TABLE OF CONTENTS

TVR-57-96-ww/D0329 TRAINING LOCAL DEVELOPMENT

EXPOSURE

Authors:

Jan Aerdts

Paul Brom

Wim Walrave

Bas Wolfs (Group leader EG)

1996-12-10

Version 1.1Philips ComponentsAbstract

Report no:TVR-57-96-WW/D0329Date: 10-12-96

Title:Training Local Development EXPOSURE

Keywords:exposure, exposure table, light distribution, local development, screen processing, TVT, CMT.

Author(s):Jan Aerdts

Paul Brom

Wim Walrave

Bas Wolfs

This document is a guideline for training participants of the course "Training Local Development; section Screen Processing" concerning EXPOSURE. It is an overview of all Exposure (and exposure related) subjects and processes such as: exposure table (construction and outlining), light sources and light distribution, lenses, filters and filter design, etc. This document is distributed among the training participants so it can be used as a reference book.Remark:Version 1.1.

Number of pages of complete report: 1Copylist abstract:PPD: L. Buijs, R. Fierkens, T. Heemstra, M. van Hoek, J. Jamar, F. Kolen, J. van Nes, J. Plessers, J. Reijerse, H. da Silva, L.Stil (RAF-1); B. Cassar, T. de Pon, R. Struik.(RAF-2); P. van Buuringen, F. Cardinaels, C. Flinsenberg, C. Kregting, H. Nillissen, H. Penners, E. vd Pols, C. Selten, B. Smith, N. van Soerland, T. Vrancken (RAF-3); B. Cuppen, E. van Donkelaar, G. van Iersel, J. Kikkert, P. Kraakman, H. Vandijck, E. Wacanno (RAF-4).

W. van Amstel, H. Broekhuize, W. Janssen, G. Landsweers, L. Loos, C. van Oostwaard, J. Verlegh, W. Verbeek, W. Verschuren, A. de Vos, H. de Vries, R. Zijl (RAD/RAF-p).

EED: H. Aarts, E. Ansems, H. de Bar, P. van Berkel, W. Fisser, J. Fransen, M. Janssen, G. Rief, B. Spolders, E. Vrijsen, H. vd Winkel (RAU); H. Meeske.(RF).

Lebring: R. Grobbauer, K. Koweindl, G.Haas, R. Peinsipp.

PDC: K. Fletcher, F. Hopkins, G. Puppos, Duane Schroeder, Darrin Schroeder.

Taiwan: D. Chen, J. Chen, T.N. Kuo (Dapon).

Dreux: V. Dejonghe, F. Dubois; Aachen: K. Altunkaya, K. Gilles, E. Kuiffen, P. Philipp, M. Pralle.

Barcelona: R. Ferrer, X. Pascual; Durham: K. Chaytors, B. Greaves, M. Kolijn, K. Watson.

Copylist complete report (including abstract):

PPD: Archive (2x), I. Durlinger, L. Elshof, D. den Engelsen, G. Goos, A. Kersten, A. Leenaars, A.v.d. Putten.

EED: G. van Acker, G. Kuipers.

Lebring: H. Wehr; Dreux: A. Singlas; Aachen: J. Schneider, J. van Holthe tot Echten; Brasil: E. Rigotti.

PDC: E. Sagolili; Barcelona: J. Rambla; Durham: L. Dawson, A. de Graft Johnson.

Hua Fei: Documentation Office (2x); Taiwan: C.C. Huang (TEF), J. Lee (Dapon).

Table of contents

1.1

1. Introduction to exposure

1.1 General1.1

1.2 Ideal situation1.1

1.3 Real situation1.1

1.4 Accuracy1.2

2. The exposure table2.1

2.1 Major parameters of the exposure table2.1

2.2 High pressure mercury capillary lamp2.2

2.3 Power Supply2.3

2.4 Lamp length (LL)2.3

2.5 Comb diaphragm (for TVT)2.4

2.6 Cylindrical lens2.5

2.7 Lamp eccentricity ( SL)2.7

2.8 Shutter2.8

2.9 Filter2.8

2.10 Exposure lens2.8

2.11 Wobble2.8

2.12 Drift2.9

3. Lens and filter3.1

3.1 Facet lens3.1

3.2 Continuous lens3.3

3.3 Filter3.3

4. Principle of outlining the exposure table4.1

4.1 Base principle4.1

4.2 Outlining units or jigs4.1

4.3 Process control4.2

5. Microscopic Light Distribution5.1

5.1 Introduction5.1

5.2 Important parameters related to the MiLD5.1

6. Screen phenomena6.1

6.1 Introduction6.1

6.2 Node-Anti Node Pattern (TVT)6.1

6.3 Snaking Effect (TVT)6.3

6.4 Island growth (Matrix: TVT+ CMT)6.5

6.5 Patchiness (matrix: TVT + CMT)6.5

6.6 Facet marking (CMT)6.6

6.7 Bright ball (or ring ) in the center (TVT+ CMT)6.8

6.8 Reflections (TVT+CMT)6.9

6.9 Flags (TVT)6.9

6.10 Mouse bites (TVT)6.9

7. Filter Design7.1

7.1 Filter function7.1

7.2 Striped filter design7.1

7.3 Filter design philosophy at PPD7.1

7.4 Flowchart of PPD filter design7.2

7.5 CMT versus TVT7.3

7.6 Input data for a new filter design7.3

7.7 Limitations in filter design7.3

7.8 Criteria for a new filter design7.4

Table of figures

Appendix A: Input data form for new filter design

Appendix B: Exposure data sheetAppendix C: Table for air coolingAppendix D: Table control data sheetsAppendix E: TerminologyAppendix F: Questions and tasks 1. Introduction to exposure

