Patent Publication Number: US-2023150885-A1

Title: Silicon carbide body with localized diamond reinforcement

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 17/248,309 filed Jan. 19, 2021. The aforementioned application is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     U.S. Pat. No. 9,469,918, issued Oct. 18, 2016, refers to a multilayer substrate which includes a diamond layer and a composite layer, where the diamond layer is grown on the composite layer, and where the composite layer includes diamond and silicon carbide (SiC), and, optionally, silicon (Si). According to U.S. Pat. No. 9,469,918, the composite layer may be formed by mixing diamond particles with SiC particles or a SiC-forming precursor. The entire disclosure of U.S. Pat. No. 9,469,918 is expressly incorporated herein by reference. 
     United States Patent Application Publication No. 2021/0002534, based on International Application No. PCT/EP2019/056457, filed Mar. 14, 2019, refers to SiC-bound hard diamond material particles. According to United States Patent Application Publication No. 2021/0002534, diamond particles may be embedded in a matrix of reaction-formed SiC. The entire disclosure of United States Patent Application Publication No. 2021/0002534 is expressly incorporated herein by reference. 
     SUMMARY 
     The present disclosure relates to a method of making a reaction-bonded silicon carbide (SiC) body, where the method includes: providing a preform including ceramic elements and carbon, wherein the preform includes one or more openings; providing a powder, wherein the powder includes diamond particles and carbon; locating the powder in the one or more surface features; and infiltrating the preform and the powder with molten silicon (Si), to form reaction-bonded (SiC) in the preform, and to form reaction-bonded SiC coatings on the diamond particles. 
     The present disclosure also relates to a reaction-bonded SiC body which includes: a main body portion and discrete elements located at least partially within the main body portion. According to one aspect of the present disclosure, the main body portion may include reaction-bonded SiC and elemental Si, but not diamond, while the discrete elements include diamond particles, reaction-bonded SiC coatings surrounding the diamond particles, and elemental Si. The present disclosure is applicable to a variety of devices, including, for example, a vacuum wafer chuck. 
     According to the present disclosure, reaction-bonded SiC parts may be provided with localized diamond reinforcement; diamond may be located where it is needed but only where it is needed, which is advantageous because, although diamond has many desirable characteristics, it may be difficult to machine (cut, grind, shape, etc.), and it may be expensive. Thus, if desired, a SiC+carbon preform may be machined to have surface features such as openings, recesses, trenches, cavities, or dimples. The surface features are at least partially filled with diamond powder. Then, the assembly is reactivity infiltrated with molten Si. The result is a dense, reaction-bonded SiC body with diamond reinforcement at only select, desirable locations. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a cross-sectional view of an example of a reaction-bonded ceramic material which does not contain diamond; 
         FIG.  2    is a cross-sectional view of a preform for a method of making the reaction-bonded ceramic material of  FIG.  1   ; 
         FIG.  3    is a cross-sectional view of an example of a reaction-bonded ceramic material which contains diamond; 
         FIG.  4    is a cross-sectional view of a preform, which may be a powder, for a method of making the reaction-bonded ceramic material of  FIG.  3   ; 
         FIG.  5    is a top view of an example of a multi-component block constructed in accordance with the present disclosure; 
         FIG.  6    is a cross-sectional view of a portion of the block of  FIG.  5   , taken along line  6 - 6 ; 
         FIG.  7    is an expanded view of a portion  7  of the cross-sectional view of  FIG.  6   ; 
         FIG.  8    is a broken-away perspective view of an example of a wafer chuck constructed in accordance with the present disclosure; 
         FIG.  9    is a perspective view of a portion of a chuck base of the wafer chuck of  FIG.  8   ; 
         FIG.  10    is a cross-sectional view of a portion of the chuck base of  FIG.  9   , taken along line  10 - 10 ; 
         FIG.  11    is a cross-sectional view of the chuck base portion of  FIG.  10    at a first stage of manufacture; 
         FIG.  12    is a cross-sectional view of the chuck base portion of  FIG.  10    at a second stage of manufacture; and 
         FIG.  13    is a cross-sectional view of the chuck base portion of  FIG.  10    at a third stage of manufacture. 
     
