US20110256811A1

US20110256811A1 - Polishing method

Info

Publication number: US20110256811A1
Application number: US13/080,821
Authority: US
Inventors: Masayuki Nakanishi; Kenya Ito; Masaya Seki; Kenji Iwade; Takeo Kubota
Original assignee: Individual
Current assignee: Ebara Corp; Toshiba Corp
Priority date: 2010-04-16
Filing date: 2011-04-06
Publication date: 2011-10-20
Also published as: JP2011224680A

Abstract

A polishing method can obtain a good polishing profile which, for example, will not cause peeling of a semiconductor layer from a silicon substrate. The polishing method includes: positioning a polishing head at a position above a polishing start position in an edge portion of a rotating substrate; lowering a polishing tool of the polishing head until the polishing tool comes into contact with the polishing start position in the edge portion of the rotating substrate and a pressure between the polishing tool and the polishing start position reaches a set pressure; allowing the polishing tool to stay at the polishing start position for a predetermined amount of time; and then moving the polishing head toward a peripheral end of the substrate while keeping the polishing tool in contact with the edge portion of the rotating substrate at the set pressure.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a polishing method for polishing a peripheral portion (edge portion and bevel portion) of a substrate, such as a semiconductor wafer, and more particularly to a polishing method for polishing or grinding a peripheral portion of a semiconductor wafer in the process of manufacturing a semiconductor device in a surface of the semiconductor wafer.
2. Description of the Related Art
A polishing apparatus, which uses a polishing tape having abrasive particles fixed on a surface, is known as a polishing apparatus for polishing a peripheral portion (edge portion and bevel portion) of a substrate, such as a semiconductor wafer (see Japanese Patent No. 4125148). In polishing of a peripheral portion (edge portion and bevel portion) of a semiconductor wafer by the use of a polishing tape, it is common practice to press a surface of the polishing tape against the peripheral portion of the semiconductor wafer, rotating in a horizontal plane, at a set pressure while supplying a polishing liquid, such as pure water, to a surface of the semiconductor wafer.
In a semiconductor wafer W shown in FIG. 1, for example, the “bevel portion” herein refers to a portion B consisting of an upper inclined portion P and a lower inclined portion Q of an upper surface and a lower surface, respectively, of the semiconductor wafer W, and a peripheral side surface portion R of the semiconductor wafer W. The “edge portion” of the semiconductor wafer W shown in FIG. 1, for example, herein refers to a portion E lying between the boundary of the bevel portion B and a device area D of the upper surface in which semiconductor devices are formed.
A commonly-known polishing apparatus for polishing an edge portion of a substrate with a polishing tape includes a horizontally movable polishing head in which a polishing tape is held movably in one direction. In operation of this polishing apparatus, the polishing head is positioned immediately above a polishing start position in an edge portion of a rotating substrate, and the polishing tape is lowered and brought into contact with the polishing start position in the edge portion of the rotating substrate. When the contact pressure (load) of the polishing tape on the edge portion of the substrate is found to have reached a set pressure, the polishing tape is allowed to move (scan) toward the peripheral end of the substrate at a predetermined movement speed while keeping the polishing tape in contact with the edge portion of the rotating substrate.
The applicant has proposed a polishing apparatus which can polish a peripheral portion (edge portion) of a substrate, including a flat portion, with a polishing tape while maintaining the original angle of the peripheral portion (see Japanese Patent Laid-Open Publication No. 2009-208214). The applicant has also proposed a polishing apparatus which is suited for polishing of a bevel portion of a substrate, can shorten the overall polishing time and can facilitate replacement of polishing tape (see Japanese Patent Laid-Open Publication No. 2009-154285).
It has recently been proposed to manufacture a bonded substrate, such as an SOI (silicon-on-insulator) substrate, by a bonding method which involves bonding, through heat treatment or the like, two silicon substrates (a device substrate having semiconductor devices and a supporting substrate). In a known method for manufacturing a bonded substrate, such as an SOI substrate, a first silicon substrate (device substrate), having a surface semiconductor layer (SOI layer) and whose surface edge portion has been polished away as necessary, and a second silicon substrate (supporting substrate), facing each other, are bonded via an insulting film, and then the back surface of the first silicon substrate (device substrate) is polished or etched away, leaving the semiconductor layer. Thereafter, an entire peripheral portion of the semiconductor layer is polished away, and an edge portion of the second silicon substrate is polished to a predetermined depth (see Japanese Patent Laid-Open Publication No. H4-85827).

