Site icon Technology Wine

9 Electron Beam Lithography Mistakes You Should Never Make

Steffy Alen
9 Electron Beam Lithography Mistakes You Should Never Make

 The method of transmitting geometric design patterns from a mask to a silicon wafer is known as lithography. Lithography is a critical step in the fabrication of integrated circuits. Photolithography, which employs UV light to reveal the design pattern on the wafer surface, is one type of lithography. Although photolithography has been able to gain a competitive advantage, various other lithography techniques, like electron beam lithography and X-Ray lithography, have emerged that do not rely on the use of UV light. Both approaches have distinct protocols that have advantages and downsides.

Electron beam lithography is a current method that employs an electron beam that has been extracted, focussed, and sped to 20kv. The three primary electron generators are thermionic emitters, light emitters, and field emitters. At the moment, electron beam lithography is mostly utilized to serve the integrated circuit industry. Because of its versatility it is suitable for creating masks that can be used other methods, such as x-ray lithography. It is also used to write complicated designs on wafers directly. Electron beam lithography techniques are nearly identical to photolithography procedures. To develop the exposed portion, both systems employ different photoresists and chemicals. Polymethylmethacrylate is the most often used electron beam photoresist (PMMA). PMMA degrades into monomers when exposed to electrons, which are then synthesized using a chemical known as methyl-isobutyl ketone (MIBK).

Electron lithography has various benefits over photolithography. For starters, and most importantly, it offers a high resolution of up to 20 nm. Second, it can directly print complicated computer-generated designs on wafers. It is a very adaptable method that can be used with a wide range of materials and an almost unlimited number of designs. Its downsides include the following: it is highly costly and sophisticated, with high maintenance costs, forward and reverse scattering issues, and slower speed. As the electrons pass through the resistor, some of them will be scattered at small angles. Because of the forward scattering issue, the beam profile at the bottom of the resistor might be substantially wider than at the top.

The control system, vacuum system, and electron gun are the three most critical electron beam lithography (EBL) equipment components. Electrons are emitted from the tip of a filament and are drawn to an anode. The released electrons are concentrated into a beam electromagnetic lenses, which specify the beam’s spot size diameter. Electromagnetic plates are also used to correct astigmatism caused beam focusing. The vacuum system is an essential component of the EBL because it protects the beam from outside interference.

Along with the electron beam lithography system, another recent technique of lithography is X-ray lithography. X-ray lithography, as opposed to UV lithography, uses collimated (parallel) X-rays to transmit geometric patterns from a mask to the surface of a silicon wafer. Photoresist, like photolithography, is placed to the top of the silicon wafer before exposure. Nevertheless, because X-rays are used, the masks required for this method are made of different materials and are thinner than those used in photolithography. X-ray mask membranes are often composed of low-atomic-number materials since high-atomic-number elements, like gold, have a high X-ray mass attenuation coefficient, implying they may absorb X-ray radiation. The membrane permits X-rays to pass through the mask and reveal the silicon wafer’s surface. An absorber is put on the membrane to capture emitted X-rays and direct them to the right region. Like electron beam lithography, X-ray lithography employs PMMA as the photoresist, which hardens upon contact with the X-ray. Unwanted areas of the design can be erased using etching procedures. Furthermore, X-ray lithography necessitates a space between the mask and the silicon wafer surface, similar to photolithography.

X-ray lithography, similarly electron beam lithography, offers several advantages and problems. One benefit of X-ray lithography is that X-rays have smaller wavelengths than UV light (about 0.4 to 4 nanometers), allowing for more energy to be transported and, consequently, improved lateral resolution. X-rays do not suffer from frequent diffraction concerns in UV light during photolithography due to an improvement in lateral resolution. The X-ray mask may be put further away from the silicon wafer due to the reduction in diffraction compared to the gap distance in the photolithography method. Masks have a longer lifespan when there is a larger gap. Furthermore, lower wavelengths allow for better accuracy, enabling the production of tiny patterns on silicon wafers. Moreover, X-rays have a consistent refraction pattern, which lowers the possibility of X-rays scattering to undesirable portions of the wafer during the exposure process.

The X-ray mask is a significant drawback of X-ray lithography. The mask membrane should be very thin because internal tension may cause the absorber to deform. Furthermore, unlike UV light, X-rays cannot be focussed using a lens. A lens is used in photolithography to concentrate UV light and generate designs on the wafer proportionately smaller than the drawings on the mask. The size of the designs on the mask will be the same as the size of the patterns on the wafer in X-ray lithography. This implies that to manufacture small designs on the silicon wafer, similar to small designs must be produced on the mask.

Furthermore, the mask is rather costly to manufacture. The membrane is made of materials with low atomic attenuation coefficients, such as diamond. Materials having high attenuation coefficients, like gold, must be used in the absorber.

Exit mobile version