Hints & Tips

Q: How can I determine implant range for non-standard materials such as silicides or photoresist?

A: The analytical implant tables in ATHENA/SSuprem4 cover implantation of the common silicon dopants (B, P, As, Sb, In) into the commonly used set of materials in semiconductor processing (Silicon, SiO2, Si3N4, polysilicon, aluminum). For other materials or implant species the lack of complete data means full analytic tables are not available. The only alternative approach was to use Monte Carlo (MC) Implant simulation.

Implantation using MC with the crystalline model is usually required for silicon implantation. For realistic 2D cases these implants may take up to 30 minutes to run on a Sparc Ultra. In order to overcome this problem an alternative approach is now available in ATHENA version4.3. This approach uses MC implant in 1D mode to run implantation simulations into the material of interest. Then the analytical implant moments are extracted from the implanted doping profile. These analytical moments can be used in a MOMENTS statement to set the correct doping profiles for an analytical implant. The syntax for this is shown in Figure 1 with a comparison of the two different implants in Figure 2.

Photoresist is a special case in ATHENA. Although analytical implant tables exist for photoresist, they are specific only to one type of photoresist (AZ-111). Photoresist materials do vary considerably in density and material abundances. Syntax exists in ATHENA to set the required parameters for MC implantation modeling.

MATERIAL        MATERIAL=my_resist DENSITY=3 \
                ABUND.1=0.6 AT.NUM.1=8 AT.MASS.1=16 \          
                ABUND.2=0.4 AT.NUM.2=6 AT.MASS.2=12


ABUND sets the relative abundance of elements in the photoresist. AT.NUM and AT.MASS set the atomic number and weight of the elements respectively. DENSITY sets the overall material density. From these parameters, MC implant can calculate the implanted profile. The syntax from Figure 1 allows the user to fit, extract and re-use the analytical moments calculated from the MC implant profile.

A similar technique can be used for implants of non-standard species too. It is possible for users to build up their own user-defined implant moment tables. An example of the use of this technique is included on the Summer 97 release CDROM with ATHENA version 4.3.

 

Figure 1. Syntax for extracting analytical
implant parameters from a Monte Carlo
implant simulation.

 

Figure 2. Comparison of doping profiles analytical
extraction versus Monte Carlo. Analytical implants
are run instantaneously whereas Monte Carlo
takes up to 30 minutes on Ultrasparc.