JP2018032832A - Wafer surface treatment device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wafer surface treatment device structure, producing an extrinsic gettering (EG) layer capable of accurately capturing heavy metals by uniformly forming scratches in the EG layer.SOLUTION: A wafer surface treatment device includes: a chuck portion 12a holding and rotating a wafer W; an EG pad 26 pressing the wafer W to produce an EG layer; and an arm 21 moving the EG pad 26 relative to the chuck portion 12a when the wafer W is pressed by the EG pad 26. The arm 21 rotates during texturing processing. Thus the EG layer can be produced while an offset between the EG pad 26 and the wafer W is adjusted.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a wafer surface treatment apparatus, and more particularly to a wafer surface treatment apparatus for forming a gettering layer on a semiconductor wafer (hereinafter simply referred to as “wafer”).

  A thin semiconductor device made of silicon is manufactured by forming a circuit on a wafer sliced from a silicon single crystal, that is, a silicon wafer.

  One of the problems in the semiconductor process is that heavy metals as impurities are mixed into the silicon wafer. When heavy metals diffuse into the device region formed on the surface side of the silicon wafer, the device characteristics are significantly adversely affected. Therefore, a gettering method is generally adopted in order to prevent heavy metals mixed in the silicon wafer from diffusing into the device region.

  In the gettering method, an extrinsic gettering layer (hereinafter simply referred to as a “gettering layer” or an “EG layer”) consisting of extremely small scratches on a wafer having a semiconductor element formed on the surface side. To form). Due to the gettering effect by the EG layer, the heavy metal mixed in the wafer is prevented from diffusing into the device region.

  In order to form such an EG layer, the back surface of the wafer is polished into a mirror surface with a polishing pad while supplying a polishing liquid, and then the polishing pad is pressed against the wafer while supplying pure water. One that forms an EG layer by forming a scratch is known (see, for example, Patent Document 1).

JP 2013-247132 A.

  However, in the processing method described in Patent Document 1, since the extremely small scratch that forms the EG layer is formed according to the circular orbit of the abrasive grains contained in the polishing pad, there is a variation in the density of the scratch. As a result, the scratches are locally sparse in the EG layer and heavy metal may pass through the EG layer.

  Therefore, a technical problem to be solved in order to generate an EG layer capable of capturing heavy metals with high accuracy arises, and the present invention aims to solve this problem.

  The present invention has been proposed to achieve the above object, and the invention according to claim 1 is a wafer surface processing apparatus for generating a gettering layer on the back surface of a wafer having a device region formed on the surface. A substrate holding mechanism that holds and rotates the wafer, a surface treatment pad that presses the wafer to generate the gettering layer, and the surface when the wafer is pressed against the surface treatment pad. There is provided a wafer surface processing apparatus comprising: a traverse mechanism that moves a processing pad relative to the substrate holding mechanism.

  According to this configuration, when the traverse mechanism moves the surface treatment pad relative to the wafer adsorbed by the substrate holding mechanism, the regular rotation trajectory of the grindstone included in the surface treatment pad changes. Since the scratch formed on the wafer also changes according to the rotation trajectory of the grindstone, scratches in various directions are formed in the gettering layer, so that the scratch is locally sparse in the gettering layer. It is possible to suppress and generate a gettering layer capable of capturing heavy metal with high accuracy.

  According to a second aspect of the present invention, in the configuration according to the first aspect, the traverse mechanism is configured so that an offset amount between a rotation center of the substrate holding mechanism and a rotation center of the surface treatment pad changes. A wafer surface processing apparatus for moving a processing pad is provided.

  According to this configuration, the traverse mechanism moves the surface treatment pad so that the offset amount changes, so that the regular orbit of the grindstone different for each offset amount changes. Since the scratch of the direction is formed, a gettering layer capable of capturing heavy metal with high accuracy can be formed.

  According to a third aspect of the present invention, in the configuration of the first or second aspect, the traverse mechanism causes the surface treatment pad to temporarily raise the surface treatment pad when the surface treatment pad passes through the wafer. Providing equipment.