SUMMARY OF THE INVENTION

With reference to the conventional polishing apparatus which includes a polishing head and in which a polishing tape is lowered and brought into contact with a polishing start position in an edge portion of a rotating substrate and, when the contact pressure of the polishing tape on the edge portion of the substrate is found to have reached a set pressure, the polishing tape is allowed to move toward the peripheral end of the substrate at a predetermined movement speed while keeping the polishing tape in contact with the edge portion of the rotating substrate, it is generally difficult to bring the polishing tape into contact with the polishing start position in the edge portion of the substrate at a set pressure upon the start of polishing and, in addition, the polishing tape stays in the polishing start position generally for only a short time. The conventional polishing apparatus, therefore, has the problem that a polished surface of a substrate, at the boundary with the non-polished surface, is likely to suffer from insufficient polishing or uneven polishing.
Especially when manufacturing a bonded wafer, such as an SOI substrate, by the above-described method in which a first silicon substrate (device substrate), having a surface semiconductor layer, and a second silicon substrate (supporting substrate), facing each other, are bonded via an insulting film, and then the back surface of the first silicon substrate (device substrate) is polished or etched away, leaving the semiconductor layer, and thereafter the entire peripheral portion of the semiconductor layer is polished away, and the edge portion of the second silicon substrate is polished to a predetermined depth, the semiconductor layer is likely to peel off the second silicon substrate (supporting substrate) if insufficient polishing or uneven polishing occurs at the boundary of the polished surface with the non-polished surface.
The present invention has been made in view of the above situation. It is therefore an object of the present invention to provide a polishing method which, e.g., when manufacturing a bonded wafer, such as an SOI substrate, by the above-described method comprising polishing away an entire peripheral portion of a semiconductor layer of a first silicon substrate, and polishing an edge portion of a second silicon substrate to a predetermined depth, can obtain a good polishing profile which will not cause peeling of the semiconductor layer from the second silicon substrate.
In order to achieve the above object, the present invention provides a polishing method comprising: positioning a polishing head at a position above a polishing start position in an edge portion of a rotating substrate; lowering the polishing head and bringing a polishing tool of the polishing head into contact with the polishing start position in the edge portion of the rotating substrate at a predetermined pressure; allowing the polishing tool to stay at the polishing start position for a predetermined amount of time; and then moving the polishing head toward a peripheral end of the substrate while keeping the polishing tool in contact with the edge portion of the rotating substrate at the predetermined pressure.
According to this polishing method, while keeping the polishing tool in contact with a polishing start position in an edge portion of a rotating substrate at a predetermined pressure, the polishing tool is allowed to stay at the polishing start position for a predetermined amount of time to polish the edge portion at the polishing start position. This can prevent the occurrence of insufficient polishing or uneven polishing at the boundary of the polished surface with the non-polished surface, making it possible to obtain a good polishing profile which, e.g., will not cause peeling of a surface film, such as a semiconductor layer, from the substrate. Furthermore, even when a film to be polished away is present in an edge portion of a substrate in an uneven distribution in the circumferential direction, the film to be polished away can be securely prevented from remaining in the edge portion of the substrate by setting the polishing tool stay time based on the location hardest to polish.
The present invention also provides a polishing method comprising: positioning a polishing head at a position above a polishing start position in an edge portion of a rotating substrate; lowering a polishing tool of the polishing head until the polishing tool comes into contact with the polishing start position in the edge portion of the rotating substrate and a pressure between the polishing tool and the polishing start position reaches a set pressure; allowing the polishing tool to stay at the polishing start position for a predetermined amount of time; and then moving the polishing head toward a peripheral end of the substrate while keeping the polishing tool in contact with the edge portion of the rotating substrate at the set pressure.
According to this polishing method, while keeping the polishing tool in contact with a polishing start position in an edge portion of a rotating substrate at a set pressure, the polishing tool is allowed to stay at the polishing start position for a predetermined amount of time to polish the edge portion at the polishing start position. This can prevent the occurrence of insufficient polishing or uneven polishing at the boundary of the polished surface with the non-polished surface, making it possible to obtain a good polishing profile which, e.g., will not cause peeling of a surface film, such as a semiconductor layer, from the substrate.
In a preferred aspect of the present invention, the predetermined amount of time is preferably at least one second.
In a preferred aspect of the present invention, during a period after contact of the polishing tool with the edge portion of the substrate until the start of movement of the polishing head, the contact pressure of the polishing tool on the edge portion of the substrate is kept higher than the set pressure.
Thus, the polishing rate can be increased when an edge portion of a substrate is polished while allowing the polishing tool to stay at the polishing start position in the edge portion of the substrate for a predetermined amount of time. This can prevent lowering of the throughput. In view of stress exerting on the substrate, it is also possible to raise the rotational speed of the substrate.
The present invention also provides a polishing method comprising: a first polishing step including (a) positioning a polishing head at a position above a polishing start position in an edge portion of a rotating substrate, (b) lowering a polishing tool of the polishing head until the polishing tool comes into contact with the polishing start position in the edge portion of the rotating substrate and a pressure between the polishing tool and the polishing start position reaches a set pressure, and (c) moving the polishing head toward a peripheral end of the substrate at a first movement speed while keeping the polishing tool in contact with the edge portion of the rotating substrate; and a second polishing including (d) moving the polishing head toward the peripheral end of the substrate at a second movement speed while keeping the polishing tool in contact with the edge portion of the rotating substrate.
By thus carrying out polishing of an edge portion of a substrate in two steps at different polishing rates, a film to be polished away, existing in the edge portion of the substrate, can be polished under polishing conditions appropriate for the particular film. Further, the inclination of a stepped portion, formed at the boundary between the polished surface and the non-polished surface of the substrate, can be arbitrarily changed by changing polishing conditions.
The second movement speed of the polishing head is preferably higher than the first movement speed of the polishing head.
This can prevent the occurrence of insufficient polishing or uneven polishing at the boundary of the polished surface of a substrate with the non-polished surface, making it possible to obtain a good polishing profile.
In a preferred aspect of the present invention, when moving the polishing head toward the peripheral end of the substrate at the first movement speed, the contact pressure of the polishing tool on the edge portion of the substrate is kept higher than the set pressure.
Thus, the polishing rate can be increased when the polishing head is moving toward the peripheral end of the substrate at the first movement speed. This can prevent lowering of the throughput. In view of stress exerting on the substrate, it is also possible to raise the rotational speed of the substrate.
In a preferred aspect of the present invention, after lowering the polishing tool and bringing the polishing tool into contact with the polishing start position in the edge portion of the rotating substrate at a lower pressure than the set pressure, the pressure of the polishing tool on the edge portion of the substrate is increased to the set pressure.
This can minimize the stress exerting on the substrate when the descending polishing tool comes into contact with the polishing start position in the edge portion of the rotating substrate. In the absence of a hard member, such as a stage, which supports an edge portion of a substrate from below, a stress exerting on the substrate could bend the substrate, which can result in the formation of a crack in the substrate and, in the worst case, breakage of the substrate. Such problems can be prevented by minimizing the stress exerting on the substrate in the above-described manner.
The polishing tool may preferably be a polishing tape which travels in one direction at a predetermined speed when it polishes the edge portion of the substrate.
In a preferred aspect of the present invention, a bevel portion of the substrate is polished while polishing the edge portion of the substrate by keeping the polishing tool in contact with the edge portion of the rotating substrate.
The throughput can be increased by thus simultaneously polishing the edge portion and the bevel portion of the substrate while rotating the substrate.
A polishing apparatus may comprises: a substrate holding section for holding and rotating a substrate in a horizontal position; a horizontally movable polishing head including a vertically movable polishing tool for polishing an edge portion of the substrate by pressing it against the edge portion of the rotating substrate held in a horizontal position by the substrate holding section; and a control section for controlling the movement of the polishing head, wherein the control section controls the polishing head in such a manner that after the polishing tool has come into contact with a polishing start position in the edge portion of the rotating substrate and the contact pressure has reached a set pressure, the polishing tool is allowed to stay at the polishing start position for a predetermined amount of time, and thereafter the polishing head moves toward the peripheral end of the substrate while keeping the polishing tool in contact with the edge portion of the rotating substrate at the set pressure.
Alternatively, a polishing apparatus may comprises: a substrate holding section for holding and rotating a substrate in a horizontal position; a horizontally movable polishing head including a vertically movable polishing tool for polishing an edge portion of the substrate by pressing it against the edge portion of the rotating substrate held in a horizontal position by the substrate holding section; and a control section for controlling the movement of the polishing head, wherein the control section controls the polishing head in such a manner that after the polishing tool has come into contact with a polishing start position in the edge portion of the rotating substrate and the contact pressure has reached a set pressure, the polishing head moves toward the peripheral end of the substrate at a first movement speed while keeping the polishing tool in contact with the edge portion of the rotating substrate, and thereafter the polishing head moves toward the peripheral end of the substrate at a second movement speed while keeping the polishing tool in contact with the edge portion of the rotating substrate.
The polishing apparatuses may further comprise a bevel polishing head for polishing a bevel portion of the rotating substrate.
The present invention makes it possible to prevent the occurrence of insufficient polishing or uneven polishing at the boundary of a polished surface of a substrate with a non-polished surface, and to obtain a good polishing profile which, e.g., will not cause peeling of a surface film, such as a semiconductor layer, from the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating a bevel portion and an edge portion of a semiconductor wafer;

