High temperature deposition of NSN and OSO stacks

ByJoe Qi

In this post, we’ll discuss a little bit about how would the deposition temperature affect the pore formation and pore morphology. I first show some previous results of the effect of deposition temperature on the porosity and pore size from Dave.

Deposition temperature effect on porosity and average diameter from Dave

From this plot, it shows that the relative low deposition temperature barely affects the porosity and average diameter. However, the average diameter decreases when the deposition temperature increases to 300C.

In my experiment, I deposited NSN and OSO stacks at 500C and 600C (see the table). The hypothesis was that high temperature deposition would create some locally order structures (silicon crystal nuclei), which would be helpful for the following RTP silicon crystallization, thus enhancing the pore formation.

After deposition, I took some TEM images of NSN stack deposited at 600C. No obvious silicon crystals can be seen from the TEM image and the diffraction image showed that the silicon film was still amorphous.

NSN stack deposited at 600°C

Samples were then RTP annealed at 1000C for 1minute. The next TEM image is the annealed NSN stack deposited at 600C. Surprisingly, very few pores are formed in this sample. The surface feature is more like pits rather than through pores.

TEM image of 600°C deposited NSN stack after annealing at 1000°C for 1 minute

Very similar features are observed from the OSO stacks after annealing. Both samples show very few pores in the silicon film.

OSO stacks after annealing, a) OSO stack deposited at 500°C, and b) OSO stack deposited at 600°C

Let’s compare the annealed NSN stacks deposited at 150C and 600C. Both samples were annealed at 1000C for 1 minute. Si crystals are much bigger in the silicon film deposited at 150°C than at 600°C.

Annealed NSN stacks deposited at a) 150°C and, b) 600°C

Similar phenomenon can be seen from the OSO stack.

Annealed OSO stacks deposited at a) 150°C and, b) 600°C

This result indicates that the pore formation and the silicon crystallization are inhibited rather than enhanced. One reason I can think of is due to the defect density. I think the defect, such as vacancy, decreases because of the higher mobility of silicon atoms at higher deposition temperature. During crystallization process, these defects help to nucleate and result in heterogenous crystallization. Since the defect density decreases at the result of high temperature deposition, the silicon crystallization and pore formation are inhibited thereafter.

In sum, here are some conclusions from this experiment.

•Few pores are formed in silicon films in both NSN and OSO stacks after annealing when silicon films were deposited at 500°C or 600°C.
•Compared with the Si film deposited at low temperature , silicon nanocrystals are smaller in these high temperature deposited Si films.
•The pore formation in these high temperature deposited Si films is inhibited, which is probably due to the decrease of defect density.
•Defects density is closely related to the pore formation.

 

 

Similar Posts

Leave a Reply