PHOTORESIST

Positive, Negative and Image Reversal Resists

Positive resists form an indene carboxylic acid during exposure making them soluble in aqueous alkaline solutions. Therefore, positive resists develop where they have been exposed, while the unexposed areas remain on the substrate. Since positive resists do not cross-link, the resist structures rounden beyond their softening point of typically 100-130°C.
Negative resists such as the AZ® nLOF series or the AZ® 15nXT or 125nXT cross-link after exposure and (not required for the AZ® 125nXT) a subsequent baking step, while the unexposed part of the resist is dissolved in the developer. The crosslinking makes the resist thermally stable, so even elevated temperatures will not deteriorate the resist profile. However, towards higher and higher process temperatures, the degree of crosslinking increases and it becomes hard or even impossible to wet-chemically remove the resist.
Image reversal resists can either be processed in positive or negative mode. In the positive mode, the process sequence is the same as for positive resists. In the image reversal mode, an image reversal bake after the exposure followed by a flood exposure without mask is required. Even in the negative mode, the degree of crosslinking of the resist is rather low, so the resist structures will rounden beyond the softening point of typically 130°C.

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Resist Coating Techniques

Spin-coating is the most common coating technique for resists. Almost all AZ® and TI resists are optimized for spin-coating and allow very smooth and homogeneous resist films. The attained resist film thickness goes with the reciprocal square root of the spin speed and thus is adjustable in a certain range for each resist. However, since the edge bead becomes more pronounced towards low spin speeds, for attaining thick films we recommend to use highly viscous resists such as the AZ® or AZ® 10XT, as well as suited spin profiles.

Spray coating allows the coating of almost arbitrary shaped and textured substrates. In order to attain a smooth and homogeneous resist film thickness as well as a good edge coverage of textures (if existing), an optimized resist composition with different solvents with low and high boiling points is required. The spray coating resists AZ® and TI Spray meet these requirements for almost all spray coating applications.

Dip coating is a suited coating technique for large, rectangular shaped substrates and the demand for a minimum resist consumption per coated area. For a homogeneous resist film thickness over the entire substrate, a certain solvent composition in the resist is required as realized in the MC Dip Coating Resist.

Fields of Application of the Resist Mask

Wet chemical etching requires an optimized adhesion to the substrate. For this purpose, we recommend the AZ® series for resist film thicknesses of 500 nm to 3 µm, the AZ® ECI series for 1-4 µm resist film thickness, or the AZ® series for films of several 10 µm thickness. In case of low resolution requirements, the PL 177 is a economically priced alternative. HF-containing etchants sometimes cause large-scale resist peeling as a consequence of HF-diffusion through the resist towards the substrate underneath. In this case, it’s generally beneficial to increase the resist film thickness using resists such as the AZ® or the AZ® 10XT.

Dry etching requires an elevated softening point of the resist as well as steep sidewalls. The high-resolution AZ® 701 MIR 14CPS or 29CPS, are optimized for both requirements and reveal a softening point of 130°C.

Thick resists: If resist film thicknesses exceeding 5 µm are required, the thick positive resists AZ® or AZ® 10XT, or the negative AZ® 15nXT or AZ® 125nXT are recommended. The two nXT resists cross-link and therefore reveal an excellent thermal stability during dry etching.

Lift-off processes recommend an undercut resist profile which can be attained with image reversal resists such as the AZ® E (resist film thickness 1-2 µm), the TI 35ESx (3-5 µm), or the AZ® nLOF (2-20 µm) negative resists. Additionally, these resists are thermally stable and therefore help to prevent a rounding of the resist structures during coating.
If the mask design requires positive resists for lift-off application, the resist sidewalls should be as steep as possible in order to prevent a coating of these sidewalls. For this purpose, we recommend the high-resolution resist AZ® 701 MIR 14CPS or 29CPS.

Electroplating requires an improved adhesion of the resist to the substrate as well as an enhanced stability of the resist in the electrolyte. The negative resists AZ® 15nXT (resist film thickness 5-30 µm) and AZ® 125nXT (up to approx. 150 µm) are optimized for these requirements. Both resists can be developed in TMAH-based developers, wet-chemically stripped in common removers, and are compatible with all common substrate materials and electrolytes for Cu-, Au-, and NiFe plating. If positive resists have to be used for electroplating, the AZ® series and the AZ® 10XT allow steep sidewalls and a good adhesion.