FIG. 2 is a schematic front view of a polishing apparatus;

FIG. 3 is a side view showing a tilt mechanism for tilting a polishing head of the polishing apparatus shown in FIG. 2;

FIGS. 4A through 4D are diagrams illustrating, in a sequence of process steps, the relationship between the polishing head and a substrate upon polishing of an edge portion of the substrate in the polishing apparatus shown in FIG. 2;

FIG. 5 is a graph showing an exemplary relationship between the movement speed of the polishing head and time upon polishing of an edge portion of a substrate in the polishing apparatus shown in FIG. 2;

FIGS. 6A though 6C are graphs showing other exemplary relationships between the movement speed of the polishing head and time upon polishing of an edge portion of a substrate in the polishing apparatus shown in FIG. 2;

FIG. 7 is a graph showing the relationship between polishing amount and radial position on a substrate in Example 1;

FIG. 8 is a graph showing the relationship between polishing amount and radial position on a substrate in Example 2;

FIG. 9 is a graph showing the relationship between polishing amount and radial position on a substrate in Comp. Example 1

FIG. 10 is a photomicrograph of a substrate surface after polishing (rough polishing) of an edge portion of a substrate, showing a surface area around the boundary between the polished surface and the non-polished surface;

FIG. 11 is a photomicrograph of a substrate surface after polishing of an edge portion of a substrate in Example 3, showing a surface area around the boundary between the polished surface and the non-polished surface;

