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Fabrication Process for Precise Control of Nozzle Dimensions

IP.com Disclosure Number: IPCOM000089627D
Original Publication Date: 1977-Nov-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 5 page(s) / 96K

Publishing Venue

IBM

Related People

Bassous, E: AUTHOR

Abstract

In the fabrication of silicon nozzles utilizing etch-through techniques, the size of the orifice is critically dependent on two factors: (a) the size of the base opening W(B) and (b) the thickness of the silicon wafer t(Si) as given by the equation Wo = W(B) - 1.41 t(Si), where Wo is the side of the square orifice resulting from a square base opening of side W(B) or a circular base opening of diameter W(B) (Fig. 1).

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Fabrication Process for Precise Control of Nozzle Dimensions

In the fabrication of silicon nozzles utilizing etch-through techniques, the size of the orifice is critically dependent on two factors: (a) the size of the base opening W(B) and (b) the thickness of the silicon wafer t(Si) as given by the equation Wo = W(B) - 1.41 t(Si), where Wo is the side of the square orifice resulting from a square base opening of side W(B) or a circular base opening of diameter W(B) (Fig. 1).

Variations in W(B) result from the photolithographic process which includes mask quality, photoresist adhesion, oxide adhesion and etching, as well as undercutting of the base opening during silicon etching. Variations in t(Si), the silicon wafer thickness, results from the slicing, lapping and polishing operations which are performed during the preparation of the wafers.

As the number of nozzles in a given array is increased to 30, 60 or more orifices per array and as the starting silicon wafer is increased in size to, e.g.,
2.25-inch diameter, 15-mil thickness, control of the size and uniformity of the nozzles becomes increasingly difficult to achieve by the etch-through technique. Furthermore, the orifices are either square or rectangular, and cannot be easily altered in geometry without additional processing.

Below, techniques are described for fabricating large multinozzle arrays having a high degree of precision and uniformity, as well as precise control over the shape of the orifices. Two masking operations are required here, as opposed to the single masking operation of the etch-through technique. Briefly, the two masking steps shown in Fig. 2 are as follows: Step 1: With reference to Figs. 2A1 and 2A2, a base hole opening 2 is defined on the back side 4 of a wafer 6, and the silicon is etched through to form an orifice 8 on the opposite or front side of the wafer. The latter is covered with an etch-resistant film 10, such as silicon nitride (Si(3)N(4)), silicon dioxide (SiO(2)) or aluminum oxide (Al(2)O(3)). The orifice obtained at this stage should be much smaller than the final size required for the array. When silicon nitride is used, the film remains in-intact, and thus no holes appear on the front side of the wafer. Step 2: A pattern of the array of nozzles is then defined on the front side 12 of the wafer, and the film protecting the front side of the wafer is then removed. Either a negative pattern 13 (Fig. 2B) or a positive pattern 13' (Fig. 2C) can be generated at this stage. The type of pattern is selected on the basis of the subsequent processing required to form the orifices. The size and shape of the orifice is determined by this second masking step.

A large number of film materials and etching techniques are known in silicon processing technology. Various approaches can be described which incorporate the two basic steps mentioned above. One method will be described in detail below, and only brief mention will be made of the variations w...