Wafer Slicing and Wire Saw Manufacturing Technology

Wire saw, with its ability to cut very thin wafers from large diameter crystalline ingots of semiconductor materials, has emerged as a leading technology for wafer production in semiconductor and photovoltaic industry. Nevertheless, the wire saw cutting process remains lacking a theoretical methodology and is not properly understood. The modern times compulsion of more accurate and efficient manufacturing has made it imperative to understand this abrasive slurry cutting process and to optimize it. As a sequel to this understanding, control tools can be developed to monitor the optimum process. In this paper, comparison are made between the wire saw and the inner diameter (ID) saw which has been used to cut semiconductor wafers. This comparison brings out superiority of wire saw over ID saw in most respects. Introduction: Wire saw, operating on the Free Abrasive Machining (FAM) technique, is an emerging technology for large diameter thin crystal wafer production in semiconductor and photovoltaic (PV) industry. Its advantages span from producing very thin wafers with small kerf loss to high yield and productivity. Since medieval times wire saws have been known to be used in cutting hard materials like granite slabs and other variety of stones. However, requirements on wire saw cutting in terms of wafer thickness and quality are very different in electronics and photovoltaic applications than the traditional use of the process. An evaluation of wire saw cutting process has shown that it is a poorly understood phenomenon and no model exists for simulation design and control. Even so, in crystal cutting applications, it has shown potential to produce better surface finish and thinner wafers with much higher yield than ID saws. This, coupled with total absence of any commercial US technology in this field makes this process worthy of detailed study. The primary objective of this initial study of the long-term research project is to evaluate the current wire saw slicing technology and to compare it with the ID saw technology most commonly used for wafer slicing. Such a comparison is expected to shed light on the superiority of wire saw over other conventional crystal sawing methods, thus in turn bringing out the importance of concentrating efforts on the wire saw. Wire saw manufacturing processes: Figure 1 shows the schematic of a wire saw. In the wire saw, a single strand of thin wire (175 μm in diameter) moves from a feed reel to a take-up reel. In between, the wire goes through the entrance side of storage system called the “carriage” and into the rectangular arrangement of fixed shafts with replaceable wire guides. The wire wraps around the wire guides which have hundreds of grooves. This creates a multiple net of parallel wires known as web through which the ingot crystal is fed together with abrasive slurry to produce a cut. wire storage (carriage)