JP4913484B2 - Semiconductor wafer polishing method - Google Patents

Description

  The present invention relates to a method of polishing a back surface on which a semiconductor wafer device such as a silicon wafer is not formed, and more particularly to a method of polishing a back surface of a semiconductor wafer whose back side is ground into a concave cross section.

  Semiconductor chips used in various electronic devices generally have a rectangular rectangular area defined by lines to be divided on the surface of a disk-shaped semiconductor wafer, and an electronic circuit such as an IC or LSI is formed on the surface of these areas. Then, it is manufactured by a method in which the back surface is ground and thinned, and is divided along a division line. Thinning processing by backside grinding is usually a method in which the backside to be ground is exposed and held on a vacuum chuck type chuck table, and the semiconductor wafer is sucked and held and pressed against the backside of the semiconductor wafer while rotating the grinding wheel for grinding. It is done in

  By the way, downsizing and thinning of electronic devices in recent years are remarkable, and accordingly, a semiconductor chip is required to be thinner, which means that it is necessary to make the semiconductor wafer thinner than before. However, when the semiconductor wafer is thinned, the rigidity is lowered, so that there is a problem that handling in the process after the thinning becomes difficult or breaks easily.

  Therefore, only the circular device region on which the semiconductor chip is formed is ground and thinned from the back surface side, and the peripheral outer peripheral region around it forms an annular protrusion that protrudes to the back surface side leaving the original thickness. Then, the entire wafer is processed into a concave cross section with the back side recessed (see Patent Documents 1 and 2, etc.). Such a semiconductor wafer is easy to handle and difficult to break because the annular convex portion serves as a reinforcing portion to ensure rigidity.

JP 2004-281551 A JP 2005-123425 A

  By the way, when the recess on the back surface side of the semiconductor wafer is formed by grinding using a grindstone, it is formed in a shorter time and with higher accuracy than methods such as polishing and sandblasting. After the grinding process, the inner surface of the concave portion is polished for the purpose of removing grinding marks that are the starting point of defects such as cracks, but the inner peripheral side corner of the annular convex portion, that is, the inner peripheral surface of the annular convex portion, In many cases, physical damage such as chipping remains due to grinding at corners formed by the back surface of the semiconductor wafer and the end surface substantially parallel to the annular convex portion. There was a risk that the part was damaged and the wafer was damaged.

  Therefore, the present invention effectively removes physical damage such as chipping remaining at the corners on the inner peripheral side of the annular convex portion with respect to the semiconductor wafer having a concave cross section formed by grinding the concave portion on the back side, An object of the present invention is to provide a polishing method for obtaining a semiconductor wafer capable of preventing damage to an annular convex portion and sufficiently withstanding stress caused by handling or the like.

According to the present invention, an outer peripheral surplus region having an annular convex portion that protrudes toward the back surface thicker than the device region is formed around the device region in which a plurality of devices are formed on the surface, thereby forming a concave cross section. A method of polishing a recess of a semiconductor wafer in which a circular recess on the back side is formed by grinding, and holding the semiconductor wafer in a rotatable holding means with the back surface exposed. , Having a diameter equal to or less than the diameter of the bottom surface of the recess and rotating about a rotation axis parallel to the rotation axis of the holding means, and having a thickness in the direction of the rotation axis that exceeds at least the depth of the recess the polishing member having a bottom surface of the recess, and the inner peripheral surface of the annular convex portion, the back surface and the flat line end surface and forms the corner portion of the semiconductor wafer in the inner peripheral surface and the annular projection of the annular convex portion the, internal to the polishing member The corner portion by causing compressive deformation against the surface as to cover the said abrasive member, is characterized in that polishing at the same time.

  According to the present invention, when polishing the concave portion on the back surface side of the semiconductor wafer formed by grinding, the inner peripheral surface of the annular convex portion in which physical damage such as chipping remains due to the grinding processing and the end surface Since the corners formed by polishing are simultaneously polished, the remaining damage can be effectively removed. For this reason, the damage of the annular convex portion is prevented, the rigidity of the semiconductor wafer is maintained, the handling after the next process is not hindered, and the damage prevention effect such as cracking of the entire wafer is secured.

