Lithography the process by FKij3B

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									                                   Glossary of Selected Terms
                     (defined in the context of micromechanical machining)

       Ablation - the removal of a material by adding heat and turning it to vapor, such as laser
       ablation

       Amplitude Ratio - in the study of a dynamic system influenced by a force, it is the ratio
       of [the steady-state amplitude of vibration of the system due to a time-varying exciting
       force] divided by [the static displacement of the system had it been influenced by a
       constant force of the same maximum amplitude as the dynamic force]. For example, if a
       spring-mass system is excited by a dynamic force, F = 20 sin(wt), it will come to some
       steady-state amplitude (maximum displacement) of vibration. The static displacement
       for the system is its equilibrium position from rest had it been subjected to the constant
       force F = 20. Amplitude ratio is used to study the vibration of a spindle, for example,
       which has an imbalance causing a dynamic and periodic force on the rest of the machine
       tool.

Analog - varying continuously without instantaneous changes

Angstrom - a unit of length equal to one ten-billionth of a meter, the spacing of atoms in solids is
      typically a few Angstroms

Atomic Force Microscope - one of the class of scanning probe microscopes which uses a small
      cantilever with a pyramidal point to interact with the surface of a sample. The deflection
      of the cantilever at the tip as it is scanned across the sample surface is measured and used
      to indicate surface topography, the AFM utilizes the attractive or repulsive forces
      between the tip and the sample to deflect the cantilever. The deflection of the cantilever
      is measured by the change in location on a split-type optical detector of a laser beam
      reflected off the back side of the cantilever.

       Cantilever Beam - a structural member which is constrained from rotation and translation
       at one end, and is free at the other.

       Chisel Edge - the apparent point of a drill, it is actually a cutting edge with a length some
       fraction the diameter of the drill. The chisel edge cuts with a very large negative rake
       angle.

       CNC - computer numerical control, usually refers to machines which operate under
       closed-loop control by means of a programmed computer

Coupled Motions - motions which are not independent of each other, motions whereby one
      motion will cause some movement of another portion of the structure (machine), present
      in many mechanisms

Cutting Force - one component of the machining force, acting along the line of action of the
       cutting speed
       Cutting Speed - the relative speed between the cutting edge of a tool and the uncut work
       material just ahead of the cutting edge

       Cutting Tool - the portion of a machine tool which has edges designed to shear the work
       material. The cutting tool is normally replaceable and can be made of different materials
       such as steel, diamond, carbides, etc depending on the application.

       Damped Natural Frequency - in the study of a dynamic system, it is the steady-state
       frequency of vibration of a system with damping. If the damping is large (over-damped)
       the system will not freely oscillate after an excitation ceases. If the damping is critical,
       the system will return to its rest position in the shortest possible time. If the system is
       under-damped, it will freely oscillate for some period of time at the undamped natural
       frequency. Therefore, this frequency depends not only on the mass and elastic
       characteristics of the system but also on the damping present.

       Deadband - in a feedback device, it is a zone where a small motion will not be
       represented by a change in the output, it is an increment of motion smaller than the
       resolution of the encoder, for example. It is more formally referred to as hysteresis.

Degree of Freedom - an independent motion (rotation or translation) of a mechanism

       Determinism - the philosophy whereby all actions which obey physical laws should be
       quantified and predictable, a philosophy whereby apparent randomness should be
       explainable and predictable

       Diamond Machining - machining with diamond (natural, polycrystalline, or synthetic) as
       the cutting tool material, generally refers to a single cutting edge, not grinding

       Digital - signals or states which have discrete values and do not vary continuously,
       opposite of analog

Displacement Transmissibility - see Transmissibility Ratio

       Edge Sharpness - the radius of the cutting edge of a cutting tool at the intersection of the
       rake face and the flank surface

Electron Beam Lithography - exposing a photoresist with electrons, it generally scans the
       electron beam across the photoresist in a programmed pattern, capable of very high
       resolution by varying the electron dose along pattern edges (referred to as proximity
       correction)

       Encoder - a feedback device, analog or digital, which provides an indication of motion,
       rotary or linear, potentiometers can be used as an analog encoder providing a
       continuously varying voltage output with position, an opaque glass scale with
       transparent slits can act as a digital encoder providing discrete pulses as position changes
       Energy Model - a method of estimating the cutting force and thrust force in machining
       based on the energy required to remove a given volume of work material

Euler Column - a slender column and one which is regarded as the weakest type of column

       Feed - the distance a cutting edge moves per revolution of the tool or work piece in
       machining, used to calculate the volume of material removed, sometime referred to as the
       tooth loading

