Synthetic Quartz Semiconductor Grade ZTSQ-02: 99.99% SiO2 Raw Material for Photomask and DUV Optics

1. Summary

Synthetic quartz semiconductor material has become the gating input for 193 nm lithography, and the ZTSQ-02 grade from NTCM (ZTT Group) is specified against the numbers that actually matter: SiO₂ purity above 99.99 %, stress birefringence from ≤2 nm/cm in grade A through ≤10 nm/cm in grade D, and no streak in one direction, all verified per lot. The material is man-made — grown from a silicon-bearing precursor rather than melted from mineral ore — so it carries none of the aluminium, iron or alkali signature that natural quartz brings with it, and the grade letter rather than the purity headline decides which optical path a blank can serve. It ships as ingots and blocks for photomask substrates, DUV lens elements, excimer windows and metrology optics, with a 20 kg minimum order, 200 metric tons per month of capacity, 30–45 day delivery on FOB Shanghai terms, and documentation to MSDS, RoHS, REACH, ISO, GS, BV and Intertek.

2. What Is a Low-OH Natural Quartz Cylinder?

Synthetic quartz is amorphous silicon dioxide produced by chemical deposition rather than by melting rock. The dominant industrial route is flame hydrolysis: silicon tetrachloride vapour (SiCl₄) is fed into an oxy-hydrogen flame, where it reacts with water to form SiO₂ particles that deposit as a porous soot body. That soot is then vitrified at roughly 1,700–1,800 °C into a dense, transparent glass. Plasma chemical vapour deposition and sol-gel routes exist alongside it and produce variants with different hydroxyl levels, but the principle is the same in all of them: the silicon arrives as a purified gas or liquid, not as a mineral, and the contamination profile is therefore set by the chemistry, not by geology.

That distinction is the whole commercial argument. Natural quartz inherits aluminium, sodium, potassium, lithium, iron and titanium from its ore at parts-per-million levels, and purification reduces rather than eliminates them. Synthetic material starts with a distilled precursor, so the residual metal content sits orders of magnitude lower, and the absence of mineral inclusions means a body with no bubbles and no particulate seeds. For deep-ultraviolet transmission, this is decisive: at 193 nm, ppm-level iron or a single inclusion is enough to absorb energy, generate colour centres and eventually damage the optic.

Four specifications define a synthetic quartz grade. Purity, stated as SiO₂ content — 99.99 % and above for the ZTSQ-02 family. Stress birefringence, the photoelastic signature of residual internal stress, reported in nanometres per centimetre: a light ray passing through stressed glass splits into two components with a path difference Δn·t, and the grade letter is simply the ceiling. Grade A holds ≤2 nm/cm, B ≤5, C ≤5, D ≤10. Streak, or striae — layered refractive-index variation left by the deposition process — which ZTSQ-02 controls to no streak in one direction. And transmission, measured per lot through the working wavelength band and critical at 193 nm and 248 nm.

Read together, those four numbers describe optical homogeneity: how much the material will bend, split or absorb light it is not supposed to touch. That is why the grade letter, not the purity figure, usually decides which synthetic quartz a lithography customer can use.

PQ800E / PQ800EH — Key Technical Parameters

3. Why It Matters: Four Advantages That Change Tool Uptime

Buyers arrive at a synthetic specification because something in their optical path has run out of margin. Four failure modes recur, and each maps to a property of the glass.

1. Absorption and solarisation at 193 nm. DUV lithography photons carry 6.4 eV, enough to break bonds and excite trace metals. A natural quartz body with a few ppm of iron absorbs in the tail of the band, heats locally and forms colour centres; transmission drops over the life of the optic. Synthetic material with no ore-derived metals has a far cleaner absorption edge, which is why every ArF photomask blank starts from a synthetic substrate rather than a natural one. For anyone searching for a synthetic quartz for photomask substrates source, this is the qualification test that decides the contract.

