Photoresist Archives - Allresist EN https://www.allresist.com/category/resist-wiki/resist-wiki-photoresist/ ALLRESIST GmbH - Strausberg, Germany Tue, 14 Jun 2022 09:33:30 +0000 en-GB hourly 1 https://wordpress.org/?v=6.5.2 Positive two- layer lift-off system https://www.allresist.com/positive-two-layer-lift-off-system/ Tue, 14 Jun 2022 09:15:10 +0000 https://www.allresist.com/?p=17557 These systems have a bottom resist that is not photosensitive but soluble in alkali. The polymers must be composed in such a way that the lacquer coat withstands a coating with a photoresist with the solvent PMA (PGMEA) without any problems. Otherwise there would be a mixing of both resist layers.

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Positive two- layer lift-off system

Currently, two positive-tone two-layer lift-off systems have successfully been employed for a couple of years; the AR-P 5400-3510 series (Allresist) and PMGI positive resist variant.

These systems have a bottom resist that is not photosensitive but soluble in alkali.  The polymers must be composed in such a way that the lacquer coat withstands a coating with a photoresist with the solvent PMA (PGMEA) without any problems. Otherwise there would be a mixing of both resist layers. The dissolving speed can be adjusted by tempering of the bottom layer. The variation of the temperature is between 95 – 150 °C. The higher the temperature, the lower the dissolving rate. A second coating with a photoresist is followed by image-wise exposure and development. The photoresist is quickly developed at the exposed areas, and then the developer begins to dissolve the bottom layer in an isotrop way (in all directions). Thus, it also develops below the photresist, which now (unexposed) is no longer affected by the developer.

By varying the development time, users are able to adjust the desired undercut of the AR-P 5400-3510 series as needed.

Fig. 1: 0.8 µm undercut

Fig. 2: 4.6 µm undercut

Undercut structures are almost exclusively used for lift-off processes. During evaporation and particularly during sputtering however high temperatures (of up to 200 °C) may occur, so that a high thermal stability of the upper layer is mandatory. In large undercuts as shown in the second picture, the upper layer tends to melt and flows off; a lift-off process is no longer possible under these conditions. Experiments to develop a thermally more stable positive resist for two-layer systems resulted in no significant improvement so far.

Investigations with negative-tone resists as upper layer in contrast showed promising results. These two-component resist developments could quickly be optimized and produced the desired undercut. For this purpose, resists of the AR-N 4300 -series and bottom layer AR-P 5400 were varied. Resists of the 4300-series are significantly more thermostable than generally used positive resists (see Alkali- and solvent-stable negative resist)

—>  See  Thermally stable two-layer lift-off systems

Overview Photoresists- Negative



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]]> Laser ablation of PPA (Phoenix 81) https://www.allresist.com/laser-ablation-of-ppa-phoenix-81/ Tue, 07 Jun 2022 10:09:22 +0000 https://www.allresist.com/?p=17456 PPA layers can also be structured by laser ablation. Substrates coated with AR-P 8100 were structured with pulsed laser light at different wavelengths at the IOM Leipzig (Dr. Klaus Zimmer). In this process, architectures with very little edge roughness could be generated. In the absorption range of PPA, at 248nm, complete ablation was achieved without damaging the silicon substrate.

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Laser ablation of PPA (Phoenix 81)

PPA layers can also be structured by laser ablation. Substrates coated with AR-P 8100 were structured with pulsed laser light at different wavelengths at the IOM Leipzig (Dr. Klaus Zimmer). In this process, architectures with very little edge roughness could be generated. In the absorption range of PPA, at 248nm, complete ablation was achieved without damaging the silicon substrate.

Fig. 1 and 2: 0,5 J/cm2, 248nm, 20ns, double-pulse exposure, 700nm PPA on Si-wafer

Although PPA shows only very little absorption at a wavelength of 355nm, selective ablation with comparatively high sensitivity is still possible. The generated structures again show very smooth edges.

Fig. 3: 0,1 J/cm2, 355nm ps-laser, single-pulse exposure, 700nm PPA on Si-wafer

The laser beam can also be used for the generation of 3d structures. Interference projection through a phase mask allows the  generation of grid structures with sinusoidal course and very little surface roughness.

