Wet Bench Wafer Holder

Semiconductor manufacturing tools utilise a broad range of components made of high performance plastics. In particular, wet process tools rely on chambers, tanks, piping systems, and parts made of thermoplastics due to their high level of chemical and corrosion resistance. By choosing the optimum polymer family, plastic components can withstand even the harshest combination of chemicals used to process and clean the wafers. 

While the wet process tanks and chemical supply systems are often made of fluoropolymers offering the highest level of chemical resistance, such materials do not offer sufficient strength and rigidity for mechanically stressed parts. For example, wafer mobility components in the wet process tools are often made of high performance thermoplastics like PEEK due to its excellent mechanical properties in combination with good chemical resistance. Wafer mobility components include wafer holders or wafer carriers which are commonly used to insert the wafers into the process tanks and move the wafers between different process steps. Besides the requirement of mechanical properties, wafer mobility parts need to provide elevated levels of ionic purity and maintain copy exact compliance. 

In this case study, the shape TECAPEEK SX natural, semiconductor grade unfilled PEEK, has been selected for a wet bench wafer holder. The function of the wafer holders is to dip multiple wafers into several chemical processing baths. The PEEK parts are holding the wafers from the sides to allow the liquid chemicals unobstructed access to the wafers when inserting to the bath. The number of wafers being held is maximised to enhance better wafer throughput, while maintaining sufficient and consistent spacing between the wafers to allow the liquids to pass through. The material must be highly dimensional stable to maintain the tight tolerances of the slot pitch spacing, thus maintain the wafer position accuracy. Moreover, the material needs to provide elevated levels of strength and rigidity, as well as wear resistance to maintain dimensional accuracy and maximise part lifetime under high wafer load and hundreds of thousands of cleaning cycles. PEEK fulfills the requirements for dimensional stability over an extended period due to high stiffness and creep resistance, as well as low water absorption. PEEK offers an excellent combination of elevated mechanical properties with a high level of chemical resistance.

As a general guideline, the following table provides an overview of resistance to common chemicals used in wet process tools, under room temperature and without mechanical load. This information is not an assurance or guarantee of the chemical resistance of our products, as the chemical resistance of plastic highly depends on the temperature, formulation, and operating conditions. Please contact us for further information about chemical resistance and material selection advice.

Chemical resistance at room temperature

Chemical	Formula	Concentration [%]	PI	PEEK	PPS	PEI	PVDF	PTFE	PET	POM-C
Deionized water	H2O	-	+	+	+	+	+	+	+	+
Hydrofluoric	HF	50		-	+	-	+	(+)	-	-
Sulfuric acid	H2SO4	95-97	-	-	+	-	+	(+)	-	-
Hydrogen peroxide	H2O2	30	-	+	+	(+)	+	+	+	(+)
2-propanol (isopropanol, IPA)	CH3CHOHCH3	100	+	+	+	+	+	+	+	+
Acetone	CH3COCH3	100	+	+	+	(+)	-	+	(+)C	+
Ethanol	(CH3)OCH3	95	+	+	+	+	+	+	+	+
Hydrochloric acid	HCI	37	-	+	+	+	+	+	-	-
Ammonia solution	NH3	25	-	(+)			+	+	+	+
Orthophosphoric acid	H3PO4	85		+	+	-	+	+	-	-
Nitric acid	HNO3	69		(+)			+	+	-	-
Acetic acid	CH3COOH	100	(+)	(+)	+	-		+	-	-

Comment: + = good, (+) = limited; - = unstable