Process for in-situ etching a hardmask stack

Details Process for in-situ etching a hardmask stack Process for in-situ etching a hardmask stack

2002-01-07

2004-02-24

Norton, Nadine G. (Department: 1765)

Semiconductor device manufacturing: process

Chemical etching

Vapor phase etching

C438S709000, C438S717000, C438S719000, C438S723000, C438S724000, C438S725000

Reexamination Certificate

active

06696365

ABSTRACT:

This invention relates to a method of etching hardmask stacks for deep trench openings in silicon. More particularly, this invention relates to a method of etching high aspect ratio deep trenches in silicon through a multilayer hard mask stack in a single chamber.
BACKGROUND OF THE DISCLOSURE
Multilayer hard mask stacks used for patterning silicon prior to etching deep, straight walled trenches in the silicon comprise a plurality of layers. One typical hard mask stack, as shown in
FIG. 1
, comprises in sequence a silicon substrate
10
, a thin layer of thermally grown silicon oxide
12
, called pad oxide, over the silicon substrate
10
; a layer of silicon nitride
14
over the pad silicon oxide layer
12
; a layer of silicon oxide hardmask
16
, which can be doped (PSG, BPSG) or undoped silicon oxide over the silicon nitride layer
14
; a polysilicon hardmask layer
18
over the silicon oxide layer
16
; an antireflective coating
20
over the polysilicon layer
18
; and a patterned layer of photoresist
22
thereover.
Patterning these different layers requires different etchants and different etch conditions, and thus the substrate and its various layers are presently transferred between up to five different processing chambers. Since processing is carried out in high vacuum plasma chambers, and since changing processing conditions in the chambers is a lengthy process, a tool has been developed that connects several reaction chambers together by means of a central vacuum chamber that connects to each of the processing chambers. A suitable device, such as a robot, picks up a substrate, such as a silicon wafer having the layers thereover as in
FIG. 1
, and inserts it into a first silicon etch chamber to open the antireflection layer
20
and the polysilicon hard mask layer
18
, as shown in FIG.
2
.
After processing, the substrate
10
is transferred to the central vacuum chamber and then into a second reaction chamber, known as an ASP or ashing chamber, to remove the remaining photoresist
22
using oxygen. The resultant substrate is shown in
FIG. 3
where the polysilicon is a patterned hard mask layer. The substrate
10
is then transferred to a third, cleaning chamber where any remaining photoresist is removed.
The silicon oxide hard mask layer
16
, the silicon nitride layer
14
and the thin pad oxide layer
12
are pattern etched in a fourth, dielectric etch chamber, as shown in FIG.
4
. The etch stops when the silicon substrate
10
is reached. The polysilicon hard mask layer
18
is then removed, as shown in
FIG. 5. A
deep trench etch is carried out next using the silicon oxide hard mask
16
as the patterning layer in a fifth etch chamber. The resultant substrate is shown in FIG.
6
.
The substrate is never exposed to the atmosphere or to non-vacuum conditions using the above tool, until all of the sequence of steps has been carried out. However, this method requires five chambers and multiple transfers of the silicon substrate by the robot, which can cause damage to the substrate and adds to the time and costs of processing.
The multiple chambers and the multiple steps carried out in the chambers is expensive both in terms of equipment costs and in terms of the time required for processing a single substrate. It would be highly desirable to reduce the amount of equipment required, the time required to process a single substrate, and to eliminate multiple transfers of the substrate.
SUMMARY OF THE INVENTION
We have found that once the photoresist and antireflective layers are patterned, the remaining layers can be etched down to the silicon substrate, and a deep trench etched therein, in a single, high aspect ratio trench etch chamber. This method can be carried out simply by changing the reactant gases and reaction conditions in the chamber. The method not only saves transfer time, but reduces damage and defects that can occur during transfers of the substrate between one chamber and another. Another advantage of this process is that it is self-cleaning. Ths use of fluorine-containing etch gases also serves to remove contaminants from the walls and fixtures of the single etch chamber.


REFERENCES:
patent: 6103632 (2000-08-01), Kumar et al.
patent: 6335235 (2002-01-01), Bhakta et al.
patent: 6498383 (2002-12-01), Beyer et al.
patent: 6528384 (2003-03-01), Beckmann et al.
patent: 6541382 (2003-04-01), Cheng et al.

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