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.

Refractive Index ValuesMaterial Refractive Index

All photoresists 1.64 + 0i

Al2O3 1.7935 + 0i

SiO2 1.4882 + 0i

Si3N4 2.0953 + 0i

Ta2O5 2.2917 + 0.0005305i

TiO2 2.8717 + 0i

Ge 4.0716 + 2.5760i

Si 6.5917 + 2.8349i

Material Refractive Index

Ag 0.17222 + 1.4703i

Al 0.37645 + 4.2852i

Au 1.5834 + 1.7706i

Cr 1.4011 + 3.3249i

Cu 1.1971 + 2.0672i

Ni 1.6220 + 2.1626i

Pt 1.6383 + 2.6361i

Ti 1.8829 + 2.8936i

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 Who’s

ResponsibleDate

Finished3/16/12 Write code to provide top-down view of mask. NR 3/30/12 Add Cl2 as an etchant. NR 2/11/14

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

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

4/20/12 Incorporate Andrew’s code for photoresist exposure. NR 4/20/12 Fix photoresist underhang problem in spin-coat code. NR

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

5/27/12 Write code to implement lift-off. NR 1/29/145/29/12 Write code to implement bake of photoresist. NR

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

AS

6/28/12 Niu suggests iterating etch code in seconds instead of minutes . NR 2/9/14

1/18/13

Provide look-up table data for 1.) CVD deposition rates based on user-supplied pressure & temperature; 2.) evaporation deposition rates based on user-supplied current & voltage; 3.) sputter deposition rates of Au, Ni, Pt, W, Si3N4, Ta2O5, TiO2, and Si based on user-supplied pressure & power.

AS

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

1/18/13 Write code to implement doping by diffusion. NR

Date Added

To-Do Item Who’s Responsible

Date Finished

3/1/13 Write code to implement projection lithography as well as contact lithography. NR

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

6/19/13 Surinder suggests automatically filling in dialog-box parameters if user clicks a point in a “View Rate” graph. NR

10/23/13 Jamshid suggests providing link in dialog boxes to display the relevant “View Rate” graph. NR 1/21/14

10/30/13 Jamshid’s student Rajput suggests making it easier for user to know which solvents etch which materials. NR 1/21/14

11/3/13 Fix bug causing photoresist spikes per Jamshid’s student Chico. NR 1/6/1411/3/13 Address performance issue per Jamshid’s student Jarrod. NR 2/2/14 Write code to track and plot time, cost, quality of user operations. NR Provide algorithm for tracking time, cost, quality of user operations. AS Write code to implement cleaning. NR Write code to implement profilometer. NR Record video clips (in .flv format) of lab operations. AS & JM Write online help text. NR Test the trainer and report problems to Nick. ALL 1/17/14 Revise CVD code to distinguish LPCVD and PECVD. NR

1/28/14 Provide empirical algorithm for finding intensity profile at resist surface given intensity, opening width, airgap, resist thickness. AS 3/14/14