# Presentation: NX2DPKU4NTCYUNT6ZWIEE5W7EZHUQG6Q

## Microcomb Fabrication Update For Constellation-X Facility Science Team Meeting

- Space Nanotechnology Laboratory
- Yanxia Sun, Ralf Heilmann, Carl Chen,
- Craig Forest, Mark Schattenburg
-   September 18, 2002

## Microcomb for Precision X-ray Foils Assembly

- Reference
- Comb’s Tooth

- Spring Comb’s
- Tooth

- Accuracy requirement for reference comb;
- Previous fabrication process and problem;
- New 2-mask fabrication process.
- Future work: “Tall-teeth” microcomb for SXT

## Accuracy requirement for Reference Comb

- Position Accuracy

- Critical Dimension

- Position Accuracy:
-             Better than 100 nm;
- Repeatability:
-             Better than 100 nm;
- Critical Dimension:
-      Not specified;

## Previous Fabrication Process

- DSP silicon wafer,
- Thermal diffusion 2 m SiO2;

- (c) Etch SiO2;

- SiO2    Si          PR  Quartz

- (b) Contact print thick PR;

- (d) DIRE with quartz handle-wafer, etch through;

- Quartz

- (e) Strip PR, BOE, Extract finished microcomb;

- 200 nm accuracy has been achieved based on 4 inch wafer process.

## Deep Reactive Ion Etch for Silicon

- Fluorine-rich ions (SF6)

- C4F8 polymerization

- 2. Etching circle

- Silicon

- Fluorine-rich plasma (SF6)

- 3. Polymer passivation circle

- Etch rate is about 1~5 m per minute.

- 1. Substrate with etching mask

- 4. Etching circle

**Notes:**
Inductively couple plasma (ICP) etcher. Sf6 dissociates in the plasma and release abundant SF ions and free fluorine atoms. Scalloping pattern, 200nm. 

## Long-term Deep Reactive Ion Etch for Silicon

- Silicon

- PR
- SiO2

-  6.07 m

- PR
- SiO2
- Silicon

- 20.1 m

- 15.4 m

- Thick Photoresist and oxide layer are required, which will introduce
- big CD loss and low repeatability.

- Thick Photoresist Profile

- After 4.5 hour Deep Reactive Ion Etch
- for Silicon

## Long-term Deep Reactive Ion Etch for Silicon

- The effect from angular ion distribution is amplified when etching deeper.

- Ions:

- Protective layer
- Siilicon

## Long-term Deep Reactive Ion Etch for Silicon

- Backside erosion

- Backside erosion when etching through;

- Rough sidewall surface if overetching;

## 20 minutes Deep Reactive Ion Etch for Silicon

- 57.2 m

- silicon

- 2 m

- silicon

- scalloping

## Mask Design

- 10 m

- 40 m

- Reference lines to
- study the accuracy

- Connected bar to keep
- the combs on wafer
- after process

## Two-mask Process

- DSP silicon wafer,
- Thermal diffusion 0.5~1 m SiO2;

- (b) Lithography for backside etch;

- (c) Backside silicon dioxide etch;

- (d) Backside silicon etch, DRIE;

- (e) Lithography for front side etch;

- (f) Front side silicon dioxide etch;

- (g) Front side silicon etch, DRIE
- with backside protection with photoresist

- (h) Clean wafer, get comb out;

- Quartz

- Quartz

- SiO2    Si          PR   Quartz

## “Tall Teeth” Micro-comb 

- 10mm long reference tooth to avoid rough edge of the mirror;
- 2.   EDM-cut metal strong-back bonded with silicon microcomb to stiffen reference tooth;

## Etch Silicon Dioxide

- PR
- SiO2

- Silicon

- SEM for Silicon oxide profile after BOE, 70 degree of sidewall angle.

- SEM for Silicon oxide profile after plasma etch, showing approximately sidewall angle of 7 degree.

-  2 m

- PR
- SiO2

- Silicon