Abstract:
The present invention provides a grinding apparatus for semiconductor wafers for preventing the silicon powder generated from the wafer grinding process and mixed with cooling water from contaminating height gauges of the grinding apparatus because the silicon powder is scattered toward them, and for preventing wear-down of the contact heads of the height gauges due to the abrasion with a wafer to be fixed on a spin-chuck and the spin-chuck. The grinding apparatus for semiconductor wafers includes a spin-chuck for fixing a wafer to be ground and rotating the wafer; a grinder for grinding the wafer fixed on the spin-chuck by rotating and contacting the wafer over the upper side of the spin-chuck; a first cooling water supply for supplying cooling water between the surface of the wafer to be ground and the grinder; a first height gauge for measuring the vertical distance from a certain standard point to the upper surface of the wafer by using an electric signal generated according to the movement ranges of a contact head which is placed to contact of the wafer fixed on the spin-chuck; and a cover for covering the top and side of the first height gauge so as to protect the first height gauge.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a grinding apparatus for semiconductor wafers, and more particularly, to a grinding apparatus for grinding semiconductor wafers while measuring the thickness of the wafers using a height gauge. 
     2. Description of the Related Art 
     In semiconductor device fabrication, a plurality of chips are formed on the wafer by carrying out various processing steps using a deposition facility, a diffusion facility, and an etching facility, etc. The wafer having a plurality of chips formed thereon is moved to an Electrical Die Sorting (EDS) facility for the EDS process, wherein the chips on the wafer go through a test to determine whether the chips are normal or abnormal, and abnormal chips are repaired. 
     In addition, the wafers after completing the EDS process, are moved to a back-grinding apparatus and a back-grinding process is carried out so as to grind the back side of the wafer to a certain thickness. 
     FIG. 1 is a plan view schematically showing a conventional back-grinding apparatus to grind the back side of the wafer, FIG. 2 is a schematic representation showing the configurations of a first height gauge, a second height gauge, a grinder, and a cooling water supply installed on the rough-grinding region and the fine-grinding region on the table depicted in FIG. 1, and FIG. 3 shows the height gauge shown in FIG.  1 . 
     The conventional grinding apparatus for semiconductor wafers includes a round table  10 , which is able to rotate 90° in any one direction. The table  10  is divided into a pie-shaped loading region  12 , a rough-grinding region  14 , a fine-grinding region  16 , and a unloading region  18 . On each region  12 ,  14 ,  16 ,  18  on the table  10 , there is a spin-chuck  20  to suction-fix a wafer  2  and be rotated at a certain speed. On the upper surface of the spin-chuck  20 , there are formed a plurality of vacuum holes (not shown), and through the plurality of vacuum holes, the air around the spin-chuck  20  is pumped inside the spin-chuck  20  so that the wafer  2  is suction-fixed on the spin-chuck  20 . 
     In addition, as shown in FIG. 2, on the upper side of the spin-chuck  20  provided on the rough-grinding region  14  and the fine-grinding region  16  on the table  10 , there is provided a grinder  30 , which contacts the wafer  2  being suction-fixed on the spin-chuck  20 , rotates, and grinds the wafer  2 . On the lower side of the grinder  30 , there is provided a diamond disk  32 . In addition, on one side of the grinder  30 , there is provided a cooling water supply  34  to supply cooling water between the wafer  2  and the diamond disk  32  of the grinder  30 . 
     Around the rough-grinding region  14  and the fine-grinding region  16  of the table  10 , there are provided a first height-gauge  4  and a second height-gauge  6 . The first height-gauge  4  measures a vertical distance (now referred to as a first vertical distance) from a standard point (not shown) under the spin-chuck  20  to the upper surface of the wafer  2  by locating a contact head  46  on the wafer  2  fixed on the spin-chuck  20 , and the second height gauge  6  measures a vertical distance (now referred to as a second vertical distance) from the standard point to the upper surface of the spin-chuck  20  by locating the contact head  46  on the spin-chuck  20 . As shown in FIG. 3, there is provided a cube-shaped bed  40  on the first height-gauge  4  and the second height-gauge  6 . 
