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Processes and micro technologies for generation of “master masks” for incremental disks divisor and vernier of

position and angular photoelectric incremental transducers

The Romanian Review Precision Mechanics, Optics & Mecatronics, 2007 (17), No. 32 957

PROCESSES AND MICRO TECHNOLOGIES FOR

GENERATION OF “MASTER MASKS” FOR INCREMENTAL

DISKS DIVISOR AND VERNIER OF POSITION AND

ANGULAR PHOTOELECTRIC INCREMENTAL

TRANSDUCERS

Ph.D. Gheorghe I. Gheorghe – Managing Director

National Institute of Research and Development in Precision Mechanics – Bucharest

Ph. D. Octavian Dontu, UPB, Mechanical Engineering and Mecatronics Faculty – Bucharest

Abstract – Precision of the transducer is directly dictated by precision of disks division, by quality of opaque-transparent contrast, by rectilearity of transparent-opaque demarcation line as well as geometry of transparent-opaque areas. Realization of incremental disks is made by photographic technique. One of the methods involves existence of an original mask that multiplies by transferring image from a transparent support on which is laid-down a metal and a photosensitive layer; as a result of corrosion, the part from metallic layer unprotected is eliminated, resulting desired configuration.

Taking in consideration very small dimensions of plotting and high density, technique method for realizing these disks is litophotographic, which allows reaching submicronic dimensions. As regards relative positioning precisions of routes, in case of settlement in X, Y coordinates (frequent in microelectronics), technique of producing masks beneficiates the following

advantage: execution of a mask less pretentious to hundreds times higher scale, which by successive reductions reaches high precisions. Keywords – micro technologies, master masks

Introduction

Fundamental Considerations

Is presented, designed and realized the

incremental angular position transducer (fig. 1).

Precision of the transducer is directly

dictated by precision of disks division, by quality of

opaque-transparent contrast, by rectilearity of

transparent-opaque demarcation line as well as

geometry of transparent-opaque areas.

Realization of incremental disks is made by

photographic technique. One of the methods

involves existence of an original mask that

multip lies by transferring image from a transparent

support on which is laid-down a metal and a

photosensitive layer; as a result of corrosion, the part

from metallic layer unprotected is eliminated,

resulting desired configuration.

Fig. 1

Taking in consideration very small dimensions of plotting and high density, technique




method for realizing these disks is litophotographic,

which allows reaching submicronic dimensions.

As regards relative positioning precisions of

routes, in case of settlement in X, Y coordinates

(frequent in microelectronics), technique of

producing masks beneficiates the following

advantage: execution of a mask less pretentious to

hundreds times higher scale, which by successive

reductions reaches high precisions.

In case of radial settlement of routes at

masks for coder d isks, where appear the problem of

angular position, technique of reducing masks

doesn’t has the effect of increasing precision, so the

quality of method for generating mask is transmitted

directly to the product.

Execution of mask at a higher scale could

bring facilities in execution, taking into account

increase of routes dimensions, but it could have

imposed the use in mult iplying flow of an

intermediary mask obtained on a reduction bank.

To eliminate this technological stage (which

besides supplementary work volume brings a lack o

quality) was used the idea of realizing masks at 1:1

scale.

Work principle for mean of generating

routes is impressing by light fascicle of photo

sensitive emulsion, from a system with laser ray.

Taking into account that in technology of

transferring image mask-sublayer, photo emulsion

enter in direct contact with photoresist and taking in

consideration weak mechanical resistance of

emulsion, for increasing work life, the work masks

has to be copies on chrome of the originals.

This involves that original masks must be

positive of disks images.

In conclusion, masks are obtained on photo

emulsion, on optical glass support, at 1:1 scale,

carrying the positive of disks configurations (with

some auxiliary traces imposed on measurement and

multip lying technology).

“Etalon mask” configuration

Aligning reticules and technological routes

At the base of establishing mask routes are

execution drawings of incremental disks divisor and

vernier.

Taking into account necessity of measuring

marks, there is the problem of materializing

incremental d isks and of tracing orig in ( = 0 ).

That is way on each mask appears a

reticular central cross and two pairs of indexes

adjusted at 900.

