Small Format Film Resolutions
The following information refers to emulsion coated polyester patterns, up to a maximum of 812mm in size.
CHOOSING RESOLUTIONS
We can write masks at 4 different resolutions, called "grades". The higher the resolution, the better the quantity. For each increase in Class, there will be a 2x improvement in the following parameters: Addressability, Minimum Line, Edge Roughness, CD Uniformity, and Alignment Accuracy.
Grade 1 : LOW Resolution. Although this resolution may resolve smaller features, we recommend keeping feature sizes above 50um as corner rounding is considerable. Edge sharpness and definition is acceptable for non critical design types, although designs with arcs/circles and lines running off 90 degree grid may show pixilation. NO features such as lines / circles / spots / squares below 40 um unless on a 'best effort' basis previously agreed with our technicians.
Grade 2 : MEDIUM Resolution. This resolution will usually resolve down to 25 micron lines with decent line edge qualities with only a slight pixilation along edges. Corner rounding is still noticeable under magnification. NO features such as lines / circles / spots / squares below 25um unless on a 'best effort' basis previously agreed with our technicians.
Grade 3 : HIGH Resolution. It offers an excellent price / quality balance. This resolution will resolve down to 12 micron lines and has very good line edge qualities with little pixilation along edges, although some circles / squares and spots may have some distortion to them. Corner rounding is usually acceptable at this level.
Grade 4 : PREMIER Resolution. It is excellent for demanding, high precision photomasks, and is the best quality that we can offer. This resolution will resolve down to 5 micron lines (depending on the geometry type ) and has good line edge qualities with little pixilation along edges, and corner rounding is only noticeable under high magnification. Note that where feature sizes are below 10um, the design cannot contain mixed negative and positive data if feature size is critical.
FEATURE TOLERANCES
There are two different values that we specify for tolerances. The first is a ‘feature tolerance’, which equates to one specific feature (also known as CD or Critical Dimension). So, if part of your mask design has a 12um channel and this is a critical feature, you can use the table below to work out possible deviations to the channel width, depending upon which resolution you choose. As a rule, the higher the resolution, then the more accurate the individual feature size will be.
All figures above in Microns....
Example, at grade 3 resolution a 10um line would have a tolerance of (1.2 + 0.1) = 1.3
DIMENSIONAL TOLERANCES
The second tolerance that customers ask us about is that of overall dimensional tolerances. These refer to the tolerances over a distance greater then 5mm – in layman’s terms, people ask us ‘how accurate will the mask be’ and these guidelines should go somewhere towards providing the tolerances in overall dimensions ,depending upon the resolution chosen. Again, it goes without saying that the higher the resolution, then the more accurate the final mask.
Our photo-mask films are produced in conditions of 21deg C / 50% humidity, and if dimensional accuracy is a concern when using the polyester mask, then you must replicate these conditions in your own clean rooms and acclimatize the mask in these conditions for up to 8 hours before you intend to use it – only then can it be considered to be dimensionally accurate and stable. We strongly recommend using glass based substrates where dimensional stability is a concern.
NOTE: When using films in your own production environment, be aware that;
1 Deg C temperature change = 18 ppm (1.8um per metre length)
1% Humidity change = 9ppm (0.9um per metre)
where L is measuring length in MM and the resulting figure is in microns.
Example, at Grade 3 resolution a 100mm line would have a tolerance of (10.0 + 0.5) = +/- 10.5um.
Our imaging process is accurate to +/- 5um, the remainder of the tolerance is due to environmental controls.
