JP5780828B2 - Wafer processing method - Google Patents

Description

  The present invention relates to a wafer having a plurality of semiconductor devices on the surface, each semiconductor device having a plurality of columnar electrodes (embedded electrodes) embedded at a predetermined depth, and processing and thinning the back surface of the semiconductor wafer. It relates to a processing method.

  In recent years, in order to achieve high integration, high density, miniaturization, and thinning of semiconductor devices, a stack of multiple semiconductor device chips such as MCP (multi-chip package) and SIP (system in package) Type semiconductor packages have been proposed.

  Such a stacked semiconductor package is formed by stacking a plurality of semiconductor device chips on a package substrate called an interposer. Generally, after interposer and semiconductor device chip electrodes, or a plurality of stacked semiconductor device chip electrodes are electrically connected with a gold wire, the semiconductor device chip is molded and sealed with resin to the interposer. Thus, a stacked semiconductor package is manufactured.

  However, this method has a problem that the package size becomes larger than the semiconductor device chip because the gold wire bonded to the electrode of the semiconductor device chip protrudes to the outer periphery of the semiconductor device chip. .

  In addition, when the mold is sealed with the resin, the wire wire is deformed to cause a disconnection or a short circuit, or the air remaining in the mold resin expands upon heating and causes damage to the semiconductor package. .

  Therefore, in the semiconductor device chip, a through electrode that penetrates the semiconductor device chip in the thickness direction and is connected to the electrode of the semiconductor device chip is provided, and the semiconductor device chips are stacked and the through electrodes are joined and electrically connected. Has been proposed (see, for example, JP-A-2005-136187).

  This method uses a wafer in which a plurality of semiconductor devices are formed on the surface of a silicon wafer, and each semiconductor device has a plurality of columnar embedded electrodes that are connected to the electrodes of the semiconductor device and extend to the back side of the silicon wafer. To do.

  A semiconductor device chip having a through electrode is manufactured in the following flow, for example. First, columnar embedded electrodes are formed from the surface of the wafer to a depth that reaches the finished thickness of the semiconductor device chip.

  Next, the back surface of the wafer in which the columnar embedded electrode is embedded is thinned to a finished thickness of the semiconductor device chip by grinding or polishing, and the end surface of the embedded electrode is exposed on the back surface of the wafer. Thereafter, by selectively etching only the wafer, the tip of the embedded electrode protrudes from the back surface of the wafer to form a through electrode.

  Next, after the back side of the wafer is coated with passivation, the passivation of the end surface portion of the through electrode (columnar electrode) is removed. Further, the wafer is divided by a cutting machine or the like to form individual semiconductor device chips.

JP 2005-136187 A

  In general, columnar electrodes contain heavy metals such as copper, so when thinning the backside of the wafer on which the columnar electrodes are formed, if the columnar electrodes are ground and polished and heavy metal cuttings adhere to the wafer, the semiconductor device is made of heavy metal. There is a risk of contamination (metal contamination).

  Therefore, after processing the back surface of the wafer until it reaches the height of the columnar electrode and thinning the wafer, the end surface of the columnar electrode is exposed from the back surface of the wafer by etching to generate heavy metal cutting waste. Can be prevented.

  However, the columnar electrode embedded in the wafer has a variation in height, and if the wafer is ground and polished to a level just before the columnar electrode, the columnar electrode may be scraped. On the other hand, if the amount of grinding or polishing is reduced, the amount to be removed by etching increases, so that there is a problem that the processing time is very long.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a wafer processing method that does not cause metal contamination of a semiconductor device by cutting waste of columnar electrodes. .

According to the present invention, a wafer processing method for processing and thinning a back surface of a wafer having a columnar electrode embedded therein, and measuring the height of the columnar electrode embedded in the wafer to measure columnar electrode height data Columnar electrode height data acquired in the measurement step, the measurement step for acquiring the wafer, the holding surface of the holding table for holding the wafer, and the processing surface of the processing means for processing the back surface of the wafer held by the holding table. And adjusting the facing state between the holding surface and the processed surface so that the distance between the back surface of the processed wafer and the end surface of the columnar electrode is substantially uniform over the entire wafer. A wafer holding step for holding the wafer on the holding table, and a wafer held on the holding table on the basis of the columnar electrode height data after performing the wafer holding step. The back surface is processed by said processing means, not exposed columnar electrodes on the back surface of the wafer, the distance between the end surface of the back surface and columnar electrodes of the wafer to thin the wafer so that the schematic uniform throughout wafer There is provided a wafer processing method characterized by comprising a wafer thinning step.

  Preferably, the wafer processing method further includes a columnar electrode exposing step of performing etching on the back surface of the wafer and exposing the end surface of the columnar electrode to the back surface of the wafer after performing the wafer thinning step.

