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Posts Tagged ‘hardmask’

3D-NAND Deposition and Etch Integration

Thursday, September 1st, 2016

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By Ed Korczynski, Sr. Technical Editor

3D-NAND chips are in production or pilot-line manufacturing at all major memory manufacturers, and they are expected to rapidly replace most 2D-NAND chips in most applications due to lower costs and greater reliability. Unlike 2D-NAND which was enabled by lithography, 3D-NAND is deposition and etch enabled. “With 3D-NAND you’re talking about 40nm devices, while the most advanced 2D-NAND is running out of steam due to the limited countable number of stored electrons-per-cell, and in terms of the repeatability due to parasitics between adjacent cells,” reminded Harmeet Singh, corporate vice president of Lam Research in an exclusive interview with SemiMD to discuss the company’s presentation at the Flash Memory Summit 2016.

“We’re in an era where deposition and etch uniquely define the customer roadmap,” said Singh,“and we are the leading supplier in 3D-NAND deposition and etch.” Though each NAND manufacturer has different terminology for their unique 3D variant, from a manufacturing process integration perspective they all share similar challenges in the following simplified process sequences:

1)    Deposition of 32-64 pairs of blanket “mold stack” thin-films,

2)    Word-line hole etch through all layers and selective fill of NAND cell materials, and

3)    Formation of “staircase” contacts to each cell layer.

Each of these unique process modules is needed to form the 3D arrays of NVM cells.

For the “mold stack” deposition of blanket alternating layers, it is vital for the blanket PECVD to be defect-free since any defects are mirrored and magnified in upper-layers. All layers must also be stress-free since the stress in each deposited layer accumulates as strain in the underlying silicon wafer, and with over 32 layers the additive strain can easily warp wafers so much that lithographic overlay mismatch induces significant yield loss. Controlled-stress backside thin-film depositions can also be used to balance the stress of front-side films.

Hole Etch

“The difficult etch of the hole, the materials are different so the challenges is different,” commented Singh about the different types of 3D-NAND now being manufactured by leading fabs. “During this conference, one of our customer presented that they do not see the hole diameters shrinking, so at this point it appears to us that shrinking hole diameters will not happen until after the stacking in z-dimension reaches some limit.”

Tri-Layer Resist (TLR) stacks for the hole patterning allow for the amorphous carbon hardmask material to be tuned for maximum etch resistance without having to compromise the resolution of the photo-active layer needed for patterning. Carbon mask is over 3 microns thick and carbon-etching is usually responsive to temperature, so Lam’s latest wafer-chuck for etching features >100 temperature control zones. “This is an example of where Lam is using it’s processes expertise to optimize both the hardmask etch as well as the actual hole etch,” explained Singh.

Staircase Etch

The Figure shows a simplified cross-sectional schematic of how the unique “staircase” wordline contacts are cost-effectively manufactured. The established process of record (POR) for forming the “stairs” uses a single mask exposure of thick KrF photoresist—at 248nm wavelength—to etch 8 sets of stairs controlled by a precise resist trim. The trimming step controls the location of the steps such that they align with the contact mask, and so must be tightly controlled to minimize any misalignment yield loss.

A) Simplified cross-sectional schematic of the staircase etch for 3D-NAND contacts using thick photoresist, B) which allows for controlled resist trimming to expose the next “stair” such that C) successive trimming creates 8-16 steps from a single initial photomask exposure. (Source: Ed Korczynski)

Lam is working on ways to tighten the trimming etch uniformity such that 16 sets of stairs can be repeatably etched from a single KrF mask exposure. Halving the relative rate of vertical etch to lateral etch of the KrF resist allows for the same resist thickness to be used for double the number of etches, saving lithography cost. “We see an amazing future ahead because we are just at the beginning of this technology,” commented Singh.

—E.K.

New Applied PVD system targets TiN hardmasks for 10nm, 7nm chips

Tuesday, May 19th, 2015

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By Jeff Dorsch, Contributing Editor

Applied Materials today introduces the Applied Endura Cirrus HTX PVD, a physical vapor deposition system for creating titanium nitride hardmask films that could be used in fabricating 10-nanometer and 7nm chips.

“Titanium nitride is the metal hardmask of choice,” harder than copper and nearly as hard as diamond, says Sree Kesapragada, Applied’s global product manager for Metal Deposition Products.

“Patterning plays key role in defining the interconnect,” Kesapragada says. “Perfect via alignment is critical for device yield. Hardmask ensures the perfect via alignment critical for yield.”

The hardmasks created with the Endura Cirrus HTX TiN system strike the required balance between neutral stress and film density hardness, he asserts. The TiN hardmask, meant to resist the erosion of etching, helps ensure that via etches land where they are supposed to, and not too close to neighboring vias, which can creates shorts.

Metal hardmask layer manages alignment errors.

Applied has worked with customers at multiple sites in developing the new PVD system over the past two to three years, according to Kesapragada. He emphasizes that the Cirrus HTX TiN system offers “precision control over TiN crystal growth,” as the process chamber is “designed for tensile high-density TiN films.” The new PVD system enables high density, tensile films thanks to a high level of ionization during deposition made possible by a high frequency source.

High film desnity is needed to prevent erosion, and a neutral-to-tensile stress is needed for pattern fidelity. CVD/ALD films have tensile stress, but are low density. Traditionally deposited TiN films have good density, but compressive stress.

The formation of “islands” of TiN crystals is almost like chemical vapor deposition, “layer by layer,” Kesapragada says, “in a PVD chamber.”

In the process chamber, the first of its kind, titanium atoms are reactively sputtered in a nitrogen-based plasma, allowing for tunable composition, according to Applied. This chamber can be used for high-volume manufacturing of semiconductors with 7nm features, covering two process-node generations, Kesapragada says.

There is also “very established integration” with chemical mechanical planarization equipment, he adds.

Applied is the market leader in TiN PVD systems, with more than 200 systems shipped, according to Kesapragada. Those PVD systems have more than 700 process chambers, he adds.

The Endura Cirrus HTX TiN PVD system is being formally introduced this week at the IEEE’s 2015 International Interconnect Technology Conference in Grenoble, France.

Applied Materials Introduces New Hardmask Process, Saphira

Monday, November 24th, 2014

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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 selectivity 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 hardmask 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 hardmask, 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.


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