    
    
     The same reference numbers or other feature designators are used in the figures to designate the same or similar features. 
     DETAILED DESCRIPTION 
       FIG.  1    is a cross-sectional view of a reaction-bonded ceramic material  20  which includes ceramic particles  22 , reaction-formed silicon carbide (SiC) particles  24 , and residual elemental silicon (Si)  26 . The ceramic particles  22  may include SiC or boron carbide (B 4 C). The ceramic material  20  may be produced by performing a reactive-infiltration process on a preform  30  ( FIG.  2   ) which includes the ceramic particles  22  and elemental carbon  32 . During the infiltration process, molten Si infiltrates the preform  30  to form the reaction-formed SiC particles  24 . That is, the molten Si reacts with the carbon  32  to form additional SiC. Despite the infiltration of Si into the preform  30 , the process may result in only a small increase in volume (the increase in volume of the ceramic material  20  compared to that of the preform  30 ) that is less than one percent. The ceramic material  20  illustrated in  FIG.  1    does not contain diamond. 
       FIG.  3    is a cross-sectional view of a reaction-bonded ceramic material  40  which includes reaction-formed SiC particles  24 , residual elemental Si  26 , diamond particles  42 , reaction-formed SiC coatings  44  located on and surrounding the diamond particles  42 , and, optionally, ceramic particles  22 . The ceramic particles  22 , if desired, may include SiC or B 4 C. The ceramic material  40  may be produced by performing a reactive-infiltration process on a preform  50  ( FIG.  4   ) which may include powder, and which includes the optional ceramic particles  22 , elemental carbon  32 , and the diamond particles  42 . During the reactive-infiltration process, molten Si infiltrates the preform  50  to form the reaction-formed SiC particles  24  and the reaction-formed SiC coatings  44 . If desired, the coatings  44  may completely surround the diamond particles  42  such that the coatings  44  appear as halos surrounding the particles  42  in the cross-sectional view of  FIG.  3   . During the reactive-infiltration process, the molten Si reacts with the carbon  32  to form additional SiC, and the molten Si also reacts with surfaces of the diamond particles  42  to produce the reaction-formed SiC coatings  44 . Despite the infiltration of the molten Si into the preform  50 , the process may result in only a small increase in volume (the increase in volume of the ceramic material  40  compared to that of the preform  50 ) that is less than one percent. 
     The material  40  illustrated in  FIG.  3   , which includes a composite of reaction bonded SiC  24 ,  44 +diamond particles  42  (Si—SiC-diamond), may be considered for many high end applications, because the material  40  may have low thermal expansion, high thermal conductivity, high hardness, high wear resistance, high stiffness, and low coefficient of friction. However, the diamond particles  42  may make the material  40  extremely difficult to machine (cut, grind, and/or shape). Thus, according to the present disclosure, discrete reinforcement elements may be provided for a reaction-bonded SiC body, where the reinforcement elements include the diamond particles  42  while the body does not contain diamond. According to the present disclosure, the diamond-containing material  40  illustrated in  FIG.  3    may be located only where needed to provide desired performance. The remainder of the body may be formed of the material  20  illustrated in  FIG.  1   , which contains reaction-bonded SiC  24  but no diamond, and which is well suited to cost-effective machining. 
     Diamond has many desirable characteristics for a variety of useful applications. Such characteristics include extremely high hardness for wear resistance, very low coefficient of friction for sliding applications, very high stiffness (Young&#39;s modulus) for structural applications, and extreme thermal stability (high thermal conductivity and low coefficient of thermal expansion (CFE)). Tables 1 through 3 list desirable characteristics of diamond compared to other materials: 
     
       
         
           
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                   
                 Young’s 
                   
                 Thermal 
               
               
                   
                   
                 Density  
                 Modulus  
                 CTE  
                 Conductivity 
               
               
                   
                 Material 
                 (g/cc) 
                 (GPa) 
                 (ppm/K) 
                 (W/mK) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Al (6061) 
                 2.7 
                 70 
                 23 
                 172 
               
               
                   
                 Steel (17-4PH 
                 7.8 
                 196 
                 11 
                 18 
               
               
                   
                 SS) 
                   
                   
                   
                   
               
               
                   
                 SiC (Sintered) 
                 3.1 
                 410 
                 3 
                 125 
               
               
                   
                 Diamond 
                 3.5 
                 1220 
                 1 
                 2200 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Material 
                 Coefficient of Friction 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Teflon 
                 0.05 
               
               
                   
                 Diamond 
                 0.1 
               
               
                   
                 Glass 
                 0.5-0.7 
               
               
                   
                 SiC 
                 0.55-0.85 
               
               
                   
                 Steel 
                 0.8 
               
               
                   
                 Aluminum 
                 1.0-1.4 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 Hardness Comparison (Knoop) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 SiSiC 
                 1100 kg/mm 2   
               
               
                   
                 RB-B 4 C 
                 1700 kg/mm 2   
               
               
                   