1.1 General

The goal of the exposure process is to get the phosphor dots and the matrix holes at the correct positions on the inside of the screen, and with the correct dimensions. Electrons pass through a mask hole, and arrive at the screen. The position where they land is determined by the direction of the electrons, i.e. by the magnetic field of the deflection unit (DU). During the exposure process we have no electrons available. Instead we use ultra-violet (UV) light. With this light we can change the structure of the photoresist, thus making it stick to the glass. It is clear that the light must pass through the mask holes in the same direction as the electrons. This is done with a lens, as will be described in the next paragraphs. The size of the matrix holes and phosphor dots is important for tube brightness and landing reserve. The size can be controlled with the light intensity. Higher light intensity means bigger line width. Light intensity is adjusted with a filter (attached to the lens), which absorbs/reflects light.

1.2 Ideal situation

If the DU is a single point source for both x- and y-deflection, we can easily mimic the electron's field of direction with UV light. We would use a point source lamp at the (virtual) location of the electron source, see Figure 1.1

Figure 1.1 Ideal exposure situation.

1.3 Real situation

In reality the DU consists of two coils (line and field deflection) which are physically separated. Thus the horizontally deflected electrons seem to come from a different point than the vertically deflected electrons. Since we can use only one lamp, the best thing to do is to put the lamp in the middle, see Figure 1.2.

Figure 1.2 Lamp position in real situation.

Figure 1.3 Concave lens provides correction for line deflection.

Now the field of direction is different for light and electrons. So the phosphor dots and matrix holes will be in the wrong positions. This can be corrected for with a lens. In x-direction the light must be deflected towards the side of the screen; in y-direction towards the center of the screen. This means that we need a concave lens for the x-direction (see Figure 1.3), and a convex lens for the y-direction (saddle shape).

1.4 Accuracy

The light's field of direction must be accurately controlled. For a typical tube design the effect of a 0.04( error in the light's angle would mean 10 m landing error. This is just acceptable for most tube types. Such an error could be caused by a lot of exposure parameters, e.g.

- lens accuracy (less than 0.1( error in the curved surface)

- lamp position shift of 250 m

- screen position shift of 250 m

etc. (indicative figures)

Since all parameters will be inaccurate at the same time the actually obtained landing error would be estimated at

m. Thus all parameters must be controlled even better.

This indicates that an exposure table must have very stable mechanics, and settings must be very accurately adjusted. Special tools have been designed for this adjustment.

2. The exposure table

2.1 Major parameters of the exposure table

H0 = distance between the reference plane and screen glass inside (at the center of the screen).

H1 = distance between the lamp plane and sealing edge of the screen glass.

H2 = distance between the lamp plane and bottom lens.

L0 = distance between the lamp plane and screen glass inside (at the center of the screen).

Figure 2.1 Major parameters of the exposure table.

2.2 High pressure mercury capillary lamp

General: This mercury lamp produces UV light of which the spectrum between 300 en 450 nm (1nm = 10-9 m) is important for the exposure process.For TVT (= tube with phosphor lines) we are using:

- mercury lamp, water cooled

- inside diameter of capillary is 1, 2 or 3mm

- arc length is 45mm (tungsten electrodes)

- lamp power range is 700 - 1600W

- power is controlled within 2%

- current is approx. 1.2A

- lifetime minimal 200hr at 1600W

- cooling-water flow is 120litre / hr

- lighthouse with a Y-movement

For CMT (= tube with phosphor dots) we are using:

- mercury lamp, air cooled.

- inside diameter of capillary is 2mm.

- arc length is 15mm (tungsten electrodes).

- lamp power range is 300 - 750W.

- power controlled within 2%.

- current is approx. 1.2A.

- lifetime is minimal 175hr at 750W.

- air cooling-flow is typically about 1200 Nlitre/min at 500W * and about 1400 Nlitre/min at

750W lamppower * (see appendix C).

- lamp holder with cylindrical lens is rotating (see Figure 2.10).

- its rotation speed is 360 r.p.m. 50Hz or 430 r.p.m. by 60Hz.

*These are practical values for lamp cooling.

For a longer lifetime of the lamp it is better to use the maximum air cooling.

Figure 2.2 Typical spectrum of a high pressure mercury lamp.

2.3 Power Supply

The purpose is to supply the lamp.

There are 2 kinds of supplies:

A. Intensity controlled and is called transductor supply.

B. Power controlled and is called thyristor supply.

2.4 Lamp length (LL)

(TVT only)

av = vertical pitch of mask holes

q = distance between mask and screen glass inside

Tube design produces a lamp length that is needed for exposure.

The lamp length is mechanically fixed into the lamp holder by means of a so called

diaphragm (see Figure 2.8 and Figure 2.9 for TVT and CMT respectively).

The aperture of a diaphragm is a measure of the UV light window.

Diaphragm range for TVT : 12.5 -15 -17.5 -19 -23 - 30mm

for CMT: 2 - 2.5 - 3 - 3.5mm

With a larger diaphragm you get more light.

