A contact (15) formed in accordance with the present invention includes rounded corners on the upper and lower surface and sloped walls in the dielectric material (10) in which the contact is formed. In one embodiment, a photolithographic mask is formed above the dielectric material (10) using photolithographic techniques well known in the art. Using reactive ion etching techniques, the contact is etched until a small portion of the dielectric material remains to be etched in the contact. The photolithographic mask is then removed. The contact is then completely etched using a reactive ion etching process. Using this technique, the contact formed has rounded upper edges.
A polycrystalline silicon film is formed on the surface of a semiconductor substrate. An oxide film having a first impurity concentration is formed to cover the polycrystalline silicon film. A polycrystalline silicon film and a refractory metal silicide are formed on the surface of the oxide film having the first impurity concentration. An oxide film having a second impurity concentration higher than the first impurity concentration is formed to cover the polycrystalline silicon film and the refractory metal silicide. The third conductive layer is formed on the surface of the oxide film having the second impurity concentration.
A method of making via holes in a double-layer insulation of nitride and polyimide. The via holes are made with one photomask only by applying a photoresist process with double exposure, and a multi-step dry etching process. The double exposure, which includes an image-wise exposure followed by blanket irradiation, achieves an edge angle in the photoresist between approx. 60.degree. and 70.degree., depending on the exposure time ratios. This angle is transferred into the polyimide layer in a dry etching process. In a first etching step with CF.sub.4 as etching gas the greater part of the polyimide is removed. For removing the residual polyimide in the via holes there now follows an etching step in O.sub.2. Etch bias is thus kept on a very low level. The nitride layer is then etched with CF.sub.4 as etching gas, with the etching process being executed in two steps, each followed by an etching step in O.sub.2 for laterally shifting the photoresist and the polyimide via the resist angle. By softening the step height a softer profile of the via holes is ensured, which permits very good covering by a second layer of metallurgy.
In a dry etching equipment, a variable gas mixture composition provides etch and ash simultaneously. For example, when a SiO.sub.2 /phospho silicate glass composite insulating layer with a respective thickness of about 300 and 600 nm masked by a patterned photoresist layer is to be etched, a CHF.sub.3 /O.sub.2 gas mixture may be used with the following steps: 1. Dry etching the composite insulating layer in an RIE equipment by a plasma action in a gas mixture containing a fluorine compound and an oxidizer with a percentage of the oxidizer of about 10-20% to form a tapered hole having the desired slope in the top PSG insulating layer; 2. Dry etching the composite layer in the gas mixture with a percentage of the oxidizer in the gas mixture of about 1-8% to transfer the desired slope from the PSG insulating layer to the bottom SiO.sub.2 insulating layer, wherein during this step the slope of the tapered hole in the PSG insulating layer has been modified; and then 3. Dry etching the composite layer in said gas mixture with a percentage of the oxidizer in the gas mixture of about 80-100% to adjust the slope in said top insulating layer to said desired slope. Therefore the method is comprised of a reduced number of operations. In addition, because the process is only based on different CHF.sub.3 /O.sub.2 flow ratios, no pumping is necessary, and therefore the process results in higher throughputs. The slope of the resulting via-hole is in the desired 55-65 deg. range.
A reactive ion etching method is described in which a silicon compound film formed on an underlying layer or a substrate is etched through a mask layer by a two-stage procedure. In the two-stage procedure, part of the silicon compound film is first etched with a gas containing a hydrogen-free carbon fluoride gas at a high etching rated and then with a gas containing a hydrogen-containing carbon fluoride gas while reducing the damage on the underlying layer or substrate. The apparatus for carrying out the method is also disclosed.
A reactive ion etching method is described in which a silicon compound film formed on an underlying layer or a substrate is etched through a mask layer by a two-stage procedure. In the two-stage procedure, part of the silicon compound film is first etched with a gas containing a hydrogen-free carbon fluoride gas at a high etching rated and then with a gas containing a hydrogen-containing carbon fluoride gas while reducing the damage on the underlying layer or substrate. The apparatus for carrying out the method is also disclosed.
