HTA's PHOTOMASK TALK
Photomask Talk was created as a communication document defining the meanings of words that have acheived new meanings relating directly to the making of Photomasks. As well as Vocabulary we include some Conversions, Acronyms, Idioms, Definitions & Idiosyncrasies.
Anti - Reflective Coating - A vacuum depositied optical coating designed to minimize or eliminate reflections of specific wave lengths of light. One of the most common AR Coatings used is MgFl Magnesium Fluoride. This is usually deposited on the phot tomask on one or both sides after the mask is made.
AR Chrome - A Chrome photomask plate with an Anti -Reflective coating deposited on the reflective chrome metal to minimize reflect - ity in the Ultra -Violet range of the spectrum. It minimizes standing wave effects and reflecitons between two sub - strates during contact printing.
Array - The area on the photomask that has repeating patterns. One or more arrays may be required on a mask. e.g. in the case of a semiconductor photomask the circuit may be the major array, a test device may be a minor array and align - ment targets may be another array of patterns. The array usually is as large as possible to cover the substrate that the mask will be printed to in order to maximize yield.
Artwork - A mask design medium that displays the finished mask layers. In the past the mask patterns were cut into rublith film and photographically reduced to make masks. Color overlays also many times are created to be mechanically aligned to view the "fit" of all the different levels of a mask set . These color overlays can be produced on diazo film or be plotted in color from the CAD data.
AutoCAD - A computer aided design software tool use to create the mask patterns of a mask set. Because this software was never intended at a mask design program there are some special requirements for the use of Auto -CAD such as closing polygons. HTA can provide more information on this.
Background - This is the background of the images in a mask design. Field is also referred to as the back ground. e.g. a dark field mask will have an opaque background with clear images.
CAD - Computer Aided Design
Calma - GDSII - This is a photomask design system that has used in the industry for many years. Many new design software programs model after this system and still have the capability of output - ting Calma Stream or GDSII data.
CD's - CD's is short for Critical Dimensions. Most images of circuit patterns have critical dimensions. One dimension (usually th smallest and most vulnerable to the process) is specified to be the most critical. The size is specified with a tolerance or varience when the mask is ordered and this image is the single pattern to be measured and documented normally.
Chrome - The most popular metallization used for photoplates. Chrome metal is usually sputtered or evaporated onto a glass sub - strate which is the plate the mask will be made with. Chrome metal was chosen in the early 1960's as a medium that was easy to deposit with good adherence to glass, and durability when used by the customer in the process.
Contact Print - A replica of a Master Photomask Tooling. This copy is us - ually made on a Contact Printer copy machine. When masks are used in contact on wafers they become damaged. Many mask users order a set of mask tooling and then have copies made over time to cut the cost of there masks.
Data Base - The original data that a mask is designed and generated from.
Defects - Mask pattern irregularities that cause the customers process to produce bad parts. e.g. opaque spots in clear areas, torn geometries, clear holes in opaque patterns ,etc.
E -Beam Lithography - A mask pattern generation tool that uses electron beam energy rather than conventional ultra violet light to expose resist.
Emulsion - A relatively soft silver halide photographic medium on glass that is used to make photomasks.
Emulsion - A relatively soft photosensitive polymer coating such as resist which is used to produce photoplates for mask making. This type of material is also used to pattern wafers and other sub - strate material in the photolithographic manufacturing process.
Field - The background of a pattern on a photomask. Usually not the digitized areas. Dark field masks have an opaque background with clear images. Clear field masks have a clear background with opaque images.
Film - The plastic sub or base material used to support photographic emulsions. The most popular film thickness in the industry is 0.007 mils. Films are still widely used to image PC boards and are typically written on laser photoplotters.
Film - A thin deposited coating of material upon another type of material for a specific purpose.
Fracturing - The breaking up of an original data base into a format that a mask making Camera requires to produce images on a mask.
Gerber - A photoplotting tool data type that is used primarily to pattern a photoplotted film mask. Gerber data can many times be trans - lated into other formats to be used on other types of mask making systems.
Glass - The substrate medium most widely used in high resolution photomasks. The most popular types of glass used are as follows: 1. Soda Lime (high thermal expansion) lowest cost 2. White Crown (high thermal expansion) low cost 3. Borosilicate ( low thermal expansion) higher cost 4. Quartz ,Fused Silica (lowest thermal expansion) high cost
Hard Surface - This term relates to the durability of a mask medium while in use. Chrome metal, Iron Oxide, and Silicon Oxide mask mediums are considered Hard Surface Mask Making materials.
Image - The working geometry or pattern of a mask. (this is usually the digitized data) Images may be dark or clear.
Inch - The english base number used to design masks. Common sub terms widely used are as follows: 1. mil ( .001 , one thousandth of an inch) 2. micro -inch ( millionth of an inch)
Iron Oxide - An orange, see - through material used as a photomask medium on any type of glass. This material is actinically opaque with an optical density of about 2.0 -2.5 O.D. to ultra violet light which is typically used to expose photoresist. This material is popular when it is require to see through the opaque areas of a mask for bettern alignment.
