Method for manufacturing a gate structure incorporating therein aluminum oxide as a gate dielectric

The present invention relates to a semiconductor device; and, more particularly, to a method for manufacturing a gate structure incorporated therein aluminum oxide (Al 2 O 3 ) as a gate dielectric.

As is well known, a semiconductor device has been down-sized by a scale down of a design rule. Therefore, a gate oxide tends to rapidly approach 30 Å in thickness and below to increase the capacitance between a gate electrode and a channel region. However, the use of silicon dioxide as a gate dielectric is limited at this thickness and below. Once silicon dioxide (SiO 2 ) is formed to a thickness of less than 30 Å, direct tunneling may occur through the gate dielectric to the channel region, thereby increasing a leakage current associated with the gate electrode and the channel region, causing an increase in power consumption.

Since reducing the thickness of the gate dielectric inherently increases the gate-to-channel leakage current, alternative methods have been developed to reduce this leakage current while maintaining thin SiO 2 equivalent thickness. One of these methods is to use a high K dielectric material such as tantalum oxide (Ta 2 O 5 ) as the gate dielectric materials to increase the capacitance between the gate and the channel.

However, if a poly-silicon is utilized as a gate electrode, the use of Ta 2 O 5 for gate dielectric materials has a disadvantage in integrating the semiconductor device. That is, an undesired SiO 2 is formed at an interface between Ta 2 O 5 and the poly-silicon, which, in turn, increases an equivalent oxide thickness. In order to overcome this problem, a barrier metal such as titanium nitride (TiN) is employed. However, the TiN makes a threshold voltage shift changed.

Therefore, there is still a demand for developing a high K dielectric as a gate oxide with excellent leakage current as well as a low interface state with both a gate electrode and a silicon substrate.

It is, therefore, an object of the present invention to provide a method for manufacturing a gate structure incorporated therein aluminum oxide as a gate oxide for use in a semiconductor device.

In accordance with one aspect of the present invention, there is provided a method for manufacturing a gate structure for use in a semiconductor device, the method comprising the steps of: a) preparing a semiconductor substrate provided with an isolation region formed therein; b) forming an aluminum oxide layer (Al 2 O 3 ) on the semiconductor substrate; c) carrying out a Si+ plasma doping on the Al 2 O 3 layer; d) annealing the Al 2 O 3 layer doped with the silicon ions; e) forming a conductive layer on top of the Al 2 O 3 layer; and f) patterning the conductive layer, thereby obtaining the gate structure.

The above and other objects and features of the present invention will become apparent from the following description of the preferred embodiments given in conjunction with the accompanying drawings, in which:

FIGS. 1, 2 , 3 , and 4 are schematic cross sectional views setting forth a method for the manufacture of a gate structure incorporated therein aluminum oxide as a gate dielectric in accordance with a preferred embodiment of the present invention.

There are provided in FIGS. 1 to 4 cross sectional views setting forth a method for manufacturing a gate structure 100 for use in a semiconductor device in accordance with a preferred embodiment of the present invention.

Referring to FIG. 1, the process for manufacturing the gate structure 100 begins with the preparation of a semiconductor substrate 110 including an isolation region 120 for defining an active region. The isolation region 120 may be formed in a structure of local oxidation of silicon (LOCOS) or in a structure of shallow trench isolation (STI).

And then, an aluminum oxide (Al 2 O 3 ) layer 130 is formed on top of the semiconductor substrate 110 by using a method such as a chemical vapor deposition (CVD) and an atomic layer deposition (ALD) technique, wherein an aluminum source utilizes a material such as trimethyl aluminum (TMA, Al(CH 4 ) 3 , Al(CH 3 ) 2 Cl, AlCl 3 or the like and an oxygen source utilizes a material such as H 2 O, oxygen (O 2 ) or the like. It is preferable that the deposition temperature is ranged from 150 Å to 700 Å and the pressure in a reaction chamber is ranged from 0.5 Torr to 10 Torr.

