JP2020205443A - Wafer surface treatment device - Google Patents

Abstract

To provide a wafer surface treatment device structure for producing an EG layer capable of accurately capturing heavy metals.SOLUTION: In a wafer surface treatment device, an EG pad unit 20 includes a chuck portion 12a that holds and rotates a wafer W, an EG pad 26 that is arranged facing the chuck portion and is formed by impregnating a pad base material with a resin material mixed with abrasive grains, and a supply line 28 that supplies an alkaline polishing aid between the chuck portion and the EG pad. The polishing aid hydrolyzes the resin material to release at least part of the abrasive grains from the EG pad and forms an EG layer on the wafer by pressing the wafer with the EG pad and rotating the chuck portion and the EG pad.SELECTED DRAWING: Figure 2

Description

The present invention relates to a wafer surface treatment device, and more particularly to a wafer surface treatment device 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, which are impurities, are mixed in 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, in order to prevent heavy metals mixed in the silicon wafer from diffusing into the device region, a gettering method is generally adopted.

In the gettering method, an entrinsic gettering layer (hereinafter, simply "gettering layer" or "EG layer" consisting of a large number of extremely minute scratches is formed on a wafer in which a semiconductor element is formed on the surface side. It is called). The gettering effect of the EG layer prevents heavy metals mixed in the wafer from diffusing into the device region.

To form such an EG layer, the back surface of the wafer is mirror-polished with a polishing pad while supplying a polishing liquid, and then the polishing pad is pressed against the wafer while supplying pure water to make ultrafine particles on the wafer. Those that form scratches to form an EG layer are known (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2013-247132.

However, in the processing method described in Patent Document 1, since the scratches constituting the EG layer are formed according to the orbits of the abrasive grains contained in the polishing pad, the scratch density varies or the scratch orientation varies. There is a problem that scratches are locally sparse in the EG layer and heavy metals may pass through the EG layer due to alignment and the like.

Therefore, a technical problem to be solved in order to generate an EG layer capable of accurately capturing heavy metals arises, and an object of the present invention is to solve this problem.

The present invention has been proposed to achieve the above object, and the invention according to claim 1 is to mirror-polish the back surface of a wafer having a device region formed on the front surface and to generate a gettering layer. An EG that is a wafer surface treatment device and is formed by impregnating a pad base material with a substrate holding mechanism that holds and rotates the wafer and a resin material that is arranged opposite to the substrate holding mechanism and contains abrasive grains. A surface treatment pad having a pad and a polishing aid supply mechanism for supplying an alkaline polishing aid between the substrate holding mechanism and the EG pad are provided, and the polishing aid hydrolyzes the resin material. By releasing at least a part of the abrasive grains from the surface treatment pad, pressing the wafer with the EG pad, and rotating the substrate holding mechanism and the EG pad, the gettering layer is formed on the wafer. Provided is a surface treatment apparatus for a wafer to be produced.

According to this configuration, the abrasive grains (fixed abrasive grains) contained in the EG pad are pressed against the back surface of the wafer, and the abrasive grains (free abrasive grains) released from the EG pad roll randomly on the EG pad. As a result, scratches in various directions are randomly formed in the gettering layer, so that scratches are suppressed from being locally sparse in the gettering layer, and heavy metals can be captured with high accuracy. Layers can be formed.

The invention according to claim 2 provides a surface treatment device for a wafer in which the resin material is a polyurethane resin in the configuration according to claim 1.

According to this configuration, when the polishing aid hydrolyzes the resin material made of polyurethane resin, some of the abrasive grains contained in the EG pad are released as free abrasive grains, and the abrasive grains are oriented in various directions in the gettering layer. Since the scratches are randomly formed, it is possible to prevent the scratches from being locally sparse in the gettering layer and to form a gettering layer capable of capturing heavy metals with high accuracy.