Dimensions of these routes are imposed by

technical characteristics of observation methods and

measuring of the masks. Also, is introduced a

measuring tracks (with 140 mm diameter) on which

is a route at each 10 increments.

For centering operations, for reproducing

and debiting disks sublayer, is necessary existence

on the mask of some concentric circles at specific

dimensions.

As regards the geometry of routes from

measuring tracks, there are two variants for

realization, according to figure 2 and figure 3.

Fig. 2 Fig. 3

Technological quotation

Taking into account technique for

generating masks in polar coordinates for each route

must be defined the following elements:

Medium ray; route thickness;

Angular position of radial symmetry

axe of the route;

Maximum and minimum ray ;

Route thicknesses corresponding to

Rmin and Rmax; respectively all there

elements disposed radially (fig. 4).




Fig. 4

According to these requests were quoted

sketches from figures 5, 6, 7, 8 and values are given

tabular for each mask, according to tables 1, 2, 3, 4.

Fig. 5

Fig. 6

Fig. 7




Fig. 8

Tabel nr. 1.

i 2Rmin i 2Rmaxi i 2xi 2yi i

1 30 34 / 2 0 10’48” 0,0471 0,0534 0

2 35 39 2 0 43’12” 0,2199 0,2450 3 / 4

3 35 39 0 21’36” 0,1099 0,1225 4 + / 4

4 35 39 0 21’36” 0,1099 0,1225 6 + / 4

5 35 39 0 21’36” 0,1099 0,1225 9 + / 4

6 35 39 0 21’36” 0,1099 0,1225 13 + / 4

7 35 39 3 1 4’48” 0,3298 0,3675 16 + / 4

Tabel nr. 2.

I 2Rmin i 2Rmaxi i 2xi 2yi i

1 30 34 / 2 0 10’48” 0,0471 0,0534 0

2 35 39 3 1 04’48” 0,3298 0,3675 49 +3 / 4

3 35 39 0 21’36” 0,1099 0,1225 52 + 3 / 4

4 35 39 0 21’36” 0,1099 0,1225 56 + 3 / 4

5 35 39 0 21’36” 0,1099 0,1225 59 + 3 / 4

6 35 39 0 21’36” 0,1099 0,1225 61 + 3 / 4

7 35 39 2 0 43’12” 0,2199 0,2450 65 + / 4

Tabel nr. 3




I 2Rmin i 2Rmaxi i 2xi 2yi i

1 30 34 / 2 0 05’24” 0,02356 0,0267 0

2 35 39 0 10’48” 0,0549 0.06126 3 / 4 8’6”

3 35 39 0 10’48” 0,0549 0.06126 2 +3 /4 29’42”

4 35 39 0 10’48” 0,0549 0.06126 5 +3 /4 1 2’6”

5 35 39 2 0 21’36” 0,109956 0,1225 9 + / 4 1 45’18”

6 35 39 0 10’48” 0,0549 0.06126 11 + 3 / 4

7 35 39 2 0 21’36” 0,1099 0,1225 14 + / 4

8 35 39 0 10’48” 0,0549 0.06126 18 + 3 / 4

9 35 39 3 0 32’24” 0,1649 0,06126 25 + 3 / 4

10 35 39 0 10’48” 0,0549 0.06126 28 + 3 / 4

11 35 39 2 0 21’36” 0,1099 0,1225 33 + / 4

Tabel 4

I 2Rmin i 2Rmaxi I 2xi 2yi i

1 30 34 / 2 0 05’24” 0,02356 0,0267 0

2 35 39 2 0 21’36” 0,1099 0,1225 102 + 3 / 4

3 35 39 0 10’48” 0,0549 0.06126 107 + / 4

4 35 39 3 0 32’24” 0,1649 0,06126 110 + 3 / 4

5 35 39 0 10’48” 0,0549 0.06126 117 + / 4

6 35 39 2 0 21’36” 0,1099 0,1225 121 + 3 / 4

7 35 39 0 10’48” 0,0549 0.06126 124 + / 4

8 35 39 2 0 21’36” 0,1099 0,1225 126 + 3 / 4

9 35 39 0 10’48” 0,0549 0.06126 130 + 2 / 4

10 35 39 0 10’48” 0,0549 0.06126 133 + / 4

11 35 39 0 10’48” 0,0549 0.06126 135 + / 4

Technological flow

Due to the special influence of

environmental conditions on dimensional precision

and masks quality, the entire process of realizing

originals is made in the laboratory, in climat ic

conditions strictly adjusted at the following

parameters:

- Temperature: 20 C 2 C;

- Humidity: 45% 5%;

- High degree of dust separation.

