GB2316497A - Forming a diffraction grating by scanning - Google Patents

Abstract

A controlled longitudinal mechanical transporting apparatus is associated with a transverse beam scanner in scanning relation with a substrate 1. A grating 2 having parallel lines 3 on a substrate 1 is made by transporting the substrate in a direction perpendicular to the intended lines, by continuous or stepping motion, and writing a line at intervals in the same line position 4. The lines may be produced by photons, electrons, ions or other scanned beam.

Description

PARALLEL LINE GRATING This invention relates to preparing a line grating having parallel lines of distinctive opacity or other property over an area or field on a substrate. The parallel lines are produced by photons, electrons, ions or other scanned beam process. The grating may be used to form a phase mask for use in reproducing numbers of geometrically similar final gratings.

When such beams are controlled in two dimensions to cover the area or field, distortions and de-focussings tend to arise, reducing the usefulness or optical performance of the grating; it has been found that such aberrations are less intrusive when the beams are controlled to scan only along one line.

According to features of embodiments of this invention, a beam is scanned over a line and a substrate for receiving a grating, whether a mask or a final product, is moved intermittently or constantly under positional control in a direction transverse to the line while it receives the beam.

An embodiment is now described by way of example in conjunction with the drawing, which shows partly schematically, and in perspective, a substrate being moved through a linearly scanned beam.

Referring to the drawing a substrate or carrier 1 for receiving a grating 2 consisting of regularly spaced parallel lines 3 is moved continuously at a constant speed, or alternatively stepped in the direction of the arrow 6, past a line 4 impinged by a scanning electromagnetic radiation or particle beam 5.

The beam is immobilized at intervals, so that spaces appear between the lines.

The beam scanning may be very fast compared with the movement of the substrate, or it may be co-ordinated with the substrate movement, so that an inclination or blaze angle of the lines 3 is produced with reference to the direction of movement, i.e. to the longitudinal dimension of the substrate. In either case, the beam could be regularly switched off as aforementioned, or could be deflected to an area which is not significant in the final product.

The invention is not limited to producing gratings, i.e. scanning an area for many other reasons will occur to the skilled person as embodiments. Single axis mechanical scan can be accurately controlled for substrate 1, whether stepped or at constant speed.

The invention takes advantage of the control that is possible in single axis mechanical systems combined with the positional control in a single axis beam scanning system (Fig. 1). The scanned beam could be photon (e.g. laser), electron or ion based. The simplicity of the arrangement is particularly suited to the formation of regular or systematically varying patterns such as uniform or chirped gratings.

The arrangement overcomes the limitations of conventional scanned beam system which have demands on the precision of either mechanical and/or scanning arrangements in more than one axis. The reduction of this complexity makes it possible to generate more perfect images, produce more complex functions with higher precision in the scanning and potentially write longer arrays of scanned lines.

Use of controlled linear axis mechanical scanning combination with an electron or other radiation source for the preparation of controlled grating structures, which gives a high degree of uniformity of grating structures formed this way and possibility of simple generation of controlled chirp or other functions in gratings.

Chirping, where the spacing between the lines is varied according to some regular geometry, can easily be provided in accurately predictable fashion, by appropriate numerical control of the mechanical drive of the substrate 1. For instance, a linear transport device known in the U.K., as an "Inch-worm" is suitable for programmed drive variations for use to produce chirping, or for constant drive in making a grating even as long as one metre.

The combination of beam scanning generally transverse to a mechanical movement of a carefully controlled intermittent or uniform character, is thus seen to give substantial advantages in the predictable and respectable scanning of areas or field.

Claims (6)

1. A method of scanning an area including the provision of a mechanical movement of a substrate co-ordinated with a scanning of a writing beam, the mechanical movement being generally transverse to the scanning of the writing beam.

2. A method as claimed in claim 1, in which the mechanical movement is continuous and at constant speed.

3. A method as claimed in claim 2, in which the substrate is to carry a grating.

4. A method substantially as hereinbefore described with reference to the drawing.

5. A diffraction grating produced directly or indirectly via a mask, by a grating made using the method of scanning as claimed in any preceding claim.

6. A combination of controlled longitudinal mechanical transporting apparatus and transverse beam scanning apparatus in scanning relationship with a substrate.