Wafer Best Practices

Implementing the right strategies while handling wafer cutting, lapping, polishing, and thin film deposition can reduce cost and raw material wastage

FREMONT, CA: It is necessary to control the flatness of these disc-shaped wafers to tight tolerances to ensure that the entire surface of the wafer is suitable for the production of integrated circuits (IC). It may be possible to reprocess a wafer if disc geometry is out of specification after cutting. If a wafer doesn't meet dimensional specifications after cutting, further processing steps such as lapping and polishing will result in significant waste and wasteful costs.

Using these applications can reduce waste and costs in the semiconductor industry, thereby increasing profitability.

Wafer cutting: Wafer sawing involves cutting silicon ingots to a specified thickness. An optical wafer is typically measured by its diameter, which is called the size, based on the diameter of its slices (e.g., 300 mm). Using the right wire saw is crucial to avoid damaging the disc and creating scrap (or requiring reprocessing). Wafer cutters must know the disc's thickness and the width of the "streets," or cut lines, that separate dies. The production of excessive dust or chipping can also result from heat buildups.

Lapping and polishing: A semiconductor lapping process involves removing excess material from a wafer substrate using a pad containing an abrasive liquid. The lapping process involves putting a wafer of a known thickness on a rotary lapping table. A rotating lapping surface removes unwanted material from the front of the wafer by facing it downward. Device types require different amounts of material to be removed, and the entire process requires close control to avoid over- or under-removal. Wafer thickness measurements and total thickness variation (TTV) support the material removal process.

Wafers are stronger and more flexible after polishing, and it eliminates subsurface damage, creates thinner discs, and remove subsurface damage. The operator must, however, possess considerable skill when applying polishing methods. They are difficult to replicate since they require even abrasion. It is possible to find an out-of-spec geometry and insufficient flatness if a cutting rate needs to be precise, consistent, and close to the tolerance.

Thin film deposition: Optimal electrical, optical, and mechanical performance of semiconductors requires uniformly thick, thin films to deposit on wafers. Wafer waste may result from an irregular pattern of thin (or thick) deposition due to the inability to meet performance requirements. It is important to measure the thickness of wafers before and after thin film deposition, regardless of whether it is chemical or physical.