                 Sp3 Diamond 
                 2300 kg/mm 2   
               
               
                   
                 Diamond-Like-Carbon (DLC) 
                 ~950-1200 kg/mm 2   
               
               
                   
                   
               
            
           
         
       
     
       FIG.  5    is a top view of an example of a multi-component block  100  constructed in accordance with the present disclosure. The illustrated block  100  includes a body  102  (an example of a main body portion) formed of the SiC-containing material  20  illustrated in  FIG.  1   , and discrete, spaced-apart features  104  formed of the diamond-containing material  40  illustrated in  FIG.  3   . The features  104  may be located in corresponding trenches  106  (examples of surface features,  FIG.  6   ) that are laser machined into the top surface  108  of the SiC-containing body  102 . In the illustrated example, each feature  104  may have a width Win a range of from 0.5 mm to 3.0 mm, preferably about 1.2 mm, and a depth D in a range of from 100 μm to 600 μm, preferably about 300 μm, and the trenches  106  may be at least partially filled with a suitable amount, such as nominally 65 μm, of diamond powder. The present disclosure should not be limited, however, to the details of the examples described herein. 
     Then, after the trenches  106  are filled with diamond powder, molten Si is simultaneously infiltrated into the body  102  and the trenches  106  to create the material  20  illustrated in  FIG.  1   , with reaction-bonded SiC  24  ( FIG.  7   ), in the body  102 , and to create the diamond-containing material  40  within the trenches  106  (and only in the trenches  106 ). As a result, the multi-component block  100  can use the discrete features  104  to provide the high performance characteristics associated with the diamond-containing material  40  only where desired, while the remainder of the block  100  (that is, the body  102 ) contains reaction-formed SiC but no diamond and therefore may be more easily machined. 
     In other words, the illustrated multi-component block  100  may have hard, thermally-conductive diamond-reinforced composite material  40  where needed (and only where needed), and reaction-bonded SiC  20  (without diamond) in other areas for ease of machining. The body  102  and the features  104  illustrated in  FIG.  5    represent one example of a wide variety of applications where local diamond-containing reinforcement may have value, such as where very hard, low-friction material is desired only at a particular location of a component where wear would otherwise occur, or to provide thermally stable, very high thermal conductivity pathways only where heat sinking and/or heat spreading are required, or to provide very stiff (i.e., high Young&#39;s modulus) regions only where low mechanical deflection is desired. 
     In the illustrated example, the reactions that occur in the trenches  106 , which involve Si+diamond, are different from the reactions that occur simultaneously elsewhere in the body  102 , which involve Si+carbon but no diamond. As a result, the residual elemental Si content in the diamond-reinforced region (within the trenches  106 ) is lower than in the rest of the block  100 . For example, the residual elemental Si in the diamond-reinforced region within the trenches  106  may be about 6.8% while the residual Si in the Si—SiC (and no diamond) region may be about 23.2%. 
     The lower residual Si content in the diamond-reinforced region may yield improved properties (hardness, stiffness, inertness, etc.), but the combination of diamond particles and low elemental Si content may make machining especially difficult, such that it may be especially advantageous to locate the diamond-containing features  104  only where needed. However, avoiding difficult machining is only one of many reasons why localizing diamond-containing features is advantageous. Another advantage of providing diamond reinforcement only where it can be put to effective use is reduced cost. In other words, it is advantageous to use high-cost diamond powder only where it is needed. 
       FIG.  8    shows an example of a semiconductor wafer chuck  200 , with diamond-reinforced pins  202 , for supporting a semiconductor (e.g., silicon) wafer  204 . The illustrated wafer chuck  200  has a chuck base  206  (an example of a main body portion). Holes  208  are formed through the chuck base  206  to provide paths for vacuum exhaust and for supporting one or more lift pins  210 . The chuck base  206  and the pins  202  may have a number of desirable characteristics for holding the wafer  204  during processing. Such characteristics include low density to allow fast motion, high stiffness for stability, low coefficient of thermal expansion for stability, high thermal conductivity to prevent distortion, high wear resistance (hardness) to maintain precision, and low coefficient of friction to prevent optical contact bonding between the wafer  204  and top surfaces  212  ( FIGS.  9  and  10   ) of the pins  202 , and the diamond-containing material  40  illustrated in  FIG.  3    may have all such characteristics. Thus, in the illustrated example, the pins  202  ( FIG.  10   ) may be formed of the diamond-containing material  40  illustrated in  FIG.  3   . Other portions of the chuck base  206 , including ring seals  214 , lift pin holes ( 210 ), mounting features, etc., may require machining and therefore may be formed of the easier-to-machine material  20  illustrated in  FIG.  1   . 