According to the present invention, when polishing the recess on the back surface side of the semiconductor wafer formed by grinding, the bottom surface of the recess forming the recess and the inner peripheral surface of the annular protrusion are simultaneously polished. a corner formed by the rear face and the flat line end face of the semiconductor wafer in the inner peripheral surface and the annular projection of the projecting portion is intended to polishing, physical chipping or the like remaining in the corner portion by the grinding Damage is effectively removed by polishing. As a result, there is an effect that it is possible to obtain a semiconductor wafer that can sufficiently withstand the stress caused by handling or the like in the subsequent steps, even though the concave portion is formed on the back surface side by grinding.

Hereinafter, an embodiment of a polishing method according to the present invention will be described with reference to the drawings.
[1] Semiconductor Wafer Reference numeral 1 in FIG. 1 indicates a disk-shaped semiconductor wafer (hereinafter abbreviated as a wafer) that is polished by the method of one embodiment. The wafer 1 is a silicon wafer or the like and has a thickness of about 600 μm, for example. On the surface of the wafer 1, a plurality of rectangular semiconductor chips (devices) 3 are partitioned by grid-like division planned lines 2. An electronic circuit (not shown) such as an IC or an LSI is formed on the surface of the semiconductor chip 3. The plurality of semiconductor chips 3 are formed in a substantially circular device region 4 concentric with the wafer 1, and an annular outer peripheral region 5 where the semiconductor chip 3 is not formed exists around the device region 4. . A V-shaped notch 6 indicating the crystal orientation of the semiconductor is formed at a predetermined location on the peripheral surface of the wafer 1. The notch 6 is formed in the outer peripheral surplus region 5.

[2] Wafer Thinning Processing In this case, the wafer 1 shown in FIG. 1 is ground and thinned only at a portion corresponding to the device region 4 on the back surface, and processed into a concave cross section. In performing this grinding process, as shown in FIG. 1, a protective tape 7 is attached in advance to the surface of the wafer 1 for the purpose of protecting the electronic circuit. As the protective tape 7, for example, a tape in which an acrylic adhesive having a thickness of about 5 to 20 μm is applied to one side of a base material such as a polyolefin having a thickness of about 70 to 200 μm is preferably used.

  A grinding device 10 shown in FIG. 2 is used for grinding the wafer 1 into a concave shape in cross section. The processing apparatus 10 is also used for polishing after grinding. Hereinafter, the processing apparatus 10 will be described.

(A) Processing Device The processing device 10 includes a rectangular parallelepiped base 11. At one end in the longitudinal direction of the base 11, a wall portion 12 erected vertically with respect to the horizontal upper surface of the base 11 is integrally formed. In FIG. 2, the longitudinal direction, the width direction, and the vertical direction of the base 11 are shown as a Y direction, an X direction, and a Z direction, respectively. On the base 11, the wall 12 side from the substantially middle part in the longitudinal direction is a processing area 11A for processing the wafer 1, and the opposite side supplies the unprocessed wafer 1 to the processing area 11A, and after processing An attachment / detachment area 11 </ b> B for collecting the wafer 1 is used.
Hereinafter, the processing area 11A and the attachment / detachment area 11B will be described.

(I) Mechanism of machining area As shown in FIG. 2, rectangular pits 13 are formed in the machining area 11A. A vacuum chuck type disk-like chuck table (holding means) 15 is provided in the pit 13 so as to be movable in the Y direction via a table base 14. The table base 14 is slidably provided on a guide rail disposed in the pit 13 and extending in the Y direction. The table base 14 is reciprocated in the same direction by an appropriate drive mechanism (not shown).

  One end of bellows-like covers 16 and 17 are attached to both ends of the table base 14 in the moving direction. The other ends of the covers 16 and 17 are the pits facing the inner surface of the wall portion 12 and the wall portion 12. Each is attached to the inner wall surface of 13. These covers 16 and 17 cover the moving path of the table base 14 and prevent the grinding scraps and polishing scraps from falling on the moving paths, and expand and contract as the table base 14 moves. The chuck table 15 is supported on the table base 14 so that the upper surface which is the holding surface of the wafer 1 is in a horizontal state and is rotatable about a rotation axis (not shown) along the Z direction (vertical direction). Has been. The chuck table 15 can be rotated clockwise or counterclockwise by a rotation driving mechanism (not shown).