Before depositing the aluminum oxide layer 130 , a silicon dioxide (SiO 2 ) thin film (not shown) can be formed on the substrate 110 . The SiO 2 thin film is thermally grown on the semiconductor substrate 110 by using a wet H 2 /O 2 or dry O 2 at a temperature ranging from approximately 650° C. to approximately 900° C. It is preferable that the SiO 2 thin film has a thickness ranging from approximately 3 Å to approximately 20 Å. Alternatively, it is possible that the silicon SiO 2 thin film can be formed by using a rapid thermal process (RTP) at a temperature ranging from approximately 700° C. to approximately 900° C. in the presence of O 2 gas or a nitrous oxygen (N 2 O) gas. It is preferable that the RTP is carried out in a pressure ranging from approximately 0.1 Torr to approximately 1.0 Torr.

In a next step as shown in FIG. 2, in order to remove metallic vacancies in the aluminum oxide layer 130 , silicon ions (Si + ) are doped by plasma. And then, a first annealing process is carried out, thereby forming an Al 2 O 3 gate dielectric layer 135 . In Si + plasma doping, Si RF coil, SiH 4 , Si 2 H 6 , SiCl 4 or the like is used as a silicon source material. In more detail, Si + plasma doping is carried out on condition that a negative bias is applied to a cathode with 100 eV to 2 keV, an ion flux is approximately 1E14 to approximately 5E15 ions/cm 2 , used power is approximately 0.1 W/cm 2 and Si + dopant is doped into the aluminum oxide layer 130 by controlling a gas flow rate. Meanwhile, by-product, e.g., H, Cl or the like, which is produced during the plasma doping, can be removed by a collector to which a positive bias is applied or be removed by means of evacuation using a high vacuum pump.

Thereafter, an organic material in the Al 2 O 3 gate dielectric layer 135 is removed by using a UV ozone (O 3 ) at 300 to 500° C. for 3 to 30 minutes. And then, a second annealing process is carried out at 650 to 850 ° C. for 10 to 60 minutes in O 2 , nitrogen (N 2 ), N 2 +H 2 (hydrogen), N 2 +D 2 (deuterium) or N 2 O rich ambient, thereby reducing the metallic vacancies in the Al 2 O 3 gate dielectric layer 135 due to a change of the silicon ions into SiO 2 .

In an ensuing step, a conductive layer 140 is formed on top of the Al 2 O 3 gate dielectric layer 135 to a thickness ranging from approximately 500 Å to approximately 2,000 Å. The conductive material can be selected from a group consisting of a doped poly-Si, amorphous-Si, W-polycide, Ti-polycide, Co-polycide, Mo-polycide, tungsten (W), tantalum nitride (TsN), tungsten nitride (WN), titanium nitride (TiN) or the like.

In the embodiment of the present invention, the conductive layer 140 is formed after the Si + plasma doping is completed. However, the Si + plasma doping process can be carried out after the conductive layer 140 is deposited to the thickness ranging from 100 Å to 300 Å.

In a following step, the conductive layer 140 A and the Al 2 O 3 dielectric layer 135 A are patterned into a predetermined configuration, thereby obtaining a gate structure 150 as shown in FIG. 4 .

In the present invention, the aluminum oxide layer is used as the gate dielectric layer. And further, in order to reduce oxide trap charge produced by the metallic vacancies in the aluminum oxide layer, Si + plasma doping upon the aluminum oxide layer and the annealing process are carried out subsequently. By using the plasma doping in the inventive method, it is possible to control a projected range (R p ) from 50 Å to 200 Å while it is impossible in case of using an ion implantation method. Thus, the silicon ions are directly doped into the aluminum oxide layer so that the substrate is effectively prevented from the damage.

Accordingly, after Si + plasma doping, the silicon ions move into the vacancy site in the aluminum oxide layer and then SiO 2 is formed through the annealing process, thereby obtaining the gate structure incorporated therein the Al 2 O 3 dielectric layer with a low oxide trap charge and enhanced dielectric property.

While the present invention has been described with respect to the particular embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.