Industrial Engineering Chapter 13 Miller Indices Wafer Silicon Referring Fig Identifythe Important Planes For The Other

Chapter 13

Fabrication of Microelectronic,

Micromechanical, and

Microelectromechanical Devices;

Nanomanufacturing

Questions

13.1 Define the terms wafer, chip, device, integrated

(2) simple electronic element such as a transis-

13.2 Why is silicon the most commonly used semi-

conductor in IC technology? Explain.

The reason is its unique capabilities regarding

13.3 What do the terms VLSI, IC, CVD, CMP, and

DIP stand for?

13.4 How do n-type and p-type dopants differ? Ex-

deposition?

strate.

13.6 Comment on the differences between wet and

dry etching.

isotropic etch patterns, and is relatively easy to

This material is protected by Copyright and written permission should be obtained from the publisher prior to any prohibited

reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or

likewise. For information regarding permission(s), write to:

Rights and Permissions Department, Pearson Education, Inc., Upper Saddle River, NJ 07458.

13.7 How is silicon nitride used in oxidation?

13.8 What are the purposes of prebaking and post-

baking in lithography?

done (prior to lithography) to remove solvent

13.9 Define selectivity and isotropy and their impor-

tance in relation to etching.

13.10 What do the terms linewidth and registration

refer to?

13.11 Compare diffusion and ion implantation.

Diffusion and ion implantation are similar. Dif-

fusion refers to the process of atom migration,

and is closely related to temperature. Ion im-

plantation involves accelerating ions and direct-

ing them to a surface where they are incorpo-

rated. Thus, both diffusion and ion implanta-

tion can be used to drive dopants into semicon-

ductor materials.

13.12 What is the difference between evaporation and

sputtering?

then condense on the workpiece. A further de-

13.13 What is the definition of yield? How important

is yield? Comment on its economic significance.

13.14 What is accelerated life testing? Why is it prac-

ticed?

long time, and thus it would not be practical to

chanical features on silicon or on other surfaces.

As shown in Fig. 13.34, surface micromachining

involves production of a desired feature through

film deposition and etching; a spacer layer is

then removed through wet etching, where the

spacer layer is easily etched while the structural

material is not etched.

13.17 What is LIGA? What are its advantages over

other processes?

This material is protected by Copyright and written permission should be obtained from the publisher prior to any prohibited

reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or

likewise. For information regarding permission(s), write to:

Rights and Permissions Department, Pearson Education, Inc., Upper Saddle River, NJ 07458.

LIGA-produced structure is a mold for further

13.18 What is the difference between isotropic and

anisotropic etching?

mask can be produced from a variety of mate-

sisted ion etching and dry plasma etching?

13.21 Which process(es) in this chapter allow(s) fab-

rication of products from polymers? (See also

Chapter 10.)

By the student. It will be noted that poly-

mers are most easily produced from LIGA and

solid freeform fabrication processes. They can

13.23 With an appropriate sketch, describe the ther-

stitching, a gold wire is welded to a bond pad

13.25 Why are ﬂats or notches machined onto silicon

wafers? Explain.

and to also indicate the crystallographic orien-

electrical connections are very difficult to make

if all of the connections must lie within a single

plane. A via allows the designer to make elec-

trical connections on a number of planes, thus

greatly simplifying layout on a board.

13.27 What is a ﬂip chip? Describe its advantages

This material is protected by Copyright and written permission should be obtained from the publisher prior to any prohibited

reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or

likewise. For information regarding permission(s), write to:

Rights and Permissions Department, Pearson Education, Inc., Upper Saddle River, NJ 07458.

13.28 Explain how IC packages are attached to a

printed circuit board if both sides will contain

ICs.

13.29 In a horizontal epitaxial reactor (see the accom-

panying figure), the wafers are placed on a stage

(susceptor) that is tilted by a small amount,

usually 1◦-3◦. Why is this procedure done?

The stage in the horizontal epitaxial reactor is

usually tilted by a small amount to provide

equal amounts of reactant gases in both the

front and back of the chamber. If the stage

is not tilted, the reactant gases would be par-

13.30 The accompanying table describes three

changes in the manufacture of a wafer: in-

crease of the wafer diameter, reduction of the

complexity

The completed table is shown below:

Effects of manufacturing changes

13.31 The speed of a transistor is directly propor-

tional to the width of its polysilicon gate, with

a narrower gate resulting in a faster transistor

and a wider gate resulting in a slower transistor.