       Feedrate - the distance a cutting edge moves in a given time, to calculate the feed the
       rotational speed of the tool or work piece must also be known

       Fixture - a structure used to securely hold a work piece during machining, the fixture is
       normally clamped to the machine tool and should not induce deformation into the
       material to be machined

       Fluence - the area energy density in laser micromachining, usually expressed in Joules
       per square centimeter, or per micrometer

       Focused Ion Beam - a method for atomic-scale machining where ions (typically gallium)
       are accelerated and focused and steered onto the work piece, all in a high vacuum, work
       piece atoms are ejected by the kinetic energy and subsequent scattering by the incident
       ions

       Frequency Ratio - in the study of a dynamic system, it is the ratio of [the frequency of
       the forcing function, force or displacement] divided by [the undamped natural frequency
       of the system]. A frequency ratio near unity can lead to large amplitudes of vibration.

       Friction Angle - the inverse tangent of the coefficient of friction between materials, in
       machining it is normally the inverse tangent of the kinetic coefficient of friction between
       the cutting tool rake face and the chip of work material leaving the cutting zone, the value
       can be altered by the presence of cutting fluids, etc

       Heat Affected Zone - the immediate region around a thermal machining process (laser
       ablation, electrical discharge machining, etc) where the mechanical properties of the
       work material are changed by rapid cooling (quenching), usually makes work material
       locally more brittle

       Interferometer - a device for measuring the displacement of an object using the
       interference of light, the beam from an optical source (usually laser) is split into a
       reference leg and a measurement leg, then recombined to form an interference (phase
       difference) pattern, as the optical path length of the measurement leg changes, the
       interferogram changes and can be measured, heterodyne-type interferometers use the
       Doppler shift in an optical beat- frequency for velocity measurement which is integrated
       to get displacement
       Lithography - the process, similar to printing a photograph, where energyby is selectively
       passed or blocked by a mask transferring the mask pattern into an energy sensitive
       material, the type of lithography is named based on the type of energy used (optical
       wavelengths, ultraviolet, x-ray, etc).

       Machine Tool - the entire structure, actuators, feedback devices, and controllers used to
       hold a work material, the cutting tool, and provide all motions and rigidity to fulfill a
       machining operation

Machining Forces - in general, all the forces and torques on the cutting tool, machine tool, and
      work piece as a result of material removal

       Mandrel - a circular structure, in microdrilling the polished portion of the drill which
       rides against the vee-block bearings and is integral with the microdrill

Mechanistic Model - a machining force model based on solid mechanics and the equilibrium of
     forces and torques, rather than energy for material removal

       Microdrilling - no formal size defines microdrilling but is generally in the sub-millimeter
       range and requires the use of a vee-block to reduce eccentricity of the drill

       Micrometer - one-millionth of a meter, visible light has a wavelength of approximately
       0.5 micrometers

       Micromilling - no formal size defines micromilling but is generally in the sub-millimeter
       range and may or may not use a vee-block, larger micromilling must be done with the
       tool held in a collet due to bending load on the tool end, the load would cause a vee-block
       mounted milling tool to loose contact with the bearing surfaces

Millimeter - one-thousandth of a meter, approximately 0.039 inches

Nanometer - one-billionth of a meter, or 10 Angstroms

       Nose Radius - for a cutting tool, the radius of the cutting edge which forms the shape of
       the tool, not the edge sharpness, a larger nose radius generally results in smoother
       surfaces for similar machining conditions

       Orthogonal - mutually perpendicular for axes, in machining a condition where the
       direction of the chip motion is not perpendicular to the cutting edge

       Photoresist - the energy-sensitive material into which the mask pattern is transferred by
       incident energy (also called resist)

       PMMA - polymethyl methacrylate (also called plexiglas), a material used as an x-ray
       photoresist and commonly in injection molding replication of microstructures, it is an
       excellent material for micromechanical machining
       Point Angle - the angle at the end of a drill which forms the chisel edge, standard point
       angle of 118 dgerees or 135 degrees for harder materials are most common

       Polymerization - the process whereby energy is used to solidify a photopolymer, such as
       laser polymerization

       Rake Angle - the angle between the normal to the cutting speed direction and the rake
       face of a cutting tool, if the rake face tilts toward the incoming work material the sign of
       the rake angle is negative, rake angle strongly affects the magnitude of the machining
       forces

       Resist - the energy-sensitive material into which the mask pattern is transferred by
       incident energy (also called photoresist)

       Resonance - in the study of a dynamic system, resonance occurs when the forcing
       function, force or displacement, has a frequency equal to the undamped natural frequency
       of the system. If there is no damping present in the system to remove energy, the
       displacement of the system will increase. This build-up of displacement requires time so
       excessive displacements can be avoided if the input frequency is not allowed to remain
       equal to the undamped natural frequency.

