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Anal. Chem. 1988, 60, 1524-1529
LITERATURE CITED Kennedy, R. T.; St. Claire, 111; R. L., White. J. G.: Jorgenson, J. W. Mlkrochim. Acta 1988, 1967, II, 37-45. Manz, Andreas; Simon, Wlihem J. Chromatogr. 1987, 387, 187-196. Yang, F. J. Chromatogr. 1982, 236, 265-277. Jorgenson, J. W.; Guthrie, E. J. J. Chromatogr. 1983, 255,335-348. Capacci, M. J.; Sepaniak, M. J. J. Liq. Chromatogr. 1986, 9(15), 3365-3376. Graessmann, M.; Graessmann, A. Methods Enzymol. 1983, 101, 482-493. Shabushnig, J. G.; Hieftje, G. M. Anal. Chim. Acta 1981, 126, 167-1 74. Vurek, G. G.; Bowman, R. L. Anal. Chem. 1984, 56, 391A-405A. McCaman, R. E.; McKenna, D. G.: Ono, J. K. Brain Res. 1977, 136, 141-147. Corson, D. W.; Fein, A. Biophys. J. 1983, 4 4 , 299-304. St. Claire, R. L., 111 PhD. Thesis, University of North Carolina at Chapel Hill, Dec. 1986. Guthrb, E. J.; Jorgenson, J. W.; Knecht, L. A,; Bush, S. G. HRC CC, J. Hiah Resolut. Chromatoor. Chromatoor. Common. 1985, 6, 566-567. Knecht, L. A.; Guthrie, E. J.; JOrQWIson, J. W. Anal. Chem. 1984, 56, 479-402.
(14) Weest. R. C. Herhibook of Chemkby and Physics, 61st ed.; CRC Press: Boca Raton, FL, 1980: p 13226. (15) Sternberg, J. C. Advances In Chromtogrephy Volume 2 ; Gddings, J. C., Keiler, R. A., Eds.; Marcel Dekker: New York, 1966; pp 205-270. (16) Karger, B. L.; Martin, M.; Guiochon, G. Anal. Chem. 1974, 4 6 , 1640-1647. (17) Guiochon. G. Anal. Chem. 1983, 35, 399-400. (18) Gluckman, J. C.; Hirose, A.; McGuffin, V. L.; Novotny, M. Chromatographk, 1983, 77, 303-309.
RECEIVED for review December 7,1987. Accepted March 28, 1988. This work was supported by the donors of the Petroleum Research Fund, administered by the American Chemical Society, and the University Research Council of the University of North Carolina. R.T.K. received support from a North Carolina Governor's Board of Science and Technology Fellowship and from an American Chemical Society Analytical Fellowship sponsored by the Society for Analytical Chemistry of Pittsburgh.
Determination of Phosphorus Distribution in the Silicon Dioxide/Silicon Layer System by Secondary Ion Mass Spectrometry Gerhard Stingeder Institute of Analytical Chemistry, Laboratory for Physical Analysis, Technical University Vienna, Getreidemarkt 9/151, A-1060 Vienna, Austria
A measurement technique for quantitative distrlbutlon analysis of phosphorus in the layer system SIOz/SI was developed. Oxygen primary Ions and an increased oxygen pressure (5 X l o 4 mbar) In the sample chamber were used for ellmlnatlon of the matrix effect. Preclse adlustment of the mass spectrometer during depth profiling wRh high mass resolution was controlled by a computer routine. Charging effects were compensated by flooding of the sample wlth electrons, optimized biaslng of the accelerating potential of the secondary ions, and nonnaikatton to a reference stgnal. A detection limit of 1 X lo'@ atoms-cm-8 and an accuracy of f30% were obtained. The improved measurement technique was used for determinatlon of segregatlon coefficlents, whlch are used as Input parameters for process modeilng in metal oxlde semiconductor transistor production.