Besides these general air-condit ioning

characteristics, there are also used local temperature

adjustments on workstations in chemical p rocessing.

Block scheme of technological flow is

given by figure 9, being evidenced large groups of

operations and base methods of realization.

Programming

The routine contains commands and

informat ion given to the system regarding

dimensions of routes, positioning, factors of tracing

cinematic and succession of operations.

All these commands are elaborated on idea

of realization high precision of circu lar d ivision and

idea of min imizing method errors (errors cumulated

resulted from a round calculation by repeated

summarizations and of a step, errors given by limits

imposed by the computer to significant dig its).

The minim increment of angular command

in polar coordinates is 0.25”. The routine is

expressed by a computer language computer own,

and the diagram that shows how is made is given by

the figures 10 and 11.




ADJUSTEMENT OF MASKS

DIMENSIONS

ADJUSTEMENT OF TRACING ALGORITM

PROGRAMMING

GENERATING PUNCHED

BAND

TRACING FOR CHECKING ROUTINE

STANDARD PROCESSING

MASKS INSPECTION

ROUTINE CORRECTIONS

TRACING SAMPLES TECHNOLOGICAL SAMPLES

PROCESSING IN CORRECTED CONDITIIONS

MASKS INSPECTION

MEASUREMENT

CORRESPOND

DATA INTERPRETATION

STOP

1

2

3

4

5

6

7

8

9

10

11

12

13

EXPOSURE CORRECTION R

b

[OKITYPER 5800]

[SISTEM PMPG R1010]

MICROSCOP MESMI 75

MICROSCOP ASAHI

MICROSCOP PERAVAL

PLATE DIVIZOR ZEISS OPTON RT 05

NO

YES

NO

YES

SISTEM PMPG

RD 0101

Fig. 9

START

CORRESPOND




START

CROSS TRACING DOUBLE RETICULAR

TRACING CIRCLE DE-MARCATION, INTERIOR

TRACING CIRCLE INTERIOR CENTERING

TRACING INDEXES

OF 0 AND 90

SUBROUTINE EXECUTION - 100 TIMES (200 TIMES)

TRACING TRACK "0"

TRACING

INTERMEGIARY CIRCLE

TRACING CIRCLE EXTERIOR

DEMARCATION


STOP

SUBROUTINE DIVISION MEASU-REMENT TRACK

SUBROUTINE EXECUTION - 8 TIMES (28 TIMES)

SUBROUTINE DIVISION

READING TRACK

TRACING INDEXES OF

0 AND 90


TRACING CIRCLE DE-MARCATION, INTERIOR

CROSS TRACING DOUBLE RETICULAR

START

TRACING TRACK OF "0"

TRACING

INTERMEGIARY CIRCLE

TRACING CIRCLE EXTERIOR

DEMARCATION


STOP

Fig. 10 Fig. 11

Tracing

The principle of system tracing [PMG R

0101 - pattern generator] is as follows: a laser spot

dimensionally controlled, whose symmetry axis is

rigorous centered, focalized in photo emulsion

plane, is moved on a direction impressing sensitive

plaque, which fixed on a gyrating table is angularly

moving (part icular case of tracing in polar

coordinates).

Carrying sublayer of photosensitive

material is fixed in a vacuuming device.

Focalizat ion is made in two stages:

Manual focalization for bringing with




approximation on adjusting range ( 0,5 m);

Automate focalizat ion, maintained during

tracing for deviations from planarity take-up

and perpendicularity at optical axis.

On the entire flow, there are used as

photosensitive materials AGFA films on polyester

support OP 81 GEVALITH for routine samples,

aligning, centering and AGFA films on glass support

HOLOTEST 10 E 56 for samples of exposing route

samples and final masks.

