Manufacturing Bits: Sept. 17

Full-chip inverse lithography; synthesizing advanced resists.


Full-chip inverse lithography
D2S has developed new hardware and software that enables a long-awaited technology--full-chip masks using inverse lithography technology (ILT).

For years, ILT has been a promising technology. ILT is a next-generation reticle enhancement technique (RET) that enables an optimal photomask pattern for both optical and extreme ultraviolet (EUV) lithography reticles. Using a complex mathematical formula, ILT improves the latitude of a process and the depth of focus for a lithography tool.

Ultimately, the industry hopes to devise “full-chip ILT masks,” which could help ease the constraints and enable the most difficult features, such as tiny contacts, cuts and vias, in IC designs.

The problem? ILT makes use of complex curvilinear shapes. And so, the processing or runtimes associated with full-chip ILT are too long, thereby limiting the practical application of the technology.

So, the industry uses ILT, but it is mainly deployed for niche applications, such as a hot spot repair on the mask.

Now, D2S appears to have finally enabled full-chip ILT masks. The company has rolled out TrueMask ILT, a GPU-accelerated hardware and software system that enables stitch-less full-chip ILT for advanced designs in a single day.

To accomplish this feat, the industry requires massive compute power with a powerful chip. It requires a large GPU/CPU pair that could process full-chip data seamlessly, but that solution doesn’t exist in the market.

So, D2S was able to build an ILT-specific computing appliance that could emulate a large GPU/CPU pair. The technology runs with D2S’ GPU-accelerated hardware platform called the computational design platform (CDP).

“For years, ILT has been seen as a promising solution to many of the challenges of advanced-node lithography, but the ability to implement ILT across the entire chip layout in a timely fashion had been out of reach,” said Leo Pang, chief product officer and executive vice president at D2S. “Wafer fabs need to deliver wafers in the shortest time possible, which requires ILT process time to be shrunk to a single day in order to be practical. D2S TrueMask ILT is the first commercial ILT solution that delivers full-chip ILT within this time constraint.”

Synthesizing advanced resists
Brookhaven National Laboratory has developed an infiltration synthesis method that enables a class new of hybrid resists for e-beam and EUV lithography.

The hybrid organic-inorganic resist from researchers exhibit a high contrast ratio. This in turn enables the development of high-resolution structures at advanced nodes.

Generally, hybrid resists require complex chemical synthesis, according to Brookhaven. Generally, hybrid resists are negative-tone in nature, which have high dose requirements, according to researchers in the Journal of Materials Chemistry C.

In response, Brookhaven National Laboratory has developed a hybrid positive-tone resist. The resists combine the organic polymer poly(methyl methacrylate), or PMMA, with inorganic aluminum oxide. Researchers can change the amount of aluminum oxide in the mix, enabling them to tune the parameters for particular applications.

In the lab, researchers used an atomic layer deposition (ALD) system to synthesize or combine PMMA and aluminum oxide. “After placing a substrate coated with a thin film of PMMA into the ALD reaction chamber, they introduced a vapor of an aluminum precursor that diffused through tiny molecular pores inside the PMMA matrix to bind with the chemical species inside the polymer chains,” according to Brookhaven National Laboratory. “Then, they introduced another precursor (such as water) that reacted with the first precursor to form aluminum oxide inside the PMMA matrix. These steps together constitute one processing cycle.”

Initially, researchers have demonstrated the hybrid resist for electron-beam lithography patterning. In terms of contrast, the resist had a six-fold enhancement over standard PMMA, according to the Journal of Materials Chemistry C. It has enables resolution down to ∼30nm with high-aspect ratios and etch selectivity.

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