Closed loop system to ensure stabilized hot Phosphoric Acid selectivity of Silicon Nitride to Silicon Oxide as a bulk system to batch or single wafer tools.
Publication Date: 2014-Jun-19
The IP.com Prior Art Database
Disclosed is a design for a Chemical Blender in a closed loop system that continuously monitors and controls the concentration of Silicon Oxide (SiO2) in a Phosphoric Acid chemical supply system.
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Closed loop system to ensure stabilized hot Phosphoric Acid selectivity of Silicon Nitride to Silicon Oxide as a bulk system to batch or single wafer tools .
Hot Phosphoric Acid (Hot Phos) has been used in the semiconductor industry for many years to remove Silicon Nitride (SiN) selective to Silicon Oxide (SiO2). This is currently used on a batch tool where many wafers can be run simultaneously in a recirculation of the chemistry in the "bath". Processing Hot Phos removes SiN and creates a by-product of silicates, which improves the selectivity of SiN to SiO2. Selectivity is directly proportional to the amount of Silicates in the bath; additional processing of wafers to remove SiN improves selectivity.
With higher selectivity, there is also defectivity; additional processing with the bath chemistry produces more defects in the bath. Defectivity is a major issue. The Original Equipment Manufacturers (OEMs) are developing a single wafer tool Hot Phos to address the defectivity. However, there is a significant impact to selectivity where the single wafer tool option is not viable. A method is needed to resolve the defectivity by using a single wafer tool while keeping the selectivity.
Throughout the industry, Hot Phos is used on batch tools because the bath needs to be conditioned to obtain the desired selectivity of SiN to SiO2. Typically, monitors or product (non-critical) is used to season the bath. Ideally, the bath is seasoned without the usual conditioning of the bath. This...