Exposure writes a latent image into photoresist; development turns it into a pattern. This guide explains how to set and calibrate the exposure dose, how to find it with an exposure series, how puddle, immersion and spray development compare, why developer volume matters, and how to trace common development faults.
In one paragraph: Dose is intensity times time; confirm whether the dose and intensity refer to the i-line or the lamp’s broader output [2]. Use an exposure series to qualify the process. For puddle development, developer capacity and exhaustion can matter; MicroChemicals gives a one-per-mille rule of thumb and describes multiple puddles for thick films [1]. Dilution changes selectivity and development rate, while temperature should be controlled [1].
1. From Latent Image to Resist Pattern
After exposure, the pattern exists only as a latent image: exposed and unexposed resist differ chemically, but the film still looks the same. Development dissolves either the exposed areas (positive resists) or the unexposed areas (negative resists) and leaves the resist mask [1]. Exposure dose and development are therefore one process with two halves. A dose that is too low leaves residues no developer can remove in a sensible time; a developer that is too aggressive erodes the areas that should stay [1][2].
Most positive and negative photoresists are developed in aqueous alkaline solutions. These are based either on diluted sodium or potassium hydroxide or on metal-ion-free TMAH (tetramethylammonium hydroxide) [1]. Many developers contain buffers against neutralisation by CO2, surfactants that wet the substrate in puddle development, and additives that remove tenacious residues [1].
This guide covers the dose first, then the development methods, with puddle development on a spin developer in the most detail. Exposure itself, from contact modes to the resolution limit, is explained in Mask Aligner Exposure: Contact vs Proximity and the Resolution Limit.
2. Setting and Calibrating the Exposure Dose
Exposure dose is intensity multiplied by time. For many conventional photoresists, dose is a useful first-order process variable, but equal doses delivered at different intensities or times are not guaranteed to produce identical results [2]. At high intensity and in thick films, heat and nitrogen released during exposure can escape too slowly and damage the resist [2].
t = exposure time (s); D = dose (mJ/cm²); I = intensity (mW/cm²) measured at the wavelength the dose refers to.
| Target dose | At 10 mW/cm² | At 20 mW/cm² | At 30 mW/cm² |
|---|---|---|---|
| 50 mJ/cm² | 5 s | 2.5 s | about 1.7 s |
| 100 mJ/cm² | 10 s | 5 s | about 3.3 s |
| 150 mJ/cm² | 15 s | 7.5 s | 5 s |
| 200 mJ/cm² | 20 s | 10 s | about 6.7 s |
Arithmetic from t = D/I. The doses are examples, not recommendations; the resist data sheet and your exposure series set the dose.
The arithmetic is simple; the units are where errors creep in. MicroChemicals points out that the exposure series in resist data sheets are usually measured with monochromatic i-line exposure, while a mercury lamp also emits g- and h-line light, and many intensity meters measure only the i-line [2]. In MicroChemicals’ own example, a mask aligner gave 8.5 mW/cm² at the i-line and about 22 mW/cm² integrated over the g-, h- and i-lines [2]. One second of that exposure is 8.5 or 22 mJ/cm², depending on which number you use. Record which one your process uses.
The substrate changes the dose the resist actually absorbs, especially for optically thin films: glass reflects about 10 % of shortwave light, silicon about 30 % and metal films more than 90 % [2].
3. Finding the Dose: Exposure Series and Contrast Curve
MicroChemicals recommends an exposure series for each new process and when the equipment or resist changes, because the useful dose depends on the resist, substrate optics and process requirements [2]. For many positive resists, the onset of development-rate saturation is a useful reference point [2], but the selected dose must also meet the pattern’s clearing, remaining-film and dimensional requirements. Do not treat saturation alone as proof that a process is qualified.
A simple series:
- Coat and bake substrates exactly as in production.
- Expose fields or substrates with a range of doses, for example in equal steps on a logarithmic scale.
- Develop all of them with the same developer, temperature, method and time.
- Measure the remaining thickness, the time to clear or the critical dimension, and pick the dose near the onset of saturation, adjusted for the pattern.