     A certain amount of oil (not shown) is contained inside the bed  40  in order to maintain the inner temperature of the bed  40  at a specific degree, and prevent the corrosion of the inside of the bed  40 . There is provided a piston  42  on the lower side of the bed  40 , and there is provided a finger  44  on the end of the piston with the contact head  46  fixed thereon so as to move up and down. In addition, on the connection point of the piston  42  and the finger  44 , there is provided a first connection body  48 , which is able to move up and down according to the up/down movement of the finger  44 . The first connection body  48  and a differential transformer  54  inside the bed  40  are connected by a second connection body  50 , and so, up/down movement of the first connection body  48  is transmitted to the differential transformer  54  through the second connection body  50 . The first connection body  48  is connected with the second connection body  50  through a through hole (not shown) formed in a rubber piece  52  provided on the side wall of the bed  40 . The differential transformer  54  outputs an electrical signal according to the movement of the second connection body  50  connected with the first connection body  48  to the outside so as to measure the vertical distance from the standard point to the end of the contact head  46 . As described above, the height gauges  4 ,  6  are well-known to those skilled in the art, and commercially widespread. 
     The wafer  2  is mounted on spin-chuck  20  installed on the loading region  12  of the table  10  by a transfer means with its upper side turned down, the air around the spin-chuck  20  is pumped to the inside of the spin-chuck  20  through the vacuum holes formed on the upper surface of the spin-chuck  20 , and the wafer  2  is suction-fixed on the spin-chuck  20 . 
     Then, with the table  10  rotating 90° in one direction, the wafer  2  on the loading region  12  of the table  10  is moved to the rough-grinding region  14  of the table  10 . Then, the contact head  46  of the first height gauge  4  is placed on the wafer  2  of the rough-grinding region  14 , and the contact head  46  of the second height gauge  6  is placed on the spin-chuck  20  of the rough-grinding region  14 . 
     Therefore, each finger  44  of the first height gauge  4  and the second height gauge  6  is moved up and down, and with the up/down movement of the finger  44 , the first connection body  48  and the second connection body  50  are moved. With the movement of the second connection body  50 , each differential transformer  54  inside the bed  40  of the first height gauge  4  and the second height gauge  6  outputs an electrical signal according to the movement of the second connection body  50  to the outside. 
     Accordingly, the first vertical distance and the second vertical distance are measured, and the wafer thickness is measured by obtaining the difference between the first vertical distance and the second vertical distance. 
     Then, the grinder  30  is moved down such that the wafer  2  fixed on the spin-chuck  20  of the rough-grinding region  14  of the table  10 , and the diamond disk  32  of the grinder  30 , are brought into contact. 
     Then, the back side of the wafer  2  is ground according to the rotation of the grinder  30  and the spin-chuck  20 , and while the grinding process goes on, the cooling water supply  34  supplies cooling water between the wafer  2  and the diamond disk  32  of the grinder  30  thereby preventing overheating due to the abrasion between the wafer  2  and the diamond disk  32 , and cleaning the silicon powder generated grinding the wafer. 
     During the grinding process, the first height gauge  4  and the second gauge  6  continuously measure the thickness of the wafer  2 , and if the wafer is ground down to a desired thickness set by the thickness measurement, the spin-chuck  20  and the grinder  30  stop their rotation. 
     Then, while the table  10  rotates 90° in one direction, the wafer  2  on the rough-grinding region  14  of the table  10  is moved to the fine-grinding region  16 , and the grinding process is carried out in the fine-grinding region  16  in the same manner as in the rough-grinding region  14 , i.e., the thickness of the wafer  2  is measured using the first height gauge  4  and the second height gauge  6  around the fine-grinding region  16 , and the back side of the wafer  2  is precisely fine-ground to a certain thickness using another grinder on the upper side of the fine-grinding region  16 . 
     While the wafer  2  is fine-ground in the fine-grinding region  16  of the table  10 , the cooling water supply  34  on one side of the grinder supplies cooling water between the wafer  2  and the diamond disk of the grinder thereby preventing the overheating due to the abrasion of the wafer  2  and the diamond disk  32 , and cleaning the silicon powder generated during the grinding of the wafer. 