General: The surface of the diaphragm is blackened to reduce reflection of

the UV light. Reflection will have bad effects on exposure. The

blackened surface has to be UV light and demineralised waterproof.

2.5 Comb diaphragm (for TVT)

Purpose: To reduce the available intensity, produced by the original lamp

lamp length, into the needed intensity.

The intensity of the lamp is directly proportional to the lamp length.

The intensity of the comb diaphragm is directly proportional to the aperture.

Range of comb aperture: 30% and 50%

Remark: Comb diaphragms are only used at matrix exposure TVT.

Figure 2.3 Schematical drawing of a comb diaphragm.

2.6 Cylindrical lens

The cylindrical lens is an essential component in the CMT exposure system. Let us consider a non-rotating lamp-cassette combination (without the cylindrical lens). Let us say that the lamp is in the East-West orientation. Now we look at the light path in two cross-sections, see Figure 2.4.

Figure 2.4 Lamp + diaphragm lifts the virtual light source for some of the light.

In the left we see the light from the lamp, which hits the screen in the North-South axis. All the light comes from the center position of the lamp. In the right we see the light which hits the screen in the East-West axis. This light does not come from a single point of the lamp. The virtual light source is in the diaphragm plane, which is several (approx. 4) millimeters above the lamp. So, with a rotating lamp holder the lamp would seem to be moving up and down. This effect is called astigmatism. Astigmatism will affect the microscopic light distribution (see furtheron), leading to unacceptable screen quality and process reserve.

To solve this the cylindrical lens is introduced. The cylindrical lens refracts the light in one direction only. If we position the flat part of the cylindrical lens in parallel with the lamp we will only refract the light of the N-S axis, see Figure 2.5.

Figure 2.5 Cylindrical lens corrects astigmatism.

The effect is that the light source for the N-S direction seems to be lifted upward, just like the light from the E-W direction. If we choose the correct lens curvature we can move the virtual light source to the diaphragm plane, i.e. to the same height for both directions. We now have a lamp which is not moving up and down when the lamp holder is rotating.

2.7 Lamp eccentricity ( SL)

Lamp eccentricity SL is a derivative from the distance between the 3 electron beams of the electron gun.

By this the places of the red and blue phosphor lines or dots are fixed w.r.t. the green phosphor lines or dots.

For a homogeneous filling of the screen with phosphor lines or dots, SL has satisfy to the following condition:

q = distance between mask and screen glass inside (= q0, at the center of the screen).

ah = horizontal pitch of the mask holes.

L0 = distance between UV light source and screen glass inside (at the center of the screen).

SL = lamp eccentricity.

Figure 2.6 Schematical graph of the light paths in exposure.

2.8 Shutter

The shutter is a vane and makes for to open and to close a rotation of 3600.

2.9 Filter

The purpose is to get the specified macroscopic light distribution on the screen.

The position is on the bottom side of the lens.

2.10 Exposure lens

The purpose is to get the pattern of matrix and phosphor at the specified position.

The bottom of the lens is always flat. This surface is parallel with the planes of lamp and sealing edge.

The center of the lens has to be positioned on the optical axis of the lamp.

The distance between the plane of the lamp and the surface of the bottom of the lens is called H2.

Standard H2 values: TVT-1100 = 60.0mm

TVT- 900 = 80.0mm

CMT-900 = 84.0mm

The cooling of the lens is specified for a temperature of max. 500C. The lenses of the matrix table have no lenscooling in order not to disturb the oxygen transport of the air to the photo sensitive layer.

2.11 Wobble

Wobble is a movement of the segmented lens.

The purpose is to avoid projections of the segmented lens on the screen.

The segmented lens moves under an angle ( w.r.t. the positive x-axis.

The movement is a shark's tooth movement.

The guide-line for the angle is the angle of the diagonal of one segment.

The guide-line for the stroke is the length of the diagonal of one segment.

The guide-line for the amount of strokes is >13 within the exposure time. One stroke is to and fro.

The mechanical part is called heart cam disc of wobble.

Figure 2.7 Shark's tooth movement (wobble of the segmented lens).

2.12 Drift

Drift is a movement of the segmented lens too.

The purpose is to avoid projections of the segmented lens on the screen and specially the projections parallel to the direction of the wobble.

The segmented lens moves under an angle ( w.r.t. the positive x-axis.

The movement is a shark's tooth movement.

The guide-line for the angle is the angle of the wobble + 900.

The guide-line for the stroke is the half length of the diagonal of one segment.

The guide-line for the amount of strokes (n) is: 4 < n < 1/4 of the amount of strokes of the wobble within the exposure time. One stroke is to and fro.

The mechanical part is called heart cam disc of drift.

Figure 2.8 Schematical drawings of a TVT lamp holder.

Figure 2.9 Schematical drawings of a CMT lamp holder.

Figure 2.10 CMT rotating lamp with cylindrical lens.

3. Lens and filter

3.1 Facet lens

3.1.1 general

Facet lenses are used for CMT applications. A facet lens consists of 357 segments (called facets) of 8x8 mm. Each facet has a flat top surface with accurately controlled top angles (( and () in x- and y-direction, see Figure 3.1.

Figure 3.1 Facet pole with ( and ( angles.

