Spin-on Silicon Oxide (SOX): Physical Properties of the Sol
- PDF / 380,349 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 15 Downloads / 217 Views
SPIN-ON SILICON OXIDE (SOX): PHYSICAL PROPERTIES OF THE SOL VIVIAN RYAN and GERALD SMOLINSKY AT&T Bell Laboratories, Murray Hill, NJ 07974-2070
ABSTRACT This paper describes an analysis of the physical properties of the sol using several complementary light scattering techniques. Polymerization and aggregation kinetics were followed through time-dependent changes in the size, shape, and density of the sol particles. The sot growth rate was controlled by choice of solvent and silicon concentration. Changes in viscosity and pH were small during the reaction period. Three different particle-growth regimes exist in which either the particle density increased, decreased, or remained the same. The addition of boron, hydrofluoric acid, or water accelerated the reaction. The sol experimental data correlate with the density and wet-etching rate of the cured films. After curing, high-density films were obtained from sols with three common characteristics: an average particle diameter >450 A, a relatively high polydispersity, and a low particle density. These criteria were generally satisfied by solutions one to two days old.
INTRODUCTION A novel polysilicate spin-on oxide, SOX, has been developed for use as a dielectric layer in the fabrication of integrated circuits.[1] Stock solutions are prepared by dissolving silicon(IV) acetate in an alcohol. After a period of time, the solution forms a sol which can be spin-coated on a patterned wafer. With proper choice of solvent, sol ripening time, and cure treatment, the resulting film can have exemplary properties: a low cure temperature (150-200 "C) but still able to withstand heating to 900 'C, a low wet-etching rate, good mechanical properties, and the ability to smooth underlying topography. In this report, we relate the physical properties of sols to the characteristics of cured films. We employed light scattering methods to monitor details of polymerization and aggregation in sol solutions. These data enabled us to correlate the reaction rate of the silicic acid in solution and the size and shape of the particles in suspension with the wet-etching rates of the films. LIGHT SCATTERING ANALYSIS Light incident on a suspension is scattered in a complex angular pattern dependent on many factors. The attenuation in the transmitted light due to this scattering is called the absorbance, A; this is related to the sol turbidity, r, through the relation, A = 'r/L, where L is the path length of the optical cell. For relatively dilute suspensions (i.e., individual particles do not multiply scatter and their positions are statistically independent of each other) of particles that are small compared to the wavelength of the incident light, absorbance measurements can be interpreted using Debye's equation:[2,3] 32n
3
2 ( - 90)2 V
(1)
*
where V is the volume of a solute particle, = nV is the volume of solute per cc of solution, X is the wavelength of incident light, p,, and gtare the indexes of refraction of the solvent and solution, respectively, and n is the number of particles per
Data Loading...