     Moreover, although the body  206  has a continuous region formed of monolithic reaction bonded SiC, the discrete (that is, separated) positioning of the diamond-reinforced pins  202  should prevent bi-metallic strip non-uniformity. In other words, an advantageous feature of providing localized diamond-containing elements according to the present disclosure is that bi-metallic strip stresses can be prevented. 
     A method of making the reaction-bonded SiC body  206  ( FIG.  10   ) with the diamond-reinforced, wafer-contacting pins  202  is illustrated in  FIGS.  11 - 13   . As illustrated in  FIG.  11   , openings  300  (examples of surface features), such as dimples, recesses, or cavities, are machined by a suitable process, for example, laser machined, into a preform  302  made of the SiC+carbon material  30  illustrated in  FIG.  2   . The openings  300  within the body  206  may be, for example, in the range of from 0.5 mm to 3 mm, preferably about 1 mm, in diameter, and in the range of from 200 μm to 700 μm, preferably about 500 μm, deep. The preform  302  may have, for example, a diameter that is suitable for use in connection with wafer-handling equipment, such as, for example, a diameter of about 100 mm. The present disclosure should not be limited, however, to the details of the examples described herein. 
     The openings  300  are then filled with a suitable amount, for example, about 30 μm, of powder  304  which contains diamond particles  42 , and then the entire assembly (the dimpled preform  302  and the powder  304  within the dimples  300 ) is subjected to a reaction bonding process, that is, infiltrated with molten Si. The reaction bonding process converts the material of the preform  302  to the material  20  illustrated in  FIG.  1    and converts the diamond-containing powder  304  to the material  40  illustrated in  FIG.  3   . 
     Referring now to  FIG.  12   , a layer  306  is then removed by simple surface grinding to produce a common top surface  308  for the reaction-bonded SiC material  20  and the diamond containing material  40 , to thereby produce diamond-reinforced pads  310  co-planar with the common top surface  308 . 
     Referring now to  FIG.  13   , valleys  312  may then be removed from the reaction-bonded SiC material  20  and the diamond containing material  40  by suitable laser-machining such that the pins  202  stand proud above the lowered top surface  314  of the chuck base  206 . The diameters of the diamond-containing pins  202  may be, for example, in the range of from 200 um to 800 um, preferably about 400 um. The heights of the pins  202  may likewise be in the range of from 200 um to 800 um, preferably about 400 um, but these are just examples of how the present disclosure may be implemented. As noted above, the present disclosure should not be limited to the details of the examples described herein. 
     The present disclosure may be applicable to a variety of semiconductor wafer handling components, including vacuum wafer chucks, electrostatic chucks, wafer arms/end effectors, and susceptors. The present disclosure may also be applicable to a variety of other applications, especially where low wear, low friction, high mechanical stiffness, and/or extreme thermal stability in local areas is/are desired, including optics and optical mounts, thermal management/heat sink devices, high energy laser (HEL) components, bearing seals, cylinder liners, gun barrels, lapping/grinding substrates, and artificial joints (hips, knees, etc.). 
     The present disclosure is applicable to a reaction-bonded SiC vacuum wafer chuck with standing-proud diamond-reinforced pins for wafer contact (to provide high wear resistance and stiffness, low friction, and high purity) while all areas requiring machining are free of diamond for ease of manufacture. The present disclosure is not limited, however, to the devices and processes described herein. The present disclosure may also be applicable to a reaction-bonded SiC heat sink with local areas of diamond reinforcement only at locations (e.g., directly under a die) where high heat flux is desired to maximize performance, while the rest of the device does not contain diamond so as to be more easily machinable during a manufacturing process. Moreover, the present disclosure may be applicable to a reaction-bonded SiC lapping/grinding plate with local diamond reinforcement at a wear face, where the reinforcing elements are in the form of discrete buttons (or other shapes) while other portions of the device are free of diamond for ease of machining. 
     What have been described above are examples. This disclosure is intended to embrace alterations, modifications, and variations to the subject matter described herein that fall within the scope of this application, including the appended claims. As used herein, the term “includes” means including but not limited to. The term “based on” means based at least in part on. Additionally, where the disclosure or claims recite “a,” “an,” “a first,” or “another” element, or the equivalent thereof, it should be interpreted to include one or more than one such element, neither requiring nor excluding two or more such elements. 
     What is claimed as new and desired to be protected by Letters Patent of the United States is: