A Laser Beam Pattern Generator focus a Helium/Cadmium laser with a lens on a mask plate covered with fotoresist. The lens used for writing a layout pattern is a 4mm lens. The practical resolution of this lens 1 micron. Due to the fact that the image field size is limited, a pattern must build up from small stripes. In this case the stripe width is set to 160 micron. Within a stripe, the laserbeam with a spotsize of .8 micron moves from left to right, and exposes the fotoresist. Infact this is a very simple explanation of the working priciple.
A design is devided in small pixels, with a pixel size 0.2 micron. As the value of a pixel can be changed from 1 to 0, the result will be the exposure of a structure or not. The small pixel size also means that from all shapes in a layout masks can be made. So triangles, dots or arcs are no problem at all for mask making.
Delta Mask produces 4 and 5 inch chrome mask plates from designs created with a layout editor like CleWin or L-Edit. These prgrams write a layout to CIF or GDSII format, which is the bases for dataprocessing for the Laser Beam PG.
Definitions we use
The specifications we need in order to fabricate:
DF or BFDo you want the filled polygons in the design to appear in chromium on the mask, which is called Bright Field (BF)? Or, do you want the filled polygons in the design to appear transparent on the mask that is called Dark Field (DF)? If you define for example waveguides as filled polygon lines and you use positive resist to protect the layer on your wafer from etching you should subsequently order BF.
CU or CDHow do you want your design to appear on the wafer? If you normally look at the mask on the Chromium side (NOT through the glass) this is named Chrome Up (CU). If you normally look at the mask THROUGH the glass on the chromium, this is called Chrome Down (CD) This in itself serves no purpose. However if you also state if the design should be mirrored :Wrong Reading (WR) or NOT mirrored :Right Reading (RR) this is usefull information.
Example 1:For example if you want your design to appear on the mask as in your design-file while looking through the glass on the chrome, you should specify: CD RR
Example 2:Some people use backside exposure but like to match it to previous frontside exposure: they specify CU RR
Mask size5 by 5 inch or 4 by 4 inch?
We recommend to keep all structures at least about 6 mm from the edge of the mask!
Some designs have not been centered on the mask on purpose, we like to know if we may center your design. We are reluctant to change the design of our clients if not clearly ordered.
If you want an additional text identifying your mask, please specify an "identifyer". If the identifyer is specified we write the identifyer in the lower left corner with 1250 microns high font (if the height is not specified).
A complete order -apart from the design file- could be as short as:
5"/DF/CU/WR Identifyer: "Your organization name Your name here Mask identification August 2002"