FIG. 12 is a photomicrograph of a substrate surface after polishing of an edge portion of a substrate in Example 4, showing a surface area around the boundary between the polished surface and the non-polished surface;

FIG. 13 is a photomicrograph of a substrate surface after polishing of an edge portion of a substrate in Comp. Example 2, showing a surface area around the boundary between the polished surface and the non-polished surface; and

FIG. 14 is a schematic view of another polishing apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 2 is a schematic front view showing a polishing apparatus. As shown in FIG. 2, this polishing apparatus includes a substrate holding section 1 for holding and rotating a substrate W, such as a semiconductor wafer, in a horizontal position, a polishing head 2 for polishing an edge portion of the substrate W held by the substrate holding section 1, and a support section 3 for supporting, from the back surface of the substrate W, the edge portion of the substrate W held by the substrate holding section 1.
The substrate holding section 1 includes a substrate stage 11 for holding the substrate W, e.g., by vacuum attraction, and a substrate rotating mechanism 12 for rotating the substrate stage 11. The substrate stage 11 has a smaller diameter than the substrate W so that the substrate W is held with the edge portion lying outside the substrate stage 11. The substrate rotating mechanism 12 has a not-shown motor which is coupled to the substrate stage 11. Thus, the substrate W held on the substrate stage 11 rotates in a horizontal plane by rotating the motor of the substrate rotating mechanism 12.
The polishing head 2 is provided with a polishing tape 10 as a polishing tool for polishing the edge portion of the substrate W by pressing it against the edge portion of the surface (upper surface) of the substrate W. In this embodiment, the polishing tape 10 is used as a polishing tool. A polishing tape having abrasive particles, such as diamond particles or SiC particles, fixed on one surface of a base film, can be used as the polishing tape 10. The surface of the polishing tape 10, on which the abrasive particles are fixed, serves as a polishing surface. The abrasive particles of the polishing tape 10 may be appropriately selected depending on the type of the substrate W, the polishing performance required, etc. For example, diamond particles or SiC particles, having an average particle size in the range of 0.1 μm to 5.0 μm, can be used as the abrasive particles. It is also possible to use a belt-like polishing cloth having no abrasive particles. A film made of a material having flexibility, such as polyester, polyurethane, polyethylene terephthalate, etc., can be used as the base film.
The substrate holding section 1, the polishing head 2 and the support section 3 are housed in a not-shown housing, and the interior space of the hosing constitutes a polishing room. The polishing tape 10 is fed to the polishing head 2 from a polishing tape supply mechanism 15 which is disposed outside the polishing room. The polishing tape supply mechanism 15 is secured to the housing or a not-shown frame, so that the position of the mechanism 15 is fixed. The polishing tape supply mechanism 15 includes a tape feeding mechanism 16 and a tape roll-up mechanism 17. The polishing tape 10 is fed from the tape feeding mechanism 16 to the polishing head 2, and is recovered from the polishing head 2 by the tape roll-up mechanism 17. Because the polishing tape 10 is thus fed continuously and gradually from the polishing tape supply mechanism 15 to the polishing head 2, polishing of the substrate W is performed always by a new polishing surface.
The polishing head 2 includes a pressing pad 20 disposed on the back side (opposite side from the polishing surface) of the polishing tape 10, and a pressing mechanism 21, e.g., comprised of a stepping motor or a servomotor, for applying a pressure to the pressing pad 20. The position and the rotational speed of the pressing mechanism 21 are controllable. The pressing pad 20 is secured to a front end of a rod 22 which extends from the pressing mechanism 21 and which is supported by a not-shown bearing slidably in the longitudinal direction thereof. A pressure is applied by the pressing mechanism 21 to the pressing pad 20 via the rod 22 so as to press the polishing surface of the polishing tape 10 against the surface of the substrate W. The pressure applied to the polishing tape 10 is detected, e.g., by a pressure sensor provided between the front end of the rod 22 and the pressing pad 20 or a torque sensor which detects the motor torque, and is controlled, e.g., at a set load (pressure), whereby the stop (stay) position of the polishing tape 10 in the vertical direction is adjusted. Examples of materials usable for the pressing pad 20 include elastic materials such as silicone rubber, a silicone sponge, fluororubber, etc., and rigid materials such as polybutylene naphthalate (PBN), fluororesin, polyether ether ketone (PEEK), etc.
Instead of the above-described motor, it is possible to use an air cylinder as a drive mechanism for the pressing mechanism 21. Also in this case, it is possible to measure the pressure applied to the polishing tape 10, e.g., with a pressure sensor provided between the front end of the rod 22 and the pressing pad 20 or with a pressure gauge which measures the air pressure in the air cylinder, and to adjust the pressure on the polishing tape 10 to a set load (pressure) by adjusting the pressure of air supplied to the air cylinder, thereby accurately controlling the pressure of the polishing tape 10 during polishing.
FIG. 3 is a side view showing a tilt mechanism for tilting the polishing head 2. The polishing head 2 is coupled to a motor 29 via an arm 26, a belt 27 and pulleys 28A, 28B, so that by the actuation of the motor 29, the polishing head 2 rotates (tilts) around the peripheral end of the substrate W on the substrate holding section 1. The arm 26, the belt 27, the pulleys 28A, 28B and the motor 29 constitute a tilt mechanism for tilting the polishing head 2.
