US 5,401,998 AGranted

Trench isolation using doped sidewalls

OwnerKuang Y. Chiu, Dan W. Petersinventors

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Abstract

A P-type substrate is immersed in a solution of potassium hydroxide (KOH) which etches exposed portions of the substrate to form trenches with sidewalls at an angle of 54.7 degrees with respect to the top surface of the substrate. A vertical boron implant is then conducted which implants boron ions into the angled sidewalls of the trenches. A layer of oxide is then deposited over the substrate surface to fill the trenches approximately flush with the surface of the substrate. NMOS transistors may then be formed in the islands surrounded by the trenches so as to be isolated from other NMOS devices. The boron doping of the sidewalls prevents the inversion of the sidewalls due to any charged contaminants in the deposited oxide. This avoids parasitic leakage currents between the N-type source and drain regions of the NMOS transistors which abut the sidewalls of the trenches.

Claims6

Dependent claims

A semiconductor structure comprising:

a silicon substrate of a P conductivity type;
one or more trenches etched into a top surface of said substrate, said one or more trenches having angled sidewalls of said P conductivity type, said sidewalls forming an angle of between 50 and 60 degrees with respect to said top surface of said substrate, said sidewalls having P type ions implanted into them to increase a P type doping concentration along said sidewalls;
an oxide layer filling said one or more trenches, said ions implanted into said sidewalls being sufficient to prevent inversion of said sidewalls due to any charged contaminants in said oxide;
and
one or more N-channel MOS transistors formed in said top surface of said substrate being isolated from other active devices by said one or more trenches, N-type source and drain regions of at least one of said MOS transistors terminating at a respective sidewall of one of said trenches, said ions implanted into said sidewalls preventing leakage currents from flowing between said source and drain regions due to positively charged ions in said oxide.

2 more elements

Dependencies are inferred from the claim text.

Facts

Application: 08/296,611Filed 26 Aug 1994 · continuation
Priority: 3 Dec 1992
Granted: 28 Mar 1995
Term ends: Not estimatedThe source records don’t support an estimate.

Classification9 codes

H10P 50/644
Chemical etching: anisotropic liquid etching
H10D 84/83
Of only field-effect components: of only insulated-gate FETs [IGFET]
H10W 10/014
Of isolation regions comprising dielectric materials: using trench refilling with dielectric materials, e.g. shallow trench isolations
H10W 10/0145
Using trench refilling with dielectric materials, e.g. shallow trench isolations: of trenches having shapes other than rectangular or V-shape