     Finally, with the table  10  rotating 90° in one direction, the wafer  2  of the fine-grinding region  16  of the table  10  is moved to an unloading region  18  of the table  10 , and the wafer  2  in the unloading region  18  is put in a cassette by a transfer means. In addition, as described above, while the table  10  rotates at every rotation by 90°, a new wafer  2  to be ground is loaded in the loading region  12 , and the grinding process continuously goes on. 
     The silicon powder as material of the wafer  2 , which is generated during grinding the back side of the wafer  2  using the grinder  30 , is mixed with cooling water supplied from the cooling water supply  34 , and is scattered to the height gauges  4 , 6  by centrifugal force due to the rotation of the grinder  30  and the spin-chuck  20 . If the silicon powder mixed with the cooling water is scattered to the rubber  52  of the height gauges  4 , 6 , the silicon powder is hardened with the passage of time, and it is introduced into the bed  40  through the through hole of the rubber  52  thereby contaminating the oil inside the bed  40 . As a result, the inner temperature of the bed  40  is changed due to the contamination of the oil, and the height gauges  4 , 6  often malfunctions. Also, corrosion occurs inside the bed  40 . In addition, if the silicon powder is scattered to the contact head  46  of the height gauges  4 , 6 , the silicon powder mixed with the cooling water is hardened with the passage of time, to form a lump of the silicon powder having a certain thickness on the end of the contact head  46 . Due to the lump of the silicon powder, the reliability of the resulting value of the thickness of the wafer  2  using the height gauges  4 , 6  is deteriorated. 
     In addition, even if cooling water is supplied between the wafer  2  and the diamond disk  32  of the grinder  30 , the cooling water is not supplied between the wafer  2  or the spin-chuck  20  and the contact head  46  of the height gauges  4 , 6  thereby generating heat due to the abrasion of the contact head  46  of the height gauges  4 , 6  and easily causing wear-down. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to provide a grinding apparatus for semiconductor wafers for preventing the silicon powder generated from the wafer grinding process and mixed with cooling water from contaminating height gauges of the grinding apparatus because the silicon powder is scattered toward them. 
     Another object of the present invention is to provide a grinding apparatus for semiconductor wafers for preventing wear-down of the contact measures of the height gauges due to the abrasion with a wafer to be fixed on a spin-chuck, and with the spin-chuck. 
     To achieve these and other advantages and in accordance with the present invention, the grinding apparatus for semiconductor wafers comprises a spin-chuck for fixing a wafer to be ground and rotating the wafer; a grinder for grinding the wafer fixed on the spin-chuck by contacting with the wafer over the upper side of the spin-chuck, and rotating; a first cooling water supply for supplying cooling water between the surface of the wafer to be ground and the grinder; a first height gauge for measuring the vertical distance from a certain standard point to the upper surface of the wafer by using an electric signal generated according to the movement ranges of a contact head which is placed to contact the upper surface of the wafer fixed on the spin-chuck; and a first cover for covering the top and sides of the first height gauge so as to protect the first height gauge. 
     The grinding apparatus for semiconductor wafers further comprises a second cooling water supply for supplying cooling water between the contact head of the first height gauge and the surface of the wafer. The second cooling water supply has a cooling water supply line and a nozzle connected with the end of the cooling water supply line, and the second cooling water supply is provided inside the first cover. 
     The grinding apparatus for semiconductor wafers further comprises a second height gauge for measuring the vertical distance from a certain standard point to the upper surface of the spin-chuck by using an electric signal generated according to the movement ranges of the contact head which is placed to contact the upper surface of the spin-chuck; and a second cover for covering the top and sides of the second height gauge so as to protect the second height gauge. The grinding apparatus for semiconductor wafers may further comprise a third cooling water supply having a cooling water supply line and a nozzle connected with the end of the cooling water supply line for supplying cooling water between the contact head of the second height gauge and the upper surface of the spin-chuck. The third cooling water supply may be provided inside the second cover. 
     In addition, the first and the second covers covering the first height gauge and the second height gauge are preferably made of transparent plastic material, such as an acrylic acid resin, etc. 
     The first and the second covers covering the first height gauge and the second height gauge are detachably installed in the first height gauge, and the second height gauge respectively. 