The polishing head 2 is supported via the tilt mechanism by a plate 30 which is provided on a sliding mechanism 31. The sliding mechanism 31 allows the plate 30 to move in the longitudinal direction of the sliding mechanism 31. The plate 30 is coupled to a linear actuator 33 whose stop position and movement speed are controllable, so that by the actuation of the linear actuator 33, the polishing head 2 moves in the radial direction of the substrate W held on the substrate holding section 1. Thus, the linear actuator 33 constitutes a movement mechanism for moving the polishing head 2 in the radial direction of the substrate W.
The polishing head 2 is disposed on the front surface (upper surface) side of the substrate W held on the substrate holding section 1, while the support section 3 is disposed on the back surface (lower surface) side of the substrate W. Thus, the polishing head 2 and the support section 3 are approximately vertically symmetrical with respect to the substrate W. The support section 3 supports the edge portion of the substrate W, which is being pressed on by the polishing head 2, from the opposite side (back side) of the substrate W from the edge portion by utilizing the pressure of a fluid, as described below.
The support section 3 is coupled via a sliding mechanism 34 to the plate 30 that supports the polishing head 2. The sliding mechanism 34 is coupled to a not-shown linear actuator mounted to the plate 30. The support section 3 is thus movable in the radial direction of the substrate W independently of the polishing head 2. The support section 3 is connected to a liquid supply source 36 via a pressure-reducing valve 35. A liquid, whose pressure is adjusted by the pressure-reducing valve 35, is supplied to the support section 3. The support section 3 has a nozzle 37 located near a back surface portion opposite to the edge portion of the substrate W. The liquid whose pressure has been adjusted by the pressure-reducing valve 35 is ejected from the nozzle 37 toward the edge portion of the back surface of the substrate W. Pure water is preferably used as the liquid.
A polishing liquid supply nozzle 40 for supplying a polishing liquid, such as pure water, onto the front surface (upper surface) of the substrate W is disposed at a position above the central portion of the substrate W held on the substrate holding section 1. The polishing apparatus also includes a control section 42 for controlling the not-shown motor of the substrate rotating mechanism 12, the pressing mechanism 21 of the polishing head 2, and the linear actuator 33 which constitutes the movement mechanism for moving the polishing head 2 in the radial direction of the substrate W.
The control section 42 controls the rotational speed of the not-shown motor of the substrate rotating mechanism 12, the pressing load and the stop position of the pressing mechanism 21 of the polishing head 2, the stop position and the movement speed of the linear actuator 33, etc.
Polishing of an edge portion of a substrate by the polishing apparatus of this embodiment will now be described with reference further to FIGS. 4 and 5.
A substrate W is transported by a not-shown transport robot into the polishing room of the polishing apparatus and placed on the substrate stage 11 of the substrate holding section 1. The substrate holding section 1, while performing centering of the substrate W, holds the substrate W, e.g., by vacuum attraction and rotates it in a horizontal plane. At the same time, a polishing liquid, such as pure water, begins to be supplied from the polishing liquid supply nozzle 40 onto the surface (upper surface) of the substrate W.
Next, the polishing head 2, located in a stand-by position beside the substrate W held on the substrate holding section 1, as shown in FIG. 4A, is moved by the actuation of the linear actuator 33 to a position immediately above a polishing start position, where the distance L₁from the peripheral end of the substrate W to the pressing pad 20 is, e.g., 1.3 mm, in the edge portion of the substrate W, as shown in FIG. 4B. By the actuation of the linear actuator 33, the support section 3 moves to a position immediately below the polishing start position in the edge portion of the substrate W.
After the rotational speed of the substrate W is found to have reached a predetermined rotational speed, the polishing tape supply mechanism 15 is actuated to allow the polishing tape 10 to travel from the tape feeding mechanism 16 to the tape roll-up mechanism 17 via the polishing head 2 and to be rolled up by the tape roll-up mechanism 17. At the same time, the pressing mechanism 21 is actuated to lower the pressing pad 20 and gradually bring the polishing tape 10 into contact with the substrate W, as shown in FIG. 4C, while a liquid is ejected from the nozzle 37 of the support section 3 toward the edge portion of the lower surface of the substrate W. Polishing of the edge portion of the substrate W at a set pressure starts when the polishing tape 10 comes into contact with the edge portion of the substrate W and the contact pressure (load) reaches the set pressure.
Though the pressing pad 20 may be moved at a somewhat high speed, the pressing mechanism 21 is preferably controlled so that the load applied from the pressing pad 20 to the substrate W increases gradually. This can minimize the stress exerting on the substrate W when the descending polishing tape 10 comes into contact with the polishing start position in the edge portion of the rotating substrate W. In the absence of a hard member, such as a stage, which supports an edge portion of a substrate from below, a stress applied to a substrate could bend the substrate, which can result in the formation of a crack in the substrate and, in the worst case, breakage of the substrate. Such problems can be prevented by minimizing the stress exerting on the substrate W in the above-described manner.
