Euv Lithography Mask

In unidirectional metal layers, tip-to-tip spacing is one of the more severe issues for single exposure patterning. For the 40 nm pitch vertical lines, an 18 nm nominal tip-to-tip drawn gap led to a genuine tip-to-tip distance of 29 nm with OPC , while for 32 nm pitch horizontal lines, the tip-to-tip distance with a 14 nm nominal gap went to 31 nm with OPC. These actual tip-to-tip distances define a lower limit of the half-pitch of the metal running in the direction perpendicular to the end.

Sub-resolution assist features are established in DUV lithography to increase the depth of focus of semi-dense and isolated features. It has been shown they can be also used to lessen the differences between your BF position of dense and isolated features , , . The impact of assist features on the phase of the near field and on the BF vs. pitch is demonstrated in Figure 17. Wider assist features decrease the difference between the diffraction spectra and the BF positions of dense

Centura® Tetra Euv Advanced Reticle Etch

Double or multiple patterning would also be required if a pattern includes sub-patterns which require significantly different optimized illuminations, because of different pitches, orientations, shapes, and sizes. In combination with the range of wavelengths, the rotated plane of incidence aggravates the already severe stochastic effect on EUV imaging. Due to different phase shifts from reflection from the EUV mask, different illumination angles bring about different shifts. The Bossung curves for two-dimensional shapes such as contacts reveal an asymmetry linked to the shadowing effect due to the EUV oblique illumination . For the 6º central incident angle case, there exists a noticeable difference of best focus (~30 nm) between the nm CDs considered along the two directions of the 150 nm pitch contact. Extreme ultraviolet phase defect characterization based on complex amplitudes of the aerial images.
Recent experiments revealed that the sort of underlayer (i.e., the layer within the photoresist film) can positively affect the SEM imaging contrast. But utilizing a different underlayer to boost the metrology will in turn impact pattern transfer, calling for optimized etch processes. To continue optimizing pattern transfer, improved metrology tools or optimized tool settings will be needed to reliably image the patterns.

  • Assist features help improve the image of isolated features to become more like dense features .
  • In both resist calibrations, the best focus range is much worse ( nm) than generally projected by aerial images (15-30 nm), due to the realistic resist behavior including absorption and secondary electron exposure.
  • These photoelectrons in turn generate secondary electrons, which slow down before participating in chemical reactions.

With further optimization of the illumination (discussed in the section on source-mask optimization), the lower limit could be further reduced to around 25 nm. EUV photomasks work by reflecting light, that is achieved by using multiple alternating layers of molybdenum and silicon. This is in contrast to conventional photomasks which work by blocking light using a single chromium layer on a quartz substrate.

Phase Shift Masks

However, the far better they are, the higher the risk that the assist feature will print . Horizontal and vertical features are focused differently in EUV optical systems. The power target for EUV lithography is at least 250 W, while for other traditional lithography sources, it really is much less.

The angular dependence of multilayer reflectance of the object differs for different wavelengths, leading to different shifts when defocused. While state-of-the-art 193 nm ArF excimer lasers offer intensities of 200 W/cm2, lasers for producing EUV-generating plasmas need to be a lot more intense, on the order of 1011 W/cm2. A state-of-the-art ArF immersion lithography 120 W light source requires only 40 kW while EUV sources are targeted to exceed 40 kW. Strategic investments in research and development and joint development programs with such companies as Cymer, Media Lario and NaWoTec continue to move forward the development of EUV lithography. Gian F. Lorusso received his PhD in solid state physics from the University of Bari, Italy, in 1992. He has been working on topics related to the semiconductor industry such as for example metrology tool development, lithography, material analysis and more. His domains of expertise include lithography, metrology, microscopy, and spectrometry.
The examples from the previous section have demonstrated the mostly unfavorable impact of 3D mask effects on the lithographic process performance. A significant element of the orientation-dependent feature placement and size effects could be compensated by a proper selection of the mask focus and by an OPC of the mask pattern. However, the dependency of the mandatory corrections on the position in the scanner slit, on feature size/pitch, and on the illumination geometry make the OPC flow increasingly difficult.

Spie Photomask Technology + Extreme Ultraviolet Lithography 2022

This technique simulates exposure and determines the deterioration of optical contrast of a defect detected in the API inspection. It also inspects the optical contrast after fixing the defect to guarantee the appropriateness of optical contrast. SEMI-KLEEN series plasma cleaner is specially made to work on semiconductor capital equipment. SEMI-KLEEN Sapphire plasma source uses a sapphire crystal tube to create the plasma source and offer pristine cleanliness for the semiconductor capital equipment.
An interference-based kind of a EUV source differs from the approach used in ASML’s high-NA EUV lasers, which vaporize tin droplets to create EUV light. The photons subsequently bounce off several mirrors within the scanner, reflect off the mask and lastly hit the resist on the wafer. While ASML’s scanners were created for mass production of chips, the interference kind of tools as used in the AttoLab won’t achieve the required full field throughput. In both resist calibrations, the very best focus range is a lot worse ( nm) than generally projected by aerial images (15-30 nm), due to the realistic resist behavior including absorption and secondary electron exposure. It is clear that while aerial images provide clues that guide us to fundamental characteristics of image defocus, the actual resist images may follow entirely different Bossung curves.
Secondary electrons may remove over 10 nm of resist from the exposed edge. In the absence of pellicles, EUV mask cleanliness would have to be checked before actual product wafers are exposed, using wafers specially prepared for defect inspection. These wafers are inspected after printing for repeating defects indicating a dirty mask; if any are found, the mask should be cleaned and another set of inspection wafers are exposed, repeating the flow until the mask is clean. GlobalFoundries and Lawrence Berkeley Labs completed a Monte Carlo study to simulate the consequences of intermixing between the molybdenum and silicon layers in the multilayer that’s used to reflect EUV light from the EUV mask. The results indicated high sensitivity to the atomic-scale variations of layer thickness. Such variations could not be detected by wide-area reflectivity measurements, but would be significant on the scale of the critical dimension .