  According to the present invention, since the wafer is thinned by processing the back surface of the wafer based on the height data of the columnar electrode embedded in the wafer, the columnar electrode is erroneously processed when the wafer is thinned to include heavy metals. Generation of cutting waste is suppressed. Therefore, the risk of metal contamination of the semiconductor device can be reduced.

  In addition, the height of the columnar electrode changes gently in the wafer plane to adjust the facing state between the processing surface of the processing means and the holding surface of the holding table based on the height data of the columnar electrode embedded in the wafer. In this case, the wafer can be thinned according to the height of the columnar electrode, and the protruding amount of the end surface of the columnar electrode can be made equal over the entire wafer.

  Furthermore, if the protruding amount of the end face of the columnar electrode can be made equal over the entire wafer, there is an advantage that it is easy to uniformly coat the passivation film in the subsequent passivation coating step.

1 is a perspective view of a polishing apparatus suitable for carrying out the wafer processing method of the present invention. It is a perspective view of a polishing unit and a polishing unit feed mechanism. It is a top view explaining the support state of a table support plate. It is a longitudinal cross-sectional view of a holding table. It is a partial cross section side view which shows the standard state of the holding surface of a holding table, and the polishing surface (processed surface) of a polishing pad. It is a surface side perspective view of a semiconductor wafer. It is a longitudinal cross-sectional view of a semiconductor wafer. FIG. 8A is a partial sectional side view showing a measurement step, and FIG. 8B is a graph showing columnar electrode height data. It is a back surface side perspective view of the semiconductor wafer by which the protective tape was stuck on the surface. It is a partial cross section side view explaining a wafer holding step. It is a partial cross section side view explaining a grinding | polishing step (processing step). It is a longitudinal cross-sectional view of the wafer after a grinding process. It is a longitudinal cross-sectional view of the wafer after an etching.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a perspective view of a polishing apparatus 2 suitable for carrying out the wafer processing method of the present invention. Reference numeral 4 denotes a housing of the polishing apparatus 2, and a column 6 is erected on the rear side of the housing 4. A pair of guide rails (only one is shown) 8 extending in the vertical direction is fixed to the column 6.

  A polishing unit (polishing means) 10 is mounted along the pair of guide rails 8 so as to be movable in the vertical direction. The polishing unit 10 is attached to a moving base 12 whose housing 20 moves in the vertical direction along a pair of guide rails 8.

  The polishing unit 10 includes a housing 20, a spindle 22 (see FIG. 5) rotatably accommodated in the housing 20, a servo motor 24 that rotationally drives the spindle 22, and a polishing pad 28 fixed to the tip of the spindle 22. A polishing wheel 26 having

  The polishing unit 10 includes a polishing unit feed mechanism 18 including a ball screw 14 and a pulse motor 16 that move the polishing unit 10 up and down along a pair of guide rails 8. When the pulse motor 16 is pulse-driven, the ball screw 14 rotates and the moving base 12 is moved in the vertical direction.

  A holding table unit 30 is disposed at an intermediate portion of the housing 4, and the holding table unit 30 is moved in the Y-axis direction by a holding table moving mechanism 44 shown in FIG. A bellows 56 covers the holding table moving mechanism.

  In the front portion of the housing 4, a first wafer cassette 58, a second wafer cassette 60, a wafer transfer robot 62, a positioning mechanism 64 having a plurality of positioning pins 66, and a wafer carry-in mechanism (loading arm) 68 are provided. A wafer unloading mechanism (unloading arm) 70 and a spinner unit 72 are disposed.

  Further, a cleaning water spray nozzle 74 for cleaning the holding table 42 is provided at the approximate center of the housing 4. The cleaning water spray nozzle 74 sprays cleaning water toward the holding table 42 in a state where the holding table 42 is positioned in the wafer loading / unloading area on the front side of the apparatus.

  Referring to FIG. 2, a perspective view of the holding table unit 30 and the holding table feed mechanism 44 is shown. The holding table unit 30 includes a support base 32, a table support plate 38 attached to the support base 32 so as to be adjustable in angle, and a holding table 42 that is rotatably arranged on the table support plate 38.

  A pair of air cylinders 34 and 36 are disposed on the support base 32 at a predetermined angle (for example, 120 degrees), and the tips 34b and 36b of the piston rods 34a and 36a of the air cylinders 34 and 36 are table support plates. 38. Reference numerals 34b and 36b act as movable support portions.

  As shown in FIG. 3, the table support plate 38 is further supported by a fixed support portion 40 that is disposed at a predetermined angle (for example, 120 degrees) away from the movable support portions 34b and 36b. With such a support structure of the table support plate 38, when the air cylinders 34 and 36 are selectively driven, the inclination angle of the table support plate 38 from the horizontal plane can be arbitrarily adjusted. Since the holding table 42 is disposed on the table support plate 38, the angle of the holding surface of the holding table 42 can be arbitrarily adjusted.

