This disclosure relates to manufacturing integrated circuits from silicon wafers and more specifically to applying a protective coating to the silicon wafer.
Individual integrated circuit dies (or “dice” as they are sometimes called) are typically manufactured by processing a silicon wafer to create a large array of dies on the wafer. After the dies are formed on the silicon wafer, they must be separated from the wafer.
Small abrasive saws can be used to cut the dies from the wafer. However, silicon wafers are brittle, especially wafers utilizing a low-dielectric constant (k) interlayer dielectric. Sawing these brittle silicon wafers can result in chipping along the edges of the saw path or kerf. This tending to chip requires larger spacing between dies, which reduces the number of dies that can be produced on a single wafer.
To help alleviate the need for larger spacing between dies, laser scribing may be used as part of the separating process. A laser creates a groove or other surface discontinuity along a line that may be subsequently sawed (with less chipping due to the smaller thickness being cut) or broken along the line to complete the separation process.
While laser scribing reduces chipping, the scribing tends to produce debris that accumulates on the surface of the silicon wafer adjacent the groove and across the wafer. This debris can cause problems with flip-chip packaging circuits that have an array of solder balls or die bumps created on the surface of the silicon wafer. These die bumps provide an electrical connection to the integrated circuit. This connection is completed by mounting the die onto a substrate and heating the assembly to create soldered connections between the die and the substrate.
Debris from the laser scribing that settles on the die bumps or solder balls prevents the solder from properly wetting during the process of attaching the silicon chip to the substrate. Debris can further contaminate other portions of the die. This failure to properly wet and the potential contamination may result in a defective device.
As a result, when laser scribing is used to separate dies from a silicon wafer, all debris from the laser scribing process should be removed from the silicon wafer prior to the packaging of the dies.
The description may be best understood by reading the disclosure with reference to the accompanying drawings.
The wafer 20 and IC dies 22 are not shown to scale for illustration purposes. A typical silicon wafer 20 will have many more IC dies 22 formed on the wafer 20 than is shown in
The protective coat 30 protects the IC die 22 and the die bumps 24 from debris 36 (see
The protective coat 30 may be a tape or a film formed from materials such as polyimides, polyvinyl alcohol, methyl cellulose, household transparent tape, PET (polyester), photoresist and soy protein. Certain characteristics of the protective coat 30 can help the protective coat effectively protect the dies 22 and die bumps 24. The protective coat 30 may be optically transparent for the visual and fiducial alignment in the laser scribing process and any potentially subsequent saw processes. The protective coat 30 may also be ablated during the laser scribe process and may be chemically non-interactive with laser energy.
The preceding embodiments are exemplary. Those of skill in the art will recognize that the concepts taught herein can be tailored to a particular application in many other advantageous ways. In particular, those skilled in the art will recognize that the illustrated embodiments are but one of many alternative implementations that will become apparent upon reading this disclosure.
Although the specification may refer to “an”, “one”, “another”, or “some” embodiment(s) in several locations, this does not necessarily mean that each such reference is to the same embodiment(s), or that the feature only applies to a single embodiment.