EP2567419A1

EP2567419A1 - Reduction of the effects of cap-like projections, due to laser ablation of a metal level by using a non-crosslinked light- or heat-crosslinkable polymer layer

Info

Publication number: EP2567419A1
Application number: EP11731442A
Authority: EP
Inventors: Marie Heitzmann; Mohammed Benwadih
Original assignee: Commissariat a lEnergie Atomique CEA; Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2010-05-07
Filing date: 2011-04-21
Publication date: 2013-03-13
Also published as: CN102918676A; US20130122648A1; KR20130067275A; FR2959865B1; FR2959865A1; WO2011138539A1; BR112012027923A2; JP2013529382A; US8580605B2

Abstract

The invention relates to the use of a laser-crosslinkable material (10) that is non-crosslinked or partially crosslinked for protecting the electrodes of an organic transistor during laser etching.

Description

REDUCING THE EFFECTS OF CAPS DUE TO LASER ABLATION OF A METAL LEVEL USING A NON-RETICULATED PHOTO- OR THERMO-RETICULABLE POLYMER LAYER

FIELD OF THE INVENTION

The invention relates to the field of organic electronics, in particular the manufacture of resistors, capacitors, diodes, transistors, etc.

In practice, it proposes a solution to the problems related to the degradation of surface during step (s) of engraving of a metallic level. It is particularly applicable in the excimer laser ablation etching step of the electrodes of an organic transistor.

PRIOR STATE OF THE ART

The excimer method, which can be implemented using a device illustrated in FIG. 1A, makes it possible to structure and "pattern" patterns solved by projection of the mask (1). Ablation of the substrate (2) is performed by the interaction between the UV (3, excimer) beam passing through the mask (1) made of glass and aluminum and the surface of the layer (substrate, 2).

The excimer laser is a gas laser that emits pulse mode in the ultraviolet between 193 and 351 nanometers depending on the gas mixture used. The gaseous medium is composed of a rare gas G (Ar, Xe, Kr) and a halogenated compound X (F ₂ , HCl). The excitation, electric or by electron beam leads to the formation of excited molecules GX * [ArF (λ = 193 nm), KrF (λ = 248 nm), XeCl (λ = 308 nm), XeF (λ = 351 nm)]. The delivered energies are of the order of the joule and the duration of pulses vary from 10 to 150 nanoseconds, the frequencies being able to reach the kHz. Appeared in 1992 Excimer high power sources _(avg emie: 500-1000 W) suggesting a development of their use for the surface treatment.

The excimer laser has specific advantages: a large energy of photons (several eV) allowing access to photochemical effects, treatments with a submicron spatial resolution and very limited thermal effects, a more effective laser-material coupling in the ultraviolet only in the infrared. Above 300 nm, optical fiber transport appears possible. During the ablation, on the edges of engraving, there is presence of melted bead or detachment of the metal called cap (Fig. 1B), according to the energy used: a weak energy gives caps whereas a Strong energy gives molten edges that usually have unglued or melted dimensions larger than a micrometer. These profiles are very problematic for the use of these patterns in the production of organic electronic components, for which active layer deposition techniques with a thickness of the order of 100 nanometers are used. Placing thin layers of 100 nanometers or less, for example semiconductors of 30 to 70 nanometers on patterns exhibiting these detachments and profiles poses many problems.

This can lead to electrical leaks, difficulties with the passage of steps, loss of dimension (for example at the level of the channel width), premature aging, etc.

However, it has been found that, whatever the metal used (Ti, Cu, Au, Ni, Pt and ...), the mask projection laser ablation technique never leaves a perfect pattern edge. This is inherent to the method and is explained by the fact that the heat of the UV during the "laser shoot" explodes the metallization.

This disadvantage is particularly worrying in the field of microelectronics, particularly in the development of transistors.