  The holding table unit 30 is moved in the front-rear direction (Y-axis direction) of the polishing apparatus 2 by the holding table moving mechanism 44. The holding table moving mechanism 44 includes a screw shaft 48 of the ball screw 46, a nut (not shown) attached to the support base 32 screwed to the screw shaft 48, and a pulse motor 50 connected to one end of the screw shaft 48. Composed.

  When the pulse motor 50 is pulse-driven, the screw shaft 48 of the ball screw 46 rotates, and the rotation direction of the pulse motor 50 is guided while the support base 32 having a nut screwed to the screw shaft 48 is guided by the pair of guide rails 52. Is moved in the Y-axis direction accordingly.

  Referring to FIG. 4, a longitudinal sectional view of the holding table 42 is shown. The holding table 42 has a frame body 76 made of SUS (stainless steel) or the like. A fitting recess 78 is formed at the upper part of the frame body 76 and a suction path 82 is formed at the center. ing. The suction path 82 is selectively connected to a vacuum suction source (not shown).

  A suction portion 80 made of porous ceramics or the like is fitted in the fitting recess 78 of the frame 76. The suction part 80 of the holding table 42 has a holding surface 80a formed in a slight mountain shape with the rotation shaft 42a of the holding table 42 as a vertex. If the radius R of the suction part 80 is 10 cm, the holding surface 80a The difference in height H between the central part and the peripheral part is about 10 to 20 μm.

  Referring to FIG. 5, the facing state between the holding surface 80a of the suction portion 80 and the polishing surface (processed surface) 28a of the polishing pad 28 during standard polishing is shown. During this standard polishing, the holding surface 80a of the suction unit 80 and the polishing surface 28a of the polishing pad 28 are maintained in parallel.

  In the state shown in FIG. 5, since the inclination angle of the holding surface 80 a of the suction unit 80 is exaggerated, the rotation shaft 42 a is depicted as being extremely inclined from the vertical direction. 42a is maintained in a substantially vertical direction.

  FIG. 6 is a perspective view of a semiconductor wafer 11 to be processed by the wafer processing method of the present invention. The semiconductor wafer 11 shown in FIG. 6 is made of, for example, a silicon wafer having a thickness of 700 μm, and a plurality of streets (division lines) 13 are formed in a lattice shape on the surface 11a. A device 15 such as an IC or LSI is formed in each partitioned area.

  The semiconductor wafer 11 configured as described above has a device region 17 in which the device 15 is formed and an outer peripheral surplus region 19 surrounding the device region 17 on its surface. A notch 21 is formed on the outer periphery of the semiconductor wafer 11 as a mark indicating the crystal orientation of the silicon wafer.

  As shown in the longitudinal sectional view of FIG. 7, a plurality of columnar electrodes 23 are embedded in the device region 17 of the semiconductor wafer 11. The columnar electrode 23 is made of heavy metal such as copper. The columnar electrode 23 embedded in the wafer 11 varies in height, and in the example shown in FIG. 7, the height of the columnar electrode 23 at the center is slightly lower than that of the columnar electrode 23 at the outer periphery. . The height variation of the columnar electrode 23 shown in FIG. 7 is an example, and there is a wafer in which the height of the columnar electrode 23 on the outer peripheral portion is lower than that of the central portion.

  In the wafer processing method of the present invention, first, a measurement step of measuring the height of the columnar electrode 23 embedded in the wafer to obtain columnar electrode height data is performed. In this measurement step, for example, as shown in FIG. 8A, the height measuring device 84 is scanned in the direction of the arrow while irradiating the back surface 11b of the wafer 11 from the height measuring device 84 with a laser beam having an IR wavelength. The columnar electrode height data as shown in FIG. 8B is obtained from the difference in intensity between the reflected light reflected from the end face of the embedded columnar electrode and the reflected light reflected from the wafer surface, and this is obtained by polishing the apparatus. The data is stored in the memory of the second controller.

  The measurement of the columnar electrode 23 is preferably carried out over the entire surface of the wafer 11. For example, only the outer peripheral portion and the central portion of the wafer 11 are measured, and the intermediate portion is interpolated with the measurement data of the outer peripheral portion and the central portion. Good.

  In a preferred embodiment of the present invention, before polishing the wafer 11 by the polishing apparatus 2, the back surface 11b of the wafer 11 is ground by a well-known grinding apparatus so that the wafer 11 has a predetermined thickness (for example, 80 μm). Thin out. Thereby, the amount of polishing by the polishing apparatus 2 shown in FIG. 1 can be reduced.

