Method and apparatus for maskless photolithography

Abstract

A method and apparatus to create two dimensional and three dimensional structures using a maskless photolithography system that is semi-automated, directly reconfigurable, and does not require masks, templates or stencils to create each of the planes or layers on a multi layer two-dimensional or three dimensional structure. In an embodiment, the pattern generator comprises a micromirror array wherein the positioning of the mirrors in the micromirror array and the time duration of exposure can be modulated to produce gray scale patterns to photoform layers of continuously variable thickness. The desired pattern can be designed and stored using conventional computer aided drawing techniques and can be used to control the positioning of the individual mirrors in the micromirror array to reflect the corresponding desired pattern. A fixture for mounting of the substrate can be incorporated and can allow the substrate to be moved three dimensions. The fixture can be rotated in one, two, or three directions.

Description

CROSS-REFERENCE TO A RELATED APPLICATION [0001] This application claims the benefit of U.S. patent application Ser. No. 10 / 179,083, filed on Jun. 25, 2002, U.S. patent application Ser. No. 10 / 179,565, filed on Jun. 25, 2002, and U.S. Provisional Application Ser. No. 60 / 301,218, filed Jun. 27, 2001, which are incorporated herein by reference.[0002] The subject invention was made with government support under a research project supported by The Office of Naval Research funding reference number NOO014-98-1-0848. The government has certain rights in this invention.BACKGROUND ART [0003] Photolithography systems are known in the art that direct light beams onto a photosensitive surface covered by a mask, etching a desired pattern on the substrate corresponding to the void areas of the mask. Maskless photolithography systems are also known in the art as described in Singh-Gasson, Sangeet et al., Nature Biotechnology 17, 974-78, 1999. The system described in this article uses an off-axis li...

AI Technical Summary

Benefits of technology

[0027] The advantages of the invention are numerous. One significant advantage is the ability to use the invention as a reconfigurable, rapid prototyping tool for creating two-dimensional and three dimensional micro and macroscopic objects. Another advantage of the invention is that it provides the ability to reduce prototyping costs and enable devices to be fabricated more quickly with less risk. Yet another advantage of the invention is the ability to utilize different designs and operating conditions on a single device. A further advantage is the ability to use computer network to transfer designs across networks for immediate light exposure of a substrate. Still another advantage of the current invention is a reduction in cost for prototyping activities realized by the elimination of physical masks and the ability to create both positive and negative tone images using the same array. Yet another advantage of the current invention is that pattern generation can be performed optically without having to use expensive vacuum system required by conventional mask-based photolithography. A particular advantage of the current invention is the ability to create three-dimensional devices using an alignment stage to selectively expose successive layers in a substrate. By modulating the movement of the micromirror arrays, the negative effects of pixelation and stiction of micromirrors is reduced.

[0028] The subject invention can allow the ability to photoform continuously variable pattern thickness on substrates by using the disclosed gray scale lithographic techniques that do not have a gray scale mask as an element in the gray scale lithographic system. Another advantage of the invention is the ability to efficiently create patterns on larger areas than conventionally possible.

[0029] By providing the ability to individually control the individual micromirrors of the mirror array, any arbitrary micro or macroscopic structure can easily and quickly be created in substrates such as polymers, metals, or ceramics. Patterns such as glasses, microfluidic networks, thin film devices, hybrid material devices, micro electromechanical machines (MEMs), photomasks and combinations of the above mentioned devices can be created using the reconfigurable, application specific photolithography system disclosed.

[0030] All patents, patent applications, provisional applications, and publications referred to or cited herein, or from which a claim for benefit of priority has been made, are incorporated herein by reference in their entirety to the extent they are not inconsistent with the explicit teachings of this specification.

Problems solved by technology

While the previously described maskless photolithography systems address several of the problems associated with mask based photolithography systems, such as distortion and uniformity of images, problems still arise.

Notably, in environments requiring rapid prototyping and limited production quantities, the advantages of maskless systems as a result of efficiencies derived from quantities of scale are not realized.

Further, prior art references lack the ability to provide rapid prototyping.

In particular, alignment of patterns with respect to target substrates in maskless systems can be problematic.

In a rapid prototyping, limited quantity environment, automated means of initial alignment are not cost effective.

In addition, conventional maskless alignment systems are normally limited to coplanar, two-dimensional alignment.

In the third dimension, computerized shifting of the mask pattern cannot compensate for misalignments in a direction parallel with an incident light beam.

Another problem with maskless photolithography systems is that the mask pattern image projected is formed by pixels, instead of continuous lines.

As a result, gaps may exist between adjacent pixels, which, when projected on a substrate, may allow the area between the pixels to be exposed, resulting in a break in the imaged pattern.

For example, if the desired pattern is a circuit, gaps may be inadvertently exposed and formed in a trace, resulting in an electrical gap.

The exposure gaps caused by the pixel nature of the micromirror arrays, or pixelation, may cause open circuits or unwanted capacitive effects where trace width or thickness is critical.

Another problem with current art systems is the phenomenon of “stiction,” wherein the individual mirrors in a micromirror area tend to “stick” in a specific orientation if left in that position for an extended period.

Thus the micromirror array consumes more power than normal and affects the reliability of the mirror.

However, the images produced using this method are halftone images, not true gray scale images.

Therefore, it is difficult to obtain consistent imaging results because of the nonuniformity of grain size.

While effective, the use of physical masks in photolithography has numerous drawbacks, including the cost of fabricating masks, the time required to produce the sets of masks needed to fabricate semiconductors, the diffraction effects resulting from light from a light source being diffracted from opaque portions of the mask, registration errors during mask alignment for multilevel patterns, color centers formed in the mask substrate, defects in the mask, the necessity for periodic cleaning and the deterioration of the mask as a consequence of continuous cleaning.

However, the x-rays are inherently dangerous and their use is highly regulated, requiring sophisticated equipment to generate and direct the radiation.

In addition, the disclosed techniques require complex translational stages to expose and generate patterns on substrates.

However, only small areas can be written at one time because of the small beamwidth of the laser, making large area patterning prohibitively time consuming.

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