NOVELTY - The silicon on insulator (SOI) substrate comprises a glass substrate (110) having a surface on which an altered layer (111) is formed, a nitrogen-containing layer provided on the altered layer, a first insulating layer provided on the nitrogen-containing layer, a single crystal semiconductor layer (122) provided on the first insulating layer, and a second insulating layer provided on the altered layer. The altered layer has a higher proportion of silicon oxide in its composition, and a lower density than the glass substrate. The nitrogen-containing layer is formed using single layer.    USE - The silicon on insulator (SOI) substrate is useful in a thin film transistor of a semiconductor device (claimed), and for manufacturing a liquid crystal display device, an electroluminescent display device, semiconductor devices such as a solar cell, a photo integrated circuit and a semiconductor memory device and electronic appliances including video cameras, digital cameras, navigation systems, audio reproducing devices (such as car audios or audio components), computers, game machines, portable information terminals (such as mobile computers, mobile phones, portable game machines or e-book readers) and image reproducing devices having storage media (DVD).    ADVANTAGE - The SOI substrate can be easily and economically be manufactured with improved size and high reliability, avoids the risk of contamination of the semiconductor layer and a gate insulating film by movable ions such as alkali metal and alkaline earth metal during its manufacture, and reduces the deficiency region of the semiconductor layer.    DETAILED DESCRIPTION - The silicon on insulator (SOI) substrate comprises a glass substrate (110) having a surface on which an altered layer (111) is formed, a nitrogen-containing layer provided on the altered layer, a first insulating layer provided on the nitrogen-containing layer, a single crystal semiconductor layer (122) provided on the first insulating layer, and a second insulating layer provided on the altered layer. The altered layer has a higher proportion of silicon oxide in its composition, and a lower density than the glass substrate. The nitrogen-containing layer is formed using single layer or a stacked layer of films including a silicon nitride film, a silicon nitride oxide film and a silicon oxynitride film. The first and second insulating layers (102) are a silicon oxide film. The silicon oxide film is formed by a chemical vapor deposition using an organosilane gas. The concentrations of alkali metal and alkaline earth metal in the altered layer are lower than those in the glass substrate. An intermediate layer is formed between the altered layer and the glass substrate. The values of the composition and a density of the intermediate layer are intermediate between values of the glass substrate and the altered layer. A chlorine atom is included in the silicon oxide film. An INDEPENDENT CLAIM is included for a method for manufacturing an SOI substrate.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of silicon on insulator substrate.    Insulating layer (102)    Glass substrate (110)    Altered layer (111)    Semiconductor layer. (122)