Application of the Month
CMP Chemical & Slurry Metering

Chemical Mechanical Planarisation (CMP) is the process during which precision polishing machines use a fine ceramic slurry to make wafer surfaces as flat ( planar ) as possible, ensuring the best resolution for the micro-lithography steps to follow. The CMP process is also used to control film thickness and removal of barrier layers. Fluid Metering pumps are used for both the chemical formulation of the slurry, as well as maintaining the mechanical properties of the slurry during the planarisation.

Hydrogen Peroxide addition
The CMP slurry mixture is typically prepared in a batch vessel, and is a mixture of abrasive ceramic particles and an oxidation agent, usually hydrogen peroxide. Fluid Metering QV & RHV Variable Speed Pumps have been selected for precise addition of hydrogen peroxide into the slurry tank because of their drift free accuracy, chemical inertness, and long term maintenance-free operation. The amount of hydrogen peroxide added to the system affects both the chemical (peroxide concentration) and mechanical (particle density) properties of the slurry.

Slurry tank humidification
Once the slurry is mixed, it is imperative that the properties of the slurry are maintained.

Recirculation and mixing systems in the slurry tank ensure a homogenous mixture of the ceramic particles, and an inert nitrogen blanket in the tank reduces the possibility of contamination & chemical changes from contact with air.

However, the nitrogen blanket will tend to dry out ceramic particles at the surface of the slurry, as well as on the tank walls. If not for a precision humidification system, ceramic particles would stick together forming larger particles, and would create scratches in the wafer during the CMP process, too large to be removed. Fluid Metering STH Pumps feed deionised water to the system which humidifies the Nitrogen blanket.

Post CMP Cleaning - Ammonium Hydroxide addition
Following the CMP polishing process, there is a small amount of residual slurry material which remains within the micro geometries on the wafer. A special process, Post CMP Cleaning uses an Ammonium Hydroxide wash to remove all remaining particles, preparing the wafer for additional photo-lithography processing.  During the wafer manufacturing process, the CMP and Post CMP Cleaning processes will be repeated many times, as layers of oxide and metal are deposited on the surface of the preceding layer. As micro geometries get smaller, and wafer diameters get larger, the importance of Planarisation process control will continue to increase dramatically the requirement for FMI's Valveless CeramPump.

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