As shown in FIG. 5, polishing is continued while keeping the vertical position of the polishing tape 10 fixed and allowing the polishing head 2 to stay at the position immediately above the polishing start position in the edge portion of the substrate W for a predetermined amount of time between time t₁and time t₂(t₂−t₁), t₁being the time when the polishing starts at the set pressure after the polishing tape 10 has come into contact with the edge portion of the substrate W and the contact pressure has reached the set pressure. The predetermined amount of time (t₂−t₁) is set based on the location hardest to polish, and is generally at least about one second, preferably at least 10 seconds, more preferably 20 to 40 seconds.
Thus, while keeping the polishing tape 10 in contact with the polishing start position in the edge portion of the rotating substrate W at the set pressure, the polishing tape 10 is allowed to stay at the polishing start position for a predetermined amount of time to polish the edge portion at the polishing start position. This can prevent the occurrence of insufficient polishing or uneven polishing at the boundary of the polished surface with the non-polished surface, making it possible to obtain a good polishing profile which, e.g., will not cause peeling of a surface film, such as a semiconductor layer, from the substrate W. Furthermore, even when a film to be polished away is present in the edge portion of the substrate W in an uneven distribution in the circumferential direction, the film to be polished away can be securely prevented from remaining in the edge portion of the substrate W by setting the stay time of the polishing tape 10 based on the location hardest to polish.
The polishing tape 10 may be allowed to stay at the polishing start position in the edge portion of the substrate W for a predetermined amount of time while keeping the polishing tape 10 in contact with the polishing start position at a pressure higher than the set pressure. According to this manner, the polishing rate can be increased when the edge portion of the substrate W is polished while allowing the polishing tape 10 to stay at the polishing start position in the edge portion of the substrate W for a predetermined amount of time. This can prevent lowering of the throughput. In view of stress exerting on the substrate, it is also possible to raise the rotational speed of the substrate W.
As shown in FIG. 5, after the predetermined amount of time has elapsed (after time t₂), the polishing head 2 is moved at a predetermined speed V₀toward the peripheral end of the substrate W while keeping the polishing tape 10 in contact with the edge portion of the rotating substrate W at the set pressure to continue polishing of the edge portion of the substrate W with the polishing tape 10. During the polishing, the angle of the polishing head 2 with respect to the substrate W may be changed by the tilt mechanism, as necessary.
After the polishing head 2 has reached a polishing end position where the distance L₂between the peripheral end of the substrate W and the pressing pad 20 is, for example, 0.4 mm, the polishing head 2 is moved at a high speed to the stand-by position beside the substrate W, as shown in FIG. 4D.
As shown in FIG. 6A, polishing of the edge portion of the substrate W may be carried out by a method comprising: carrying out a first polishing step of moving the polishing head 2 at a first movement speed V₁, e.g., not more than 50 μm/sec, toward the peripheral end of the substrate W from time t₁when the polishing tape 10 has come into contact with the edge portion of the substrate W and the contact pressure reaches the set pressure, while keeping the polishing tape 10 in contact with the edge portion of the rotating substrate W; carrying out polishing for a certain distance (up to time t₃); and carrying out a second polishing step of further moving the polishing head 2 at a second movement speed V₂, e.g., 50 μm/sec to 100 μm/sec, toward the peripheral end of the substrate W while keeping the polishing tape 10 in contact with the edge portion of the rotating substrate W.
This polishing method can significantly shorten the polishing time while preventing the occurrence of insufficient polishing or uneven polishing at the boundary of the polished surface with the non-polished surface. In addition, the polishing amount can be made smaller in the surface area lying closer to a peripheral end of a substrate. This polishing method is thus especially effective for a substrate in which a film to be polished away is thinner on the peripheral end side.
The contact pressure of the polishing tape 10 on the edge portion of the substrate W during the movement of the polishing head 2 at the second movement speed V₂may be changed from that during the movement of the polishing head 2 at the first movement speed V₁. This can further shorten the polishing time.
In this case, the first movement speed of the polishing head 2 may be increased linearly from the movement speed V₁to the movement speed V₂, as shown in FIG. 6B, or may be increased gradually from the movement speed V₁to the movement speed V₂, as shown in FIG. 6C so as to avoid a rapid change in the movement speed of the polishing head 2.
The accuracy of positioning of the polishing head 2 is very important in the above-described embodiment. Because the movement speed of the polishing head 2 is as low as about 1 μm per second, it is also very important to enhance the accuracy of the movement speed (amount of change, error) of the polishing head 2. It is, therefore, preferred to perform positioning of the polishing head 2 with high accuracy and accurately control the movement speed of the polishing head 2 by using, for example, a servomotor or a stepping motor as the linear actuator 33.
Further, it is preferred that setting values for time to stop the polishing head 2, the movement speed of the polishing head 2, etc. can be easily changed through program control by digitalizing and inputting process sequence, process conditions, etc.

