Method for selective etching of antireflective coatings

Details Method for selective etching of antireflective coatings Method for selective etching of antireflective coatings

2000-02-01

2001-03-13

Utech, Benjamin L. (Department: 1765)

Semiconductor device manufacturing: process

Chemical etching

Liquid phase etching

C438S756000, C438S757000, C252S079100, C252S079200, C252S079300, C252S079400

Reexamination Certificate

active

06200909

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to the fabrication of integrated circuit devices, and more particularly, to a method of etching inorganic antireflective coatings (also referred to as Dielectric Antireflective Coatings or DARCs) without etching excessive amounts of the underlying oxide layer.
BACKGROUND OF THE INVENTION
Inorganic antireflective coatings are used to counteract the overexposure which can occur with structures that reflect exposure light. To illustrate, referring to
FIG. 1
, there is shown a partially completed integrated circuit. Field oxide regions
11
have been formed in and on a semiconductor substrate
10
. Polysilicon or polycide gate electrodes
14
have been formed. A dielectric layer
16
covers the gate electrodes. An oxide layer
20
, typically borophosphosilicate glass (BPSG), is grown over the dielectric layer
16
. A layer of photoresist is coated over the oxide layer
20
and patterned to form a mask. Because of the reflective surface of the oxide layer
20
and the intensity of the deep ultraviolet light
22
used, the light rays
22
are reflected onto the photoresist layer (PR) causing overexposure. The resulting photoresist mask has a notch in it. Therefore, when subsequent layers are patterned according to the photoresist mask and etched, a notch
24
will result, as shown in top view in FIG.
2
.
In order to counteract this problem, an antireflective coating (DARC)
24
is commonly used, as shown in FIG.
3
. The DARC
24
is generally composed mostly of Si, with the next most abundant element being O, and the balance N. Once exposure is complete, the DARC is removed using wet etching.
Wet etching solutions significantly, and sometimes even preferentially, attack silicon oxides such as BPSG. Accordingly, when performing wet etches, excessive amounts of the underlying oxide layer
20
may be removed, especially when using BPSG. When this occurs, as illustrated in
FIG. 4
, an overhang of the DARC
24
is produced. This overhang can interfere or react with subsequent depositions, for example, when layers are deposited into a cavity over which the DARC
24
extends.
Prior art etching techniques refer to the use of particular solvents for etching in certain circumstances. Wei et al., U.S. Pat. No. 5,449,639, refers to a method of metal etching using a solution of hydrogen peroxide, ammonia, and water. Izumi et al., U.S. Pat. No. 5,022,961, refers to etching thermal oxide films of silicon with hydrofluoric acid (HF) or other halide-containing species in combination with alcohol. Maeda et al., U.S. Pat. No. 4,746,397 describes etching SiO
2
films with the use of a flourine-containing species and an alcohol, ketone or carboxylic acid.
What are still needed, however, are methods designed for the selective etching of DARCs while preventing or minimizing the etching of the adjacent oxide.
SUMMARY OF THE INVENTION
By “selectively” etching the DARC it is meant that the etch is preferential to the DARC relative to the adjacent oxide and that the DARC is etched at a rate greater than the oxide. The present invention provides a method for selectively etching antireflective coatings such as DARC.
According to one aspect of the present invention, DARC is selectively etched using a flourine-containing, ionizable compound in solution with an acid or a base. In a preferred embodiment, the etchant is composed of about 35-40 wt. % NH
4
F and about 0.9-5.0 wt. % H
3
PO
4
in an aqueous solution.
According to another aspect of the present invention, oxidizing agents are added to etchants to produce DARC/BPSG etch rates >1. A preferred embodiment of this method includes adding about one part of hydrogen peroxide (H
2
O
2
), and between 30 and 300 parts of an etchant comprised of about 39.2-39.9 wt. % ammonium fluoride, and about 0.9 wt. % phosphoric acid in an aqueous solution. Another preferred embodiment of this method uses an etchant comprised of about 1 part TMAH (25 wt. % tetramethyl ammonium hydroxide and 75 wt. % aqueous solution, preferably water) and between about 6 and 7 parts of aqueous solution, preferably water.
According to yet another aspect of the present invention, the pH level of an etchant is raised to between 11 and 14.
These and other objects, features and advantages of the invention will become apparent from the following detailed description of preferred embodiments of the present invention.


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Jenq et al., Manufacture of polysilicon conductive line-avoiding bottle-necking effect on non-flat field oxide edge, Abstract of TW 313701A, Aug. 1997.

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