Microelectronics has conventionally developed around inorganic materials such as silicon (Si) or galium arsenide (GaAs). Another path is now explored around organic materials, such as polymers, because of their ease of manufacture on a large scale, their mechanical strength, their flexible structure or their ease of reprocessing. It has been designed screens based on organic diodes (OLED) or based on organic thin-film transistors (OTFTs). In addition, the use of layer deposition techniques, for example by spinning, inkjet or screen printing, is made possible by the use of so-called polymers.

However, the stacking of different organic and / or inorganic layers presents a number of difficulties. In particular, the design of a transistor requires two conducting levels: In high gate architecture (FIG 2A), the conductive level 1 (4) is deposited on the substrate (5) and the source and drain electrodes (6, 7) are etched by various types of process such as laser ablation type excimer. This step requires a very good adjustment of the energy of the laser beam, in order to minimize the effects of caps.

In low gate architecture (FIG 3A), the conductive level 2 (4) is deposited on the gate dielectric (9), and the source and drain electrodes (6, 7) are etched by laser ablation. In the same way, this step requires a very good adjustment of the energy of the laser beam in order to minimize the effects of caps as well as the degradation of the gate dielectric.

There is therefore a clear need to develop technical solutions for minimizing these effects in engraving pattern edges.

SUMMARY OF THE INVENTION

Thus, the proposed invention makes it possible to reduce the appearance of caps and beads at the edge of the pattern, inherent to the laser ablation process.

Thus, the invention relies on the use of a material crosslinkable to the laser and being in uncrosslinked or partially crosslinked form to protect a metal layer to be laser etched.

In other words, it relates to a method of structuring a metal layer by etching or laser ablation, wherein a protective layer is disposed on the back of the metal layer to be etched or ablated.

More specifically, the invention relates to a method of laser etching a metal layer which comprises the following steps:

depositing a protective layer on a substrate, said layer comprising a material crosslinkable by laser and being in uncrosslinked or partially crosslinked form;

depositing the conductive layer on the protective layer;

laser etching of the conductive layer. A suitable substrate for carrying out the process according to the invention may be a plastic substrate (PEN, PET, etc.), a plastic substrate covered with metal (Au, Al, Ag, Pd,. between 10 and 200 nanometers or a metal surface (Au, Al, ...) or a conductive surface (for example PEDOT PSS).

Typically according to the invention, the protective layer comprises or consists of a material crosslinkable by laser and is in uncrosslinked or partially crosslinked form. The principle underlying the present invention is the presence of a material capable of absorbing a portion of the energy of the laser which, in fact, less deteriorates the laser-treated metal layer. Indeed, the final properties of a crosslinkable polymer depend on its degree of crosslinking. A fully crosslinked polymer material will be harder than a polymer material having a few cross-linking nodes, which will then have more elastic properties ("J. Phys Chem C 2009, 113, 11491-11506"). Thus, this elasticity will allow to absorb the wave and the low degree of crosslinking will allow the crosslinking.

In other words, the invention is based on the fact of not completely cross-linking the layer below the level to be ablated. In this way, the excess energy of the laser beam is partially absorbed by this protective layer and the etching edge effects are significantly attenuated. In addition, depending on the energy required for the etching, the ablation can be done either by 1 shot at this energy, or by several shots at lower energies.

Such a protective layer typically has a thickness of between 10 to 1500 nanometers, advantageously between 100 and 1000 nanometers. It may be deposited on the substrate by any technique known to those skilled in the art, for example by means of a spin coating.

Within the scope of the invention, the term "laser" (Light Amplification by Stimulated Emission of Radiation) is intended to mean a device producing concentrated radiation in a very fine beam of monochrome light whose coherence is very high and whose energy is very directive.

Such a device is for example an excimer laser which emits in the ultraviolet (UV) range, with wavelengths between 100 and 400 nanometers, in particular 157, 248, 308 and 351 nm. In known manner, such a device is generally used in combination with a mask to structure or "pattern" patterns on the layer of interest.