Knowing that the manufacturing process has a

certain variation for the gate width, say ±0.1

µm, how might a designer alter the gate size of

a critical circuit in order to minimize its speed

variation? Are there any penalties for making

this change? Explain.

in speed would be expected. However, if the

gate width is increased to 0.8 µm, the speed

This material is protected by Copyright and written permission should be obtained from the publisher prior to any prohibited

reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or

likewise. For information regarding permission(s), write to:

Rights and Permissions Department, Pearson Education, Inc., Upper Saddle River, NJ 07458.

effect?

13.33 The MEMS devices described in this chapter

use macroscale machine elements, such as spur

gears, hinges, and beams. Which of the follow-

ing machine elements can or cannot be applied

to MEMS, and why?

54.74°

13.35 Referring to Fig. 13.23, sketch the holes gener-

ated from a circular mask.

The challenge to this problem is that conical

sections are difficult to sketch. Note, however,

This material is protected by Copyright and written permission should be obtained from the publisher prior to any prohibited

reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or

likewise. For information regarding permission(s), write to:

Rights and Permissions Department, Pearson Education, Inc., Upper Saddle River, NJ 07458.

(b) 100 µm spur gear could be produced

through micromachining; if silicon is not

(e) 100 mm gear could best be machined (see

Class-1?

room.

13.38 Describe the difference between a microelec-

tronic device, a micromechanical device and

ing a micromechanical device and integrated mi-

13.39 Why is silicon often used with MEMS and

MEMS devices?

13.40 Explain the purpose of a spacer layer in surface

micromachining.

13.41 What do the terms SIMPLE and SCREAM

SIMPLE stands for silicon micromachining

13.42 Which process(es) in this chapter allow the fab-

rication of products from ceramics? (See also

Chapter 11.)

By the student. Note that ceramic products are

13.44 Describe the differences between stereolithogra-

phy and microstereolithography.

in Section 13.16, microstereolithography uses

This material is protected by Copyright and written permission should be obtained from the publisher prior to any prohibited

reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or

likewise. For information regarding permission(s), write to:

Rights and Permissions Department, Pearson Education, Inc., Upper Saddle River, NJ 07458.

13.45 Lithography produces projected shapes; conse-

three-dimensional shapes, such as lenses?

13.46 List and explain the advantages and limitations

of surface micromachining as compared to bulk

micromachining.

•Very good dimensional tolerances.

•Complex shapes in multiple layers.

ers.

•The process is effectively limited to silicon

as the substrate material.

•Wet etchants can result in structures that

13.47 What are the main limitations to the LIGA pro-

cess?

13.48 Describe the process(es) that can be used to

make the microtweezers shown in Fig. 13.49

other than HEXSIL.

compliant and lightweight structure. Although

processes such as SCREAM (pp. 855-857) can

be used, the required aspect ratio will be diffi-

bers to aid in molding. However, a structure

that serves the same function can be produced,

even though vertical sidewalls cannot be pro-

duced.

13.49 A certain wafer manufacturer produces two

equal-sized wafers, one containing 500 chips and

the other containing 300 chips. After testing, it

are defective. What are the yields of the two

wafers? Can any relationship be established be-

tween chip size and yield?

This material is protected by Copyright and written permission should be obtained from the publisher prior to any prohibited

reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or

likewise. For information regarding permission(s), write to:

Rights and Permissions Department, Pearson Education, Inc., Upper Saddle River, NJ 07458.

50)/300 = 83.3%. Thus, given the same num-

ber of defects per wafer, the wafer with smaller

chips (i.e., more chips per wafer) will have a

13.50 A chlorine-based polysilicon etch process dis-

resist and exposed oxide will be consumed in

etching 350 nm of polysilicon? What should

the polysilicon:oxide selectivity be in order to

remove only 4 nm of exposed oxide?

13.51 During a processing sequence, four silicon-

dioxide layers are grown by oxidation: 400 nm,

150 nm, 40 nm, and 15 nm. How much of the

silicon substrate is consumed?

