Semiconductor device manufacturing: process – Chemical etching – Liquid phase etching
Reexamination Certificate
2001-10-25
2004-04-27
Coleman, W. David (Department: 2823)
Semiconductor device manufacturing: process
Chemical etching
Liquid phase etching
C438S749000, C438S751000
Reexamination Certificate
active
06727188
ABSTRACT:
The present invention claims the benefit of Korean Patent Application No. P2000-64526 filed in Korea on Nov. 1, 2000, which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an etchant used during copper etching in a semiconductor substrate fabrication process, and more particularly, to an etchant with an additive to control change in the copper etch rate over passage of time and also to a method of fabricating a substrate for an electronic device using the additive-containing etchant.
2. Discussion of the Related Art
A substrate can be used to fabricate various electronic devices such as a thin film transistor (TFT) for a liquid crystal display (LCD) device, a solar battery, an electroluminescent display device, or a touch panel. The substrate for an electronic device includes lines and electrodes of various patterns for driving the device. A Cu deposition film, for example, Cu or Cu/Ti (Titanium) having excellent low resistance characteristics, is mainly used as a material for the above-mentioned lines and electrodes. To form desired lines and electrodes by using a material such as Cu or Cu/Ti, photolithography and etching processes must be performed on the substrate.
A related art etchant and a method for fabricating a substrate for an electronic device using that etchant is explained below with reference to
FIGS. 1 and 2
.
FIG. 1
is a plane view of a general TFT substrate, and
FIG. 2
is a graph showing variations in etch rate against the number of sheets of processed substrates according to the related art. The TFT substrate is an example of a substrate for an electronic device, and the TFT is a constituent part of a TFT-LCD panel. As shown in
FIG. 1
, the TFT substrate includes gate lines
1
and data lines
2
arranged in a matrix form that divides a unit pixel; a TFT (of elements
4
-
7
) formed on a crossing point between a gate line
1
and a data line
2
; and a pixel electrode
9
electrically connected to the TFT.
As shown in
FIG. 1
, the TFT includes deposition films for a gate electrode
4
, a semiconductor layer
5
, a source electrode
6
and a drain electrode
7
. The TFT serves as a switching device that turns a data signal on and off according to a scanned gate voltage applied to its gate electrode
4
.
To form the patterns for gate lines, data lines and various electrodes, photolithography and etching processes must be performed on the TFT substrate. The photolithography relies on a chemical reaction in which a specific photoresist reacts chemically to light and changes its own properties. During photolithography, the desired circuit pattern is formed on the substrate using a mask and selective irradiation of light onto the substrate with the mask. Thereafter, the mask is removed and the substrate is etched to obtain the desired circuit pattern on the substrate.
Etching is a process used after photolithography to selectively eliminate the photoresist and other deposition films along patterns formed on the photoresist to obtain a real thin film circuit pattern. The etching process uses physical and chemical methods and consists of both dry-etching in which a gas is used and wet-etching in which an etchant such as acid liquid is used. It is noted that to etch a Cu deposition film of, for example, Cu or Cu/Ti, a wet-etching is preferably used.
Thus, the gate lines, the gate electrodes, the data lines, and the source and drain electrodes are finally formed with a wet-etching of a Cu deposition film using an etchant. Some examples of related art etchants include a Cu etchant containing KHSO
5
; a Cu/Ti etchant containing HF, KF, and KHSO
5
; or a Cu/Ta etchant.
An etching reaction of Cu is derived from hydrolysis of KSHO
5
, that is, KHSO
5
+H
2
=>KHSO
4
+H
2
O
2
. The following formulas 1 and 2 express the etching reactions of Cu.
Cu+KHSO
5
==>CuO+KHSO
4
[Formula-1]
Cu+KHSO
5
==>CuSO
4
+2K
2
SO
4
+2H
2
O+O
2
[Formula-2]
However, as shown in
FIG. 2
, when a single layer of copper (Cu) is wet-etched, the etch rate of Cu is not constant per number of sheets of processed substrates that include the single layer of Cu. The etch rate, as shown in
FIG. 2
increases or decreases depending on the number of sheets of processed substrates. The increase in etch rate is caused by a reaction resulting in CuSO
4
that has an increased concentration as the Cu film is etched. The generated CuSO
4
increases the etch rate of Cu.
Table-1 given hereinbelow shows a critical dimension loss (CD-loss) of a Cu/Ti (1500 Å/300 Å) deposition film and a &Dgr;L according to the number of sheets of processed substrates that include the Cu deposition film, where the Cu/Ti deposition film is etched by an etchant in which HF, KF, and oxone are mixed with a rate of 0.1%, 0,2%, and 2% respectively. The oxone, as used herein, is a mixture of 2 KHSO
5
, KHSO
4
, and K
2
SO
4
. In Table-1, the CD-loss represents a length difference between a desired pattern length and an etched pattern length that is etched more than the desired pattern length. The &Dgr;L is a numerical value obtained by subtracting the initial CD-loss from the CD-loss of the corresponding number of sheets of processed substrates.
TABLE 1
CD-loss (Å)
&Dgr;L (Å)
Initial stage
3000-3500
Process for 450 sheets
4600-7700
1600-4200
Process for 800 sheets
6400-7700
3400-4200
Process for 1200 sheets
5400-6100
2400-2600
Process for 1600 sheets
1500-1700
1500-1800
Process for 1800 sheets
—
—
Table-1, like
FIG. 2
, demonstrates that the etch rate varies as the number of sheets of processed substrates increases. This change in the etch rate over passage of time makes a uniform management of a Cu profile difficult, which causes deterioration in yield.
To obtain a uniform Cu pattern profile with a related art etchant, the etchant should be replaced after processing 450 sheets of substrates, leading to complicated processes and increased production costs due to increased etchant consumption.
Thus, a related art method of fabricating the substrate for an electronic device has the following problems. First, since it is difficult to manage a pattern profile uniformly because of the change in the etch rate over the passage of time when a deposition film of Cu or Cu/Ti is etched by a related art etchant, devices with inferior accuracy are produced. Second, to obtain a profile of a uniform Cu pattern, the prior art etchant must be replaced periodically. Because the period for replacing an etchant becomes short, the production cost increases.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to an etchant and a method for fabricating a substrate for an electronic device using that etchant. The etchant and the method of the present invention substantially obviate one or more problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an etchant and a method for fabricating a substrate for an electronic device using the etchant, where the etchant controls the etch rate of a Cu deposition layer (containing Cu, Cu/Ti, or Cu/Ta) over passage of time.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the etchant according to the present invention contains a predetermined additive to control the etch rate of a Cu deposition layer (containing Cu, Cu/Ti, or Cu/Ta) over passage of ti
Chae Gee Sung
Jo Gyoo Chul
Brewster William M.
Coleman W. David
LG.Philips LCD Co. , Ltd.
Morgan, Lewis & Bocklius LLP
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