In term of sensitivity, spectral sensitivity,

exposing lamp characteristics, dimensional

corrections proposed for routes in optical route are

interposed color filters and transmission filters.

Values for wave lengths and transmission

coefficients have a theoretical base, being then

experimentally adjusted for obtaining desired results

on both qualities of film.

Chemical microtechnologies for master masks

processing

Together with exposing and sensitivity of

photographic plaque, chemical processing is

considered as being the third critical factor in

obtaining images with high resolution. Standard

technique for processing exposed masks (negative

process) presents a series of variables, with more o r

less stages, in term of photosensitive materials. But a

complete process will necessary involve the

following stages:

1 – alkaline treatment for deantiholoing (variab le

only for antiholo layer plaques);

2 – washing with flowing water (also for plaques

with antiholo treatment);

3 – developing with continuous swirling;

4 – washing in flowing water;

5 – fixing in fixing solution with frequent swirling;

6 – washing in flowing water;

7 – drying.

If the alkaline treatment applied in case of

plaques endowed on the back side with antiholo

layer doesn’t represent a special problem, chemical

reactions from developing operation are significant

for the process.

A typical developing solution will contain:

1 • solvent (which is water); 2 • reducing agent; 3 •

activator; 4 • maintaining agent; 5 • modeler.

Basic reaction is reducing granules of silver

halide exposed to metallic silver with help of

reduction agent, which is a reactive from phenols

series (is exemplified by hydroquinone) and in

alkaline solution is in a ionized state and in a

relatively high concentration (fig. 12).

+2H++2Ag

++2OH

-→2Ag

0+ +2H2O

OH

OH

O-

O

O

O

Fig. 12

This reaction begins in latent status image

fall into silver halide granules exposed and continue

until developing is stopped.

Metallic silver wires resulted produce

optical density of image resulted in emulsion. As

typical moderator is used potassium bromide which

delays developing at unexposed granules level,

forming some kind of area electrostatic charged

around them, which act as a barrier to reducing

agent. Maintaining agent is alkaline antioxidant type

sodium sulphite that slows oxidation of active

reducing agent and is situated in developing solution

in contact with atmospheric oxygen.

Because developing reaction is produced

especially in emulsion with exposed granules, a

slight agitation is indicated to allow fresh developing

agent to dispel inside.

Developing reaction can be stopped in the

following phase of washing in flowing water and

more rapid ly, although not indicated (because

produces malformations at emulsion level) in

slightly acid solutions.

Developing stage is especially critical and

necessitates a rigorous control of the process.

Selectiv ity of the silver halide granules towards

reducing agent from developer is limited to a short

period of time, if the process continues, reduction

reaction will continue as well with a decreasing

speed until reducing the entire quantity of silver

halide, exposed or unexposed to metallic silver.

Practical experience demonstrates that

activity degree of developing, time, temperature and

agitation state of solution is in connection with

quantity of silver developed. Rigorous control of

these factors leads to endowment of development

baths from processing installations, extra towards

other baths (which have submicronic filtering and

agitation) with precision thermometers of 0,2 C,

chronometers and pH indicators for activ ity level o f

developer. In fixing stage, takes place removing

silver halide remained in unexposed areas.

Reaction takes place between salt cake or

ammonia sulphate, in water solution of fixing agent

in ionized state and silver halide, which forming in

this way soluble complexes, can be removed by

washing: 32)302(SAG

2302S AgX şi

X52)302(SAG (1)

Traces of disulphide in emulsion, not




removed by washing, can later produce defects of

image.

The last stage of masks drying and which is

also a part of processing technology, although

appears unimportant, was hardly studied.

Thereby is very important that no mater

which method of drying is used, washing that

precedes it to be made in clean water, so after drying

to not appear on the mask from previous operations

traces of chemicals, reaction products, colorants or

other types of materials.

There are used for basic techniques for

drying masks, each with a higher or smaller

extension:

Drying by evaporating water: the main

advantages are: long period of t ime when drying

takes place at room temperature or danger for

deforming image when drying temperature

exceeds a certain value. Also, the system

presents a high degree of danger for mask

contamination.

