KR20000004221A - Method for manufacturing a gate electrode of semiconductor devices - Google Patents

Abstract

PURPOSE: A fabrication method of a gate electrode having W-polycide structure is provided to improve a GOI(gate oxide integrity) of devices by forming a conductive tungsten nitride by RF(radio frequency) plasma using WF6 and N2 as a diffusion preventing layer. CONSTITUTION: The method comprises the steps of: sequentially forming a gate oxide layer(11) and a doped polysilicon layer(12) on a semiconductor substrate(10); forming a tungsten nitride layer(13) on the doped polysilicon layer(12) by RF PECVD(plasma enhanced CVD) method using WF6 and N2 gas as the diffusion preventing layer; forming a tungsten silicide layer(14) on the tungsten nitride layer(13); and annealing the resultant structure.

Description

Method for manufacturing gate electrode of semiconductor device

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device. In particular, a high frequency using WF ₆ and N ₂ on a surface of a doped polysilicon before deposition of tungsten silicide (W-Silycide) in the production of a gate of a tungsten-polyside structure The conductive oxide tungsten nitride (WN _x ) diffusion barrier layer is deposited at room temperature by in-situ plasma enhanced chemical vapor deposition (PECVD) to improve the gate oxide integrity (GOI) characteristics of the device. A method for manufacturing a gate electrode of a semiconductor device that can be improved.

In view of improving signal processing speed due to high integration of devices, a gate of a tungsten-polyside structure is used in place of a conventional polysilicon. In general, a deposition method of tungsten silicide (WSi _x ) is performed by reducing SiH ₄ (monosilylene; MS) to WF ₆ and depositing SiH ₂ Cl ₂ (dichloroxylene; DCS) to WF ₆ . There is a DCS process.

Both DCS and MS processes use WF ₆ as the reducing gas for the silicon source gas, so within the deposited WSi _x layer, 10 ¹⁶ to 10 ¹⁷ at./cm ³ for the DCS process and 10 ¹⁹ to 10 ²⁰ at for the MS process. Fluorine (F) is contained at a concentration of ./cm ³ . F in the WSi _x layer diffuses toward the gate oxide layer during the subsequent thermal process to increase the thickness of the gate oxide layer and at the interface of the doped poly-Si and the gate oxide layer, a fixed charge center To form a decrease in GOI (Gate Oxide Integrity) properties.

Therefore, the DCS process is preferred to the MS process, and the deposition of the WSi _x layer by the DCS process also prevents diffusion of F because F is contained in the WSi _x layer at a concentration of 10 ¹⁶ to 10 ¹⁷ at./cm ³ . At the same time, there is a need for a diffusion barrier having electrical conductivity. In the case of DCS process WSi _x is deposited at a temperature of 550~650 so ℃ lower doping agent of poly (P) in the silicon is deposited and diffused into the surface of the tungsten at the interface between the WSi _x and WSi _x doping agent polysilicon-rich ( W-rich) composition is secured, resulting in lowering of oxide characteristics, subsequent oxidation of the tungsten-polycide layer (gate oxidation process, spacer oxide deposition process) and adhesion strength of the WSi _x layer. Therefore, the conductive diffusion barrier film is also essential for suppressing the diffusion of P.

The diffusion barrier layer may be formed using silicon nitride (SiN _x ) and tungsten nitride (WN _x ).

Conventionally, an N ₂ O atmosphere annealing method, an NH ₃ plasma nitridation method, a nitrogen ion implantation method, or the like have been used to form a SiN _x layer or WN _x on the surface of a doped polysilicon layer. However, in the case of the N ₂ O atmosphere annealing method and the NH ₃ plasma method, a complex gas is used at a high temperature, and the process is complicated, and the dopant concentration in the doped polysilicon layer is increased. It is accompanied by problems due to thermal budgets such as distribution changes, and in the case of nitrogen ion implantation, a single gas is used because a SiN _x layer (or WN _x ) containing a large number of defects is formed to degrade the etch characteristics. In addition, a new process for forming a diffusion barrier film having excellent crystal state at room temperature is required.

Accordingly, in forming the SiN _x layer, the surface of the doped polysilicon layer before the WSi _x deposition is nitrided in-situ by high-frequency nitrogen plasma in fabricating a tungsten-polyside structure gate. The method of forming a SiN layer at room temperature was used.

However, SiN _x has a problem in that it is inadequate as a diffusion barrier in comparison with WN _x . Table 1 compares the characteristics of SiN _x and WN _x .

