IMPROVING THE ELECTRICAL PARAMETERS OF A VARICAP USING GETTERING

Abstract

Nickel is widely used for the manufacture of ohmic contacts for semiconductor devices. Nickel is well wetted by solder and allows the connection of conductors by soldering, forms silicides with silicon that are stable in a wide range of temperatures, and allows the electrolytic formation of local contacts. These advantages make it possible to use simpler methods of assembling semiconductor devices, to exclude from the technological process the operations of photolithography on a metal layer when forming an ohmic contact (as is the case, for example, when forming an ohmic contact based on aluminum) and thus to increase the efficiency of device production and reduce their cost. However, as practice has shown, the use of nickel to create ohmic contacts is associated with its negative effect on the reverse branch of the varicap's current-voltage characteristic, which is especially pronounced in the presence of structural defects in silicon. It has been shown that the reason for the low yield of varicaps is the significant effect of structural defects and foreign impurities on their reverse characteristics. It was established that the cause of the degradation of the reverse branch of the volt-ampere characteristic of a varicap with a nickel ohmic contact is oxidative packaging defects formed in silicon during high-temperature technological operations. To prevent the formation of structural defects in silicon, it was necessary to choose an effective gettering method. The conducted studies have shown that the most effective method of eliminating oxidative packaging defects that have already formed is to carry out additional boron injection into the working side of the plates after the second photolithography at a temperature of 1080°C for 30 minutes in a mixture of argon and oxygen. The proposed technology for manufacturing varicap structures using gettering using additional boron injection into the working side of the plates is considered in detail. Experimental results of the study of the influence of the gettering process on the reverse characteristic of the varicap are presented, and possible mechanisms of this influence are also analyzed. The effectiveness of the proposed technology using gettering is shown in terms of reducing the level of reverse currents and increasing the yield of suitable devices.