Drying and gas or vapor contact with solids – Material treated by electromagnetic energy – Infrared energy
Reexamination Certificate
2002-12-02
2004-04-27
Bennett, Henry (Department: 3743)
Drying and gas or vapor contact with solids
Material treated by electromagnetic energy
Infrared energy
C034S406000, C034S467000, C034S092000, C438S906000
Reexamination Certificate
active
06725565
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method for vacuum drying of a substrate, such as a semiconductor wafer, and more particularly to a method for vacuum drying of a substrate applicable for a finer patterning of devices.
BACKGROUND OF THE INVENTION
Conventionally, devices on semiconductor wafers have been fabricated by repeating a series of steps comprising film-forming, wafer processing step mainly consisting of lithography and etching, cleaning, and drying step. In particular, the technology for drying a substrate in the drying step is used to eliminate the residue of the ultrapure water used mainly in rinsing the cleaning liquid or the remaining moisture included in the cleaning liquid adhered to the substrate during the cleaning step. The conventional technology for drying a substrate can be roughly classified into spin-drying, organic solvent displacement drying, heat drying, and decompression drying.
However, due to the finer patterning and three-dimensional geometry of the devices in recent pursuit of a higher density of LSI, an event has arisen where none of the above drying technology can sufficiently dry substrates.
More particularly, in the processing step, contact holes or via holes to lead electrodes are formed after formation of interlayer insulator films accompanied with the finer and three-dimensional device structure, and the diameters and depths of such holes have become remarkably smaller and deeper due to the finer patterning of the devices. In the case where the pattern size of the LSI is approximately 0.5 &mgr;m or less, it is quite difficult to physically blow out and eliminate the remaining moisture accumulated in and/or between high aspect ratio patterns which are mainly the contact holes or via holes by simply centrifugal force in the spin drying, and it is also difficult to dry the moisture after the moisture is simply displaced with organic solvent in the organic solvent displacement drying technology.
Therefore, particularly with the trend that the pattern size of the substrate has become smaller and smaller, several new drying technology have begun to be used. One of such technologies is known as IPA vapor drying method that displaces the water on the wafer with isopropyl alcohol (hereinafter referred to as IPA) by use of the vapor of heated IPA and also by use of the difference of vapor pressure between the IPA and pure water, and then places the whole substrate into the atmosphere or a reduced pressure atmosphere in order to immediately vaporize and eliminate the IPA with which the water is completely displaced. On the other hand, the Marangoni drying technology utilizing so-called Marangoni effect has been developed and used, which vaporizes the IPA with which the water is displaced, while the IPA being free-fallen on the wafer surface by use of the high permeability and high water-solubility of the IPA and also by use of the difference in surface tension gradients of the IPA and water.
However, due to the finer and three-dimensional device in recent pursuit of a much higher density LSI, the aspect ratio of the entire patterns which are mainly contact holes or via holes has been further increasing and then so-called low dielectric constant insulating materials have been developed and begun to be used.
More specifically, due to the finer patterning of devices, low dielectric constant insulating materials have been developed as interlayer insulating films in order to achieve high performance multi-layer interconnection wiring.
FIG.
3
and
FIG. 4
are examples of magnified cross sectional views of the metal wiring layers formed on a finely patterned wafer immediately after the processing. As shown in FIG.
3
and
FIG. 4
, an insulating layer is formed on a silicon layer, and a contact hole or via hole H is formed running through the insulating layer. Low dielectric constant insulating material may be, for example, an inorganic or organic material (lowk A in
FIG. 3
) consisting of siloxane-family for Al—Cu, and a porous material (lowk B in
FIG. 4
) for Cu to achieve a lower dielectric constant.
The former siloxane-family material is weak against heat and thus its composition can be damaged when heated to above 200° C., thereby the risk that moisture can be produced in the film, is increased. Moreover, depending on the conditions of the processing step, moisture can be produced in the film due to the effect of the processing step conditions themselves, or moisture can be impregnated in the film due to the ultra pure water used in the cleaning step after the processing step.
On the contrary, the latter porous material may be inorganic in most cases and can be an effective film to realize low dielectric constant, however, its porous structure presents a problem in that it tends to absorb moisture in the film inside.
In the interconnection wiring step, such moisture in the hole configuration or in the film which forms the device can be the main cause for corroding metal wiring due to the reaction due to the remaining moisture in the hole after the wirings being formed and the metal of the wiring material, or may be the cause of after-corrosion due to the occurrence of cracks in the insulating films.
Either of them may be significant loss of quality to the semiconductor wafer products.
Accordingly, it is essential to completely eliminate the moisture remaining in the device prior to the film-forming processing.
In this respect, it is necessary to raise the temperature of the wafer for the conventional heat drying technology, which may require excessive heating (for example, over 100□) in order to effectively eliminate the moisture impregnated in the insulating film. In this case, the risk can be increased such that the heat causes deterioration or damage to the device itself that is formed on the wafer surface. Moreover, in the recent ultra-finer patterning devices, the applied heat tends to cause pattern deformation or film deterioration because of the unevenness of the high aspect ratio patterns which are mainly contact holes or via holes formed on the wafer surface. Particularly, in the case that the interlayer insulating film is a siloxane-family material, the heat in the presence of oxygen adversely results in additional moisture produced in the film as described above.
Therefore, it is quite difficult or almost impossible to effectively dry and eliminate the moisture impregnated inside only by the heat drying, maintaining device quality.
On the other hand, in the conventional decompression drying technology, it is necessary to increase vacuum pressure and physically evacuate the inside moisture out of the wafer surface in order to effectively eliminate the moisture impregnated in the insulating film, increasing high vacuum pressure. However, due to the unevenness of the high aspect ratio patterns which are mainly contact holes or via holes formed on the wafer surface, even if the high vacuum pressure is increased, the inside moisture cannot be evacuated or, even if possible, it takes a significant amount of time due to the effect of the surface tension of the water remaining in the holes or the effect of the hydrophilic deposition film. Particularly, in the case that the interlayer insulating film is a porous material, it is difficult to physically evacuate the moisture in the holes because of its porous structure.
In the conventional drying technology using IPA, it is quite difficult to diffuse the IPA into water within a specified time period (for example within 2 minutes), and it is difficult to eliminate the water. Moreover, the IPA is designated as a hazardous material under the Fire Defense Law and is classified to alcohol in the 4
th
category, therefore and it is flammable and explosive, it is desirable to avoid the use of the IPA from the point of view of safety and control cost, if possible.
In view of the above, a drying technology which can cope with various aspects such as electric reliability, cost, and safety in finely patterning the devices is strongly needed recently.
Embodiments of the present inventio
Harano Riichiro
Watari Toru
Nguyen Camtu
Slater & Matsil L.L.P.
Sprout Co., Ltd.
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