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Method to Reduce Work Function Shift Due to RIE Damage During WFM Etch in a Multichannel VFET

IP.com Disclosure Number: IPCOM000244776D
Publication Date: 2016-Jan-14
Document File: 3 page(s) / 71K

Publishing Venue

The IP.com Prior Art Database


Disclosed is a method for depositing and patterning a block level mask before performing the workfunction metal (WFM) reactive ion etching (RIE) during the process flow for vertical Field Effect Transistors (VFETs). This protects the WFM within the devices from any RIE damage, while permitting an extended RIE to remove WFM from any topographical regions between the devices.

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Method to Reduce Work Function Shift Due to RIE Damage During WFM Etch in a Multichannel VFET

A typical process flow for vertical Field Effect Transistors (VFETs) involves forming a vertical gate along the fin sidewalls. This is achieved by depositing a gate workfunction metal (WFM) over the fins, and then performing an anisotropic etch, typically a reactive ion etch (RIE). (Figures 1a, 1b)

The primary function this serves is to remove WFM from the isolation regions between two adjacent VFET devices (e.g., in the images below, the three fins over Drain 1 comprise a first device, and the three fins over Drain 2 comprise a second, adjacent device). This, in turn, results in separate gates for each of the first and second devices . However, this creates the potential for the RIE to cause etch damage to the WFM . This etch damage may, in turn, change the workfunction value of the WFM and therefore alter the threshold voltage (Vt) of the device.

Figure 1: Typical process flow for VFETs

An additional problem arises from this type of process flow when VFETs of multiple gate lengths are being fabricated, or otherwise anything that can result in topography throughout the isolation material. Figures 2a and 2b illustrate this problem at the same aforementioned step in the process flow. Here, the device on the right side comprises taller fins (to enable a longer vertical channel length) and a corresponding recess in the isolation material between the left- and right-side de...