We have already explained about laser spectrum and exposure performance under “E95 and Lithography Process” on the Technology page. This article focuses on the original Bandwidth Control Module (BCM) that Gigaphoton has developed to allow direct control of the spectrum by precisely measuring the spectrum performance. The BCM is mounted on Gigaphoton laser models GT61A and after, which require further narrowing of the bandwidth, as a standard feature. Also, it is available as an option for the models before GT61A*.
* The option varies depending on the particular model.
In addition, we plan to mount the “sMPL”*1 spectrum control technology which achieves a wider depth of focus on the next-generation ArF excimer laser model GT63A for multi-patterning immersion lithography as a standard feature.
The sMPL (Spectrum Multi-Positioning LNM) technology increases the laser spectrum control width to 10 times that of conventional technology with focus drilling, thus creating a greater depth of focus. It enables expansion of the lithography process window for contact holes, trenches and vias, which is not possible with conventional technology, while avoiding negative effects upon critical dimension uniformity (CDU), overlay and productivity. This sMPL technology was tested in a high-volume manufacturing environment in partnership with a leading scanner manufacturer and device manufacturer.
*1) sMPL is available as an option for the models before GT61A.
Simulator “prolith v9.3” was used to simulate the impact of the spectrum performance (E95) of the laser upon the CD during exposure of contact holes under the following conditions:
Figure 2 shows the simulation result.
Figure 2. Impact of E95 upon CD
The simulation result indicated that the impact of E95 upon the CD of a contact hole when the spectrum bandwidth E95 changes by 0.1 pm (nm/0.1 pm) increased in the minus direction as the contact hole size decreased. For example, if a contact hole of 90 nm in diameter is exposed by the laser with E95 = 0.5 pm, the CD sensitivity is approx. -2 nm/0.1 pm; if that of 40 nm in diameter is exposed by the laser with E95 = 0.5 pm, the CD sensitivity is approx. -6 nm/0.1 pm. That is, the impact of E95 upon the CD becomes 3 times greater. In addition, if E95 is increased, its impact upon the CD tends to become greater. If a contact hole of 40 nm in diameter is exposed by the laser with E95 = 0.35 pm and that with E95 = 0.5 pm, the impact of E95 differs by almost double between these two exposure runs.
As is apparent from this simulation result, the variation and absolute value of the laser spectrum needs to be minimized if the device pattern becomes finer. In order to provide a laser beam with minimized variation of the spectrum, Gigaphoton has successfully developed the Bandwidth Control Module (BCM) and incorporated the BCM into its laser products.