Thermal Stress in Doped Silicate Glasses (B,P) Deposited by PECVD and LPCVD
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THERMAL STRESS IN DOPED SILICATE GLASSES (B,P) DEPOSITED BY PECVD AND LPCVD
H. BOUCHARD 1, A.AZELMAD 2 , J.F. CURRIE 13, M.MEUNIER 1 , S. BLAIN 3 AND T. DARWALL 1: Groupe des Couches Minces, Department of Engineering Physics, E~cole Polytechnique, C. P. 6079, Succ. A,Montr6al, Quebec, Canada, H3C 3A7 2: Goal Electronics Inc. Waterloo, Ontario, Canada, N2L 6J7 3: Mitel S.C.C.,18 boul. de I'Aeroport, Bromont, Qu6bec, Canada, JOI 110 ABSTRACT
Using an in situ stress measurement technique which measures stress as a function of annealing temperature, we have investigated the effect of phosphorous and boron doping of silicon dioxide glass films deposited by low-pressure chemical vapor deposition (LPCVD) and plasma-enhanced chemical vapor deposition (PECVD). The stress at room temperature is oi. Upon heating, it increases to a maximum, crm, corresponding to a temperature Tm, above which the stress is reduced to zero at a temperature To. All these parameters plus the expansion coefficient are dependent on dopant concentrations and deposition technique. INTRODUCTION
Compact and fast electronics are achieved using multilevel metallization and submicron devices. To isolate those multilevel conductive lines, intermetallic dielectrics must be used. Moreover, to avoid reliability problems, those dielectrics must also smooth the circuit's topography. For the future, intermetallic dielectric layers require [1]: lower defect densities, improved planarization and better stress control. One of the most widely used dielectrics in the CMOS technology are silicate glasses. Thin films of silicate glass were doped with phosphorous and boron to planarize at low temperature. Dopants change thermal expansion coefficient and water diffusion coefficient [2,3]. Hence mechanical stress stability of those films is of primary importance. With high mechanical stress, cracking of dielectric films or voiding in conductor lines can occurred. We report here on the comparison of the mechanical properties of silicate glasses produced by low-pressure chemical vapor deposition (LPCVD) and plasma-enhanced chemical vapor deposition (PECVD). EXPERIMENTAL PROCEDURES
The silicon substrates used in this study were 525 pm thick, 4 in. diameter and (100) orientation. Films of 1 pm were deposited by LPCVD and PECVD. Lowpressure depositions were done at 390 °C and 400 mT approximately. Using plasma, we did the depositions around 400 °C and 2.2 T. Boron and phosphorous concentrations have been determined by ionic chromatography. To study the mechanical stresses of our films, we used silicon wafers as substrates and we measured wafer curvature with a TFSMA (model F2400) from TENCOR-FLEXUS. The curvature is measured continuously by laser beam deflection. Stress is function of substrate's Young modulus (E), substrate's Poisson coefficient (v), radius of curvature (R)and thickness of the substrate (t) and the film (tf).
This apparatus may be used 0to determine the stress as a function of temperature. A thermal cycle from 20 C to 900 0C and back to room temperature a
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