BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the field of semiconductor technology. More particularly, the present invention relates to a method for forming a semiconductor device.

2. Description of the Prior Art

Advanced complementary metal oxide semiconductor (CMOS) devices may increasingly be utilizing metal gate materials to avoid “poly-Si depletion” and “boron penetration” effects. The selection of a particular metal for a gate material can be guided by a number of considerations, for example, the work function and electrical resistivity desired, the type of gate dielectric, the thermal budget that the gate metal will be expected to survive, etc. In the “dual-metal/dual-work function” CMOS manufacturing method, different gate metals suitable for p-FET (high work function) and for n-FET (low work function) are used.

In general, metal gates for CMOS devises can comprise one or more layers of a pure metal or alloy, a metal or metal alloy silicide, or a metal-containing conductive oxide or nitride, where at least one of these layers is in contact with the device's gate dielectric. A bilayer metal gate might comprise, for example, a thin bottom “cladding” or “work function-setting layer (in contact with an underlying gate dielectric) and a thicker upper “fill layer” to provide good conductivity.

For example, an existing method is to first form a tantalum nitride barrier layer, then deposit a titanium nitride layer on the tantalum nitride barrier layer as a P work function layer, and then cover the PMOS region with a photoresist layer, and then etch the titanium nitride layer in the NMOS region, and then the N work function layer is deposited. However, the disadvantage of the above method is that when the titanium nitride layer in the NMOS region is removed by etching, titanium nitride residues may be generated. In addition, removing the titanium nitride layer in the NMOS region by etching is likely to damage the underlying tantalum nitride barrier layer.

SUMMARY OF THE INVENTION

It is one object of the present invention to provide an improved method of forming a semiconductor device in order to solve the above-mentioned shortcomings or deficiencies of the prior art.

One aspect of the invention provides a method of forming a semiconductor device. A substrate having a first device region and a second device region is provided. A metal nitride barrier layer is deposited to cover the first device region and the second device region. A titanium layer is then deposited on the metal nitride barrier layer. The titanium layer is selectively removed from the second device region, thereby exposing the metal nitride barrier layer in the second device region. The titanium layer in the first device region is then transformed into a titanium nitride layer. The titanium nitride layer is a work function layer on the first device region.

According to some embodiments, the method further includes the steps of forming a dielectric layer on the substrate; and forming a trench in the dielectric layer.

According to some embodiments, the metal nitride barrier layer conformally covers the dielectric layer and an interior surface of the trench.

According to some embodiments, the method further includes the step of forming a high dielectric constant dielectric layer before depositing the metal nitride barrier layer.

According to some embodiments, the first device region is a PMOS region and the second device region is an NMOS region.

According to some embodiments, the titanium layer is selectively removed from the second device region by using diluted HF or hydrogen peroxide-sulfuric acid mixture (SPM).

According to some embodiments, the method further includes the step of depositing an N work function metal layer on the first device region and the second device region after transforming the titanium layer in the first device region into the titanium nitride layer.

According to some embodiments, the N work function metal layer comprises titanium aluminum.

According to some embodiments, the method further includes the step of depositing a gap-filling conductive layer on the N work function metal layer.

According to some embodiments, the gap-filling conductive layer comprises aluminum or tungsten.

These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.

