JP2011040511A - Method of grinding wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of grinding a wafer that can expose all embedded electrodes on a reverse surface of the wafer. <P>SOLUTION: The method of grinding the wafer includes: a predetermined load current value storing step of previously storing, as a predetermined load current value, a load current value of a motor when all the embedded electrodes are exposed on the reverse surface of the wafer when the reverse surface of the wafer is ground; a surface protecting step of arranging a protective member on a top surface of the wafer; a holding step of sucking and holding the side of the wafer where the protective member is arranged by a chuck table; a reverse surface grinding/load current value measuring step of performing grinding feeding of a grinding means to grind the reverse surface of the wafer held by the chuck table and also measuring the load current value of the motor during the grinding; a load current value determining step of determining whether the load current value of the motor during the grinding reaches the predetermined load current value; and a grinding-feeding stopping step of stopping the grinding feeding when the load current value of the motor reaches the predetermined load current value. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention has a plurality of semiconductor circuits on the surface, and each semiconductor circuit grinds the back surface of a semiconductor wafer having a plurality of embedded electrodes embedded at a predetermined depth, and all the embedded electrodes are ground on the back surface of the wafer. The present invention relates to a method for grinding a wafer to be exposed.

  In recent years, in order to achieve high integration, high density, miniaturization, and thinning of semiconductor devices, a stacked type in which a plurality of semiconductor chips such as MCP (multi-chip package) and SIP (system in package) are stacked. Semiconductor packages have been proposed.

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

  However, in this method, since the gold wire bonded to the electrode of the semiconductor chip protrudes to the outer peripheral surplus region of the semiconductor chip, there is a problem that the package size becomes larger than the semiconductor 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, a technique has been proposed in which a through electrode is provided in the semiconductor chip to penetrate the semiconductor chip in the thickness direction and connected to the electrode of the semiconductor chip, and the semiconductor chips are stacked and the through electrodes are joined to each other for electrical connection. (For example, refer to JP-A-2005-136187).

  In this method, a plurality of semiconductor circuits are formed on the surface of the silicon wafer, and each semiconductor circuit uses a wafer in which a plurality of embedded electrodes connected to the electrodes of the semiconductor circuit and extending on the back side of the silicon wafer are formed. .

  The embedded electrode has a height equal to or higher than the finished thickness of the semiconductor chip, and the back surface of the wafer is ground by a grinding device to reduce the thickness to the finished thickness of the semiconductor chip, and the embedded electrode is exposed on the surface of the wafer. Thereafter, by selectively etching only the silicon wafer, the tip of the embedded electrode protrudes from the back surface of the wafer to form a through electrode.

JP 2005-136187 A

  However, depending on the wafer, the height of the embedded electrode varies, and there may be an embedded electrode that does not appear on the back surface of the wafer even if the wafer is ground to the finished thickness of the chip.

  If selective etching is performed with a buried electrode that does not appear on the backside of the wafer, the tip height of the protruding through electrode varies, and conduction failure occurs when divided into semiconductor chips and stacked with other semiconductor chips. There is a problem that it occurs.

  The present invention has been made in view of these points, and an object of the present invention is to provide a wafer grinding method capable of reliably exposing all the embedded electrodes on the back surface of the wafer. .

  According to the present invention, a semiconductor circuit is formed in each region defined by a plurality of division lines formed in a lattice pattern on the surface, and a plurality of semiconductor circuits from the semiconductor circuit to a depth equal to or greater than the finished thickness of the wafer. A wafer grinding method for grinding a back surface of a wafer in which embedded electrodes are embedded and exposing all embedded electrodes on the back surface of the wafer, comprising: a chuck table for holding a wafer; and a wafer held on the chuck table. A grinding apparatus comprising: a grinding wheel having a grinding wheel for grinding; a grinding means including a spindle on which the grinding wheel is mounted and a motor for rotationally driving the spindle; and a grinding feed means for grinding and feeding the grinding means. When the back surface of the wafer is ground, all the embedded electrodes are exposed to the back surface of the wafer. A predetermined load current value storing step for preliminarily storing the load current value as a predetermined load current value; a surface protection step for disposing a protective member on the surface of the wafer; and the protective member for the wafer on the chuck table. A holding step for sucking and holding the other side, and grinding and feeding the grinding means to grind the back surface of the wafer held by the chuck table and measuring the load current value of the motor during grinding. A value measuring step, a load current value determining step for determining whether or not the load current value of the motor being ground has reached the predetermined load current value, and the load current value of the motor has reached the predetermined load current value There is provided a grinding method for a wafer, characterized by comprising a grinding feed stop step for stopping the grinding feed at the time.