  According to this configuration, since the surface treatment pad moves in a non-contact state with the wafer, so-called edge chipping in which the surface treatment pad cuts the periphery of the wafer when the surface treatment pad passes through the wafer can be suppressed. .

  According to the present invention, the traverse mechanism moves the surface treatment pad relative to the wafer attracted by the substrate holding mechanism, thereby changing the regular rotation trajectory of the grindstone included in the surface treatment pad. Since the scratch formed on the wafer also changes according to the rotation trajectory of the grindstone, scratches in various directions are formed in the gettering layer, so that the scratch is locally sparse in the gettering layer. It is possible to suppress and generate a gettering layer capable of capturing heavy metal with high accuracy.

It is a schematic plan view which shows the surface treatment apparatus of the wafer to which this invention is applied. FIG. 2 is a partial side view of a polishing / texturing unit in the wafer surface treatment apparatus shown in FIG. 1, (a) is a view for explaining a surface treatment pad, and (b) is a view for explaining a pad dresser. It is a schematic diagram explaining the processing process of a wafer, (a) is an explanatory diagram of a grinding process, (b) is an explanatory diagram of a polishing and texturing process, (c) is an explanatory diagram of a cleaning process, (d) is a rinse It is explanatory drawing of a process. An example of a wafer on which an EG layer is generated is shown, (a) is an overall view thereof, (b) is a partially enlarged sectional view thereof, and (c) is a partially enlarged perspective view thereof. It is a plane schematic diagram which shows the offset amount of a surface treatment pad and a wafer. It is a figure which shows the rotation track | orbit of the grindstone contained in a surface treatment pad. It is an image which shows the direction of the scratch formed in the wafer periphery. It is a schematic diagram which shows a mode that the offset amount of a surface treatment pad and a wafer is adjusted.

  The present invention is a wafer surface processing apparatus for generating a gettering layer on the back surface of a wafer having a device region formed on the front surface side in order to achieve the object of generating an EG layer capable of capturing heavy metals with high accuracy. A substrate holding mechanism for holding and rotating the wafer, a surface treatment pad for generating a gettering layer by pressing the wafer, and the surface treatment pad when the wafer is pressed against the surface treatment pad. This is realized by including a traverse mechanism that moves relative to each other.

  Hereinafter, a wafer surface processing apparatus 10 according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic plan view showing a wafer surface treatment apparatus 10. A wafer surface treatment apparatus 10 shown in FIG. 1 includes cassettes 11a and 11b for storing a plurality of wafers W (for example, silicon wafers), and chuck portions 12a to 12d as four substrate holding mechanisms, and performs index rotation. A turntable 13, a cleaning unit 14 for cleaning the four chuck portions 12a to 12d, and a transfer robot 15 for transferring the wafer W.

  Further, as shown in FIG. 1, in the wafer surface treatment apparatus 10, a rough grinding unit 16, a finish grinding unit 17, and a polishing / texturing unit 18 are arranged in order along the outer periphery of the turntable 13. . The rough grinding unit 16 roughly grinds the back surface Wa of the wafer W with a rough grinding wheel (not shown), and the finish grinding unit 17 finish-grinds the back surface Wa with a finish grinding wheel (not shown).

  FIG. 2 is a partial side view of the polishing / texturing unit 18 that finish-polishes the back surface of the wafer W into a mirror surface and generates an EG layer on the wafer W. The polishing / texturing unit 18 includes an EG pad unit 20 shown in FIG. 2 (a) and a pad dress unit 30 shown in FIG. 2 (b).

  In the EG pad unit 20 shown in FIG. 2A, a motor 22 is suspended at the tip of an arm 21. A disk-like pad support 23 is attached to the output shaft 22a of the motor 22 so as to be horizontally rotatable. Also, a disk-shaped subpad 24 is bonded and fixed to the lower surface of the pad support 23 via a resinous adhesive 25. Further, the disk-shaped surface treatment pad EG is also fixed to the lower surface of the subpad 24. The pad 26 is bonded and fixed via a resinous adhesive 27, and the pad support 23, subpad 24, and EG pad 26 are integrated. Accordingly, the pad support 23, the sub pad 24, and the EG pad 26 can be lowered in the thickness direction of the wafer W integrally with the arm 21, and can be rotated in the horizontal direction.

