The present invention relates to a mask that may be used for selectively growing a solid over a substrate during the manufacture of a semiconductor device. The mask defines a region in which the solid is to be grown. The present invention also relates to a manufacturing method of such a mask, and a method for selectively growing a solid using the mask.
Selective growth of a solid is a common technology required during the manufacture of a semiconductor device, in which silicon (Si) or gallium arsenide (GaAs) is selectively grown on a defined region of a semiconductor substrate. Currently, a semiconductor such as Si or GaAs, a metal such as tungsten (W) or aluminum (Al); and a silicide compound have been used as a material for a thin film, which is capable of being grown selectively.
During a selective growth process, the surface of the substrate is covered with a mask so as to suppress the growth of a solid on an undefined region covered by the mask. The material for the mask is determined by taking into consideration the types of substrate and solid material to be grown. Typical materials for a mask includes silicon dioxide which is obtained through the thermal oxidation of silicon or a vapor deposition method, and silicon nitride, which is formed by the vapor deposition method. In general, the thickness of a mask is several tens of nanometers (nm) or more. Also, the region in which a solid is to be selectively grown is defined by depositing a photoresist over the mask and then patterning the mask by photolithography.
However, as semiconductor devices become smaller, a technology for reducing the size of the selective growth region from units of submicrons into units of nanometers is required together with an ultra thin mask for use in this process, having a thickness of several nanometers or less, e.g., below 10 nm. Also, as the thickness of the mask is reduced, a mask material with both reaction selectivity and stability is required. However, such thin film cannot be formed of a single chemical composition.
The above problem will be explained using a thin mask formed of silicon dioxide by way of example. Firstly, if the mask is thin, the mask will be susceptible to defects such as fine voids or holes, so that the selectivity will be deteriorated. Therefore, it is favorable to form such an ultra thin mask at a lower temperature than a conventional method so as to precisely control the thickness of the thin mask. However, these low-temperature conditions can easily cause other defects in the mask. In order to reduce the density of defects in the mask, a high-temperature annealing is favorable. However, a silicon dioxide film with a thickness of several nanometers or less, e.g., below 10 nm, is thermally unstable on the silicon substrate. As a result, the silicon dioxide film decomposes and desorbs during any annealing step performed at approximately 800.degree. C. or more. Thus, it is not possible to anneal the silicon dioxide film at a high temperature.
A second problem occurs when the mask is used as an insulating layer in a final device. By using the phenomenon of a desorption of oxygen by irradiating electron beams onto the silicon dioxide film, a fine pattern having a thickness of several nanometers, e.g., below 10 nm, can be formed directly by irradiating electron beams onto the mask without using a resist. However, it is necessary to limit the desorption of oxygen from the mask within the surface layer, which is caused by the irradiation of electron beams, so as to use the mask as an insulating layer later. However, the general electron beams, which have an energy of 10 keV, because of their long free path of 10 nm or more within the solid, pass over the entire silicon dioxide with a thickness of several nanometers. In other words, the mask layer formed of only silicon dioxide cannot be used as an insulating layer if oxygen is desorbed from it by irradiating the electron beams.