  According to the present invention, the load current value of the spindle motor when all the embedded electrodes are exposed to the back surface of the wafer by grinding is stored in advance as a predetermined load current value, and the spindle motor load current value during grinding is measured. In order to control the grinding feed to stop when the spindle motor load current reaches the stored load current value by grinding and feeding the grinding means, all embedded electrodes are placed on the wafer back side. It can be surely expressed.

It is a surface side perspective view of a semiconductor wafer. 1 is a schematic cross-sectional view of a semiconductor wafer. It is a back surface side perspective view of the semiconductor wafer by which the protective tape was stuck on the surface. It is typical sectional drawing of the semiconductor wafer by which the protective tape was stuck on the surface. 1 is an external perspective view of a grinding apparatus suitable for carrying out the grinding method of the present invention. It is a flowchart which shows the grinding method of this invention embodiment. It is a graph which shows the relationship between the grinding time of a semiconductor wafer, and load current value. It is explanatory drawing of a holding step. It is explanatory drawing of a back surface grinding and load current value measurement step. It is a longitudinal cross-sectional view of the semiconductor wafer ground by the grinding method of this invention.

  Hereinafter, a wafer grinding method according to an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a perspective view of a semiconductor wafer 11 before being processed to a predetermined thickness. The semiconductor wafer 11 shown in FIG. 1 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. Semiconductor circuits 15 such as ICs and LSIs are formed in a plurality of partitioned areas.

  The semiconductor wafer 11 configured as described above includes a device region 17 in which the semiconductor circuit 15 is formed, and an outer peripheral surplus region 19 surrounding the device region 17. 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.

  Referring to FIG. 2, a schematic cross-sectional view of the semiconductor wafer 11 is shown. From each semiconductor circuit 15 formed on the semiconductor wafer 2, a plurality of embedded electrodes 25 embedded at a depth equal to or greater than the finished thickness t1 of the semiconductor device extend to the back surface 11b side.

  Before grinding the back surface 11b of the semiconductor wafer 11, the protective tape 23 is attached to the front surface 11a of the semiconductor wafer 11 by a protective tape attaching process. Therefore, the front surface 11a of the semiconductor wafer 11 is protected by the protective tape 23, and the back surface 11b is exposed as shown in FIG. FIG. 4 is a schematic cross-sectional view of the semiconductor wafer 11 having a protective tape 23 attached to the surface.

  Hereinafter, a grinding apparatus 2 suitable for grinding the back surface 11b of the semiconductor wafer 11 thus configured to expose all the embedded electrodes 25 on the back surface 11b will be described with reference to FIG. Reference numeral 4 denotes a housing (base) of the grinding apparatus 2, and two columns 6 a and 6 b are provided upright 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 6a. A rough grinding unit 10 is mounted along the pair of guide rails 8 so as to be movable in the vertical direction. The rough grinding unit 10 is attached to a moving base 12 whose housing 20 moves up and down along a pair of guide rails 8.

  The rough grinding unit 10 includes a housing 20, a spindle (not shown) rotatably accommodated in the housing 20, a servo motor 22 that rotationally drives the spindle, and a plurality of rough grinding grinding wheels fixed to the tip of the spindle. A grinding wheel 24 having 26 is included.

  The rough grinding unit 10 includes a rough grinding unit moving mechanism 18 including a ball screw 14 and a pulse motor 16 that move the rough grinding 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 pair of guide rails 19 (only one is shown) 19 extending in the vertical direction are also fixed to the other column 6b. A finish grinding unit 28 is mounted along the pair of guide rails 19 so as to be movable in the vertical direction.

  The finish grinding unit 28 is attached to a moving base (not shown) in which the housing 36 moves in the vertical direction along the pair of guide rails 19. The finish grinding unit 28 includes a housing 36, a spindle (not shown) rotatably accommodated in the housing 36, a servo motor 38 that rotationally drives the spindle, and a grinding wheel 42 for finish grinding fixed to the tip of the spindle. A grinding wheel 40 is included.

  The finish grinding unit 28 includes a finish grinding unit moving mechanism 34 including a ball screw 30 and a pulse motor 32 that move the finish grinding unit 28 in the vertical direction along the pair of guide rails 19. When the pulse motor 32 is driven, the ball screw 30 rotates and the finish grinding unit 28 is moved in the vertical direction.

  The grinding device 2 includes a turntable 44 disposed so as to be substantially flush with the upper surface of the housing 4 on the front side of the columns 6a and 6b. The turntable 44 is formed in a relatively large-diameter disk shape, and is rotated in a direction indicated by an arrow 45 by a rotation drive mechanism (not shown).

