JP6843553B2 - Wafer surface treatment method - Google Patents

Description

The present invention relates to a wafer surface treatment method, and more particularly to a wafer surface treatment method 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. ") Is formed. Due to the gettering effect of the EG layer, heavy metals are trapped in the EG layer, and the heavy metals mixed in the wafer are prevented 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 to remove grinding strain capable of capturing heavy metals adhering to the back surface of the wafer, and then pure water is formed. It is known that the polishing pad is pressed against the back surface of the wafer while supplying the wafer to form an EG layer on the wafer (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2013-247132.

However, in the processing method described in Patent Document 1, when a heavy metal adheres to the back surface of the wafer between the polishing step of removing the grinding strain and the step of forming the EG layer on the wafer, the device region of the heavy metal is reached. There was a problem that it was difficult to suppress the spread of the wafer.

Therefore, when the EG layer is formed on the wafer, a technical problem to be solved in order to prevent heavy metals from adhering to the wafer 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 side and to generate a gettering layer. This is a method for surface treatment of a wafer, and is between a holding step of holding the wafer by a substrate holding mechanism and a surface treatment pad having an EG pad formed by impregnating the wafer with a resin material mixed with abrasive grains. An alkaline polishing aid is supplied, and the polishing aid hydrolyzes the resin material to release at least a part of the abrasive grains from the surface treatment pad, and the fixed abrasive grains contained in the EG pad are said. by free abrasive grains released from the EG pad by rotating the substrate holding mechanism and the surface treatment pad in a state of being pressed to the wafer rolls on the wafer, polishing the back surface of the wafer to mirror-like Provided is a surface treatment method for a wafer including a surface treatment step for forming the gettering layer.

According to this configuration, the surface treatment pad removes the grinding damage on the back surface of the wafer and finishes it in a mirror shape, and at the same time, a gettering layer is generated on the wafer. It can be suppressed from being mixed in.

Further, since the wafer polishing and the gettering layer are generated in parallel, the surface treatment step can be performed more efficiently than in the conventional case where these are performed independently.

The invention according to claim 2 has the substrate holding mechanism and the surface treatment while supplying pure water between the wafer and the surface treatment pad after the surface treatment step in the configuration according to the first aspect. Provided is a method for surface treatment of a wafer, which comprises a rinsing step of rotating a pad to wash away the polishing aid remaining on the back surface of the wafer.

According to this configuration, it is possible to prevent the wafer from being corroded by the polishing aid by washing away the polishing aid remaining on the wafer after the surface treatment step.

The invention according to claim 3 provides a surface treatment method for a wafer in which the wafer and the surface treatment pad rotate in a non-contact state in the rinsing step in the configuration according to claim 2.

According to this configuration, the rotation of the wafer and the surface treatment pad forms a water flow in the pure water interposed between the wafer and the surface treatment pad, so that the polishing aid remaining on the wafer is smoothed. Since it is washed away, it is possible to prevent the wafer from being corroded by the polishing aid.

The invention according to claim 4 can provide a surface treatment method for a wafer in which the substrate holding mechanism and the surface treatment pad are relatively reversely rotated in the rinsing step in the configuration according to claim 3.

According to this configuration, the wafer and the surface treatment pad rotate in relatively opposite directions to form a complicated water flow in the pure water interposed between the wafer and the surface treatment pad, thereby forming a complicated water flow on the wafer. Since the polishing aid remaining in the wafer is smoothly washed away, it is possible to further prevent the wafer from being corroded by the polishing aid.

The invention according to claim 5 is the configuration according to any one of claims 2 to 4, wherein a pad dresser is pressed against the processed surface of the surface treatment pad during the surface treatment step and the rinse step. Provided is a method for surface treatment of a wafer, which includes a dressing step of wiping the processed surface.

According to this configuration, the polishing aid remaining on the surface treatment pad is removed by the pad dresser before the rinsing step, so that the polishing aid is transferred from the surface treatment pad to the wafer in the rinsing step, and the wafer is transferred. Can be prevented from being corroded by the polishing aid.

