NOVELTY - A coating fluid comprises a boron compound, an organic binder, a silicon compound, an alumina precursor, and water and/or an organic solvent.    USE - To diffuse boron into a silicon substrate to form a p-type diffusion layer used for fabricating a semiconductor device such as solar cell (claimed).    ADVANTAGE - The coating fluid can form a uniform p-type diffusion layer in a substrate; forms a coating having a sufficient impurity content and a sufficient thickness on a substrate surface through spin coating step; and the addition of silica and alumina precursor allows for uniform boron diffusion. Since the boron diffusion coating fluid is formulated so as to contain an organic binder and silica and to be amenable to a spin coating step, a coating having sufficient impurity content can be uniformly formed on a substrate surface by spin coating step. Even when the substrate used has a texture, typically a pattern of pyramids on its surface as often found in the solar cell fabrication process, a p-type diffusion layer having in-plane uniformity can be formed. Since the alumina precursor is uniformly dispersed in the coating formed from the coating fluid, a dense alumina layer is formed during heat treatment, which layer inhibits outward diffusion of boron dopant and enhances retention. This facilitates to form a p-type diffusion layer having in-plane uniformity. Thus a p-type diffusion layer having uniformity can be formed over the substrate surface, which has been covered with the coating fluid. This leads to improved electrical properties of a semiconductor device, typically solar cell.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for method of fabricating a semiconductor device using the coating fluid involving providing a n-type silicon substrate with a texture, applying the coating fluid to one surface of the silicon substrate, causing a p-type diffusion layer to form, forming a n-type diffusion layer on the other surface of the silicon substrate, forming an antireflective coating on each of the diffusion layers, and forming electrodes.