The walls of the facets are perfectly vertical to avoid lens action. In Figure 3.2 a cross-section of a facet lens is given.

Figure 3.2 Cross-section of a facet lens.

The lens consists of 2 parts: a glass carrier at the bottom and facets at the top. The carrier is 8.0 mm thick, and is made of B270 glass (n=1.52). The facets are made of acrylic material, a fluid which hardens under UV illumination (n=1.60). The acrylic material thickness is 0.8 mm in the middle of each facet.

3.1.2 lens production

The shape of the facets is determined by a metal mould (see next section). A (predetermined) amount of acrylic material fluid is dispersed over the surface of this mould. The glass plate's surface is prepared with silane to ensure good adhesion between glass and acrylic material. Then the glass is pressed onto the fluid, until all fluid is neatly dispersed over the mould area. The distance between mould and glass plate is measured at the four corners. It is adjusted to 0.8mm. Now a UV light source is used to harden the acrylic material. The facet lens must be taken off the mould carefully.

3.1.3 mould production

A mould is made out of 357 (17x21) steel poles, which are clamped together. Each pole has an identification mark to find its position in the mould. Each pole is cut and polished to size (8 x 8 mm). Tolerances are very narrow (approx. 1 m) in order to keep all facet poles clamped together. The top surface is cut and polished to give optical surface quality.

The poles are assembled on a jig. The jig consists of 357 metal pins (with rounded top) and side walls to support the poles. The poles are placed with the polished side on the pins. The pins contact the middle of the poles. Thus the middle of the poles are all at the same level. The poles are clamped together at the four sides. In order to prevent mould-to-acrylic material adhesion an adhesion spoiling silane is applied to the mould.

3.1.4 measurements

The top angles of each pole is checked by the machine factory. Top angles of individual poles can be controlled to within (0.03(. The first lens from a new mould is measured on a 3D machine. The accuracy of a facet in a lens will be worse than (0.03( due to torque, caused by clamping, and the lens production process. Facet accuracy is typically better than (0.06(.

3.1.5 lens transmission

Lens transmission in UV is determined by the acrylic material. Typical lens transmission spectrum is depicted in the figure below.

Figure 3.3 Transmission spectrum of facet lens.

Below 400 nm the transmission drops quickly. The effective transmission for our application is approx 40%. The absorption of UV light has another adverse effect. The UV light slowly affects the chemical structure of the acrylic material. This leads to a gradual reduction of the transmission. This so-called ageing can be seen in old lenses: blue light is absorbed somewhat, making the lens look slightly yellow. The effective life time of a facet lens is 1-2 years.

3.2 Continuous lens

3.2.1 general

Continuous lenses are used for TVT applications. They are made of glass (WG320, n=1.62). The top surface is curved, while the bottom surface is flat to accommodate for a filter.

3.2.2 lens production

A glass plate is cut to size (14.4 mm thickness) and polished. It is put on a metal mould, with the polished side facing up. Mould plus glass plate are put in an oven, which cycles a certain temperature profile (cycle time 27 hours). Highest temperature is typically 521 (C. At this temperature the glass becomes viscous and starts flowing over the mould, thus taking the shape of the mould. After this so-called sagging process both sides of the lens have taken the shape of the mould. The bottom side is processed to make it flat, with optical surface quality. Next the lens is cut to size and mounted in a metal ring, if required. Throughout the process the lens orientation is guaranteed through marks in the glass.

3.2.3 mould production

The mould is cut by a machine factory, based on computer data generated by the LCG (Landing Coordination Group). Typical mould accuracy is (15 m. Before sagging the mould is covered with a thin layer of boron nitride to prevent adhesion to the glass.

3.2.4 measurements

Typically the top surface of the glass will deviate from the bottom surface, due to slight horizontal movement of the glass during sagging. Therefore each lens is measured in 8 locations on a 3D machine. Based on this information the actual lens action can be calculated. Deviations from the desired lens action can be corrected in first order by polishing the bottom of the lens under an angle. Remaining landing errors are estimated from the data, and are used as a reject criterion.

3.3 Filter

3.3.1 general

The filter is at the bottom side of the lens. All filters are so-called stripe filters. They consist of stripes of opaque material (chromium), where the ratio of transparent and opaque area determines the transmission. Each stripe is made up of small segments, see Figure 3.4. Each segment is 1 mm long. The Cr has a constant width over the length of this 1 mm. The pitch of the stripes is everywhere 0.3 mm. Thus the width of the Cr stripes determines the transmission. The 0.3 mm pitch is small enough to obtain a smooth intensity profile on the screen, since all lamps are at least 2mm in size. All new filters have diagonal stripes to prevent moir (e.g. with the lamp's comb diaphragm).

Figure 3.4 A filter is made up of stripes with fixed length and pitch.

3.3.2 filter production

Filters are made using a lithography process. A thin Cr layer is evaporated onto the bottom side of the lens. Photo resist is applied onto the chromium. It is exposed with UV light, with the master close to the lens. The master is aligned to the lens with alignment marks in the master. After development the resist is left only in those places which were illuminated by the UV light. Where the resist has gone the Cr can be etched. After resist stripping a stripe pattern in the chromium remains.

3.3.3 master production

Master design input is generated by the PPD exposure group. It is sent to a photo plotter, which makes black stripe patterns in a photo-emulsion.

