NanoFab Simulator Layout

Nick Reeder, Dec 16, 2011

Proposal: Structure of User Activity

• User is presented with a starting wafer (which may or may not be blank) and a desired ending wafer. User must perform process(es) in sequence to get from start to finish.

• Example: Start Finish

Proposal: History Tab

• At any point, user can review the processes he has performed so far and their cumulative effect on the wafer.

Decision: “Revert To” Option?

• If user wants to undo one or more completed processes, does he have the option to revert to a prior stage in the history, or must he start over again?

Decision: Processes or Resources?User chooses which process to perform next.

User chooses which resources to use next.

Decision: How to Represent Various Materials in 2-D Cross Sections?

Colors Fill textures

Decision: List of Materials That Can Appear in 2-D Cross Sections?

• Substrate (Is this always silicon?)– Intrinsic– Doped

• Contaminants– Dust– Residue from chemical rinsing

• Photoresist (of specified type)– Liquid– Baked

• Deposited film (of specified type)• …Others?

Decision: Displaying Dimensions?Dimensions always displayed

Dimensions displayed at user’s request

Never displayed. User must measure.

Decision: Menus or Toolbars?

Menus Toolbar

Decision: Instantaneous or Real-time?

• When user initiates a process, does it complete immediately, or take a realistic amount of time to complete?

• How many of the processes require visual monitoring by the user to decide when process is complete? (We discussed having videos of spin coating process that show changing appearance of photoresist as time passes.)

Decision: Number of Views?

• Is cross-section view adequate, or for masking (and perhaps other processes?), do we need to provide a top view as well?

Decision: How Many Modes of Operation?

• Possible modes:– Demo– Single-process– Sequence

• Are assessment results to be recorded in a database for instructor’s use, or just self-assessment for student?

Spin Coating Simulation

Nick Reeder, Dec 16, 2011

Task Analysis

• For each process to be simulated, we must perform a detailed task analysis that identifies, for each process:– Equipment and materials required– Input parameters to be set– User actions

• We must then decide which of these actions and parameters to include in the simulation.

Example: Task Analysis for Spin Coating Process1. Setup (in any order?)

– Turn power on.– Place wafer in spin coat machine.– Select type of photochemical and apply to wafer.– Set parameters:

• Time• Revolutions per minute.• Acceleration.

– Activate vacuum.– Activate nitrogen purge.– Place napkins to absorb excess photochemical.

2. Activate motor and wait until it stops automatically.3. Wrap-up (in any order?)

– Remove wafer.– Remove napkins.– Deactivate vacuum.– Deactivate nitrogen purge.– Turn power off.

Questions: Photochemicals

• AZ 6632• AZnLOF 2070• LOR 3A• LOR 10B• LOR 30B• ma-P 1275-HV• MCC Primer• PMMA

• SPR 505• SPR 955• SU8 2015• SU8 2025• SU8 2050• SU8 Thinner• Thinner P• UVN 30

• How many classes of chemicals are we simulating?• Photoresist (Positive and negative? Lift-off?)• Thinner• Primer

• Which of these chemicals do we want to include?

Questions: Governing Equations

• Curve fitting from AZ 6632 datasheet, where y = film thickness (m) and x = spin speed (rpm)

y = 5.712e-1E-04x for 2000 x 6000• Is it correct to use exponential fit? Can we extrapolate

outside the range of x given in the datasheet?• How do we model effect of time and acceleration?• Is Laurell’s spin-speed calculator reliable? “This calculator

is based on the principle that the thickness of a coating generally varies inversely with the square root of a corresponding spin speed.” http://www.laurell.com/support/spin_speed_calc.php

General Question

• If we spin coat a wafer with an uneven surface (such as one that’s already been etched), do we get a layer of uniform thickness, or of uniform height, or neither?