Evolution of Manufacturing Accuracy Definition for Normal, Precision & Ultraprecision Machining

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Brussels, September 10-19, 2001

Laboratoire de Mécanique Appliquée – UMR CNRS 6604 – Université de Franche Comté Institut des Microtechniques de Franche Comté

2 Machining Technologies on the Micrometer Scale

A/ Conventional Tool-Machining Techniques B/ Photofabrication Techniques

B 1 / The LIGA Process

B 2 / The Silicon-Based Micromachining Technology B 21 / Bulk Micromachining

B 22 / IC- Compatible Polysilicon Surface Micromachining

NATO Advanced Study Institute RESPONSIVE SYSTEMS … / MEMS CourseBrussels, September 10-19, 2001

Laboratoire de Mécanique Appliquée – UMR CNRS 6604 – Université de Franche Comté Institut des Microtechniques de Franche Comté

Evolution of Manufacturing Accuracy

Definition for Normal, Precision & Ultraprecision Machining Left si de: ordinate:i ncrease of manuf acturi ng accuracy over time. Right side: Increase of transistor density over time.

From M . M a dou, Fundamentals of M icrofabrication (1997) chievabl e Manufacturin g ccuracy in µm - Taniguchi Devices per cm

2

/ Moore’ s Law

Turnin g

Diamond Turning

Ultraprecision Machining

IC Lithography

FIB

NATO Advanced Study Institute RESPONSIVE SYSTEMS … / MEMS Course Brussels, September 10-19, 2001

Cutting, turning, drilling, milling and shaving can be done using highly specialized machines…

Finest details that can be machined using conventional tool-machining technology are in the range of 10 to 100

microns…

One to two orders larger than what photolithography makes possible…

One of the greatest advantages of tool-machining is that components are not restricted to flat substrates…

Conventional Tool-Machining Techniques on the Micrometer Scale

Microcar Machined using Ultra-High Diamond Precision Tool.

From Teshigura et al. (1995) Single-Crystal Diamond Tool

Rice Tips

Molded Microcar. The Mold is Machined Through EDM.

From Yu et al. (1998) 7 mm

100 µm

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3D Laser-Machined Shapes

SEM Micrographs of Devices Cut into Silicon Through Laser Micromachining.

The Beam Spot Used is 1µm and the Objective is Lowered in 1µm increments.

Etch Rate is 100,000 µm

³

/ sec.

From Dr. D. Ehrlich, Revise, Inc.

The most important difference with

Photolithography-based fabrication technologies is that using conventional technology, the components must

be made piece by piece.

Miniaturization (2D; 3D) OK Multiplicity ! ?

Integration ! ?

Tool-Machining

From Tool-Machining to Photo-Fabrication Techniques

Technologies Based on Photolithography

1

2 Q uartz

Substra

Substra Photorésin

Photorésin Photorésine élim inée au

U V

- In photolithography light impinges a transparent plate with opaque regions (mask) - Below the mask a photosensive material is placed, which can be developed after illumination - The illuminated regions are dissolved (or the non-illuminated ones)

- The underlying material is accessible to further processing

Mask

Photosensive Material Substrate

Remaining Photoresist Substrate

Dissolved Photoresist

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Technologies Based on Photolithography

Lithography, Galvanoformung, Abformung Process : LIGA

Single Crystal Silicon Bulk-Micromachining

Polycristalline Silicon Surface-Micromachining

The main difference of silicon micromachining with most other machining techniques is that S.M. is suitable for batch processing…

LIGA process is in some aspects similar to S.M.

Comparing Manufacturing Options

Millimeter Size Traveling Wave Piezoelectric Actuator Machined Through Conventional “Watch Making”

Technology.

The Fabrication of a Single Actuator Requires Several Months of Prototyping as Well as Human Dexterity…

( Doc. LMARC/CETEHOR)

Micrometer Size Electrostatic Actuators Realized Through Polysilicon Surface Micromachining. Millions of Prototypes can be Easily duplicated Within a Single Process Flow…

(Doc. LMARC)

Shaping Limitations using Photo-Fabrication Techniques

Shaping Limitations Using Masks & Photo-Fabrication Techniques

LIGA: - 2D Vertical Structures - High Aspect-Ratio

- Parts Ranging from the Micrometer Up to the Millimeter Scale

- Very Expensive Bulk-Micromachining: - 2D & “3D” Structures

- Shaping Restrictions in the Plane - Process Well Established (Pressure

Sensors…)