  The EG pad 26 is made of a polyurethane resin pad base material formed in a disk shape with a thickness of about 4.8 mm, and fine SiC (silicon silicon) of about 0.6 μm, tungsten, alumina, or other abrasive grains. It is mixed in the resin material and impregnated in the resin pad base material. The abrasive grains impregnated with the resin material on the pad base material contribute to forming an EG layer by giving an extremely fine scratch to the back surface Wa of the wafer W. On the other hand, the sub pad 24 is formed in a disk shape having a thickness of about 0.9 mm, and has a lower hardness than the EG pad 23 and is provided so as to easily follow the surface shape of the wafer W during processing. ing. Needless to say, the resin material for mixing the abrasive grains is not limited to polyurethane.

  The EG pad unit 20 is provided with a supply line 28 connected to a supply source for supplying water (pure water) and a polishing aid as a polishing aid between the wafer W and the EG pad 23. The polishing aid is obtained by diluting, for example, a solution (5 to 10%) containing an amine (such as piperazine).

  In the pad dress unit 30 shown in FIG. 2B, a dresser head 32 is attached to a support member 31 connected to an output shaft of a motor (not shown) so as to be horizontally rotatable. In this embodiment, the dresser head 32 is provided with a polishing layer 33 in which diamond abrasive grains are impregnated in a resin material on the upper surface of a non-woven fabric formed in a disk shape facing the lower surface (processed surface) of the EG pad 26. Become.

  In the wafer surface processing apparatus 10, the polishing / texturing unit 18 performs processing that causes extremely fine damage to the back surface Wa side of the wafer W to generate an EG layer having gettering ability and finish it in a mirror surface. Can be done.

  The operation of the wafer surface treatment apparatus 10 of the present invention will be described below. First, one wafer W is taken out from the cassette 11a by the transfer robot 15, and transferred to the chuck unit 12a as a substrate holding mechanism for holding and rotating the wafer W.

  The wafer W is sucked and held by the chuck portion 12a with the back surface Wa facing upward. The chuck portion 12a is previously cleaned by the cleaning unit 14. Thereafter, the turntable 13 is rotated by an index, and the chuck portion 12a is moved to the rough grinding unit 16. At this time, another wafer W is transferred to another chuck portion 12d by the transfer robot, and the same processing is performed.

  In the rough grinding unit 16, the back surface Wa of the wafer W is roughly ground by a known method with a rough grinding wheel (not shown). Next, the turntable 13 is rotated by an index, and the chuck portion 12 a is moved from the rough grinding unit 16 to the finish grinding unit 17. In the finish grinding unit 17, the back surface Wa of the wafer W is finish ground by a finish grinding wheel (not shown).

  The turntable 13 is index-rotated again, and the chuck portion 12 a is moved from the finish grinding unit 17 to the polishing / texturing unit 18.

  On the back surface Wa of the wafer W after the grinding process, there are grinding marks as shown in FIG. Therefore, in the polishing / texturing unit 18, as shown in FIG. 3B, the EG pad 26 rotates horizontally together with the arm 21 and moves above the chuck portion 12a. Thereafter, the EG pad 26 is lowered while the EG pad 26 and the wafer W are rotated, and the EG pad 26 is pressed against the wafer W. Further, a polishing aid is supplied between the EG pad 26 and the wafer W. In this way, a polishing / texturing process (surface treatment) in which the wet polishing for removing the grinding traces on the back surface Wa of the wafer W and polishing to a mirror surface and the texturing for generating an EG layer on the wafer W are performed in parallel. Step) is executed.

  Specifically, abrasive grains contained in the EG pad 26 (hereinafter referred to as “fixed abrasive grains”) and abrasive grains released from the EG pad 26 (hereinafter referred to as “free abrasive grains”) cooperate with each other. Polishing and texturing. The EG pad 26 and the wafer W rotate while the fixed abrasive is pressed against the back surface Wa of the wafer W, and the loose abrasive rolls on the wafer W. The loose abrasive grains are those in which a part of the fixed abrasive grains contained in the EG pad 26 is released from the EG pad 26 by the resinous adhesive 27 being swollen and hydrolyzed by the polishing aid.