Attainable Resist Film Thicknesses

Generally, the last two digits of the resist name indicate the film thickness attained by spin coating (without gyrset) at rpm in 100 nm units. The thickness approximately decreases with the (increasing) square-root of the spin speed, so a given resist allows a certain range in the attainable resist film thickness. If the desired resist film thickness can/should not be realized by varying the spin speed, the usage of a different available viscosity of the given resist is recommended. Otherwise, the following has to be considered:

Dilution of high-viscosity resists with PGMEA (= AZ® EBR Solvent) allows to perform several applications with different film thicknesses using only one resist. However, diluted resists are sensitive to particle formation with a reduced expiry date depending on the resist, the dilution ratio and the storage temperature and -time for the diluted resist. Since the particles partially consist of the photo active compound, a particle filtration before usage increases the dark erosion and decreases the development rate of the resist. For information on specific dilution recipes please contact us.

Realizing thick films with low-viscosity resists is problematic for two main reasons:  i) The required low spin speeds increase the edge bead, and ii) in case of positive or image reversal resists, the rather high concentration of the photo active compound (low optical transparency) in typical 'thin resists' requires high exposure doses for a sufficient exposure, which makes steep resist profiles hard to realize and may cause popping and foaming by N2-bubbles formed during exposure.

Lateral Resolution and Aspect Ratio

The photoresist itself as well as the resist film thickness limit the theoretical resolution. Under optimum conditions, high-resolution thin resists such as the AZ® 701 MIR allow feature sizes of approx. 300 nm using i-line exposure.Beside a high absolute resolution, some processes require a high aspect ratio (ratio of the feature height to their width). Modern thick resists such as the AZ® 10XT allow an aspect ratio of 6-10, and even higher values under optimized process conditions.In many cases not the resist, but the equipment and process parameters limit the attainable resolution. In order to maximize the resolution of a given resist, besides the exposure conditions (no gap between mask and resist caused by particles, bubbles, or an edge bead), also the softbake parameters, the exposure dose, and the development (developer and its concentration, development time) have carefully to be optimized.

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Spectral Sensitivity

The optical absorption (fig. right-hand) of unexposed positive photoresists ranges from approx. 460 nm in the VIS to near UV, which is matched to the emission spectrum of Hg lamps in mask aligners. This absorption spectrum causes the typical reddish-brownish colour of many photoresists. During exposure, photoresists almost completely bleach down to approx. 310 nm. Some modern positive resists such as the AZ® E or AZ® 10XT are not sensitive at g-line, while most negative resists such as the AZ® nLOF series, or the AZ® 15nXT and 125nXT are only sensitive near i-line and therefore appear almost uncoloured to the human eye.The optical absorption range does not end abruptly towards higher wavelengths. Therefore, high illumination intensity (e. g. laser scribing) or -times allow an exposure also some 10 nm towards the visible part of the spectrum. Some resists such as the PL 177, MC PC20 or AZ® 520D are dyed which makes it more easy to inspect the coating result.

Accessibility Statement

• www.rayzist.com
• July 20,

Compliance status

We firmly believe that the internet should be available and accessible to anyone, and are committed to providing a website that is accessible to the widest possible audience, regardless of circumstance and ability.

To fulfill this, we aim to adhere as strictly as possible to the World Wide Web Consortium’s (W3C) Web Content Accessibility Guidelines 2.1 (WCAG 2.1) at the AA level. These guidelines explain how to make web content accessible to people with a wide array of disabilities. Complying with those guidelines helps us ensure that the website is accessible to all people: blind people, people with motor impairments, visual impairment, cognitive disabilities, and more.

This website utilizes various technologies that are meant to make it as accessible as possible at all times. We utilize an accessibility interface that allows persons with specific disabilities to adjust the website’s UI (user interface) and design it to their personal needs.

Additionally, the website utilizes an AI-based application that runs in the background and optimizes its accessibility level constantly. This application remediates the website’s HTML, adapts Its functionality and behavior for screen-readers used by the blind users, and for keyboard functions used by individuals with motor impairments.

If you’ve found a malfunction or have ideas for improvement, we’ll be happy to hear from you. You can reach out to the website’s operators by using the following

Screen-reader and keyboard navigation

Our website implements the ARIA attributes (Accessible Rich Internet Applications) technique, alongside various different behavioral changes, to ensure blind users visiting with screen-readers are able to read, comprehend, and enjoy the website’s functions. As soon as a user with a screen-reader enters your site, they immediately receive a prompt to enter the Screen-Reader Profile so they can browse and operate your site effectively. Here’s how our website covers some of the most important screen-reader requirements, alongside console screenshots of code examples:

1. Screen-reader optimization: we run a background process that learns the website’s components from top to bottom, to ensure ongoing compliance even when updating the website. In this process, we provide screen-readers with meaningful data using the ARIA set of attributes. For example, we provide accurate form labels; descriptions for actionable icons (social media icons, search icons, cart icons, etc.); validation guidance for form inputs; element roles such as buttons, menus, modal dialogues (popups), and others. Additionally, the background process scans all the website’s images and provides an accurate and meaningful image-object-recognition-based description as an ALT (alternate text) tag for images that are not described. It will also extract texts that are embedded within the image, using an OCR (optical character recognition) technology. To turn on screen-reader adjustments at any time, users need only to press the Alt+1 keyboard combination. Screen-reader users also get automatic announcements to turn the Screen-reader mode on as soon as they enter the website.

