Method for fabricating mos transistors

Abstract

In PMOS having a gate electrode 7 of a p-type polysilicon film 5 along with a silicon nitride film 13, boron diffusion from the p-type polysilicon film 5 and boron punching through the gate oxide film 4 are prevented, thereby stabilizing the properties of the PMOS. Hydrogen existing in the silicon nitride film 13 accelerates boron diffusion from the film 5. To prevent it, all subsequent steps after the step of forming the silicon nitride film 13 are effected within a temperature range within which the boron diffusion is not accelerated by hydrogen. Forming the silicon oxide film 14 through reduced pressure CVD is effected in a furnace at a temperature lower than 850.degree. C. Annealing for dopant activation in the compensation region 17 to be formed on the substrate in the bottom of the contact hole 16 is effected in a manner of RTA (rapid thermal annealing) at a temperature lower than 1000.degree. C.

Description

BACKGROUND OF THE INVENTION[0001] 1. Field of the Invention[0002] The present invention relates to a method for fabricating MOS transistors, in particular to a method for fabricating MOS transistors having both a p-type gate electrode of a p-type MOS transistor (PMOS) and a silicon nitride film on a substrate, in which boron (B) in the p-type gate electrode is effectively prevented from diffusing away and from punching through the adjacent gate oxide film.[0003] 2. Description of the Related Art[0004] Complementary MOS transistor (CMOS) circuits having both an N-type MOS transistor (NMOS) and a p-type MOS transistor (PMOS) on one and the same substrate have the advantages of reduced power consumption and quick operation as fine patterning to increase the degree of integration in fabricating them is easy, and they have many applications, for example, for memory units and logical units and for other various LSI devices.[0005] Various films of n.sup.+-type polysilicon films as well as ...

AI Technical Summary

Benefits of technology

[0035] Specifically, to attain its object as above, the invention provides a method for fabricating MOS transistors, which comprises a step of forming a gate electrode of a p-type silicon film on a gate insulating film as formed on the surface of a semiconductor substrate, and a step of forming a silicon nitride film on the substrate, and in which all steps after the step of forming the silicon nitride film are effected within a temperature range within which the diffusion of the p-type dopant existing in the p-type silicon film is prevented from being accelerated by the hydrogen existing in the silicon nitride film.

Problems solved by technology

However, in such embedded channel-type MOS transistors, the tip of the depletion layer extending from the source / drain region is too near to another one adjacent thereto in the deep part of the substrate, as being influenced by the gate electric field, thereby often causing punch-through.

This means the difficulty in controlling the short channel effect in coming deep sub-micron generation devices in the art.

However, the boron implantation is problematic in that the boron introduced into the silicon film often diffuses away when the substrate is exposed to high temperatures in subsequent steps.

At present, however, it is extremely difficult to form a silicon nitride film not containing hydrogen, and it is therefore also difficult to retard the boron diffusion that shall be accelerated by hydrogen.

However, the former is problematic in that the crystal defects as caused by ion implantation or dry etching could not be restored sufficiently, and will increase leak current; and the former is also problematic in that the dopants could not be activated sufficiently so that the resistance of the diffusion layer and the interconnection layer will increase.

However, this method is still problematic in that the thickness of the gate insulating film thus processed increases and the carrier mobility lowers to degrade transistor characteristics, and that the fixed charge and the interfacial level increase to lower the reliability of the gate insulating film.

For these reasons, the method is not always favorable.

Therefore, it could not be said that silicon grains could grow all the time to a satisfactory degree in that method, and, in addition, it could not also be said that the grain growth in the method may be all the time reproducible.

As in the above, at present, the conventional measures for preventing boron diffusion from p-type gate electrodes are not finally conclusive.

Images