Removing through physical methods of the

water: is realized by forced drying with air jet o r

centrifuging. By air jet, dry ing can result in

photo masks with residuum traces in marginal

areas, where water leaved the plaque,

centrifuging method representing this fault, but

in general is accessible in a limited area of the

mask.

Dilution with rapid evaporation of the solvent:

is also method applied in practice, uses

methanol (very toxic) or ethanol, polar solvents

slightly volatile and with water forms mixtures

miscible in any proportion.

The process includes three successive baths

where the solvent grows from 25% to 100% in the

last bath, allowing that water extraction from

gelatine to be made with a moderate speed without

degraded it (blue veil phenomena).

Movement with solvent with high drying speed;

drying involves overlapping of two phenomena:

Replacing water from dried surface with a

liquid with superficial low vo ltage;

Movement of water droppings at the surface

(water having lower density) and gathering

them in a system with separator, liquid being

recircu lated.

In studies also appear a variant of this

system called “drying with spaces within phases”.

The two phases that participate to water

removal can be for example tricloretine and a

mixture of alcohol with Freon.

The process takes place as shown in the

figure below (fig. 13), where there are displayed the

six stages if the process that takes place:

The drop of water from the surface of the

plaque that was immersed in solvents mixtu res;

A part of alcohol is extracted from the drop of

water;

Following modification of the density as well as

superficial voltage towards plaque, the drop is

removed from the plaque and is lifted;

At the surface is formed a d istinct phase from

water and alcohol;

Plaque extracted from solvent, which has on the

surface a layer absorbed by the alcohol, Freon

which rep laced water, this is found on solvent

surface in equilibrium with a layer from solvent

vapors;

By rap id evaporation at air, this layer is

removed.

Fig. 13

In figure 14, is also reproduced a system

that realize quick d rying of photo plaques by this

method.

The system is applicable at realizat ion in

large series of the mark.

Even in best systems of exposing and

processing of the masks, the result cannot be

represented as very precise areas of passing from

opaque to transparent, as a result of optical exposure

systems imperfect ions, as well as limitations of

processing solutions selectivity.

Wa

ter

se

pa

rato

r

water

Processing compartment

D

eca

nte

r re

se

rvo

ir

Wa

ter

at

dra

inin

g

Freon – alcohol vapors layer

water

Freon – alcohol

distillate

Fig. 14




In figure 15, can be seen the influence of

exposure and developing on emulsion thickness. Can

be seen at the final phase exposed and developed (d)

how as a result of the process appeared thickness

differences of opaque areas and there are unwanted

especially in t ransfer through contact method.

Emulsion transparent substrate glass

Effect of exposure and developing on

glass mask emulsion thickness

2,0

3

6,0

0 μ

m

C A

4,0

0 μ

m Emulsion(opaque)

4,0

0 μ

m

2,0

3 μ

m Emulsion (transparent)

B D

• Unexposed and undeveloped

• Developed and unexposed areas

• Unexposed and undeveloped • Exposed and developed

Emulsion

Fig. 15

In figure 16, is reproduced the curve of

image profile of a HRP-KODAC plaque – processed

by negative process where is observed behavior of

emulsion towards light energy absorbed at exposure

and who made that line of 100 m (2,54 inch) to

have the aspect from the figure.

Fig. 16




Moreover, experimentation showed that as

line narrows, is less dense, so in the same image of

the mask we have wider lines with higher density

and narrow and less dense lines. If density control of

the mask were made on wider areas, we must have a

higher density here to assure convenient values at

thicker lines (narrower surfaces). But the differences

in density between wider and narrower lines depend

on too many factors, first of all on developing lens.

