P-Glass reflow technique

DETAILED DESCRIPTION What is claimed is: 1.
A method for reflowing a P-glass layer which comprises: (a) overcoating said P-glass layer with a radiation absorbing material whose reflectivity increases upon melting; (b) exposing said radiation absorbing material to radiation to heat said radiation absorbing material to its melting point; and (c) continuing the radiation exposure of said radiation absorbing material until said P-glass layer has reflowed, said P-glass layer being heated at least in part by conduction of heat from said radiation absorbing material.
2.
The method of claim 1 wherein said radiation is provided by a laser.
3.
The method of claim 1 wherein said radiation absorbing material is a phosphorous doped polysilicon.




Description:
Phosphosilicate glass (P-glass) is the most common insulating layer used in integrated circuits before metallization.
To avoid metallization failures due to excessively steep steps formed in the P-glass deposition process, the P-glass is heated to cause the P-glass to flow and thus smooth the steps.
The high temperature treatment also eliminates pinholes in the P-glass layer.
Temperatures exceeding 1000.
degree.
C.
are commonly used.
These extreme temperatures, however, can have a detrimental effect on the doped metal oxide semiconductor (MOS) materials underlying the P-glass causing significant diffusion of the dopants.
The corresponding lateral diffusion is a particularly serious limitation for one micron or submicron MOS devices.
The P-glass flow temperature can be decreased by increasing the phosphorous concentration, but the hydroscopic nature of heavily doped P-glass leads to fabrication and reliability problems.
Another method of reducing the problem is to use transient localized heating with laser beams to minimize substrate heating.
The laser radiation heating of the P-glass layer, however, depended on the topography of the material and the varying optical properties of the underlayers.
The invention as claimed is intended to provide a remedy for the above problems and provide further improvement