13.6, the ratio of oxide to the amount of silicon

13.52 A certain design rule calls for metal lines to be

no less than 2 µm wide. If a 1 µm-thick metal

layer is to be wet etched, what is the minimum

photoresist width allowed? (Assume that the

wet etch is perfectly isotropic.) What would be

the minimum photoresist width if a perfectly

anisotropic dry-etch process were used?

A perfectly isotropic wet-etch process will etch

equally in the vertical and horizontal directions.

Therefore, the wet-etch process requires a min-

imum photoresist width of 2 µm, plus 1 µm per

side, to allow for the undercutting, hence a to-

2µ.

13.53 Using Fig. 13.18, obtain mathematical expres-

sions for the etch rate as a function of temper-

Direc- 1/T Etch rate ln(Etch

3.3 4 1.386

h100i2.55 70 4.248

3.3 2 0.6931

h111i2.55 2 0.6931

3.3 0.015 -4.200

ln(y) vs. 1/T curve, and bis the y-intercept.

From the data in the table above, we can ob-

tain the following

h111i-6.524 17.33

in the h100idirection:

y=1.236 ×107e−4.74/T

in the h111idirection:

y=3.3×107e−6.524/T

13.54 If a square mask of side length 100 µm is

placed on a {100}plane and oriented with a

side in the h110idirection, how long will it

take to etch a hole 4 µm deep at 80◦C using

ethylene-diamine/pyrocatechol? Sketch the re-

This material is protected by Copyright and written permission should be obtained from the publisher prior to any prohibited

reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or

likewise. For information regarding permission(s), write to:

Rights and Permissions Department, Pearson Education, Inc., Upper Saddle River, NJ 07458.

bottom as a function of time for the mask shown

in Fig. 13.17b.

or

x=ht

and (9.13).

W=18.998g/mole

6.023 ×1023atoms/mole

= 1.62 ×10−12 s

13.57 Calculate the undercut in etching a 10-µm-deep

The following table can now be constructed:

made of silicon oxide?

This material is protected by Copyright and written permission should be obtained from the publisher prior to any prohibited

reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or

likewise. For information regarding permission(s), write to:

Rights and Permissions Department, Pearson Education, Inc., Upper Saddle River, NJ 07458.

Time to

etch

Etch 10 µm SiO2Observed

rate trench removed Ref. undercut

Etchant (µm/min) (min) (nm) (nm) (nm)

HF:HNO3: 20 0.5 15 10000 9985

CH3COOH

KOH 2 5 50 100 50

EDP 0.75 13.33 2.66 280 277

N(CH3)4OH 1.5 6.67 0.667 20 19.3

SF60.5 20 0 0 0

13.61 Examine the hole profiles in the accompanying

figure and explain how they might be produced.

This material is protected by Copyright and written permission should be obtained from the publisher prior to any prohibited

reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or

likewise. For information regarding permission(s), write to:

Rights and Permissions Department, Pearson Education, Inc., Upper Saddle River, NJ 07458.

Fig. 13.23 on p. 831 to understand this solution

below. We can state the following:

from the dimensions given, but there is ei-

Fig. 13.17a on p. 824).

(b) The crystal workpiece is aligned so

that has undercut the mask. Compared

to the top right figure, this figure suggests

13.62 A polyimide photoresist requires 100 mJ/cm2

per µm of thickness in order to develop prop-

erly. How long does a 150 µm film need to

develop when exposed by a 1000 W/m2light

source?

t=1000 Nm

1000 W h= 150 s

13.63 How many levels are required to produce the

micromotor shown in Fig. 13.22d?

•Pin or bearing (it must protrude past the

rotor).

13.64 It is desired to produce a 500µm by 500 µm

diaphragm, 25 µm thick, in a silicon wafer 250

a proper opening with a diffusion bonding step

such as shown in part 3 of Fig. 13.41a on p. 849.

Using a wet etchant, a cavity as shown in part

2 of Fig. 13.41a will be produced, with an in-

This material is protected by Copyright and written permission should be obtained from the publisher prior to any prohibited

reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or

likewise. For information regarding permission(s), write to:

Rights and Permissions Department, Pearson Education, Inc., Upper Saddle River, NJ 07458.