Typically, such a device has a fluence of between 10 and 1000 mJ / cm ² , for example equal to 54 mJ / cm ² . The pulse durations may vary from 10 to 150 nanoseconds, for example equal to 30 ns, the number of pulses may also be variable, typically from 1 to 10.

In the context of the invention, the expression "laser crosslinkable" is intended to mean that said material is capable of forming a three-dimensional network by creating bonds between the macro-molecular chains under the action of the laser. In practice, the material therefore undergoes partial or total crosslinking under the action of UV radiation or heat related to the laser, depending on whether it is photo-crosslinkable or heat-curable, respectively.

In the case where, at the end of the laser exposure, the material is only partially cross-linked, the crosslinking can be continued by exposure to the UV lamp (for a few minutes, with a power of a few hundred watts) in order to achieve photo-crosslinking or complete thermo-reticulation.

Typically, the crosslinkable laser material used in the context of the present invention is a polymer.

Such a material may also have other particular properties adapted to the intended application.

In the context of the manufacture of organic transistors, the material that can be crosslinked by laser and that is in non-crosslinked or partially crosslinked form is advantageously electrically insulating. In addition, it is advantageous for the crosslinkable polymer to have good electrical compatibility with the semiconductor. For this, a material with a permittivity of less than 5 is preferred.

Such a material is, for example, chosen from the group comprising: polyacrylates, epoxy resins, epoxy acrylates, polyurethanes, silicones, polyimides and copolyimides, poly (sisesquioxanes) s, poly (benzocyclobutene) s, polyvinylcinnamates, perfluorinated aliphatic polymers, poly (vinylphenol). In the context of the fabrication of transistors, which constitutes a preferred application of the present invention, the step of etching the source and drain electrodes, and possibly the gate, is particularly delicate and requires the implementation of the method according to the invention. invention.

Thus, the invention relates to a method of manufacturing an organic transistor comprising the following steps:

depositing a conductive layer for forming the source and drain electrodes or the gate of the transistor, on the protective layer;

laser etching of the conductive layer resulting in the formation of the source and drain electrodes or the gate of the transistor;

deposition of a dielectric layer;

deposition of the grid or source and drain electrodes on the surface of the dielectric.

In this method and conventionally for a transistor, a semiconductor layer is further deposited on the surface of the source and drain electrodes.

According to a particular embodiment, the deposition of the gate or source and drain electrodes at the end of the process is performed by depositing and laser etching a conductive layer.

Suitably and advantageously, the dielectric layer is also made using a material crosslinkable by laser and is in uncrosslinked or partially crosslinked form. Alternatively, a protective layer is also deposited between the dielectric layer and the gate or source and drain electrodes.

The method according to the invention allows both the manufacture of transistors in high gate architecture and low gate. A high grid architecture typically has the following succession of layers:

a substrate;

drain and source electrodes;

an organic or inorganic semiconductor;

a so-called gate dielectric;

a grid. In this architecture, it is therefore to insert the protective layer between the substrate and the metal layer for the creation of the drain and source electrodes, and / or between the gate and its gate dielectric. Note that in the latter case, the dielectric can act as a protective layer.

For the manufacture of a high gate architecture transistor using the method according to the invention, the semiconductor layer is deposited after the laser etching of the source and drain electrodes and before the deposition of the dielectric layer.

In this architecture, the polymer is advantageously electrically insulating so as not to disturb the semiconductor layer deposited above (in the case of the source and the drain) or below (in the case of the grid). It is advantageously chosen from the group consisting of polyacrylates, epoxy resins, epoxy acrylates, polyurethanes and silicones.

The present invention therefore makes it possible to obtain an organic transistor in a high gate architecture comprising the following structure:

a substrate;

a layer comprising at least partially crosslinked material;

source and drain electrodes;

an organic or inorganic semiconductor;

a dielectric layer;

a grid.

As already stated, a layer comprising at least partially crosslinked material may also be present between the dielectric layer and the grid.

According to another aspect, the method according to the invention allows the manufacture of an organic transistor in low gate architecture.