3.3.4 measurements

Each master is checked for line width deviations, using a special test pattern. Typical line width accuracy is better than (0.5 m. Each filter is measured on a transmission measuring device which scans the east-west axis. Filters are rejected when their transmission deviates more than (3% from target. This is a relative deviation, i.e. target transmission of 20% gives rejects below 19.4% and above 20.6%. Process and master give line width tolerances of less than 1.5 m. In order to guarantee a maximum transmission deviation of 3% the filter transmission must be larger than 15% (45m stripe width). This is a boundary condition for each filter design.4. Principle of outlining the exposure table

4.1 Base principle

The size of the screen is the reference; this means the x-axis, y-axis and sealing edge form the base. These parameters are translated to 3 points on the outside of the screen and the plane of the sealing edge. From this plane we take only 3 points, called supports. 3 Points define one plane.

4.2 Outlining units or jigs

1. Locating jig

2. Adjusting microscope

3. Adjusting jig

4. Parallelism jig

5. Aligning apparatus

6. Jig for y-movement

7. Several jigs specially for a CMT table

1. The locating jig (Figure 4.2) is the master and contains:- the x-axis and y-axis of the screen(= the plane of the sealing edge)- the x-axis and y-axis of the plane of the lamp- the z-axis between the plane of sealing edge of the screen and the plane of the lamp(=H1) - the parallelism and the rotation between the planes of sealing edge and lamps. The distance H1 is devided in two distances. One distance is fixed and the other is adjustable. The adjustable distance has a ruler with a length of 15mm. This part is called: the adjustable unit. The x-axis of the plane of the lamp is a ruler. This ruler lies on the centerline of the y-axis. There is no ruler for the y-direction. Therefore it is not possible to adjust in y-direction on an easy way.

2. The adjusting microscope (Figure 4.3) makes a copy of all the distances of the locating jig and is a submaster now.This submaster is the jig for adjusting the table, you can place it on the table.

3. The adjusting jig (Figure 4.4) is a dummy lamp holder-cassette-combination and contains: - all the distances - the centerlines of x-axis, y-axis and z-axis - the parallelism and the rotation between the planes of sealing edge and lamp.You has to place it into the table.Note: Adjusting the table is only possible with the microscope and the adjusting jig together.4. With the parallelism jig (Figure 4.5) you can adjust the parallelism between the planes of sealing edge and exposure lens. The parallelism between the planes of exposure lens and mounting plane of combination is fixed in the design of the table.

The centerlines of the x-axis, y-axis, and rotation of the lens are fixed in the table too.

5. With the aligning apparatus (Figure 4.6) you can align the line light source. Than the optical x-axis, z-axis, rotation and parallelism in the plane of the lamp are equal for each combination. At a point light source the optical x-axis, y-axis and z-axis are equal for each combination. Further it is possible to measure the macroscopic light distribution at 5 points.

6. With the jig for y-movement (Figure 4.7) you have to adjust the y-axis of the plane of the lamp w.r.t. the y-axis of the plane of the lens. This adjustment is only necessary for tables with a y-movement for the lamp.

7. There are several special jigs for a CMT table. E.g: - to set the wobble angle - to check the wobble length - to adjust the distance and the parallelism between the planes of lens and lamp- to set the x-axis and y-axis of the lens - to adjust the parallelism between the planes of lamp and the sealing edge- to adjust the rotation between the planes of lamp and the sealing edge

Remark: a. On the bottom side of the lens the filter is positioned.

b. There is no jig for to check the drift length and the centerline of

the drift w.r.t. the centerline of the exposure lens.

4.3 Process control

There are 3 important items for to get a good tube: 1. Landing.

2. Brightness.

3. Landing reserve.

4.3.1 TCA

- To check landing in an exposure table is to check the mechanical and optical settings. A quick and easy check for to do this is with the aid of a Table Checking Apparatus (TCA).

- The check can be devided in three applications:

A. Comparing the lamp and/or the lens positions of various tables

B. Comparing the lamp and/or the lens positions of the same table (periodical check)

C. Determination of the eccentricity of the lamp, the height of the lamp and the influence of the lens

- The TCA can only used for CHECK and not for ADJUSTMENT. All measurements are RELATIVE to one another instead of ABSOLUTE.

Principle

On the mounting plate two optical viewers can be moved to east-west direction and vica versa by means of turning two spindles.

The viewer position can be read from the spindle. The viewer is supplied with a duo photo diode, by means of which the lamp position can be determined. The position of the lamp image on the duo photo diode is visualised on a led array display.

Trouble shooting on the exposure table with the aid of the TCA:

1. Possible errors caused by the lamp holder-cassette-combination (lcc):

-- Incorrect lamp adjustment on the aligning apparatus

-- Lcc out of adjustment due to transport from the aligning apparatus to the table

-- Lcc was not mounted correctly into the table

2. Possible errors caused by the exposure table:

-- Incorrect adjustment of height and/or eccentricity

-- Incorrect position of lens

-- Incorrect lens

The prescription and the manual of the TCA is archived in:

SA TCA 7322 318 8302.0 group 160 page 1 up to and including 7

group 165 page 1 and 2

group 582 page 1 up to and including 16

group 591 page 1

4.3.2 Ratio meter

- The relationship between brightness in a tube and in a screen is the line width. Mostly the line width depends on the dose: Dose = Intensity * Time.

