European Team Integrates IPL Process Development Tool
Aaron Hand, Managing Editor -- Semiconductor International, 11/1/2000
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IPL should be ready for mass production by 2005 or 2006, according to Albrecht Ehrmann, project manager of the European IPL Development Program's stencil mask project. To reach the necessary state of readiness, the team - working as part of the MEDEA project - still has tight specifications that it needs to meet for the stencil masks, and it must demonstrate experimental results of the projection tool to show its industrial feasibility. The placement fidelity of the stencil mask is a particularly difficult challenge that developers face, said Ehrmann, who works for Infineon Technologies AG (Munich, Germany).
But the MEDEA team - which also includes researchers from ASM Lithography (Veldhoven, Netherlands), Leica Microsystems Lithography GmbH (Jena, Germany), Ionen Mikrofabrikations Systeme GmbH (Vienna, Austria) and the Institute for Microelectronics Stuttgart (Germany) - has already achieved several steps in proving that IPL can handle high-volume sub-100 nm semiconductor manufacturing. These have included routinely manufacturing 6-in. stencil masks; developing a layer to protect the mask's silicon layer from degradation by helium ions; and designing a radiative cooling system to protect masks from heating by ion irradiation. The researchers also have successfully tested several commercially available resists, achieving the necessary resolution with the predicted low doses, Ehrmann said.
In its latest move toward volume production, the research team has designed and integrated a process development tool. The researchers have assembled and fully integrated the ion-optical column, pattern lock system and a metrology stage. The electronic integration of the projection tool is ongoing, Ehrmann noted.
By using field composable lens (FCL) electrodes, ion-optical performance may be electronically fine-tuned. Individual voltages can be applied to the electrically isolated segments of the electrodes, Ehrmann said, so that the electrical field in the optics system can be easily tuned.
The group has been working to control the in-plane distortion (IPD) of the stencil mask by modeling silicon membrane stress. By pre-calculating the distortions that arise from the mask patterning process, the developers can shift and distort the design accordingly. The researchers were particularly interested in the relationship between boron doping and silicon membrane stress. Using analytical and experimental models, they found that there is ~1.5 MPa tensile stress at zero doping (caused by the mask-wafer blank fabrication process), compared with ~11 MPa stress at doping concentrations of 1.5 x 1019 atoms/cm3. In applications, a pattern pre-distortion of the mask writing data will compensate for stress-related pattern IPD.
Finite element analysis also enabled the researchers to improve the mask frame and the mounting concept. As a result of their studies, they changed the mounting system from an eight-point to a three-point support system; and, for pattern placement measurements, they mounted a titanium plate to the backside of the mask frame to avoid vibrations caused by airflow.
Although a majority of participants in International SEMATECH's latest NGL Workshop gave the nod to extreme ultraviolet (EUV) and electron projection lithography (EPL), the chips are not down for IPL, Ehrmann contends. "It does not mean that a qualified minority would not have the opportunity to succeed finally," he said.
The critical issue, Ehrmann said, is whether IPL development can get the money that is needed to achieve final production quality. Although the ion projection program may not receive funding from International SEMATECH, it has been funded by European governments and private companies since 1997, he said. "As long as major financial contributions for the next phases are still in the planning phase, there is the chance to convince the market when showing good alpha-phase results." The results that come from next year's IPL, EUV and EPL larger-field exposure tools could bring about major changes in the opinions of industry players, he added.