A low grid architecture, as for it, presents classically the succession of following layers:

a substrate;

a grid;

a so-called gate dielectric;

drain and source electrodes;

an organic or inorganic semiconductor. For the manufacture of a low gate architecture transistor using the method according to the invention, the semiconductor layer is deposited after the deposition of the source and drain electrodes.

According to the invention, a protective layer is therefore added between the substrate and the grid.

Advantageously, the dielectric layer is produced using a material which is crosslinkable by laser and is in non-crosslinked or partially crosslinked form.

Alternatively, a protective layer is added between the dielectric layer and the drain and source electrodes.

In this architecture, the polymer is advantageously chosen from the group consisting of: polyimides and copolyimides, poly (sisesquioxanes) s, poly (benzocyclobutene) s, poly (vinylcinnamate) s, perfluorinated aliphatic polymers, poly (vinylphenol) and poly ( acrylate) s.

The present invention thus makes it possible to obtain an organic transistor in a low gate architecture having the following structure:

a substrate;

a layer comprising at least partially crosslinked material;

a grid ;

a dielectric layer;

source and drain electrodes;

an organic or inorganic semiconductor.

As already stated, a layer comprising at least partially crosslinked material may also be present between the dielectric layer and the source and drain electrodes.

In other words, the use of a material crosslinkable to the laser and being in non-crosslinked or partially crosslinked form to protect a metal layer of the laser etching, in the context of the manufacture of an organic transistor, can take several forms :

For a transistor in high gate architecture:

a layer inserted between the substrate and the source and drain electrodes; and or

the dielectric layer under the gate or a layer inserted between the dielectric and the gate. For a transistor in low gate architecture:

a layer inserted between the substrate and the grid; and or

the dielectric layer under the source and drain electrodes or a layer inserted between the dielectric and the source and drain electrodes.

The present invention undeniably relates the positive effect of the presence of a crosslinkable material, but not crosslinked or only partially crosslinked, placed under a metal layer to be treated laser: a significant decrease in caps and melted edges, and an improvement electrical characteristics are observed.

BRIEF DESCRIPTION OF THE FIGURES

The manner in which the invention can be realized and the advantages which result therefrom will emerge more clearly from the following exemplary embodiments, given by way of non-limiting indication, in support of the appended figures in which:

FIG. 1 represents a device for implementing the excimer process (A) and the disadvantages observed at the level of the etching (B).

FIG. 2 represents an embodiment diagram of a high gate architecture according to the prior art (A) or according to the invention (B).

FIG. 3 represents a diagram of realization of a low gate architecture according to the prior art (A) or according to the invention (B and C).

FIG. 4 corresponds to SEM observations of a 30 nanometer gold layer ablated by the excimer type laser process at the same fluence (54 mJ / cm ² ): comparison between a totally crosslinked dielectric (A) and the same uncrosslinked dielectric (B).

FIG. 5 illustrates the electrical results obtained with two organic low-gate architecture transistors from samples A and B, respectively.

DETAILED DESCRIPTION OF THE INVENTION

1 / High grid architecture:

The implementation of the invention in the context of a high gate architecture is illustrated in Figure 2B. It is based primarily on the deposition of an insulating polymer (10) uncrosslinked or partially crosslinked, and thus crosslinkable, between the substrate (5) and the conductive level (4). a / Cross-linkable insulating polymer:

The crosslinkable insulating polymer, which can be used in high grid architecture, may be chosen from the following list:

polyacrylates;

epoxy resins;

epoxy acrylates;

polyurethanes;

silicones.

