Improving low-temperature APCVD SiO₂ passivation by rapid thermal annealing for Si devices

Abstract

The quality of low-temperature ( 400 C) atmospheric pressure chemical vapor deposited (APCVD) silicon dioxide (SiO 2 ) films has been improved by a short time rapid thermal annealing (RTA) step. The RTA step followed by a low temperature (400 C) forming gas anneal (FGA) results in a well-passivated Si-SiO 2 interface, comparable to thermally grown conventional oxides. Efficient and stable surface passivation is obtained by this technique on virgin silicon as well as on photovoltaic devices with diffused (n + + + p) emitter surface while maintaining a very low thermal budget. Device parameters are improved by this APCVD/RTA/FGA passivation process.

High-rate plasma-deposited SiO2 films for surface passivation of crystalline silicon

“…The best values reported on low resistivity n-type substrates were in the 100-400 cm/ s range obtained on slightly higher resistivity substrates ͑3-6 ⍀͒, 12,13 and it is generally found that the effective surface recombination velocity decreases for increasing wafer resistivity. The surface recombination velocity shows only a limited injection level dependence, similar to what is observed for silicon carbide, amorphous silicon, and silicon nitride on low resistivity n-type crystalline silicon.…”

“…The effective surface recombination velocity on the commonly used p-type c-Si substrates with a resistivity of 1 ⍀ cm was only in the range of 700 cm/ s. 11 Leguit et al and Sivoththaman et al were able to reach minimal effective surface recombination velocities of ϳ100 cm/ s on moderately doped p-or n-type c-Si. 12,13 However, for higher doping levels the effective surface recombination velocity strongly increases. 12,13 It should be noted that the surface passivation of the as-deposited SiO 2 films in all these studies was rather poor and a 20 min or 15 h anneal at 350-400°C in a forming gas ͑commonly 10% H 2 in nitrogen͒ was required to achieve the reported level of surface passivation.…”

“…12,13 However, for higher doping levels the effective surface recombination velocity strongly increases. 12,13 It should be noted that the surface passivation of the as-deposited SiO 2 films in all these studies was rather poor and a 20 min or 15 h anneal at 350-400°C in a forming gas ͑commonly 10% H 2 in nitrogen͒ was required to achieve the reported level of surface passivation. [11][12][13] Furthermore, a forming gas anneal or alneal is also essential to obtain a good level of surface passivation for both wet or thermal oxide.…”

“…12,13 It should be noted that the surface passivation of the as-deposited SiO 2 films in all these studies was rather poor and a 20 min or 15 h anneal at 350-400°C in a forming gas ͑commonly 10% H 2 in nitrogen͒ was required to achieve the reported level of surface passivation. [11][12][13] Furthermore, a forming gas anneal or alneal is also essential to obtain a good level of surface passivation for both wet or thermal oxide. 3,14 In the aforementioned studies of the surface passivation of plasma-deposited SiO 2 films, SiH 4 -O 2 or SiH 4 -N 2 O gas mixtures were used to deposit the SiO 2 films.…”

“…3,14 In the aforementioned studies of the surface passivation of plasma-deposited SiO 2 films, SiH 4 -O 2 or SiH 4 -N 2 O gas mixtures were used to deposit the SiO 2 films. [11][12][13] However, also organosilicons such as tetraethoxysilane ͑TEOS͒, hexamethyldisiloxane ͑HMDSO͒, or octamethylcyclotetrasiloxane ͑OMCTS͒ can be used for the deposition of SiO 2 films. Organosilicons are relatively inexpensive, nonflammable, and have a low toxicity rating; hence, no special safety installation is required as in the case of SiH 4 .…”