterized in that the component has a bending strength of 1300 ° C of at least 200 MPa.

17. The method according to claim 13, further characterized in that the environment is a fast ramp furnace, and the exposure includes the step to increase the ambient temperature at a speed between 40 and almost 100 ° C / minute.

18. The method according to claim 13, further characterized in that the drying oven accessories component is a bell chamber, and the exposure includes the step to increase the ambient temperature at a speed of at least about 150. ° C / minute.

19. - The method according to claim 18, further characterized in that the component has a thermal impact resistance of 500 ° C of at least 230 MPa.

20. The method according to claim 18, further characterized by comprising the exposure including the step to reduce the ambient temperature at a speed of at least 150 minutes.

21. The process for producing a silicon carbide material of high purity, resistance to thermal impact and high resistance, comprising the steps of: a) providing a SiC body of porous converted graphite having at least 71 % by volume of SiC, and b) the siliconization of the SiC body of porous converted graphite to density in full essence to produce a body of silicon carbide mixed material.

22. The process according to claim 21, further characterized in that the porous converted graphite body of step a) is obtained by the step of exposing a porous graphite body to a reactive agent in a manner sufficient to produce a body of SiC of graphite turned porous to at least 71% by volume of SiC.

23. The method according to claim 21, further characterized in that the porous graphite body has a total metal impurity content of not more than 10 ppm of total metallic impurity.

24. The process according to claim 21, further characterized in that the converted graphite SiC comprises at least 90% by weight of beta-SiC and the siliconization step is carried out at a low enough temperature to avoid substantial conversion of the beta - SiC of converted graphite and the body of the mixed material comprises at least 90% by volume of beta-SiC.

25. The method according to claim 21, further characterized in that the step of siliconizing produces a mixed material having a density of at least 96% theoretical density.

26, - The method according to claim 21, further characterized in that the SiC body of porous converted graphite comprises between 75% by volume and 95% by volume SiC.

27. The process according to claim 21, further characterized in that less than 10% by weight of the SiC matrix of the converted graphite SiC body comprises SiC grains greater than 30 microns.

28. The method according to claim 21, further characterized in that the siliconization is carried out at a temperature of at least 1600 ° C.

29. The method according to claim 21, further characterized in that the siliconization is carried out at a temperature of at least 1700 ° C.

30. The method according to claim 21, further characterized in that it comprises the step of: c) recrystallizing the SiC body from a temperature of at least 1600 ° C before the siliconization of step b).