In this architecture, the insulator (10) allows, if it is not or partially crosslinked, to reduce the caps during the step of ablation of the upper layer (4). It must be electrically insulating so as not to disturb the semiconductor layer (11) deposited above. b / Method of manufacturing the high grid architecture:

Step 1: Substrate (5)

Step 2: Deposition of the uncrosslinked insulation (10) on the substrate (5)

Step 3: Deposition of a conductive layer (4) on the entire surface

Step 4: etching by laser ablation of the conductive layer (4) through a mask (1) giving rise to the formation of the source and drain electrodes (6, 7)

Step 5: thermo- or photo-cross-linking of the insulation (10)

Step 6: Obtaining an organic field effect transistor by successive deposition of a semiconductor (11), a dielectric (9) and a gate (8)

2 / Low grid architecture:

The implementation of the invention in the context of a low gate architecture is illustrated in Figure 3B and 3C. It is based primarily on the deposition of an insulating polymer (10) uncrosslinked or partially crosslinked, and thus crosslinkable, between the substrate (5) and the conductive level (4). a / Crosslinkable dielectric polymer:

The crosslinkable dielectric polymer (10), which can be used in low gate architecture, can be chosen from the following list (A. Fachetti et al., Adv Mater, 2005, 17, p. This is for example a photo-crosslinkable organic dielectric, and more specifically an epoxy resin. It is a mixture of 49.5% by weight of poly (4-vinylphenol) (PVP), 49.5% by weight of trimethylolpropane triglycidyl ether, 0.5% by weight of benzoyl peroxide and 0.5% by weight. by weight of triphenylsulfonium triflate.

This mixture is diluted to 10% by weight in cyclohexanone and deposited by screen printing or spin coating on the substrate (5). The resulting film is annealed at 100 ° C on a hot plate for 5 minutes to evaporate the residual solvents of the thin polymer layer.

This dielectric (10) is crosslinked by applying a UV dose, for example under the following conditions:

power of the lamp = 600W;

10 min of sunstroke. b / Method of manufacturing a transistor in low gate architecture:

Step 1: etching of the metallic level 1 by photolithography or laser ablation to create the grid (8). The etch edges have little impact at the grid level on the electrical properties of the transistor, the gate being much wider than the channel, the effects of caps are then outside the channel. However, the method according to the invention could also be implemented for etching the grid (8) by interposing, between the substrate (5) and the metal level 1, a crosslinkable polymer, under the same conditions as described above. below for the etching of the source and the drain

Step 2: Sputter deposition of the epoxy-type dielectric described above (10), annealed for 5 min at 100 ° C on a substrate (5) PEN / Au (30 nm); dielectric thickness of about 800 nanometers

Step 3: PVD deposition of a gold conductive layer (4) (30 nm) over the entire surface

Step 4: excimer laser ablation (fluence = 54 mJ / cm ² , λ = 248 nm, 30 ns tap) of the conductive layer (4), so as to create the source and drain electrodes (6, 7)

Step 5: thermo- or photo-crosslinking of the dielectric polymer, more specifically insolation crosslinking (UV lamp, 10 min, 600 W)

Step 6: Deposition of a p-type semiconductor (11), for example modified pentacene. Then encapsulation with a fluorinated aliphatic polymer type dielectric.

According to Figure 3C, a protective layer (10) is further deposited on the substrate (5) to protect the grid (8) from laser ablation. c / Comparison of two samples A and B:

By way of comparison, the process described above in point b / was carried out on two samples A and B. Sample B strictly underwent steps 1 to 6, with crosslinking by exposure (UV lamp, 10 min. 600 W) in step 5, i.e. after laser ablation. Sample A, for its part, underwent this exposure to the UV lamp (10 min, 600 W) at the end of step 2, that is to say before laser ablation. The essential difference between samples A and B therefore lies in the fact that the crosslinkable polymer (10) is crosslinked before or after laser ablation of the metal level (4), respectively.

The characteristics of these two samples are illustrated in Figures 4 and 5.

FIG. 4 reveals, for the crosslinked dielectric (A), the important presence of caps and remelted on the ablated upper layer. On the other hand, in the case of the uncrosslinked dielectric (B), there is a marked decrease in caps and remelted on the ablated upper layer.

