Valakh, B. N. Romanyuk, I. V. Rudskoy, and V. V. Stre|chuk. Institute of Semiconductors, Ukrainian Academy of Sciences, Prosp. Nauki 45,. SU-252650 Kiev-28, ...
Appl. Phys. A 51,264--267 (1990)
Applied Physics A Surfaces "" © Springer-Verlag 1990
Raman Spectroscopic Studies of Planar Gettering Effects V. V. Artamonov, M. Ya. Valakh, B. N. Romanyuk, I. V. Rudskoy, and V. V. Stre|chuk Institute of Semiconductors, Ukrainian Academy of Sciences, Prosp. Nauki 45, SU-252650 Kiev-28, USSR Received 20 May 1989/Accepted 22 February 1990
Abstract. Raman scattering spectroscopy is used to study the elastic stress distribution in the epitaxial silicon operating areas in the vicinity of planar getter areas, the latter being created by previous ion implantation of the substrate. Data concerning the effect of the operating element size and the dose of implantation into the getter area are obtained. The results are compared with those of X-ray topographic analysis of the structures. PACS: 78.30.Gt
Various methods of point defect and impurity gettering are now widely used in studies of silicon and integrated circuits (IC) technology [-1, 2]. During the epitaxial growth of Si films, the gettering suppresses the growth of packing defects, or at least reduces their number. For this purpose damage is usually applied to the rear side of the wafer by means of grinding, argon ion bombardment with subsequent annealing in NE atmosphere, covering by SiaN 4 film etc. The techniques of getter formation on the operating side of the wafer (so-called planar gettering) [3] are of special interest. In this ease the growth of the epitaxial Si film is continuously affected by surface getter areas located outside the IC active areas. The latter fact enables the gettering time to be reduced, provides conditions for rapid surface diffusion of the point defects in the drain area, makes it possible to decrease the process temperature, and to combine the gettering technique with the planar technology of IC production. In the present paper we study structures with getter areas formed on the operating side of the wafer in close proximity to the IC active areas by local Ar + ion implantation and subsequent film growth. As a result, the gettering effect accompanies the epitaxial growth process. In this case a non-equilibrium situation in the density of thermally generated defects arises, leading to a difference in the processes of formation of the structural properties of the films in the operating and getter areas.
One of the essential factors determining the efficiency of gettering processes, is the emergence of substantial elastic stress in the near-surface layer of the film. Its distribution in the IC operating areas has been investigated by Raman scattering. To study the planar gettering processes during the epitaxial growth of the films a special mask (Fig. 1) has been made, enabling the formation of operating areas of square shape with sides from 100 lain to 5 mm on the (111) Si wafer. 50 keV Ar + ions at j = 1 ~tA/cm 2, their dose ranging from 1013 to 1016 cm -2, were implanted into the getter areas. After the mask had been removed, the slices were annealed at 1100°C for 15 min, and the Si film was grown epitaxially to a thickness of 5.1 Ixm. An argon laser beam (2=514.5 nm, P~ 1 0 1 5 c m - Z a reverse shift of the maximum is observed, which may be associated with the elastic stress relaxation in this range of the implantation doses. The elastic stress in the epitaxial film, built-up on the implanted silicon substrate, has been estimated I-7] to achieve, at • ~ 2 x 1015 cm-2, values characteristic of the emergence of the shear deformations in the epitaxial film grown at II00°C. As a result, at ~ > 2 x 1015 cm -2 in the getter area of the structure under consideration a plastic deformation may occur, leading to the elastic stress relaxation. Our experiment has shown that this is manifested by a decrease of the elastic stress in the neighbouring operating area of the film as well. Thus, in spite of the fact that the gettering area structure at high implantation dose possesses the highest capacity for point defects and impurities, the gettering efficiency, being essentially determined by the mechanical stress gradient, is, however, reduced with increasing dose. The getter regions' long-range effect is of special interest. Figure 3 presents the dependence of v upon
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the scattering along the axis, parallel to the side of the 3 x 3 mm 2 area for different implantation doses into the getter area. At a dose ~ = 3 x 1014 cm -2 (curve a) an increase of tensile stress up to a distance of 600 pm is observed, while in the centre of the square the stress is practically absent. (The zero stress line is indicated by dashes.) At ~ = 4 . 6 x 1014cm -2 (curveb) the longrange effect increases to 1200 gm. The central stressfree area of the square is substantially narrowed. A further increase of the implantation dose results in an increase of the stress over the whole operating area of 3 x 3 mm. The asymmetric character of the stress distribution at the opposite sides of the square area in question should be noted. This fact is confirmed by scanning in the perpendicular direction. Thus, the stress distribution pattern is symmetric with respect to one of the square diagonals. The reason for such an asymmetry will be discussed below. It should be noted that Raman scattering studies did not reveal any essential changes in F at any implantation dose. In each case F was close to the value characteristic of the single crystal.
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Fig. 3a-c. Variation ofphonon peak frequency v and corresponding stretching stress ~r across the operating area (3 x 3 mm) at different values of the dose implanted into the getter: a • = 3 x 1014 cm-2: b ~=4.6 x 10x4 cm-2: e ~=6.2 x 10TM cm -2
Fig. 4. X-ray topogram of Si implanted by Ar + ions in the getter region. The implantation dose is ~=3 x 1014 em -2 Similar studies ofa 1 × i mm 2 area have also shown an increase in the tensile stress as the implantation dose increases from 3.9 to 6.2 x 1014 cm -2. In this case the non-strained central area is absent, for the longrange effect of the stress exceeds 500 gin. The asymmetry in the stress distribution at the opposite sides is again observed. We have also studied the stress arising in these structures by means of X-ray topography. The patterns were recorded by an intermediate contrast technique, providing maximal sensitivity to the crystallographical defects and elastic stress fields [9]. An X-ray topogram of the sample, in which the getter area had been formed by 3 x 101'~ cm -2 Ar + ion implantation, is shown in Fig. 4. The dark and light lines, framing the border of the implanted and non-implanted areas, characterize the direction of the surface component of the mechanical stress vector o-with respect to the diffraction vector q. The dark lines corresponds to their coincidence, and the light ones to opposite directions of o- and q. The stress vector is seen to be directed along the diagonal of the "pure" square areas. This fact explains the above mentioned asymmetry in the a distribution along the side of the square area of the "purified" structure. The reason for this is the fact that the diagonal of the operating square area was parallel to the [110] direction. The latter is known to be the glide direction for the Si (111) plane; and the diffusion of defects and impurities in this direction is considerably facilitated. This is the first work in which Raman scattering is applied to spectroscopic studies of the stress distribution of wafer operating areas in order to establish the long-range efficiency of the planar getter areas versus the implanted dose of Ar + ions. We have also confirmed the high quality of the epitaxial film in the "purified" areas.
Raman Spectroscopic Studies of Planar Gettering Effects
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