Stress inducing spacers
View Patent ↗A substrate under tension and/or compression improves performance of devices fabricated therein. Tension and/or compression can be imposed on a substrate through selection of appropriate gate sidewall spacer material disposed above a device channel region wherein the spacers are formed adjacent both the gate and the substrate and impose forces on adjacent substrate areas. Another embodiment comprises compressive stresses imposed in the plane of the channel using SOI sidewall spacers made of polysilicon that is expanded by oxidation. The substrate areas under compression or tension exhibit charge mobility characteristics different from those of a non-stressed substrate. By controllably varying these stresses within NFET and PFET devices formed on a substrate, improvements in IC performance have been demonstrated.
1. A method for making stressed spacer structures for devices in a substrate, the devices including devices of a first conductivity type and devices of a second conductivity type, the devices each having a gate terminal and a channel for conducting charge extending in the substrate in a longitudinal direction, the method steps comprising:
forming a first spacer structure on the sidewalls of the gate terminal of a first device of the first conductivity type, the first spacer structure comprising a first stress inducing material adjacent to both the sidewall of the first one of the device's gate terminal and its channel which applies a first type of mechanical stress on the first one of the devices at least in the longitudinal direction, the first type of mechanical stress being one of tensile stress and compressive stress; and
depositing a second spacer material on the sidewalls of the gate terminal of a second device of the second conductivity type, the second spacer structure comprising a second stress inducing material adjacent to both the sidewall of the second one of the device's gate terminal and its channel which applies a second type of mechanical stress different from the fist type of the mechanical stress, on the second one of the devices at least in the longitudinal direction, the second type of the mechanical stress being the other of the tensile stress and the compressive stress,
said first and second conductivity type devices being respectively an NFET and PFET devices, and said first and second type mechanical stress being respectively induced by a tensile material and a compressive induced material.
2. The method of claim 1 wherein the steps of forming the first and second spacer structure includes:
covering the gate terminal of the first one of the devices with a first spacer material; and
covering the gate terminal of the second one of the devices with a second spacer material.
3. The method of claim 2 , wherein the steps of covering the gate terminals of the first and second ones of the devices further includes:
covering both the first and second ones of the gate terminals with the first spacer material; and
blocking the first one of the devices with a block mask while removing the first spacer material from the second one of the devices.
4. The method of claim 3 , further comprising the steps of:
covering both the first and second ones of the gate terminals with the second spacer material; and
blocking the second one of the devices with a block mask while removing the second spacer material from the first on of the devices.
5. The method of claim 4 , further comprising the step of:
etching the devices to remove the first and second spacer materials from a top surface of the gate terminals of the first and second ones of the devices, respectively.
6. The method of claim 1 , wherein the step of forming a first spacer structure comprises:
depositing a first spacer material on sidewalls of the gate terminal of the first one of the devices and on the top surface of the substrate.
7. The method of claim 1 , wherein the step of forming a second spacer structure comprises:
depositing a second spacer material by HDP on the sidewalls of the gate terminal of the second one of the devices and on the top surface of the substrate.