Figure 5 illustrates that in terms of the electrical characteristics of these two samples, the B sample is significantly better compared to the A sample. Indeed, the ID vs. VD curves of the B sample reflect a very good contact and a good injection of electrons between the two source and drain electrodes. Thanks to this process, the injection of electrons into the channel is thus improved, as well as the mobility of the electrons. The current is more important in open regime.

Claims

1. A method of manufacturing an organic transistor comprising the following steps:

depositing a protective layer (10) on a substrate (5), said layer comprising a material crosslinkable by laser and being in uncrosslinked or partially crosslinked form;

depositing a conductive layer (4), intended to form the source and drain electrodes (6, 7) or the gate (8) of the transistor, on the protective layer (10);

laser etching the conductive layer (4) resulting in the formation of the source and drain electrodes (6, 7) or the gate (8) of the transistor;

depositing a dielectric layer (9);

depositing the gate (8) or the source and drain electrodes (6, 7),

a semiconductor layer (11) being deposited on the surface of the source and drain electrodes (6, 7).

2. A method of manufacturing an organic transistor according to claim 1, characterized in that the deposition of the gate (8) or the source and drain electrodes (6, 7) is achieved by deposition and laser etching of a layer. conductive (4 ').

3. A method of manufacturing an organic transistor according to claim 1 or 2, characterized in that the dielectric layer (9) is made using a material crosslinkable laser and is in uncrosslinked or partially crosslinked.

4. A method of manufacturing an organic transistor according to claim 1 or 2, characterized in that a protective layer (10) is deposited between the dielectric layer (9) and the gate (8) or the source and drain electrodes (6, 7).

5. A method of manufacturing an organic transistor according to one of claims 1 to 4, characterized in that the organic transistor is a high gate architecture transistor and in that the semiconductor layer (11) is deposited between the laser etching of the source and drain electrodes (6, 7) and the deposition of the dielectric layer (9).

6. A method of manufacturing an organic transistor according to one of claims 1 to 4, characterized in that the organic transistor is a transistor in low gate architecture and in that the semiconductor layer (11) is deposited after the deposition of the source and drain electrodes (6, 7).

7. Process for manufacturing an organic transistor according to one of claims 1 to

6, characterized in that the laser etching is performed using a UV laser, preferably with excimer.

8. Process for manufacturing an organic transistor according to one of claims 1 to

7, characterized in that after the laser etching, the protective layer (10), and optionally the dielectric layer (9) undergoes a crosslinking step, preferably by photo- or thermo-crosslinking.

9. Process for manufacturing an organic transistor according to one of claims 1 to

8, characterized in that the laser-crosslinkable material which is in uncrosslinked or partially crosslinked form is electrically insulating.

10. Process for manufacturing an organic transistor according to one of claims 1 to

9, characterized in that the laser cross-linkable material in non-crosslinked or partially crosslinked form has a permittivity of less than 5.

11. Process for manufacturing an organic transistor according to one of claims 1 to

10, characterized in that the material which can be crosslinked by laser and which is in non-crosslinked or partially crosslinked form is chosen from the group comprising: polyacrylates, epoxy resins, epoxy acrylates, polyurethanes, silicones, polyimides and copolyimides, poly (sisesquioxanes) s, poly (benzocyclobutene) s, poly (vinylcinnamate) s, perfluorinated aliphatic polymers, poly (vinylphenol).

12. Organic transistor in high gate architecture, capable of being manufactured using the method according to one of claims I to 5 and 7 to 11, comprising the following structure:

a substrate (5);

a layer comprising at least partially crosslinked material (10); source and drain electrodes (6, 7);

an organic or inorganic semiconductor (11);

a dielectric layer (9);

a grid (8).

13. Organic transistor in low gate architecture, capable of being manufactured using the method according to one of claims I to 4 and 6 to 11, comprising the following structure:

a substrate (5);

a layer comprising at least partially crosslinked material (10); a grid (8);

a dielectric layer (9);

source and drain electrodes (6, 7);

an organic or inorganic semiconductor (11).