Vector scanning

Figure 40. Operating modes for electron beam systems left — raster scan coupled with continuous table motion right — vector scan, step and repeat.

Figure 41. Comparison of vector scan and raster scan writing schemes.

Characteristics. Electron-beam exposure experiments were carried ut by using a prototlype HL-600 Hitachi Electron-Beam Lithography System which is a vector scanning type variable-shaped electron-beam machine. The acceleration voltage was 30 kV. Resist films were formed on silicon wafers by spin-coating and prebaked at 80 C for 20 min before exposure. 

Modifications to Electron Beam System. The retarding potential field was introduced into our vector scan system by attaching a O-to-20 KV, 2 mAmp external power supply to the wafer holder. This is shown diagrammatically in Figure 2. Whereas the wafer is at ground potential in the standard system, in our modified system the net potential at the wafer can vary from 0 to 20 KV. Thus, the electrons are accelerated down the column at a standard operating potential, exit the final lens and are retarded by the variable electrostatic field near the wafer plane. 

Lithography. Electron beam exposures were carried out with an IBM vector scan e-beam exposure tool at 20 keV. X-ray exposures were carried out under vacuum by Al-Ka radiation, and UV exposures with a Cannon PLA 500, Oriel illuminator, Hybrid Technology Group Model 345-10, or Optical Associates Inc. Model 780 in contact... 

Patterning of the Resist Resists were delineated with a vector scanning type, shaped electron-beam drafting machine, specially designed by the Hitachi Central Research Laboratory. The acceleration voltage was 30kV. 

EBES systems are based on raster scans. In contrast, vector scanning has more resemblance to a small floodlight than a pencil beam. Here, the beam moves on a vector path that directly exposes the entire region needed, before turning on the beam and writing the pattern. Next, the beam is turned off and repositioned over another pattern for exposure. The vector scan is faster because the beam wastes no time rastering over areas that do not need exposure. However, it is more difficult to scale since all vectors must be recalculated to reduce size. ... 

Figure 15.2 shows the different types of EBLs, along with their writing strategies. This figure also illustrates how the exposure tool has evolved from being a tool that used a Gaussian beam (in raster scan or vector scan mode) to print one pixel at a time on the wafer, to one that used a shaped beam (with fixed or variable shape) to print one pixel at a time on the wafer, then to one that used a shaped beam to project and print an entire cell or character at a time on the wafer, and then to one... 

A notable improvement in the vector-scanning strategy that has been reported involves the imaging of two apertures simultaneously, which enables the size and shape of the beam to be varied, thereby minimizing the number of flashes of the electron beam required to expose the area to be patterned. ... 

Lithographic Processing / Evaluation. Standard thermal processing and development were used in the microlithographic experiments (8), unless otherwise specified. An EBMF lOcs/120 e-beam machine operated at 40 KV, and a prototype vector scan e-beam operated at 20-30 KV were used for e-beam exposures. An Oriel illuminator was used for deep UV exposures. The standard film thickness measurement and SEM techniques were employed for lithographic evaluation. 

Conventionally, electron-beam exposure is carried out using a pencil of focussed electrons to write the pattern using a beam deflector driven by a computer system. The beam in this case is scanned across the substrate to be exposed using either vector scan or raster scan methods (Fig. 7.16). Vector scanning writes patterns in a similar way to which shapes might be filled in with a bail-point pen whilst the raster uses a system similar to that of a television tube where the entire surface is scanned and the beam tinned on and off as necessary. Each method has advantages vector scan machines have to scan smaller areas but this is compromised by the need for a more sophisticated deflection system. The raster scan by contrast, whUst having to irradiate the entire substrate, can be operated at faster scan speeds. Normally the vector scan uses less exposure time when less than around one sixth of the area has to be exposed. 

Analyze the testability of the design prior to scan insertion using the check.test command. A default test protocol is inferred and simulated on executing the check test command. The default test protocol consists of the following initialization vectors, scan-in/scan-out, parallel measure, capture and scan out strobe. 

Laser scanning is the step needed to convert pre-designed CAD patterns into real structures. Two basic modes for direct laser scanning can be utilized, raster-scan mode and vector-scan mode, of which the concepts are illustrated in Figs. 31a, b. 

Fig. 31 Two basic scanning modes for two-photon photopolymerization microfabrication. Conceptive illustration of how the two scan modes could be utilized for writing a character s . a raster scan and b vector scan. The solid and open circles denote exposed and unexposed dots, respectively, all scanned by the laser focal point. The dashed open circles in the right part means the dots that aren t scanned...

Fig. 32 A micro-bull scupture produced by vector scanning. Only the crust was defined by the two-photon process the inside was solidified by illumination under an mercury lamp. In this particular structure, the two-photon scanning time was reduced by 90% due to the use of a vector scanning mode...

In the vector scanning method, voxels were actually classified into two categories those on the surface layers are the least necessary points to define a structure and those inside the structure solely have the supporting... 

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