Method of depositing thin films of small dimensions utilizing silicon nitride lift-off mask

DETAILED DESCRIPTION Accordingly, it is a primary object of the invention to provide an improved tear-free thin film deposition process in which the dimensions of the film are very precisely controllable and in which the width of the film can be made exceedingly small with correspondingly small distances between adjacent areas of deposited film.
It is another object of the present invention to provide such a thin film deposition method in which the various masking layers can be deposited with a uniform thickness and in which the etch rates of the various layers can be precisely controlled.
It is still a further object of the present invention to provide such a thin film deposition method in which the dimensions of the deposited film are determined precisely by a photolithographic mask.
Yet another object of the present invention is to provide such a thin film deposition technique in which the photolithographic mask can be optically aligned without the use of specially provided alignment areas which reduce the amount of available wafer area.
These, as well as other objects of the invention, may be met by a method in which an integrated circuit substrate or wafer is first covered with a first masking layer, preferably of an organic polymeric material such as a photoresist material, which is rendered non-photosensitive.
This may be baked on to promote adherence.
Upon the first masking layer is then deposited a layer of silicon nitride material.
Apertures are formed in the layer of silicon nitride material using standard photolithographic and ion etching techniques.
For example, the layer of silicon nitride material may be covered with a second masking layer of photoresist material, the second masking layer of photoresist material exposed through a photolithographic mask and developed to remove the portions of the second layer of masking material which correspond to the desired aperture patterns in the layer of silicon nitride material.
The silicon nitride material may be then etched through the apertures in the second masking layers, for example, as by reactive ion etching using carbon tetrafluoride