     According to another aspect of the present invention, a grinding apparatus for semiconductor wafers comprises a table which is round and rotatable over a certain angle, and divided into a loading region for loading a wafer to be ground, an unloading region for unloading a ground wafer, and a plurality of process regions for carrying out the grinding process; a plurality of spin-chucks, each of which provided in the loading region, the unloading region, and the process regions, for fixing and rotating the wafer; a plurality of rotating grinders for grinding the wafers by contacting the wafers fixed on the spin-chucks installed in the process regions of the table; and a first cooling water supply for supplying cooling water between the wafer and the grinders; a first height gauge for measuring the vertical distance from a certain standard point to the upper surface of the wafer by using an electric signal generated according to the movement ranges of the contact head which is placed to contact the upper surface of the wafer fixed on the spin-chuck on the process region of the table; a second height gauge for measuring the vertical distance from a certain standard point to the upper surface of the spin-chuck by using an electric signal generated according to the movement ranges of the contact head which is placed to contact the upper surface of the spin-chuck provided on the process region of the table; a first cover covering the top and sides of the first height gauge for protecting the first height gauge; and a second cover covering the top and sides of the second height gauge for protecting the second height gauge. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
     FIG. 1 is a plan view schematically showing a conventional grinding apparatus to grind the back side of the wafer; 
     FIG. 2 is a schematic representation showing the configurations of a first height gauge, a second height gauge, a grinder, and a cooling water supply installed on the rough-grinding region and the fine-grinding region on the table depicted in FIG. 1; 
     FIG. 3 shows the height gauge shown in FIG. 1; 
     FIG. 4 is a plan view schematically showing a grinding apparatus to grind the back side of the wafer according to the present invention; 
     FIG. 5 is a schematic representation showing the configurations of the grinding apparatus of the semiconductor wafers depicted in FIG. 4 according to one embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, detailed descriptions of preferred embodiments of the present invention will be described with reference to the accompanying drawings; however the scope of the invention is not limited to the embodiments set forth herein. 
     FIG. 4 is a plan view schematically showing a grinding apparatus to grind the back side of the wafer according to the present invention, and FIG. 5 is a schematic representation showing the configurations of the grinding apparatus of the semiconductor wafers depicted in FIG. 4 according to one embodiment of the present invention. Like numbers refer to like elements shown in the FIGS. 1 and 2. 
     As shown in FIG. 4, the grinding apparatus for semiconductor wafers according to the present invention comprises a round-shaped indexing table  10  which is able at a time in rotate 90° to one direction. The table  10  is divided into a loading region  12  for loading a wafer  2  to be ground, a rough-grinding region  14  for rough-grinding the loaded wafer  2 , a fine-grinding region  16  for precisely grinding the rough-ground wafer to a certain thickness, and an unloading region  18  for unloading the ground wafer  2  to a certain location. On each region  12 , 14 , 16 , 18  on the table  10 , there is a rotary chuck referred to as a spin-chuck  20  to suction-fix a wafer  2  and be rotated at a certain speed. On the upper surface of the spin-chuck  20 , there are formed a plurality of vacuum holes (not shown), and through the plurality of vacuum holes, the air around the spin-chuck  20  is pumped inside the spin-chuck  20  so that the wafer  2  is suction-fixed on the spin-chuck  20 . 
     In addition, as shown in FIG. 2, there is provided a grinder  30  on the upper side of the spin-chuck  20  provided on the rough-grinding region  14  and the fine-grinding region  16  on the table  10 , and the grinder  30  contacts with the wafer  2  being suction-fixed on the spin-chuck  20 , rotates, and grinds the wafer  2 . On the lower side of the grinder  30 , there is provided a diamond disk  32  having diamonds of a certain size spaced a certain distance apart from each other attached thereon. In addition, on one side of the grinder  30 , there is provided a cooling water supply  34  to supply cooling water such as deionized water between the wafer  2  and the diamond disk  32  of the grinder  30 . 
     There is provided a first height gauge  4  on the rough-grinding region  14  and the fine-grinding region  16  of the table  10 , the first height gauge  4  measuring a vertical distance (now referred to as a first vertical distance) from a standard point (not shown) on the lower side of the spin-chuck  20  to the upper surface of the wafer  2 . 