  As shown in FIG. 2, the chuck table 15 is moved together with the table base 14 toward the wall 12 and is positioned at a predetermined processing position. A spindle unit 20 is disposed above the processing position. The spindle unit 20 is attached to the wall portion 12 of the base 11 through a moving plate 32 and a guide rail 31 so as to be movable up and down, and is moved up and down by a feed mechanism 33 driven by a motor 30.

  As shown in FIG. 3, the spindle unit 20 includes a cylindrical spindle housing 21 whose axial direction extends in the Z direction, a spindle 22 that is coaxially and rotatably supported in the spindle housing 21, and the spindle housing 21. A motor 23 that is fixed to the upper end of the spindle 22 and rotationally drives the spindle 22, and a disk-shaped flange 24 that is coaxially fixed to the lower end of the spindle 22. As shown in FIG. 2, in the spindle unit 20, the spindle housing 21 is fixed to the moving plate 32 via a block 34. In the spindle unit 20, when the wafer 1 is ground, a grinding tool 40 is detachably attached to the flange 24 by means such as screwing. FIG. 2 shows the processing apparatus 10 with the grinding tool 40 attached to the flange 24.

  As shown in FIG. 3, the grinding tool 40 is fixed to a lower end surface of a frame 41 having a disk shape and a lower conical shape by arranging a large number of grindstones 42 in an annular shape over the entire outer periphery of the lower end surface. It has been done. As the grindstone 42, for example, a vitreous sintered material called vitrified, which is obtained by mixing and firing diamond abrasive grains, etc., is used. Are preferably used. As shown in FIG. 3B, the outer diameter of the circular grinding locus made up of a large number of grindstones 42 is set to be approximately equal to the radius of the device region 4 of the wafer 1. Although not shown, a grinding water supply nozzle that supplies grinding water to a processing point where the grindstone 42 of the grinding tool 40 grinds the wafer 1 is disposed in the processing area 11A. The processing area 11A is also provided with a polishing slurry supply nozzle that supplies polishing slurry (polishing liquid mixed with appropriate abrasive grains) to the polishing processing point during polishing.

(Ii) Mechanism of attachment / detachment area As shown in FIG. 2, a rectangular pit 18 is formed at the center of the attachment / detachment area 11B. 60 is installed. Around the transfer robot 60, a supply cassette 61, an alignment table 62, a swing arm type supply arm 63, a recovery arm 64 having the same structure as the supply arm 63, a spinner A cleaning device 65 and a recovery cassette 66 are arranged.

  The supply cassette 61, the alignment table 62, and the supply arm 63 are means for supplying the wafer 1 to the chuck table 15. The recovery arm 64, the cleaning device 65, and the recovery cassette 66 are used for cleaning the wafer 1 whose back surface has been ground or polished. It is means for collecting from the chuck table 15. Each cassette 61, 66 accommodates a plurality of wafers 1 in a stacked state, and is set at a predetermined position on the base 11.

  When one wafer 1 is taken out from the supply cassette 61 by the transfer robot 60, the wafer 1 is placed on the alignment table 62 with the back side facing up, and is determined at a fixed position. . Next, the wafer 1 is picked up by the supply arm 63 and picked up from the alignment table 62 and placed on the chuck table 15 waiting at the attachment / detachment position. On the other hand, the wafer 1 on the chuck table 15, whose back surface is ground or polished by the spindle unit 20 and positioned at the attachment / detachment position, is attracted and picked up by the recovery arm 64, transferred to the cleaning device 65, washed with water and dried. The wafer 1 cleaned by the cleaning device 65 is transferred and accommodated in the collection cassette 66 by the transfer robot 60.

  A nozzle 67 that cleans the chuck table 15 by spraying cleaning water and high-pressure air onto the chuck table 15 is disposed between the supply arm 63 and the recovery arm 64. The processing position of the wafer 1 by the spindle unit 20 is a range moved by a predetermined distance from the attaching / detaching position to the wall 12 side, and the chuck table 15 moves between the processing position and the attaching / detaching position by the movement of the table base 14. Go back and forth. Cleaning of the chuck table 15 by the nozzle 67 and supply of water are performed at the attachment / detachment position.