- To check brightness in an exposure table is to check the intensity, the intensity distribution (macroscopic light distribution) and exposure time. A quick and easy check to do the intensity measurement is the aid of a Ratio Meter necessary. To do the time check a stopwatch is OK.

- The check can be devided in three applications:

A. Intensity measurement of the table at screen height

B. Ratio measurement of the table between several preferred measuring points at screen height

C. For old type of tables to adjust the docotor (dose control detector)

Principle

The instrument contains a sensor and display unit. The sensor is called rator (radiation detector). The sensitivity of the rator is UV-radiation and is adjusted. Therefore all measurements of intensity, for different Ratio Meters and equal intensity, are the same. The display is calibrated in arbitrary units. There are some measuring modes. The important modes are:

Intensity screen

Ratio screen

Matrix

- The value in mode Intensity screen means an absolute intensity

- The value in mode Ratio screen is a relative intensity. You can compare several measuring points or the same measuring points from other dates

- The value in mode Matrix is like Intensity screen, but the value in the display is 10x higher.

Remark:

1. The mode matrix is not a single mode, but always together with Intensity screen or Ratio screen

2. If you measure a lot of points than this is called: macroscopic light distribution

Dummy screen

The principle is measuring at screen height. This means at the same height as inside of the screen, where the photo layer is laying. Therefore a dummy screen of polyester is designed. In this screen bushes are fixed for placing the rator. The position of the measuring points are written in ULAS and is a standard coordinate system.

- Two measuring points are called: process steering points. In ULAS these have the name -5, 0 and +5, 0. The relationship with the screen is 2/3 west and 2/3 east.

Trouble shooting on the exposure table with the aid of the Ratio Meter:

-- Lamp not clean; life time of lamp is over

-- Tube of lamp holder not clean

-- Lamp diaphragm not clean; damaged; incorrect positioned

-- Lens/filter not clean; damaged

-- Cylindrical lens/quartz plate (rotating light house) not clean; damaged

-- Diaphragm set for 1100 not triple; for 900 not quadruple; not black; incorrect dimensions

-- Dummy screen incorrect position on the table

-- Rator window not clean; damaged

-- Ratio Meter not properly functioning

The prescription and the manual of the Ratio Meter is archived in:

SA RATIO METER 7322 314 1055.0 group 582 page 1 up to and including 10

Remark:

The chapter measuring of line width is written in the training of screen processing department.

Figure 4.1 Overview of the planes in an Exposure table.

Figure 4.2 The locating jig, containing the major dimensions of the exposure table.

Figure 4.3 Adjusting microscope to copy the major dimensions to the exposure table.

Figure 4.4 Adjusting jig (dummy lamp holder-cassette-combination).

Figure 4.5 Parallelism jig to obtain parallel planes of lens and sealing edge.

Figure 4.6 Aligning apparatus to adjust the lamp in the cassette.

Figure 4.7 Adjusting jig for Y-movement of the TVT lamp.

Figure 4.8 Table Checking Apparatus.

Figure 4.9 Ratiometer and dummy screen for measuring the light intensity at various positions of the screen.

5. Microscopic Light Distribution

5.1 Introduction

When a mask-screen combination is exposed to UV light at the exposure table, behind each mask hole a small light spot with a specific intensity distribution exists at the corresponding position on the screen. This distribution is called the Microscopic Light Distribution (MiLD).

The MiLD originates from two fundamental optical effects:

Diffraction of light at a slit (Fresnel/Fraunhofer).

Halfshadow effects due to the dimensions of the light source.

Furthermore disturbing contributions such as stray-light can affect the MiLD significantly.

A typical MiLD is shown in Figure 5.1

Figure 5.1 A typical Microscopic Light Distribution behind a mask hole.

5.2 Important parameters related to the MiLD

5.2.1 (MAC

(MAC is defined as the intensity of the UV light measured at the inside screen on the exposure table (no shadowmask present). The distribution of (MAC over the screen is called the Macroscopic Light Distribution (MaLD).

In Figure 5.1 the MiLD is normalised to (MAC= 1.0 (or 100%). The center of the MiLD ((O , which is sometimes a relative minimum), is determined by (MAC , but is not necessary equal to this value. In general (O / (MAC = 0.9...1.05.

The absolute value of (MAC (and so (O) is determined by various geometrical and optical aspects.

5.2.2 Process level (P-level)

The process level is the theoretical threshold value of the light intensity above which sufficient photochemical reaction takes place in the photoresist, to obtain adhesion to the glass surface.

Important: The P-level is only a chemical property of the photoresist, and is a measure of the sensitivity of the photo-resist to the UV-light in the exposure table.

In Figure 5.1 this level is indicated with ("P-level"). When the relative intensity of the UV-light exceeds the P-level, the photoresist will adhere to the glass surface, resulting later on in the processing in a matrix window or a phosphor dot.

Due to non uniformity in temperature, humidity, layer thickness, etc. ... of the photo sensitive layer, this process level depends on the position on the screen (P-level distribution).

5.2.3 Mask hole Reduction/Magnification

In order to make black matrix CRT tubes it is necessary to be able to make the matrix window width (MWW) smaller than the phosphor width (PW):

The existence of the Microscopic Light Distribution makes it possible to reduce the size (Dh) of the mask hole (matrix) or to magnify it (phosphor), when projected at the screen.