The invention according to claim 3 provides a wafer surface treatment apparatus in which the substrate holding mechanism and the surface treatment pad rotate in a relatively reverse manner in the configuration according to claim 1 or 2.

According to this configuration, the wafer and the EG pad rotate in relatively opposite directions, so that a complicated water flow is formed in the polishing aid interposed between the wafer and the EG pad. The free abrasive grains tend to roll randomly between the EG pad and the wafer, and scratches in various directions are randomly formed in the gettering layer, so that the scratches are locally sparse in the gettering layer. This can be suppressed to form a gettering layer capable of capturing heavy metals with high accuracy.

The invention according to claim 4 provides a wafer surface treatment apparatus in which the surface treatment pad is arranged above the substrate holding mechanism in the configuration according to any one of claims 1 to 3. Can be done.

According to this configuration, the polishing aid containing the free abrasive grains remains on the wafer, and the free abrasive grains roll between the surface treatment pad and the wafer for a long period of time, thereby scratching in the gettering layer. Is efficiently formed, so that a gettering layer composed of high-density scratches can be formed.

The invention according to claim 5 is the configuration according to any one of claims 1 to 4, wherein the surface treatment pad is a pad support that supports the EG pad, and the EG pad and the pad support. Provided is a wafer surface treatment apparatus comprising a sub pad interposed between them and softer than the EG pad.

According to this configuration, the sub-pad is deformed according to the waviness or warpage of the wafer, so that the EG pad follows the surface shape of the wafer to generate a gettering layer on the wafer. Therefore, regardless of the surface shape of the wafer. A gettering layer capable of capturing heavy metals with high accuracy can be formed.

According to the present invention, the abrasive grains (fixed abrasive grains) contained in the EG pad are pressed against the back surface of the wafer, and the abrasive grains (free abrasive grains) released from the EG pad roll randomly on the EG pad. As a result, scratches in various directions are randomly formed in the gettering layer, so that scratches are suppressed from being locally sparse in the gettering layer, and heavy metals can be captured with high accuracy. Layers can be formed.

It is a schematic plan view which shows the surface treatment apparatus of the wafer to which this invention is applied. FIG. 1 is a partial side view of a polishing / texturing unit in the same wafer surface treatment apparatus shown in FIG. 1, where FIG. 1A is a diagram for explaining a surface treatment pad, and FIG. 1B is a diagram for explaining a pad dresser. It is a schematic diagram explaining a wafer processing procedure, (a) is an explanatory diagram of a grinding process, (b) is an explanatory diagram of a polishing and texture processing process, (c) is an explanatory diagram of a cleaning process, and (d) is a rinse. It is explanatory drawing of a process. It is a figure which shows the state of forming an EG layer on a wafer schematically. An example of the wafer on which the EG layer is formed 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 between a surface treatment pad and a wafer. It is a figure which shows the rotation trajectory of the grindstone included in the surface treatment pad. It is an image which shows the direction of the scratch formed on the peripheral edge of a wafer. It is a schematic view which shows the surface treatment pad provided with the tilt mechanism, (a) is the plan view, (b) is the side view.

In order to achieve the object of generating an EG layer capable of accurately capturing heavy metals, the present invention is a wafer in which the back surface of a wafer having a device region formed on the front surface is mirror-finished and polished to generate a gettering layer. The surface treatment apparatus of the above has a substrate holding mechanism for holding and rotating a wafer, and an EG pad arranged so as to face the substrate holding mechanism and impregnating a pad base material with a resin material mixed with abrasive grains. It is provided with a surface treatment pad and a polishing aid supply mechanism that supplies an alkaline polishing aid between the substrate holding mechanism and the EG pad, and the polishing aid hydrolyzes the resin material to at least a part of the abrasive grains. Was released from the surface treatment pad, the wafer was pressed by the EG pad, and the substrate holding mechanism and the EG pad were rotated to form a gettering layer on the wafer.