Scanning Tunneling Microscope - one of the class of scanning probe microscopes which uses a
      relatively small wire in very close proximity to a sample surface with a small electrical
      potential difference causing electrons to jump across the gap (tunneling current), the wire
      is moved vertically as it scans across the surface to maintain a constant tunneling current,
      the vertical motion is mapped to provide an indication of the electrochemistry of the
      surface

Scanning Electron Microscope - a microscope which operates similar to a cathode ray tube,
      electrons are focused and scanned across a sample causing electrons to be released from
      the surface, the electrons are gathered and converted to an electrical signal proportional to
      the number and energy of the liberated electrons, this signal is sent to a synchronized
      CRT display where an image of the surface is built by rastering of the incident and
      display beams

Scanning Probe Microscope - a class of microscopes based on a thin cantilever used to measure
      deflection due to surface roughness, surface mechanical, electrical, magnetic, etc
      properties, using a bi-morph cantilever very small temperature changes can be detected, if
      caused to vibrate very small masses can be measured, for example

       Shear Plane Angle - the approximate plane along which the chip is separated from the
       work material in a cutting operation, the angle is measured from the line of action of the
       cutting speed

Spade Drill - a type of drill which does not have spiral flutes to help remove chips from a hole
      being drilled, due to the complex geometry of a twist drill they are not available smaller
       than 50 micrometers in diameter, a spade drill is made of intersections of planes which
       can be ground and polished at very small sizes

       Specific Cutting Energy - the experimentally measured amount of energy needed to
       remove a unit volume of work material, it also has the same units as the power required
       for a volumetric removal rate of work material, it also has the units of stress or pressure
       so it is sometimes called cutting pressure

Structural Loop - the structure of a machine tool which has a common point at the interface of
       the cutting edge of the cutting tool and the newly generated surface of the work material,
       the loop starts at the cutting edge goes through the tool, tool holder, kinematic slides and
       spindles, the structure of the machine, and back into the work piece

       Synchrotron - a device used to generate a high energy collimated beam of x-rays used in
       deep x-ray lithography, see for example: www.nsls.bnl.gov/ ; www.src.wisc.edu/ ;
       www.tn.cornell.edu/

       Thrust Force - the component of the machining forces which is perpendicular to the
       cutting force and the line of action of the cutting speed, the thrust force normally tries to
       separate the cutting edge of the tool from the newly generated material surface

       Transmissibility Ratio - in the study of a dynamic system influenced by a displacement
       of the boundary to which the system is attached through spring(s) and damper(s), it is the
       ratio of [the steady-state maximum amplitude of vibration of the system] divided by [the
       maximum amplitude of displacement of the boundary]. For example, if the floor under a
       precision machine tool is vibrating with a function described by Y = 5 cos(wt) due to a
       another nearby piece of machinery, then the maximum amplitude of steady-state
       vibration of the spindle of the precision machine tool (X) will be the maximum amplitude
       of the boundary displacement Y = 5, times the transmissibility ratio.

Twist Drill - a drill having helical flutes to help remove chips from the drilled hole, the type of
       drill commonly found in machine shops

       Undamped Natural Frequency - in the study of a dynamic system, it is the frequency at
       which the system will prefer to freely vibrate (with no external periodic excitation) due to
       its mass and elastic characteristics. For a simple spring-mass system with no damping
       (all materials have some internal damping), the undamped natural frequency is given by
       the square root of {K / M} where K is the spring constant and M is the suspended mass.
       The undamped natural frequency is usually referred to as the natural frequency (opposed
       to the damped natural frequency).

       Vee-Block - a type of bearing whereby the drill or milling tool is supported by four
       contact pads, it is a centerless-type chucking arrangement which, so long as the drill was
       ground in a vee-block, eliminates virtually all eccentricity in rotation

       Warpage - in spindles an eccentric motion causes by the fact that the spindle is bent, in
an air spindle differential temperature in and on the spindle surface can cause differential
expansion or contraction which will cause the spindle to bend

Windage - in air spindles the aerodynamic effect of turbulence around a face plate or
chuck attached to the spindle, air spindles have lower stiffness than mechanical bearings
and aerodynamic forces on the rotating faceplate can cause the spindle to rotate
eccentrically

								
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