Method and Apparatus for Adhering a Tape or Sheet to a Semiconductor Wafer

1. Field of the Invention

This invention relates to a method and apparatus for adhering a tape or sheet to a semiconductor wafer.

2. Description of the Related Art

In the production of semiconductor devices, such as integrated circuits (IC), large scale integrated circuits (LSI), and very large scale integrated circuits (VLSI), a disk-like semiconductor wafer is formed with a number of electrical patterns on the surface thereof and then cut into a predetermined number of squares to obtain semiconductor chips for individual devices. The cutting is usually effected by a diamond cutter in a so-called dicing process. However, before the cutting, an adhesive-backed tape or sheet is conventionally adhered to the back surface of the wafer to prevent cut chips from scattering into individual pieces.

When adhering the tape or sheet to the back surface of the wafer, if an excessive pressure is used to press the tape against the wafer, the wafer surface will be damaged, or it will become difficult to obtain uniform adhesion between the tape and wafer. Therefore, an improved technique for uniformly adhering a tape or sheet to a semiconductor wafer has long been desired.

A method for adhering a tape to a wafer is known in the prior art, in which method a patterned semiconductor wafer is placed on a wafer supporting table and an adhesive-backed tape, made of, for example, vinyl chloride, is then brought into contact with the wafer surface. Then, the entire surface of the adhesive-backed tape is rolled or brushed with a rubber roller or brush. However, in this method, there is a disadvantage in that the patterned surface of the wafer which is in contact with the supporting table could be damaged by a physical pressure applied to the back surface of the wafer by this rolling or brushing. In addition, air bubbles might form between the tape and wafer, thus preventing a uniform adhesion of the tape to the wafer.

In another known method, a patterned semiconductor wafer is placed on a wafer supporting table in a vacuum chamber. In the vacuum chamber, an adhesive-backed tape is brought into contact with the wafer by a pressure difference created on the respective sides of the tape. According to this method, air bubbles are prevented from forming between the tape and wafer. However, this method has a disadvantage in that the patterned surface of the wafer which is contact with the supporting table could be damaged when the tape is pressed against the wafer by the pressure difference applied to the tape.

Accordingly, an object of the present invention is to provide a method and apparatus for adhering a tape or sheet to a semiconductor wafer, in which air bubbles are not formed between the tape and wafer and a uniform adhering property is ensured.

Another object of the present invention is to provide a method and apparatus for adhering an adhesive-backed tape or sheet to a semiconductor wafer, in which the patterned surface of the wafer is not damaged when the tape is adhered to the entire back surface of the wafer.

Still another object of the present invention is to provide a method and apparatus for adhering an adhesive-backed tape or sheet to a semiconductor wafer, capable of improving the productivity of semiconductor devices by being applicable to an automatic production system.

According to one aspect of the present invention, there is provided an apparatus for adhering an adhesive-backed tape or sheet to a semiconductor wafer, comprising; a housing means defining therein a vacuum working chamber; a table in the vacuum working chamber for supporting a disk-shaped semiconductor wafer, having a front surface on which electrical patterns are formed and a back surface, in such a manner that only the peripheral portion of the wafer is in contact with the table; means for holding an adhesive-backed tape or sheet having at least one adhesive surface at a predetermined position in the chamber, in such a manner that the adhesive surface thereof is located opposite to the back surface of the semiconductor wafer and a predetermined small clearance is maintained therebetween; means for physically pressing the adhesive-backed tape or sheet with a slight force against the semiconductor wafer, so that the adhesive-backed tape or sheet is provisionally adhered to the back surface of the wafer at least over an area of the peripheral portion of the wafer; and, means for regulating the air pressure in the working chamber.

According to another aspect of the present invention, there is provided a method for adhering an adhesive-backed tape or sheet to a semiconductor wafer, having a front surface on which electrical patterns are formed and a back surface, the method comprising the following steps of: placing a disk-shaped semiconductor wafer on a table in a working chamber, in such a manner that only the peripheral portion of the wafer is in contact with the table; setting an adhesive-backed tape or sheet having at least one adhesive surface at a predetermined position in the chamber, in such a manner that the adhesive surface thereof is located opposite to the back surface of the semiconductor wafer and a predetermined small clearance is maintained therebetween; reducing the air pressure in the working chamber; physically pressing the adhesive-backed tape or sheet with a slight force against the semiconductor wafer, so that the adhesive-backed tape or sheet is provisionally adhered to the back surface of the wafer at least over an area of the peripheral portion of the wafer; and, increasing the air pressure in the working chamber to completely adhere the tape or sheet to the entire back surface of the semiconductor wafer due to the change in pressure.

FIG. 1 is a cross-sectional view of an apparatus for adhering a tape or sheet to a semiconductor wafer according to the present invention;

FIG. 2 is a view taken along the line II-II in FIG. 1;

FIG. 3 is a sectional view taken along the line III-III in FIG. 1; and

FIG. 4 is a perspective view of a semiconductor wafer.

FIG. 1 shows an adhering apparatus according to the present invention, in which an upper housing 1 and a lower housing 2 cooperate to constitute a vacuum chamber 3. An O ring seal 3' is arranged between the abutting faces of the upper and lower housing 1 and 2 to ensure an airtight seal of the chamber 3. The lower chamber 2 is provided with an air outlet 4 connected, via a vacuum line 5 having an air valve 6, to a vacuum pump 7, so that air pressure in the chamber 3 can be reduced to about 20 Torr or less. The upper chamber 1 is provided with an air inlet 8 which is open to the atmosphere via an air line 9 having an air valve 10, so that air pressure in the chamber 3 can be increased to atmospheric pressure or a value in the vicinity thereof.