2. Polarisation budget in projection optics. Stress birefringence does not just blur a wavefront; it rotates and retards polarisation, and modern scanners control illumination polarisation precisely to improve image contrast. A lens element at 10 nm/cm contributes retardance that the illumination optimiser cannot compensate for. Grade A at ≤2 nm/cm exists because the optical design assumes it. Specifying the grade is cheaper than redesigning the compensator.

3. Imaging uniformity and striae. Deposition-grown glass can carry fine, layered index variations — striae — that print as low-frequency non-uniformity across a field. A “no streak in one direction” statement is the supplier's assertion that the body is optically usable in the intended orientation, and it belongs in the purchase specification, not just the brochure. For a high homogeneity fused silica requirement, striae and birefringence are the two measurements that separate real grade from marketing grade.

4. Supply risk of natural quartz. Semiconductor-grade natural quartz depends on a small number of ore deposits with consistent chemistry, and that chain tightens whenever demand rises. Synthetic capacity is capital-intensive but feedstock-independent: it scales with reactors, not with mines. A 200 metric ton per month capacity, a 20 kg minimum order that supports NPI builds, 30–45 day delivery, and six certification routes (MSDS, RoHS, REACH, ISO, GS, BV, Intertek) make the synthetic route a practical second source rather than a lab curiosity. Buyers benchmarking synthetic fused silica price per kg against the cost of a failed lithography lot rarely find the arithmetic close.

The adjacent benefit is documentation. Each lot can be characterised by the same optical and chemical methods the customer uses, so the incoming inspection is a verification step rather than an act of faith — from photomask blanks and excimer windows to wafer-inspection optics and reference flats.

4. How It Works in Real Production: From Cylinder to Qualified Component

Synthetic quartz is straightforward to buy and unforgiving to specify badly. The sequence below is how the material moves from a ZTSQ-02 block to a qualified optical component, with the parameters that belong in the purchase order.

Step 1 — Fix the wavelength and the grade together

Grade follows wavelength and geometry. A 193 nm photomask substrate in a scanner with polarisation control needs grade A (≤2 nm/cm) and a transmission measurement at the working wavelength; a 248 nm excimer window in an industrial laser can often accept grade B or C, where ≤5 nm/cm is adequate because the beam is not imaging. A metrology reference flat may take grade D at ≤10 nm/cm. Writing the grade letter and the measurement method into the specification prevents the classic dispute where supplier and customer each believe they shipped or bought “standard” material.

Step 2 — Size the blank with polishing allowance

ZTSQ-02 is supplied as ingots and blocks; finished substrates are cut, ground, lapped and polished from them. State finished thickness, flatness, surface quality and the stock you need removed at each operation. Stress birefringence is a bulk property, so a blank with excessive residual stress cannot be polished out of the problem — but a badly sequenced grind can add it. Annealing and stress-relief steps between coarse and fine grinding are what keep the delivered number inside the grade.

Step 3 — Specify the inspection, then verify it

Four measurements carry the qualification. Birefringence by polarimeter or crossed-polariser mapping, reported as a maximum and a distribution across the clear aperture, not a single spot value. Transmission by spectrophotometer across 190–250 nm, referenced to the customer's own baseline. Striae by shadowgraph or dark-field inspection in the orientation of use. Trace metals by ICP-MS, element by element — total purity figures hide exactly the elements that matter at DUV. Ask for the raw data, not the pass stamp.

Step 4 — Clean and handle for the class of the tool

Standard flow is a controlled acid or HF-based etch where the design permits it, overflow rinsing in deionised water to 18.2 MΩ·cm, then filtered-nitrogen drying. Packing for shipment is a clean plastic sealing bag inside a master carton inside a wooden crate — the same sequence used for the standard 20 kg pack. Anything touched after cleaning has to be re-cleaned; optics handled in a non-cleanroom area arrive with the contamination they were protected from.

