US 6,207,538 B1Granted

Method for forming n and p wells in a semiconductor substrate using a single masking step

AssigneeTaiwan Semiconductor Manufacturing Company, Ltd.

InventorsKuo-Hua Pan, Chu-Wei Hu, Chung-Te Lin, Chin-Hsiung Ho

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Abstract

A method for forming both n and p wells in a semiconductor substrate using a single photolithography masking step, a non-conformal oxide layer and a chemical-mechanical polish step. A screen oxide layer is formed on a semiconductor substrate. A barrier layer is formed on the screen oxide layer. The barrier layer is patterned to form a first opening in the barrier layer over regions of the substrate where first wells will be formed. We implant impurities of a first conductivity type into the substrate to form first wells. In a key step, a non-conformal oxide layer is formed over the first well regions and the barrier layer. It is critical that the non-conformal oxide layer formed using a HDPCVD process. The non-conformal oxide layer is chemical-mechanical polished stopping at the barrier layer. The barrier layer is removed using a selective etch, to form second openings in the remaining non-conformal oxide layer over areas where second well will be formed in the substrate. Using the remaining non-conformal oxide as a mask, we implant impurities of the second conductivity type through the second openings to form second wells. The remaining non-conformal oxide layer and the screen oxide layer are removed.

Claims17

Dependent claims

a) forming a screen oxide layer on a semiconductor substrate;
b) forming a barrier layer on said screen oxide layer;
c) coating a photoresist layer over said barrier layer;
d) exposing said photoresist layer and developing said photoresist layer to form a photoresist mask having an opening to said barrier layer where first wells are to be formed;
e) etching away said exposed barrier layer to expose said underlying screen oxide layer to form a first opening in said barrier layer over regions of the substrate where first wells will be formed;
f) implanting impurities of a first conductivity type into said substrate to form first well regions;
g) removing said photoresist layer;
h) forming a non-conformal oxide layer over said first well regions and said barrier layer;
said non-conformal oxide layer formed using a high density plasma chemical vapor deposition (HDPCVD) process using a sputter/deposit process;
i) chemical-mechanical polishing said non-conformal oxide layer stopping at the barrier layer;
j) removing said barrier layer using a selective etch, to form second openings in the remaining non-conformal oxide layer over areas where second well will be formed in said substrate;
k) using the remaining non-conformal oxide as a mask, implanting impurities of the second conductivity type through said second openings to form second wells;
and
l) removing the remaining non-conformal oxide layer and said screen oxide layer.

11 more elements

a) forming a screen oxide layer on a semiconductor substrate;
b) forming a barrier layer on said screen oxide layer;
said barrier layer comprised of silicon nitride;
(1) said barrier layer has a thickness of between about 6000 and 8000 Å;
c) coating a photoresist layer over said barrier layer;
d) exposing said photoresist layer and developing said photoresist layer to form a photoresist mask having an opening to said barrier layer where first wells are to be formed;
said barrier layer is comprised of first and second barrier blocks;
said first barrier block is wider than said second barrier block;
e) etching away said exposed barrier layer to expose said underlying screen oxide layer to form a first opening in said barrier layer over regions of the substrate where first wells will be formed;
f) implanting impurities of a first conductivity type into said substrate to form first well regions;
(1) said first conductivity type impurities are N-type impurities of P or As and the implant is performed at a dose between about 1E2 and 1E4 atom/cm2;
and an energy between about 300 and 500 KeV and said first wells have a impurity concentration between 1E15 and 1E18 atom/cc and said first well has a depth between about 8000 and 12000 Å;
g) removing said photoresist layer;
h) forming a non-conformal oxide layer over said first well regions and said barrier layer;
said non-conformal oxide layer formed using a high density plasma chemical vapor deposition (HDPCVD) process;
(1) said non-conformal oxide layer is formed using a HDPCVD process comprising:
an oxygen flow rate between 150 and 300 sccm;
SiH4 flow between 70 and 200 sccm;
and a pressure between 3 and 10 mTorr;
a RF power between 2000 and 5000 W;
a wafer temperature between 600 and 750 C.°;
a HDPCVD sputter rate between 1000 and 2000 Å/min;
a deposition to sputter (deposition to etch) ratio between 2.5:1 and 4:
1;
and said conformal oxide layer has a thickness between 2000 and 12000 Å;
i) chemical-mechanical polishing said non-conformal oxide layer stopping at the barrier layer;
j) removing said barrier layer using a selective etch, to form second openings in the remaining non-conformal oxide layer over areas where second well will be formed in said substrate;
(1) using the remaining non-conformal oxide as a mask, implanting impurities of the second conductivity type through said second openings to form second wells;
(2) said second conductivity type impurities are P-type impurities of B or Indium and the implant is performed at a dose between about 1E2 and 1E4 atom/cm2;
and an energy between about 100 and 200 KeV;
said second wells have an impurity concentration between 1E15 and 1E18 atom/cc and a depth between about 8000 and 12000 Å below the substrate surface;
k) removing the remaining non-conformal oxide layer and said screen oxide layer.

29 more elements

Dependencies are inferred from the claim text.