Conditions for practical realizing of processing

Realizing masks processing (AGFA -

GEVERT) was made in following stages:

Developing: 4 minutes at 20 C 0,1 C in

developer G 2820 (a part concentrated + 2 parts

distilled water);

Washing in flowing water at 20 C for 2

minutes;

Fixing in fixative G 333 c (1 part

concentrate + 4 parts distilled water at 20 C 1 C,

for 2 minutes);

Washing in flowing water for 10 minutes;

Drying no. 1 in 25% ethanol + 75%

distilled water for 30 seconds;

Drying no. 2 in 50% ethanol + 50%

distilled water for 30 seconds;

Drying no. 3 in 100% ethanol (absolute

ethylic alcohol) for 45 seconds;

Dry ing at air in niche with laminar flow

for 10 seconds;

Measuring masks is possible after

approximately 1 hour from processing when they

reached constant temperature from measuring

chamber.

Control of tracing and processing quality

Taking into consideration functionality of

divided lines in incremental transducer and taking

into account traces configurations, control

technology followed determining parameters:

Contrast;

Quality of demarcation opaque-transparent line;

Observation of imperfections of traces

continuity.

Microtechnologies for obtaining masks

being closed loop type, all informat ion given by

inspecting masks lead to applying corrections in

various phases of realizations.

Appreciations on contrast give informat ion

on processing exposing parameters, being in this

way corrected: power of exposing laser, filters

values, tracing speed, adjustment of laser light flow

in transitory regime (accelerations, decelerations).

The quality of severance line between transparency

zones and opacity zones leads to controls and

alignments of optical components placed in the

luminosity way of exposition and on the adjustment

of laser light spot focusing.

The comparison of geometrical routes with

widths that are propose in theoretical way, determine

the effectuation of direct adjustment on equipment,

and indirect by interposing of filters on the optical

path of the routes that represents deviance. Routes

break are determined by additions from the medium

and by emulsion imperfect ions, leads to resume of

operations with warning as much as is possible,

about the factors that are responsible for these

disorders.

The necessary data for inspection of the

masks are determinate using laboratory equipment,

follow as:

Stand for measuring lengths with laser

interferometer with microscopic

visualizat ion [MESMIT 5];

Stand for measuring angular

displacements on divisor tables

[ZEISS-OPTON-RT 05] with

microscope [X-Y ASAHI];

- interfential microscope [PERAVAL]

Measurement of master mask

Measurement of the mask refers to

determination of angular precision for traces

positioning disposed on incremental track. This

characteristic of divisor disk (transmitted by the

original mask) gives the quality of angular

incremental transducer.

Measurement of the mask is made on stand

[PMPG R 0101] with the following principles:

a rotary movement is imposed around

their center;

on one side and the other of the mask

there are illuminating laser system,

respectively reception system of a

photoelectric microscope;

each black white border distinguished

by the microscope is transmitted to

measurement system.

Measurement system is dimensioned for

high overall size disks, so it was necessary to bring

certain constructive modificat ions. Besides these

modifications, is necessary that in measurement, to

apply an indirect technique that consist in

measurement of angular positioning error of some

technological routes generated in this purpose. So,

for each tenth division of increments track (φ 40)

correspond a division of measurement track (φ 70),

the two divisions being rigorously on the same ray.

So position deviation of two divisions on

measurement track will be error between division




“n” and “n + 10” on the incremental t rack:

precision of measurement stand: 0,5 sec.;

measurement orig in: first indexed trace;

measurement direct ion: trigonometric;

Errors diagonals represent angular

deviations between symmetry axes of traces.

Figurative data contain, beside mask deviations,

errors of measurement which cannot be eliminated

taking into account that mask is drawing in

prescribed tolerance.

Verniers errors are:

for vernier disk, for 1000 divisions/

circumference;

+ 1 second arc; - 1,5 second arc;

for vern ier d isk, for 2000 d ivisions/ circumference:

+ 0,5 seconds arc; - 1,5 seconds arc.

Errors of incremental d ivisor disks (fig. 17 and

18).

Fig. 17

Fig. 18

for incremental div isor disk with 1000

divisions/ circumference: + 1,5 seconds arc; -

2,5 seconds arc;

for incremental div isor disk with 2000

divisions/ circumference: + 1,5 seconds arc; -

1,5 seconds arc.

References

Gheorghe, I. Gh: Instruments Engineering –

Photoelectric incremental systems and

transducers of displacement and position used in

precision mechanics, mecatronics and robotics;

Cefin; ISBN 973-99591-0-5/ISBN 973-99591-1-3; 1999;

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