     There is provided a second height gauge  6  on the rough-grinding region  14  and the fine-grinding region  16  of the table  10 , the second height gauge  6  measuring a vertical distance (now referred to as a second vertical distance) from a standard point (not shown) to the upper side surface of the spin-chuck  20 . According one manufacturing variation, only the first height gauge  4  is installed on the rough-grinding region  14  and the fine-grinding region  16 , respectively, and the thickness of the wafer  2  can be achieved by subtracting a second vertical distance measured by many methods from the first vertical distance measured by the first height gauge  4  so as to carry out the grinding process. As shown in FIG. 5, the height gauges  4 , 6  each include a rectangular oil housing or bed  40 . 
     That is, a certain amount of oil (not shown) is contained inside the bed  40  in order to maintain the interior of the bed  40  at a specific temperature, and to prevent the corrosion of the inside of the bed  40 . There is provided a piston  42  on the lower side of the bed  40 , and there is provided a finger  44  having the contact head  46  fixed thereon on the end of the piston  42  so as to move up and down. In addition, on the connection point of the piston  42  and the finger  44 , there is provided a first connection body  48 , which is able to move up and down according to the up/down movement of the finger  44 . The first connection body  48  and a differential transformer  54  are connected by a second connection body  50 , and so, up/down movement of the first connection body  48  is transmitted to the differential transformer  54  through the second connection body  50 . The first connection body  48  is connected with the second connection body  50  through a through hole (not shown) formed on a rubber piece  52  provided on the side wall of the bed  40 . The differential transformer  54  outputs an electrical signal according to the movement of the second connection body  50  connected with the first connection body  48  to the outside so as to measure the first vertical length or the second vertical length. As described above, the height gauges  4 , 6  are well-known to those skilled in the art, and commercially widespread. 
     There is provided a cover  60  for covering the top and sides of the first height gauge  4  and the second height gauge  6 , respectively, for preventing the first height gauge  4  and the second height gauge  6  from being contaminated. The cover  60  is detachably installed from the first height gauge  4  and the second height gauge  6 , and the cover  60  is made of transparent plastic material such as acrylic acid resin, etc. 
     In addition, there is provided a cooling water supply line  62  inside the cover  60  of the first height gauge  4  with a nozzle  64  on its end for supplying cooling water such as deionized water between the wafer  2  and the contact head  46 , and there is also provided a cooling water supply line  62  inside the cover  60  of the second height gauge  6  with a nozzle  64  on its end for supplying cooling water between the spin-chuck  20  and the contact head  46 . According to one manufacturing variation, the cooling water supply line  62  having a nozzle  64  on its end may be installed outside the cover  60  of the first height gauge  4  and the second height gauge  6 . 
     Accordingly, if the wafer  2  is mounted with its front side turned down on the spin-chuck  20  of the loading region  12  of the table  10  by transfer means, the air around the spin-chuck  20  is pumped inside the spin-chuck  20  through the vacuum hole, and the wafer  2  is suction-fixed on the spin-chuck  20 . 
     Then, with the table  10  rotated 90° in one direction, the wafer  2  on the loading region  12  of the table  10  is moved to the rough-grinding region  14  of the table  10 . Then, the contact head  46  of the first height gauge  4  is placed on the wafer  2  on the rough-grinding region  14 , and the contact head  46  of the second height gauge  6  is placed on the spin-chuck  20  on the rough-grinding region  14 . Then, each finger  44  of the height gauges  4 , 6  move up and down, and with the movement of the finger  44 , the first connection body  48  and the second connection body  50  move. With the movement of the second connection body  50 , the differential transformer  54  inside the bed  40  outputs an electrical signal according to the movement of the second connection body  50  outside. 
     Accordingly, the first vertical distance and the second vertical distance are measured, and by subtracting the second vertical distance from the first vertical distance, the thickness of the wafer can be obtained. 
