Semiconductor device manufacturing: process – Miscellaneous
Reexamination Certificate
2001-06-27
2003-10-14
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Miscellaneous
C134S078000, C134S030000, C134S001300, C134S025500
Reexamination Certificate
active
06632751
ABSTRACT:
FIELD OF THE INVENTION
The present invention is related to methods and tools used for treating and in particular cleaning and drying surfaces of substrates such as semiconductor substrates used in the production of integrated circuits or flat panel displays, and equally of foil like substrates or wires.
STATE OF THE ART
The complete and efficient removal of a liquid from a surface of a substrate is a frequently repeated step in e.g. the fabrication process of integrated circuits. Such a step can be performed after a wet etching step, a wet cleaning step, a wet rinsing step or any other step used in the fabrication process wherein a substrate is treated by, exposed to or immersed in a liquid. The substrate can be a semiconductor wafer or a part thereof or a glass slice or any other slice of material. It can also be a continuous film or foil or a wire or a set of parallel wires.
The manufacturing of integrated circuits evolves towards processing of each wafer individually rather than in batches of several wafers. In state of the art IC manufacturing, most processing steps such as e.g. implantation steps or deposition steps are already performed in a single wafer mode. On the other hand, wet processing steps such as e.g. cleaning steps and subsequent liquid removal steps are typically performed in a batch mode because of lack of appropriate alternatives. Therefore, differences in waiting times are created for each individual wafer between a wet processing step, performed in a batch mode and another processing step, performed in a single wafer mode. Such variability is undesirable with regard to process control. Moreover, this mixed batch and single wafer processing increases the cycle time, which is also undesirable. Therefore, there is a general interest in the development of competitive single wafer or more generally, single substrate wet processing steps. Also, a method for treating and drying continuous foil or film like substrates and wire-like substrates is not present in the current state of the art.
With regard to the drying process, simultaneous drying of both sides of a substrate is desired in a reduced timespan. Knowing that in state of the art production lines a substrate is processed typically every 1 to 2 minutes, ideally, in order to avoid equipment duplication, the combined liquid process step and liquid removal step should be completed in at least such a time frame.
The principle of immersing a substrate in a treatment liquid and subsequently removing said substrate in such a way that a minimum of liquid remains attached to the substrate, is known. However, all existing methods and tools based on this principle possess fundamental drawbacks.
In the document EP-A-385536, a method is disclosed of drying substrates after treatment in a liquid by pulling said substrates out of a tank containing said liquid. While being slowly taken from the tank, the substrates are brought directly in contact with a vapor which is miscible with said liquid. When mixed with the liquid, the mixture has a surface tension lower than that of the liquid, i.e. the vapor works as a ‘tensio-active’ gaseous substance.
An important drawback of the method described in EP-A-385536 relates to the fact that virtually all the liquid in the tank must remain there after the substrates have been removed, which implicates that pulling the substrates out of the liquid must take place slowly. As a consequence, this method is typically applied to the simultaneous treatment of batches of substrates in order to meet throughput requirements. The flow of the tensio-active vapor is provided through two sets of nozzles, one set on each side of a substrate, causing two opposite flows of vapor, colliding in the middle of the substrate. As a result, in this middle part, drying will be less efficient than at the substrate's edges.
In document EP-A-817246, a method and apparatus is described for wet cleaning or etching of flat substrates. This document is related to an apparatus comprising a vessel partially filled with a liquid. A substrate is pulled through said stationary liquid by way of slits in the vessel's sides under the liquid surface. The vessel is placed in a gaseous environment, preferably comprising a tensio-active gas. In this method the wafer is moved preferably horizontally. The horizontal position can be undesirable in terms of tool-footprint minimization or for integration of the drying method with other manufacturing equipment. Besides that, the apparatus described in this document is designed so as to allow no liquid to leave the vessel before, after and most importantly during the transit of the substrates, so as not to wet these substrates. This means that the substrate needs to be removed from the vessel slowly. Because no flow of liquid takes place through the slits, this potentially causes the problem of particle build-up in the slit: small particles become attached to the side walls of the slit and attach to the substrate's surface as it is passing through. Another drawback is that the slit through which the substrate is removed, is necessarily very narrow (order of 1.5 mm for a 0.75 mm thick substrate). Moreover, narrow horizontal slits are difficult to combine with large substrates (&tgr; 300 mm in diameter), which often suffer from a significant ‘bow’ phenomenon, i.e. a bending of the central part with respect to the edges, as a result of asymmetric stress, e.g. thermal stress, or simply as an effect of gravity in case of the horizontal or tilted position of substrates.
U.S. Pat. No. 5,660,642 describes an apparatus wherein a substrate is pulled out of a tank, while being sprayed with a liquid inside said tank, above a stationary liquid surface. A porous medium or other solvent vapor source is placed around the opening through which the substrate is pulled out, and produces vapors to be adsorbed by the substrate in order to remove liquid attached to it. No liquid is allowed to flow out of said tank while the substrate is being pulled out. Also, no flow of a tensio-active gas is directed at the substrate, which is merely passively brought into contact with a vapor, not a flow of vapor. This necessarily puts a constraint on the allowable removal speed of the substrate, which renders this technique unable to fulfill current treatment speed requirements. Also, a spray is often undesirable, as it deteriorates the subsequent drying performance: after spraying, residues can be detected (with reactive light scattering inspection techniques) on the surface, e.g. on hydrophobic surfaces sprayed with water, when the drying step is completed.
Document DE-A-4413077 describes a method and apparatus for treating and/or cleaning and drying a substrate, by lifting said substrate or preferably a batch of substrates, out of a cylindrical bath. Liquid is allowed to flow over the edge of said bath during the removal of the substrate. The substrate may be lifted out of the bath and into an enclosure filled with a tensio-active gas, for drying the substrate. Once again, this passive contact with a tensio-active gas is detrimental for efficient and especially for fast drying.
A drawback of many of the existing tools and methods is the necessary footprint, i.e. the surface in the clean room occupied by a tank or a vessel. Tools that work with batches of substrates or which handle individual substrates in a horizontal position tend to occupy a large area in the clean room, which results in high costs, since clean room space is very expensive due to the costs of maintaining an ultra-pure atmosphere.
Document WO-A-99/08057 describes another method and apparatus for drying a substrate. The apparatus comprises a tank. The substrate can be held in the tank by a holder at different holding points. The tank comprises a fluid. The substrate is dried by lowering the level of fluid in the tank relatively to the stationary substrate. A flow of a tensio-active vapor is directed parallel to the substrate and the fluid surface. U.S. Pat. No. 5,571,337 equally describes a method wherein a liquid level is lowered.
Mertens Paul
Meuris Marc
Interuniversitair Microelekronica Centrum (IMEC VZW)
Le Thao
McDonnell & Boehnen Hulbert & Berghoff
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