Surface-Micromachining: - 2D Vertical Structures

- Low Aspect-Ratio & Mechanical Interference Between Structural Layers - No Shaping Restriction along the Wafer

Plane

- IC-Compatible Multi-Layer Structures

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The LIGA Process (Lithography, Galvanoformung, Abformung)

“The LIGA Process exposes PMMA plastic with synchrotron radiation through a mask. The exposed PMMA is then washed away leaving 2D vertical structures with spectacular accuracy. Metal is plated onto high aspect ratio PMMA structures (metal takes the place of PMMA that was watched away). The metal piece can become

the final part, or can be used as an injection mold for parts made out of a variety of plastics”.

From [LEH 95] / LIGA Technique Commercial Brochure-IMM Institute für Mikrotechnic GmbH, Mainz-Hechtsheim.

The Development of microsystems using LIGA is very expensive, because many masks must be made before

a process is stable and the system has the desired architecture.

LIGA is economically feasible only for very large production volumes.

Polymer microcomponents fabricated through LIGA- injection molds are on the market now…

Silicon Micromachining Technology as an alternative to decrease fabrication costs in semi-large production

volumes…

NATO Advanced Study Institute RESPONSIVE SYSTEMS … / MEMS CourseBrussels, September 10-19, 2001

Laboratoire de Mécanique Appliquée – UMR CNRS 6604 – Université de Franche Comté Institut des Microtechniques de Franche Comté

Silicon-Based Technology (Preparation of wafers)

Single Pure Crystal of Silicon

- Diameter: 3 to 12 in ches - Length: several meters

Wafers are Sliced out from Single Crystal of Silicon (SCS)

Polishing of the Wafer Faces and M achining of Flats:

- Primary Flat : <110> Crystallographic Direction

- Secondary Flat: Cryst. Surface Orientatio n and Dopi ng Condi tions

Laboratoire de Mécanique Appliquée – UMR CNRS 6604 – Université de Franche Comté

Silicon Bulk-Micromachining

Chemicals Etch the Different Crystallographic Planes within the Silicon at Different Rates

(Anisotropic Etching of <111> Planes Much More Slower than Other Planes) Differential Etching Allows the Fabrication of an Amazingly Wide Range of Parts

Plan (100) Plan (110) Plan (111)

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Anisotropic & Isotroping Etching of SCS

From web site: mems.colorado.edu

<100> Surface Orientation Same Etch Rate

Surface – Micromachining

From web site: mems.colorado.edu

Layer thickness, number of layers and materials depend on the fabrication

technology that is used

IC-Compatible Polysilicon Surface Micromachining

Doc. LMARC (4 inches Silicon Wafer Micromachined with Clean Room Facilities of EPFL)

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Sharing Clean Room Infrastructures needed for Advanced MEMS Development

Sharing Clean Room Facilities…

Standard Three-Layer Polysilicon Surface Micromachining Process (CRONOS Integrated Microsystems)

From MUMPs Design Handbook / CRONOS Integrated Microsystems Prototyping: 4000$ / design (15 modules 10 x10 millimeters)

Chemical / Mechanical Polishing (CMP)

Impact of Conformal Polysilicon on Unplanarized Surfaces:

From [KRY 98] / Sandia National Laboratories Mechanical Interference with

Underlying Polysilicon Layers Elimination of interference by CMP

of Sacrificial Oxide

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Device Complexity by Structural Layer

From [KRY 98] / Sandia National Laboratories

Four – Layer Design Example (Standard SUMMIT IV Technology)

From Sandia National Laboratories

Five – Layer Design Example (Standard SUMMiT-V Technology)

From Sandia National Laboratories

Prototyping: 10,000$ / design (100 unreleased modules 4660 x4660 microns) Substrate

Poly 0

Surface- Micromachining Technologies Available from US Foundries

S.M. device’s aspect ratio still restricted according to micrometer thick structural layers

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High Aspect Ratio Combined Poly and Single-Cristal Silicon (HARPSS)

From [AYA 00] / The University of Michigan

Monolithic Integration of Microelectronics with Surface- Micromachined Polysilicon Structures (CMOS/MEMS)

From Sandia National Laboratories

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Laboratoire de Mécanique Appliquée – UMR CNRS 6604 – Université de Franche Comté Institut des Microtechniques de Franche Comté

Concept of Parallel Hybridization of MEMS-Based Components

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