Evauation of particle removal efficiency of filters in high temperature sulfuric acid using 30 nm liquid particle counter — Tomoyuki Takakura

Since the scale of semiconductor devices are continuously reducing, the control level of size and numbers of particles are also becoming stricter during the manufacturing process; the role of filtration is of great importance for the control of particle level. Thus, it is a critical issue to use an appropriate filter in each process tool. A criterion for selecting an appropriate filter is the removal rating, which claims the size of particles to be removed by the filter. The rating of the filters used for semiconductor device manufacturing is performed in the deionized water (DIW) at ambient temperature [1]. In the actual manufacturing process, however, the filters are used in various chemical and temperature, and in such condition, it is empirically known that removal efficiency of the filters differs from that in the standard atmosphere (i.e. DIW at ambient temperature). Thus, it is important to know the actual particle removal efficiency (PRE) in the actual chemical. In the semiconductor cleaning process, high temperature sulfuric acid is commonly-used chemical, and there are some studies on PRE evaluation of filters in the chemical: One is in 120 °C sulfuric acid using a liquid particle counter (LPC) which can detect 60 nm and larger particles [2], and another is in 150 °C sulfuric acid using a LPC which can detect 40 nm and larger [3]. However, the measurement ranges of these LPCs are coarser than the filter rating used for the leading-edge semiconductor processes (<; 20 nm), and finer measurement range would be preferred. In this study, we conducted PRE evaluation of filters in high temperature sulfuric acid using a LPC with sensitivity of 30 nm which is the currently finest one available in the chemical, and discussed the effect of the measurement range difference on PRE. Also, an effect of flow rate on the PRE was studied.