1. A method of positioning a thin semi-conductor plate and patterns to be successively projected thereon on a reduced scale in elementary zones of the plate in a photorepeater, said patterns corresponding to successive different levels of a circuit to form on a reduced scale on said plate by direct photorepetition, said method comprising the successive steps of: recording at least one reference mark on each of said patterns to be projected at places intended to be superposed during successive projections; recording said reference mark carried by the first of said patterns in said plate during the formation of the first of said levels by photorepetition of said first pattern; and, after each treatment and rough positioning of said plate in said photorepeater; illuminating, by means of an auxiliary illuminating device, a first of said elementary zones, said first zone being situated on one side of said plate on a reference axis of said photorepeater; forming on a following pattern, positioned in the same way as said first pattern, an image of said reference mark recorded in said zone; centering said image of said reference mark and said reference mark carried by said following pattern by moving said plate in its plane along two orthogonal axes X and Y of said photorepeater; moving said plate along said reference axis by a distance D until said auxiliary illuminating device illuminates a second elementary zone on the other side of said plate; moving the thin plate along axes X and Y for centering the image of said reference mark of the second zone and said reference mark of the following pattern, the global displacement d thus effected equal to D sin .alpha. being measured, .alpha. being the angle of rotation of the thin plate relative to its initial position; rotating the thin plate in the plane X Y of the angle .alpha.; and finally moving the plate along axes X and Y enabling the alignment of said plate and said pattern to be adjusted.