1. Field of the Invention
The invention relates to a method of producing a semiconductor device, and more particularly to a method of isolating elements of a semiconductor device. In addition, the invention also relates to a semiconductor device which has elements isolated by a trench.
2. Description of the Related Art
Conventional insulating isolation between elements of a semiconductor device was generally made with a relatively thick oxide layer formed by a selective oxidizing method. But, when a thick oxide layer is formed by this method, biting which is referred to as a so-called bird's beak into an element-forming region is made by the oxide layer, and a region required for the insulating isolation of elements is made to have a broader width, resulting in one of the causes preventing a semiconductor device from being highly integrated. Therefore, there has been adopted in recent years a method by which a trench is formed on a silicon substrate, and an insulating material such as SiO.sub.2 is particularly filled in the trench to provide isolation between the elements.
One way to provide a highly integrated semiconductor device, it is required to form a trench so deep that a depth becomes several times greater than a width of the trench (an aspect ratio), and the trench is filled with an insulating material such as a silicon oxide layer. Therefore, it has been considered to form an oxide layer by a chemical vapor deposition (CVD) method which provides a good coated form and a CVD method which uses as a material gas an organic silane such as tetraethyl orthosilicate and ozone (TEOS/O.sub.3).
But, since the CVD method forms a layer at a relatively low temperature, it is necessary to heat the formed oxide layer at a high temperature of about 1000.degree. C. to densify the layer. Upon heating, the oxide layer filled in the trench is densified and contracted to apply a stress to the silicon substrate on which elements are to be mounted, adversely affecting on the characteristics of a semiconductor device.
To remedy the above-described disadvantage involved in the production method which effects the trench-filling insulating isolation, it has been demanded for an element-insulating isolation step which uses an oxide layer having a good embedding property and insulating property and suffering from a minor volume change while it is heat-treated at a high temperature.
As described above, using an oxide layer formed by the CVD method to embed the trench has a disadvantage of causing a stress in the silicon substrate because the embedded layer is densified and contracted by the high-temperature heating treatment which is performed to improve the layer quality.
The invention has been completed to remedy the above disadvantage, and aims to provide a method of producing a semiconductor device incorporating insulating isolation by embedding a trench, wherein a volume change rate which is caused in an embedded silicon oxide layer while it is being heat-treated at a high temperature is decreased.