  Further, the surface layer side of the back surface Wa of the wafer W comes into contact with the polishing aid and the oxide film (SiO2) is softened by modifying it to SiOH, so that the back surface Wa of the wafer W is easily polished. Further, the free abrasive grains roll between the EG pad 26 and the wafer W, so that the free abrasive grains A2 bite into the wafer W and the polishing is not forcedly performed by an external force. An EG layer is generated in the wafer W by forming an extremely fine scratch.

  4A and 4B show an example of the wafer W that has undergone the polishing and texturing process. FIG. 4A is an overall perspective view of the wafer W viewed from the back side, and FIG. 4B is a partially enlarged view of the wafer W. Sectional drawing and the same figure (c) are the partial expansion perspective views. The wafer W shown in FIG. 4 has a defect-free layer 40 formed on the surface Wb side, and a plurality of semiconductor elements 41 are provided on the surface of the defect-free layer 40. Further, in order to protect these semiconductor elements 41, a protective film 42 is attached to the front surface Wb of the wafer W during back surface grinding. On the other hand, an EG layer 43 is formed on the back surface Wa side. The EG layer 43 is composed of a large number of scratches and is formed with a surface roughness (Ra) of 1.0 nm to 1.7 nm.

  After the polishing / texturing step, a cleaning step is performed on the processed surface 26a of the EG pad 26 as shown in FIG. In this step, the EG pad 26 is horizontally rotated together with the arm 21, and the EG pad 26 is moved above the dresser head 32. Then, while rotating the EG pad 26 by driving the motor 22, the EG pad 26 is lowered integrally with the arm 21 in the thickness direction of the wafer W, and on the dresser head 32 rotated by a motor (not shown). The EG pad 26 is lightly pressed to wipe a predetermined range in the thickness direction from the processed surface 26a of the EG pad 26, and the polishing aid remaining on the processed surface 26a of the EG pad 26 is removed. Thereby, it can avoid moving to the grinding | polishing auxiliary agent which remained on the process surface 26a in the rinse process mentioned later.

  After the cleaning process, a rinsing process is performed on the back surface Wa of the wafer W as shown in FIG. In this step, the EG pad 26 rotates horizontally together with the arm 21 and moves above the chuck portion 12a. Thereafter, the EG pad 26 is lowered to approach the wafer W. Then, while supplying pure water between the back surface Wa of the wafer W on the rotating chuck portion 12a and the processed surface of the EG pad 26, the wafer W and the EG pad 26 are rotated in opposite directions. The EG pad 26 is disposed in close proximity to the wafer W in a non-contact state. In this state, the wafer W and the EG pad 26 are rotated in opposite directions to form a water flow on the back surface Wa of the wafer W. be able to. In this way, the rinsing process is performed with the supplied water, and the polishing aid remaining on the back surface Wa of the wafer W is washed away and removed.

  Next, the scratch which comprises the EG layer 43 is demonstrated based on drawing. FIG. 5 is a schematic plan view showing an offset amount between the EG pad 26 and the wafer W. As shown in FIG. FIG. 6 is a view showing the rotation trajectory of the grindstone included in the EG pad 26. FIG. 7 is an image showing the direction of the scratch formed on the periphery of the wafer W.

  As shown in FIG. 5, the rotation axis a1 of the EG pad 26 and the rotation axis a2 of the chuck portion 12a are separated by an arbitrary distance (hereinafter referred to as “offset amount”). As shown in FIG. 6, since the rotational trajectory of the fixed abrasive grains A1 included in the EG pad 26, that is, the density and directionality of the scratch, varies depending on the offset amount, the gettering ability of the EG layer 43 to be applied to the wafer W Accordingly, the offset amount is arbitrarily adjusted. That is, the rotation trajectory of the fixed abrasive grain A1 having zero offset shown in FIG. 6A goes from the center o of the wafer W coincident with the rotation axis a2 of the chuck portion 12a toward the outer periphery while slightly curving in the circumferential direction. On the other hand, as shown in FIGS. 6B and 6C, the rotational trajectory of the fixed abrasive grains A1 is greatly curved in the circumferential direction of the EG pad 26 as the offset amount increases. Further, the scratch formed on the wafer W becomes sparser toward the outside of the wafer W. Further, as shown in FIG. 7, the periphery of the wafer W tends to be regularly formed so that the directions of the scratches are aligned.

