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Method for Improved Rf Coupling in Plasma Process Disclosure Number: IPCOM000241040D
Publication Date: 2015-Mar-21
Document File: 6 page(s) / 125K

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We are disclosing the use of a sacrificial'shunt' layer to provide improved plasma coupling, in a reactive ion (RIE) etch process, for etch a dielectric film on a silicon-on-insulator wafer. Use of this shunt layer address the problem of cross-wafer RIE non-uniformity. We have determined RIE non-uniformity on SOI wafers is related to bias non-uniformity and poor RF coupling between the wafer chuck and the front side of the wafer where the RIE is directed.

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Method for Improved Rf Coupling in Plasma Process

In processing silicon-on-insulator wafers, we have discovered cross-wafer non-unformity, in etching dielectric films. We have determined this non-uniformity is unique to the SOI wafer type, specifically SOI with high-resistivity substrate, or handle wafers.

We have shown that the use of a sacrificial conductive shunt layer, across the dielectric surface is effective at addressing this non-uniformity.

The problem is illustrated in Figure 1 (below). In the near-edge of the wafer, etch rate is much lower, due to inability to deliver uniform RF bias from the tool chuck (source) to the front or top surface of the wafer, where the RIE process is occurring. The rate is lower because there is a high resistance patch from the handle wafer, through the insulating oxide, to the front surface of the wafer. In the region of the wafer that protrudes from the edge of the chuck, the rate is very low (see Figure 2)

Our solution is shown in Figures 3 and Figure 5, as embodiment #1 and embodiment #2. Specifically, we describe the inclusion of a sacrificial conductive layer that provides uniform RF bias, laterally across the wafer. Some possible materials include doped polysilicon, titanium, titanium nitride or tungsten. Etch depth results, for the 'shunt implementation' are shown in figure 4, in comparison with the 'no shunt' or POR case. We demonstrated a 10-15% loss in etch rate, for the 'no shunt' case center-edge and a 4-5% increase in etch...