EBL may be used to create photolithography masks for a variety of tasks. EBL is time-consuming, because it necessitates writing the pattern in a certain order. Various techniques are used to shorten the writing time. EBL devices used in industrial settings generally apply extremely high acceleration voltages (50 kV).
However, more cost-effective instruments are used in many research environments by the e beam lithography companies. However, they are slow and designed for writing in high resolution. In general, even for low-resolution applications, they aren’t regarded adequate for creating large-scale structures with a high pattern density. In this work, the authors show that adjusting the writing parameters may cut writing time by over 40 times when compared to conventional instrument settings utilizing the Raith e LiNE EBL.
The authors’ optimization technique yielded very precise photolithography masks. Most commonly used settings took 14 days to write, according to the instrument software. Our pattern definition outperforms chrome masks that are already on the market.
There are several ways to print without using a mask. Electron beam lithography, direct laser writing 1,2, and interference lithography are the most popular. Alternative techniques, such as beam lithography and dip-pen lithography, are becoming more important nowadays.
EBL is widely utilized in various nanotechnology-related research disciplines due to its capacity to write patterns with great precision down to a few nanometers. Electron beam lithography (EBL) reveals a resistor by illuminating it with a narrowly focused electron beam. The resist pattern can be treated in many ways to generate the final structure. Because electrons have a wavelength in the picometer region or below, EBL is not diffraction-limited under ordinary working circumstances. High resolution in an EBL system is difficult because of the resists and subsequent processing processes.
In electron lithography, resist exposure, stage movement (for structures bigger than a single write-field), and electron beam settling take up the majority of patterning time. To make sure the beam is steady at every new position, you can use EBL software. In this case, the settling period is already included in. There is a physical limit to the greatest beam current that can be achieved due to space charge effects. This number limits the patterning time when just one beam is used for serial exposure. Shaped beams and multi-beam exposure tools can be more quickly since the total beam current is larger while using these instruments.
To enhance the write speed of any EBL device, both the exposure time and the idle time must be reduced. Newer resists, such as the negative tone resist SU-8, have been shown to be as sensitive as 3.6 C/cm2 when subjected to a 50 kV electron beam.
Look at these secret techniques for improving electron beam lithography systems in lithography companies:
How to determine the acceleration you have
As acceleration voltage rises, so does the dosage required to overcome resistance. Why? Because forward-scattered electrons are more effective at transferring energy to the resistor at lower acceleration voltages (10 kV), clearance dosage needs are reduced, albeit at the cost of a wider incident beam spot and rougher line surfaces.
Additionally, the quantity of clearance dosage required varies greatly according on the developer type and development procedure.
Collimation Aperture Size Selection
You may use a beamline with interchangeable apertures to collimate and current-limit an electron beam. To boost the beam current, a collimating aperture with a diameter of 120 microns was employed. This allowed more electrons from the filament to reach the sample. A collimating aperture in the electron column is a common component of an electron microscope. Essentially, it’s a method of altering the beam’s numerical aperture. Lower apertures produce a smaller numerical aperture and, as a result, a greater depth of focus.
The high current mode should be enabled.
There is a “high current” option available from Raith that alters the focusing characteristics of the condenser lens to produce a narrower, more parallel beam. This setting increases the beam current by about twofold. The ultimate resolution will be slightly lowered due to the effects of space charge, but the narrower, parallel beam will enhance the depth of focus. We observed a beam current of 6.8 nA using a collimating aperture with a 120-meter diameter and an acceleration voltage of 10 kV.
Enter the field size
A writing field is typically 100 m by 100 m in size. We were able to recreate the pattern even with a 100-fold reduction in the number of write fields since we utilized such a big write-field (the maximum is 2000 m 2000 m). Sample stage moving and settling time will be reduced by 100 as a result of the sample stage moving and settling being faster. Using bigger write fields has a variety of disadvantages. It’s necessary to lower the minimum step size due to the pattern generator’s digital-to-analog converter (DAC) having a limited addressable resolution. For write fields of 1000 m 1000 m, the addressable step size of the EBL is still rather tiny.
There are two techniques to move the beam around in a write-field: raster scan and vector scan. By far the most straightforward approach, however, it takes the longest time to complete. Unblanking occurs as the beam travels over exposed regions. Technically more complex, the vector scan guides the beam to each region that needs to be exposed and only scans over the parts that require exposure. Utilizing a vector scan can save you time, but it is extremely reliant on the pattern being produced, so keep that in mind while using it.
Step size and beam speed
The GDSII Raith lithography module is used in the e LiNE design program. The GDSII format is widely used for integrated circuits. Other file types can be imported as well as bitmaps and other pattern file formats. The “bitmap as reference” feature in e LiNE software lets you import a bitmap. When utilizing the line or meander modes, you may also utilize the “bitmap as reference” format. Un- and exposure blanking will occur as the laser scans the whole write field.