Slicing semi-conductor wafers form ingots produces a damage layer that ha to be completely removed by complex polishing and etching processes. Nondestructively controlling the machining process is desirable. Laser induced surface acoustic waves are demonstrated to be a promising method to characterize the state of the surface.
Absence of a good resist selectivity is a key issue in the metal etch. It becomes increasingly critical when the geometry shrinks below the sub-half micron and the resist thickness reduces further for lithography to get smaller features resolved. Measured values are often quoted based on various techniques like surface profiler or cross section analysis, etc. For a multi step etch recipe we analyzed step by step the etched photoresist cross section for feature sizes between 0.40 . . . 0.65 micrometer and bondpads by using a scanning electron microscope (SEM). We found that the real photoresist margin is independent on the feature size which we explain using a simple geometrical model. However, this value is remarkably smaller than the height of the remaining photoresist on top of the center part of a bondpad measured using a surface profiler. Subsequently, the profiler measurements result in selectivity values which are considerably higher than those measured at small features with cross section SEM analysis. We discuss advantages and limitations of profiler measurements. The comparison between the results of both methods open the possibility to utilize the advantages of surface profiling (e.g. non-destructive approach) by reducing the risk to get overestimated selectivity values for small features. This method is very useful in metal etch process development and forecasting the requirements for the future technology as well as to interpret absolute selectivity often quoted.
The High Speed Framing Camera (HSFC) is a new high speed camera for investigations of processes in the ranges of nanoseconds and micrometers. This camera was designed especially for our studies of deposition processes. In pulsed laser deposition (PLD), vacuum arc deposition (VAD) and material deposition by channel spark the target material is evaporated and ionized in a fast process of some nanoseconds duration. New depositional applications require higher efficiency and modified plasma parameters. Therefore the processes of explosive plasma production must be studied with an adequate temporal and spatial resolution. The HSFC combines a microscopical resolution of 10 micrometers with a nanosecond time resolution and a very high optical sensitivity. Therefore a high resolution long-distance microscope QUESTAR is combined with a four channel intensifying CCD camera.
The main parameters and dimensions of cathode spots were under discussion for years. To solve these current questions, a new system was especially designs. The image converting High Speed Framing Camera, which combines a microscopical resolution of 5 micrometers with a nanosecond time resolution and a very high optical sensitivity. This camera was used to study the microscopical behavior of vacuum arc cathode spots in a pulsed high current arc discharge on copper. The direct observation of these spots with high resolution revealed the conclusions that one single cathode spot, as normally observed by optical means consists of a number of simultaneously existing microscopical sub-spots, each of them with a diameter of about 15 micrometers and a mean distance of 30...50 micrometers between them. The mean existence time of these sub-spots on copper was found to be about 3.2 microsecond(s) , where the position of a sub-spot remains unchanged (with an upper limit of about 2...3 micrometers ) during its existence time. An upper limit of the crater surface temperature was estimated by a comparison between the brightness of a cathode spot and of a black body radiation lamp to about 3000 K.
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