Abstract
Organosilicate glass (OSG) is often used as an interlayer dielectric (ILD) in high performance integrated circuits. OSG is a brittle material and prone to stress-corrosion cracking reminiscent of that observed in bulk glasses. Of particular concern are chemical-mechanical planarization techniques and wet cleans involving solvents commonly encountered in microelectronics fabrication where the organosilicate film is exposed to aqueous environments. Previous work has focused on the effect of pH, surfactant, and peroxide concentration on the subcritical crack growth of these films. However, little or no attention has focused on the effect of the conjugate acid/base concentration in a buffer. Accordingly, this work examines the “strength” of the buffer solution in both acidic and basic environments. The concentration of the buffer components is varied keeping the ratio of acid/base and therefore pH constant. In addition, the pH was varied by altering the acid/base ratio to ascertain any additional effect of pH. Corrosion tests were conducted with double-cantilever beam fracture mechanics specimens and fracture paths were verified with ATR-FTIR. Shifts in the threshold fracture energy, the lowest energy required for bond rupture in the given environment, GTH, were found to shift to lower values as the concentration of the base in the buffer increased. This effect was found to be much larger than the effect of the hydroxide ion concentration in unbuffered solutions. The results are rationalized in terms of the salient chemical bond breaking process occurring at the crack tip and modeled in terms of the chemical potential of the reactive species.
Highlights
INTRODUCTIONDoes not alter the intrinsic bond strength of the system but reduces the bond density resulting in reduced fracture toughness.[12]
Organosilicate glass consists of a siloxane network similar to that of amorphous silicon dioxide where some of the bridging oxygen atoms have been replaced by organic groups such as methyl (-CH3) or methylene (-CH2-).[1,2,3]
Organosilicate glass (OSG) is vulnerable to subcritical crack growth because of the Si-O bonds in its structure
Summary
Does not alter the intrinsic bond strength of the system but reduces the bond density resulting in reduced fracture toughness.[12]. The molecule must be able to donate electrons to the formation of a bond with the Si atom at the crack tip; 2. The molecule must be small enough to fit into the crack tip These requirements are summarized as electron donation, H atom availability, and small size. Where Y represents an unbroken bond, in the present case Si-O-Si, X is a reactive species, the activated complex is denoted with a *, Z represents the reaction products which are the broken bonds in this case, and n is the number of reactive molecules per crack tip bond. Where [X] is the concentration of any reactive species that meets the aforementioned criteria for stress corrosion cracking (electron donation, H atom availability, and small size). The work focuses on measuring the properties of the as cured OSG material in order to form a baseline for future studies on OSG modified by plasma processes
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