WO1990009730A1

WO1990009730A1 - A process for manufacturing an electrode pattern on a substrate

Info

Publication number: WO1990009730A1
Application number: PCT/NO1990/000032
Authority: WO
Inventors: Jan E. Marthinsen; Frode Meringdal
Original assignee: Autodisplay A/S
Priority date: 1989-02-07
Filing date: 1990-02-07
Publication date: 1990-08-23
Also published as: NO894656D0; AU5097190A; NO894656L

Abstract

A process for manufacturing an electrode pattern (8; 9, 9') for dot matrix displays on transparent substrates (2) of an insulating material provided with a layer (1) of an electrically conductive material, by evaporating or transforming portions of the electrically conductive layer into an insulating material by use of one or a plurality of focused laser beams (3'; 3'') having a wavelength of less than 1 micrometer.

Description

A process for manufacturing an electrode pattern on a substrate

The present invention relates to a process for manufacturing an electrode pattern for dot matrix display devices on transparent substrates of an insulating material, on top of which a layer of electrically conductive material is provided. More precisely, the invention is suitable for to providing an electrode pattern for flat panel image displays in order to improve both their performance and their production capacity.

A number of flat panel image displays, e.g. liquid crystal (LCD), electroluminicent (EL and TFEL) or electrochromatic (EC) display devices, are based on the fact that an electric field, possibly with an associated electric current, is formed between two substrates on whiph there is an electrode pattern of electrically conductive material. The electrically conductive material is generally a very thin layer of metal or a metal compound, e.g. indium-tin-oxide (ITO) or gold.

The remaining manufacturing process before and after manufacture of the electrode display device may be one of a number of known processes for manufacturing flat image display devices.

Especially when the image display device is a dot matrix display for producing images of substantially arbitrary geometry with high resolution (many image dots per surface unit), it is essential that the ratio between active surface area (the image dot proper) and passive surface area (space between image dots) is as high as possible. This is the case, both to avoid an impression of a raster image, and to achiev maximum surface contrast. The contrast between on and of state of a surface comprising many iamge dots will be limite by said ratio if the contrast between on and off state is high for one single image dot.

An example of the above mentioned is that the distance between centers of image dots may be less than 200 micro¬ metres, and that a passive space between dots of less than 20 micrometres is, thus, required for a surface contrast of more than 10:1. For such display devices to satisfy modern requirements, more than 1000 dots may be necessary in each row of points. This corresponds to lateral edges of more than 20 cm.

The most common process for manufacturing such electrode patterns is photolithography, even though other processes are also disclosed (inter alia, in EPC Patent Application No. 82304204.9, in which Crossland et al. disclose a scribing process, if desired, in combination with electroerosion).

Photolithography is a multi-step process generally comprising application of photoresist, curing said photoresist, exposing, developing, etching, and removal of residual photoresist.

Each of said process steps involves a certain hazard of errors which, in turn, will cause reduced production capacity. The equipment for some of said steps must be of exceptionally high quality and is sensitive to mechanical and chemical influence, and the etching process involves utilization of aggressive chemicals which are harmful to the environment. The equipment is also bulky and occupies expensive space in ultrapure rooms.

The etching process being a wet process, and the entire process requiring repeated washing steps, any possible utilization of plastic material in the substrates may cause adverse absorption of water and other substances, resulting in swelling and reduced life. Treatment of material by laser is a technology known since about 1965, when high power lasers were developed. Most applications were based on thermal effects, even though, e.g. DE-OS No. 38 22 766 discloses a photochemical process to transform an insulator into a conductive material.

Laser radiation was used for cutting, scribing, and for transforming surface structures, e.g. of metals. Generally used lasers are CO2 and YAG, but other kinds of laser were also used. In the field of manufacture of electrically conductive patterns, e.g. DE-OS No. 32 45 272 disclosed a process for manufacturing conductive patterns for thick film and thin film component carriers by burning off electrode material.

Other related applications are (micro)lithography, based on substituting part of a conventional process of manufacture by using laser light to manufacture a pattern in an etch resist material, with subsequent etch-off of the electrode material.

