Apparatus for Grinding a Wafer

Abstract

An apparatus for grinding a wafer comprises a grinding member. The grinding member has a grinding element for grinding a first section of a wafer surface and a wafer contact element planar with and adjacent the grinding element. The wafer contact element is configured to contact a second section of the said wafer surface when the grinding element is grinding the first section.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the invention ensue from the description below of a preferred embodiment and from the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a known back grinding technique;

FIG. 2 is a side view of a section of an apparatus for grinding a wafer according to the invention;

FIG. 3 is a schematic view of a grinding surface of an apparatus for grinding a wafer according to the invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Referring now to FIG. 2, a wafer 10 having a chip active side 11 and a back side 12 has undergone metallization with a metal layer 13, for example copper, and has been partially cut through from the active chip side 11 to form cuts 14 defining blind slit apertures at chip boundaries in the chip active side 11 of the wafer 10. A protective film 15 has been attached to the active chip side 11 after the formation of cuts 14 so as to prepare the wafer 10 for back grinding.

A grinding wheel 20 (only the half of the grinding wheel covering the chip surface is shown in FIG. 2) has a grinding element 21 and a wafer contact element 22 provided on a grinding surface 23. The wafer contact element 22 can form a substrate upon which the grinding element 21 can be formed. Alternatively, the wafer contact element 22 can itself be formed on a substrate separately from the grinding element 21. The grinding element 21 is formed by depositing grinding material in the substrate so that the grinding element 21 is provided in the centre of the grinding surface 23 and is surrounded by the wafer contact element 22. This is shown more clearly in FIG. 3. The grinding wheel 20 is generally disk-shaped, such that its thickness is small in comparison with its diameter, and its central axis of rotation is perpendicular to the grinding surface 23. A shaft 24 connects the grinding wheel 20 with a drive means (not shown). The central vertical axis of the shaft 24 is coincident with the central axis of rotation of the grinding wheel 20. The shaft 24 is driven so as to allow the grinding wheel 20 to simultaneously rotate about its central axis of rotation and move in the same plane as the grinding surface 23.

To grind down the wafer 10 from its back side 12, the grinding wheel 20 is held against the surface of the back side 12 of the wafer 10 and rotated by the shaft 24 about its central axis of rotation, perpendicular to the surface of the wafer 10, such that it rotates over the surface of the wafer 10. The grinding wheel 20 can be made to rotate by any suitable drive means (not shown), for example an electric motor.

As the grinding wheel 20 rotates over the surface of the wafer 10, the grinding element 21 grinds down the section of the surface of the wafer 10 that is in contact with the grinding element 21, while the wafer contact element 22 provided in the outer section of the wheel 20 contacts the part of the surface of the wafer 10 that is not undergoing grinding and supports it. Therefore, as the wafer 10 is ground down and becomes thinner, loose chips are prevented from sticking up above the surface of the back side 12 of the wafer 10. Ideally, the grinding surface 23 should be in contact with the wafer 10 at all times as it is moved across the surface of the backside 12 of the wafer 10.

At the same time as the grinding wheel 20 is rotated about its central axis of rotation against the wafer 10, it is also moved over surface of the wafer 10 (by moving the shaft so that the wheel 20 rotates eccentrically about its central axis of rotation, or otherwise) so that the outer edge of the grinding element 21 is coincident with the centre of the wafer 10 and the grinding element 21 is eventually brought into contact with the entire surface of the back side 12 of the wafer 10, while the section of the wafer 10 that is not being background is supported by the wafer contact element 22. In this way the whole of the wafer 10 can be ground down to the same desired thickness.

Provision of the wafer contact element 22 on the grinding surface 23 for supporting the wafer 10 during grinding provides the advantage that the wafer 10 can be ground down to a smaller thickness without damage. This enables chips to be separated from the wafer 10 after back grinding without a further cutting operation. To separate chips from the wafer 10 after back grinding, the surface of the wafer 10 is simply stretched on the back side 12 in a direction parallel with the wafer surface, and/or bent by applying stress to the back side 12 in a direction perpendicular to the wafer surface, so that the wafer 10 breaks between the blind ends of the cuts 14 and the back side 12 to form individual chips.

Although the present invention has been described hereinabove with reference to specific embodiments, it is not limited to these embodiments and no doubt further alternatives will occur to the skilled person which lie within the scope of the invention as claimed.

For example, the grinding member is not limited to being disk-shaped and rotatably moveable relative to the wafer surface. The grinding member could be rectangular, for example, and be configured to move across the surface of the wafer in a straight line backwards and forwards relative to the surface of the wafer.

Claims

1. An apparatus for grinding a wafer on a wafer surface generally opposing a chip active surface, the apparatus comprising: a grinding member, the grinding member having a grinding element for grinding a first section of a said wafer surface and a wafer contact element planar with and adjacent the grinding element, the wafer contact element being configured to contact a second section of the said wafer surface when the grinding element is grinding the first section.

2. The apparatus according to claim 1, wherein the wafer contact element is peripheral to and surrounding the grinding element.

3. The apparatus according to claim 1, wherein the grinding member is generally disk-shaped.

4. The apparatus according to claim 1, wherein the grinding member is operable to rotate about a central axis of rotation.

5. The apparatus according to claim 1, wherein the grinding member is operable to move relative to the wafer surface in the same plane as the wafer surface.

6. The apparatus according to claim 1, wherein a minimum diameter of the grinding member is equal to twice the wafer diameter.

7. The apparatus according to claim 1, wherein the grinding element and the wafer contact element are integrally formed.

8. The apparatus according to claim 1, wherein the wafer contact element is provided as a substrate on the grinding member and the grinding element is formed on the substrate.

9. The apparatus according to claim 1, further comprising a control means for controlling movement of the grinding member against the wafer surface.

10. A method of separating a semiconductor chip from a wafer, the method comprising the steps of: cutting the wafer on a chip-active surface to form a plurality of blind apertures defining chip boundaries;grinding the wafer on a wafer surface generally opposing the chip-active surface in a first section by means of a grinding member, which includes a grinding element and a contact element, whereby the wafer contact element is contacting a second section of the wafer surface, which is not contacted by the grinding element when the grinding of the first section is taking place; andapplying pressure to the first section of the wafer surface thereby breaking the wafer between the wafer surface and a blind end of each of said apertures.