LER is found to correlate strongest with the background, or flare, portion of the lithographic aerial image contrast, when compared with the image slope and “standard” (max - min)/(max + min) contrast. A large pool of collected data and rigorous statistical analysis of variance conclude with far greater than 99% confidence that as any of these measures of aerial image profile degrade, LER increases. However, the relation between background exposure and LER is by far the most significant.
Correlations between LER and various types of aerial image contrast were examined for three different commercial resists. LER was more tightly correlated with the standard (max-min) definition of contrast than with the others examined, suggesting that background flare is most accountable for aerial image profile-induced LER. The relationship was nearly inverse, with LER proportional to α (contrast)-0.85. In the latter portion of this paper, an image deblurring technique to recover more accurate LER data from SEM images was devised. This technique showed that, at times, LER can vary significantly before and after deblurring. Some initial tests to prove the validity of this LER measurement enhancement technique were performed, all with positive results.
The effect of aerial image contrast upon line edge roughness (LER) of four different commercial resists-UV210, SEPR-463, Apex-E, and UVII-HS-is examined via scanning electron microscopy (SEM) and atomic force microscopy (AFM). Image contrast is varied by exposing both a detailed foreground pattern and a large open area background pattern on the same wafer location. Contrast varies from 0.37 to 1.0. In the case of UV210, LER measured via AFM is 2.55 nm at 1.0 contrast, 2.16 nm at 0.54 contrast, and 3.6 nm at 0.37. Results from other resists follow this trend, wherein no consistent correlation between LER and aerial image contrast can be drawn. SEM measurements also demonstrate no significant correlation between LER and image contrast in any resist type.
The Lithography Analysis using Virtual Access (LAVA) web site at http://cuervo.eecs.berkeley.edu/Volcano/ has been enhanced with new optical and deposition applets, graphical infrastructure and linkage to parallel execution on networks of workstations. More than ten new graphical user interface applets have been designed to support education, illustrate novel concepts from research, and explore usage of parallel machines. These applets have been improved through feedback and classroom use. Over the last year LAVA provided industry and other academic communities 1,300 session and 700 rigorous simulations per month among the SPLAT, SAMPLE2D, SAMPLE3D, TEMPEST, STORM, and BEBS simulators.
In order to shrink minimum feature sizes, many next-generation resists are being developed. One novel resist, based on a hyperbranched, dendritic polymer chemistry, is examined and compared to UVII-HS and APEX-E standard resists in order to determine its effectiveness and manufacturability. Data to date shows that many parameters of the dendritic hyperbranched resist are quite comparable to these standard resists: it is sensitive to 35 kV e-beam at 6uC/cm2, i-line (365 nm) at 600uC/cm2 and 248 nm light. The resist is nearly as resistant to etching as current resist technologies. It can also act as either a positive or negative tone resist. Preliminary line edge roughness data show that the dendrimer resist appears to be at least comparable if not superior to standard resists in this regard as well. The expected benefits envisioned in the development of dendritic resist materials (by Frechet group, ref 1) appear to be attainable in practice. Namely that higher polymer density and improved geometry allow smaller end-to-end chain lengths.