In production of display devices laser is disclosed for use in modifying or repairing an electrode pattern which is substantially manufactured by conventional methods, e.g. as disclosed in GB-PS No. 1 573 699. There are, however, problems in connection with utilization of very long-wave light to produce electrode patterns on a substrate for display devices, since the thickness of the electrode material is of the same order as that of the wavelength of the light to be transparent to visible light and, thus, shows poor absorption of laser light. This means that applied laser effect must be so high that the substrate material is damaged due to absorption of much light causing it to be heated, which results in melting.

It is, thus, an object of the present invention to eliminate said known disadvantages. According to the invention it is proposed to modify the surface or layer on the substrate by removing the electrically conductive layer completely or partly, e.g. by evaporating or transforming portions of the electrically conductive layer into insulating material by use of one or a plurality of focused laser beams. By the expression "evaporation" is especially meant a process called "photo ablation".

Photo ablation occurs when the photo energy of the laser light is so high, i.e. the wavelength of the laser light is so short, that the molecules in the irradiated material are completely or partly decomposed without this being caused only by heating. A vapour-like or gas-like substance is formed which consists of fragments of the removed material. Laser light of such high photo energy can, e.g. be produced by the aid of a so called eximer laser producing light in the ultraviolet range.

wlien the expressions "removal" or "remove" are used below, it is to be understood that this should mean evaporate or transform into an insulating material.

Further characterizing features of the present invention will appear from the following claims, and from the disclosure below, with reference to enclosed drawings, in which

Figure 1 illustrates a first embodiment of the process according to the invention,

Figure 2a illustrates a second embodiment of the process according to the invention,

Figure 2b illustrates a modification of the embodiment of Figure 2a,

Figures 3-7 illustrate different variants for carrying out the process as indicated in Figure 2b,

Figure 8 illustrates another variant of the process, Figure 9 illustrates yet another variant of the process,

Figures 10-12 illustrate alternatives for removal of the remaining portion of material which was partly removed by laser removal, Figure 13 illustrates a process with use of laser for improved removal of the material.

Coherent light, e.g. laser light, may be focused on dots of a diameter corresponding to a few wavelengths. With light, e.g. having a wavelength of approximately 700 nm, this provides for a minimum dot size of less than 2 micrometers. Corresponding smaller dot sizes may be achieved for light of shorter waves. At the same time as the dot size is small, the light effect per surface unit is correspondingly high. It is, thus, possible to form dots of light with a diameter of approximately 10 micrometers and a power of approximately 10 megawatt per m² by the aid of a laser having an effect of 1 milliwatt. According to the invention use of laser beams having a wavelength shorter than 1 micrometer is intended.

In extremely short wavelengths the energy of individual photons will also be so high that molecular bonds can be broken. This phenomenon is known as photo ablation.

An electrically conductive material 1 forming a conductive layer is provided on an insulating substrate 2. Layer 1 which is to be removed completely or partly in desired locations, is generally very thin so as to be translucent. An ITO-layer may, e.g. have a thickness in the order of 100 nm. Con¬ sequently, the energy per surface unit necessary for complete or partial removal of said layer 1 will be low.

Complete or partial removal of layer 1, e.g. by absorption of light 3 causes certain problems. Due to the fact that layer 1 is very thin and generally translucent, it will be necessar to ensure sufficient absorption of light 3. In the show example light 3 is a coherent light beam, preferably a laser beam. Sufficient absorption of the light may be ensured b selecting a wavelength of the light which coincides with a absorption band of the material used in electrode layer 1, or by coating electrode layer 1 with a thin layer of a pigment which absorbs the light and turns it into local heating. This is a common method in treating metal with laser light.

The present invention substantially comprises three concepts to provide the desired electrode pattern.

The first concept comprises utilization of a technique corresponding to that which is used in laser printers.

With this concept which is indicated in Figure 1 one or a plurality of laser beams 3 scan the object in a transversal direction (A), while the object moves (B) in a direction normal to the scanning direction (A). The laser light from laser 4 will pass through a modulator 5 or a controllable light valve letting light pass when the position coincides with a dot where electrode material 1 is to be removed, and bars the laser light where it is desired to maintain electode material 1. Pulse modulation of laser 4 is an alternative which is considered to be technically equivalent to the modulator or light valve 5.

