Semiconductor device manufacturing: process – Chemical etching – Vapor phase etching
Reexamination Certificate
1998-10-30
2001-05-22
Powell, William (Department: 1765)
Semiconductor device manufacturing: process
Chemical etching
Vapor phase etching
C156S345420, C216S092000, C438S748000
Reexamination Certificate
active
06235641
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method and system for establishing and maintaining precise concentrations of dissolved gas in a liquid. More particularly, the invention relates to a method and system of establishing and maintaining a precise concentration of dissolved gas in a liquid by indirectly or directly contacting a gas blend comprising a sufficient concentration of the desired gas so as to be in equilibrium with the desired concentration of the gas to be dissolved in the liquid, i.e., a “matched gas blend”.
BACKGROUND OF THE INVENTION
The manufacture of semiconductor devices involves numerous steps that are generally directed toward forming one or more layers on a semiconductor wafer substrate. For example, in the case of silicon wafers, a wafer is generally oxidized to form a layer of silicon dioxide on the surface of the wafer. All, or selective portions, of this silicon dioxide layer are subsequently removed via etching to expose the silicon wafer therebelow. Following etching, additional layers may be added to the etched silicon wafer, via thin film deposition or growth processes. These layers may then also be etched or otherwise treated to produce functional features on the surface of the silicon wafer.
The processes utilized to deposit and/or etch these layers, as well as the processes used to clean the wafers between steps, rely heavily on chemical reagents. In many instances, these chemical reagents comprise one or more gases dissolved in a liquid. Inasmuch as process parameters, such as the etch rate, quality of the etch, uniformity of the etch, and the like, are at least partially dependent upon on the concentration of the dissolved gas in the liquid, the concentration of the dissolved gas in the liquid is desirably controlled within tight specifications. If the concentration of the dissolved gas in the liquid is allowed to vary, undesirable manufacturing variations may result, or in the least, these chemical reagents will not perform optimally.
Unfortunately, controlling the concentration of a dissolved gas in a liquid to the degree necessary for such admixtures to be useful in many semiconductor manufacturing processes is difficult. As a result, variations in concentration can affect processing quality. For example, in some manufacturing processes of semiconductor devices, it is desirable to controllably etch copper so as to provide functional features on the surface of a semiconductor wafer. However, some copper etching applications may require etching precisely 5 nm of copper with less than a 5% variation. At least in this instance, variations in gas concentration are unacceptable.
Furthermore, although several methods of controlling the concentration of dissolved gas in a liquid are known, each of these prior art methods has limitations that render them inadequate for certain applications. For example, bubbling the gas that is to be dissolved directly into the liquid has been used as a method to dissolve gases into a variety of different kinds of liquids. Such a technique, however, does not optimize the quantity of gas dissolved or the amount of gas that remains in solution at the point of use. Control over the dissolved gas concentration when utilizing this approach is complicated by the pressure of the liquid into which the gas will be dissolved.
Additionally, several methods utilize cooling to increase the quantity of gas that may be dissolved into a liquid. Although such methods claim to increase the quantity of dissolved gas, these methods do not focus upon precise control of the concentration of the dissolved gas either at the outset or at the point of use. Thus, it is possible that the increased amount of gas, if any, that is dissolved into the liquid as a result of cooling the liquid will effervesce out of the liquid admixture at the point of use.
Thus, there is a need for an efficient method of establishing and maintaining a precise quantity of dissolved gas in a liquid admixture, not only to minimize the amount of gas that must be utilized, but also to provide liquid admixtures comprising sufficiently precise concentrations of dissolved gas so as to be useful for applications requiring tight specifications.
SUMMARY OF THE INVENTION
According to the present invention, the above objectives and other objectives apparent to those skilled in the art upon reading this disclosure are attained by the present invention which is drawn to a method and system for establishing and maintaining precise concentrations of dissolved gas in a liquid. Specifically, the method and system of the present invention utilize a “matched gas blend,” i.e., a gas blend that has been prepared to have a concentration of the gas (or gases) to be dissolved that would be in equilibrium with a liquid admixture comprising the desired concentration of the gas(es). By directly or indirectly contacting the liquid with the matched gas blend before and/or at the point of use, a precise amount of gas dissolves in the liquid as the liquid comes to equilibrium with the gas. It is possible, as a result, to controllably adjust the amount of dissolved gas in a liquid with great precision within a wide range of possible concentrations merely by adjusting the composition of the matched gas blend. In this manner, the present invention provides an exceptionally effective method and system for producing and using liquid admixtures comprising precise amounts of dissolved gas in applications subject to tight specifications. As a result of the ability of the system of the present invention to establish and maintain a precise concentration of dissolved gas in a liquid, the resulting admixtures are expected to be particularly useful to prepare liquid admixtures that may be utilized to treat, i.e., clean, oxidize, develop, etch, etc., substrates processed in the manufacture of semiconductor devices.
In one aspect, the present invention provides a system for contacting a substrate with a liquid including a predetermined concentration of a gas dissolved in the liquid. The system comprises a chamber in which at least one substrate can be positioned for treatment with the liquid containing the dissolved gas. A liquid supply comprising the liquid is provided. A liquid supply line is in fluid communication with the chamber through which the supply comprising the liquid can be dispensed into the chamber. A matched gas supply comprising a matched gas blend is also provided. At least one gas supply line is in fluid communication with the chamber so that the matched gas supply comprising the matched gas blend can be dispensed into the chamber, preferably concurrently with the liquid supply. Optionally, the at least one matched gas supply line is in mass transfer contact with the liquid supply line so that a predetermined concentration of the gas can be pre-dissolved in the liquid supply before the liquid supply is dispensed into the chamber.
In another aspect, the present invention provides a method of treating a substrate with a liquid admixture comprising a dissolved gas. Generally, the method involves causing a matched gas blend to directly or indirectly contact a liquid such that the liquid comes to equilibrium with the matched gas blend, thus forming the liquid admixture which comprises the liquid and a concentration of the dissolved gas. The resulting liquid admixture comprising the liquid and the dissolved gas is then caused to contact a substrate, thereby treating at least a portion of the surface of the substrate.
The matched gas blend may be caused to come into direct or indirect contact with the liquid in a number of ways, which may be carried out alone or in combination. For example, the liquid may be atomized in the presence of the matched gas blend, the liquid may be atomized by impact with the matched gas blend, the liquid may be pre-contacted with the matched gas blend prior to being dispensed at the point of use, the liquid may be atomized with itself in the presence of the matched gas blend, the liquid may be pre-contacted with the matched gas and then dispensed into a define
Faegre & Benson LLP
FSI International Inc.
Powell William
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