Simultaneous double-disk grinding: Machining process for flat, low-damage and material-saving silicon wafer substrate manufacturing

The strict International Technology Roadmap for Semiconductors (ITRS) demands call for novel preparation processes of the silicon monocrystal substrates which enable 1.) material-saving preparation sequences, 2.) shorter overall process chains, 3.) increased flexibility, and 4.) low-damage processing. For future substrate planarization, simultaneous double-disk grinding (DDG) is a promising candidate to combine the best of both worlds defined by the established conventional processes: 1.) double-side batch lapping (pros: free-floating workpieces; cons: highly damaging loose-grain abrasive slurry) or 2.) sequential single-side single-wafer grinding (pros: fixed-grain abrasive; cons: coining of deficiencies due to chuck-mounting). In DDG both sides of a wafer are planarized - one wafer at at time and with the wafer floating chuck-lessly during processing - concurrently between two opposite collinear, thus force-balanced, grinding spindles. In this article we compare and discuss the different DDG machine designs proposed by the various machine tool makers from the viewpoint of resulting wafer substrate quality parameters: TTV (global thickness variation), ATHK (wafer end-thickness variation), the ability to swallow residual waviness from previous multi-wire slurry slicing, MWS), surface roughness, and throughput. A key role plays the workpiece guide during DDG semi-chucked to truly free-floating) in affecting these parameters.