Engineering Sciences 65

The Science and Technology of Micro-machines

LABORATORY 1: The Micro-Cantilever

Authors: A. K. Henning and C. G. Levey

Revision: March, 1995

Purpose and Description:

This laboratory presents the fundamental operations in most electromechanical devices created using the techniques of surface micro-machining.

In particular, a number of critical structures will be built, using an existing set of photolithographic masks. The central device will be the micro-cantilever, though other devices will also be built.

Your will work in groups of approximately four. Each group will fabricate several silicon wafers. Some experimental variations will be utilized, to demonstrate how the behavior of micro-machines depends upon the properties of the constituent materials, which are determined by their material and physical structure.

Process Flow Representation (PFR[1]):

Language is frequently the major barrier to technological understanding. Recall the general description of process steps from class:

*Etch A step which removes material

*Deposit A step which adds material

*Implant A step which implants dopants or defects

*Diffusion A step which heats material, in a gaseous, liquid or solid ambient

atmosphere

*Exposure A step which exposes a photoresist layer to light

General Step Specific Step Description Monitor/Measurement

1. Initialization: Starting material Four-point probe/Resistivity

100mm <100> silicon

2. Etch: RCA Clean[2]

3. Diffusion: Wet Oxidation (sacrificial) Ellipsometer/Film thickness

4. Photolithography

4a. Deposit: Spin on photoresist Ellipsometer/Film thickness

Microscope/Visual inspection

4b. Diffusion: Pre-exposure bake photoresist Time, Temperature

4c. Exposure: Anchor Hole Definition Time, Light Intensity

4d. Etch: Develop photoresist Microscope/Visual inspection

4e. Diffusion: Post-exposure bake photoresist Time, Temperature

5. Etch: Anchor Hole Cut Time, Temperature

Microscope/Visual inspection

6. Etch: Photoresist strip Time, Temperature

Microscope/Visual inspection

7. Deposition: Polysilicon Deposition Ellipsometer/Film thickness

Microscope/Visual inspection

8a. Diffusion: Polysilicon Anneal Time, Temperature

Microscope/Visual inspection

8b. Diffusion: Dry Oxidation (hard mask) Time, Temperature

Microscope/Visual inspection

9. Photolithography

9a. Deposition: Spin on photoresist Ellipsometer/Film thickness

Microscope/Visual inspection

9b. Diffusion: Pre-exposure bake photoresist Time, Temperature

9c. Exposure: Cantilever Definition Time, Light Intensity

9d. Etch: Develop photoresist Microscope/Visual inspection

9e. Diffusion: Post-exposure bake photoresist Time, Temperature

10a. Etch: Oxide mask etch Time, Temperature

Microscope/Visual inspection

11. Etch: Photoresist strip Time, Temperature

Microscope/Visual inspection

12. Etch: Polysilicon etch Time, Temperature

Microscope/Visual inspection

13. Dice wafers

14. Etch: Oxide Release Time, Temperature

Microscope/Visual inspection

Detailed Step Description (including cross-section [side view] and plan [top] view pictures):

1. Initialization: Starting material

3" <100> silicon

2. Etch: RCA Clean

On a microscopic scale, the three steps of this clean (developed by Werner Kern at the RCA Corporation in the 1960's) remove organics, metallics, and residual oxide.

3. Diffusion: Wet Oxidation

(sacrificial)

4a. Deposit: Spin on photoresist

4b. Diffusion: Pre-exposure bake

photoresist

4c. Exposure: Anchor Hole

Definition

4d. Etch: Develop photoresist

4e. Diffusion: Post-exposure bake

photoresist

5. Etch: Anchor Hole Cut

6. Etch: Photoresist strip

7. Deposition: Polysilicon

Deposition

8a. Diffusion: Polysilicon Anneal

8b. Diffusion: Dry Oxidation

9a. Deposit: Spin on

photoresist

9b. Diffusion: Pre-exposure

bake photoresist

9c. Exposure:Cantilever Definition

9d. Etch: Develop

photoresist

9e. Diffusion: Post-exposure bake

photoresist

10. Etch: Oxide mask etch

11. Etch: Photoresist strip

12. Etch: Polysilicon etch

13. Dice wafers

14. Etch: Oxide Release

13. PLAN VIEW OF CANTILEVER:

Structure Catalog (Mask Road Map):

(Under Construction)

Guckel Rings

Cantilevers

In-Process Measurements and Post-Process Characterization:

(Under Construction)

Four-point probe resistivity measurement

Ellipsometry

Thin-film stress

Scanning Electron Microscopy

Pre-Lab Problems:

These problems must be turned in individually, prior to beginning this laboratory. Some problems will be assigned as a part of the regular homework.

1) Given an oxidation temperature of 1000 deg.C: How long must the Wet Oxidation diffusion last, in order to obtain 2 um of silicon dioxide?

2) Using L-Edit, design a device of your own for inclusion in the fabrication process. Describe the intended behavior of the device.

Laboratory Reports:

Laboratories will be done in groups of four. An Interim Lab Report will be turned in by the Lab Group at the conclusion of the processing portion of the lab. Toward the end of the course, following additional characterization of the fabricated structures, a Final Lab Report will be turned in, again as a group. See the document, "General Description of Lab Reports" for information on Lab Report format and expectations.


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