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Fabrication of Via Holes With Adjustable Sidewall Slopes in Thick Insulating Layers

IP.com Disclosure Number: IPCOM000042637D
Original Publication Date: 1984-Jun-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 3 page(s) / 32K

Publishing Venue

IBM

Related People

Hendricks, CJ: AUTHOR [+2]

Abstract

The present system deals with the problem of fabricating the tapered via holes in the insulating layer which may be glass, polyimide or some other material. Wet chemical approaches have been tried to generate these holes but have largely been unsuccessful due to the isotropic nature of the wet chemical etching and the difficulty in etching some of the constituent materials in the materials as in, for example, glass. The basic apparatus for laser-activated chemical etching is shown in the figure. Provision is made to maintain and control the mask-to- substrate distance accurately over the entire area of the substrate. This distance is in the range of 30 to 300 mm for a 45Πwall angle slope for a via hole with a nominal 100 mm diameter.

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Fabrication of Via Holes With Adjustable Sidewall Slopes in Thick Insulating Layers

The present system deals with the problem of fabricating the tapered via holes in the insulating layer which may be glass, polyimide or some other material. Wet chemical approaches have been tried to generate these holes but have largely been unsuccessful due to the isotropic nature of the wet chemical etching and the difficulty in etching some of the constituent materials in the materials as in, for example, glass. The basic apparatus for laser-activated chemical etching is shown in the figure. Provision is made to maintain and control the mask-to- substrate distance accurately over the entire area of the substrate. This distance is in the range of 30 to 300 mm for a 45OE wall angle slope for a via hole with a nominal 100 mm diameter. Provision is made to vary in a controlled manner the incident power of the laser arriving at the substrate surface during the period of the etch. This may be accomplished by direct control of the laser power or by means of an addition to the optical system to control the transmitted light intensity. Once the range of reaction threshold area is defined by the wavelength of the incident light and the mask-to-substrate distance, the actual area excited above the threshold energy at any point in time is controlled by the illumination intensity. This may be accomplished by direct control of the laser or by additions to the optical system. In this manner the diameter of the etched feature may be controlled as the process proceeds and thus a controlled, tapered wall slope may be achieved. The illumination wavelength and mask-to-substrate distance are adjusted to get the desired Fresnel diffraction. Then, by controlling the incident optical power, the substrate surface area reacting chemically is adjusted, allowing for real-time wall taper control. For instance, as the incident optical power is decreased, the etching threshold moves in along the gradient defined by the Fresnel diffraction and the etched hole diameter will decrease. Real-time control leads to the ability to tailor the wall slope of the etched feature. As an example, if it is desired to get a 45OE...