8.31 Sspd_chapter 6_part 10_simulation of mosfet  (Page 3/5)

Thermal Process Simulation, such as diffusion, oxidation or silicidation, is the focal point of SUPREME4.

When we open the ATHENA Diffuse Menu, we have the following options:

#Time is to be adjusted from 0 to 500 minutes. ###########################

#We have Temperature option which can be chosen from 500°C to 1300°C.####

#The ‘Ambient’ option has Dry O ₂ , Wet O ₂ (Argon or Nitrogen is bubbled through water),N ₂ , Gas Flow.#################################################

#We have gas pressure option. We can choose from 1 atmosphere to 10 atmosphere.########################################################

#HCl percentage option.##############################################

#Comment#########################################################

We have the option of ramping up or ramping down the temperature as we do in Rapid Thermal Anneal(RTA).

Small concentration of HCl , in this case 3%, helps reduce Oxide defect densities and reduce contamination levels.

4HCl + O ₂ → 2H ₂ O + 2Cl ₂ .

HCl reacts with Oxygen to form Chlorine. Chlorine reacts with trace metals and other contaminants in the furnace to produce volatile chlorides as by products.

We have the following statements.

#pwell formation including masking off of the nwell

This statement means that we will be process simulating the (E)NMOS in P Well only and extracting the threshold voltage from its transfer characteristics.

#

diffus time=30 temp=1000 dryo2 press=1.00 hcl=3

In the above statement we are doing dry oxidation for 30 minutes at 1000°C in 1 atmospheric pressure with a mixed ambient which contains 3% HCl acid vapour.

The above parameters of dry diffusion gives 0.03µm thick oxide from the look-up table.

The oxide is retained over N Well and completely etched out from P Well portion.

For this we open Athena Etch Menu:

#Etch Method: Geometrical-Machine################################################

#Geometrical Type:All-Left-Right-Dry Thickness-Any Shape############################

#Material- Oxide or Poly Si.#######################################################

#Etch Location################################################################

Geometrical Etch is the default method of Etch.

We can choose the material to be etched and we can specify the portion to be etched.

We may etch out the entire surface(All) or RIGHT of a point situated at xo from the left edge or LEFT of a point situated at x1 from the right edge or the entire thickness over the entire surface area or etch out in a specific polygonal area as described by four or more points in the menu.

#

etch oxide thick=0.02

Since our previous step was Oxidation 0.03µm thick hence in P-Well region again 0.02 µm has to be etched out leaving 10nm screen oxide over P-Well which will randomize the Boron implant into P-Well region. 30nm thick oxide will completely shield the N-Well region from Boron Implant..

Now we have to carry out the Boron Implant for P-Well.

Ion-implantation is the main method to introduce doping impurities into semiconductor structure. This allows critical dimensions , shallow implant depth, high doses and tilted implants.