Vacuum tweezers

Abstract: Vacuum tweezers for handling a semiconductor wafer comprises a handling section having at least one suction port opened in the same plane as the surface of the wafer and located within an area smaller than that of the surface of said wafer, a pressure reduction means connected to the suction port, a means for releasing negative pressure produced by the pressure reduction means, and a grip integrally coupled to the handling section.

Description: BACKGROUND OF THE INVENTION The present invention relates to vacuum tweezers for easily handling a semiconductor wafer which is required to be handled very carefully. It has been known in the art of ceramic sheets to use a vacuum-operated handler for transferring the ceramic sheets to and from various process equipments. A device of this nature is disclosed, for example, in the IBM Technical Disclosure Bulletin (Vol. 24, No. 4. Sept. 1991) wherein the handler comprises of an enclosure covering the ceramic sheet but contacting only the sides or corners of the sheet by way of a vacuum applied through apertures to the sheet. The device also comprises of a handle element secured to the enclosure for manual operation. However, in the case of semiconductor wafers such a device would be unsuitable in view of its bulk size and weight. On the other hand, conventionally a semiconductor wafer is handled while being pinched on the front and back sides thereof with a pair of tweezers. However, the handling of the semiconductor wafer with the tweezers has problems mentioned below. Namely, when the semiconductor wafer is pinched with the tweezers, stress is concentrated to the portion of the wafer which is in contact with the tweezers. Since the semiconductor wafer such as a single crystal of silicon and a single crystal of gallium arsenide (GaAs) is a damageable material and has a very small thickness, the wafer is likely to crack from its portion in contact with the tips of the tweezers. When the semiconductor wafer is pinched at about the center of gravity thereof, that is, at about the center of a flat-shaped wafer, with the tweezers in order to reduce the likelihood of cracking or damaging of the wafer, the processed region of the wafer is likely to be damaged by the tips of the tweezers. Since the stress against the semiconductor wafer concentrates to its very small portion where the tweezers contacts the wafer in the pinching of the wafer with the tweezers, it is necessary to be very careful in handling the wafer. However, the wafer is still likely damaged in the handling thereof with the tweezers even if the wafer is very carefully handled. If the tips of the tweezers are coated with a soft material for protecting the semiconductor wafer from damage, the tips of the tweezers are made so thick and round as to deteriorate the operating property of the tweezers for picking up the semiconductor wafer which is, for example, put on a flat rest. For a Si chip, vacuum tweezers are conventionally used. Fig. 1 shows such a conventional vacuum tweezers. A nozzle 40 is attached to the tip of a grip 42. The air in the inside of the grip is exhausted through a hose 43 connected to a vacuum pump (not shown). When the nozzle 40 is made contact with a chip and a hole 41 is closed by an operator's finger, the chip is absorbed to the nozzle. When the finger is released from the hole, the chip is separated from the nozzle. However, since the nozzle of the conventional vacuum tweezers has only one through hole, a comparatively large stress is applied to the chip at its small portion where the vacuum tweezers contact with the chip. Although the conventional vacuum tweezers are originally intended to be used for the handling of the chip, they are applicable for a Si wafer in some cases. Since a Si wafer is less brittle and generally thicker than a GaAs wafer, the conventional vacuum tweezers are applicable for the Si wafer. However, they have not been used for a GaAs wafer. SUMMARY OF THE INVENTION It is an object of the present invention to provide a device by which the above-mentioned problems are solved to easily and safely handle a semiconductor wafer. The present invention achieves its object in providing vacuum tweezers comprising the features as set out in claim 1. Since one or more suction ports are provided in the handling section, the vacuum tweezers of the present invention have the advantage that the force for sucking the semiconductor wafer is divided. The handling section of the vacuum tweezers has the suction ports in the suction side thereof, which face the surface of the semiconductor wafer. The negative pressure is produced in each suction port by the pressure reduction means so that the semiconductor wafer is sucked to the handling section when the suction ports are brought into contact with the wafer. Various kinds of means can be used as the pressure reduction means. Since a pressure reducer such as a vacuum pump is installed in many cases of handling of semiconductor wafer, the negative pressure can be easily and stably produced by connecting the pressure reducer to the vacuum tweezer through a pressure-proof tube. Since the weight of the semiconductor wafer is small, a simple manual pump can be also used as the pressure reduction means and integrally coupled to the handling section. The means for releasing the negative pressure can be made of an opening provided in a pressure reduction line and communicating with the atmosphere. When the semiconductor