   These adjustments are compatible with all popular screen readers, including JAWS and NVDA.

2. Keyboard navigation optimization: The background process also adjusts the website’s HTML, and adds various behaviors using JavaScript code to make the website operable by the keyboard. This includes the ability to navigate the website using the Tab and Shift+Tab keys, operate dropdowns with the arrow keys, close them with Esc, trigger buttons and links using the Enter key, navigate between radio and checkbox elements using the arrow keys, and fill them in with the Spacebar or Enter key.Additionally, keyboard users will find quick-navigation and content-skip menus, available at any time by clicking Alt+1, or as the first elements of the site while navigating with the keyboard. The background process also handles triggered popups by moving the keyboard focus towards them as soon as they appear, and not allow the focus drift outside it.

   Users can also use shortcuts such as “M” (menus), “H” (headings), “F” (forms), “B” (buttons), and “G” (graphics) to jump to specific elements.

Disability profiles supported in our website

• Epilepsy Safe Mode: this profile enables people with epilepsy to use the website safely by eliminating the risk of seizures that result from flashing or blinking animations and risky color combinations.
• Visually Impaired Mode: this mode adjusts the website for the convenience of users with visual impairments such as Degrading Eyesight, Tunnel Vision, Cataract, Glaucoma, and others.
• Cognitive Disability Mode: this mode provides different assistive options to help users with cognitive impairments such as Dyslexia, Autism, CVA, and others, to focus on the essential elements of the website more easily.
• ADHD Friendly Mode: this mode helps users with ADHD and Neurodevelopmental disorders to read, browse, and focus on the main website elements more easily while significantly reducing distractions.
• Blindness Mode: this mode configures the website to be compatible with screen-readers such as JAWS, NVDA, VoiceOver, and TalkBack. A screen-reader is software for blind users that is installed on a computer and smartphone, and websites must be compatible with it.
• Keyboard Navigation Profile (Motor-Impaired): this profile enables motor-impaired persons to operate the website using the keyboard Tab, Shift+Tab, and the Enter keys. Users can also use shortcuts such as “M” (menus), “H” (headings), “F” (forms), “B” (buttons), and “G” (graphics) to jump to specific elements.

Additional UI, design, and readability adjustments

1. Font adjustments – users, can increase and decrease its size, change its family (type), adjust the spacing, alignment, line height, and more.
2. Color adjustments – users can select various color contrast profiles such as light, dark, inverted, and monochrome. Additionally, users can swap color schemes of titles, texts, and backgrounds, with over seven different coloring options.
3. Animations – person with epilepsy can stop all running animations with the click of a button. Animations controlled by the interface include videos, GIFs, and CSS flashing transitions.
4. Content highlighting – users can choose to emphasize important elements such as links and titles. They can also choose to highlight focused or hovered elements only.
5. Audio muting – users with hearing devices may experience headaches or other issues due to automatic audio playing. This option lets users mute the entire website instantly.
6. Cognitive disorders – we utilize a search engine that is linked to Wikipedia and Wiktionary, allowing people with cognitive disorders to decipher meanings of phrases, initials, slang, and others.
7. Additional functions – we provide users the option to change cursor color and size, use a printing mode, enable a virtual keyboard, and many other functions.

Browser and assistive technology compatibility

We aim to support the widest array of browsers and assistive technologies as possible, so our users can choose the best fitting tools for them, with as few limitations as possible. Therefore, we have worked very hard to be able to support all major systems that comprise over 95% of the user market share including Google Chrome, Mozilla Firefox, Apple Safari, Opera and Microsoft Edge, JAWS and NVDA (screen readers).

Notes, comments, and feedback

Despite our very best efforts to allow anybody to adjust the website to their needs. There may still be pages or sections that are not fully accessible, are in the process of becoming accessible, or are lacking an adequate technological solution to make them accessible. Still, we are continually improving our accessibility, adding, updating and improving its options and features, and developing and adopting new technologies. All this is meant to reach the optimal level of accessibility, following technological advancements. For any assistance, please reach out to

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