Plate Size: 3" (75mm)
Base Thickness: 2.2mm (0.090")
Base Material: Quartz Fused Silica
Reflectivity: Low reflective
Coating: Chrome OD3
This product is a Special Material photomask, which means that it is generally made out of materials that are not stocked on a regular basis and are usually overstock from previous custom production runs. Once stock levels have depleted , it may take 2-4 weeks before replacement materials are bought into stock and this might be subject to minimum order quantites.
Please see the specification TAB for information on the materials.
We can write masks at 4 different resolutions, called "classes". The higher the resolution, the better the qualtity. Please see the section SPECIFICATIONS to see the impact that class resolution has on dimensional accuracy and feature tolerances.
Class 1 : This represents a resolution that is equivalent to approximately 64k dpi (previously known as High Resolution). Although this resolution may resolve smaller features, we recommend keeping feature sizes above 10um 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 10 um unless on a 'best effort' basis previously agreed with our technicians.
Class 2 : This represents a resolution that is equivalent to 128k dpi (previously known as Super High Resolution). This resolution will resolve down to 4 micron lines and has good line edge qualities with only a small pixilation along edges. Corner rounding is below 3um but still visible. NO features such as lines / circles / spots / squares below 4um unless on a 'best effort' basis previously agreed with our technicians.
Class 3 : This represents our most common resolution for demanding, high precision photomasks. It is equivalent to 256k dpi , and offers an excellent price / quality balance. This resolution will resolve down to 2 micron lines and has very good line edge qualities with no pixilation along edges, and corner rounding is kept to a minimum.
Class 4 : This represents our highest resolution, which is equivalent to 512k dpi (a brand new offering !) , and is the best quality that we can offer. This resolution will resolve down to 1 micron lines and has excellent line edge qualities with no pixilation along edges, and corner rounding is barely visible.
Data formats listed above are only a small section of what is available. If your chosen format is not listed, please contact us for further information and clarification. We are also able to provide a full drafting service whereby we can create your designs from drawings and descriptions.
Masks are normally referred to as Clearfield (positive) & Darkfield (negative)
Positive means that the data you have drawn in CAD will be Chrome on the mask, with the background (the field) being clear glass.
Negative is the opposite of this, where the items drawn on CAD will be clear and the background will be chrome.
We also need to know which way round the mask has been designed on your screen. The easiest way to select this is to add some reference text (anything you like) to the design somewhere - maybe in the corner - and then specify if the text needs to be right reading or wrong reading.
Our standard production turnaround is 3-4 days from receipt of the artwork, purchase order and related documents. We can offer faster services if required for more urgent orders.
Standard : We firstly inspect the piece by eye for flaws, design inaccuracies and contaminations. We also inspect a test coupon (placed in the bottom corner of the mask) for line width accuracy and edge definition. Next we measure the overall dimension of the mask, and record both of these measurements on our internal inspection records. Finally, we find the CD of the mask, measure that, record it, and also take a digital photo that is saved with the inspection log. We use Nikon MM40 at 900x magnification and an OGP ZIP 300 at 400 x magnifications for this.
Enhanced : In addition to the standard inspection process described above, we will then document them via a Certificate of Conformance which we supply with the mask. Tolerances are per our standard tolerances.
Full Certificate : By selecting this option during the ordering process, we will inspect upto 10 customer defined measurements, with customer supplied tolerances. You will need to send us a document, or a separate layer of the design, showing us where you want us to take the measurements from. There can be upto 10 positions defined by the customer. These dimensions are then programmed on the co-ordinate measuring system and the mask is compared to this unique program. A certificate of conformity is given if the mask passes the inspection process.
Please see the TECHNICAL sections, DOWNLOAD sections and FAQ for further information. If you still require clarification, pleas either email or click for LIVE SUPPORT.
Soda Lime Glass is the most common substrate used for masks, due to its good quality/price ratio. The glass is optically good, very flat and has no imperfections. If used in a photo-lithographic process, glass can be used with a very wide variety of light sources from 350nm upwards, with an excellent UV transparency. Soda Lime glass has a thermal co-efficient expansion of 93 (10-7) which is approximately 10 ppm (parts per million) , and a transmittance value of 88% at 375-450nm, with a glass flatness class of 5um for the smaller plates and 10um for the larger plates. Some of the very big plates of 14" and above, may have a bigger flatness tolerance of upto 40um. We would recommend always using Soda Lime glass where it is suitable due to its relative inexpense.