(B) Grinding of wafer by processing apparatus Next, a method of grinding and thinning only the portion corresponding to the device region 4 on the back surface of the wafer 1 by the processing apparatus 10 and processing the wafer 1 into a concave section will be described. . In performing this grinding process, as shown in FIG. 1, a protective tape 7 is attached to the surface of the wafer 1 in advance for the purpose of protecting the electronic circuit.

  First, a large number of wafers 1 each having a protective tape 7 attached on the surface thereof are accommodated in the supply cassette 61. One of the wafers 1 is transferred to the alignment table 62 by the transfer robot 60 and positioned. Subsequently, the supply arm 63 is placed on the chuck table 15 that stands by at the attachment / detachment position and is operated in a vacuum so that the wafer 1 exposed with the back surface facing up is concentrically placed, and a protective tape. 7 is brought into close contact.

  Next, the table base 14 moves in the direction of the wall 12, and the wafer 1 is sent to a grinding position below the cutting unit 20. Then, the chuck table 15 is rotated and the wafer 1 is rotated. The spindle unit 20 lowered by the feeding mechanism 33 is brought close to the wafer 1, and the spindle 22 is rotated at a high speed to move the grindstone 42 of the grinding tool 40 to the wafer 1. The portion corresponding to the device region 4 is ground by the rotating grindstone 42 and is thinned to a predetermined thickness (for example, about 200 to 100 μm or about 50 μm). In this grinding process, an appropriate amount of grinding water is supplied to the grinding surface of the wafer 1.

  As shown in FIG. 3, the grinding position of the wafer 1 (the relative position in the horizontal direction with respect to the spindle unit 20) is not concentric with the spindle 22, but is the most chuck table 15 among the many grindstones 42 arranged in an annular shape. 3B in the direction of the attachment / detachment area 11B (FIG. 3B) so that the substantially central portion of the blade thickness (the length in the radial direction) of the cutting edge of the grindstone 42 located on the inner side is located on a vertical line passing through the center of the chuck table 15. The position is offset in the right direction). The wafer 1 rotates at this position, and the grindstone 42 rotating on the back surface is pressed, whereby the portion corresponding to the device region 4 on the back surface is ground. Note that the rotation speed and rotation direction of the wafer 1, that is, the chuck table 15, the rotation speed and rotation direction of the grinding tool 40, the load of the grindstone 42 on the wafer 1, and the like depend on the thickness of the wafer 1 and the required machining removal rate. To an appropriate value. In addition, the arrow of Fig.3 (a) has shown the rotation direction of the wafer 1 and the grinding tool 40, and although both are counterclockwise in this case, it is not restricted to this.

  When the portion corresponding to the device region 4 on the back surface of the wafer 1 is ground and thinned to a predetermined thickness, the spindle unit 20 is raised to separate the grindstone 42 from the wafer 1 and stop the chuck table 15 from rotating. . On the back surface of the wafer 1, a recess 1 </ b> A is formed in the region corresponding to the device region 4 by this grinding as shown in FIG. 4, and the original thickness remains in the portion corresponding to the outer peripheral surplus region 5. An annular convex portion 5A protruding to the back side is formed, and the entire wafer 1 is processed into a concave cross section. As shown in FIG. 4 (a), on the bottom surface 4a of the recess 1A, the grinding streak 9 by the grindstone 42 having a shape in which a large number of arcs are drawn radially from the center remains. The grinding striation 9 is a trajectory of crushing processing by abrasive grains in the grindstone 42, and physical damage remains. Similar damage is also formed on the inner peripheral surface 5a of the annular convex portion 5A and the corner portion 5c formed by the inner peripheral surface 5a of the annular convex portion 5A and the end surface 5b parallel to the bottom surface 4a of the annular convex portion 5A. Yes. In particular, physical damage such as chipping remains in the corner 5c in many cases.

