By PETE SINGER, Editor-in-Chief
A new hardmask material and process was introduced this month by Applied Materials. Designed for advanced logic and memories, including DRAM and vertical NAND, the hardmask is transparent, which simplifies processing. It also exhibits very high selectivity, low stress and good mechanical strength. It’s also ashable, so that it can be removed after etching is completed. Called Saphira, the process was developed in conjunction with Samsung and other customers. An Applied Materials-developed process for stripping the hardmask was licensed to Korea-based PSK.
Hardmasks are used for etching deep, high aspect ratio (HAR) features that conventional photoresists cannot withstand. Applied Materials first introduced an amorphous carbon hardmask in 2006, and now has a family of specialized films. The Advanced Patterning Films (APF) family now includes APFe, which enables deposition of thicker layers than APF (e.g., in capacitor formation and metal contacts for memory devices), and APFx, design to address patterning of metal lines and contacts at 5xnm and beyond.
The new Saphira APF process – which runs on the Applied Materials Producer XP Precision CVD chamber and works with PSK’s OMNIS Asher systems — introduces new film properties that include greater selec- tivity and transparency. The Saphira APF deposition and resolve major issues to improve patterning of more complex device structures at advanced technology nodes.
“It’s a materials solutions,” said Terry Lee, vice president of strategy and marketing for the dielectrics systems and modules group at Applied Materials. “It’s delivered with the patterning film itself, Saphira, as well as the combination of technologies and processes, whether it’s in the CVD chamber or etch chamber, reducing process steps and simplifying process complexity.
Applied Materials isn’t saying exactly what the Saphira hard mask is composed of, but a recent patent filing describes it as boron-rich amorphous carbon layer. The patent notes that, compared to carbonaceous masking layers, boron-doped carbonaceous layers, which include between 1 wt. % and 40 wt. % boron provide even greater etch resistance.
Lee said the Saphira film “In general, behaves very much like a ceramic. But unlike most ceramics, it’s ashable. It’s structurally hard like a ceramic, but it’s ashable like our standard carbon hard mask,” he said. In general, the selectivity of Saphira is twice the conventional masking materials on the open market, Lee said.
The new process reduces process complexity and cost in a couple of different ways. Because it’s transparent, no extra step is needed to open the mask to find the alignment mark. And because the film has high selectivity, fewer masking steps are required. That all reduces the process complexity. Lee said that with conventional masks, in order to mask these high aspect ratio features, a thicker mask material is often needed.
“When you have a thicker mask and you need to etch fine features, what you wind up with is a very narrow mask. In order to prevent the mask itself from collapsing or titling, you need very strong mechanical strength. With Saphira, we have that high mechanical strength and it resists the deformation,” he said.
Saphira can also reduce the need for multiple hardmasks.
“Instead of having the hard mask, oxide and poly (see figure), it drops down to a one mask that’s thinner because the selectivity is higher,” Lee explained. “What we’re seeing is that we can reduce around 20 steps. When you reduce steps, you reduce cost. What we’re seeing based on our calculations is something like 35% reduction in cost of this one module. Across multiple modules, that adds up to a lot of money,” he added.