After modulator/light valve 5 it is preferred to provide a focusing lens system 6. Scanning proper is carried out by a scanner 7, e.g. in the form of rotating or oscillating mirrors, prisms, or corresponding devices providing the same technical effect.

The advantages of this concept are that arbitrary electrode patterns 8 may be provided which can readily be transferred from a graphic program on a computer or the like (not shown). The disadvantage of the process is that it requires a rapid operating mechanical device. The process is, thus, most suitable for small volumes of production and for manufactur¬ ing prototypes. The second concept is based on the substrate 2 with its electrically conductive layer 1 passing a single laser ray 3', as shown in Figure 2a, or a beam of rays 3'', see Figure 2b in a substantially linear movement in the direction of conveyance B. Between each passage the substrate is displaced laterally C, and the substrate and laser beam 3' or laser beam 3'* are, thus, mutually displaced.

The number of times the substrate passes the laser beam or beams will, obviously, determine the number of grooves 9 formed and, thus, the desired number of insulating areas.

Since parallel interspaces between electrically conductive areas are formed in this process, the process will be most suitable for image displays of the dot matrix type. The process is especially suitable for high volume production, but it is also suitable for smaller volumes.

The third concept is based on direct imaging 20 of a mask 18 onto substrate 1. As will appear from Figure 8, the mask may be placed at various locations of the optical system, provided that the imaging on the substrate is clear enough. It will be suitable to guide laser beams 19 passing mask 18, via a lens unit 17 to achieve an image 20 which is defined with maximum clarity on substrate 1.

A variant of the embodiment of Figure 8 is shown in Figure 9. Mask 18 is here provided directly on the substrate and a collecting lens 17 causes the scanning laser beam 19 to leave the mirror in the form of successive parallel rays 19 before they hit the mask 18 and cause imaging 20 on the substrate.

For the rest, the relative movement of substrate and imaging may be based on the same principles as in case of the other processes as mentioned above. An important issue of the mentioned concepts is that very moderate requirements are set to the accuracy of the relative movement of substrate and laser beam or beams, provided that the laser light is always sufficiently focused to ensure sufficient local power density for complete removal of the electrode material. In Figure 2b numeral 6' designates the focusing lens system, and correspondingly, in Figure 2b numeral 6'' designates the lens system.

As mentioned above, Figures 3-7 relate to alternative concepts for generating beams 3' ' , i.e. more than one laser beam. In Figure 3 at least two parallel lasers are used with a focusing lens system 6' A An alternative possibility is utilization of one or a plurality of parallel lasers, the beams of which are split into a plurality of beams. In Figure 4 it is shown by way of example, how a laser 4 has its laser beam 3 split up by a diffraction grid 10 into a plurality of laser beams 3' A It will appear from Figure 5 how laser 4 emits a laser beam 3 which passes, via a collimator 11, which is considered to be technically equivalent to the focusing lens system mentioned in connection with the previous Figures. The laser beam 3 then passes on to a bunch 12 of fibres and is spread to individual fibres 13 to form a set of laser beams 3''. The laser beams 3'' pass through a focusing optical system 6' A as in previously mentioned Figures, and the laser beams 3'' arriving from the focusing optical system are directed towards the electrically conductive material, as Illustrated in Figure 2b.

In Figure 6 another concept is shown, in which a laser beam 3 from a laser 4 is deflected in a holographic light beam deflector to form the set of beams 3' A

A variant of the embodiment in Figure 6 is indicated in Figure 7. Laser beam 3 is deflected by a suitable optical interference means 16 to form said set of laser beam 3''. In order to prevent redeposition of the removed material on substrate 1 and for more efficient removal of said material, it is essential that the dot where the laser beam 19 hits the substrate is exposed to pressure from a gas 27 or a vacuum 27, see Figure 13. The composition and temperature of this ambient at in the point of reaction is of importance to the efficiency of material removal and to the surface structure of any remaining material. An alternative to heated pressurized gas is heating the substrate, such heating performable by radiation or use of a heating plate below the substrate.

