In:
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena, American Vacuum Society, Vol. 12, No. 6 ( 1994-11-01), p. 3555-3560
Abstract:
The effects of the local electric fields generated during the e-beam inspection of high resolution resist features at low voltage are discussed. A theoretical model based on the Monte Carlo technique was developed to simulate the effect of the induced electrical fields on the primary beam and on emitted secondary electrons. It is here proved that reentering secondary electrons act as a negative feedback to the local positive retarding field when at least one of the insulating materials of the sample being inspected has a secondary electron yield bigger than one. Such a recombination mechanism is more important than primary electron absorption, as this last factor takes place far from the escape depth layer. The positive charge compensation prevents the local positive field from growing as the number of line scans increases and allows the local field to reach stability. At the top of resist features, potential values as high as 40 V were found. Although the scanning electron microscope image is highly affected by induced voltage contrast, critical dimension (CD) information is not distorted when the stability conditions are fulfilled; namely, a CD control threshold algorithm can be applied by properly choosing the threshold signal level. The modeling of secondary electron emission and absorption requires a single loop, composed of Monte Carlo simulation, local field computation, and electron ray tracing, to be iterated several times. This computation strategy is applied to feature sizes from 1 μm down to 0.25 μm and to geometries such as line arrays and isolated lines. Two different accelerating voltages are studied, namely 1.2 and 1.5 keV. Probe beam currents of 3 and 10 pA are also considered. In addition, the effect of a sample tilting of 20° is also accounted for. Computation accuracy is proved by comparing theoretical data to experimental data obtained by a cold cathode tungsten field emission microscope.
Type of Medium:
Online Resource
ISSN:
1071-1023
,
1520-8567
Language:
English
Publisher:
American Vacuum Society
Publication Date:
1994
detail.hit.zdb_id:
3117331-7
detail.hit.zdb_id:
3117333-0
detail.hit.zdb_id:
1475429-0
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