  Therefore, in the wafer surface treatment apparatus 1, the arm 21 functioning as a traverse mechanism rotates in the horizontal direction during texturing, thereby adjusting the offset amount between the EG pad 26 and the wafer W while adjusting the EG layer 43. Can be generated. For example, as shown in FIG. 8A, after performing the polishing and texturing process in a state where the offset amount between the EG pad 26 and the wafer W is large, the EG pad 26 is removed as shown in FIG. By performing horizontal movement and performing the polishing and texturing process in a state where the offset amount between the EG pad 26 and the wafer W is small, scratches in different directions can be formed in an overlapping manner, particularly at the periphery of the wafer W.

  Further, when the EG pad 26 is horizontally moved in order to reduce the offset amount between the EG pad 26 and the wafer W, the arm 21 temporarily raises the EG pad 26 and then the EG pad 26 is horizontally moved to a desired position. Then, by lowering the EG pad 26, so-called edge chipping in which the EG pad 26 cuts the peripheral edge of the wafer W is suppressed.

  The wafer surface treatment apparatus 10 performs the polishing step and the texturing step in parallel using the alkaline polishing aid as described above. For example, the polishing is performed using the alkaline polishing aid. You may perform a texturing process using a pure water after performing a process.

  As described above, according to the wafer surface treatment apparatus 10 according to the present invention, the arm 21 moves the EG pad 26 relative to the wafer W attracted to the chuck portion 12a, whereby the EG pad 26 is moved. Since the regular rotation trajectory of the fixed grindstone included in the wafer changes, and the scratch formed on the wafer W also changes according to the rotation trajectory of the fixed grindstone, scratches in various directions are formed in the gettering layer 43. Therefore, it is possible to suppress the local sparseness of the scratch in the EG layer 43 and to generate a gettering layer capable of capturing heavy metals with high accuracy.

  It should be noted that the present invention can be variously modified without departing from the spirit of the present invention, and the present invention naturally extends to the modified ones.

  As described above, in addition to processing the back surface 20b of the wafer W, the present invention can be applied to apparatuses for processing various plate-like surfaces.

10 Wafer surface treatment apparatuses 11a and 11b Cassettes 12a to 12d Chuck part (substrate holding mechanism)
13 Turntable 14 Cleaning unit 15 Transport robot 16 Rough grinding unit 17 Finish grinding unit 18 Polishing / texturing unit 20 EG pad unit 21 Arm (traverse mechanism)
22 Motor 22a Output shaft 23 Pad support 24 Sub pad 25 Resin adhesive 26 EG pad (surface treatment pad)
26a Processing surface 27 Resin adhesive 28 Supply line 30 Pad dress unit 31 Support member 32 Dresser head 33 Non-woven fabric

Claims (3)

A wafer surface treatment apparatus for generating a gettering layer on the back surface of a wafer having a device region formed on the front surface,
A substrate holding mechanism for holding and rotating the wafer;
A surface treatment pad that presses the wafer to generate the gettering layer;
A traverse mechanism that moves the surface treatment pad relative to the substrate holding mechanism when the wafer is pressed against the surface treatment pad;
A wafer surface treatment apparatus comprising:   2. The wafer according to claim 1, wherein the traverse mechanism moves the surface treatment pad so that an offset amount between a rotation center of the substrate holding mechanism and a rotation center of the surface treatment pad changes. Surface treatment equipment.   The wafer surface processing apparatus according to claim 1, wherein the traverse mechanism temporarily raises the surface processing pad when the surface processing pad passes through the wafer.