ecm clas type

7/30/2019 Ecm Clas Type

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Chemical-mechanical polishing (CMP) Electrochemical machining (ECM) Electrochemical grinding (ECG)

ELID grinding Electric discharge machining (EDM) Abrasive water jet machining Ultrasonic grinding

Electron beam machining Laser beam machining Ion beam machining . . . . .


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Chemical-Mechanical Polishing (CMP)

A method of controlling the planarity of themultiple metal and dielectric layers

A process of physically removing material from

places of high topography to flatten and levelthe wafer surface (IC wafer planarization)

A wafer surface planarization technology

applied in the manufacturing of sub-0.35 umsemiconductor devices.


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Planarization

Non-planar and planar interconnect layers

[Borst, Grill and Gutmann 2002, pg. 46 -CMP of low dielectic constant polymersand organosilicate glasses, CL Borst, W. Gill, R.J. Gutmann]

Planarity across the die is important for photolithography processes,which projects a pattern of light onto the wafer surface


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Principle of CMP Process

[Borst, Grill and Gutmann 2002, pg. 48]

A slurry consisting of chemical regents and abrasive particles isdispensed to create a lubricating layer between the pad surface andthe wafer. The slurry contains chemicals that react with the wafersurface, and abrasive particles that impact the wafer surface toachieve mechanical removal.


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CMP Process Parameters

The wide array of parameters and the competing interactionof effects makes CMP a difficult process to model andpredict


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CMP Abrasives

The choice of slurry abrasive particle (vary in size, shape andhardness) is vital for achieving the desired removal rate andsurface roughness of a material.

CeO2, ZrO2 and SiO2 in high pH solutions are commonly used topolish silicon oxide, and Al2O3 is most commonly used for metal

(Cu W, AL) CMP.


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CMP- material removal

Chemical-mechanical planarization chemical reactionandmechanical energycombined to achieve material removal fromhigh regions on the wafer surface, leaving the low regionsrelatively untouched

[Borst, Grill and Gutmann 2002, pg. 49]


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CMP Process Models

Fluid mechanics-based:

2-step removal process=

chemical modification offilm surface layerfollowed by abrasion ofthe modified layer

Contact mechanics-based:

30-40mm thickliquid slurry film

Combination of pressure and velocity

Lubricatinglayer


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CMP - Process

Surface roughness nano-finish achievable

AFM scan before polished

AFM scan after polished

Nanometer-scale scratches observed

High roughness and scratchingcaused by large mechanicalabrasion. Low roughness andscratching suggest the presenceof a protective layer


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CMP - SPCR

Solid phase chemical reaction (SPCR)

[Chen, Shu and Lee 2003] J. of Matl Proc Techn, 140 (2003) 373-78

Chemical passivation layer generated: process ofinducing and removing the chemical passivation layerthru force of action

Silicon wafer as substrateand BaCo3 as abrasive


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CMP Machines

- self-leveling upper head with both rotational and linear(both vertical for loading and unloading and horizontalfor oscillating) motions, which holds a wafer or wafercoupon of any shape from 0.25 to 4,

- mechanically applied servo-controlled normal loadprogrammable from 5 to 500 N thus producing contactpressures from 0.05 to 500 psi,

- self-leveling spring-loaded upper holder with passiverotation, which holds a conditioner or another specimenfrom 0.5 to 4.25,

- either rotational or orbital lower platen for a polishingpad from 1 to 9. - slurry feeding and draining.

Example:

(source: http://www.cetr.com/Brochures)


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Electrochemical Machining (ECM)

A controlled anodic electrochemical dissolutionprocess of the workpiece (anode) with the tool(cathode) in an electrolytic cell, during an electrolysis

process

(source: http://www.unl.edu/nmrc/ecm1/ecm1.htm)

Scheme of electrochemical machining (ECM) process


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Principle of ECM (1)

An electrochemical anodic dissolution process inwhich a direct current with high density and lowvoltage is passed between a workpiece and a pre-shaped tool (the cathode).

At the anodic workpiece surface, metal is dissolvedinto metallic ions by the deplating reaction, and thusthe tool shape is copied into the workpiece.

A relatively new and important method of removingmetal by anodic dissolution and offers a number ofadvantages over other machining methods.


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Example:electrochemical reactions during ECM of ironin sodium chloride (NaCl) electrolyte

At the anode (+):

At the cathode (-) :

electrolysis has involved thedissolution of iron from theanode, and the generation ofhydrogen at the cathode. Noother actions take place atthe electrodes.


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Metal removal is effected by a suitably shaped toolelectrode, and the parts thus produced have thespecified shape, dimensions, and surface finish.

ECM forming is carried out so that the shape of thetool electrode is transferred onto, or duplicated in, the

workpiece.

