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SEMI MF674-0705 © SEMI 2003, 2005 3 8.3 Wax — Glycol pht halate or ot her similar wax having a melting temperature o f less than 150°C. 8.4 Dry Air or Nitrogen — Source of clean, dry air or nitr ogen suitable for dry ing…
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4 Referenced Standards and Documents
4.1 SEMI Standard
SEMI M59 — Terminology for Silicon Technology
NOTICE: Unless otherwise indicated, all documents cited shall be the latest published versions.
5 Terminology
5.1 Definitions
5.1.1 Terms relating to silicon technology are defined in SEMI M59.
6 Summary of Practices
6.1 Silicon specimens are polished using fine-grain diamond compound in a non-aqueous fluid. Polishing of silicon
wafers or other large-area specimens is done against a nonwoven polishing cloth; bevel polishing of small
specimens is done against a frosted lapped glass surface. When polishing is complete, residual polishing compound
is removed by an organic solvent.
FRONT-SURFACE DIAMOND POLISHING
7 Apparatus
7.1 Polishing Machine — Oscillating-tub polisher or other similar small laboratory-scale polishing machine capable
of providing randomized motion of the silicon specimen over the polishing pad.
7.2 Mounting Block and Fixture — To support and apply vertical load to the silicon specimen during polishing.
7.3 Polishing Pad — Nonwoven cloth pad of a texture specified as being compatible with the grain size of diamond
used during polishing. The polishing pad should be adhesive-backed for attaching to a support plate.
NOTE 2: The preferred material is of a type identified as a “chemotextile.”
7.4 Support Plate — Of glass or other similar hard material compatible with the chosen polishing machine and
capable of providing a flat support for the polishing pad during polishing.
7.5 Microscope — Optical microscope having a total magnification of at least 30× and provision for oblique
illumination of the specimen.
7.6 Hot Plate — Capable of heating the sample mounting block and wax to 150°C.
8 Reagents and Materials
8.1 Diamond Slurry — Synthetic or natural diamond with grain size in the range 0.5 to 3 m, inclusive, suspended
in a nonaqueous liquid or paste carrier.
NOTE 3: The predominant causes of variation in the surface finish of the silicon specimen are expected to result from (1) the
uniformity of particle size in the diamond grit, (2) the inclusion of a large fraction of needle-shaped grains (fines) in addition to
the preferred symmetric grains (blocky diamond), and (3) in the case of diamond suspended in paste, the uniformity of the
diamond distribution in the paste. For a fixed diamond grain size, whether the diamond is natural, single-crystal synthetic, or
polycrystalline synthetic should make little difference in the resulting surface finish. However, the abrasive breakdown
mechanisms differ somewhat for the different types of diamond. Consequently, the size and type of diamond should be chosen to
give an acceptable cutting rate for the specimen and machine conditions that are used.
NOTE 4: For use with large-area specimens, the appropriate size diamond grain and, in part, the type of diamond to be used
should be compatible with (1) the starting surface texture of the silicon, which may range from as-sawn to prepolished, and (2)
the load that is applied during polishing.
8.2 Solvent — Suitable nonaqueous solvent for removing diamond slurry subsequent to polishing.
NOTE 5: The choice of solvent is governed in part by the composition of the carrier liquid or paste. The supplier of the diamond
slurry should be consulted regarding the appropriate solvent. Acetone [(CH
3
)
2
CO] and methanol (CH
3
OH) are known to work
well for removing many commercial diamond compounds.
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8.3 Wax — Glycol phthalate or other similar wax having a melting temperature of less than 150°C.
8.4 Dry Air or Nitrogen — Source of clean, dry air or nitrogen suitable for drying the specimen.
9 Procedure
9.1 If not previously done, attach the polishing pad to the rigid plate and place several drops of diamond polishing
slurry at random locations on the polishing pad surface. Spread drops of slurry in a reasonably uniform manner over
the pad so that the pad surface becomes damp and so that there are no freestanding layers of slurry. If the diamond
is suspended in paste, be sparing in the amount of paste applied to the pad.
NOTE 6: Some polishing slurry adheres to the specimen and mounting fixture and is lost every time a specimen is removed and
cleaned. Replenish the slurry on the pad regularly with a few drops of fresh slurry.
9.2 With the hot plate, heat the mounting block to the melting temperature of the wax. Mount the silicon specimen
to the block with the wax. Allow the block to cool to room temperature.
9.3 Assemble the mounting block and attach specimen to the sample mounting fixture and place this assembly on
the polishing pad in the polishing machine.
9.4 In accordance with the manufacturer's instructions for the polishing machine, polish until the specimen surface
exhibits a uniform density of random-direction scratches comparable to the pattern shown in Figure 1. For this test,
remove the polishing slurry from the specimen surface and examine that surface with the microscope.