  On the turntable 44, three chuck tables 46 are arranged so as to be rotatable in a horizontal plane, spaced from each other by 120 ° in the circumferential direction. The chuck table 46 has a suction chuck formed in a disk shape by a porous ceramic material, and sucks and holds the wafer placed on the holding surface of the suction chuck by operating a vacuum suction means.

  The three chuck tables 46 arranged on the turntable 44 are rotated in accordance with the turntable 44, so that the wafer loading / unloading area A, rough grinding area B, finish grinding area C, and wafer loading / unloading are performed. The region A is sequentially moved.

  In the front portion of the housing 4, a wafer cassette 50, a wafer transfer robot 54 having a link 51 and a hand 52, a positioning table 56 having a plurality of positioning pins 58, a wafer carry-in mechanism (loading arm) 60, and a wafer carry-out A mechanism (unloading arm) 62, a spinner cleaning device 64 that cleans and spin-drys the ground wafer, and a storage cassette 66 that stores the ground wafer that has been cleaned and spin-dried by the spinner cleaning device 64 are provided. ing.

  A spinner cleaning device 64 shown in FIG. 5 is provided with a spinner table 68 having a diameter smaller than that of the semiconductor wafer 11 that rotates while sucking and holding the ground semiconductor wafer 11. Reference numeral 70 denotes a cover of the spinner cleaning device 64.

  Next, a wafer grinding method according to an embodiment of the present invention will be described in detail with reference to FIGS. Referring to the flowchart of FIG. 6, in the grinding method according to the embodiment of the present invention, first, in step S10, the load current value of the motor 38 when all the embedded electrodes 25 are exposed on the back surface of the wafer is stored in advance as a predetermined load current value. Remember it.

  That is, before carrying out the grinding method of the present invention, the back surface 11b of the semiconductor wafer 11 is ground to the predetermined thickness (thickness at which the embedded electrode 25 does not appear on the back surface) with the rough grinding unit 10, and then the finish grinding unit 28. Is used to finish-grind the back surface 11b of the semiconductor wafer 11.

In this finish grinding, since the embedded electrode 25 is ground simultaneously with silicon, the load current value of the motor gradually increases as the number of embedded electrodes 25 to be ground increases as shown in FIG. load current value and the embedded electrode 25 is exposed on the rear surface 11b becomes constant at a predetermined value I _0. Storing the load current value in the memory as the predetermined load current value I _0.

  That is, since the embedded electrode 25 is made of copper or copper dungsten, grinding is more difficult than silicon. Therefore, as the number of embedded electrodes 25 to be ground increases, the load current value of the motor increases stepwise.

  Since the semiconductor circuit 15 is formed on the surface of the semiconductor wafer 11, a protective tape 23 is attached to the surface of the semiconductor wafer 11 in step S11. Instead of the protective tape 23, a substrate such as glass or silicon may be attached to the surface of the wafer 11.

  A plurality of the semiconductor wafers 11 having the protective tape 23 adhered to the surface in this way are accommodated in the wafer cassette 50, and the wafer cassette 50 is placed on the base 4. The semiconductor wafer accommodated in the wafer cassette 50 is transported by the vertical motion and the forward / backward motion of the wafer transport robot 54 and placed on the wafer positioning table 56.

  The wafer placed on the wafer positioning table 56 is centered by a plurality of positioning pins 58 and then turned on the chuck table 46 positioned in the wafer loading / unloading area A by the turning operation of the loading arm 60. And sucked and held by the chuck table 46. That is, the holding step of step S12 shown in FIG. 8 is executed here.

  Next, the turntable 44 is rotated 120 degrees counterclockwise, and the chuck table 46 holding the wafer is positioned in the rough grinding region B. While rotating the chuck table 46 at, for example, 300 rpm with respect to the wafer thus positioned, the grinding wheel 24 is rotated in the same direction as the chuck table 46, for example, at 6000 rpm, and the rough grinding unit moving mechanism 18 is operated to perform roughing. A grinding wheel 26 for grinding is brought into contact with the back surface of the wafer.

  Then, the grinding wheel 24 is ground by a predetermined amount at a predetermined grinding feed speed, and rough grinding in step S13 is performed. While measuring the thickness of the wafer with a contact type or non-contact type thickness gauge, the wafer is ground to a desired thickness, that is, a thickness just before the embedded electrode 25 appears on the back surface 11b of the wafer 11.

  The chuck table 46 holding the wafer after the rough grinding is positioned in the finish grinding region C by rotating the turntable 44 counterclockwise by 120 degrees, and is finished by the finish grinding unit 28 having the finish grinding wheel 42. Grinding is performed. In this finish grinding, the back surface grinding is performed while measuring the load current value of the motor 38. Therefore, the back surface grinding / load current value measuring step of step S14 is performed.

