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Method for inorganic coating for wafer protection during laser scribing

IP.com Disclosure Number: IPCOM000101569D
Publication Date: 2005-Mar-16
Document File: 4 page(s) / 131K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for inorganic coating for wafer protection during laser scribing. Benefits include improved functionality, improved performance, and improved yield.

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Method for inorganic coating for wafer protection during laser scribing

Disclosed is a method for inorganic coating for wafer protection during laser scribing. Benefits include improved functionality, improved performance, and improved yield.

Background

      Laser scribing the silicon wafers to singulate dies is being performed on packages to prevent cracking of an interlayer dielectric (ILD) prior to sawing a wafer into individual die. At the required throughput rates, the laser scribe process generates large amounts of debris from the various die stack up and silicon layers.

      When no protective measures are taken, the laser scribe debris is deposited on the die-bump surfaces, especially the die bumps close to the laser-scribed streets. The contaminated dies, when processed through chip attach, result in areas where the solder does not flow. The laser scribe induced dry areas constitute yield loss (as high as 100%). To prevent the yield loss, organic protective coatings are being added. However, when exposed to the high temperatures of laser scribe, these coatings leave a permanent residue on the die surface, though no critical failures have been attributed to the presence of this residue.

      Technology with more silicon layers is expected for the future. The laser must scribe through them, so more thermal damage is envisioned. The effects of this debris on no-flow underfill (NUF) processing technology, is not known. As a result, more thermally stable materials, such as inorganic materials, are required.

      The most thermally stable organic materials rapidly degrade at temperatures in the range of 300° to 500°C. In comparison, inorganic materials have very high melting points, typically over 1500°C and even higher boiling points, typically about 3000°C. For example the melting point of Al2O3 is 2053°C and the melting point of SiO2 is 1722°C. The inorganic coatings should provide stronger protection at the high temperatures observed during the laser scribe process.

              Conventionally, a water soluble polymer coating is implemented to protect the wafer during laser scribe.

General description

      The disclosed method uses inorganic materials as coatings to protect wafers, which have fragile ILD layers, during singulation by laser scribing and/or sawing. The inorganic coating has high thermal stability for protection from the hot debris produced during laser scribing. The coating is easily removed without leaving a permanent residue.

              The key elements of the disclosed method include:

•             Application of inorganic materials to form a protective coating on the active side of a wafer

•             Laser scribing for the purpose of precutting the fragile ILD material to prevent cracking during sawing

•             Removing the coating and sawing the wafer to singulate the die

Advantages

              The disclosed method provides advantages, including:

•             Improved functional...