Latent Image - an exposed image that has not been developed and is not visible. Some photographic mediums such as a silver halide emulsion can have a latent image decay with time.
Mask - A material or medium that works to withold another material.
Meter - A unit of measure that is widely used in mask design. Sub terms of this measurment unit representing smaller increments are as follows: 1. cm centimeter 1/100 th of a meter 2. mm milli -meter 1/1000 th of a meter 3. micron - 1/1,000,000 of a meter
Mil - A unit of measurement that is verbalized and written widely in mask design. It is equivalent to 0.001 inch. (one thousandth of an inch)
Millimeter - A metric unit of measure that is widely used in mask design. It is 0.001 meter or (one thousandth of a meter)
Negative - A process or mask type that results with its use to change to field of the image to the opposite of the original. e.g. a negative process will turn clear images into opaque (dark) images.
Nominal - This term relates primarily to Critical Dimensions. The Nominal size of an image is the ideal size and there usually is a tolerance + - range specified as an acceptable variance.
Optical Density - This is a measurement of opacity of a mask medium. a certain optical density may be required to hold back light with various light sources. Common optical densities used in the photomask industry are 2.5 - 4.0 . A 4.0 O.D. is considered opaque to conventional light souces. When a user needs greater O.D. it is possible to achieve this with thicker metals as a mask medium. it is difficult to measure actual O.D. greater than 4.0. The tool used to measure O.D. is a densitometer. Most Chrome photo blank suppliers have an O.D. of 3.0 as a standard.
Pattern Generation - A photolithographic camera system that is designed to produce random irregular shaped patterns on a photomask.
Parity - In mask making this relates to Mask Orientation. Frontwards or backwards. Mirror image mask patterns are considered Right Reading of the Titles through the back of the glass mask. Right reading also relates to Working Plate or Master Parity. This is also stated as right reading chrome down. Right reading while looking at the mask images from the front or image side is called Sub Parity or Right Reading Chrome up
Photoplot - A mask patterned by a photoplotter, usually on film.
Photomask - a substrate with a design of opaque patterns which is to be used to with hold light during its use. It will mask out selected area of light during the patterning of other substrates. Photomasks can be made on glass or film substrates. The opaque patterns can be made of silver, chrome, chrome oxide iron oxide, copper, aluminum, silicon oxide and other materials.
Photoresist - A photosensitive polymer emulsion coated onto a substrate for the purpose of patterning that substrate. Photoresists can be positive or negative working. The most popular in mask making is positive.
Plate size - Plate sizes and thicknesses vary according to customer needs. Usually the photomask plate size is larger than the substrate to be exposed. Standard Photomask plate sizes are as follows in Inches: 1. 2.5x2.5x.060 6. 6.0x6.0x.090/120 2. 3.0x3.0x.060 7. 7.0x7.0x.090/120 3. 4.0x4.0x.060/.090 8. 9.0x9.0x.090/120/230/250 5. 5.0x5.0x.060/.090
Polarity - Polarity relates to the field or background density. e.g. if you wish to change the polarity of a mask you would change it from clear field to dark field or vice versa.
Positive - Usually means "the same" or yielding the same density in a replication as the original.
Positive Process - Produces the same density as the original. In photolithgography the exposed areas become clear.
Reticles - A mask used to produce a Step & Repeat mask. In a stepper an array of the Reticle patterns will be produced on the final mask.
Reversal Process - A photographic process whereby the original exposed and developed pattern is removed from the mask and the remaining photo medium is used to produce the mask patterns. The most popular reversal process is with the silver halide materials whereby a clear field mask when replicated becomes a clear field mask at final.
Ruby - Abbreviation for Rubylith. This is a plastic film with a dark red emulsion which can be cut and peeled precisely on a coordinograph and photographically reduced to become a mask.
Silicon Oxide - An orange, see -through mask material used to make high quality photomasks. This material is not commercially available at this time.
Step & Repeat - a method of creating an array of patterns on a mask. Step & Repeat can be used in CAD to make 1X mask data or on a Step & Repeat Camera system.
Substrate - The base material onto which patterns are produced. Typical substrates in mask making are glasses or films. In the man - ufacture of micro -electronics they could be silicon wafers, alumina, quartz, sapphire, etc.
Target CD - Usually the specific image and Critical Dimension specified by the customer for the mask maker to measure.
Test Patterns - A secondary array of circuit patterns on a wafer or mask to test the semiconductor manufacturing process.
Tolerance - A quality tolerance for the measurement of a Targe CD or critical pattern.
X Axis , Y Axis , Z Axis ,Theta Axis - In mask making, the X axis and Y axis can be different on different staging systems. Typically the X is from right to left., the Y is front to back, Z Axis is up & down and Theta is rotation.