# Advanced Diffusion Models Released in ATHENA 4.0

**ATHENA Version 4.0 **contains the latest
model developments from universities and research institutes worldwide.
For process simulation of deep sub-micron devices, accurate and
robust implantation and diffusion models are essential. **ATHENA
Version 4.0 **includes a significant number of new implant and
diffusion models for simulating high dose and RTA effects.

**New Stanford Diffusion Models**

- 311 Cluster Model
- Dislocation Loop Model
- High Dose Model
- Scaleable implant damage model

This set of three diffusion models developed at Stanford University
together with a scaleable implant damage model developed at **Silvaco
**allow users to model Transient Enhanced Diffusion processes
such as RTA. The model extents the previous `FULL.CPL`

model for point defects. It adds defect clusters that dissolve over
time releasing interstitials and dislocation loops that act as point
defect sinks. A model to derive cluster and loop concentrations
and locations as a function of implant profile is also included.**[1]**
**[2] **An example of RTA simulation using this model is shown
in Figure 1.

**CNET Diffusion Models**

- Impurity-defect pairing statistics
- Static clustering
- Percolation
- Correlated interstitial and vacancy mediated impurity diffusivities
- Bimolecular recombination of defect through impurity states

This set of five diffusion models can be
used as extensions to the current `FULL.CPL `

model.
These models were developed and implemented through a cooperative
agreement with Daniel Mathoit of **CNET.** The models apply particularly
at very high dopant concentrations. Figure 2 shows the comparison
of experimental data for this model to 900C predisposition of phosphorus.**[3]
[4]**

**Ion Implant Enhancements**

- Three-Level Lateral Straggle Description

- Simple scaling factor for lateral range (LAT.RATIO)

- User control over lateral standard deviation - Full control of all moments for depth dependent lateral straggle

The reduction in post-implant diffusion
for **ULSI** processes means that accurate models for lateral
implant straggle are required to produce good agreements with```
MOSFET
```

Leff. A hierarchical approach
has been adopted in this release of **ATHENA**. The simplest
level is a single scaling parameter** (LAT.RATIO)** which can
be used to shift the lateral moments as a function of the default
model **(See Figure 3).** At a more complex level the user has
full control of depth or dose dependent lateral straggle though
the `MOMENTS`

statement.

- Improved User Access to Implant Moments

- allow users to add their own tables

-allow lateral straggle definition in the tables

New data for implant moments is continually
becoming available from research institutions and universities.
The `USER_TABLE `

parameter
of the `MOMENTS`

statement
will allow user to add new tables of implant moments to be used
by **ATHENA**. The** ATHENA **executable and the tables of
implant ranges are now decoupled. This will allow **Silvaco**
to issue new and updated implant range tables asynchronously from
**ATHENA** code releases. In the future new implant tables could
be downloaded from the **Silvaco WWW site. **

- Extended High Energy Implant Statistics (up to 8MeV into SiO2)
- Allow printing of ion implant moments used
- Ability to plot the Monte Carlo ion implant
racks and secondary recoils in Tonyplot.
**(See Figure 4)** - Ability to model silicon implants into silicon for pre-amorphisation of the substrate
- Automatic extraction of spatial implant moments from Monte Carlo implant calculations

**Updated Parameters for Interstitials **

Updated model file values for Interstitial
`KSURF, THETA and KRAT`

to fall in line with FLOOPS **[5].**
This change will result in more accurate and quicker diffusion results
using ```
TWO.DIM or FULL.CPL
```

models. Although results may vary from
the previous release.

**Adaptive Meshing **

- New Base Mesh Algorithm
- New Global Smoothing Algorithm
- Improved 1D To 2D Transition
- Template Grid Rules Derived For Common Technologies

A series of improvements have been made
to the adaptive meshing routines in **SSuprem4.** Efficient adaption
in 1D mode can now be performed. A transition to 2D mode can be
made using an automated base mesh generator. For the most common
technologies the meshing rules have been supplied as templates.
Examples for `MOSFETS, CCDs, BJTs`

, and
large power structures are available.

**Model Enhancements**

- Power Device diffusion model

For devices with extremely large geometry's (in
the order 10um) some of the physics included in **SSuprem4**
is not required. In order to speed up simulation times of these
large devices a new option **METHOD POWER** has been added. Results
obtained using this method are identical for large devices with
a 5x speed up.

- Clustering Model Extended

A generalized **SSUPREM4** clustering
model is implemented to simulate impurity activation for both p-type
and n-type impurities. The model can be selected by specifying parameter
`CLUSTER.S4`

on the ```
METHOD
```

statement.

- Extend Boron Solid Solubility Data Down To 700C
- Oxide Threshold Model
- Temperature Dependent Fractional Interstitialcy
- Addition of Indium dopant

**Void formation**

An algorithm to allow formation of keyhole voids in deposited films has been added to Elite. Void boundary conditions are correctly handled so subsequent deposits do not fill the void. Void formation can be followed by simulation of viscous flow of the deposited material to reduce or eliminate the void.

Plasma Etch Model

- Plasma ion flux based etch rates
- Concentration dependent etch rates
- Stress dependent etch rates

A Monte Carlo based plasma etching model has been added to Elite. It calculates the angular dependence of ions emitted by the dark spaces heath in RIE etchers. Etch rates over complex topography are calculated along with angle dependent sputtering efficiency. Shadowing effects are included.

Since Elite is a grid-based topography simulator it is also able to treat the etch rate dependence on physical quantities in the substrate.Etch rates as a function of doping or stress can be modeled. Faster and More Automated Lithography Simulation

- Speed up of 10x in the calculation of aerial images
- Speed up of 5x in the exposure calculation
- Simpler CD extraction procedure
- Tighter integration of
**OPTOLITH i**nto VWF to allow characterization of lithography processes

The main area of Optolith enhancements has been
in the numerics of the imaging and exposure calculation. For the
imaging a conservative estimate of the speed-up is 10x the previous
**ATHENA **version. This means that the imaging of very complex
masks can be done in a reasonable** CPU **time. New routines
have allowed Optolith to be used within the VWF automation tools
for characterizing lithography processes. Figure 8 shows a contour
plot of CD as a function of exposure and defocus. This is stored
as a behavioral model in VWF to allow experimentation with second
order parameters such as resist thickness or development rates.

**References**

[1] "TED Modeling in ATHENA" Simulation Standard Aug 96.

[2] S. Crowder et al , IEDM 1995 p 427.

[3] "CNET Physical Diffusion Model in ATHENA" Simulation Standard Feb 96.

[4] D. Mathiot, Electrochemical Soc. Poc. 95-5 p 13.

[5] Journal Applied Physics, Park and Law. 72(8), p. 3431, Oct. 15, 1992.