  When the grinding process is completed as described above, the table base 14 is moved to the attachment / detachment position, and the vacuum operation of the chuck table 15 is stopped. Next, the wafer 1 is transferred into the cleaning device 65 by the recovery arm 64 and washed with water, and then the water is removed. Then, the wafer 1 is transferred and accommodated in the recovery cassette 66 by the transfer robot 60. Further, cleaning water and high-pressure air are sprayed from the nozzle 67 toward the chuck table 15 stopped at the supply / recovery position, and the chuck table 15 is cleaned.

[3] Polishing processing of concave portion by processing device Next, the grinding tool 40 attached to the processing device 10 is replaced with the polishing tool 50 shown in FIG. 5, and the inner surface of the concave portion 1A is polished by the polishing tool 50. In the polishing tool 50, an annular polishing pad (polishing member) 52 is fixed to the lower end surface of a frame 51 similar to the frame 41. The polishing pad 52 is made of a general polishing cloth made of a non-woven fabric or the like, is not mixed with abrasive grains, and is polished by pressing the polishing slurry against the workpiece. The outer diameter of the polishing pad 52 is not particularly required as long as it is smaller than the diameter of the recess 1A formed in the wafer 1, but is preferably as large as possible from the viewpoint of processing efficiency.

  Further, as another condition, as shown in FIG. 7B, the thickness t2 is set so that the depth t1 of the recess 1A is sufficiently large so that the bottom surface 4a and the corner 5c of the recess 1A can be polished simultaneously. It is an essential condition that the thickness is set to exceed. Further, if it is added, the preferred specifications are that the compression rate is 2 to 15%, the Asker hardness is 55 to 90, and the compression modulus is about 60 to 90%. These conditions are that when the polishing pad 52 is strongly pressed against the inner peripheral surface 5a of the annular convex portion 5A, the outer peripheral surface is compressed and deformed, thereby polishing the corner portion 5c and the end surface 5b of the annular convex portion 5A. The pad 52 is soft enough to be covered and polished.

  The polishing tool 50 is set by attaching a frame 51 to the flange 24 of the spindle unit 20, and the wafer 1 is processed in the same manner as the grinding step, that is, from the supply cassette 61 through the alignment table 62, The back surface on which the concave portion 1A is formed is placed concentrically on the chuck table 15, and the table base 14 moves to a polishing position below the spindle unit 20, where the inner surface of the concave portion 1A of the wafer 1 is placed. When the polishing process is completed and the polishing process is completed, the cleaning process is performed by the cleaning device 65, and then the process is stored in the recovery cassette 66.

  Of course, the polishing process is different from the grinding process. As shown in FIGS. 6 and 7, the polishing process lowers the spindle unit 20 while rotating the wafer 1 by rotating the chuck table 15. Then, the polishing pad 52 of the polishing tool 50 is pressed against the bottom surface 4a of the concave portion 1A of the wafer 1 and the inner peripheral surface 5a of the annular convex portion 5A. In this case as well, the rotational speed and rotational direction of the wafer 1, that is, the chuck table 15, the rotational speed and rotational direction of the polishing tool 50, the load of the polishing pad 52 on the wafer 1, etc. are the thickness of the wafer 1 and the necessary processing removal. An appropriate value is set according to the rate. 6A and 7 indicate the rotation directions of the polishing tool 50 and the wafer 1. In this case, both are counterclockwise, but the present invention is not limited to this.

  FIG. 7 shows a state in which the recess 1 </ b> A of the wafer 1 on the chuck table 15 is being polished by the polishing pad 52. As shown in the figure, the lower surface of the polishing pad 52 of the polishing tool 50 is pressed against the bottom surface 4a of the concave portion 1A, and the outer peripheral surface is pressed against the inner peripheral surface 5a of the annular convex portion 5A, thereby forming the concave portion 1A. Those bottom surface 4a and inner peripheral surface 5a are polished. According to this method, as shown in FIG. 7B, since the thickness t2 of the polishing pad 52 is sufficiently thicker than the depth t1 of the recess 1A, as shown in FIG. The outer peripheral surface is strongly pressed against the inner peripheral surface 5a of the annular convex portion 5A. Therefore, the corner 5c bites into the outer peripheral surface of the polishing pad 52, and the outer peripheral surface is compressed and deformed, whereby the corner 5c is simultaneously polished as shown in FIG. 8B. Further, the inner corner 5d formed by the bottom surface 4a of the recess 1A and the inner peripheral surface 5a of the annular protrusion 5A is also simultaneously polished by the polishing pad 52.

