Maskless lithography

• US 5,870,176 A
• Filed: 06/18/1997
• Issued: 02/09/1999
• Est. Priority Date: 06/19/1996
• Status: Expired due to Term

• Current Assignee: National Technology & Engineering Solutions Of Sandia LLC (Honeywell International Inc.)
• Original Assignee: Sandia Corporation (Martin Marietta Corporation)
• Inventors: Sweatt, William C., Stulen, Richard H.
• Primary Examiner(s): Mathews, Alan A.
• Application Number:
  US08/878,444
• Time in Patent Office: 601 Days
• Field of Search: 355/53, 355/67, 355/71, 250/492.1, 250/492.2, 250/492.3, 359/245, 359/254, 359/224, 359/871, 359/872, 348/771, 430/312, 378/34, 347/239, 347/255
• US Class Current: 355/53
• CPC Class Codes: G02B 26/0841 the reflecting element being moved or deformed by electrostatic means
• CPC Class Codes: G03F 7/70091 Illumination settings, i.e. intensity distribution in the pupil plane or angular distribution in the field plane; On-axis or off-axis settings, e.g. annular, dipole or quadrupole settings; Partial coherence control, i.e. sigma or numerical aperture [NA]
• CPC Class Codes: G03F 7/70291 Addressable masks, e.g. spatial light modulators [SLMs], digital micro-mirror devices [DMDs] or liquid crystal display [LCD] patterning devices
• CPC Class Codes: Y10S 359/904 Micromirror

Abstract

The present invention provides a method for maskless lithography. A plurality of individually addressable and rotatable micromirrors together comprise a two-dimensional array of micromirrors. Each micromirror in the two-dimensional array can be envisioned as an individually addressable element in the picture that comprises the circuit pattern desired. As each micromirror is addressed it rotates so as to reflect light from a light source onto a portion of the photoresist coated wafer thereby forming a pixel within the circuit pattern. By electronically addressing a two-dimensional array of these micromirrors in the proper sequence a circuit pattern that is comprised of these individual pixels can be constructed on a microchip. The reflecting surface of the micromirror is configured in such a way as to overcome coherence and diffraction effects in order to produce circuit elements having straight sides.

Claims

1. A mask for scanning projection lithography, comprising:

a) a two-dimensional array of individually addressable micromirrors, each said micromirror comprising a plurality of moveable substrates having a reflecting surface, said reflecting surfaces for reflecting light from a light source into an imaging means entrance pupil, said reflecting surfaces modified by coating said surfaces with a non-reflecting coating and etching away only a portion of said non-reflective coating, thereby providing said reflecting surfaces with features for substantially eliminating coherence and diffraction effects in said reflected light, said features comprising;

i) a reflecting surface having a shape consisting essentially of an octagon having regular trapezoidal projections laying at every other side of said octagon and wherein the wider base of each of said trapezoidal projections is contiguous with said octagon,

ii) a reflecting surface having a size which is about one-half of a center-to-center distance between adjacent micromirrors; and

iii) a reflecting surface have an edge which includes a plurality of phase reversed features and small light attenuating features along said edge;

said light reflected by each of said micromirrors comprising a pixel having a light distribution profile, said reflected light imaged by said imaging means at a distant focal plane, said imaged light comprising rows or columns of pixels arranged so that adjacent pixels adds constructively to providing continuous, substantially smooth, straight regions of light and dark lines, said lines having a minimum width which is a single row or a single column of said pixels;

b) means for individually moving each of said micromirrors in said two-dimensional array of micromirrors;

c) means for controlling the movement and orientation of each of said micromirrors such that said reflected light is directed either into or away from said imaging means entrance pupil; and

d) sequencing means in communication with said controlling means, said sequencing means for causing each of said micromirrors to move in proper sequence so as to scan a predetermined coordinate pattern across said two dimensional array of micromirrors, in a scan direction, thereby causing said pattern to be reproduced at said focal plane, said sequencing means including temporally interleaving rows of said micromirrors where said rows are parallel to said scan direction.

2. The apparatus of claim 1, wherein said light source comprise a pulsed light source.

3. The apparatus of claim 2, wherein the pulsed light source is a pulsed laser.

4. The apparatus of claim 2, wherein said light source includes a discharge source.

5. The apparatus of claim 4, wherein the discharge source is configured to produce a light pulse.

6. The apparatus of claim 4, wherein the source is a pulsed plasma.

7. The apparatus of claim 1, wherein said reflected light is imaged into said imaging means entrance pupil as an annular or quadrapole shape or as off-axis illumination.

8. The apparatus of claim 1, wherein the two-dimensional array of micromirrors is produced by optically interleaving at least two separate arrays of micromirrors.

9. The apparatus of claim 1, wherein the two dimensional array of micromirrors comprise at least two sets of micromirrors, wherein the two sets are separate and offset from one another and temporally interleaved.

10. The apparatus of claim 1, wherein the size of the reflecting surface is configured such that coherence effects between nearby pixels are substantially eliminated.

11. The apparatus of claim 1, wherein the reflecting surfaces of the micromirrors are coated with a precisely matched multilayer Bragg reflection.

12. The apparatus of claim 11, wherein the multilayer Bragg coating is Mo/Si or Mo/Be having bilayer periods equal to about one-half of said reflected light wavelength at normal incidence.

13. The apparatus of claim 11, wherein the multilayer coating is deposited with graded multilayer periods to maintain the wavelength of peak reflectance as the angle of incidence changes across each micromirror.