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SEMI MF1366-0305 © SEMI 2003, 2005 3 6.1.1 Specimens of single crystal silicon (on e float-zone silicon specimen, two calibration specimens, and the test specimen) are loade d into a sam ple holder. 6.1.2 The holder with…

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SEMI MF1366-0305 © SEMI 2003, 2005 2
3.3 There are no effects upon the oxygen ion yield from the dopants for dopant densities less than 1 × 10
20
atoms/cm
3
.
2
3.4 The SIMS oxygen instrumental background as measured on the float zone silicon specimen should be as low as
possible and stable before the analyses are begun.
3.5 The specimen surface must be flat in the specimen holder windows so that the inclination of the specimen
surface with respect to the ion collection optics is constant from specimen to specimen. Otherwise, the accuracy and
precision can be degraded.
3.6 The accuracy and precision of the measurement significantly degrade as the roughness of the specimen surface
increases. This degradation can be avoided by using chemical-mechanical polished surfaces.
3.7 Variability of oxygen in the calibration standards can limit the measurement precision.
3.8 Bias in the assigned oxygen of the calibration standards can introduce bias into the SIMS measured oxygen.
4 Referenced Standards
4.1 SEMI Standards
SEMI MF43 — Test Methods for Resistivity of Semiconductor Materials
SEMI MF723 — Practice for Conversion between Resistivity and Dopant Density for Arsenic-Doped, Boron-
Doped, and Phosphorus-Doped Silicon
SEMI MF1188 — Test Method for Interstitial Atomic Oxygen Content of Silicon by Infrared Absorption
4.2 ASTM Standard
E 122 — Practice for Choice of Sample Size to Estimate a Measure of Quality for a Lot or Process
3
NOTICE: Unless otherwise indicated, all documents cited shall be the latest published versions.
5 Terminology
5.1 Definitions
5.1.1 IOC-88 — calibration factor
4
for infrared absorption measurements of oxygen in silicon that gives a value
equivalent to that found by the SIMS method.
5.1.2 ion mass spectrometry — the separation and counting of ions by their mass-to-charge ratio.
5.1.3 primary ions — ions created and focussed by an ion gun onto the specimen surface to sputter ionize surface
atoms.
5.1.4 secondary ions — ions that leave the specimen surface as a result of the primary ion beam sputter ionizing the
specimen surface atoms.
5.1.5 secondary ion mass spectrometry — mass spectrometry performed upon secondary ions from the specimen
surface.
6 Summary of Test Method
6.1 SIMS is utilized to determine the bulk concentration of oxygen in single crystal silicon substrate.
2 Bleiler, R. J., Chu, P. K., Novak, S. W., and Wilson, R. G.,“ Study of Possible Matrix Effects in the Quantitative Determination of Oxygen in
Heavily Doped Czochralski Silicon Crystals,” Seventh International Meeting on Secondary Ion Mass Spectrometry, SIMS VII (John Wiley and
Sons, 1990), p. 507.
3 Annual Book of ASTM Standards, Vol 14.02, ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428. Telephone: 610-
832-9500, Fax: 610-832-9555, Website:
www.astm.org
.
4 Baghdadi, A., Bullis, W. M., Croakin, M. C., Li Yue-zhen, Scace, R. I., Series, R. W., Stallhofer, P., and Watanabe, M., “Interlaboratory
Determination of the Calibration Factor for the Measurement of the Interstitial Oxygen Content of Silicon by Infrared Absorption,” J.
Electrochem. Soc. 136, 2015–2034 (1989). Baghdadi, A., Scace, R. I., and Walters, E. J., “Semiconductor Measurement Technology: Database
for and Statistical Analysis of the Interlaboratory Determination of the Calibration Factor for the Measurement of the Interstitial Oxygen Content
of Silicon by Infrared Absorption,” NIST Special Publication 400-82, July 1989.
SEMI MF1366-0305 © SEMI 2003, 2005 3
6.1.1 Specimens of single crystal silicon (one float-zone silicon specimen, two calibration specimens, and the test
specimen) are loaded into a sample holder.
6.1.2 The holder with the specimens is baked at 100°C in air for 1 h and then transferred into the analysis chamber
of the SIMS instrument.
6.1.3 A cesium primary ion beam is used to bombard each specimen. The negative secondary ions are mass
analyzed.
6.1.4 The specimens are presputtered sequentially to reduce the instrumental oxygen background.
6.1.5 The specimens are then analyzed, in locations different from the presputtering locations, for oxygen and
silicon in a sequential manner throughout the holder. Three measurement passes are made through the holder.
6.1.6 The ratio of the measured oxygen and silicon secondary ion intensities (O
/Si
) is calculated for each
specimen.
6.1.7 The relative standard deviation (RSD) of the ratio is then calculated for each specimen.
6.1.8 If any specimen other than the float zone specimen has a RSD of the ratio greater than 3%, more analyses are
performed.
6.1.9 The SIMS average O/Si ratios are then converted to infrared-equivalent concentrations by utilizing either the
load-line calibration method
5
,
6
or the load factor calibration method
2
with the calibration specimens in the load.
