Patent GB-1312825-A (GB)
Title: Method and apparatus for bringing a mask and a semiconductor body  into register with one another
IPC: G02B27/00
Filed: 1970-04-13
Abstract: 1312825 Photo-electric registering of semiconductors LICENTIA PATENT-VERWALTUNGSGmbH 13 April 1970 [19 April 1969 17 Oct 1969] 17471/70 Heading G1A [Also in Division H4] Photo-electric apparatus is used to bring into register two articles a mask and a semi-conductor body both of which are provided with sufficient register marks for the number of co-ordinate directions of movement required. Register may be absolute alignment i. e. superimposition of a mark 4 on one sheet 2 over a mark 3 on a second sheet 1, Fig. 1, or location of such sheets so that there is a predetermined distance between the marks in the co-ordinate plane, Figs. 2-4 (not shown). In the latter case, alignment of each sheet with, or at a predetermined distance from, the optical axis of a photo-electric microscope is carried out separately, the photo-electric microscope as a unit, or part of it only, being moved through this distance after alignment of one sheet. Alternatively, two photo-electric arrangements separated by the predetermined distance may share a common microscope objective. Photo-electric microscope. After the microscope objective, one or more differential arrangement(s) of photo-cells are associated with means to define a reference axis or plane and divide light from the sheets for detection by the respective detectors. In typical arrangements, an inverted mirrored prism Fig. 7 (not shown) or a slit-shaped diaphragm associated with a pair of photo-cells, may be used. The slit or prism may be oscillated. When two dimensional register is required, a cross-shaped aperture and quadrant arrangement of photo-cells are used. The differential output(s) of the photocells is used to control servo motors moving one or both of the sheets into register with the optical axis. Register Marks on sheets. The sheets may be viewed by reflected or transmitted light and have dark marks on a light field or vice versa. Marks on respective sheets may be identified by providing them as affected by a particular wavelength or wavelength range of light (e.g. transmitting a particular wavelength). Thus corresponding filters may be associated with the detectors for the marks of a particular sheet. Reflective marks may be of silver, dark ones of chromium or graphite other materials mentioned in the structure of sheets are ZnSe, Cds, GaP, photographic emulsion, photo-laquer, metals, etc. which provide a particular spectral transmission characteristic. The phenomenon of interference contrast may be used to differentiate marks, using silicon oxide and nitride, photo-laquer, etc. layers. Reflective marks may also be of Mo, Ta, Cr, Ti, Au or Al. The register marks of one sheet may be thicker than those of the other or be weighted by cross marks Figs. 10, 11 (not shown). Marks may be formed by vapour deposition or etching. Typical register operations may involve an x, y registration using separate x and y or common (cross-shaped) marks and a rotation (y) register using further cross-shaped marks spaced from the firs cross-shaped marks also allow non-parallism or scale differences between sheets to be compensated for, when a third set of marks may also be needed. Marks may be pairs of lines. Methods and apparatus for contact and projection printing involving registering of the mark with the substrate are described, Figs. 5, 6 (not shown), illumination of the sheets being to reflect light off or transmit through the sheets. In registering by alternate investigation of marks on the two sheets, a diaphragm may be used to block out light from each sheet in turn.