Influence of through-hole etching process parameters on key dimensions, contour patterns and electrical properties of atmospheric plasma cleaning machine

Influence of through-hole etching process parameters on key dimensions, contour patterns and electrical properties of atmospheric plasma cleaning machine:

The film material composition of the typical copper-through-hole atmospheric plasma cleaning machine etching process is composed of etching stop layer, interlayer dielectric layer, hard mask layer, anti-reflection coating and photoresist from bottom to top.

The copper through hole etching process consists of four steps: the bottom anti-reflection layer and hard mask layer etching, main etching, over-etching and photoresist ashing. The bottom anti-reflection layer and the hard mask layer are etched by the atmospheric plasma cleaner using a combination of fluorine based gas and oxygen, such as CF4, CHF3, O2, to jointly complete the etching of the organic anti-reflection coating and the hard mask layer. Because hard mask layer is usually a silicon oxide, with CF4 and CHF3 common etching polymer can be created, and accumulated in the protective layer and interlayer dielectric layer on the lateral wall of, if let polymer deposition on the wall, the subsequent etching the abnormal graphics to transfer to the bottom of the hole, become a through hole at the top to the bottom of the stripes, increased the hole wall roughness, seriously affected the subsequent electroplating copper filling integrity, and, as a defect, prone to electromigration (EM), in turn, affects the reliability of the circuit. Therefore, in order to avoid the formation of such stripes, the deposition of polymer in the side wall of the interlayer protective layer must be strictly controlled during the etching of the bottom anti-reflective coating. Sun wu, etc by against reflector etching process parameters were studied, including atmospheric plasma cleaning machine CHF3 / CF4 etching gas ratio, plasma power and etching process time and so on, the results of the study showed CHF3 / CF4 ratio is lower, the stripe is less, this is because the more CF4 reduces the etching gas C/F ratio, thus can reduce the production of polymer. Low plasma power will significantly improve the striped phenomenon, this is due to the low power can reduce the concentration of in vitro, thereby directly reducing the generation of polymer, at the same time, the low power also weakened the atmospheric plasma cleaning machine plasma physics bombardment of photoresist, which in turn reduces the [C] content in plasma, from another Angle to reduce the generation of polymer. In addition, the shorter etching process time reduces the total amount of polymer, thus improving the striation phenomenon.

In addition, there is another mechanism for the formation of streaks. High source power and high bias power are usually used in the main etching step of the through-hole to etch the through-hole. High source power increases plasma concentration, and high bias power produces high-energy physical bombardment, which will accelerate the consumption of photoresist, especially in the area with dense graphics. Under high bias power, the consumption of photoresist will be faster. Whenever the photoresist is exhausted before the end of all the through hole etching process, the plasma of the atmospheric plasma cleaning machine will directly bombage the interlayer protective layer and interlayer dielectric material. With the gradual reduction of the photoresist mask, it is no longer able to protect the underlying material well, which leads to the phenomenon of a second stripe, which usually exists only at the top of the through-hole, and in bad cases, the bridging of the through-hole may occur.

To avoid the second stripe, more polymers need to be produced in the main etching step and deposited on the surface of the photoresist to reduce the loss of the photoresist, i.e. the selection ratio of photoresist needs to be improved. Therefore, the main etching step usually uses the etching gas with a relatively high C/F ratio, which is more likely to produce polymers, such as C4F8, C4F6, CH2F2, etc. Through the study of the process parameters of the main etching step, the results show that the higher the CxFy/O2 ratio is, the less the second fringe is. This is because the increase of CxFy will produce a large number of polymers. Reduced at the same time, the dosage of O2, makes the reaction of polymer by dissociation, removal rate will be reduced greatly, so the accumulation of the surface of the photoresist polymer will increase, can well protect the dielectric material bombarded by atmospheric plasma cleaning machine plasma or chemical etching, so as to avoid the phenomenon of the second kind of stripes. In addition, the bias of low power/source power can also improve the ratio of the second stripe phenomenon, because of the bias power main control is in the plasma ion acceleration, the source of power control is the concentration of plasma, a low bias power can reduce the ion bombardment energy, and the source of the high power will increase atmospheric plasma cleaning machine plasma density, ion collisions between proportion increase itself, abate the directionality of the plasma, also reduced plasma physics bombardment effect; At the same time, the higher source power also disintegrates more [C], resulting in more polymers that pile up on the surface of the photoresist and protect it from plasma bombardment. Therefore, lower bias power and higher source power are practical directions for reducing the second stripe, but this power ratio also brings a disadvantage, the directivity of plasma downward etching is reduced, which will reduce the safe process window through the hole for etching. In addition, higher pressure, which is equivalent to an increase in plasma concentration, can also reduce bombardment and improve streaking to some extent.