Methods for forming openings in a substrate and apparatuses with these openings and methods for creating assemblies with openings

Abstract

Methods for forming openings having predetermined shapes in a substrate and apparatuses with these openings. The methods may be used to form assemblies which include the substrate with its openings and elements which are disposed in the openings. In one example of a method, each of the elements include an electrical component and are assembled into one of the openings by a fluidic self assembly process. In an particular example of a method to create such an opening, the substrate is etched through a first patterned mask and is later etched through a second patterned mask. Typically, the second patterned mask is aligned relative to the opening created by etching through the first patterned mask and has an area of exposure which is smaller than an area of exposure through the first patterned mask. In another example of a method, a photosensitive material is exposed through a patterned mask to oblique sources of light such that some of the light impinges into a first portion of the photosensitive material which is under the patterned mask, and the patterned mask and a second portion of the photosensitive material, which is under the patterned mask, is removed. In another example of a method, an opening in a first layer, which comprises silicon dioxide, is formed by depositing a second layer over the first layer and depositing a tungsten layer over the second layer. The tungsten and second layers are patterned to expose a portion of the first layer, and this portion is etched. Various apparatuses which may be made using these methods are also described.

Description

RELATED APPLICATIONS [0001] This application is a divisional of co-pending U.S. patent application Ser. No. 10 / 154,899, filed May 23, 2002 which is a divisional application of U.S. patent application Ser. No. 09 / 432,512, filed on Nov. 2, 1999 entitled “Method and Apparatus for Forming Openings in A Substrate and Apparatuses with these Openings and Methods for Creating Assemblies With Openings” and now issued as U.S. Pat. No. 6,479,395.GOVERNMENT RIGHTS NOTICE [0002] This invention was made with government support with at least one of these contracts: Grant (Contract) Nos. AFOSR 91-0327; F49620-92-J-059-1; F33615-96-C-5111 with USAF / AFMC / ASC; DAA016-00-C-9234 USAMCAC (US Army); Northrop Grumman PO #8200014995 (subcontract, NOOO14-99-C-0395 (prime)); North Dakota State University Subcontract #4080, DMEA 90-01-C-0009 (prime) and University of Alaska, Fairbanks PO#FP201509 (subcontract), DMEA 90-01-C-0009 (prime). The Government has certain rights to this invention.FIELD OF THE INVENTIO...

AI Technical Summary

Benefits of technology

This approach enhances the efficiency of forming deep, narrow openings that prevent inverted elements from lodging, improves the yield of functional arrays, and allows for the use of a wider range of substrates, including glass and plastic, while reducing waste and assembly time.

Problems solved by technology

As is well known in the art, it is difficult to produce a completely flawless active matrix liquid crystal display (LCD), when the display area is large, such as the LCD's on modem laptop computers.

Silicon VLSI can be used to produce such an array over a silicon wafer's surface, but silicon wafers are limited in size, limited in conductivity, and not transparent.

Further, processing of large areas on silicon wafers can be expensive.

Single crystal silicon can be bonded to a glass substrate and then etched to remove most of the area to achieve transparency, but this is intrinsically wasteful in that, for the sake of maximizing light transmission, the majority of the processed material is discarded and becomes chemical waste.

The under-utilization of the precious die area wastes resources, causes greater amounts of chemical waste to be generated in the process, and is generally inefficient and expensive.

Large arrays of silicon photodiodes with concentrating lenses have been made by sawing wafers and using a pick and place assembly, but thermal dissipation is poor for large elements, and the small elements require too much assembly time.

These approaches avoid the limitations of the size of the available single crystal silicon wafers, and avoid the cost of the single crystal wafers, but require expensive deposition of the semiconductor layer, and they still require processing of the entire large substrate to form the active elements in an array, still resulting in the production of much chemical waste and wasted resources.

These processes also limit the choice of the substrate; for example, plastic substrates cannot be used due to the nature of the processes which deposit the semiconductor layers.

Furthermore, amorphous or polycrystalline silicon semiconductor elements do not perform as well as those made from single crystal semiconductor material.

For displays, as an example, it is often difficult or impossible to form some of the desired circuitry out of the amorphous or polycrystalline semiconductor materials.

Thus, high frequency edge drivers may be impossible to form out of these materials.

This results in the difficulty and expense of attaching an electrical lead for each and every row and column of an array, such as an active matrix liquid crystal display array.

As noted above, another difficulty with the existing techniques is that the large number of elements in a large array results in a low probability that all of them will work properly and thus the yield of acceptably good arrays from the manufacturing process is low.

Furthermore, there is no possibility of testing any of the elements until the assembly is complete, and then any imperfection in the array must be tolerated or the entire array could be discarded or special and expensive techniques must be used to repair it.

These problems result from the fact that the various elements in the array are fabricated on the array rather than separately.

Pick and place methods place devices generally one at a time, and are generally not applicable to very small or numerous elements such as those needed for large arrays, such as an active matrix liquid crystal display.

One issue in forming an opening is to create its sidewalls so that blocks will self-align into the opening and drop into the opening.

The structure shown in FIG. 2D has the drawback that a monocrystalline silicon layer is required in order to use the KOH etch to form the hole.

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