Frequently asked questions

Q: What is new in the SWHL technology if googling "Holographic Lithography" you can easily find over 15 000 links?

A: Overwhelming majority of these links are related to Interferential lithography that is able to create only periodic images while SWHL is able to produce any image you need. And those few, there are related to holography, cannot get acceptable resolution and a large field.

Q: Why has nobody done it before?

A: The calculation of the SWHM capable of creating an image of the size needed (1х1cm and more) requires high computer capacity, which became accessible only in the beginning of the XXI century. Besides, a number of mathematical questions, highly important for this kind of calculation, were not worked out in enough detail because of the same reason.

Q: What is the principal difference between the holographic masks and steppers, and DUV masks and steppers/scanners?

A: The holographic stepper does not need a lens. For SWHM there is no one-to-one correspondence between a point on the mask and a point on the image; the whole mask participates in the creation of every point of an image. An important result of this is that the image is insensitive to local mask defects.

Q: What are HoloPhaseShift and HoloOptimization, and what are the main differences between them and OPC, Phase-Shift and SMO, which are used in DUVL?

A: These are algorithms of mathematical optimization, performed while calculating SWHM. Unlike Phase-Shift and OPC used in DUVL, HoloOptimization and HoloPhaseShift are purely virtual and do not lead to a complication of the mask architecture. The HoloOptimization method is quite similar to SMO, but posseses more capabilities of optimization as it does not have any technological limitations for mask architecture.

Q: Why local defects of holographic masks have practically no effect on the quality of aerial images, created by them?

A: Because there is no one-to-one correspondence between a point on the mask and a point in the image. The whole mask participates in the creation of every point of an image. A local defect on the mask affects the whole image, but it has very little influence in every specific point.

Q: How slight changes in the source wavelength allow to scale aerial image?

A: The image in SWHL is formed only by means of electromagnetic wave diffraction by the elements of SWHM. Beam deflection in diffraction is in direct ratio to the wavelength. That is why changing the wavelength will proportionally scale the whole image.

Q: How is simultaneous creation of high-quality aerial images possible in planes, the distance between which along the optical axis is many times higher than depth of focus (DoF)?

A: It is a general feature of holography. The SWHL technology allows to create any wavefront that does not contradict the laws of physics. In calculating the SWHM the wavefront is selected so that different parts of the image are focused on different distances.

Q: Why does the cost of holographic masks appear to be significantly lower than the cost of DUV masks for the same technological nodes?

A: Because SWHM, although it is called sub-wavelength holographic mask, does not contain any sub-wavelength elements (sub-wavelength is related only to the image created). The mask consists of uniform transmission areas with minimal size of 0.7 wavelengths and typical size of 2.5—5 wavelengths.

Q: Why was sub-wavelength resolution using the holographic mask first obtained by means of the SWHL technology?

A: In the SWHL technology the sub-wavelength resolution is available due to a special optical scheme, which allows to use numerical apertures without overlaying the target image with parasitical diffraction orders.