Fig 4: experimental structure interference projection

Fig. 5 and 6: SEM micrograph of generated PPA grid with sinusoidal course (period ~750nm); 248nm, 20ns pulse, number of pulse: 10, 700nm PPA on Si-wafer

Overview Photoresists- Positive



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]]> ATLAS 46 in general https://www.allresist.com/atlas-46-in-general/ Tue, 07 Jun 2022 09:16:06 +0000 https://www.allresist.com/?p=17445 The resists Atlas 46 S = AR-N 4600-10 and Atlas 46 R = AR-N 4650-10 are photoresists with negative effect and high layer thickness with extremely stable resist structures. In addition, AR-N 4650-10 is removable easily and thus very well suited for photolithographic and electro-plating applications. The characteristics of AR-N 4600-10 are comparable to those of SU-8.

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ATLAS 46 in general

The resists Atlas 46 S = AR-N 4600-10 and Atlas 46 R = AR-N 4650-10 are photoresists with negative effect and high layer thickness with extremely stable resist structures. In addition, AR-N 4650-10 is removable easily and thus very well suited for photolithographic and electro-plating applications. The characteristics of AR-N 4600-10 are comparable to those of SU-8.

The resists consist of poly[(o-cresyl glycidyl ether)-co-formaldehyde] in an organic solvent mixture with the main ingredient 1-methoxy-2-propyl-acetate (PGMEA) and various acid generators. Both resists are developed within a few seconds with the solvent mixtures AR 300–12 or AR 600-70. For a slower and higher-contrast development, AR 600-07 is suitable.

The layer thicknesses of both resists are adjusted to 10 µm at 1000 rpm, further layer thicknesses in the range of 100 nm up to 100  µm are available upon request. It is recommended to softbake on the hot plate at 65° 5 min over 3min ramp at 95 °C for 5 min.

Both resists can be structured by i-line or UV exposure. Prior to exposure, the substrates should be cooled down to room temperature. It is recommended to temper subsequently on the hot plate at 105°C – 110°C for about 2 min, to achieve cross-linking.

For a quick development of a few seconds (5 – 10 s), AR 300-12 or AR 600-70 is recommended. Developing for too long may cause an increase of dark erosion in the case of AR-N 4650-10. A suitable stopper is AR 600-60. The resist layers must be rinsed with DI-water and dried immediately after developing.

The sensitivity for a layer thickness of 10 µm is approximately 120 – 140 mJ/cm2 in broadband UV.

Fig. 1 and 2: Atlas 46S and Atlas 46R are very well suited for the generation of defined structures with vertical walls.

Atlas 46S can be structured at a wavelength of 365nm (i-line), but it is significantly more sensitive in the wavelength range of 250 – 320nm and nearly transparent at 405nm or respectively 436nm (h- or respectively g-line). By use of optimized PAG’s, the photosensitivity of the resist version SX AR-N 4610-10/1 can be significantly increased at 365nm:

Fig. 3: Overlap spectrum of a mercury vapor discharge lamp (blue line) and the absorption curve of SX AR-N 4610-10/1

The new special resist SX AR-N 4620-10/1 can even be structured in the wavelength range of 405 nm up to 436 nm.

The different absorption characteristics can be used to generate well-defined 3d structures:

Fig. 4: Process overview for the generation of three-dimensional architectures in the two-layer process with AR-N 4600-10 as bottom resist and SX AR-N 4610-10/1 or respectively SX AR-N 4620-10/1 as top resist

The process was applied successfully for the generation of bridged resist structures:

Fig. 5: 3d structures generated in two-layer process

Overview Photoresists- Positive



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]]> Black resist https://www.allresist.com/black-resist/ Wed, 01 Jun 2022 11:30:36 +0000 https://www.allresist.com/?p=17432 For a surprisingly high number of applications, it is important to disable the transparency of the substrates completely, while still having the option to generate structures.