Example 1

Polishing of an edge portion of a substrate was carried out using the polishing apparatus shown in FIG. 2. A tape having #4000 diamond abrasive particles fixed thereon was used as a polishing tape, and a resin pad whose lower end, which is to make contact with the polishing tape, has a radius of curvature of 0.5 mm was used as the pressing pad of the polishing head. While allowing the polishing tape to travel at a speed of 10 mm/min, the polishing tape was pressed against a polishing start position in the edge portion of the substrate, rotating at 500 rpm, at a load of 10 N by the pressing pad of the polishing head whose position was fixed, thereby polishing the edge portion at the polishing start position for 20 seconds. Thereafter, polishing was continued by pressing the polishing tape against the edge portion of the substrate, rotating at 500 rpm, at a load of 10 N while moving the polishing head toward the peripheral end of the substrate at a movement speed of 5 μm/min. The results of the polishing, i.e., the relationship between polishing amount and radial position (measurement position) on the substrate, are shown in FIG. 7.
In FIG. 7, the “notch” curve represents the polishing amount on a line connecting the center and a notch of the substrate (center-notch line); the “90°” curve represents the polishing amount on a line corresponding to the center-notch line as it is rotated by 90 degrees counterclockwise; the “180°” curve represents the polishing amount on a line corresponding to the center-notch line as it is rotated by 180 degrees counterclockwise; and the “270°” curve represents the polishing amount on a line corresponding to the center-notch line as it is rotated by 270 degrees counterclockwise. This holds true for FIGS. 8 and 9.

Example 2

Polishing of an edge portion of the same substrate was carried out in the same manner as in Example 1 except that the edge portion at the polishing start position was polished for 40 seconds. The results of the polishing, i.e., the relationship between polishing amount and radial position (measurement position) on the substrate, are shown in FIG. 8.

Comp. Example 1

Polishing of an edge portion of the same substrate was carried out in the same manner as in Example 1 except that polishing of the edge portion of the substrate was started by pressing the polishing tape against the polishing start position in the edge portion of the substrate, rotating at 500 rpm, at a load of 10 N by the pressing pad of the polishing head and, immediately after the start of polishing, the polishing head was moved toward the peripheral end of the substrate at a movement speed of 5 μm/min. The results of the polishing, i.e., the relationship between polishing amount and radial position (measurement position) on the substrate, are shown in FIG. 9.
As can be seen in FIGS. 7 through 9, the inclination at the boundary between the polished surface and the non-polished surface is steeper in Examples 1 and 2 than in Comp. Example 1. Further, the inclination is steeper in Example 2 than in Example 1.

Example 3

First, an edge portion of a substrate was subjected to polishing (rough polishing) with a polishing tape having #4000 diamond abrasive particles fixed thereon. FIG. 10 shows a photomicrograph of a surface area around the boundary between the polished surface and the non-polished surface of the substrate after the rough polishing. Thereafter, polishing of the edge portion of the substrate was carried out in the same manner as in Example 1 except that the edge portion at the polishing start position was polished for 10 seconds by using a polishing tape having #12000 diamond abrasive particles fixed thereon and pressing the polishing tape against the polishing start position of the rotating substrate by the pressing pad of the polishing head whose position was fixed. FIG. 11 shows a photomicrograph of a surface area around the boundary between the polished surface and the non-polished surface of the substrate after the polishing.

Example 4

Polishing of an edge portion of the same substrate was carried out in the same manner as in Example 3 except that an edge portion at the polishing start position was polished for 20 seconds. FIG. 12 shows a photomicrograph of a surface area around the boundary between the polished surface and the non-polished surface of the substrate after the polishing.

Comp. Example 2

Polishing of an edge portion of the same substrate was carried out in the same manner as in Example 3 except that polishing of an edge portion of the substrate was started by pressing the polishing tape against the polishing start position in the edge portion of the substrate, rotating at 500 rpm, at a load of 10 N by the pressing pad of the polishing head and, immediately after the start of polishing, the polishing head was moved toward the peripheral end of the substrate at a movement speed of 5 μm/min. FIG. 13 shows a photomicrograph of a surface area around the boundary between the polished surface and the non-polished surface of the substrate after the polishing.
As can be seen in FIGS. 11 through 13, sawtooth irregularities due to uneven polishing were formed in the vicinity of the boundary between the polished surface and the non-polished surface of the substrate after the polishing in Comp. Example 2, whereas no such irregularities were formed in Examples 3 and 4. This demonstrates that the polishing method according to the present invention can prevent the occurrence of uneven polishing.
FIG. 14 schematically shows another polishing apparatus. This polishing apparatus, in addition to the polishing head 2 of the above-described embodiment for polishing an edge portion of a substrate, further includes a bevel polishing head 50 for contact with a bevel portion of a rotating substrate W to polish the bevel portion. The bevel polishing head 50 is disposed lateral to the substrate W held on the substrate stage 11 of the substrate holding section 1. The bevel polishing head 50 includes a polishing tape 52, a pressing pad 54 disposed on a back side (opposite side from a polishing surface) of the polishing tape 52, and a pressing mechanism 56, e.g., comprised of a cylinder, for applying a pressure to the pressing pad 54.
In operation, while supplying a polishing liquid from the polishing liquid supply nozzle 40 onto a surface of a substrate W, which is held on the substrate stage 11 and is rotating at a predetermined rotational speed, the polishing tape 10 of the polishing head 2 is pressed against the edge portion of the substrate W at a predetermined pressure and the polishing tape 52 of the bevel polishing head 50 is pressed against the bevel portion of the substrate W at a predetermined pressure to simultaneously polish the edge portion and the bevel portion of the substrate W. This embodiment can thus increase the throughput and, in addition, can reduce the usage of a polishing liquid, thereby reducing the production cost.
When there is a difference between the time it takes to polish the bevel portion of the substrate W and the time it takes to polish the edge portion of the substrate W, the polishing rate can be lowered for the polishing head for the less time requiring polishing. Thus, the traveling speed of the polishing tape can be slowed down, or the usage of the polishing tape can be reduced. This can reduce the polishing cost.
Further, the overall polishing time can be shortened. This can reduce the risk of contamination of a substrate surface in which devices are formed.
Further, when there is an imbalance in processing time between polishing and other processing, the processing times can be balanced by simultaneously carrying out polishing of an edge portion of a substrate and polishing of a bevel portion of the substrate. It thus becomes possible to operate the apparatus in the most efficient manner.
While the present invention has been described with reference to preferred embodiments, it is understood that the present invention is not limited to the embodiments described above, but is capable of various changes and modifications within the scope of the inventive concept as expressed herein.

