Glossary

Here is a list of terms and meanings used in the photomask and optical pattern industry. This list is not exhaustive, we have omitted words that are now not in regular use because the technology is no longer needed, but it has been put togther with help from the American National Standards Institute (ANSI), along with The Society of Photo -optical Instrumentation Engineers (SPIE)


PHOTOMASK TYPES

Blank - The substrate (quartz or glass) coated with chrome and photoresist , ready for imaging and processing.

Clear field - The "field" behind the pattern - or the background area surrounding the pattern geometry - is clear. This usually infers that the drawn pattern is opaque. Also known as "Positive"

Correct reading - A photomask that is properly oriented (as designed) so that when looking through the substrate at the back of the coated side of the photomask all lettering or printing is read normally

Dark field - The background area surrounding the pattern is opaque, and the pattern itself is transparent. Also known as "negative".

Emulsion - A photoplate coated with a suspension of a salt of silver in gelatin or collodian which is exposed and developed to produce a photomask

Field tone - The appearance (dark or clear) of the background area surrounding the pattern.

Hard surface - A photoplate coated with a relatively hard (nonemulsion) coating which is selectively etched to produce a photomask (e.g., chromium, aluminium

Lateral Reversal - Producing a mirror image of a photomask without changing polarity (i.e., positive image remains positive and negative image remains negative)

Layer (CAD) - one of a series of overlaying CAD layers .

Layer (PLATE) - One of a sequential series of overlaying photomasks which make up a device series

Mask - Photomask

Negative - A photomask on which the information or images are clear (rather than opaque), sometimes referred to as dark -field photomasks

Parity - Whether an image is right reading or wrong reading (mirror image).

Photomask (syn. mask, plate) - a substrate with a design of opaque patterns which is to be used to withhold 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 chrome, aluminium, emulsion.

Photoplot - A pattern created by a photoplotter, usually on film.

Polarity - Referenced as to whether a photomask is positive or negative

Polarity reversal - To produce the same image but with a change of polarity (i.e., positive image to negative; negative image to positive).

Positive - A photomask on which the information or images are opaque, sometimes referred to as clear -field photomasks.

Reverse reading - Mirror image of a correct -reading photomask

Semiconductor - A material whose ability to conduct electrical current can be alter, for example silicon. The term semiconductor is sometimes used synonymous with IC.

Wafer - a thin slice of silicon, the substrate used in producing integrated circuits (ICs).

Wafer fab - the clean room manufacturing area where wafers are processed to produce integrated circuits (ICs).


PHOTOMASK COMPOSITION

Alignment mark - A reference mark or series of marks used in the alignment of the various photomask layers required for a single device

AR - Abbreviation for anti-reflective coating., as applied with special coating techniques after a pattern has been applied (not to be confused ith LRC)

Array - The arrangement of dies or patterns into rows and columns on a plate for further processing such as dicing, or to just acheive the best yield possible from the materials.

C.D. - see critical dimension

Clear - An area on the plate where the chrome or emulsion has been removed and is transparent.

Clear area - A transparent area.

Clearance - The distance between the nearest edges of elements in the photomask

Chrome - The most popular metallization used for photo glass plates. Chrome metal is sputtered in very thin layers onto a glass substrate, and often has an oxide coating over the top.

Critical Dimension - One part of the pattern (usually the smallest and most vulnerable to the process) is often specified to be the most critical. The size is specified with a tolerance or variance when the pattern is ordered, and this part of the pattern is the to be measured and documented.

Compact – Samll plastic containers in which photomasks are stored and shipped.

Dark area - An opaque area

Dots - Round shapes, in both clear or dark areas.

Fiducials - Patterns, located outside of the array, used to align different layers to one another during wafer fabrication.

Film - The plastic base material used to support photographic emulsions. Often, the terminoplogy can express the base polyester with the emulsion coating on the surface.

Geometry - Intended pattern or image on the photomask.

Glass - A generic term for the substrate medium most widely used in high resolution patterns. The most popular types of glass used are Soda Lime (high thermal expansion) and Quartz ,Fused Silica (lowest thermal expansion)

Image - Any intended structure on a photomask.

Labeling - Information identifying the photomask relative to device , layer, and /or any other pertinent information; usually written outside the photomask array in a vertical or horizontal line

Lines - Relatively long and narrow shapes, in both clear or dark areas.

LRC Chrome - A Chrome photo-mask plate with an Low-Reflective oxide coating deposited on the reflective chrome metal to minimize reflections in the Ultra-Violet range of the spectrum and is widely used with photomasks in Mask Aligners.

Matrix - The set of elements arranged in an array on a photomask (SYN. array)

Pattern - Any set of images forming a part of the artwork or mask. Geometric forms which make up a photomask element.

Resist (syn. photoresist) - a thin photosensitive material used both in the manufacturing of photomasks and wafer fabrication for exposing design images onto a substrate.

Substrate - The underlying material. For chrome materials this refers to the type of glass - for film materials, the polyester base.

Test pattern - A test and /or alignment pattern placed inside an element.

X -axis - Horizontal direction of a photomask.

Y -axis - Vertical direction of a photomask.


PHOTOMASK GENERATION

Artwork - Any set of original images produced by any manual process specifically intended for producing an intermediate or photomask.

AutoCAD - One of the most comnmon computer aided design software tools, used to create the pattern geometry.

CAD - Computer Aided Design; computer aided placement of images to give the desired circuit performance and complying with the required tolerances.