13.65 If the Reynolds number for water ﬂow through

a pipe is 2000, calculate the water velocity if

turbulent or laminar? Explain.

η

where vis the velocity, Dis the channel diame-

If the channel diameter is 10 mm, then

(0.01)(1000) = 0.178 m/s

(0.0001)(1000) = 17.8 m/s

13.66 The accompanying figure shows the cross sec-

3 Oxide etch 4. Resist removal

n

pn

p

17. Aluminum etch 18. Resist removal

222

This material is protected by Copyright and written permission should be obtained from the publisher prior to any prohibited

reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or

likewise. For information regarding permission(s), write to:

Rights and Permissions Department, Pearson Education, Inc., Upper Saddle River, NJ 07458.

13.67 Referring to the MOS transistor cross section in

the accompanying figure and the given table of

design rules, what is the smallest transistor size

Wobtainable? Which design rules, if any, have

no impact on the magnitude of W? Explain.

R1

R3 R2

R4 R6 R5

W

metal spacing

The smallest transistor size, W, that can be

obtained using the given design rule is:

13.68 The accompanying figure shows a mirror that

is suspended on a torsional beam; it can be in-

The device shown in the problem was produced

at the University of California at Berkeley Sen-

sor and Actuator Center. As can be noted,

the layer below the mirror is very deep and

has near-vertical sidewalls; hence, this device

of this approach.)

13.69 Referring to Fig. 13.36, design an experiment to

find the critical dimensions of an overhanging

cantilever that will not stick to the substrate.

through surface micromachining, followed by

rinsing, some of the cantilevers attach them-

This material is protected by Copyright and written permission should be obtained from the publisher prior to any prohibited

reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or

likewise. For information regarding permission(s), write to:

Rights and Permissions Department, Pearson Education, Inc., Upper Saddle River, NJ 07458.

13.70 Explain how you would manufacture the device

shown in Fig. 13.32.

13.71 Inspect various electronic and computer equip-

ment, take them apart as much as you can, and

identify components that may have been man-

ufactured by the techniques described in this

teresting projects also can arise from this ex-

periment. One project, for example, would

13.72 Do any aspects of this chapter’s contents and

the processes described bear any similarity to

the processes described throughout previous

chapters in this book? Explain and describe

are similar to the polishing and grinding pro-

cesses, described in Chapter 9. Producing sil-

icon wafers involves the Czochralski (CZ) pro-

cess (see Fig. 5.30 on p. 235). Printed circuit

boards are stamped and the holes are drilled,

as described in previous chapters. Packaging

involves potting and encapsulation of polymers

(p. 636). The students are encouraged to com-

ment further.

13.73 Describe your understanding of the important

Clean rooms are described in Section 13.2. Stu-

dents are encouraged to search for additional in-

13.74 Describe products that would not exist without

the knowledge and techniques described in this

chapter. Explain.

found impact on our lives, and any product

that contains an integrated circuit would ei-

music players. The students are encouraged to

comment further, with numerous examples of

their own.

This material is protected by Copyright and written permission should be obtained from the publisher prior to any prohibited

reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or

likewise. For information regarding permission(s), write to:

Rights and Permissions Department, Pearson Education, Inc., Upper Saddle River, NJ 07458.

the wafer will have a barrel shape, which is ben-

13.76 It is well known that microelectronic devices

may be subjected to hostile environments (such

By the student. This is a good topic for stu-

13.77 Conduct a literature search and determine the

smallest diameter hole that can be produced by

(a) drilling; (b) punching; (c) water-jet cutting;

(d) laser machining; (e) chemical etching and

(f) EDM.

By the student. This is an interesting topic for

a web-based research project. Specific dimen-

13.78 Design an accelerometer similar to the one

By the student. The students should draw upon

13.79 Conduct a literature search and write a one-

page summary of applications in biomems.

screening for many conditions. In-vivo applica-

tions of MEMS are relatively few in number as

of today.

13.80 Describe the crystal structure of silicon. How

does it differ from the structure of FCC? What

is the atomic packing factor?

This material is protected by Copyright and written permission should be obtained from the publisher prior to any prohibited

reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or

likewise. For information regarding permission(s), write to:

Rights and Permissions Department, Pearson Education, Inc., Upper Saddle River, NJ 07458.