Gate metal patterning for tight pitch applications
Gate metal patterning techniques enable the incorporation of different work function metals in CMOS devices such as nanosheet transistor devices, vertical FETs, and FinFETs. Such techniques facilitate removal of gate metal from one region of a device without damage from over-etching to an adjacent region. The fabrication of CMOS devices with adjoining nFET/pFET gate structures and having very tight gate pitch is also facilitated. The techniques further enable the fabrication of CMOS devices with adjoining gate structures that require relatively long etch times for removal of gate metal therefrom, such as nanosheet transistors. A nanosheet transistor device including dual metal gates as fabricated allows tight integration.
1. A method of fabricating dual work function metal gate transistors, comprising:
obtaining a first structure including:
a substrate having a first region and a second region,
a first FET structure on the first region of the substrate, the first FET structure including a semiconductor channel region and a dielectric layer adjoining the semiconductor channel region,
a second FET structure on the second region of the substrate, the second FET structure including a semiconductor channel region and a dielectric layer adjoining the semiconductor channel region,
a first gate metal layer having a first portion extending over the first region of the substrate and a second portion extending over the second region of the substrate, the first gate metal layer further adjoining the dielectric layers of the first and second FET structures, and
a mask covering the first FET structure;
depositing a protective layer partially covering the first gate metal layer extending over the second region of the substrate;
subjecting the first structure to an etching process subsequent to depositing the protective layer, thereby removing the second portion of the first gate metal layer while leaving the first portion of the first gate metal layer intact;
removing the mask subsequent to removing the first gate metal layer from the second FET structure, and
forming a second gate metal layer on the first and second FET structures, the second metal gate layer adjoining the dielectric layer of the second FET structure and having a different work function value than the first metal gate layer.
2. The method of claim 1 , wherein depositing the protective layer includes depositing flowable oxide material.
3. The method of claim 1 , wherein depositing the protective layer includes directionally sputtering the protective layer over the second region of the substrate.
4. The method of claim 1 , wherein the first and second FET structures are nanosheet field-effect transistor structures.
5. The method of claim 1 , wherein each of the first and second FET structures includes a stack of nanosheet channel layers, the stack of nanosheet channel layers of the first FET structure being spaced from the stack of nanosheet channel layers of the second FET structure by a distance between 30 nanometers and 50 nanometers.
6. The method of claim 5 , wherein the nanosheet channel layers have widths between 10 nanometers and 50 nanometers.