Influence of AsH[sub 3], PH[sub 3],and B[sub 2]H[sub 6] on the Growth Rate and Resistivity of Polycrystalline Silicon Films Deposited from a SiH[sub 4]-H[sub 2] Mixture

Abstract

The deposition rate of polycrystalline silicon from a SiH4-H2 mixture is significantly influenced by the addition of ASH3, PH3, and B2H6. At a deposition temperature of 680~ AsH3 causes a decrease by a factor of 7, PH3 causes a decrease by a factor of 2.5, while a two times higher deposition rate is obtained with B2H6 addition. Out of these three dopant hydrides AsH~ and PH3 do not affect the activation energy of the deposition reaction compared to undoped growth (37 kcal/mole). The Arrhenius plot for the deposition of silicon from a B2H6-SiH4 mixture shows two activation energies: 20 kcal/mole at T = 620~176 and 7 kcal/mole below 620~ The experimentally found minimum values of the resistivity of doped polycrystalline silicon can be explained in terms of solid solubility and carrier mobility. At deposition temperatures below 700~ with and without addition of dopants the polycrystalline silicon surface is mirror-like. Significant differences have, however, been observed by electron microscopy. Compared to undoped growth boron was found to lower the etch rate of the polycrystalline silicon film markedly.Increasing interest is being shown in the use of polycrystalline silicon in silicon device technology. The application of polycrystalline silicon films is compatible with silicon device processing where polycrystalline silicon is mainly used as gate material in MOS structures (1) (self-aligned gate).Polycrystalline silicon can be deposited in different ways: by evaporating, by sputtering, and by chemical vapor deposition. Chemical vapor deposition is superior because it permits uniform deposition over oxide steps. To obtain a mirror-like surface, which enables very fine patterns to be etched in it, comparable with those in silicon oxide, the grain size of the polycrystalline silicon film should be as small as possible. DeLuca (2) has found that the grain size of the polycrystalline silicon film decreases with decreasing temperature. However, the deposition rate also decreases with decreasing temperature. At 650~176 an acceptable compromise between growth rate and grain size is realized. In this temperature region most polycrystalline silicon films suitable for high resolution I.C. processing are grown.In the case where polycrystalline silicon is used as the gate material for MOS structures, it may be deposited undoped and subsequently doped by impurity diffusion. In the case where design considerations prohibit high-temperature processing after polycrystalline silicon deposition, doping by codeposition becomes necessary.The present paper reports on the growth of doped polycrystalline silicon films by codeposition of silicon and either arsenic, phosphorus, and boron from the corresponding hydrides using hydrogen as a carrier gas. In particular the temperature dependence of the growth rate was studied. The effects of deposition temperature and dopant concentration on growth rate and resistivity are discussed. ExperimentalThe polycrystaUine silicon films were prepared in an uncooled vertical reactor. The substrates wer...

Influence of the Doping Gas on the Axial Uniformity of the Growth Rate and the Electrical Properties of LPCVD In-Situ Doped Polysilicon Layers

“…Concerning the resistivity, Ap/p(x) is 40 %, 60 %%, 55 % and 20000 % for the same pressures. Secondly, as mentionned by several authors who have studied the incorporation of boron in polysilicon with the couple of gas @2&,S@), we observe that the growth rate of boron doped films is higher than those of undoped f k s [7,8]. This exaltation effect of diborane seems to be quite dependent on the total pressure since the variation of V, with TO is strongly different in all cases.…”

“…at x = 4 cm, the maximum variation of Vg are 20 %, 100 %, 150 % and 20 % for 1, 10, 30 and 90 Pa respectively. In fact, the dopant element boron is assumed to be the exalting factor of the growth rate [8]. So, it appears that the total pressure plays an important role in the heterogeneous and homogeneous reactions that occur when diborane and silane come in the hot zone, and this leads to a deposition or a "disappearance " of boron.…”

Effect of diborane on the microstructure of boron-doped silicon nanowires

“…The addition of B 2 H 6 has previously been reported to result in an increased growth rate of Si thin films grown by CVD [9], plasma-enhanced CVD (PECVD) [7,8] and low-pressure CVD (LPCVD) [10][11][12] using SiH 4 as the Si source. In particular, for LPCVD growth of Si at 550 1C, the growth rate enhancement with B 2 H 6 became significant when the boron concentration in the film exceeded a threshold of about 10 19 cm À3 [12], which is similar to the boron levels measured in the highly doped SiNWs.…”

“…A growth-rate enhancement is observed frequently when B 2 H 6 is used as a dopant in Si thin-film chemical vapor deposition (CVD) [9][10][11][12]. Intentional doping of SiNWs, however, is fundamentally different from CVD since the growth is via a vapor-liquid-solid (VLS) mechanism.…”

Arsenic Doping of Chemical Vapor Deposited Polycrystalline Silicon Using SiH4 ‐ H 2 ‐ AsH3 Gas System

“…Next, the mass transport of As atoms in gas phase is considered, assuming a model analogous to that for the deposition of Si epitaxial layer (12, 13). Then, the number of As atoms (nT) transported towards the wafer surface per square centimeter per second is nT = ~(nl --n2) [3] May 1980 nl = PAsHa(i)/kT [4] n2 --[PAs (s) + 2PAs2 (s) -~-4PAsd(S)]/kT [5] where it is also assumed that all the transfer coefficients of As-containing species have the same value and that As molecules, As2 molecules, and As4 molecules are the most abundant As-containing species at the wafer surface, but the other As-containing species such as AsHa molecules are not. ~ is the transfer coefficient for As atoms in H2; nl and n2, the number of As atoms introduced into the reactor and that existed at the wafer surface, respectively.…”