Papers

AVS2001 Session DI-WeA: Low K Dielectrics

Wednesday, October 31, 2001 2:00 PM in Room 130

Wednesday Afternoon

Start	Invited?	Item
2:00 PM		DI-WeA-1 Materials Issues and Recent Development of Low k Dielectrics for Advanced Interconnects P.S. Ho (The University of Texas at Austin) Materials Issues and Recent Development of Low k Dielectrics for Advanced Interconnects Low k dielectrics are being developed for on-chip interconnects beyond the 0.13 micron generation. To replace silicon dioxide, there are stringent requirements on materials properties imposed on the low k dielectrics. The challenge is how to maintain the thermomechanical properties of the material while decreasing its dielectric constant, particularly for porous materials with dielectric constant less than 2. In spite of this difficulty, several materials have been developed and process integration demonstrated recently. The materials issues and characterization of low k dielectrics will be presented. Recent developments based on optimization of molecular structures will be discussed.
3:40 PM		DI-WeA-6 Formation of Self-Assembled Molecular Layers on the Low Dielectric Porous Methyl Silsesquioxane J.C. Hu, C.W. Wu, L.J. Chen (National Tsing Hua University, Taiwan, R.O.C.); C.H. Li (National Chiao Tung University, Taiwan, R.O.C.); T.C. Chang (National Sun Yat-Sen University, Taiwan, R.O.C.); C.J. Chu (Nanmat Technology Co., Taiwan, R.O.C.) Porous methyl silsesquioxane (PMSQ) with a low dielectric constant (~1.8) is of great interest for ULSI applications. However, many hydrophilic methyl groups (-CH₃) on the PMSQ were destroyed under O₂ plasma ashing. Hydroxyl groups (-OH) were bonded with Si dangling bonds on the PMSQ films. H₂ plasma post-treatment is usually used to decrease -OH bond formation. In the present work, bottom-up growth behavior of self-assembled molecular layers (SAMs) on the PMSQ was investigated. Diclorodimethylsilane was used to form SAMs on the PMSQ at the room temperature. Structural properties of the PMSQ films were investigated using FTIR. The absorption peaks of Si-C (781 cm^-1), Si-C (1273 cm^-1), and C-H (2975 cm^-1) in PMSQ samples disappeared after O₂ plasma treatment for 5 min. It indicated that the majority of methyl groups in the films were removed and Si dangling bonds were exposed. The Si-O cage-like structures in the PMSQ films also decreased due to its loose structure arrangement. As a result, the low dielectric characteristic of PMSQ would be damaged. On the other hand, the absorption peaks of Si-C and C-H were present for the PMSQ films dipped in diclorodimethylsilane solution with and without ultrasonic system. The purpose of using ultrasonic system was to accelerate formation rate of SAMs on the PMSQ. The results revealed that the hydrophobic dimethylsilane groups have been formed on the surface of PMSQ. The Si-OH bonds on the PMSQ changed to Si-O-Si(CH₃)₂. The thickness of SAMs was less than 1.0 nm. The -CH₃ groups of SAMs on the Si-O network surface of the PMSQ films were apparently of ordered array structure owing to minimal steric hindrance arrangement.
4:00 PM		DI-WeA-7 Temperature-dependent Current Transport in Low-k Inorganic Polymer Dielectrics J.W. Tringe, R.A.B. Devine (U.S. Air Force Research Laboratory) Low-k dielectrics are an increasingly important class of materials for high-performance integrated circuits, promising to significantly increase processing speeds by lowering resistance-capacitance delays in global interconnects. However, since these new dielectrics are anticipated to cover large areas of the chip they also represent a potential reliability risk. It is therefore important to understand how charge transport occurs in the low-k films over a range of temperatures in order to avoid breakdown or excess leakage current during circuit operation. Low-k dielectric films based on inorganic polymers such as FOx flowable oxide from Dow Corning have been examined. Spun-on films, 3000 Å thick, were patterned into metal-insulator-semiconductor capacitor structures, then probed to measure current and capacitance as a function of voltage. Temperature-dependent current-voltage measurements, over the range 26 to 150 °C, show that current conduction is predominately via either Schottky or Frenkel-Poole emission. A field-independent thermally activated barrier height of approximately 0.1-0.2 eV is deduced. The measured exponential term proportional to the square root of the electric field in the current-voltage dependence is smaller than expected for Frenkel-Poole emission, however. Additionally, the temperature and field dependences of the exponential prefactor do not enable us to clearly distinguish between Schottky or Frenkel-Poole emission over the experimental temperature range.
4:20 PM		DI-WeA-8 Characterization of SiC Films for Cu/low-k Integration F.G. Celii, T. Tsui, R. Willecke, J. Large (Texas Instruments, Inc.) Silicon carbide (SiC) is being evaluated for integration into Cu/low-k backend process flows. Potential applications include use as a patterning hardmask and as an etch stop layer with Cu diffusion properties. This paper reports the physical and optical characterization of SiC films. Films were deposited on 200 mm wafers in a commercial reactor using plasma-enhanced chemical vapor deposition (PE-CVD). Film composition and bonding were elucidated using SIMS, XPS and FT-IR spectroscopies. Optical properties of the films were determined from variable-angle spectroscopic ellipsometry into the vacuum ultraviolet region (~140 nm). Under some processing conditions, we observed ellipsometry data consistent with a vertical gradient in the SiC refractive indices. The optical constants of the film, along with reflectance modeling using Prolith, suggest SiC can be used as an anti-reflection coating (ARC) layer for lithographic patterning at either 248 or 193 nm. To test the optical modeling results, we have prepared various film stacks containing SiC and organosilicate glass (OSG) on Si or Cu. The reflectivity vs. wavelength will be measured and compared with the calculated reflectivity values. Initial patterning results will also be presented.