US 5,963,802 AGranted

CMOS process for forming planarized twin wells

AssigneeTexas Instruments - Acer Incorporated

InventorShye-Lin Wu

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Abstract

This invention proposes a process to form planarized twin-wells for CMOS devices. After depositing a pad oxide and a silicon nitride layers, a high-energy phosphorus ion implantation is performed to form the N-well by using a photoresist as s mask. A thick oxide layer deposited by liquid phase deposition process is then grown on the N-well region part of the silicon nitride layer, but not on the photoresist. After stripping the photoresist, a high-energy boron ion implantation is carried out to form the P-well by using the LPD-oxide layer as a mask. The thick LPD-oxide layer is removed by BOE or HF solution. A high temperature steam oxidation is performed to grow field oxides. The dopants are activated and driven in to form twin-wells at this step. After removing the pad oxide and the silicon nitride layer, the CMOS device is fabricated by standard processes.

Claims15

Dependent claims

A process for forming planarized twin wells, said process comprising:

forming a pad oxide layer on a semiconductor substrate;
forming a silicon nitride layer on said pad oxide layer;
patterning a photoresist on a portion of said silicon nitride layer, said patterned photoresist defining a first conductive well region;
implanting ions of first type into said semiconductor substrate to form a first conductive well using said patterned photoresist as a mask;
depositing a silicon oxide layer on said silicon nitride layer in the regions not cover by said patterned photoresist, said silicon oxide layer being formed by a liquid phase deposition process;
removing said patterned photoresist;
implanting ions of second type into said semiconductor substrate to form second conductive well using said silicon oxide layer as a mask;
removing said silicon oxide layer;
etching said silicon nitride layer and said pad oxide layer to define active regions on said semiconductor substrate;
and
heating said semiconductor substrate in an oxygen-steam environment to form field oxides between said active regions and to drive in both types of said ions to form said twin-wells.

8 more elements

Dependencies are inferred from the claim text.