Plasma Treatment Effects on Molecular Structures at Dense and Porous Low-k SiCOH Film Surfaces and Buried Interfaces

Abstract

The effects of oxygen plasma treatment on molecular structures at low-k organosilicate (SiCOH) film surfaces and buried interfaces were investigated using sum frequency generation (SFG) vibrational spectroscopy and Raman spectroscopy. SFG and Raman spectra were acquired from pristine and plasma-treated low-k SiCOH films to characterize the interfacial and bulk molecular structures of the films before and after plasma treatment. Two SiCOH films with similar molecular structures but different porosities were investigated to correlate the effects of plasma treatment to the porosity of low-k films. SFG spectra indicated that the surface molecular structure of dense SiCOH films was more resistant to plasma damage than the surface molecular structure of porous SiCOH films. Furthermore, the ratio of SFG peak intensities before and after plasma treatment enabled quantification of methyl depletion at the surface of SiCOH films after plasma treatment. The molecular structure at buried Si/SiCOH interfaces was characterized by simulating SFG spectra from pristine and plasma-treated SiCOH films. SFG spectra from plasma-treated low-k films were simulated by adjusting the methyl orientation and number density parameters at the low-k/air interface to match experimental results. Simulated SFG spectra indicated that methyl groups at the buried interface of both dense and porous SiCOH films were oriented with a high tilt angle before and after plasma treatment. The developed methodology is general and can be extended to characterize the effects of many different plasma treatments, wet chemical treatments, and surface repair treatments on the interfacial molecular structures of many polymer or organic films.

Studying Polymer Surfaces and Interfaces with Sum Frequency Generation Vibrational Spectroscopy

“…SFG was used to investigate molecular structures of surfaces and buried interfaces of pSiCOH films on Si provided by Intel. 170 The thin film thickness is 100 nm for all the samples; therefore, the SFG ssp spectra collected from these samples are dominated by the contribution from the surfaces, while the SFG ppp spectra contain signal contributions from both the surfaces and the buried interfaces. Two samples with a similar structure but different porosities (7% and 25%) before and after oxygen plasma treatment were examined to understand how sample porosity influences the plasma treatment effect on pSiCOH film surface and interfacial structures.…”

“…Raman spectroscopy was used as a supplemental tool to show that the bulk film structures of both samples were not changed under the plasma treatment. 170 A similar approach was applied to study the low-k SiCOH samples provided by IBM. 172 This time, the SiCOH thin film was plasma treated with ammonia for 18 s. It was found from the SFG ssp spectra that the SiCOH film surface was altered by the ammonia plasma treatment, the surface methyl groups tilted more toward the surface, and 40% of the surface methyl groups were removed by plasma.…”

“…It was reported that the surface and interfacial molecular structures of a low-k pSiCOH thin film deposited on silicon wafer could be characterized using SFG. − The methodology was developed on the basis of the approach used to study polymer thin films on metal surfaces with a series of different film thicknesses. The SFG spectra collected from a model low-k film (PMSQ, Figure a, model for pSiCOH) have contributions from both the PMSQ surface and the buried PMSQ/silicon interface.…”

Sum Frequency Generation Vibrational Spectroscopy for Characterization of Buried Polymer Interfaces

“…However, uncontrolled plasma treatment may harm the porous low- k films. The surface and interface of plasma-treated PMSQ materials were studied using SFG-VS. 101,112 It was found that the surface structure of dense organosilicate films was more resilient to plasma treatment than that of the porous films. 112…”

“…One example is the interfaces between polymer and adhesives, which have been reviewed previously. [102][103][104][105][106][107][108][109][110][111][112][113][114][115][116][117][118][119][120] Another example is the rubbing and sliding between two polymers, which will be discussed in the following section.…”