Batch Sequencing for Run-to-Run Control:  Application to Chemical Mechanical Polishing

Abstract

This work compliments and extends the capability of the run-to-run (R2R) control by sequencing the incomings such that improved control performance can be achieved. Unlike chemical or mechanical systems, this is important for semiconductor manufacturing processes because some prior information about the incoming wafers is generally available. First, the limitation of a R2R control type of feedback system is explained. The frequency domain explanation is as follows: a negative feedback system is effective rejecting a low-frequency type of disturbance. From the feedback property, then the answer to the feed sequencing problem becomes clear: arrange the feed (which we are capable of doing) in such a way that it gives a low-frequency characteristic. Furthermore, a scalar load strength indicator is derived, and an engineering approach is taken to sort the incomings effectively. Two policies, from thin to thick (in terms of prethickness, policy L2R) and from thick to thin (policy R2L), are proposed, and they are shown to provide a better control performance over the conventional random feed policy (R). The feed sequencing problems are tested for systems with different dimensions, e.g., single input single output, single input multiple output, and multiple input multiple output systems, which include the model of an experimental chemical mechanical polishing process, and the results show that an improved control performance can be obtained simply by arranging the feeds.

On the interaction between measurement strategy and control performance in semiconductor manufacturing

“…Del Castillo [2] summarizes results on the design and performance of the most popular R2R controllers: EWMA and double-EWMA. Chen et al [15] discuss the effects of sequencing on incoming wafers for run-to-run control; and Qin and Good [8] analyze the stability of double-EMWA controllers in the presence of metrology delay, and extended the results to MIMO controllers [9]. Qin [26] also discusses the fab-wide control structure for electrical parameters.…”

Control relevant issues in semiconductor manufacturing: Overview with some new results

“…By disturbance rejection, it means maintaining the product quality in the face of process changes. Typical sources of process variations in IC fabrication include: (1) toolinduced disturbances which are generally known as process drift and/or process shift, (2) product-induced disturbance which typically comes from the IC foundry where high-mix products are manufactured, and (3) incoming disturbances which are often referred to as the variations which are a direct consequence of proceeding processing steps (Chen, Shiu, Yu, & Shen, 2005;Patel, Miller, Guinn, & Jenkins, 2000). Generally, some prior knowledge about the quality of the incoming wafers is available in semiconductor manufacturing processes.…”

“…Generally, some prior knowledge about the quality of the incoming wafers is available in semiconductor manufacturing processes. Thus, feedforward control (FF) or feed sequence arrangement can be devised to mitigate incoming disturbances (Chen et al, 2005). A similar approach can be applied to product-induced disturbance.…”