Quartz (Fused Silica) is not as common due to the expense of the material, but quartz brings the very best stabilised material thermally, along with a very clear base that allows a wide variety of wavelengths to pass through at very good transmission rates. The thermal co-efficient expansion is 5(10-7) which is approximately 0.5 ppm (parts per million). Flatness of this material is best-in-class, with 2um flatness for small plates, and 5um for mid sized plates.
B270 or BOROFLOAT® are made out of Borosilicate, and are ideal for high temperature and harsh environment applications. Unlike common borosilicate that is drawn flat, BOROFLOAT® is produced by a float technique that yields superior surface accuracy. BOROFLOAT® is about three times more resistant to thermal shock than standard soda lime glass, and has a thermal co-efficient expansion is 35 (10-7) which is approximately 4 ppm
Flashed opal has a pearlescent base which is used for light diffusion, such as that of a lightbox. It offers a more thorough diffusion with a distribution close to Lambertian, with the brightness of the diffuser being independent of the viewing angle. With an average transmission of approximately 35%, it can be heat strengthened or tempered and is scratch resistant, non-deforming, and non-combustible. The transmission properties of White Flashed Opal glass are for the most part dependent solely upon the white layer, the thickness of which varies over the manufacturing width and is generally in the order of 0.45 ± 0.2mm. The visual light transmission in the case of standard illuminate A is on average τ vA = 35 % (± 10 %). The flashing sits on the glass surface, so this product cannot be lapped or polished before use - therefore it remains fairly non-flat surface that can only accommodate large feature sizes in the pattern ( > 50um)
Nextrema WHITE is a specialist ceramic "white" glass that offers a white opaque surface , and is ideal for high temperature and harsh environment applications due to its very low thermal co-efficient which is nearing that of Quartz.
Aluminium coatings are very soft and can easily be damaged during use and even cleaning. However, their conductive/resistive properties make them useful for certain applications, as well as the Aluminium being a better conductor of heat than chrome, so the material does not heat up as much during laser ablation processes.
Chrome Coatings are much more robust materials and can be cleaned fairly easily without fear of damage. It is coated onto the plates in very thin layers, which thickness may vary depending upon the OD (Optical Density) required - but generally ranges in the 0.1um to 0.15um thick.
We can coat with other materials, such as Titanium, Gold and ITO..but specialist coatings means that we have to run a complete chamber full so there will be minimum order quantities required, varying between 5 and 30 plates depending upon the plate size.
Low Reflective Chrome: The chrome that is coated on the plate would normally have a bright mirror-like finish to it, reflecting at about 75%. We need to protect this surface with an oxide coating (chrome oxide) , and this oxide is applied to not only protect the surface but also to change the reflectivity of the plate. Our standard product is a LRC (Low reflective Chrome) which reflects around 12% in the UV wavelengths and therefore is most suitable for applications using Mask Aligners and other UV exposure equipment. Low Reflective refers to the oxide coating which is applied to the top surface of the chrome plate. This oxide makes the surface appear “yellow/gold” to our eyes when we hold the plate in a way that the light reflects off it. Because this oxide is applied after coating, the underneath surface of the chrome – the surface that sits against the glass – will remain bright/shiny with a mirror like finish.
High Reflective Chrome: We also have a small range of High Reflective chrome. This chrome still has an oxide coating over the surface, so is not as reflective as the "underneath" side of the plate, but still reflects high at around 50%
Blue chrome: We stock a small amount of “blue” reflective chrome. This is low reflective when using the plate in the visible spectrum, so is the best solution for components that are used optically. With this material, our default is to have the oxide applied to both surface of the chrome so it will appear identical when looked from the front (chrome side) or the back (glass side), meaning internal reflections are kept to a minimum.
OD3 - Optical Density is a measurement given to the chrome optical characteristics, and will change depending upon the wavelength used. OD3 means that the chrome surface will transmit only 0.15% of light in the visible spectrum, and equates to a chrome thickness of approximately 0.1um
OD5 - The chrome is coated to a thicker layer of approximately 0.15um thick, allowing even less light to transmit through (0.015% in the visible spectrum)
OD1 - Some customers actually want a large amount of light to transmit, therefore bringing the contrast ration down. Our OD1 plates are coated very thinly, and appear "see through" to the human eye. They can be sued in specialist graphics applications or to replicate an Iron-Oxide plate which allows for easy registration of the plate to sub layers.