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Black resist

For a surprisingly high number of applications, it is important to disable the transparency of the substrates completely, while still having the option to generate structures.  The optically protected area should possibly cover the whole UV/VIS range from 200 – 1.000 nm. For the area of 200 -350 nm this is quite simple, since the resist components already absorb sufficiently there. For wave lengths > 350 nm, colorants must be added, which generate the desired absorption for longer waves.

We now have developed a resist which fulfills the requirements. First experiments resulted in a sufficiently high absorption up to 800 nm, the layer thus can be regarded as optically dense. We have mixed a negative resist with black and dark blue colorants and measured the absorption of the resulting layer thickness. Fig. 1 shows the absorption spectrums. At a thickness of 23 µm, the area of 300 – 800 nm is optically dense.

Fig. 1 UV/VIS spectrums of the black resist layers

Fig. 2 Visual image of the optical density (5 µm, 10 µm, 23 µm)

Even at a layer thickness of 23 µm, structuring is still possible. Common photolithography can be used here. This layer, however, needs a very strong aqueous-alkaline developer  (AR 300-26 or AR 300-73 1 : 1 diluted).

Fig. 3 AR logo structures in black resist

Overview Photoresists- Positive



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]]> General: Resist composition https://www.allresist.com/general-resist-composition/ Wed, 01 Jun 2022 10:20:07 +0000 https://www.allresist.com/?p=17426 The resists most widely used by far are the positive photo resists, followed by negative photo resists. However, there are other special resists as well.
Image reversal resists are positive resists with an additional amine. Depending on the manufacturing process, positive or negative images can be generated.

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General: Resist composition

The resists most widely used by far are the positive photo resists, followed by negative photo resists. However, there are other special resists as well.

Image reversal resists are positive resists with an additional amine. Depending on the manufacturing process, positive or negative images can be generated. Moreover, there are special resists such as the positive polyimide resists and negative polyimide resists (high temperature application > 400 °C, polymer polyimide), negative polyhydroxystyrene resists (high temperature application > 300 °C), negative PMMA photo resists (non-aqueous development for sensitive substrates, polymer PMMA and cross-linker), positive and negative two-layer photo resists (lift-off technology, polymer copolymer PMMA).

Overview Photoresists- Positive



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]]> Ready-to-use spray resists with EVG devices (positive and negative) https://www.allresist.com/ready-to-use-spray-resists-with-evg-devices-positive-and-negative/ Tue, 31 May 2022 11:43:25 +0000 https://www.allresist.com/?p=17422 Spray coating is often used for the coating of complex topologies. There are various manufacturers of spray coating equipment, probably the best known are EV Group and Süss Microtec. Both producers use different strategies and devices for spraying, and therefore ready-to-use spray resists must be adjusted for the particular equipment.

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]]> Thermally stable two-layer lift-off systems https://www.allresist.com/thermally-stable-two-layer-lift-off-systems/ Wed, 25 May 2022 12:20:00 +0000 https://www.allresist.com/?p=17418 The Resist Wiki article "Positive two-layer lift-off systems" describes the principle of these two-layer systems. During the application of lift-off structures, temperatures above 150 °C occur frequently, for example during sputtering. If the usual photo resists are used as top layer, the lift-off structure melts and thus becomes useless for the process.

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Thermally stable two-layer lift-off systems

The Resist Wiki article “Positive two-layer lift-off systems” describes the principle of these two-layer systems. During the application of lift-off structures, temperatures above 150 °C occur frequently, for example during sputtering. If the usual photo resists are used as top layer, the lift-off structure melts and thus becomes useless for the process.

Using the thermostable positive resist SX ARP 3500/8 as top layer, however, yields a heat-resistant lift-off structure which also withstands sputtering processes. See Resist-Wiki “Negative two-layer lift-off system” and “Thermostable photo resists”.

Overview Photoresists- Positive



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]]> Dilution of resists https://www.allresist.com/dilution-of-resists/ Wed, 25 May 2022 09:15:28 +0000 https://www.allresist.com/?p=17414 Almost all photo resists contain PMA (PGMEA) as a solvent. This solvent is therefore the most common thinner and offered by us as AR 300-12 angeboten. The PMA is often used for the removal of edge beads.