  FIG. 9 shows the wafer 1 in which the concave portion 1A has been polished. The bottom surface 4a of the concave portion 1A is finished to a mirror surface by removing the grinding striations 9 shown in FIG. 4A. Further, the inner peripheral surface 5a of the annular convex portion 5A is similarly finished, and the corner portion 5c formed by the inner peripheral surface 5a and the end surface 5b of the annular convex portion 5A and the corner portion 5d on the inner surface side have a R-shaped cross section. Finished. In particular, the corner portion 5c where physical damage such as chipping remains due to grinding is polished so that the damage is effectively removed. Damage such as chipping is a starting point of breakage such as cracking, but since the damage has been removed, damage to the annular convex portion 5A is prevented. As a result, the function of maintaining the rigidity of the wafer 1 which is the purpose of the annular convex portion 5A is maintained, the handling of the subsequent processes is not hindered, and the damage preventing effect of the entire wafer 1 is secured.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1A is a perspective view and FIG. 2B is a side view of a wafer to be polished according to an embodiment of the present invention. It is a perspective view of the processing apparatus used for the grinding process and polishing process of a wafer back surface. FIG. 5A is a perspective view and FIG. 5B is a side view showing a state in which a grinding tool is attached to a spindle unit included in the processing apparatus and the wafer back surface is ground with the grinding tool. It is the (a) perspective view and (b) sectional view of the wafer by which the part corresponding to the device area | region of a back surface was grind-processed and it was made into concave shape cross section. It is a perspective view of an abrasive tool. FIG. 4A is a perspective view and FIG. 5B is a side view showing a state in which a polishing tool is attached to a spindle unit included in a processing apparatus and a recess on the back surface of the wafer is polished with the polishing tool. It is the (a) perspective view and the (b) side view which show the state where a polish tool polishes a crevice of a wafer back. It is sectional drawing which shows the state which grind | polishes the recessed part of a wafer back surface with a grinding | polishing tool, (a) shows the grinding | polishing initial stage, (b) shows the grinding | polishing final stage. It is the (a) perspective view of the wafer by which the recessed part of the back surface was grind | polished, (b) It is sectional drawing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Semiconductor wafer 1A ... Recessed part 3 ... Semiconductor chip (device)
DESCRIPTION OF SYMBOLS 4 ... Device area | region 4a ... Bottom surface of a recessed part 5 ... Outer peripheral surplus area 5A ... Annular convex part 5a ... Inner peripheral surface of an annular convex part 5b ... End surface of an annular convex part 5c ... Corner | angular part 10 ... Processing apparatus 15 ... Chuck table (holding means) )
22 ... Spindle (rotating axis of polishing pad)
52. Polishing pad (polishing member)
t2: Thickness of polishing pad t1: Depth of recess

Claims (1)

Around the device region where a plurality of devices are formed on the surface, an outer peripheral surplus region having an annular convex portion that protrudes thicker than the device region and protrudes toward the back surface is formed into a concave cross section, and the circular shape on the back surface side A method of polishing the concave portion of the semiconductor wafer in which the concave portion is formed by grinding,
Holding the semiconductor wafer in a rotatable holding means in a state where the back surface is exposed;
It has a diameter equal to or less than the diameter of the bottom surface of the recess and rotates around a rotation axis parallel to the rotation axis of the holding means, and the thickness in the rotation axis direction exceeds at least the depth of the recess. By a polishing member having a thickness ,
And the bottom surface of the recess, and the inner peripheral surface of the annular convex portion, and said back surface and the flat line end surface and forms the corner portion of the semiconductor wafer in the inner peripheral surface of the annular protrusion and the annular convex portion,
A method for polishing a semiconductor wafer, wherein the polishing member is pressed against the inner peripheral surface and compressed and deformed so that the corners are covered with the polishing member, and polishing is performed simultaneously.

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