A model is presented to calculate the step coverage of blanket tungsten low pressure chemical vapor deposition (W-LPCVD) from tungsten hexafluoride (WF6). The model can calculate tungsten growth in trenches and circular contact holes, in the case of the WF6 reduction by H2, Sill4, or both. The step coverage model predictions have been verified experimentally by scanning electron microscopy (SEM). We found that the predictions of the step coverage model for the Ha reduction of WF 8 are very accurate, if the partial pressures of the reactants at the inlet of the trench or contact hole are known. To get these reactant inlet partial pressures, we used a reactor model which calculates the surface partial pressures of all the reactants. These calculated surface partial pressures are used as input for our step coverage model. In this study we showed that thermodiffusion plays a very important role in the actual surface partial pressure. In the case where Sill4 was present in the gas mixture trends are predicted very well but the absolute values predicted by the step coverage model are too high. The partial pressure of HF, which is a by-product of the Ha reduction reaction, may be very high inside trenches or contact holes, especially just before closing of the trench or contact hole. We found no influence of the calculated HF partial pressure on the step coverage. Differences between step coverage in trenches and contact holes, as predicted by the step coverage model, were found to agree with the experiments. It is shown that the combination of the step coverage and reactor model is very useful in the optimization towards high step coverage, high throughput, and low WF6 flow. We found a perfect step coverage (no void formation) in a 2 ~m wide and 10 i~m deep (2 x 10 i~m) trench using an average WF6 flow of only 35 sccm, at a growth rate of 150 nm/min. In general, it is shown that the reduction ofWF 6 by SiH~ offers no advantages over the reduction by H2 as far as step coverage is concerned.

Ksurf. 0 = le-6 Ksurf. E = 0; vacan silicon/gas Ksurf. 0 = le-6 Ksurf. E = 0.We have set the value of the recombination constant, not applicable to FINDPRO, Eq.[15]: inter silicon Kr. 0 = le-12 Kr. E = 0; vacan silicon Kr. 0 = le-12 Kr. E = 0. In fitting the data for Fig. 1, the only fitting parameters have been/(i, ~p, Dl~ and the electrically active portion of the total P which we have taken to saturate at 2.5 x 1020 cm -3. We set the solubility of P in SUPREM-IV above this phos ss. temp = 874 ss. conc = le21We set the transfer coefficient for P from the gas to Si at a high value phos silicon/gas Trn. 0 = le3 Trn. E = 0 Finally, we eliminated the traps from SUPREM-IV trap silicon total = 0 frac. 0 = 0 In both programs the 1-D mesh was set to extend at least to 60 microns, a point at which, for these parameters, I did not increase from its initial equilibrium value I0. REFERENCES 1. a. R. W. Knepper, S. P. Gauer, F.-Y. Chang, and G. R.Srinivasan, IBM J. Res. Dev., 29, 218 (1985).b. G. P. Ho, J. D. Plummer, S. E. Hansen, and R. W.Dutton, IEEE Trans. Electron Devices, ED-39, 1438ED-39, (1983.2. S. M. Hu, J. Appl. Phys., 57, 4527 (1985). 3. S. M. Hu, P. Fahey, and R. W. Dutton, ibid., 54, 6912 (1983).4. T. Y. Tan, U. G6sele, and F. F. Morehead, Appl. Phys., A31, 97 (1983).5. D. Mathiot and J. C. Pfister, J. Appl. Phys., 55, 3518 (1984).6. M. Orlowski, Appl. Phys. Lett., 53, 1323Lett., 53, (1988. 7. M. R. Kump and R. W. Dutton, IEEE Trans. ComputerAided Design, 7, 191 (1988 Lett., 53, 1917 (1988 Ot \ Ox ~ ] \--~x /where K = e~, ~/= F/RT, and 9 is the electric field strength, dr In the original version, 9 was defined as -dr and the signs before the last terms in Eq.[12] and [13] are opposite to those printed above. However, all subsequent equations are correct and the findings of the work are unchanged.In the paper "Transport Phenomena in Tungsten LPCVD in a Single-Wafer Reactor," by C. R. Kleijn, C. J. Hoogendoorn, A. Hasper, J. Holleman, and J. Middelhoek [This Journal, 138, 509-517 (1991)] the following corrections should be made:In the 5th and 6th lines of the Abstract and in the 8th line of the right column on page 513 "with the WF6 inlet pressure" should read "with decreasing WF~ inlet pressure."In the left column of page 510, the reference in the 22nd line from the bottom should be (41).In In the caption for Fig. 4, "mole predictions" should be "model predictions."In the List of Symbols, the unit g should be in m -s-2; I should be I, vin should be v~., and superscript c should be C.In Ref. (1,4,15,17, 43), B. Blewer should be R. S. Blewer.In the paper "Modeling Calculations of an AluminiumAir Cell" by Kwong-Yu Chan and Robert F. Savinell [This Journal, 138, pp. 1976-1984(1991] in Table I, column 1, 5m = 1 should be ~k m -'~ 1; in column 2, 5p = 1 should be k~ = 1 and E~ q should be E~ q = -0.9058 V; and in column 3 ir in A/cm 2, ~c in volts.

The influence of the WF~ concentration on the growth rate in tungsten LPCVD from WF6 and H2 has been studied both experimentally in a coldwall single-wafer reactor and with the use of a mathematical simulation model, predicting the gas flow, heat transfer, species transport, and chemical reactions in the reactor. Model predictions were in very good agreement with experimental growth rates and uniformities. The growth rate was found to be independent of the WF6 inlet pressure above a certain value Petit, whereas for WF6 inlet pressures below Pcr,t the growth rate decreases linearly with the WF6 inlet pressure. It is shown that this transition is due to mass-transfer limitations rather than a change in the reaction mechanism. The value of Petit depends on the reactor geometry and process conditions and may be obtained experimentally or from model simulations as presented in this study. It is shown that large concentration gradients may be present in CVD reactors, even at low reactant conversion rates, and that criteria for "gradientless" reactor operation based on conversion rates are incorrect. We propose a better criterion, based on the value of Pcrit. It is also shown that thermal diffusion phenomena in coldwall reactors are very important. As a result, WF6 concentrations at the wafer surface will al~vays be significantly lower than the inlet concentration.