NanoFab Trainer Update Nick Reeder, April 11, 2014

Update to Exposure Code

• • New code creates UV intensity profile based on incident intensity, width of mask opening, distance of mask from surface, and thickness of resist layer.

Intensity profile is a Gaussian function whose width is based on a 2-dimensional look-up table, with opening width and distance-plus one-half-resist-thickness as the look-up parameters. How to populate this look-up

table with realistic numbers?

Sample Runs with Varying Mask Height

• Next two slides compare two 10-second exposures with same mask and same resist layer, but with mask at different heights above the surface.

Note that exposed area is wider but degree of exposure is less.

•

Sample Runs with Varying Distance between Mask Openings

Next three slides compare three 10-second exposures with same resist layer and same mask height, but with two mask openings separated by different distances.

Is it reasonable that exposed areas merge at the top but not at the bottom?

Update to Materials Database

• • • To model the effect of layers between the resist and the substrate, materials database now contains a value for the complex refractive index (at 365 nm) of each material. Values are from http://refractiveindex.info/ (except for photoresists).

See next slide for values used.

Material

All photoresists

Refractive Index

1.64 + 0i Al2O3 SiO2 Si3N4 Ta2O5 TiO2

Refractive Index Values

1.7935 + 0i 1.4882 + 0i 2.0953 + 0i 2.2917 + 0.0005305i

2.8717 + 0i

Material

Ag Al Au Cr Cu Ni Pt Ti

Refractive Index

0.17222 + 1.4703i

0.37645 + 4.2852i

1.5834 + 1.7706i

1.4011 + 3.3249i

1.1971 + 2.0672i

1.6220 + 2.1626i

1.6383 + 2.6361i

1.8829 + 2.8936i

Ge Si 4.0716 + 2.5760i

6.5917 + 2.8349i

Update to Exposure Code

• • Code now handles layers of material between the resist and the substrate. – Current assumptions: All layers have uniform thickness across the width of the structure.

– Resist is the top layer.

Sample Runs with Multiple Layers

• • – Next three slides compare 10-second exposure with layers of: Photoresist above glass substrate – Photoresist above SiO2 above glass substrate – Photoresist above Al above glass substrate

Should users have the option of using non-Si substrate (such as glass)?

Ten-second exposure, photoresist above glass substrate.

Ten-second exposure, photoresist above SiO2 layer above glass substrate.

Ten-second exposure, photoresist above Al layer above glass substrate.

• • Note emergence of standing-wave pattern. Is it reasonable that exposed area is also wider with Al than in previous samples?

•

Next Steps: Varying Layer Thicknesses

Code needs to handle cases such as: – Layer thicknesses constant for each mask opening, but different for different openings.

– Layer thicknesses vary within a mask opening.

How to handle this?

•

Next Steps: Resist Under Other Layers

–

What should happen if there is a layer of some other material on top of the resist?

Is this a realistic scenario that we should address, or should we somehow prevent the user from doing it in the first place?

• •

MNT Conference

June 4-6 in Albuquerque.

I plan to distribute software on CDs so that people can start using it and provide feedback.

Date Added To-Do Item

3/16/12 Write code to provide top-down view of mask.

3/30/12 Add Cl 2 3/30/12 Write code to implement polish, given user parameters of grit size & time.

as an etchant.

3/30/12 Provide algorithm to determine polish rate given material and grit size.

4/20/12 Incorporate Andrew’s code for photoresist exposure.

4/20/12 Fix photoresist underhang problem in spin-coat code.

5/4/12 Write code to implement stopping powers of layers to determine whether underlying Si is doped during implantation.

5/27/12 Write code to implement lift-off.

5/29/12 Write code to implement bake of photoresist.

5/31/12 Provide realistic limits on the following user-provided parameters: pressure and temperature when performing CVD; dose and ion energy when performing implantation.

6/28/12 Niu suggests iterating etch code in seconds instead of minutes .

Provide look-up table data for 1.) CVD deposition rates based on user 1/18/13 supplied pressure & temperature; 2.) evaporation deposition rates based on user-supplied current & voltage; 3.) sputter deposition rates of Au, Ni, Pt, W, Si 3 N 4 , Ta 2 O 5 , TiO 2 , and Si based on user-supplied pressure & power.

1/18/13 Write code to implement annealing after implantation.

Who’s Responsible

NR NR NR JM NR NR NR NR NR AS NR AS NR

Date Finished

2/11/14 1/29/14 2/9/14 1/18/13 Write code to implement doping by diffusion.

NR

Date Added To-Do Item

3/1/13 4/14/13 6/19/13 10/23/13 10/30/13 11/3/13 11/3/13 1/17/14 1/28/14 Write code to implement projection lithography as well as contact lithography.

Decide whether to accept Nick’s suggested edits (sent on 4/14/13 and 5/8/13) to Andrew’s seventeen tutorial chapters.

Surinder suggests automatically filling in dialog-box parameters if user clicks a point in a “View Rate” graph.

Jamshid suggests providing link in dialog boxes to display the relevant “View Rate” graph.

Jamshid’s student Rajput suggests making it easier for user to know which solvents etch which materials.

Fix bug causing photoresist spikes per Jamshid’s student Chico.

Address performance issue per Jamshid’s student Jarrod.

Write code to track and plot time, cost, quality of user operations.

Provide algorithm for tracking time, cost, quality of user operations.

Write code to implement cleaning.

Write code to implement profilometer.

Record video clips (in .flv format) of lab operations.

Write online help text.

Test the trainer and report problems to Nick.

Revise CVD code to distinguish LPCVD and PECVD.

Provide empirical algorithm for finding intensity profile at resist surface given intensity, opening width, airgap, resist thickness.

Who’s Responsible

NR AS NR NR NR NR NR NR AS NR NR AS & JM NR

ALL

NR AS

Date Finished

1/21/14 1/21/14 1/6/14 2/2/14 3/14/14