This mechanism is illustrated in Figure 5.2 (a/b):

Figure 5.2 a

Figure 5.2 b

Figure 5.2 The mechanism of hole size reduction (a) and hole size magnification (b).

Matrix is exposed with 'the P-level high in the MiLD', resulting in a matrix window which is smaller than the mask hole (Figure 5.2 a). Consequently the light intensity for matrix is relatively low. Phosphor is exposed with "the P-level low in the MiLD", resulting in a phosphor line (or dot) which is larger than the mask hole (Figure 5.2 b). Consequently the light intensity needed for phosphor is relatively high. However, the fact that the phosphor process needs much more intensity (up to a factor 10) than the matrix process, is caused by the different UV-sensitivities of the different resists used in both processes.

In general:

MWW < Dh < PW

P/(O = 0.5-0.8, 0.25-0.3, 0.15-0.20

5.2.4 Background intensity level

As can be seen from the Figure 5.1 of the MiLD, the light intensity ((MIC) is not zero at the edges. The minimum level is called the background intensity level ((BACK ) . This background can certainly not be neglected with respect to the phosphor process level.

(BACK is caused by:

Light originating from neighbouring mask holes.

Light scattered and reflected from diverse (optical and mechanical) components within the exposure table (Stray light).

5.2.5 Upper/Lower contrast

The upper contrast in the MiLD is defined as

.

This parameter is an indication for:

The process reserve for matrix: When CUP becomes to close to 1, only a very small fraction of the total light intensity will be used to develop the photoresist, which makes the matrix process less reproducible. The possibility of closed matrix windows increases.

The island reserve for matrix (see chapter "screen phenomena").

In general a CUP > 1.5 is required.

The lower contrast in the MiLD is defined as

.

This parameter is an indication for:

The process reserve for phosphor: When the background intensity becomes too large with respect to the process level of the phosphor photosensitive layer, the phosphor dot definition decreases.

'Haze' reserve for phosphor: A small lower contrast can result in phosphor residues of the wrong colour in a matrix hole. This is observed as a greyish haze over the screen.

In general a CUP > 5...10 is required.

5.2.6 Linewidth Growth

From the MiLD the linewidth growth (LW-growth) can be calculated, expressed in (m/% relative light intensity. In fact it is the reciproke of the slope of the MiLD at a specific intensity level:

[(m/%].

As can be seen from the formula the linewidth growth is dependent on the working level

in the MiLD. For example: when the MiLD should have had a constant slope, the LWGROW at a high intensity level would be smaller than at a lower intensity level.

Linewidth growth measurements are a useful tool to compare the theoretical model of the MiLD with the practical situation. These measurements are done with one mask (to exclude the mask spread) and consist of measuring the LW at a range of intensity levels (around the actual used exposure level).

Typical values of the linewidth growth lie roughly within the range 0.3 ...2.0 (m/%.

5.2.7 Phosphor Adhesion

Due to the thickness of the phosphor layer two important effects occur:

A fraction of the incoming UV-light will be absorbed, before it will reach the glass-phosphor interface. Because at this interface the adhesion has to take place, a sufficient incoming UV-intensity is needed. The upper contrast for phosphor is an indicator for the phosphor adhesion. The wish for a high CUP strokes with the wish for a sufficient lower contrast. A tube designer has to find a compromise here.

The MiLD at the glass-phosphor interface is modified by light scattering within the phosphor layer (the MiLD becomes wider), which makes it difficult to predict how this will influence the phosphor adhesion.

5.2.8 Lamp diameter

The shape of the MiLD strongly depends on the diameter of the UV lamp. A larger lamp diameter makes the MiLD smoother (wider), resulting in an increased LWGROW. A larger lamp diameter is used to reduce the patchiness effect in matrix (see 'screen phenomena'). To realise the same matrix window width, the process level has to be higher in the MiLD, and less light intensity is needed. This means a decrease of the process reserve for matrix (as explained earlier (CUP)).

5.2.9 Radiation profile of the lamp

The light source, which is schematically represented in Figure 5.3, consists of a high pressure mercury lamp with a specific length and internal diameter. Due to its geometrical dimensions the lamp will have a specific radiation profile.

Along the axial direction (N-S) the radiation intensity will be nearly constant, whereas in the x-direction (E-W) the profile is a typical cos2(x) function, as illustrated in the figure. This profile is very important, for it influences the shape of the MiLD significantly.

Figure 5.3 Radiation profile of a long UV-lamp.

6. Screen phenomena

6.1 Introduction

In this chapter a number of well-known (but not always well understood) phenomena, visible at the screen will be discussed. Only screen effects which are in any way related to exposure will be mentioned here (Most effects however, originate from several processing conditions). Recognition and understanding of the phenomena will result in the ability to solve a problem effectively on a short term.

6.2 Node-Anti Node Pattern (TVT)

This pattern is visible as an alternating matrix window width along the black matrix lines as is shown in Figure 6.1.

Figure 6.1 Visualisation of the node- anti node effect in the striped matrix pattern.

Origin:This effect is caused by the geometry of the shadow mask, which consists of a regular pattern of vertical holes, separated from each other by a small bridge. When a screen is exposed with a very small (short) light source through such a shadow mask, the bridges of the mask will leave a shadow at the screen. Result is that at those, not exposed positions, the photoresist will not develop. The bridges will be seen in the black matrix.

