By David Lammers

Applied Materials today (Nov. 29^th) unveiled the Onyx atomic-level treatment process for low-k dielectrics, which the company said restores carbon lost during process steps and improves both the low-k value and the hardness of the dielectric.

Applied will offer Onyx as an integrated chamber on its Producer single-wafer deposition platform, initially aimed at the 14nm and 20nm nodes.

While low-k surface treatments have been widely studied, Terrance Lee, chief marketing officer of Applied’s dielectric systems and CMP group, said Onyx is fundamentally different from surface treatments. “Onyx involves a re-bonding (of carbon) in the film’s atomic structure, rather than putting an overcoat on it. We struggled to find a name, and finally decided to call it an atomic-level film treatment. The bonding is not on the surface; it permeates the bulk. It is really a form of molecular-level engineering.”

Russ Perry, global product manager for blanket films at Applied’s Silicon Systems Group, said about one-third of a chip’s total power consumption is expended in the interconnect stack. “There is a pull from our customers, and our customers’ customers, to reduce the amount of power lost in the dielectrics and metal lines. Their target is now on longer battery life, and Onyx was developed to address that.”

One rule of thumb is that interconnect power can be cut by about 10 percent by reducing the k-value by .4. “The challenge is not only to the absolute dielectric constant. As customers scale the features, including the metal pitch and height, the lines get shorter, and that puts more pressure on the dielectric constant,” Perry said.

As chip makers strive to reduce the RC delay by reducing the dielectric constant, they must also improve the dielectric’s hardness, particularly for the packages used for large die. Foundries face a wide variety of customers with complex packaging needs, and maintaining and improving the mechanical strength of the low-k film is essential to delivering high yields.

Applied introduced its Black Diamond 3 low-k chemistry at Semicon West last July. While the first-generation Black Diamond film was a carbon-doped oxide aimed at the  90nm node, with a k-value in the 2.7-2.8 range, Black Diamond 2 introduced porosity, and UV curing, while reducing the k-value. Customers in the field achieve a k-value in the 2.4 to 2.55 range for Black Diamond 2, Perry said.

Black Diamond 3 is based on a redesigned chemistry which provides less interconnection between the pores, reduced damage, and an increase in mechanical strength. Applied claims that Black Diamond 3 shifts the modulus up by 50 percent at the same dielectric constant; it is being evaluated for insertion at the 20nm and 14nm nodes.

Simultaneously, Applied researchers began working on what is now called Producer Onyx as a complement to Black Diamond. “This is no longer just about dielectric deposition. This is atomic-level treatment, which has the ability to turbocharge those films, to improve the dielectric constant and the mechanical strength,” Perry said.

Customers have varied strategies for Black Diamond 3 and the Producer Onyx offerings. Perry said “there is plenty of opportunity for Black Diamond 3 to make it into 20nm products. Customers are using 14nm development as a test vehicle, and then can backtrack to 20nm.”

Similarly, Onyx is being developed for use at the 14nm technology generation, but Perry said “there is no reason Onyx can’t be added to what customers are running today, at 28nm and 20nm. Even 40nm is possible for Onyx. We take the same film, but make it better, which means there are more legs there for backhauling.”

The need for Onyx springs in part from degradation of the low-k film during the hundreds of process steps in interconnect creation. “Films see a lot of harsh environments which impact the film. We would see an increase in the effective k value if we just stand still. With Onyx, we take the film after it is exposed to all these different processes and restore the film,” Perry said.

As the terminating methyl groups are exposed to wet cleans, photoresist stripping, etch, and CMP, the methyl groups can be stripped away, with O-H as the most common inserter. As carbon is removed and O-H bonds to silicon, the dielectric film shifts to a higher k-value. With Onyx, carbon is added back and carbon -hydrogen (C-H) bonds to the silicon. Perry declined to describe the details of how Onyx works, offering that it is an “atomic-level treatment on the sidewalls which restores lost carbon and strengthens the film structure.”

The first opportunity to apply Onyx may come after the etch step to create the damascene structure of vias and trenches, and before creation of the barrier seed layer. Onyx could be used to improve the dielectric film’s properties before metals are deposited.

Onyx also is likely to be used after CMP and the copper oxide removal steps. The low-k materials can be damaged by the CMP and ammonia plasma treatments used prior to barrier deposition. “Onyx is a great fit with the barrier film deposition. We can treat the dielectric right on top without breaking vacuum and exposing it to air. That removes any worries about re-oxidation.”

In tests of the Onyx process at Applied’s Maydan Technology Center, researchers measured a 6 percent reduction in RC delays, and a larger improvement in power lost through the interconnect stack. Perry estimated that the Onyx treatment enables a ~20% lower integrated k-value.

Asked about the modulus value, Perry said “it is premature to quote a number, but there is an improvement of modulus relative to the initial film state. Ten percent is a reasonable ballpark number, and it can be plus or minus from there depending on the initial film condition and the final treatment condition.”

Terrance Lee said some customers may choose to start with a higher modulus film, with a higher dielectric constant, and then apply the Onyx treatment to put in more  carbon to get to a lower dielectric constant. “This moves some of the boundary conditions. Before, customers needed a certain minimum threshold of carbon. With Onyx, some of those restrictions can be eased. We can put the carbon back in there, and improve the modulus of the film. It gives customers some latitude.”

Tags: Applied Materials, low-k, Onyx, Producer Onyx, semiconductor manufacturing

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