The contrast curve
Plotting the remaining film thickness after development, normalised to the original thickness (d′/d0), against the logarithm of the dose gives the contrast curve [2]. A perfect positive resist would show a step. Real curves start below 1 at zero dose, because unexposed resist also erodes (dark erosion), then fall to zero at the dose to clear; the slope of the drop defines the contrast [2]. The contrast belongs to the whole process, not only the resist: film thickness, softbake, rehydration, temperature and developer all enter [2].
For modelling, Dill and co-workers characterised positive photoresist exposure with absorption and bleaching parameters measured on the resist film itself [3], and exposure and development-rate models are treated in lithography textbooks [4]. For day-to-day work, the measured series is what counts.
Negative resists behave differently. Their development rate depends only indirectly on the dose, because the unexposed areas are developed; excessive doses can partly expose neighbouring dark areas and make small holes or narrow trenches difficult to open [1][2].
4. Immersion, Puddle and Spray Development
Three ways of bringing developer to the resist are common:
| Method | How it works | Points from MicroChemicals [1] |
|---|---|---|
| Immersion (dip) | Substrate held in developer in a beaker or tank, often with agitation | Basically all developers are suitable; strong mechanical recirculation can make surfactant-containing developers foam |
| Puddle | A puddle of developer is dispensed on the substrate on a spin chuck, left to act, then spun off and rinsed | Surfactants are a prerequisite for rapid, even wetting and a homogeneous result over the substrate |
| Spray | Developer sprayed onto the rotating substrate | Foam from surfactant-containing developers can make development uneven |
Method descriptions are general practice; the comments in the third column are from MicroChemicals [1].
A puddle sequence on a spin developer
Puddle development turns the spin chuck into a small, repeatable development bath. Each substrate gets fresh developer, the timing is programmed, and rinse and drying follow without handling. A typical sequence is:
- Dispense. Developer is dispensed on the stationary or slowly rotating substrate until a continuous puddle covers it. A surfactant-containing developer wets quickly and evenly [1].
- Develop. The puddle rests for the development time while the resist dissolves.
- Spin off and repeat if needed. For thick resist films, MicroChemicals recommends two or more successive puddles, spinning off the exhausted developer briefly between them, without drying in between [1].
- Rinse. Water stops development and carries dissolved resist away; the more resist the developer carries, the more important a rapid and sufficient rinse becomes to avoid residues on cleared areas [1].
- Dry. Spin drying, often with a nitrogen stream.
Each step is a line in the program: dispense volume and speed, rest time, number of puddles, rinse time and drying speed. Once fixed, they make development as reproducible as the coating step.
5. Developer Volume, Exhaustion and Multiple Puddles
A puddle holds only a limited volume of developer, so it can exhaust before the resist has cleared. MicroChemicals gives a rule of thumb: once about one part per thousand (by volume or weight) of developed resist is dissolved in the developer, the development rate drops noticeably, and from a ratio of 1:100 a large fraction of the hydroxide is consumed and the rate approaches zero [1].
A rough estimate shows why this matters for thick films. A 100 mm wafer has an area of about 78.5 cm². With a 2 µm resist film of which half is developed away, about 0.008 cm³ (0.008 mL) of resist is dissolved. At one part per thousand, that already corresponds to about 8 mL of developer. With a 10 µm film it is five times as much.
| Resist thickness (50 % developed, 100 mm wafer) | Resist dissolved | Developer at which 1 per mille is reached |
|---|---|---|
| 1 µm | about 0.004 mL | about 4 mL |
| 2 µm | about 0.008 mL | about 8 mL |
| 5 µm | about 0.020 mL | about 20 mL |
| 10 µm | about 0.039 mL | about 39 mL |
Illustrative arithmetic for a 100 mm wafer with an assumed 50 % open area, using the cited one-per-mille rule of thumb [1]. This is not a universal minimum developer volume or an equipment specification; the appropriate volume depends on the resist, developer, pattern and process.
That is the reason behind multiple puddles for thick films: each fresh puddle restores the development rate [1]. The same logic applies to beakers. Open containers also absorb CO2 from the air, which lowers the activity of the developer once any buffer is used up; MicroChemicals recommends changing beakers at least daily and keeping developer containers closed [1].
