Second-oxidation properties of thin polysilicon films grown by LPCVD and heavily in situ boron-doped

• Published in: Thin solid films 1998-12, Vol.335 (1), p.70-79
• Main Authors: Boukezzata, M., Birouk, B., Bielle-Daspet, D.
• Format: Article
• Language: English
• Subjects: Boron; Chemical vapor deposition (including plasma-enhanced cvd, mocvd, etc.); Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; In situ doped; LPCVD-Si layers; Materials science; Methods of deposition of films and coatings; film growth and epitaxy; Oxidation; Physics; Second-oxidation; Surface treatments
• ISSN: 0040-6090; 1879-2731
• DOI: 10.1016/S0040-6090(98)00894-3

In this work, we present a comparative study between first- and second-thermal-oxidations properties of low pressure chemical vapor deposition (LPCVD) thin polysilicon films. These films are heavily in situ boron-doped with a concentration level of around 2×10 20 cm −3. The first- and second dry oxidations experiments are systematically conducted under the same conditions. Their properties are analysed using electrical and structural characterization means. The thermal-oxidation processes are performed on submicron layers of 200 nm deposited at temperatures T d ranged between 520 and 605°C and thermally-oxidized in dry oxygen ambient at temperatures T ox =945 , 1000, and 1050°C. As presented in a previous study, the first-oxidation of these layers is known to have an enhanced oxidation rate compared to similar undoped, boron-implanted layers, and single crystal silicon. In the used range of the deposition temperature T d, we have found that the second-oxidations present a completely different behaviour compared to what is observed in the first ones. The second-oxidation rate becomes too weak and seems to be dependent of the first-oxidation time t ox1. Furthermore, if the first dry oxide is etched off and a second dry oxide is grown, it is found that the second oxide contains less dopant than the first one. Obviously, the loss of the oxidation rate is comprehensively discussed if we assume that the film structure is subjected to a deep modification at the first stage of the oxidation process. These results will be also correlated with other specific phenomena that we have evidenced in a previous work.