Chemical etching - The dissolution of coating material of a surface by subjecting it to the corrosive action of an acid or alkali

Clean room - Controlled environment facility; facility capable of limiting particulate contaminants and controlling humidity and temperature.

Coating - The covering of a substrate from which the images are created (usually emulsion, chromium, iron oxide, silicon, or chromium oxide)

Data base - The original CAD data that a pattern is designed and generated from.

Develop - To subject exposed photosensitive material to chemical treatment designed to produce an image.

Exposure - Subjecting a photosensitive material to light or other radiant energy.

Exposure Test - An exposure made as part of a process to establish the amount of incident radiation that will produce a satisfactory image; a test of emulsion sensitivity

Gerber - A CAD data type . Gerber data is our standard format for patterning.

GDSII - This is a photo-mask design system format that has used in the industry for many years. The format is very simple but includes powerful array features and embedded patterns.

Image - The working geometry or pattern of a mask. (this is usually the digitized data) Images may be dark or clear.

Lithography (syn. write) - Exposure and processing to pattern the desired images onto a photo sensitive medium such as chrome or film.

Photoresist - A radiation -sensitive material, which when properly applied to a variety of substrates and then properly exposed and developed, selectively masks portions of the substrate with a high degree of integrity.

Photoresist, negative - A photoresist which, after proper application to a substrate, is resistant to removal from the substrate by the developer following exposure to radiation to which it is sensitive.

Photoresist, positive - A photoresist which, after proper application to a substrate, is resistant to removal from the substrate by the developer until it is exposed to radiation to which it is sensitive

Step and repeat (stepping) - the repetitive exposing or placing of a single image in different specified places on the wafer. See also Array

Stripping - A process of completely removing a coating.

Substrate - Underlying structure which forms a base for a coating


PHOTOMASK INSPECTION

Accuracy - Absolute measurement; referenced to an accepted standard with known deviation.

Align - To put in proper relative position or orientation.

Calibration - To adjust an instrument to give the proper reading within a given range of a known accurate standard

Densitometer - A device which measures the amount of light transmitted through a given surface.

Defects - Mask pattern irregularities e.g. opaque spots in clear areas, clear holes in opaque patterns ,etc

Defect density - The number of defects per unit area

Diffraction - The spreading of waves resulting from passage through an aperture or past obstacles.

Diffusion - Spreading of light; can be caused by reflection from an irregular surface.

Flatness - The degree to which the working surface of a substrate is warped or bowed, usually measured relative to some reference point on the surface with the substrate held or mounted in the same manner in which it will be used. Stated in amount of surface variation per lateral distance

Linewidth - Width of an opaque line.

Magnification power - Degree of magnification of a microscope expressed as a ratio of the diameters of image and object (e.g., 10X, 20X).

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 the opacity of a masking medium. A certain optical density may be required to hold backlight with various light sources. Common optical densities used in the photo-mask industry are 2.5 - 4.0, whereby 4.0 is considered opaque to conventional light sources. The tool used to measure O.D. is a densitometer.

Precision - Repeatable measurement; may be inaccurate but each measurement gives results within a stated tolerance of previous measurements.

Reflectance - Amount of light intensity reflected (expressed as a ratio of the reflected intensity to the incident intensity)

Registration - The alignment and positioning of patterns on one layer to corresponding patterns on other layers within the same device.

Resolution - Smallest image that can be clearly discerned with the instrument and technique used

Scan - To systematically examine an area larger than the field of view of the viewing device by moving the field of view sequentially to different areas.

Transmittance - The amount of light passing through a surface (expressed as a ratio of the light intensity passing through to the incident intensity).


PHOTOMASK DEFECTS

Abrasion - A wide scratch or smear of varying opacity.

Adhesion - The ability of a coating to cling to the substrate.

Graininess - Non -uniform spatial opacity on a developed emulsion image. Density variation on a microscale.

Mouse nip - Small area of the coating which is thinner than the surrounding area, usually caused by residue on substrate before coating (SYN. clam shell, pit).

Pinholes - Small holes in the coating allowing transmission of light through an otherwise opaque area. Degree of severity is a function of size, number, and location of holes

Smear - A large area of partially removed coating or deposited foreign material

Bleeding - Poor edge acuity; slowly varying optical density when going from an opaque to clear area; poor edge quality.

Bridging - An extension between two areas of the same image polarity across an intended area of opposite image polarity.

Centrality - The degree to which the array of elements is centered on the substrate

Fdelity - Degree of correspondence of a photomask relative to the original, usually expressed in subjective terms.

Intrusion - A clear area extending into an intended opaque area; unintentional local narrowing of image (ANT. protrusion).

Perpendicularity - The accuracy of the angle between rows and columns conforming to a right angle (90 °).

Protrusion - An opaque area extending into an intended clear area; unintentional local widening of image (ANT. intrusion).

Run -in - A negative cumulative period error.

Run -out - A positive cumulative period error.

Scratch - A line -like cut in the surface of a substrate or its coating.

Scum - Unwanted residue or contamination on a photomask (SYN. density stain, smear).

Spot - A small opaque dot in a clear area.

Torn image - Image broken by movement of coating.

Undercutting - Lateral etching under a coating (between the coating and the substrate).

Visual defects - Defects which can be identified by a skilled observer (with or without the aid of a microscope) without having to make a measurement or comparison (e.g., pinholes, slugs, spots, protrusions, etc.)