A benchtop mask aligner in a photolithography room under amber yellow light, a cream-white plastic housing 61 centimetres wide sloping up toward the back, its sloping front a plain smooth salmon-pink panel with a row of round black knobs and four square lit push-buttons in blue, green, orange and red, in the centre a grey binocular microscope on a column above a round stage with a pale blue wafer holder, on it a mirror-bright silicon wafer beneath a square glass mask with a faint grid of fine lines, two hands in white nylon gloves turning the knurled micrometer knobs, an operator in a white coat and hood seen from behind.
What it was used for
The contact aligner pressed the chrome mask directly onto the resist-coated wafer and exposed through it. The Karl Suss MJB3 operating instructions, as university cleanrooms still issue them, give a 350-watt mercury arc lamp at about 20 milliwatts per square centimetre at 405 nanometres and three modes: standard contact, in which nitrogen pressure pushes the substrate against the mask; soft contact, using only the chuck's mechanical pressure; and high precision, in which a vacuum is drawn between mask and sample. One full turn of the Z micrometer changes the contact height by 150 micrometres.
What was new
Nothing about this tool was new; what is characteristic is what it cost. Direct contact, Kato's chronology notes, can damage the mask or contaminate the wafer - which is why Kasper introduced the first contact aligner with proximity capability in 1973, lifting the mask by a small gap. The harder the contact, the better the resolution and the faster the mask wears out. In the section on loading the mask, the MJB3 instructions warn twice, explicitly, about broken masks: against scratching the chuck or mask holder, and against failing to check the vacuum. The barb: the aligner that was to be superseded from 1973 onward still stands in research cleanrooms 50 years later - at the University of Southern California as a classic contact aligner for education and prototyping.
What the sources leave open: The MJB3 manual opened here is a present-day university user version, not a contemporary data sheet; it gives neither resolution nor mask or wafer sizes. No introduction year for the MJB3 could be verified in the sources opened, so none is stated in the text.
Connections
Every connection names its kind. “Forerunner” on its own would be a claim.