Investigation into Chemical Mechanical Polishing Mechanism of Hard-to-Process Materials Using a Commercially Available Single-Sided Polisher

Abstract

Chemical mechanical polishing (CMP) is one of the most important processes for fabricating highly planarized substrates such as sapphire for light emitting diodes (LEDs). However, sapphire is categorized as a hard-to-process material; therefore, a long processing time is required because of the low polishing efficiency (i.e., removal rate). This study investigates the CMP mechanism for hard-to-process materials using the following polishing evaluation parameters: (1) the velocity ratio, which is defined as the ratio of slurry flow velocity between the wafer and polishing pad during CMP to the pad tangential velocity, (2) the standard deviation of the velocity ratio distribution, and (3) the polisher vibration acceleration during CMP. Each parameter was measured at five rotational speeds and two polishing pressures for a total of ten conditions using a commercially available single-sided polisher. Moreover, the influence of each parameter on the removal rate was demonstrated via a multiple correlation analysis. As a result, we revealed that the velocity ratio and polisher vibration acceleration are strongly related with the removal rate.