OD1.8 - Another thin chrome coating giving a transparent basis.
The way that the masks are manufactured means that we have a "keep out" area that we cannot write critical features to - this equates to a 10mm border around the edge of the plate. This is because the resist is slightly thicker in the corners and edges, where it builds up during the spinning process. We use ‘fringeless’ blanks wherever possible, so can image outside of this area if necassary, but recommend only text and references marks in this outer area.
The specification of the raw materials and the photo-resist, mean that there may be minor defects that appear randomly across the image. Usually these defects are cosmetic only, and most often the defect actually causes no working problem with the design. A defect is defined as having a size greater than the required rate, and can take many forms such as a "pinhole" in what should be the chrome/emulsion part of the mask, or it can be a chrome / emulsion spot in the clear part of the mask (also referred to as 'shorts' or 'breaks'). A defect is any flaw affecting the geometry that passes the authorised specification for the order.
The customer may indicate the size of defects that will affect their process (defect spec). All defects which break these rules must be repaired, or if they cannot be repaired, the mask must be rejected and rewritten. Where no defect spec is given by the customer, we use our own internal standards.
There is also a class of defects known as cosmetic defects. These are defects that may not affect the geometry but still may not be acceptable to the customer. Cosmetic defects include scratches on the chrome outside the array, damaged or partially removed AR coating, contamination on the chrome, glass chips on the edge of the mask, etc.
The Customer Defect Specification Form is to be used by customers to inform us of their defect specifications. It may be supplied to cover every order within a given time frame, or on a per order basis. If the form is not submitted, our own internal specifications take over. These specifications will be used by our front end engineers to asses if masks can be written before going into the write phase, and customers will be informed where specifications are deemed to be unachievable.
Q: What is the smallest feature that you can do ?
A: This depends upon the resolution that we image at, the material that we use, the tone of the photoomask, and most importantly the feature type (Spot, square, line etc). This all makes it very hard to give a figure, but as a very rough guide we can make 2-3um on an "everyday" basis , and down to 1um and possibly below using our highest resolution services (please ask).
Q: How accurate are the features, what tolerances do you work to ?
A: This is dependant upon the resolution that we image the photomask at. The QUICK REFERENCE brochure in the DOWNLOADS section will give you a chart, specifying both feature and dimensional tolerances.
Q: What resolution should i pick ?
A: The higher the resolution, then the sharper the edges of the features, the smaller the features possible, the more accurate the features will be, the sharper the corners in of the features, and also the smoother the circles. Some customers will notice this difference straight away, some will hardly notice any difference. Every customer has different requirements and different priorities. If in doubt, chose a higher resolution to ensure your requirements are met, but we are happy to advise if you send us your database.
Q: What does the term POLARITY and FIELD mean ?
A: Polarity is the tone of the photomask. In layman terms, this is usually described as POSITIVE or NEGATIVE. When you draw your photomask design, polarity determines whether the features on the mask are CLEAR or DARK on the final plate. The field refers to the background tone of the mask. So, a DARKFIELD mask would have the items you have drawn as CLEAR, with the background of the mask as DARK. Obviously this is the opposite for CLEARFIELD, where the field behind is clear and the design features are DARK. Remember, this is polarity or tone of the mask that we manufacture, and NOT the polarity of the wafer you are using. If used in contact lithography, the tone of the photoresist that you use will also affect which polarity to order.
Q: I've designed my photomask with the wrong polarity - what do i do ?
A: We can use the original design file and simply reverse the tone of the photomask. This is much easier than supplying new data.
Q: What is Right Reading, Wrong Reading and Mirrored.
A: Right Reading Chrome side Down is the most common way to describe a photomask that will be used for contact lithography. When you hold the mask in your hands with the chrome side facing down closest to the wafer, the image on the mask will be correct or how it should appear on the wafer. This is equivalent to Wrong Reading Chrome side Up. For us to make this happen we have to Mirror the image of your photomask before we write it.