wafer is to be sucked to the vacuum tweezers, the opening is closed by a finger, for example. When the wafer is to be released from the vacuum tweezers, the finger is separated from the opening to release the negative pressure. The means for releasing the negative pressure can thus be constituted easily. Since only the suction ports of the vacuum tweezers is made contact with the unprocessed region or peripheral portion of the surface of the semiconductor wafer in a preferable embodiment of the present invention, the tweezers never damages the processed region or central portion of the surface of the wafer. Since the contact area of the semiconductor wafer with the handling portion of the vacuum tweezers is much larger than that of a semiconductor wafer with convention tweezers, the stress which is applied to every point of the wafer by the vacuum tweezers to support the wafer is much smaller than that applied by the conventional tweezers. Also, since the semiconductor wafer is sucked on the vacuum tweezers by the negative pressure of a fluid, the stress applied to the wafer at one suction port is equal to the stress applied to the wafer at another suction port. These are desirable effects of the present invention, which can be further enhanced by increasing the number of the suction ports or extending the suction port as a slit along the total length of the contact portion between the handling section and the semiconductor wafer. Further, in the device of the present invention, an elastic member is provided on the portion of the handling section, which is brought into contact with the semiconductor wafer, so that the elastic member acts to efficiently suck the wafer to the vacuum tweezers and protect the surface of the wafer from damage. The elastic member also serves as a sealing member between the wafer and the suction port of the vacuum tweezers and reacts to the stress applied to the wafer due to the negative pressure. For that reason, it is desirable that the area of the contact of the elastic member with the wafer is made as large as possible. Further, since the vacuum tweezers only need to be moved downward to the semiconductor wafer when sucking the wafer to the tweezers, the tweezers can be easily and safely operated even for the wafer placed on a flat rest. In view of this operation, the grip of the vacuum tweezers has such a form as to make it easy to operate the tweezers from the upper and side positions. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a side view of a conventional vacuum tweezers, Fig. 2(a) is a plan view of vacuum tweezer according to the present invention, Fig. 2(b) is a side view of the vacuum tweezers of Fig. 2(a), and Fig. 3 is a perspective view of the vacuum tweezers of Fig. 2(a). BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention is hereafter described in detail with reference to the drawings attached hereto. Since the embodiment is only an example, the present invention is not confined thereto. Fig. 2(a) shows a plan view of vacuum tweezers according to the embodiment of the present invention. Fig. 2(b) shows a side view of the vacuum tweezers of Fig. 2(a). Fig. 3 shows a perspective view of the vacuum tweezers of Fig. 2(a) to enable better understanding. The same members or portions shown in these drawings are designated by the same reference symbols. As shown in Fig. 2(a), the vacuum tweezers are mainly composed of a handling section 1 which is C-shaped when being seen from the upper position, and a grip 2 extending outward from almost the center of the handling section. Since a semiconductor wafer 3, which is shown to be circular in Fig. 2(a), is normally notched in a portion thereof, the handling section 1 is made to be C-shaped. Although a plurality of independent negative pressure lines can be provided for the annular handling section 1 to cope with the form of the notched semiconductor wafer 3, the provision of a plurality of negative pressure lines results in complicating the constitution of the device. Therefore, it is not preferable to provide a plurality of independent negative pressure lines. As shown in the drawings, the handling section 1 is hollow and has a plurality of openings 11 at the side which faces the semiconductor wafer 3. The openings 11 act as suction ports to suck the wafer 3 to the vacuum tweezer. As shown in Fig. 2(b), an elastic sealing member 12 is provided on the surface on which the suction openings 11 are provided, and covers them the openings. The dimensions of the elastic sealing member 12 are determined so that the inner portion 12a(see Fig. 2(a)) of the sealing member is located outside the processed region 31 of the semiconductor wafer and the outer portion 12b of the sealing member 1 located inside the peripheral edge of the semiconductor wafer. The sealing member 12 is thus constructed to keep airtightness between the sucked wafer 3 and the suction openings 11 and not to damage the wafer. The grip 2 has an opening 21 at the end of the grip, which is connected to the handling section 1. The opening 21 is located at the opposite side to the suction openings 11 of the handling section 1 and communicates with the internal cavity of the handling section. The other end of the grip 2 is connected to a flexible pressure-proof tube 22 coupled to a vacuum pump not shown in the drawings. The grip 2 is made slightly oblique upward from the handling section 1 to make it easy to horizontally put the handling section to the semiconductor