It is therefore that for TVT (line tube) a long lamp is used (with its long axis in the N-S direction parallel to the black matrix line). Using a long lamp will result in a constant intensity level as is shown in Figure 6.2 when the proper lamp length (LL) is chosen. This is the case when

In which L is the lamp screen distance, q the mask screen distance and av the vertical pitch of the mask holes.

Figure 6.2 Exposure through a TVT shadow mask (N-S direction) with a long lamp.

Y-movement:A problem is that the lamp screen distance as well as the mask screen distance changes over the screen, so an optimal lamp length can only be found for one position. The change in the factor L/q can be so big, that at other positions on the screen (for which LL is not optimal), the node- anti node pattern becomes visible.

It is therefore necessary to move the lamp along its long axis (= Y-movement). By doing so the lamp intensity distribution is spread out in the North-South direction, resulting in a smoothed intensity distribution at those locations where LL is not optimal. This way the node- anti node pattern is suppressed.

The used Y-movement is usually equal to the lamp length.

Critical positions:

North and South, due to the curvature of the screen (projected LL decreases).

East and West, due to increasing value of L (projected LL increases).

LL is optimised for the 2/3 areas.

Figure 6.3 Change of optimal lamp length with respect to an optimised LL (=1) in the center of the screen.Note:In CMT also a small range of different lamp diaphragms is used (2.0, 2.5, 3.0, and 3.5mm).

The larger sizes however, are only applied to increase the UV intensity (to the disadvantage of a decrease in the process window).

6.3 Snaking Effect (TVT)

Although the use of a long lamp with corresponding Y-movement suppresses the node-anti node pattern generation, it can cause on the other hand the so called snaking effect. This effect reveals itself very much like the node-anti node pattern, as is shown in the picture of Figure 6.4, but the origin of the effect is basically different.

Figure 6.4 Result of the snaking effect on the matrix pattern.

Origin:

The most striking difference between the node-anti node and the snaking effect is that the first is oriented perfectly along the North South Axis of the screen, whereas the latter shows a rotated pattern with respect to the vertical axis of the matrix lines.

This snaking effect is caused by the curved contour of the screen in combination with the length of the lamp and its Y-movement. The projections of the lamp through the mask holes, on the surface of the screen are not lying in a straight line, but somewhat tilted. This is schematically represented in Figure 6.5.

Figure 6.5 Lamp projection on the screen with and without tilting.

Because of this rotated projection, the Y-movement causes in the corners beside a pure North-South movement, also a drift component in the East-West direction (In the center and on the N-S and E-W axis no lamprotation occurs).

The final result of this tilted projection is, that the matrix windows are not straight, but somewhat twisted, like the movement of a snake. Because the area of the matrix holes decreases by this rotation, dark corners will be observed at the screen.

Worst case it is even possible to get bridge building between the graphite lines.

Critical positions:

Only the corners are sensitive to the snaking effect, dependent on the contour of the screen.

It will be obvious that an increased lamp length (and corresponding Y-movement) will enhance this snaking effect.

6.4 Island growth (Matrix: TVT+ CMT)

An example of island growth in the matrix process is visualised in Figure 6.6 a (microscopically). In between two dark (wide) matrix lines, a small dark line (island) is observed. In case of the CMT matrix a round hole with a small black dot in the middle would be observed. This effect is unacceptable for it decreases the transmission of the black matrix and results in dark areas on the screen.

Figure 6.6 a

Figure 6.6 b

Figure 6.6 Visualisation and explanation of islands in the matrix pattern (TVT example).

Origin:

The island growth is a direct result of the MiLD when it exhibits a relative minimum (dip) in the center (Figure 6.6b). When the level of exposure becomes so high (in order to make the required MWW), that it reaches this dip in the top of the MiLD, the intensity in the center will drop below the process-level. As a result a small dark line will remain at the screen, indicated with (W (island width) in Figure 6.6 b.

Critical positions:

Most critical for island growth are the North and South areas of a screen. In general the (0 of the MiLD shifts more and more towards the process level in N and S direction due to an increase of the mask hole reduction (which is a design property).

In E and W direction the diffraction pattern behind a mask hole changes in such a way, that the 'dip' in the MiLD disappears.

6.5 Patchiness (matrix: TVT + CMT)

Patchiness is visible as somewhat dark areas on the screen after matricizing. These darker areas have a characteristic inhomogeneous gray appearance. This effect is caused by non uniformity in the size of the matrix holes.

Origin:

Patchiness finds its origin in the spread of the mask holes together with the so-called mask hole enhancement. The spread in the size of the mask holes depends on type and manufacturer, and is difficult (expensive) to reduce. The solution to solve the problem of patchiness must be found in minimising the differences in the LW when projected as matrix pattern on the screen.

An important parameter in this is the mask enhancement, which is defined as:

In which Dh is the size of the mask hole (mask slotwidth).

When this factor is larger than 1, it will magnify the spread in the mask hole size. A decrease in mask enhancement will make the patchiness less visible. One way to do this is increasing the lamp diameter, which results in a smoother (wider) MiLD and therefore an increased linegrowth. Furthermore the factor depends strongly on the design of the tube type (important parameters herein are: mask slot width, matrix window width and the mask-screen distance).

Critical positions:

In general the mask enhancement is small (