Maskless lithography with sub-pixel resolution

• US 20030206281A1
• Filed: 05/01/2002
• Published: 11/06/2003
• Est. Priority Date: 05/01/2002
• Status: Active Grant

• Current Assignee: Anvik Corporation
• Original Assignee: Anvik Corporation
• Inventors: Jain, Kanti
• Granted Patent: US 6,717,650 B2
• Time in Patent Office: Days
• US Class Current: 355/53
• 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: G03F 7/70466 Multiple exposures, e.g. combination of fine and coarse exposures, double patterning or multiple exposures for printing a single feature stitching G03F7/70475

Abstract

Sub-pixel digital resolution is provided in a maskless microlithography system by a sub-pixel voting system using multiple, slightly-offset, digitally-controlled, unit-pixel, partial exposures with cumulative voting identifying regions of full exposure for sub-pixel-selection. Computer control of a virtual-mask pixel-selection device of unit-pixel resolution usually provides pixel-resolution patterns. To achieve sub-pixel resolution, the virtual mask, after a first partial exposure, is offset by less than a pixel-width and a second partial exposure is made. If the offset is {fraction (1/2 )} pixel-width, then an image region of half-pixel size with full exposure is realized. Finer voting can be defined by number of pulses, by significantly changing the offset, and by offset in another dimension, and by increasing the multiplicity of exposures, thus enabling resolution enhancement by large multiples. The same offsetting techniques can be used for other than binary voting, for example to drill controlled-depth vias or to provide topography controls for laser-milling a controlled microsurface.

Claims

1. A maskless lithographic system of sub-pixel resolution having a radiation source and an optical system with unit-pixel resolution pattern defining means between radiation source and a substrate mounted on a high-precision stage characterized by:

a) means to provide a first set of virtual-mask partial exposures on a unit-pixel basis; and

b) means to provide at least one subsequent set of virtual-mask partial exposures on a unit-pixel basis, partially overlapping and offset from said first set;

whereby overlapping sub-pixel partial exposures form full exposures at sub-pixel areas, thus providing properly defined image areas of sub-pixel size.

2. A maskless lithographic system according to claim 1, in which the system mode is photoresist exposure with developing and subsequent processing for discrimination between partially and fully exposed sub-pixel-size regions.

3. A maskless lithographic system according to claim 1, in which the system mode is photoablation with selection of sub-pixel areas by discrimination between partially and fully exposed sub-pixel-size regions.

4. A maskless lithographic system according to claim 1, in which the system mode is photoablation for surface profiling.

5. A maskless lithographic system according to claim 1, in which the system mode is photoablation for via drilling.

6. A maskless lithographic system according to claim 1, in which the pattern defining means is a spatial light modulator with pixel-to-pixel selectivity.

7. A maskless lithographic system according to claim 6, in which the pattern defining means is a digital micromirror device.

8. A maskless lithographic system according to claim 6, in which the pattern defining means is a liquid crystal device.

9. A maskless lithographic system according to claim 6, in which the pattern defining means is a grating light valve.

10. A maskless lithographic system according to claim 8, in which the pattern defining means is a membrane mirror array.

12. A maskless lithographic system according to claim 1, in which sub-pixel-width offset of the virtual mask is by stepped motion of the stage for sub-pixel resolution.

13. A maskless lithographic system according to claim 1, in which sub-pixel-width offset of the virtual mask is by motion of the stage with synchronized laser pulses and spatial light modulator pixel-selection for sub-pixel resolution in virtual mask offset to provide full-exposure illumination to selected sub-pixels.

14. A maskless lithographic system according to claim 1,

further characterized by:

a) means to supply description of the full image information to the system control computer;

b) software means to determine the sets of partial exposures necessary to achieve full exposure at the desired image location; and

c) software means to optimize the sets of partial exposures so as to minimize their number.

11. A maskless lithographic method for providing sub-pixel resolution from components having unit-pixel resolution, in the following steps:

a) partially imaging in a first set of exposures on a unit-pixel basis with exposure values less than full exposure at both unselected sub-pixel locations and selected sub-pixel locations; and

b) partially imaging at least one subsequent set of exposures on a unit-pixel basis with exposure values less than full exposure at both unselected sub-pixel locations and selected sub-pixel locations during the subsequent set of exposures, with offset to said first set of exposures, in such fashion that selected sub-pixel locations receive cumulative exposure equal to full exposure as a composite of both said first set of exposures and said subsequent set of exposures.

15. The maskless lithographic method according to claim 11, for providing sub-pixel resolution from components having unit-pixel resolution, carried out with the addition of the following steps:

a) supplying a description of the full image information to the system control computer;

b) determining with software means all the sets of partial exposures necessary to achieve full exposure at the desired image locations; and

c) optimizing with software means the sets of partial exposures so as to minimize their number.