wafer 3 placed in a horizontal position. The operation of the vacuum tweezers constructed as described above is now described. The vacuum pump is driven to produce negative pressure in the internal cavity of the vacuum tweezers through the pressure-proof tube 22. The opening 21 of the grip 2 is then closed by a finger so that the negative pressure acts through the suction openings 11. The handling section 1 is moved down in a horizontal position to the semiconductor wafer 3 so that the wafer is sucked to the bottom of the handling section by the negative pressure. At that time, the sealing member 12 is located between the handling section 1 and the wafer 3 to keep airtightness between the handling section and the wafer. Therefore, the wafer 3 does not come off the handling section 1 as long as the negative pressure is maintained in the vacuum tweezers. Since the sealing member 12 is put into contact with only the unprocessed region of the wafer 3, the wafer is substantially not damaged. After the semiconductor wafer 3 sucked on the vacuum tweezers as described above is lifted and moved to a desired position, the finger is separated from the opening 21 of the grip 2 to release the negative pressure in the vacuum tweezers so that the internal pressure thereof approaches to the atmospheric level. As a result, the sucking force to the wafer 3 is lost so that the wafer is released from the handling section 1. The vacuum tweezers of the present invention was applied for GaAs wafers having the diameters of 5.08, 5.08, 7.62 and 7.62 cm (2, 2, 3, and 3 inches) and the thickness of 450, 200, 620 and 200 µm, respectively. The sucking force applied to the wafers was 6, 3, 20 and 7 gf, respectively. For the 7.62 cm (3-inch) wafer with 200µm thick, the sucking force of 5 - 10 gf may be applied, and the most preferable value is 7 gf. As a result, no damage was observed for any of GaAs wafers. As described above, a fragile semiconductor wafer can be very easily handled with vacuum tweezers provided in accordance with the present invention. The handling of the semiconductor wafer with the vacuum tweezers is performed through such simple operation that a negative pressure release means is closed, a handling section is put to the top of the wafer, the wafer is sucked to the handling section, the tweezers and the wafer sucked thereto are moved together, and the negative pressure release means is opened to release the wafer from the tweezers. The vacuum tweezers have a very simple constitution and can be made of a material such as plastic which is easy to be acquired and processed. In addition to the advantage of the simple operation of the vacuum tweezers, the tweezers have further advantage. That is, the tweezers are not brought into contact with the processed region of the semiconductor wafer, and the area of the surface of the vacuum tweezers, which is brought into contact with the semiconductor wafer, is much larger than that of the surface of the conventional tweezers, so that the vacuum tweezers hardly damage or break the semiconductor wafer. Namely, the safety of the vacuum tweezers is extremely higher than that of the conventional tweezers. Therefore, the use of the vacuum tweezers not only facilitates the handling of the semiconductor wafer but also enhances the yield thereof.

Claims: Vacuum tweezers handling a semiconductor wafer, comprising: a hollow C-shaped handling section (1) having a plurality of suction ports (11) opened in the same plane as the major surface of said semiconductor wafer, said handling section being located within an area smaller than the surface of said wafer and said C-shape being adapted to contact the peripheral portion of said major surface of said wafer; a grip (2) integrally coupled to said handling section, said grip (2) extending outward from the centre of said handling section and upward at an oblique angle; a pressure reduction means (22) connected to said suction ports; a means (21) for releasing negative pressure produced by said pressure reduction means; and an elastic member (12) provided on said handling section at the suction port side thereof, said elastic member being hermatically interposed between said handling section and the surface of said semiconductor wafer and keeping the negative pressure produced by said pressure reduction means. Vacuum tweezers according to claim 1, in which the arrangment of said suction ports in said handling section corresponds to an unprocessed region of said semiconductor wafer. Vacuum tweezers according to claim 1, in which said handling section (1) is coated with a soft material at the suction port side thereof for protecting the surface of said semiconductor wafer from damage. Vacuum tweezers according to claim 1, in which said pressure reduction means (22) is a vacuum pump connected to said suction ports through a connection pipe. Vacuum tweezers according to claim 1, in which said means for releasing the negative pressure is an opening (21) provided in said grip (2), said opening communicating with a pressure reduction line between said suction port and said pressure reduction means and having such a size that said opening can be closed by a finger.

Inventors: NISHIGUCHI MASANORI, SEKIGUCHI TAKESHI, NISHIGUCHI, MASANORI C/O YOKOHAMA WORKS, SEKIGUCHI, TAKESHI C/O YOKOHAMA WORKS
Applicants: SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO ELECTRIC INDUSTRIES LIMITED
Application year: 1987
Main classification: H01L21
IPC codes: H01L21, B25B11