High accuracy in shape duplication and high rates of

metal removal, effected at very high current densities ofthe order 10 100 A/cm2, at relative low voltage from 8to 30 V, while maintaining a very narrow machining gap(of the order of 0.1 mm) by feeding the tool electrode inthe direction of metal removal from the work surface,with feed rate from 0.1 to 20 mm/min.


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Common Uses for ECM

Duplicating, drilling and sinking operations in themanufacture of dies, press and glass-making moulds,turbine and compressor blades for gas-turbine engine,the generation of passages, cavities, holes and slots in

parts, and the like

Electrochemical sinking operation

NC electrochemical contouring usingsimple-universal tool-electrode


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ECM Machining System

the machine itself the power supply

the electrolyte circulation system the control system

ECM die sinking machine tool (courtesy AEG-Elotherm-Germany)


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Operating Parameters of ECM

Working voltage between the tool electrode(cathode) and workpiece (anode)

Machining feed rate

Inlet and outlet pressure of electrolyte (orflow rate)

Inlet temperature of electrolyte


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Typical parameters and conditions of ECM

Power supply -

Type: Direct Current

Voltage: 5 to 30 V (continue or pulse)

Current: 50 to 40,000 A

Current Density: 10 to 500 A/cm2 [ 65 to 3200 A/in2]

Electrolyte -Type and Concentration

Most used: NaCl at 60 to 240 g/l [ to 2 lb/gal]

Frequently used: NaNO3

at 120 to 480 g/l [1 to 4 lb/gal ]

Less Frequently used: Proprietary Mixture

Temperature : 20 to 50o C [68 to 122oF]

Flow rate: 1 l/min/100A [0.264 gal/min/100A]

Velocity : 1500 to 3000 m/min [5000 to 10,000 fpm]

Inlet Pressure: 0.15 to 3 MPa [22 to 436 psi]

Outlet Pressure: 0.1 to 0.3 MPa [15 to 43.6

Frontal Working Gap : 0.05 to 0.3mm [0.002 to 0.012 in]Feed rate: 0.1 to 20mm/min [0.004 to 0.7 in/min

Electrode material: Brass, Copper, Bronze

Tolerance -2-dimensional shapes: 0.05-0.2 mm

[0.002- 0.008 in]

3-dimensioanl shapes: 0.1mm [0.004 in]

Surface Roughness (Ra) 0.1 to 2.5 mm

[4 to 100 microinches]


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ECMed Parts

Examples of machined parts byECM (AEG-Elotherm-Germany)

Examples of machine parts after deburring(AEG-Elotherm-Germany)


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Summary of ECM

The rate of material machining depend on workpiecematerial, is equal from 1,200 to 2,500 mm3 for each1,000A of power supply

The accuracy of ECM depend on shape and dimensions of

machining workpiece and approximately from 0.05 mm to0.3 mm at using continuous current, and from 0.02 mm to0.05 mm at using pulse ECM;

The surface roughness of machined surface is decreasingwith increasing machining rate (for typical materials),approximately from Ra=0.1 mm to Ra= 2.5 mm;

ECM generates no residual stress into material ofworkpiece; and there is no tool wear.


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Nano Machining:

Micro Machining:

A work material removed process by cutting tools under

micro scales. That is the cutting parameters used are in

micrometer scales: 1 ~ 999 mm depth of cut or 1 ~ 999 mm

undeformed chip thickness.

A work material removed process by cutting tools under

nano scales. That is the cutting parameters used are in

nanometer scales: 1 ~ 999 nm depth of cut or 1 ~ 999 nm

undeformed chip thickness.

Non-conventional Precision Machining


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Precision Finishing (1)

Precision grinding involved a maximumprecision to about 1.0 mm and expected toreach 100nm

SPDT (single-point diamond turning), UPDG(ultra-precision diamond grinding), ELIDgrinding (electrolytic in-process dressing), etc.

Applications to optical and electronicindustries


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Precision Finishing (2)

SPDT, UPDG processes are similar in thatchips of usually small size

Capable of producing surfaces with mirrorfinishing w/o polishing

Using specially designed machine tools of

high rigidity with air bearing spindles


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SPDT vs. UPDG

Major problems is the appearance ofsubsurface defects in the form ofmicrocracks

SPDT is performed on very soft ductilemetals, e.g. pure copper, while UPDGusually performed on very hard brittle

materials, e.g. glasses and ceramics.


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Ductile Mode Machining

Especially for brittle materials, is a machining processthat work materials are removed by dislocation orplastic deformation rather than cracks propagation.That is, the cutting process is dominated bydislocation rather than flaw extension.

Comparison with brittle fracture:

Easy controlling of machining process; Free of cracks;

Smoother surface.