Claims

1. A polishing method comprising:

positioning a polishing head at a position above a polishing start position in an edge portion of a rotating substrate;

lowering the polishing head and bringing a polishing tool of the polishing head into contact with the polishing start position in the edge portion of the rotating substrate at a predetermined pressure;

allowing the polishing tool to stay at the polishing start position for a predetermined amount of time; and then

moving the polishing head toward a peripheral end of the substrate while keeping the polishing tool in contact with the edge portion of the rotating substrate at the predetermined pressure.

2. The polishing method according to claim 1, herein the predetermined amount of time is at least one second.

3. The polishing method according to claim 1, wherein the polishing tool is a polishing tape which travels in one direction at a predetermined speed when it polishes the edge portion of the substrate.

4. The polishing method according to claim 1, wherein a bevel portion of the substrate is polished while polishing the edge portion of the substrate by keeping the polishing tool in contact with the edge portion of the rotating substrate.

5. A polishing method comprising:

lowering a polishing tool of the polishing head until the polishing tool comes into contact with the polishing start position in the edge portion of the rotating substrate and a pressure between the polishing tool and the polishing start position reaches a set pressure;

moving the polishing head toward a peripheral end of the substrate while keeping the polishing tool in contact with the edge portion of the rotating substrate at the set pressure.

6. The polishing method according to claim 5, wherein the predetermined amount of time is at least one second.

7. The polishing method according to claim 5, wherein during a period after contact of the polishing tool with the edge portion of the substrate until the start of movement of the polishing head, the contact pressure of the polishing tool on the edge portion of the substrate is kept higher than the set pressure.

8. The polishing method according to claim 5, wherein after lowering the polishing tool and bringing the polishing tool into contact with the polishing start position in the edge portion of the rotating substrate at a lower pressure than the set pressure, the pressure of the polishing tool on the edge portion of the substrate is increased to the set pressure.

9. The polishing method according to claim 5, wherein the polishing tool is a polishing tape which travels in one direction at a predetermined speed when it polishes the edge portion of the substrate.

10. The polishing method according to claim 5, wherein a bevel portion of the substrate is polished while polishing the edge portion of the substrate by keeping the polishing tool in contact with the edge portion of the rotating substrate.

11. A polishing method comprising:

a first polishing including

(a) positioning a polishing head at a position above a polishing start position in an edge portion of a rotating substrate,

(b) lowering a polishing tool of the polishing head until the polishing tool comes into contact with the polishing start position in the edge portion of the rotating substrate and a pressure between the polishing tool and the polishing start position reaches a set pressure, and

(c) moving the polishing head toward a peripheral end of the substrate at a first movement speed while keeping the polishing tool in contact with the edge portion of the rotating substrate; and

a second polishing including

(d) moving the polishing head toward the peripheral end of the substrate at a second movement speed while keeping the polishing tool in contact with the edge portion of the rotating substrate.

12. The polishing method according to claim 11, wherein the second movement speed of the polishing head is higher than the first movement speed of the polishing head.

13. The polishing method according to claim 11, wherein when moving the polishing head toward the peripheral end of the substrate at the first movement speed, the contact pressure of the polishing tool on the edge portion of the substrate is kept higher than the set pressure.

14. The polishing method according to claim 11, wherein after lowering the polishing tool and bringing the polishing tool into contact with the polishing start position in the edge portion of the rotating substrate at a lower pressure than the set pressure, the pressure of the polishing tool on the edge portion of the substrate is increased to the set pressure.

15. The polishing method according to claim 11, wherein the polishing tool is a polishing tape which travels in one direction at a predetermined speed when it polishes the edge portion of the substrate.

16. The polishing method according to claim 11, wherein a bevel portion of the substrate is polished while polishing the edge portion of the substrate by keeping the polishing tool in contact with the edge portion of the rotating substrate.