A cylindrical supporting table 11 horizontally arranged on legs 12 is provided in the lower housing 2. The table 11 has a circular-shaped supporting top surface 11a, as seen from FIG. 2, on which a substantially disk-shaped semiconductor wafer 13 is horizontally placed so that the peripheral edge 13a thereof is in contact with the supporting surface 11a of the table 11. A tape-mounting jig 14 is also arranged in the lower housing 2 on legs 15, outside the periphery of the table 11. The tape mounting jig 14 is used to fixedly secure a sheet adhering unit 16 by any one of a not shown conventionally known means. The sheet adhering unit 16 comprises, as shown in FIG. 3, a thin adhesive-backed sheet 17, made of, for example, vinyl chloride, and having a resin adhesive surface on one surface, and a mounting frame 18 for securing the adhesive-backed sheet 17 by the peripheral edge thereof.

The inner wall of the upper housing 1 is provided with horizontal guide shafts 21 along which a roller base 22 is movably supported. A roller 23 is made of, for example, rubber, is rotatably mounted on a roller frame 24 having a vertical shaft 33 movably supported on the roller base 22. The roller base 22 is connected to a drive belt 25 which extends between a drive pulley 26 attached to an output shaft of a drive motor 27 mounted on the upper housing 1 and an idle pulley 28 rotatably mounted on the upper housing 1, so that the roller base 22, and accordingly, the roller 23, can be moved by the motor 27 in the horizontal direction by a predetermined stroke along the guide shafts 21. The roller frame 24 has a pair of cam members 29a and 29b which engage with a pair of rollers 30a and 30b, respectively, rotatably mounted on the side walls of the upper chamber 1, so that the roller frame 24, and accordingly, the roller 23, is raised and separated from the adhesive-backed sheet 17 at the respective ends of the stroke of the roller 23.

The upper housing 1 is rigidly secured to an arm 31 which is pivotably moved, in the directions shown by an arrow, about a shaft 32 connected to a machine base (not shown) by any suitable means known in the prior art, so that the chamber 3 can be opened by lifting the upper housing 1 to separate it from the lower housing 2.

The steps of adhering the tape or sheet 17 to the semiconductor wafer 13 will now be describe. First, the chamber 3 is opened by lifting the upper housing 1 and separating it from the lower housing 2. Note, in another embodiment of the present invention, the lower housing 2 may be moved downward to open the chamber 3. A disk-like semiconductor wafer 13 having electrical patterns already formed on the front surface thereof is placed on the cylindrical table 11, as mentioned above. In this state, the major central part of the front surface of the semiconductor wafer 13 on which the above mentioned electrical patterns are formed is not in contact with the upper supporting face 11a of the table 11. After being set on the table 11, the wafer 13 is positioned so that its back surface faces upward. Then, the sheet adhering unit 16 is fixedly set on the tape-mounting jig 14 so that the adhesive side of the adhesive-based sheet 17 faces downward and a small clearance, for example, 0.4 to 0.5 mm, is maintained between the sheet 17 and the back surface of the wafer 13. Then, the upper housing 1 is lowered and the chamber 3 is closed, as mentioned above, and air pressure in the chamber 3 is reduced by the vacuum pump 7 to 20 Torr or less. When this vacuum condition is established, the motor 27 drives the roller base 22 along the guide shafts 21. After the cam member 29a or 29b moves away from the guide roll 30a or 30b, the roller 23 is allowed to roll over the back surface of the semiconductor wafer 13 and slightly press the adhesive-backed sheet 17 against the wafer 13 by a pressure substantially equal to that exerted on the roller 23 by the force of gravity, i.e., about 200 to 300 g, so that the adhesive-backed sheet 17 is provisionally adhered to the back surface of the wafer 13, over at least the area of the peripheral edge of the wafer 13 indicated by A in FIG. 2. At the end of its stroke, the roller 23 is raised and separated from the adhesive-backed sheet 17, as mentioned above. Note, in another embodiment of the present invention, a brush is used in place of the roller 23. After the roller 23 is raised, the air valve 10 is opened to introduce atmospheric air into the chamber 3 so that the pressure in the chamber 3 becomes equal to the atmospheric pressure or a value in the vicinity thereof. Due to this pressure increase, the thin adhesive-backed sheet 17 is drawn against the semiconductor wafer 13 and the completely adhered to the entire back surface thereof. Therefore, a uniform, stable adhesion between the sheet 17 and the wafer 13 is established and air bubbles are not formed therebetween. Then the upper housing 1 is raised to open the chamber 3, and the sheet adhering unit 16 is removed together with the semiconductor wafer 13 adhered thereto.

The semiconductor wafer 13 is then cut along a plurality of dotted lines, as seen in FIG. 4, into a number of square-shaped semiconductor chips for individual devices, by a so-called dicing process. During this process, the individual cut pieces are prevented from scattering into individual pieces, as a uniform and stable adhesion without air bubbles is maintained between the wafer 13 and adhesive-backed sheet 17. As is obvious, the surface of the wafer 13 is not damaged, since no unfavorable external force is applied to the front surface of the semiconductor wafer 13 during the adhering operation. Each of the cut individual semiconductor chips are used, as mentioned previously, for producing semiconductor devices, such as integrated circuits (IC), large scale integrated circuits (LSI), or very large scale integrated circuits (VLSI).