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High hardness

High strength

Good fracture toughness High wear resistance

Good chemical stability

Good thermal stability

Characteristics ofBrittle Materials


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A transition in the chip formation from brittle to ductile

as the depth of cut decreases to very small

Grinding brittle materials in a ductile manner early in

1954 by King and Tabor The first systematic studies of grinding ductility in 1979

by Swain

Other experiments of single grit abrasion tests on many

brittle materials including semiconductors, glasses andadvanced ceramics

Grinding of Brittle Materials


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Form/Dimensional

Accuracy < 0.1um

Surface Roughness

< 10 nm

Nano Precision Machining

Toshiba ULG 100C Diamond Turning Machine


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Silicon (111) Wafer:

3 inches Diameter

0.5 mm Thickness

Single Crystal Diamond Tool (orSPDT):

Rake Angle 0

Nose Radius 0.3 mm

Cutting Edge Radius 40 nm

Cutting Conditions:

Spindle Rotation Speed 1000 rpm

Nanomachining experimental setup

on an ultra-precision machine tool

Nano Surface Machining by SPDT


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(photos of silicon wafer surfaces)

(a)Diamond turning surface (b) Original polished surface

Mirror Surface Finishing

Mirror surface finish of hard and brittle material can be possible

when material removal taking place thru plastic deformationratherthan fracture


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Aspheric glass lens

Spherical mirror Mirror finish by diamond turning

Machining of aspheric glass mould

Mirror Finished Products


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ELID Grinding (1)

Schematic illustration of ELID grinding [Lim et al, 2002]

The wheel is continuously dressed while the part is machined The difference between ELID and conv. Grinding is the applicationof a current during grinding. Applications incl. grinding of silicon wafer, nano surface finishingon difficult-to-machine materials, e.g. glasses, ceramics, etc.


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ELID Grinding (2)

Set-up of the continuous ELID of a metal-bonded diamond wheel[Shaw 1996]

The bond is depleted continuously by a pulsed d.c. power

supply, enabling optimum protrusion at all timesProcess applicable to grinding of either electrical conducting ornon-conducting work materials but only with metal-bondedwheels


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ELID Grinding (3)

Schematic diagram of the experimental set-up

[Lim et al, 2002]


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NUS Experimental Setup

Machine tool: Deckel Maho DMU50V 5 Axis

Grinding wheel: #325,#1200,#4000 @3000rpm

Feed Rate : 100~600mm/min

Dressing Current : Duty ratio 10~60% @90V


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Principle of ELID Grinding

Cast-iron bonding material for holding the diamond particles is removed

by the electrolysis during in-process dressing and fresh diamond particles

protrude out for grinding.

Super fine diamond grit (grit size up to #150,000)


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Without ELID(0.3795mm) With ELID (Ra 0.1491mm)

Effect of ELID

Grinding conditions: Feedrate: 500mm/min

Spindle: 3000rpm

Electric power: 0%, 30%@90V

Wheel : CIB-D wheel #1200

Silicon afe plana i ation b


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Workpiece

Tool

dynamometer

Wheel

Electrode

Highly efficient due to high removal rate

Uniform ground surface across the wafer

Relatively low cost involved in this process

Silicon wafer planarization byELID Grinding

Ra 3nm (10nm required)

Multi-process Miniature Machine Tool


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Multi-process Miniature Machine Toolfor-machining

Multi purpose machine toolfor micro machining

(-turning, -milling, -

drilling, -EDM, -ECM)

Working area :

200100100mm

(Resolution 0.1 m)

DI water /Oil for EDM

medium

Design of motion controller

6.5 micron Hole1.5 mm length shaft

Contact: Dr. A.S. Kumar,[email protected], MicroTool

Interchangeable

spindle unit

Micro WEDG

MicroEDMMicro Milling

Micro Turning

Micro WEDM

On MachineMeasurement
mailto:[email protected]:[email protected]


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References

1. C.L. Borst, W.N. Gill and R.J. Gutmann, Chemical-Mechanical Polishing of Low Dielectric ConstantPolymers and Organosilicate Glasses, KluwerAcademic Publishers,, Boston,2002

2. M. C. Shaw, Principles of Abrasive Processing,Clarendon Press, Oxford, 1996

3. C.C. Chen, L.S. Shu and S.R. Lee, J. of MaterialsProcessing Techn, 140(2003), pp.373-78

4. ECM, http://www.unl.edu/nmrc/ecm1/ecm1.htm5. H.S. Lim, K. Fathima, et al., Intl J. of Machine Tool &Manufacture, 42 (2003) pp935-43.
http://www.unl.edu/nmrc/ecm1/ecm1.htmhttp://www.unl.edu/nmrc/ecm1/ecm1.htm

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