Measurement and interpretation of stress in copper films as a function of thermal history
- PDF / 306,428 Bytes
- 4 Pages / 612 x 828 pts Page_size
- 24 Downloads / 200 Views
Since copper has some advantages relative to aluminum as an interconnection material, it is appropriate to investigate its mechanical properties in order to be prepared in advance for possible problems, such as the cracks and voids that have plagued aluminum interconnect systems. A model previously used to interpret the behavior of aluminum films proves to be, with minor modification, also applicable to copper. Although the thermal expansion of copper is closer to that of silicon and, consequently, the thermally induced strains are smaller, the much larger elastic modulus of copper results in substantially higher stresses. This has implications for the interaction of copper lines with dielectrics.
I. INTRODUCTION The increasingly severe demands made on interconnections by continually shrinking submicron technologies have led to increasing interest in alternatives to aluminum-based alloys for metal lines. Copper is an obvious metal to investigate, since it is a significantly better conductor than aluminum, and its higher melting point should result in improved electromigration resistance relative to aluminum-based materials. Since mechanical failure (stress-induced cracks and voids) has been a continuing problem with aluminum lines for many years,1"5 it seems worthwhile to investigate and attempt to understand the mechanical behavior of copper films.
of these two orientations. Measurements on samples deposited with different power levels indicated that as the deposition power is increased (and presumably the effective deposition temperature) the sharpness of the distribution is increased and the amount of material with {220} orientation is decreased. Measurements on an annealed sample show only a broadened peak corresponding to the {111} texture; the peaks from the {220} 100000 T90000 -
.£• 80000 -
II. FILM PREPARATION AND FILM TEXTURE The films used in this study were prepared by Tom Rucker of Intel by sputtering in a Perkin-Elmer 4450 at power levels from 1 to 5 kw. The films were 1 //m in thickness, deposited on 100 mm silicon wafers with 100 nm of thermal oxide. The "texture" (distribution of crystallite orientation) was determined by x-ray diffraction, using the Generalized Focusing Diffractometer at Stanford University.6 The result for a typical film is shown in Fig. 1. The measurements were carried out with a fixed Bragg angle of 144.7 degrees, corresponding to diffraction by the {420} planes of copper, and the value of a, the angle between the incident x-ray beam and the sample, was varied. The main peak is centered at a = 33.1 degrees. At this value of a, those crystallites with their {111} planes parallel to the surface are correctly oriented to diffract. The smaller peaks at a = 21.6 and a = 53.9 are due to diffraction from crystallites whose {220} planes are parallel to the surface. The sharpness of the peaks shows that almost all the crystallites are within a few degrees of one or the other 1498
http://journals.cambridge.org
J. Mater. Res., Vol. 6, No. 7, Jul 1991
Downloaded: 17 Mar 2015
70000 -
Data Loading...
