Method for forming dual oxide layers at bottom of trench

Details Method for forming dual oxide layers at bottom of trench Method for forming dual oxide layers at bottom of trench

2002-08-29

2004-11-23

Smith, Matthew (Department: 2825)

Semiconductor device manufacturing: process

Coating of substrate containing semiconductor region or of...

Insulative material deposited upon semiconductive substrate

C438S424000, C438S435000, C438S756000, C438S757000

Reexamination Certificate

active

06821913

ABSTRACT:

CROSS-REFERENCES TO RELATED APPLICATIONS
This application claims priority from R.O.C. Patent Application No. 090124497, filed Oct. 4, 2001, the entire disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates generally to semiconductor manufacturing and, more particularly, to an improved method for forming dual oxide layers at the bottom of a trench of a substrate.
To achieve an increase in integration and smaller ICs (integrated circuits), the DMOS (Double Diffused Metal Oxide Semiconductor) is commonly used in semiconductor manufacturing. The manufacturing of DMOS requires the formation of an oxide layer, called bottom oxide layer, at the bottom of a trench to reduce the charge produced from turning on the DMOS and to decrease the leakage current.
The conventional procedure for forming dual oxide layers at the bottom of a trench is described as follows. Referring to
FIG. 1
a
, a semiconductive substrate
100
having a trench
110
and a mask layer
120
is provided.
Referring to
FIG. 1
b
, an oxide layer
130
is formed on the sidewall and the bottom of trench
110
. The oxide layer
130
is a self-aligned contact oxide layer formed by thermal oxidation.
Referring to
FIG. 1
c
, a HMDS (hexamethyl disilazane) coating treatment
140
is performed. The HMDS coating treatment
140
is used as a priming treatment before coating photoresist.
Referring to
FIG. 1
d
, a photoresist layer
150
is deposited on the mask layer
120
, and the trench
110
is filled up with the photoresist layer
150
.
Referring to
FIG. 1
e
, a curing treatment
160
is performed to cure the photoresist layer
150
.
Referring to
FIG. 1
f
, the photoresist layer
150
is partially etched to leave a remaining photoresist layer
150
′, wherein the thickness of the remaining photoresist layer
150
′ is lower than the depth of trench
110
.
Referring to
FIG. 1
g
, the mask layer
120
and part of the oxide layer
130
are removed by BOE (buffered oxide etchant) treatment, wherein the bottom of trench
110
is left with a remaining oxide layer
130
′ and a remaining photoresist layer
150
′.
Referring to
FIG. 1
h
, the remaining photoresist layer
150
′ is removed.
Referring to
FIG. 1
i
, another conformal oxide layer
170
is formed on the substrate
100
, the sidewall of the trench
110
and the remaining oxide layer
130
′. The region
180
includes the remaining oxide layer
130
′ on the bottom of trench
110
and the portion of the conformal oxide layer
170
on the bottom of trench
110
. In specific embodiments, the height of the dual oxide layer structure
180
on the bottom of the trench
110
is about 0.2 &mgr;m to about 0.3 &mgr;m.
The disadvantage of the method of prior art is that when the depth of the trench
110
is very deep in
FIG. 1
e
, especially deeper than 1.0 &mgr;m, vaporization of the solvent of the photoresist
150
in the trench
110
is very difficult. This causes the adhesion between the remaining photoresist layer
150
′ and the oxide layer
130
to be weak. Then, when performing the BOE treatment in
FIG. 1
f
to
FIG. 1
g
, the BOE etchant will damage the interface
200
between the remaining photoresist layer
150
′ and the oxide layer
130
. The oxide structure at the bottom of trench
110
is also damaged, as illustrated in the FIG.
2
.
BRIEF SUMMARY OF THE INVENTION
Embodiments of the present invention are directed to an improved method for forming dual oxide layers at the bottom of a trench of a substrate. Instead of curing the photoresist layer prior to partial etching, the photoresist curing treatment is performed after partial photoresist ashing or etching. This allows the easy vaporization of the solvent of the remaining photoresist in the trench. By performing a curing treatment to completely, or substantially completely, vaporize out the solvent of the remaining photoresist layer in the trench, the method produces a strong interface between the remaining photoresist layer and the first bottom oxide layer. As a result, the damage to the interface between the remaining photoresist layer and the first bottom oxide layer by the BOE etchant is minimized, and improved dual oxide layers can be produced by forming the second bottom oxide layer over the first bottom oxide layer.
In accordance with an aspect of the present invention, a method of forming dual oxide layers at the bottom of a trench comprises providing a substrate having a trench which includes a bottom and a sidewall. A first oxide layer is formed on the sidewall and the bottom of the trench of the substrate. A photoresist layer is formed on the substrate, filling the trench of the substrate. The method further comprises partially etching back the photoresist layer to leave a remaining photoresist layer in the trench. The height of the remaining photoresist layer is lower than the depth of the trench. A curing treatment of the remaining photoresist layer is performed. A portion of the first oxide layer is removed to leave a remaining first oxide layer at the bottom of the trench. The remaining photoresist layer is removed. A second oxide layer is formed on the substrate covering at least the remaining first oxide layer.
In some embodiments, the trench is formed on the substrate by forming a mask oxide layer on the substrate; defining the mask oxide layer to form a patterned mask oxide layer and exposing a partial surface of the substrate to form a window; and using the patterned mask oxide layer as an etching mask to form the trench in the window. The patterned mask oxide layer is removed before forming the second oxide layer. The patterned mask oxide layer and the portion of the first oxide layer are removed to leave a remaining first oxide layer at the bottom of the trench by 10:1 BOE treatment. The mask oxide layer comprises a silicon oxide layer formed by thermal oxidation. The trench is formed in the window by dry etching.
In specific embodiments, an HMDS coating is formed on the surface of the first oxide layer before forming the photoresist layer. A heat treatment is performed on the HMDS coating. The heat treatment may be performed at about 70-150° C. for about 40-100 seconds. The second oxide layer is a conformal oxide layer formed on the remaining first oxide layer, the sidewall of the trench, and the surface of the substrate. The method may further comprise performing a curing treatment on the photoresist layer after the photoresist layer is formed on the substrate filling the trench of the substrate. The first oxide layer comprises a self-aligned contact silicon oxide layer formed by thermal oxidation. The photoresist layer may be partially etched back by O
2
plasma ashing. The curing treatment of the remaining photoresist layer may be performed at about 120-200° C. for about 60-100 seconds. The second oxide layer comprises a silicon oxide layer formed by thermal oxidation. Performing the curing treatment of the remaining photoresist layer comprises at least substantially completely vaporizing out solvent of the remaining photoresist layer in the trench.
Another aspect of the present invention is directed to a method of forming dual oxide layers at the bottom of a trench wherein a substrate has a trench which includes a bottom and a sidewall, wherein the trench is formed on the substrate by forming a mask oxide layer on the substrate, defining the mask oxide layer to form a patterned mask oxide layer and exposing a partial surface of the substrate to form a window, and using the patterned mask oxide layer as an etching mask to form the trench in the window; wherein a first oxide layer is formed on the sidewall and the bottom of the trench of the substrate, wherein a photoresist layer fills the trench of the substrate; wherein the patterned mask oxide layer and a part of the first oxide layer are removed to leave a remaining first oxide layer at the bottom of the trench; wherein the photoresist layer is removed; wherein a second oxide layer is formed on the substrate covering at lea

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