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Dilution of resists

Almost all photo resists contain PMA (PGMEA) as a solvent. This solvent is therefore the most common thinner and offered by us as AR 300-12. The PMA is often used for the removal of edge beads (→ Removal or respectively, minimization of edge beads during coating).

Each resist can only cover a certain layer thickness range dependent on the variation of centrifuge speed (see coating). For achieving thinner layers with the resist than can be obtained by the highest revolution speed, it is possible to dilute the resist. It is vital to use only the recommended thinners.

The following diagram shows the ratio of layer thickness and solid content (see image). In the process of thinning, the resist must always be put in first and the thinner carefully added while stirring. If the resist is poured into the thinner, sedimentation may occur during the first drops due to the extreme dilution (solvent shock). It is recommended to fine filter after the dilution, for otherwise particles might interfere with the coating.

Figure: Influence of solid content in the resist on layer thickness.

The single resist types differ slightly, therefore it is only an estimation. For example, in order to bring a resist with a solid content of 33 % from 2,0 µm to a layer thickness of 0,5 µm, a solid content of approximately 17 % must be adjusted. In this case, the ratio of resist and thinner would be fifty-fifty.

When diluting resists,  it must be considered that additives such as tensides (in all resists), colorants (e.g. AR-P 3840) or adhesive agents (e.g. AR-P 3110) are diluted as well, of course.  This hardly affects the colorants and adhesive agents, since the percentage remains the same in relation to the solid content. For tensides, however, a very strong dilution may lead to a decrease of the surface smoothing effect and radial striations.

Overview Photoresists- Positive



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]]> Adhesive strength https://www.allresist.com/adhesive-strength/ Tue, 24 May 2022 11:13:42 +0000 https://www.allresist.com/?p=17411 Adhesive agents serve to improve adhesion, e.g. the adhesion promoter AR 300-80, which is applied by spin coating as thin layer of approximately 15 nm immediately before the resist coating. It is also possible to evaporate HMDS on the substrate, in this process, the monomolecular coat on the wafer surface improves adhesion, because it becomes hydrophobic and better attaches to the resist.

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Adhesive strength

Adhesive agents serve to improve adhesion, e.g. the adhesion promoter AR 300-80, which is applied by spin coating as thin layer of approximately 15 nm immediately before the resist coating. It is also possible to evaporate HMDS on the substrate, in this process, the monomolecular coat on the wafer surface improves adhesion, because it becomes hydrophobic and better attaches to the resist. Spin coating of HMDS onto the wafer is not recommended, since too little remains on the wafer surface, besides, the spin coater gets impure. See Resist-Wiki “Other resist components)”.

Overview Photoresists- Positive



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]]> One-layer and two-layer lift-off https://www.allresist.com/one-layer-and-two-layer-lift-off/ Tue, 24 May 2022 10:36:13 +0000 https://www.allresist.com/?p=17395 Lift-off structures are needed for many technologies. There are one-layer and two-layer processes. For one-layer, only one resist is used. Typical examples are negative resists, see Resist-Wiki "Generation of undercut structures with negative resists". However, there are also positive resists (AR-P 5300) for the lift-off. There is only a slight difference, though in most cases, which, however, is sufficient for many procedures.

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One-layer and two-layer lift-off

Lift-off structures are needed for many technologies. There are one-layer and two-layer processes. For one-layer, only one resist is used. Typical examples are negative resists, see Resist-Wiki “Generation of undercut structures with negative resists”. However, there are also positive resists (AR-P 5300) for the lift-off. There is only a slight difference, though in most cases, which, however, is sufficient for many procedures.

Two-layer systems consist of a bottom resist (below) and a top resist (above). In contrast to the top layer, the lower resist is not photosensitive, see Resist-Wiki “Positive two-layer lift-off system” or “Negative two-layer lift-off system”.

Attempts to coat two photosensitive resists with a layer thickness of less than 2 µm (the insensitive above, the sensitive below, which would enable a lift-off) on top of one another, fail due to mixing of the resists during coating. Only a layer thickness of 10 µm or above enables multiple coating.

Overview Photoresists- Positive



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