Step 5 — Deploy into the optical path

In photomask blanks, the synthetic substrate is the mechanical and optical foundation for the absorber stack, so flatness and birefringence propagate directly into overlay and critical dimension. In DUV projection lenses, elements are stacked in groups where each surface's retardance adds; a grade A blank at the front of the stack buys margin for the whole assembly. In excimer laser windows, the requirement is absorption plus damage resistance at 193 or 248 nm under pulsed fluence. In wafer inspection and metrology, a low-birefringence flat determines whether a phase-sensitive measurement is real. In each case the same block, different grade and finish.

Step 6 — Lock the replenishment model

Synthetic quartz is a recurring input, not a one-off. With 200 metric tons per month of capacity, a 20 kg minimum order and 30–45 day delivery on FOB Shanghai terms, the workable model is a rolling forecast with buffer stock sized to the polishing cycle. L/C, D/A, D/P and T/T cover the range from an NPI sample order to an annual agreement. Send the drawing, the wavelength and the grade letter, and the quotation follows without a round of clarification.

5. FAQ

Q1. What is synthetic quartz and how does it differ from natural quartz?

Synthetic quartz is SiO₂ grown from a purified silicon precursor — typically by flame hydrolysis of SiCl₄ — then vitrified into glass. Natural quartz is melted from mineral ore. The synthetic route carries no ore-derived aluminium, iron or alkali, produces no mineral inclusions, and gives far tighter optical homogeneity, which is why DUV lithography uses it.

Q2. What does stress birefringence grade A, B, C or D mean?

The grade is the ceiling on residual stress birefringence measured in nanometres per centimetre of path: grade A ≤2 nm/cm, grade B ≤5, grade C ≤5, grade D ≤10 on the ZTSQ-02 datasheet. Lower values matter for polarisation-sensitive imaging. Grade A is normally specified for 193 nm photomask substrates and projection lens elements.

Q3. Why does “no streak in one direction” matter?

Streak, or striae, is layered refractive-index variation left by the deposition process. It prints as low-frequency non-uniformity across an imaging field and cannot be corrected by polishing. A statement of no streak in the direction of use confirms the body is optically usable in that orientation, and it belongs in the purchase specification rather than the brochure.

Q4. What MOQ, lead time and capacity are available?

Minimum order quantity is 20 kg, which covers engineering and NPI builds. Delivery runs 30–45 days on FOB Shanghai terms, with L/C, D/A, D/P and T/T accepted. Monthly capacity is 200 metric tons, so scaling after qualification does not require a new supply chain or a new qualification cycle. Ask for the shipping schedule to be issued with the quotation.

Q5. Which purity and documentation should we require?

Specify SiO₂ above 99.99 % with trace metals reported element by element by ICP-MS, plus lot data for birefringence, striae and transmission. ZTSQ-02 ships documented to MSDS, RoHS, REACH, ISO, GS, BV and Intertek standards, with a lot-level certificate. This is the set that most lithography and optics audits request.

Q6. Can the material be supplied as finished polished parts?

ZTSQ-02 is supplied as ingots and blocks, and finished substrates are cut, ground and polished from them. Send the finished drawing with flatness, thickness and surface quality, and we will confirm which grade and blank size will hold the specification after polishing, including the stress-relief steps required between grinding operations. Finished-part supply is quoted per drawing.

6. Conclusion

Synthetic quartz is not a premium version of natural quartz; it is a different material with a different contamination physics. Purity above 99.99 %, controlled stress birefringence and no streak in the direction of use are what allow a 193 nm optical path to hold its polarisation budget and its transmission across a production lifetime. A natural body with ppm-level iron will absorb and solarise; a body at 10 nm/cm will retard the polarisation the scanner just optimised.

So the specification is the product. State the wavelength, the grade and the aperture, and the material either meets it or it does not — which is exactly the clarity an optical programme needs.

ZTSQ-02 delivers those three numbers with a 20 kg entry point, 200 metric tons of monthly capacity and 30–45 day delivery from FOB Shanghai. Next step: send your drawing, working wavelength and required birefringence grade — we will return a material recommendation, a blank size and a quotation, or download the ZTSQ-02 datasheet to compare specifications before your next qualification cycle.