     Then, the grinder  30  on the upper side of the rough-grinding region  14  of the table  10  is moved down, and contacts the wafer  2  fixed on the spin-chuck  20 . Then, with the grinder  30  and the spin-chuck  20  rotated at high speed, the back side of the wafer  2  is ground. While the grinding process goes on, the first height gauge  4  and the second height gauge  6  continuously measure the thickness of the wafer  2 . When the wafer  2  is ground to a desired thickness, the spin-chuck  20  and the grinder  30  stop their rotation. While the grinding process is performed on the rough-grinding region  14 , cooling water is supplied between the wafer  2  and the diamond disk  32  of the grinder  30  from the cooling water supply  34  on one side of the grinder  30  a thereby preventing the abrasion of the wafer  2  and the diamond disk  32 . With the cover  60  on the first height gauge  4  and the second height gauge  6 , the rubber piece  52  of the height gauges  4 , 6  and the contact head  46  can be protected from the silicon powder which is generated from the grinding of the wafer  2 , and scattered toward the height gauges  4 , 6 . 
     In addition, by manufacturing the cover  60  with transparent plastic material such as acrylic resin, etc., the operators can detect the contamination on the surface of the height gauges  4 , 6  easily, and the cover  60  can be easily replaced with a new one by manufacturing it detachably from the height gauges  4 , 6 . 
     In addition, by supplying cooling water between the wafer  2  and the first height gauge  4 , and between the spin-chuck  20  and the second height gauge  6 , the wear-down due to the abrasion of the contact head  46  of the height gauges  4 , 6  and the wafer  2 , or the spin-chuck  20 , can be prevented. 
     Continuously, with the table  10  rotated at 90° in one direction, the wafer  2  of the rough-grinding region  14  of the table  10  is moved to a fine-grinding region  16  of the table  10 , and the fine-grinding process is performed for the rough-ground wafer  2  in the same manner as in the rough-grinding process using the first height gauge  4 , and the second height gauge  6 , and measuring the thickness of the wafer  2 , and using the grinder  30  so that the back side of the wafer  2  is precisely fine-ground until reaching a certain thickness. While the fine-grinding process is performed on the fine-grinding region  16  of the table  10 , the cooling water supply  34  on one side of the grinder  30  supplies cooling water between the wafer  2  and the diamond disk  32  of the grinder  30 , thereby preventing abrasion of the wafer  2  and the diamond disk  32  by their rotation, and cleaning the silicon powder generated from the grinding of the wafer  2 . 
     In addition, with a cover  60  provided on the height gauges  4 , 6  around the fine-grinding region  16  like the cover  60  provided on the height gauges  4 , 6  around the rough-grinding region  14 , the contamination of the rubber piece  52  of the height gauges  4 , 6  and the contact head  46 , due to the silicon powder which is generated from the grinding of the wafer  2  and scattered mixed with cooling water, can be prevented. 
     In addition, by supplying cooling water between the wafer  2  of the fine-grinding region  16  of the table and the contact head  46  of the first height gauge  4 , and between the spin-chuck  20  of the fine-grinding region  16  and the contact head  46  of the second height gauge  6 , wear-down of the contact head  46  of the height gauges  4 , 6  and the spin-chuck  20  due to the abrasion of their rotation can be prevented. 
     Then, with the table  10  rotated 90° in one direction, the wafer  2  of the fine-grinding region  16  of the table  10  can be moved to the unloading region  18  of the table  10 , and the wafer  2  on the unloading region  18  of the table  10  is moved to a cassette by a transfer means. While the table  10  is rotated by 90°, a new wafer  2  to be ground is loaded on the loading region  12  of the table  10 , and the grinding process continuously goes on. 
     Therefore, according to the present invention, the contamination of the height gauges by the silicon powder mixed with cooling water is prevented, and also, the corrosion inside the bed due to the contamination of the oil inside the bed by the silicon powder introduced into the bed is prevented by providing a cover on the height gauges. 
     In addition, formation of the lump on the end of the contact head, due to the silicon powder attached/hardened on the contact head, is prevented thereby improving the reliability of the resulting value for the thickness of the wafer. 
     In addition, wear-down of the contact head is prevented by supplying cooling water around the contact head of the height gauges. 
     It will be apparent to those skilled in the art that various modifications and variations of the present invention can be made without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.