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Mapper has installed its first product, the FLX–1200, at CEA-Leti in Grenoble (France). This is a maskless lithography system, based on massively parallel electron-beam writing with high-speed optical data transport for switching the electron beams. The FLX-1200, containing 65,000 parallel electron beams, has a 1 wph throughput at 300 mm wafers and is capable of patterning any resolution and any different type of structure all the way down to 28 nm node patterns. The system has an optical alignment system enabling mix-and-match with optical 193 nm immersion system using standard NVSM marks. Mapper Lithography and CEA-Leti are collaborating to develop turnkey solution for specific applications.
In figure 1 the basic operation principle of the Mapper technology is shown. The electron optics have no central crossovers making them intrinsically insensitive to Coulomb forces (electron repulsion). The electron optics are modular and much cheaper than high-NA DUV optics, and can be replaced or upgraded in the field. The wafer exposure happens one column of fields at a time and always in the same direction. There is no need to meander. The focus and leveling is performed during stage fly-back to reduce metrology overhead. Each column of fields is aligned separately, with dedicated alignment targets.
Figure 1, Basic operation of the Mapper technology.
In figure 2 the way the beams are distributed over the electron optics slit is shown. The writing strategy is as follows:
- There are up to 5 slits, staggered in X direction for reasons of wafer coverage. The approach is roughly analogous to an inkjet printer
- Each slit area consists of 204 x 13 individual groups of beamlets, organized in a hexagonal array.
- All beamlets are simultaneously horizontally deflected over a range of 2µm while the wafer is scanned vertically.
- Each group comprises 49 individual beamlets (7x7). Each of the 49 beamlets can independently be switched on and off during exposure.
- Each beamlet results in a Gaussian spot on the wafer with 25 nm FW50 diameter (10.6nm 1).
- Total beamlet count will therefore equal 5 x 204x13 x 49 = 649,740. In the FLX-1200 and FLX-1300 the central 10% are used (one half slit area): 65,000
A more detailed description of the principles of operation is given in [2].
Figure 2,Distribution of the beams over the electron optics slit.
The focus of presentation will be the reporting of the performance achieved of the tool installed at CEA-Leti during endurance runs in full tool configuration. This includes status of:
- Exposure throughput
- Achieved resolution and CD uniformity
- Stitching performance
- Matched Machine Overlay
- Tool availability and uptime
Also the different application areas for such a maskless system are discussed.
In figure 3 a preview of a CD uniformity measurement result is shown. On a 300 mm wafer fields of 5mm x 5mm have been exposed containing 60nm dense lines and spaces. The main source of CD variation is caused by differences between the groups of beamlets. To measure this variation we have taken 824 SEM images, each taken of a pattern written by a different beam group. The result is shown in figure 3. The variation is 8nm 3s, and follows a Gaussian distribution of 6nm 3s.
Figure 3, Distribution of 824 CD measurements results on 60nm dense lines and spaces
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