6. Concentration, Compatibility and Temperature
Concentration and selectivity. MicroChemicals defines selectivity as the ratio of the dissolution rate of the resist to be developed to that of the resist that should stay [1]. Dilution raises the selectivity but lowers the rate: in their example with a KOH-based developer, doubling the dilution from 1:2 to 1:4 increased the selectivity by a factor of five, at the expense of a much lower development rate [1]. MicroChemicals describes the 2.38 % TMAH developers it discusses as ready to use, with further dilution only for very high resolution in thin films [1]; follow the data sheet of the developer you use.
Metal ions. Metal-ion-free (TMAH) developers are needed where sodium or potassium residues could diffuse into a semiconductor substrate in later high-temperature steps; otherwise metal-ion-containing developers perform comparably [1]. Mixing the two types even at ppm levels can slow the metal-ion-containing developer, so keep dispensing lines and containers separate [1].
Substrate compatibility. With a pH of about 13, most developers attack alkali-sensitive metals such as aluminium and copper, and various compound semiconductors [1]. Check this before developing over exposed metal.
Temperature. The development rate depends on temperature, in a way that differs between developers [1]. Causes of drift include room temperature changes, developer stored at a different temperature, heat of mixing, the temperature of the dilution water and evaporative cooling from flow or exhaust [1]. Measuring the developer temperature, at least by sampling, helps to avoid under- or over-development [1].
7. Troubleshooting Development
| Symptom | Likely causes | What to try |
|---|---|---|
| Resist residues in cleared areas | Dose too low, developer exhausted, insufficient rinse [1][2] | Exposure series; fresh developer or an extra puddle; longer, faster rinse |
| Slow or slowing development | Developer exhausted by dissolved resist or CO2, low temperature for the developer used [1] | Fresh developer, more puddles, measure temperature |
| Thinned or rounded remaining structures | Dark erosion from too concentrated developer or too long development [1][2] | Dilute (within the supplier’s range) or shorten development |
| Uneven development across the substrate | Poor wetting in puddle development, foam in spray development [1] | Surfactant-containing developer for puddles; avoid foaming |
| Overhang at the top of positive resist lines (T-topping) | Surface inhibition layer; the explanations are disputed [1] | Review exposure and bake conditions |
| Small holes or trenches will not open (negative resist) | Excessive dose exposing dark areas [1][2] | Reduce dose; exposure series |
| Attack on aluminium or copper | High pH of the developer [1] | Choose a developer compatible with the metal |
Summarised from MicroChemicals [1][2]; the remedies are starting points, not guaranteed fixes.
Coating defects that survive into the developed pattern, such as comets and bubbles, start at the spin coater; see Photoresist Spin Coating: From Viscosity to Target Thickness and Uniformity. The softbake, rehydration and post-exposure bake that sit between coating and development are covered in Soft Bake, Post-Bake and Annealing on a Hot Plate: What Each Step Does.
8. Levon™ Spin Developer
The table quotes the Levon™ spin developer product page; “Not stated” means the page does not give the value.
| Specification | DM200-SE |
|---|---|
| Supported wafer size | From fragments to 200 mm (8-inch) wafers |
| Spin speed | 20–3,000 rpm (no load); resolution ±1 rpm |
| Spin acceleration | 20–10,000 rpm/s (no load) |
| Programs | Single-step or multi-step mode, 100 customizable programs |
| Recipe time | 0–3,000 s per step (0.1 s); maximum spin time 30,000 s |
| Developer channels | 3 channels, including 1 × rinse and 1 × nitrogen drying; 4-channel configurations as a tailored option |
| Chamber and interior | Fully enclosed development chamber; Teflon-coated stainless steel interior |
| Vacuum, flow and suction | Adjustable vacuum pressure with live monitoring; adjustable liquid delivery and recovery (suction) |
| Developer chemistry compatibility | Not stated |
Specifications as published on the Levon™ product page on 22 October 2026, where “no load” is stated by the page. The page lists three channels including a rinse and a nitrogen drying channel and does not name the third; the supplied configuration is confirmed in the quotation.