In case of partial removal of the material, remaining portions may be removed by the aid of chemicals or plasma etching. Plasma etching (see Figure 12) may be carried out by introducing substrate 2 into a chamber comprising a gas inlet 26 and a gas outlet 26A two electrodes 25, 25' with an electric voltage between them. By the aid of a correct composition of gases and an electric voltage between electrodes, a plasma Is formed which will remove the remaining portions of the material.

Removal of remaining portions of material by use of chemicals may be carried out by spraying chemical 21 by the aid of a spray means 22 (see Figure 10), by immersing substrate 2 in a vessel 23 containing the selected chemical 23' (see Figure 11) or by contacting the substrate with the chemical i another manner.

Claims

CLAIMS :

1.

A process for manufacturing an electrode pattern (8; 9; 9') for dot matrix displays on transparent substrates (2) of an insulating material provided with a layer (1) of an electri¬ cally conductive material, c h a r a c t e r i z e d i n that the surface or layer (1) on substrate (2) is modified by complete or partial removal of electrically conductive layer, e.g. by evaporating or transforming portions of said layer to insulating material by use of one or a plurality of focused laser beams (3'; 3' ').

2.

A process as stated in claim 1, c h a r a c t e r i z e d i n that the laser beam (3') scans substrate (2) across (A) the direction of movement (B) of the substrate, and that the laser beam is modulated (5) or interrupted for selective removal or transformation of portions of the electrically conductive layer (1).

3.

A process as stated in claim 1, c h a r a c t e r ! e d i n that the laser beam (19) is caused to scan, via a mask (18) which is provided at a distance from the substrate, that those beams passing said mask are directed towards substrate (1), via a lens unit (17), and that an image (20) of the mask is formed on the substrate.

4.

A process as stated in claim 1, c h a r a c t e r i z e d i n that laser beam (19) is, via a lens unit (17), caused to scan across a mask (18) which is provided directly on the substrate, causing an image (20) of the mask to be formed on substrate (2).

5.

A process as stated in claim 1, c h a r a c t e r i z e d i n that laser beam (3') or laser beams (3'') are kept substantially stationary during the passage of substrate (2) (Figures 2-7).

6.

A process as stated in one or several of the preceding claims, c h a r a c t e r i z e d i n that the laser beam or beams (3'; 3'') are generated to have a wavelength which coincides with an absorption band of the electrically conductive layer (1), preferably a wavelength of less than 1 micrometer.

7.

A process as stated in one or several of claims 1-3, c h a r a c t e r i z e d i n that the laser beam or beams Is/are absorbed by a pigment layer which is provided on the electrically conductive layer (1).

8.

A process as stated in one or several of claims 1, and 3-7, c h a r a c t e r i z e d i n that the laser beam or beams is/are split into a plurality of rays before focusing on the substrate.

9.

A process as stated in claim 8, c h a r a c t e r i z e d i n that splitting occurs by the aid of a diffraction grid

(10).

10.

A process as stated in claim 9, c h a r a c t e r i z e d

1 n that splitting occurs by the aid of fiber optics (12,

13).

11.

A process as stated in claim 8, c h a r a c t e r i z e d i n that splitting occurs by the aid of a holographic deflecting device (15).

12.

A process as stated in claim 8, c h a r a c t e r i z e d i n that splitting occurs by the aid of interference optics

(16).

13.

A process as stated in one or several of the preceding claims, with partial removal of portions of the conductive material (1), c h a r a c t e r i z e d i n that the remainder of the partially removed material (1) is removed, either by contacting the substrate with a chemical (21, 23') in the form of vapour, liquid, or solid substance, or by plasma etching (25, 25', 26, 26').

14.

A process as stated in one or several of claims 1-12, c h a r a c t e r i z e d i n that the dot at which the laser beam (19) hits substrate (1,2) is flushed with a pressurized gas (27) or subjected to the influence of a vacuum.