NOTE 7: The time required to reach a uniform surface finish depends on specimen surface area, size of diamond grains, static
load applied, rate of movement of the specimen surface over the polishing pad, and previous surface finish.
NOTE 8: The coarseness of the scratch damage on the specimen surface is related to the size of diamond grit used.
a. 0.5
m Diamond b. 3 m Diamond
Figure 1
Surface Texture of Large-Area Silicon Specimen Polished with Diamond Against Chemotextile Pad
9.5 When an acceptable surface finish has been reached, thoroughly swab or flush the specimen with the solvent to
remove all diamond slurry residues. Use dry air or nitrogen to blow the specimen surface dry prior to carrying out
any spreading resistance measurements.
DIAMOND BEVEL POLISHING
10 Apparatus
10.1 Glass Plate — Of suitable area for convenient use, which has been given a frosted surface by lapping with a
water slurry of nominal 3 to 12 m aluminum oxide, or similar abrasive, and thoroughly cleaned subsequent to
lapping.
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10.2 Sample Mounting Block and Fixture — For holding the silicon specimen at the desired beveling angle during
the bevel-polishing process.
10.3 Microscope — Optical microscope having a total magnification of at least 30× and a system for illuminating
the stage obliquely.
10.4 Hot Plate, capable of heating the mounting block and wax to 150°C.
11 Reagents and Materials
11.1 Diamond Slurry — Synthetic or natural diamond with a grain size in the range 0.05 to 0.25 m, inclusive,
suspended in a liquid or paste carrier.
11.2 Solvent — Suitable nonaqueous solvent for removing diamond slurry subsequent to polishing (see Note 5).
11.3 Wax — Glycol phthalate or other similar wax having a melting temperature of less than 150°C.
11.4 Wipe, Lint-Free Paper, or Cloth — Suitable for cleaning the glass plate.
11.5 Oil Extender — Compatible with the diamond slurry (see ¶11.1).
12 Procedure
12.1 Prior to beveling each specimen, clean the frosted surface of the glass plate by swabbing with the solvent using
the lint-free wipe.
NOTE 9: Because of the rigidity of the glass surface, excessive damage to the beveled silicon surface can result from
contamination of the polishing slurry with foreign material whose size is larger than that of the diamond grit.
12.2 Apply a small amount of diamond slurry (or paste) to the surface of the glass. Distribute the slurry (or paste)
with a clean flexible metal or plastic spatula or other lint-free applicator so that a thin, uniform film results over an
area whose dimensions are several times larger than the lateral dimension of the fixture used to support the beveling
block. An oil extender may be used to prolong the life of the slurry. The oil extender generally slows the cutting
somewhat and aids lubrication during beveling.
12.3 With the hot plate, heat the mounting block to the melting temperature of the wax. Mount the silicon specimen
to the block with the wax. Allow the block to cool to room temperature.
12.4 Assemble the sample mounting block with specimen attached to the mounting fixture, and place this assembly
on the glass plate. Lower the piston of the polishing fixture carefully and gently onto the glass plate to minimize the
risk of chipping or otherwise damaging the silicon chip.
12.5 Polish the specimen by orbital, figure-eight, or reciprocating movement of the polishing fixture over the glass
plate.
NOTE 10: Use of the above polishing procedure, wherein the specimen and its fixture are moved upon a stationary glass plate,
risks the generation of random deep scratches on the beveled surface due to accumulated coarse debris on the polishing plate. It
has been found that using a rotating glass plate while holding the specimen mounting fixture so that the leading edge of the
beveled chip always faces into the direction of plate rotation reduces the risk. However, if each chip to be beveled is positioned
at the same, or nearly the same, radial distance from the plate's center of rotation, uneven wear of the plate in the form of a
channel, or wide groove, is likely to result. Such channeling of the polishing plate can be minimized or eliminated either by
moving the specimen mounting fixture slowly along the plate radius while polishing, or by choosing a different radial position on
the plate for each chip to be beveled.
12.6 Clean and inspect the specimen periodically to determine whether an adequate amount of specimen surface has
been exposed by beveling (see Note 5).
12.7 Repeat ¶12.5 and ¶12.6 as necessary until an adequate extent of beveled surface is obtained.
NOTE 11: At the beginning of the beveling process an extremely small area of silicon supports the static load of the polishing
assembly, and pressures on the silicon are extremely high. To minimize the possibility of fracture of the edge of the silicon chip,
it has been found advisable to begin bevel polishing with a relatively slow rate of motion of the polishing assembly.
12.8 When the desired amount of specimen surface has been exposed by beveling, thoroughly clean the specimen
by flushing or swabbing with the appropriate organic solvent (see ¶11.2). Inspect the beveled surface for quality of