7 Apparatus
7.1 SIMS Instrument, equipped with a cesium primary ion source, electron multiplier detector and Faraday cup
detector, and capable of measuring negative secondary ions.
7.1.1 The SIMS instrument should be adequately prepared (that is, baked) so as to provide the lowest possible
instrumental background.
7.2 Cryopane1, liquid nitrogen- or liquid helium-cooled, which surrounds the test specimen holder in the analysis
chamber.
7.3 Test Specimen Holder.
7.4 Oven, for baking test specimen holder.
8 Sampling
8.1 Since this procedure is destructive in nature, a sampling procedure must be used to evaluate the characteristics
of a group of silicon wafers. No general sampling procedure is included as part of this test method, because the
most suitable sampling plan will vary considerably depending upon individual conditions. For referee purposes, a
sampling plan shall be agreed upon before conducting the test. See ASTM Practice E 122 for suggested choices of
sampling plans.
9 Specimen Requirements
9.1 Sample specimens must be flat and smooth on the side used for analysis.
9.2 Sample specimens must be cleaved or diced to fit within the sample specimen holder.
10 Calibration
10.1 The two calibration standards in each load must be lightly doped Czochralski silicon
7
in which the oxygen
concentration is measured by infrared absorption spectroscopy (see SEMI MF1188), and the measured values of the
5 Goldstein, M., and Makovsky, J., “The Calibration and Reproducibility of Oxygen Concentration in Silicon Measurements Using SIMS
Characterization Techniques,” Semiconductor Fabrication: Technology and Metrology, ASTM STP 990, Dinesh C. Gupta, Ed. (ASTM, 1988) pp.
350–360.
6 Makovsky, J., Goldstein, M., and Chu, P., “Progress in the ‘Load Line Calibration’ Method for Quantitative Determination of [O] in Silicon by
SIMS,” Seventh International Meeting on Secondary Ion Mass Spectrometry, SIMS VII (John Wiley and Sons, 1990) p. 487.
7 Czochralski silicon is available from most silicon substrate suppliers.
SEMI MF1366-0305 © SEMI 2003, 2005 4
two standards bracket the expected values for the test specimen (that is, one calibration standard is higher in oxygen
and one is lower, compared to the expected value in the test specimen).
10.2 The calibration standards must be measured by infrared absorption to determine the concentration and
homogeneity of the oxygen within the standards; each standard is assigned the averaged infrared absorption oxygen
value (IOC-88) for the substrate.
10.3 Calibration standards that are included in the SIMS analyses must be taken from that portion of the wafer that
provided a homogeneous measurement in the Fourier transform infrared (FT-IR) spectrophotometer analysis; this
portion is typically the central portion of the wafer.
10.4 Each calibration standard specimen must be the same size and have the same polished surface as the test
specimen.
10.5 The float zone specimens that are included in the SIMS analysis to measure the instrumental oxygen
background must be measured by infrared absorption to determine if the oxygen concentration is low enough to
measure the instrumental SIMS background. Oxygen concentrations below 0.5 ppma in the float zone specimen are
normally sufficient.
10.6 Each float zone specimen must be the same size and have the same polished surface as the test specimen.
11 Procedure
11.1 Specimen Loading
11.1.1 Load the specimens into the SIMS sample holder, checking to see that the specimens are flat against the
backs of the windows and cover the windows as much as is possible. A specimen load includes one float zone
silicon specimen, two or more standard specimens, and the test specimen.
11.1.2 Bake the loaded sample holder at 100C ± 10°C for a minimum of 1 h in air.
11.2 Instrument Tuning
11.2.1 Turn on the instrument in accordance with the manufacturer’s instructions.
11.2.2 Fill the liquid nitrogen or helium cold trap.
11.3 Analytical Conditions
11.3.1 Use a cesium primary ion current and focus, which maximizes the ion count rate for an appropriate silicon
isotope.
11.3.2 Typical analytical conditions are a 250 m by 250 m raster and 1-s integrations. Choose apertures to keep
the oxygen count rate on the electron multiplier detector below 1 × 10
5
counts per second for the test specimen.
11.4 Analysis of Specimen
11.4.1 Position the specimen holder so that the sputtered crater in the specimen will form near the center of the
window.
11.4.2 Center the primary ion beam and begin a SIMS profile.
11.4.3 Repeat ¶11.4.1 and ¶11.4.2 for all the specimens in the holder until all the specimens have been presputtered.
This is called a presputtering round and is intended to reduce the instrumental oxygen background. No oxygen data
are taken or used from these profiles.
11.4.4 Now make a second round of measurements on all the samples according ¶11.4.1 and ¶11.4.2, but in
locations near the presputtered craters of the specimen. Do not make the second round of measurements in the same
craters as the presputter craters.
11.4.5 At the end of each profile in the second round of craters, measure and record the
16
O
count rate on the
electron multiplier detector and the
30
Si
, or other Si isotope as appropriate, matrix ion count rate on the Faraday cup
detector.