Wet etching system for manufacturing semiconductor devices

Details Wet etching system for manufacturing semiconductor devices Wet etching system for manufacturing semiconductor devices

1999-06-01

2002-06-04

Utech, Benjamin L. (Department: 1765)

Adhesive bonding and miscellaneous chemical manufacture

Differential fluid etching apparatus

With microwave gas energizing means

C118S726000

Reexamination Certificate

active

06398904

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a wet etching system for manufacturing semiconductor devices and a wet etching method using the same, and more particularly, to a wet etching system and method for etching a nitride layer, formed on a semiconductor substrate, for a short period of time while maintaining the concentration of phosphoric acid (H
3
PO
4
) constant.
2. Description of the Related Art
Generally, semiconductor devices are manufactured by forming multiple insulating layers or conductive layers on a semiconductor substrate, and then forming a specific electrical pattern on the layers according to desired characteristics of the particular semiconductor device being manufactured.
The formation of the specific pattern is achieved by selectively removing designated portions of the insulating layers and/or the conductive layers by an etching process. There are two types of etching processes: dry etching using a plasma generated in a reaction chamber, and wet etching using a particular chemical that is capable of removing the layer to be etched. The wet etching process is carried out using a wet etching system employing a tank containing the chemical etchant.
FIG. 1
schematically illustrates a conventional etching system for manufacturing semiconductor devices, employing a chemical bath comprising a tank
10
for containing a chemical
16
for etching a certain layer on the semiconductor substrate. Normally, the chemical
16
is diluted with deionized water, with the degree of dilution being controlled depending on the etching process.
A heater
12
heats the chemical
16
inside the tank
10
to a certain temperature sufficient for the process conditions of the etching process. Typically, bar-shaped heaters
12
are disposed in the chemical
16
at opposing sides of the tank
10
.
A bubbler
14
is connected to the tank
10
and is used to generate bubbles in the chemical
16
inside the tank
10
in order to improve the reaction of the chemical
16
and a wafer placed in the chemical bath.
The temperature of the chemical
16
and the etching process time are important parameters in the etching process. However, heating the chemical
16
causes the deionized water, which was used to dilute the chemical, to evaporate. As a result, the concentration of the chemical
16
within the tank
10
is increased due to the evaporation of the deionized water, and thus, deionized water must be supplied in an amount equal to the evaporated amount in order to maintain the chemical
16
concentration constant. In some cases, additional amounts of chemical
16
are supplied to the tank
10
to maintain the chemical
16
concentration constant.
However, precisely controlling the concentration changes of the chemical due to the evaporation of the deionized water is not easy, despite the continuous supply of the deionized water, because the concentration of the chemical
16
inside the tank
10
is not constant.
Although the chemical concentration changes can be detected by changes in the etch rate observed during the etching process, such observations occur after a particular wafer may have suffered a fatal defect caused by a failure of the pattern profile during the etching process. In other words, precise control of the etching process is difficult when using data generated after the etching process is performed.
Another drawback of the conventional wet etching system is that the temperature of the chemical
16
decreases as the deionized water is continuously supplied to the tank
10
, and thus the heater
12
must be continuously driven to heat the chemical
16
to the desired etching temperature, which shortens the life span of the etching system itself.
Referring to
FIG. 1
, the etching process for a nitride layer is described. First, a chemical
16
for etching the nitride layer, such as phosphoric acid (H
3
PO
4
), is supplied in the tank
10
. The concentration of the phosphoric acid (H
3
PO
4
) is 85%, with the remainder being deionized water. Although the phosphoric acid concentration is relatively high, the etch rate for the nitride layer is good at this concentration value.
The phosphoric acid (H
3
PO
4
) is heated so as to maintain its temperature between about 170° C. to 174° C. according to the process conditions of the etching process, and then, the etching process is carried out. The etching process time depends on the thickness of the nitride layer.
However, as describe above, the required continuous supply of deionized water and the chemical to the tank
10
causes difficulties in trying to precisely control the chemical concentration inside the tank
10
, which causes uneven etch rates. Further, because the heater
12
is bar-shaped, it takes a long time to heat the phosphoric acid (H
3
PO
4
) and maintain its temperature, which may damage the heater and shorten the life time of the etching system.
Moreover, after the etching process is completed, the disposal and the cleaning of the remaining waste solution, including the deionized water, the chemical, etc. due to the continuous supply thereof remains a difficult problem.
SUMMARY OF THE INVENTION
The present invention is directed to a wet etching system for manufacturing semiconductor devices and a wet etching method using the same, which provides efficient and precise execution of the etching process while maintaining the concentration of the chemical etchant constant.
Another object of the present invention is to provide a wet etching system for manufacturing semiconductor devices and a wet etching method using the same, which decreases the process temperature of the chemical to one that is lower than the conventional art, and increases the etch rate of the etching process, while maintaining the concentration of the chemical constant to thereby reduce the etching process time.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the wet etching system for manufacturing semiconductor devices comprises an open topped tank containing a chemical diluted with deionized water to wet-etch a certain layer on a semiconductor substrate. A heater is disposed in the tank, and a cover is employed to cover the open top of the tank. The cover includes a cooling apparatus that condenses the deionized water evaporated by the heating of the heater.
The lower surface of the cover gradually slopes downwardly from opposing edges of the cover toward either a central lateral or longitudinal axis thereof, which facilitates collection of the condensed deionized water. A discharge opening is provided in the cover, in flow communication with the ambient outside of the tank, so that gas can be easily discharged from the tank.
The tank and the cover may be made of a chemically-resistant material, such as TEFLON™, and the surface of the heater may be coated with TEFLON™ as well.
In another aspect of the present invention, there is provided a wet etching method comprising supplying a chemical diluted with deionized water into a tank having a top portion with a cover arranged thereon, the cover having a cooling apparatus formed therein. A semiconductor substrate, having a layer thereon to be etched, is placed into the tank. A heater disposed within the tank maintains the chemical within a temperature range. The deionized water evaporates when the temperature range is greater than a boiling point of the deionized water. The deionized water then condenses on the cooler cover, before flowing back into the tank. The etching process is carried out while the evaporation and condensing steps are performed.
Where the layer to be etched is a nitride layer, the chemical supplied into the tank is a phosphoric acid (H
3
PO
4
) diluted with deionized water, the concentration of the phosphoric acid (H
3
PO
4
) being from 80% to 90%. The chemical is heated to maintain its temperature between about 153° C. to 157° C.
It is to be understood that both the foregoing general description and the following detailed description are exempla

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