  FIG. 9A is a perspective view showing the relationship between the wafer 11 held on the chuck table 46 during finish grinding and the finish grinding unit 28, and FIG. 9B shows a front view thereof. A spindle 37 that is rotationally driven by a motor 38 is accommodated in the housing 36 of the finish grinding unit 28, and a wheel mount 39 is fixed to the tip of the spindle 37. A grinding wheel 40 having a grinding wheel 42 for finish grinding is detachably attached to the wheel mount 39.

  In this back grinding / load current value measurement step, as in the rough grinding by the rough grinding unit 10, the grinding wheel 40 is rotated in the arrow b direction at, for example, 6000 rpm while the chuck table 46 is rotated in the arrow a direction at, for example, 300 rpm. At the same time, the finish grinding unit moving mechanism 34 is operated to bring the grinding wheel 42 for finish grinding into contact with the back surface of the wafer.

Then, the grinding wheel 40 is ground and fed downward by a predetermined amount at a predetermined grinding feed speed, and the back surface grinding of the wafer 11 is performed. This back surface grinding is performed while measuring the load current value of the motor 38 with an ammeter 74 connected in series between the power source 72 and the motor 38. The load current value measured by the ammeter 74 is input to the controller 76 and compared with a predetermined load current value I ₀ stored in advance in the memory 78 by the controller 76.

Load current of the motor 38 in step S15 of FIG. 6 it is determined whether or not reached a predetermined load current value I _0, if it is determined to reach stops grinding feed in step S16. That is, when the load current value of the motor is determined to have reached the predetermined load current value I ₀ in step S15, all the embedded electrode 25 as shown in the graph of FIG. 7 is exposed on the back surface 11b of the wafer 11 Therefore, the grinding feed is stopped at this point.

  And what is called spark out grinding which performs grinding in the state where grinding feed was stopped at Step S17 is carried out. FIG. 10 shows a longitudinal sectional view of the semiconductor wafer 11 in a state where the spark-out grinding in step S17 has been completed. All the embedded electrodes 25 protrude from the back surface 11 b of the semiconductor wafer 11.

  The chuck table 46 holding the wafer 11 after finish grinding is positioned in the wafer loading / unloading area A by rotating the turntable table 44 by 120 degrees counterclockwise.

  After the suction holding of the wafer held on the chuck table 46 is released, the wafer is adsorbed by the wafer unloading mechanism (unloading arm) 62, and is transported to the spinner cleaning device 64 by turning the unloading arm 62. The

  The wafer conveyed to the spinner cleaning device 64 is cleaned and spin-dried here. Next, the wafer is stored in a predetermined position of the storage cassette 66 by the wafer transfer robot 54.

  After grinding of the semiconductor wafer 11, in order to make the embedded electrode 25 protrude from the back surface of the wafer 11, only a few μm of silicon is removed by well-known plasma etching, and the embedded electrode 25 protrudes from the back surface of the semiconductor wafer 11 by a predetermined amount. This is a through electrode.

2 Grinding device 10 Coarse grinding unit 11 Semiconductor wafer 15 Semiconductor circuit 23 Protective tape 25 Embedded electrode 28 Finish grinding unit 44 Turntable 46 Chuck table

Claims (1)

A semiconductor circuit is formed in each region partitioned by a plurality of division lines formed in a lattice pattern on the surface, and a plurality of embedded electrodes extending from the semiconductor circuits to a depth greater than the finished thickness of the wafer are embedded. A wafer grinding method in which the back surface of the wafer is ground and all embedded electrodes are exposed on the back surface of the wafer.
A grinding table including a chuck table for holding a wafer, a grinding wheel having a grinding wheel for grinding a wafer held by the chuck table, a spindle on which the grinding wheel is mounted, and a motor for rotationally driving the spindle; The load current value of the motor when all the embedded electrodes are exposed on the back surface of the wafer when the back surface of the wafer is ground using a grinding device having a grinding feed means for grinding and feeding the grinding means. Is stored in advance as a predetermined load current value, a predetermined load current value storage step,
A surface protection step for disposing a protective member on the surface of the wafer;
A holding step for sucking and holding the side of the wafer on which the protective member is disposed with the chuck table;
Grinding and feeding the grinding means to grind the back surface of the wafer held by the chuck table, and measuring the load current value of the motor during grinding, a back surface grinding / load current value measuring step;
A load current value determining step for determining whether or not the load current value of the motor during grinding has reached the predetermined load current value;
A grinding feed stop step for stopping the grinding feed when the load current value of the motor reaches the predetermined load current value;
A method for grinding a wafer, comprising:

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