Behavior of Transition Metals Penetrating Silicon Substrate through SiO₂and Si₃N₄Films by Arsenic Ion Implantation and Annealing

Abstract

The behavior of metals penetrating the silicon substrate through a screen SiO 2 or Si 3 N 4 film by the collision of arsenic ion and surface metals are quantitatively demonstrated. We have found using silicon step etching followed by ICP-MS and SIMS that 0.1∼8% of surface metals (Fe, Cr, Ni, Cu, and W) penetrate silicon even when implanted through screen SiO 2 film, depending on metal species and the film thickness. The surface metals on a CVD Si 3 N 4 film can also penetrate into the silicon during ion implantation and/or subsequent annealing. W is most difficult to penetrate the thermally-grown SiO 2 film, while W and Cr can easily penetrate a CVD Si 3 N 4 films. We have also found using microwave photoconductive decay measurements that recombination centers are generated in silicon by low level metal penetration even when implanted through screen Metallic contamination on silicon surfaces has a detrimental impact on the performance and yield of ULSI devices. Surface metal impurities degrade the gate oxide integrity while metal impurities dissolved in silicon cause recombination centers and these result in junction leakage, degrade retention characteristics in DRAMs, and cause dark currents in image sensors. Surface metal impurities often penetrate the silicon by thermal diffusion in ULSI processing. The diffusion behavior of these metal impurities in silicon is well-known. [1][2][3] Most metallic contamination occurs during wafer processing, particularly reactive ion etching and ion implantation 4-6 and here it has been reported that metals transported with dopant ion from an ion source or acceleration tube in ion implantation equipment can be deposited on silicon surfaces. 5,6 On the other hand, the behavior of surface metal impurities penetrating by the collision with a dopant ion has not been known. The ion implantation may assist surface metal impurities penetrating the screen films and silicon. The collided metal atoms' penetrating silicon can be prevented by screen films such as SiO 2 or Si 3 N 4 films, 7 in which the diffusion coefficients of metal impurities such as Ni and Cu are smaller than in Si. 8 In this paper, the behavior of metals penetrating the silicon substrate through a thermally grown SiO 2 or CVD Si 3 N 4 film by the collision of dopant ion and surface metals and subsequent annealing are quantitatively demonstrated. The generation of recombination centers due to the metal penetrating silicon is also discussed. ExperimentalCzochralski (CZ) Si (100), (p-type, 8-12 cm), 200 mm diam. wafers were used in this study. A group of wafers was oxidized to form silicon oxides on the surface. The thickness of the silicon oxide was 5 nm, 20 nm, 80 nm, 120 nm, and 160 nm. A Si 3 N 4 film was deposited on the surface of another group of wafers at 700• C by low pressure CVD. The thickness of the Si 3 N 4 film was 20 nm.Next, the silicon wafers were cleaned with NH 4 OH/H 2 O 2 /H 2 O mixture and HCl/H 2 O 2 /H 2 O mixture. The surfaces of the SiO 2 and Si 3 N 4 films of the wafers were hydrophilic. ...

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