Hereinafter, the wafer surface treatment 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. The 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 for index rotation. A turntable 13 for cleaning, a cleaning unit 14 for cleaning the four chuck portions 12a to 12d, and a transfer robot 15 for conveying the wafer W are included.

Further, as shown in FIG. 1, in the wafer surface treatment apparatus 10, the rough grinding unit 16, the finish grinding unit 17, and the polishing / texturing unit 18 are sequentially arranged along the outer circumference 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 mirror-finishes the back surface of the wafer W and forms 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, the motor 22 is suspended at the tip of the arm 21. A disc-shaped pad support 23 is attached to the output shaft 22a of the motor 22 so as to be horizontally rotatable. Further, a disk-shaped sub-pad 24 is adhesively fixed to the lower surface of the pad support 23 via a resin adhesive 25, and an EG as a disk-shaped surface treatment pad is further adhered to the lower surface of the sub-pad 24. The pad 26 is adhesively fixed via a resin adhesive 27, and the pad support 23, the sub pad 24, and the EG pad 26 are integrated. Therefore, 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 a pad base material made of polyurethane resin formed in a disk shape having a thickness of about 4.8 mm, and fine SiC (silicon silicon) of about 0.6 μm, tungsten, alumina, and other abrasive grains are applied to the pad base material. It is mixed in a resin material and the pad base material is impregnated with the resin. The abrasive grains impregnated with the resin material on the pad base material contribute to forming an EG layer by giving ultrafine scratches 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, is lower in hardness than the EG pad 26, and is provided so as to easily follow the surface shape of the wafer W during processing. ing. It goes without saying that the resin material that confuses the abrasive grains is not limited to polyurethane.

The EG pad unit 20 is provided with a supply line 28 connected between the wafer W and the EG pad 26 to a supply source for supplying water (pure water) and a polishing aid as a polishing aid. The polishing aid is, for example, a diluted solution (5 to 10%) containing an amine type (piperazine or the like).

In the pad dress unit 30 shown in FIG. 2B, a dresser head 32 is horizontally rotatably attached to a support member 31 connected to an output shaft of a motor (not shown). In this example, 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.

Then, in the wafer surface treatment apparatus 10, in the polishing / texturing unit 18, the back surface Wa side of the wafer W is subjected to extremely fine damage to generate an EG layer having gettering ability and to finish the wafer in a mirror shape. You can do it.

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

The wafer W is suction-held by the chuck portion 12a with the back surface Wa facing upward. The chuck portion 12a is pre-cleaned by the cleaning unit 14. After that, the turntable 13 rotates by index, and the chuck portion 12a is moved to the rough grinding unit 16. At this time, another wafer W is conveyed to another chuck portion 12d by a 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 using a rough grinding wheel (not shown). Next, the turntable 13 rotates by index, and the chuck portion 12a 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 grinded by a finish grinding wheel (not shown).

The turntable 13 is index-rotated again, and the chuck portion 12a 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 step, there are grinding marks as shown in FIG. 3A. Therefore, in the polishing / texturing unit 18, as shown in FIG. 3B, the EG pad 26 horizontally rotates together with the arm 21 and moves above the chuck portion 12a. Then, while rotating the EG pad 26 and the wafer W, the EG pad 26 is lowered to press the EG pad 26 against the wafer W. Further, a polishing aid is supplied between the EG pad 26 and the wafer W. In this way, a polishing / textured step in which the wet polishing of removing the grinding marks on the back surface Wa of the wafer W and polishing the back surface Wa in a mirror surface and the texture treatment for forming an EG layer on the wafer W are performed in parallel. (Surface treatment step) is executed.