The AC200 product page also lists a custom automatic developer configuration with published acceptance criteria. It is a custom configuration quoted on request, not a specification of the standard developer above:
| AC200-DEV-CTM (custom configuration, quoted on request) | Published value on the AC200 page |
|---|---|
| Process | Automatic desktop developer; fragments to 8-inch wafers |
| Swing arm | PTFE-coated aluminum alloy; automatic lifting and swinging; 0–30°/s, adjustable |
| Pipeline | 3 channels: developing liquid, pure water, nitrogen; adjustable liquid flow rate |
| Nozzles | Cylindrical or fan-shaped |
| Acceptance criteria | Linear patterns developed with 2.38% TMAH using 2 puddles, after adhesion promotion and exposure; line width not smaller than 5 µm; CD uniformity not greater than ±4% within and between chips; 4-inch wafers, 5 points per wafer, 3 wafers |
Values as published for the custom configuration on the AC200 product page on 22 October 2026; a custom configuration is defined in the quotation.
How this connects to the guide: the DM200-SE runs single- or multi-step programs with 100 customizable recipes, which is what a puddle sequence with dispense, rest, spin-off, rinse and dry needs (Section 4). Its speed range starts at 20 rpm for slow puddle and rinse steps, and the rinse and nitrogen drying channels cover the last two steps. The page does not state developer chemistry compatibility, so confirm it for your developer. The custom configuration on the AC200 page has published acceptance criteria based on two puddles of 2.38 % TMAH, the multiple-puddle approach of Section 5. Exposure is covered by the MA200-BE mask aligner, and softbake or post-exposure bake by the HP100 programmable hot plates. Questions about a specific configuration can be sent through the contact form.
9. Keep Exploring the Lithography Knowledge Hub
Start here
- Solution-Processed Thin Films: Choosing Spin, Dip, Slot-Die or Blade Coating — thin-film coating methods compared
- Spin Coating Explained: Stages, Physics and Film Thickness — stages and physics of spin coating
Lithography steps
- Photoresist Spin Coating: From Viscosity to Target Thickness and Uniformity — coating the resist to target thickness
- Soft Bake, Post-Bake and Annealing on a Hot Plate: What Each Step Does — softbake and post-exposure bake
- Mask Aligner Exposure: Contact vs Proximity and the Resolution Limit — contact and proximity exposure
- Edge Bead Removal and Backside Rinse: EBR/BSR in Spin Processing — edge bead removal and backside rinse
Links will be added as each article is published.
Equipment
- DM200-SE Spin Developer — fragments to 8-inch, 20–3,000 rpm, 100 programs
- MA200-BE Mask Aligner — 365 nm exposure, four exposure modes
- HP100 Programmable Hot Plate — RT to 300 °C or 400 °C, auto-lift proximity baking
- Levon™ Spin Developers — all spin developers
Questions about a specific instrument can be sent through the contact form.
10. FAQ
How do I calculate exposure time from dose?
Divide dose by intensity: t = D/I. 100 mJ/cm² at 20 mW/cm² takes 5 s [2].
How do I find the right exposure dose?
Run an exposure series. For many positive resists the onset of development-rate saturation is a useful reference point [2]; the chosen dose must also meet the clearing, remaining-film and dimensional requirements of the pattern.
What is puddle development?
Developer is applied to cover the substrate, allowed to act for the specified time, then removed before the qualified rinse and drying steps. Surfactants can support even wetting for the developer systems described by MicroChemicals [1].
How much developer does a puddle need?
MicroChemicals gives a rule of thumb: development slows noticeably once about one per mille of resist is dissolved in the developer [1]. Treat it as an order of magnitude; the volume needed depends on the resist, developer, pattern and process.
Why use two puddles?
For thick resists, a second fresh puddle restores the development rate; spin off between puddles without drying [1].
Should I dilute my developer?
Dilution can increase selectivity while lowering the development rate. MicroChemicals describes 2.38 % TMAH developers as ready to use in its stated context; follow the selected developer’s data sheet and do not dilute unless its instructions permit it [1].