  Before carrying out such a grinding process, in order to protect the device 15 formed on the surface 11a of the wafer 11, a protective tape 25 is stuck on the surface 11a of the wafer 11 as shown in FIG.

  After the measurement step, the wafer 11 ground to a predetermined thickness is, as shown in FIG. 10, a holding surface 80a of a holding table 42 that holds the wafer 11, and a back surface 11b of the wafer held by the holding table 42. The polishing surface (processing surface) 28 of the polishing pad 28 of the polishing apparatus 2 for polishing the surface is relatively inclined based on the columnar electrode height data acquired in the measurement step, and the holding surface 80a and the polishing surface 28a are The wafer holding step of adjusting the facing state and holding the wafer 11 with the holding table 42 after adjustment is performed.

  In the present embodiment, in the measurement step shown in FIG. 8 (A), the height of the columnar electrode 23 in the central portion of the wafer 11 as shown in FIG. 8 (B) is lower than the outer circumference. Since the data is obtained, the rotation shaft 42a ′ of the holding table 42 in the standard state is rotated by a very small angle θ so that the rotation shaft 42a is slightly raised so that the central portion of the holding surface 80a is slightly higher than the standard state. adjust.

  After adjusting the facing state between the holding surface 80 a and the polishing surface 28 a in this way, the wafer 11 is sucked and held by the suction portion 80 of the holding table 42. After performing the wafer holding step, based on the columnar electrode height data as shown in FIG. 8B, the back surface 11b of the wafer 11 held by the holding table 42 is polished on the polishing pad 28 as shown in FIG. A wafer thinning step (polishing step) is performed to thin the wafer 11 so that the columnar electrode 23 is not exposed on the back surface 11b of the wafer 11 by polishing.

  In this polishing step, while the holding table 42 is rotated in the direction of arrow a, the polishing pad 28 rotating in the direction of arrow b is pressed against the back surface 11b of the wafer 11, and a well-known polishing liquid is supplied to the polishing surface 28a. carry out.

  FIG. 12 is a cross-sectional view showing a state where the wafer thinning step by polishing is completed. As is apparent from FIG. 12, the central portion of the wafer 11 is more polished than the outer peripheral portion, and the distance between the end surface 23a of the columnar electrode 23 and the wafer back surface 11b is formed substantially uniformly over the entire wafer. Yes.

  After the wafer thinning step, a columnar electrode exposure step is performed in which the back surface 11b of the wafer 11 is etched to expose the end surface 23a of the columnar electrode 23 on the back surface 11b of the wafer 11.

  A sectional view of the wafer 11 after the columnar electrode exposure step is shown in FIG. As an etching method, any method of dry etching such as plasma etching or wet etching using an etching solution may be used.

  In the above-described embodiment, the example in which the wafer processing method of the present invention is performed by the polishing apparatus 2 has been described. However, the processing means is not limited to the polishing apparatus 2, and the grinding wheel and cutting tool of the grinding apparatus are not limited. You may make it implement the wafer thinning step of this invention using the cutting tool etc. of an apparatus.

2 Polishing apparatus 10 Polishing unit 11 Semiconductor wafer 15 Device 23 Columnar electrode 28 Polishing pad 28a Polishing surface (processing surface)
42 Holding Table 80 Suction Part 80a Holding Surface 84 Height Measuring Device

Claims (3)

A wafer processing method for processing and thinning the back surface of a wafer having a columnar electrode embedded therein,
A measurement step of measuring the height of the columnar electrode embedded in the wafer to obtain columnar electrode height data;
The holding surface of the holding table holding the wafer and the processing surface of the processing means for processing the back surface of the wafer held by the holding table are relatively inclined based on the columnar electrode height data acquired in the measurement step. And adjusting the facing state between the holding surface and the processed surface so that the distance between the back surface of the processed wafer and the end surface of the columnar electrode is substantially uniform over the entire wafer, and the wafer is held by the holding table. A wafer holding step to hold,
After performing the wafer holding step, the back surface of the wafer held by the holding table is processed by the processing means based on the columnar electrode height data, and the columnar electrode is not exposed on the back surface of the wafer. A wafer thinning step for thinning the wafer so that the distance between the back surface of the columnar electrode and the end face of the columnar electrode is substantially uniform over the entire wafer;
A wafer processing method characterized by comprising:   The wafer processing method according to claim 1, wherein the processing means includes any one of a grinding wheel, a polishing pad, and a cutting tool.   3. The wafer processing method according to claim 1, further comprising a columnar electrode exposure step in which after the wafer thinning step is performed, etching is performed on a back surface of the wafer to expose an end surface of the columnar electrode on the back surface of the wafer.

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