Specifically, the abrasive grains (hereinafter referred to as "fixed abrasive grains") A1 contained in the EG pad 26 and the abrasive grains (hereinafter referred to as "free abrasive grains") A2 released from the EG pad 26 cooperate with each other. Then, polishing and texture processing are performed. The EG pad 2 and the wafer W rotate while the fixed abrasive grains A1 are pressed against the back surface Wa of the wafer W, and the free abrasive grains A2 roll on the wafer W. In the free abrasive grains A2, a part of the fixed abrasive grains A1 contained in the EG pad 26 was released from the EG pad 26 as shown in FIG. 4 when the resin adhesive 27 was swollen and hydrolyzed by the polishing aid. It is a thing.

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 modified to SiOH to soften the wafer W, so that the back surface Wa of the wafer W can be easily polished. Further, by rolling the free abrasive grains A2 between the EG pad 26 and the wafer W, the wafer W is not forcibly polished by an external force such as the free abrasive grains A2 biting into the wafer W, but by a natural force. An EG layer is formed in the wafer W by forming ultrafine scratches on the wafer W.

FIG. 5 shows an example of the wafer W that has undergone the polishing / texturing process. FIG. 5A is an overall perspective view of the wafer W as viewed from the back surface side, and FIG. 5B is a partially enlarged view of the wafer W. The cross-sectional view and FIG. 3C are partially enlarged perspective views thereof. In the wafer W shown in FIG. 5, a defect-free layer 40 is 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 surface Wb of the wafer W during backside grinding. On the other hand, the EG layer 43 is formed on the back 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, as shown in FIG. 3C, a cleaning step is performed on the machined surface 26a of the EG pad 26. 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. After that, 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 is placed on the dresser head 32 which is also 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. This makes it possible to prevent the polishing aid remaining on the machined surface 26a from being transferred to the wafer W in the rinsing step described later.

After the cleaning step, as shown in FIG. 3D, a rinsing step is performed on the back surface Wa of the wafer W. In this step, the EG pad 26 rotates horizontally together with the arm 21 and moves above the chuck portion 12a. After that, 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 arranged close to the wafer W in a non-contact state, and 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 water supplied is used for rinsing, and the polishing aid remaining on the back surface Wa of the wafer W is washed away and removed.

Next, the scratches constituting the EG layer will be described with reference to the drawings. FIG. 6 is a schematic plan view showing the amount of offset between the EG pad 26 and the wafer W. FIG. 7 is a diagram showing a rotation trajectory of the grindstone included in the EG pad 26. FIG. 8 is an image showing the orientation of scratches formed on the periphery of the wafer W.

As shown in FIG. 6, 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. 7, since the rotation trajectory of the fixed abrasive grains A1 included in the EG pad 26, that is, the density and directionality of scratches differ depending on the offset amount, the gettering ability of the EG layer 43 to be imparted to the wafer W The offset amount is arbitrarily adjusted accordingly. That is, the rotation trajectory of the fixed abrasive grain A1 having a zero offset amount shown in FIG. 7A is slightly curved in the circumferential direction from the center 0 of the wafer W corresponding to the rotation axis a2 of the chuck portion 12a toward the outer periphery. On the other hand, as shown in FIGS. 7 (b) and 7 (c), 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 scratches formed on the wafer W become sparse toward the outside of the wafer W. Further, as shown in FIG. 8, the peripheral edge of the wafer W tends to be regularly formed so that the scratch directions are aligned.

In addition to the scratches provided by the fixed abrasive grains A1, in the EG pad 26, the free abrasive grains A2 rolling on the EG pad 26 form scratches. The free abrasive grains A2 do not move regularly like the fixed abrasive grains A1 described above, but move randomly between the EG pad 26 and the wafer W. Therefore, the regularly moving fixed abrasive grains A1 and the randomly moving free abrasive grains A2 cooperate to apply scratches to the wafer W, thereby suppressing the scratches in the EG layer 43 from being locally sparse. it can.

As shown in FIG. 9, the EG pad 26 may be provided with a tilt mechanism 50 in order to reduce variations in the scratch density in the EG layer 43.

