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Quantifying delineation errors in thin film resistors
392
Thin Solid Films, 90 (1982) 392 ELECTRONICS AND OPTICS
QUANTIFYING DELINEATION ERRORS IN THIN FILM RESISTORS* A. PELED AND M. HASPEL ELTA Electromcs Ltd., P.O. Box 330, Ashdod (Israel)
The main method of preparing thin film resistor networks is by the photolithography-etching method. The metallic thin films are obtained by vacuum deposition onto suitable insulating substrates. Photolithography is used in order to obtain an etch-resistive pattern over the metallic layers. Etching is effected by a suitable solution. At the end of the resistor delineation process, there is usually some departure of the resistor's physical geometric dimensions from those defined in the photolithographic mask. Such deviations, even when mi~imiT~i by a wellcontrolled process, may be of the order of several micrometres. However, for narrow linewidth resistors, such a deviation may be very substantial. This effect causes parametric overvalues and results in a low device yield. In order to quantify these errors, the final resistor pattern dimensions may be measured by optical methods and compared with the dimensions in the mask. However, this method is very tedious, and for devices with many resistors quite impractical. A mathematical model investigated in this work allows easy quantification of the resistor's delineation errors. This model assumes an over-etching function which predicts the resistances of the actual resistors when the linewidths are comparable with the amount o.f over-etching or under-cutting. By using this error function, several effects occurring in thin film etching were revealed. One effect relates to the fundamental inability of obtaining a complete range of accurate geometric linewidths over a span of about three or more linear dimension decades. This effect is probably a consequence of the basic limitation imposed by the optical imaging technique. The other effect influencing the resistor delineation accuracy arises from the inhomogeneity of the etchant's surface tension across the various photoresist-gap patterns. Our mathematical approach allows the necessary corrections to be made in the mask so that it will take into account the above-mentioned deviations. Finally, the method may also be applied to other planar resistor technologies such as integrated circuits and thick films.
* Abstract of a paper presented at the Fifth InternaUonai Thin Films Congress, Herzlia-on-Sea, Israel, September 21-25, 1981. 0040-6090/82/0000-0000/$02.75
©Elsevter Sequoia/Printed in The Netherlands
Thin Solid Films, 90 (1982) 392 ELECTRONICS AND OPTICS
QUANTIFYING DELINEATION ERRORS IN THIN FILM RESISTORS* A. PELED AND M. HASPEL ELTA Electromcs Ltd., P.O. Box 330, Ashdod (Israel)
The main method of preparing thin film resistor networks is by the photolithography-etching method. The metallic thin films are obtained by vacuum deposition onto suitable insulating substrates. Photolithography is used in order to obtain an etch-resistive pattern over the metallic layers. Etching is effected by a suitable solution. At the end of the resistor delineation process, there is usually some departure of the resistor's physical geometric dimensions from those defined in the photolithographic mask. Such deviations, even when mi~imiT~i by a wellcontrolled process, may be of the order of several micrometres. However, for narrow linewidth resistors, such a deviation may be very substantial. This effect causes parametric overvalues and results in a low device yield. In order to quantify these errors, the final resistor pattern dimensions may be measured by optical methods and compared with the dimensions in the mask. However, this method is very tedious, and for devices with many resistors quite impractical. A mathematical model investigated in this work allows easy quantification of the resistor's delineation errors. This model assumes an over-etching function which predicts the resistances of the actual resistors when the linewidths are comparable with the amount o.f over-etching or under-cutting. By using this error function, several effects occurring in thin film etching were revealed. One effect relates to the fundamental inability of obtaining a complete range of accurate geometric linewidths over a span of about three or more linear dimension decades. This effect is probably a consequence of the basic limitation imposed by the optical imaging technique. The other effect influencing the resistor delineation accuracy arises from the inhomogeneity of the etchant's surface tension across the various photoresist-gap patterns. Our mathematical approach allows the necessary corrections to be made in the mask so that it will take into account the above-mentioned deviations. Finally, the method may also be applied to other planar resistor technologies such as integrated circuits and thick films.
* Abstract of a paper presented at the Fifth InternaUonai Thin Films Congress, Herzlia-on-Sea, Israel, September 21-25, 1981. 0040-6090/82/0000-0000/$02.75
©Elsevter Sequoia/Printed in The Netherlands