dopant elements, oxidation, and nitriding). To obtain physical data, suitable experiments have to be developed (see for example ref 1 and 2) and depth distributions of dopant elements have to be determined with high accuracy (3-6). Phosphorus is one of the major n-dopants in silicon. Its diffusion mechanism in silicon is still under intensive discussion (for a review see ref 7). Also, the redistribution in the layer system Si02/Si is of great importance for the optimization of the oxidation process in metal oxide semiconductor (MOS) production. To study the segregation, simultaneous measurements of P in Si02 and Si are necessary. Chu et al. (8) performed quantitative determination of high concentrations of P in borophosphosilicate glass without separation of the interfering SiH and obtained a detection limit of -0.1 atom %. Measurements of the distribution of P with secondary ion mass spectroscopy (SIMS) down to concentrations of 1015 a t ~ c m -are ~ difficult because high mass resolution is necessary to separate the 30Si1Hinterference. In a previous paper we have presented an analytical approach for the quantitative determination of P in silicon with an accuracy of f25% (relative) and a detection limit of 1015 a t ~ c m -(9). ~ In this paper optimization of the measurement technique for quantitative distribution analysis of P in the layer system Si02/Si is presented. This approach is generally applicable to depth profiling with high mass resolution in insulating (poorly conducting) materials. For quantitative measurements the following three requirements have to be fulfilled: (1)precise peak switching of the mass spectrometer between analytical masses and the
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In very large scale integration (VLSI) technology, tolerances of process parameters are decreasing. Process modeling (specifically the simulation of dopant profiles) has become an essential development tool. Due to rapid downscaling in the last few years, process models have to be improved to describe the dopant profiles with sufficient accuracy for integrated circuit manufacturing. Temperature steps (typical temperatures 800-1100 "C) are used in every production process. In order to obtain models with a sound physical base, understanding of the physical processes influencing the diffusion of dopants and self-diffusion is very important (e.g. mutual diffusion of different
0003-2700/88/0360-1524$01.50/00 1988 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 60, NO. 15, AUGUST 1, 1988
1
, r
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I t
'"id-------
I
I 0
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lE
1 M 31 SiH-
P-dM
500
1000
1500
2000 TIME [SI
Figure 1. Depth profiles of 30Si-(reference mass), 30Si'H- (interfer-
ence), 31P-(analytical mass) and at (M(31P)- AM) amu (P - dM; AM = 0.007 82 amu) performed with PSAC every second measurement cycle. Negligible contrlbution of P- to SiH-. I(P - dM) < lo4 X I(P-). Sample preparation: implantation, 100-keV P, 1 X 10" ern-,. Analyticai conditions: 14.5-keV Cs', I = 500 nA, R = 500 X 500 pm2, d , = 60 pm, mass resolution M/&M 4500.
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reference mass, (2) elimination of charging effects, and (3) elimination of the matrix effect.
EXPERIMENTAL SECTION In this work a Cameca IMS 3f secondary ion mass spectrometer was used. For analysis of P in Si, Cs+ primary ions are normally used because the sensitivity is increased by approximately 2 orders of magnitude compared to that of 02+ primary ions (without using an increased oxygen pressure in the vicinity of the sample). In the following paragraphs it will be shown that for analysis in the primary ions have to be used, because layer system Si02/Si, 02+ with Cs+, charging and matrix effects cannot be eliminated sufficiently and thus quantification at the interface is not possible. Peak Switching Autocontrol. Depth profiling with high mass resolution requires the highest standards of instrumentation and optimization of operational conditions and measurement techniques. For precise adjustment of mass peaks a peak-switching autocontrol (PSAC) routine similar to the routines used in isotopic measurements of small inclusions (-10 pm) (10,11) was developed (9). This routine performs an optimized adjustment before measurement and autocontrol of the magnetic field during depth profiling by scanning the magnetic field. To minimize hysteresis effects, the magnetic analyzer is switched -30 times through the roughly adjusted measurement cycle. Afterward, the exact adjustment of the mass scale is performed with the PSAC routine by using the centroid method. During depth profiling, PSAC is performed a t each measurement cycle or with an optional sequence. The routine needs about 3 s. The time delay of the routine has to be taken into account in order to reconstruct a h e a r depth scale. At count rates smaller than -500 counts s-l the routine is not used, because the integration time to determine the correct value of the magnetic field would be too high. For example, Figure 1 shows the profile in which PSAC was performed for every second measurement cycle. The mass dif-
21
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H 30 Si-
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1525
P
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Flgure 2. Influence of a higbdose implantation of As on the diffusion of P. Technoiogical r o w s steps: 30-nm thermal oxide, implantation, 50-keV P, 5 X 101Pcm-2: 100-keV As, 1 X loie cm-2. Annealing: 1000 OC, 10 min, O2i- 3% HCI (60-nm SO2); 1000 'C, 10 min, N,; 400-nm CVD-SO,, 900 'C, 260 min, N,. The oxide layer was etched with HF before measurement.
ference AM between P and SiH is 0.007 82 m u . The background of a mass line at a distance of AM is