The tilt mechanism 50 includes one fixed support portion 51 arranged on the tip end side of the EG pad 26, and two movable support portions 52 arranged on the proximal end side of the EG pad 26. The fixed support portion 51 and the movable support portion 52 are attached to a tilt table 53 that is tiltable relative to a fixed member such as a spindle that accommodates a motor (not shown).

The fixed support portion 51 is a bolt or the like that fastens the tilt table 53 to the fixed member.

The movable support portion 52 is interposed between the tilt table 53 and the fixing member, and is, for example, a known ball screw mechanism that separates the tilt table 53 and the fixing member by screwing a ball screw.

The two movable support portions 52 and 52 independently move the tilt table 53 with respect to the fixed member, so that the tilt table 53 is tilted at an arbitrary angle with the fixed support portion 51 as a fulcrum. As a result, the scratch density in the EG layer 43 can be partially changed by locally pressing the EG pad 26 against the back surface Wa of the wafer W in a non-uniform manner.

As described above, according to the wafer surface treatment apparatus 10 according to the present invention, the fixed abrasive grains A1 contained in the EG pad 26 are pressed against the back surface Wa of the wafer W, and the free abrasive grains released from the EG pad 26 are released. Since A2 randomly rolls on the EG pad 26, scratches in various directions are randomly formed in the EG layer 43, so that scratches are suppressed from being locally sparse in the EG layer 43. Therefore, the EG layer 43 capable of capturing heavy metals with high accuracy can be formed.

It should be noted that the present invention can be modified in various ways as long as it does not deviate from the spirit of the present invention, and it is natural that the present invention extends to the modified ones.

As described above, in addition to processing the back surface 20b of the wafer W, it can also be applied to an apparatus for processing various plate-like surfaces.

10 Wafer surface treatment devices 11a, 11b Cassettes 12a to 12d Chuck section (board holding mechanism)
13 Turntable 14 Cleaning unit 15 Conveying robot 16 Rough grinding unit 17 Finish grinding unit 18 Polishing / textured unit 20 EG pad unit 21 Arm 22 Motor 22a Output shaft 23 Pad support 24 Sub pad 25 Resin adhesive 26 EG pad (surface) Processing pad)
26a Processed surface 27 Resin adhesive 28 Supply line 30 Pad dress unit 31 Support member 32 Dresser head 33 Polishing layer 43 EG layer 50 Tilt mechanism 51 Fixed support 52 Movable support 53 Tilt table A1 Fixed abrasive grains A2 Free abrasive grains

Claims (5)

A surface treatment device for a wafer in which the back surface of a wafer having a device region formed on the front surface is mirror-finished and polished to generate a gettering layer.
A substrate holding mechanism that holds and rotates the wafer,
A surface treatment pad having an EG pad which is arranged to face the substrate holding mechanism and is formed by impregnating a pad base material with a resin material mixed with abrasive grains.
A polishing aid supply mechanism that supplies an alkaline polishing aid between the substrate holding mechanism and the EG pad,
With
The polishing aid hydrolyzes the resin material to release at least a part of the abrasive grains from the surface treatment pad, presses the wafer with the EG pad, and rotates the substrate holding mechanism and the EG pad. A wafer surface treatment apparatus, characterized in that the gettering layer is generated on the wafer by allowing the wafer to be formed. The wafer surface treatment apparatus according to claim 1, wherein the resin material is a polyurethane resin. The wafer surface treatment apparatus according to claim 1 or 2, wherein the substrate holding mechanism and the surface treatment pad rotate in a relatively reverse direction. The wafer surface treatment apparatus according to any one of claims 1 to 3, wherein the surface treatment pad is arranged above the substrate holding mechanism. The surface treatment pad is
A pad support that supports the EG pad and
A sub-pad that is interposed between the EG pad and the pad support and is softer than the EG pad,
The wafer surface treatment apparatus according to any one of claims 1 to 4, wherein the wafer surface treatment apparatus is provided.