Photolithography Photolithography is the transfer of patterns, circuits, device structures, etc. to a substrate or wafer using light and a mask or stencil to stop the light. Photolithography was used extensively in the progression of microelectronics. Today, because of the sizes involved in current computer microprocessor devices, other methods like direct patterning using electron beams are used. Photolithography is still used for dimensions down to about 0.5um. The wavelength of UV light is .35-.45 um.

Starting material is a 100mm (4 inch) wafer of silicon - shown in an edge view

Wafers are cleaned first

Silicon Dioxide (SiO2 ) is grown on the silicon creating a dielectric or insulating layer

High temperature tube furnace for the formation of silicon dioxide (SiO2)

A conductor metal (student choice) is vacuum deposited on to the wafer

CVC 601-sputter deposition Conductor vacuum deposition tools in the ECE Microelectronics Clean Room Cooke-thermal deposition CVC 601-sputter deposition CHA Mark 50 e-beam deposition Varian 3125 e-beam deposition

UV light sensitive material called photoresist is spin coated on to the conductor side of the wafer

Light sensitive material is stored in amber dropper bottles – Use 1813 Wafers are spin coated with Shipley 1813 UV sensitive photoresist spin coating produces a uniform coating Spin speed is set here Light sensitive material is stored in amber dropper bottles – Use 1813 A vacuum chuck holds the wafer

The antenna design, arrayed on a transparency sheet, is placed on top of the wafer. This transparency is called a photo mask. Production photo masks would be made on glass plates with high precision patterns.

The array of antenna will be cut to just larger than the wafer The antenna pattern, arrayed and printed on a transparency paper, is used as a mask The array of antenna will be cut to just larger than the wafer

Ultraviolet light is projected down on to the photoresist coated wafer

HTG mask aligner and UV light source The UV light source is a mercury vapor lamp at 436nm wavelength UV light with filter surrounding it Clear glass plates are used to make sure the transparency lays flat to the wafer Exposure time set on timer Wafer is held by vacuum, mask is placed on top and brought into contact with wafer

The wafer is developed, leaving photoresist where no UV light has penetrated the mask

Solitec automatic developer Vacuum switch Start switch

Conductors are etched using chemicals specific to the metal Gold, silver, nickel, and copper etch Chrome etch Aluminum etch

After etching, the antenna pattern, in the conductor of choice, will be left on the wafer

In the clean room Complete one wafer first Determine the number of complete antennas on the wafer. Partial antenna can not be counted. Record this number. It is needed for the cost analysis. Evaluate cost – cost analysis will be next lesson Redesign if appropriate

Homework Find Excel and PowerPoint programs on Mosaic Begin learning how to use both programs A cost analysis for your antenna design will be due shortly Your project presentation will be done on PowerPoint