According to the present invention, since the surface treatment pad removes the grinding damage on the back surface of the wafer to finish it in a mirror shape and forms a gettering layer on the wafer, a heavy metal is formed in the wafer between the polishing step and the EG layer forming step. It can be suppressed from being mixed in. Further, since the wafer polishing and the gettering layer are generated in parallel, the surface treatment step can be performed more efficiently than in the conventional case where these are performed independently.

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 rinsing. 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.

In the present invention, in order to achieve the object of suppressing the adhesion of heavy metals to the wafer when the EG layer is formed on the wafer, the back surface of the wafer in which the device region is formed on the front surface side is mirror-finished and polished. This is a surface treatment method for a wafer that also produces a gettering layer, in which the wafer is held by a substrate holding mechanism and the surface treatment is performed while supplying an alkaline polishing aid between the wafer and the surface treatment pad. This was achieved by pressing the pad against the wafer, rotating the substrate holding mechanism and the surface treatment pad, polishing the back surface of the wafer in a mirror shape, and forming a surface treatment step to generate a gettering layer.

Hereinafter, the wafer surface treatment apparatus 10 to which the wafer surface treatment method according to the embodiment of the present invention is applied 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. It includes 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.

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 / textured unit 18 are arranged in order 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 impregnated in the resin pad base material. The abrasive grains impregnated with the resin material in 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 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 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 23 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 impregnated with diamond abrasive grains 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, a polishing process is performed in which the back surface Wa side of the wafer W is subjected to extremely fine damage to generate an EG layer having a gettering ability and to finish it in a mirror shape. Can be done.

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, an alkaline polishing aid is supplied between the EG pad 26 and the wafer W. In this way, a polishing / texturing step in which a wet polish for removing grinding marks on the back surface Wa of the wafer W and polishing the back surface Wa in a mirror surface and a texturing process 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 texturing are performed. The EG pad 26 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 back surface Wa of 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 at the time of 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 clutches 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. As a result, in the rinsing step described later, it is possible to prevent the polishing aid remaining on the machined surface 26a from being transferred to the wafer W.

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 by rotating the wafer W and the EG pad 26 in opposite directions in this state, a complicated water flow is created on the back surface Wa of the wafer W. Can be formed. In this way, the supplied water is used for rinsing treatment, and the polishing aid remaining on the back surface Wa of the wafer W is washed away and removed.

As described above, according to the wafer surface treatment apparatus 10 according to the present invention, the EG pad 26 removes the grinding damage of the back surface Wa of the wafer W to finish it in a mirror shape, and at the same time, forms the EG layer 43 on the wafer W. It is possible to prevent heavy metals from being mixed into the wafer W between the polishing step and the EG layer forming step.

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 Finishing 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 Pat dress unit (Pat dresser)
31 Support member 32 Dresser head 33 Non-woven fabric A1 Fixed abrasive grains A2 Free abrasive grains

Claims (5)

A surface treatment method 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.
The holding process of holding the wafer by the substrate holding mechanism and
An alkaline polishing aid is supplied between the wafer and a surface treatment pad having an EG pad formed by impregnating a resin material mixed with abrasive grains, and the polishing aid hydrolyzes the resin material to obtain the above. and at least a portion of the abrasive particles released from the surface treatment pad, the EG pad fixed abrasive grains contained in the EG pad by rotating the substrate holding mechanism and the surface treatment pad in a state of being pressed against the wafer A surface treatment step in which the free abrasive grains released from the wafer roll on the wafer to mirror-polish the back surface of the wafer and generate the gettering layer.
A wafer surface treatment method comprising. After the surface treatment step, while supplying pure water between the wafer and the surface treatment pad, the substrate holding mechanism and the surface treatment pad are rotated to remove the polishing aid remaining on the back surface of the wafer. The wafer surface treatment method according to claim 1, further comprising a rinse step of rinsing. The wafer surface treatment method according to claim 2, wherein in the rinsing step, the wafer and the surface treatment pad rotate in a non-contact state. The wafer surface treatment method according to claim 3, wherein in the rinsing step, the substrate holding mechanism and the surface treatment pad are relatively rotated in the reverse direction. Any one of claims 2 to 4, wherein a dressing step of pressing a pad dresser against the processed surface of the surface treatment pad to wipe off the processed surface is included between the surface treatment step and the rinse step. The wafer surface treatment method according to the item.