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Use of Ethylene Glycol Based Coolant for TDT Sapphire Lapping

IP.com Disclosure Number: IPCOM000223808D
Publication Date: 2012-Nov-29
Document File: 2 page(s) / 198K

Publishing Venue

The IP.com Prior Art Database

Abstract

Ethylene glycol (EG) based coolant was used together with a TrizactTM diamond tile (TDT) pad for sapphire wafer lapping. It was found that the lapping performance was significantly improved, as compared to the use of an aqueous based coolant. The material removal rate (MRR) was at least 50% higher, while the pad wear rate (PWR) and surface finish improved by a factor of at least two, for both single and double sided lapping processes.

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Use of Ethylene Glycol Based Coolant for TDT Sapphire Lapping

Abstract

 Ethylene glycol (EG) based coolant was used together with a TrizactTM diamond tile (TDT) pad for sapphire wafer lapping. It was found that the lapping performance was significantly improved, as compared to the use of an aqueous based coolant. The material removal rate (MRR) was at least 50% higher, while the pad wear rate (PWR) and surface finish improved by a factor of at least two, for both single and double sided lapping processes.

Introduction

 Surface modification of synthetic sapphire for industrial needs has become more important, due to the growing markets in the field of LEDs, silicon on sapphire (SOS) for CMOS, scratch resistant windows and remote sensing applications. After wire saw cutting, multiple grinding/polishing steps are typically required for sapphire wafers, in order to achieve the desired surface finish.

 For grinding processes, fixed abrasive pellet products are commonly used, however, it is often difficult to appropriately obtain balanced properties for abrasive systems [1]. Abrasive slurry techniques are also used for both grinding and lapping processes. In the lapping process, use of diamond slurry with metal platen is an industrial standard, however, the consumable sets are relatively expensive and intermittent resurfacing of a metal platen is required for maintaining acceptable thickness variations of work pieces. In addition, it is moderately difficult to apply this technique to double sided lapping systems.

 TrizactTM Diamond Tile (TDT) has gained a solid reputation for glass lapping in various industrial applications [2], and is further proven to be a promising technique to meet the required performance for sapphire lapping [3]. It can be used with existing lapping systems, without major modification of the tools, and is applicable for both single and double sided lapping processes. In the following sections, efforts to enhance the lapping performance of TDT products for sapphire wafers are described.

Experimental

 Figure 1 shows a schematic diagram of a TDT double sided lapping/polishing system (image on the right). In the TDT lapping process, work pieces, driven by carriers, are sandwiched by the top and bottom TDT pad surfaces, while applying a specific force. Figure 1 also shows a top view of a TDT pad surface (upper left image) and transitional changes in height of a single abrasive feature (lower left image), which would occur during lapping as a result of active conditioning of the pad. Conditioning of the pad is important to expose fresh abrasive particles, typically diamond, to aggressively interact with the sapphire surface. The conditioning of the TDT pad can be conducted by an in-situ conditioning, which employs a conditioning abrasive contained in the coolant [4].

Figure 1. Schematics of TD...