Properties SiNx WNx Remarks Crystal structure Deposition: After amorphous heat treatment: Hexagonal lattice During deposition: After amorphous heat treatment: Square grid WN _x structure similar to WSi _x (glasses in terms of CV characteristics) Diffusion of F 10 ¹⁴ ~10 ¹⁶ at / ㎠ 10 ¹² ~10 ¹⁴ at / ㎠ WN _x has excellent F diffusion prevention function (GOI characteristic improvement is advantageous) Work Function Aberration with WSix 0.5 eV 0.3 eV Less change in transistor characteristics for WN _x Thermal stability Stable up to 950 ℃ Stable up to 1200 ℃ Excellent for WN _x . resistance 90-100μΩ㎝ 60 to 80 μm WN _x is advantageous. permittivity 10 to 17 ㎊ / cm 20 to 21 ㎊ / cm Good CV characteristics for WN _x . Adhesive strength 20 ~ 40㎏ / ㎠ 15-18㎏ / ㎠ In the case of SiN _x , the adhesive strength with the doped polysilicon layer is good. Natural oxide film thickness 3-5 Å 7-10Å SiN _x is easy to clean.

In this way, SiN _x has a conductive diffusion preventing film for preventing the diffusion of the doping agent Poly the bonding strength and the native oxide film generated a thickness surface of the silicon layer is advantageous because the drop in physical properties than the WN _x Otherwise, F, or P is more WN _x There are inadequate disadvantages.

Accordingly, the present invention provides a conductive tungsten nitride diffusion barrier layer at room temperature by in-situ plasma chemical vapor deposition by high-frequency plasma using WF ₆ and N ₂ on the surface of the doped polysilicon layer before depositing tungsten silicide (WSi _x ). It is an object of the present invention to provide a method for manufacturing a gate electrode of a semiconductor device which can be deposited to improve the characteristics of the device.

According to an aspect of the present invention, there is provided a method of manufacturing a gate electrode of a semiconductor device. Forming a layer, forming a tungsten silicide layer on the tungsten nitride layer, and patterning the layers, followed by heat treatment.

1 (a) to 1 (c) are cross-sectional views of a device shown for explaining the gate electrode manufacturing method according to the present invention.

<Description of the symbols for the main parts of the drawings>

10 semiconductor substrate 11 gate oxide layer

12: doped polysilicon layer 13: tungsten nitride layer

14: tungsten silicide layer

Hereinafter, with reference to the accompanying drawings will be described in detail the present invention.

1 (a) to 1 (c) are cross-sectional views of a device shown for explaining a method of manufacturing a gate electrode according to the present invention.

As shown in FIG. 1A, the gate oxide layer 11 and the doped polysilicon layer 12 are sequentially formed on the semiconductor substrate 10.

Here, the gate oxide layer 11 is formed to a thickness of 50 to 100 GPa. On the other hand, the doped polysilicon layer 12 is deposited by a chemical vapor deposition method using a silica (SiH ₄ ) gas as a reaction gas at a temperature of 500 ~ 700 ℃ using a PH ₃ as a dopant (dopant). At this time, the mixing ratio of SiH ₄ and PH ₃ is set to 1.1: 1.5 to 1.5: 1.8, and the thickness of the doped polysilicon layer 12 formed under such conditions is set to 500 to 1000 kPa.

Thereafter, as shown in FIG. 1B, a tungsten nitride (WN _x ) layer 13 to be used as a diffusion barrier is formed on the entire structure.

Material to be used as a diffusion prevention film while the thermal stability WSi _x layer and the doping agent poly low reactivity with the silicon layer 12, WSi _x layer and the doping agent work function of the polysilicon layer 12, the car down the flat-band voltage ( It should not cause a change in Vfb) and should have high electrical conductivity. Materials satisfying these characteristics include titanium nitride (TiN) and WN _x , and TiN has an unsuitable defect as a conductive diffusion barrier due to the reactivity between titanium and doped polysilicon. Accordingly, in the present invention, WN _x is used as the diffusion barrier.

In order to form the most suitable WN _x as a conductive diffusion barrier against F in the WSi _x layer and P in the doped polysilicon, a reaction of the following Chemical Formulas 1 to 3 must be performed in the tungsten-polyside gate. .

N ₂ → N + N

WF ₆ → W + 2F ₃

W + N → WN _x

This reaction proceeds at about 850-1000 ° C. where the reaction free energy value becomes negative, but WN _x is most suitable as a conductive diffusion barrier by reaction between activated N ⁺ ions and W ⁺ ions when using RF plasma. Can proceed. In addition, when the plasma is formed by RF discharge, the formation of the same charge accumulation layer in the DC discharge plasma is suppressed, so that the ion of the same charge does not move to the reaction surface due to the reaction phenomenon, that is, the electrostatic repulsion. Since this is excluded, the reaction efficiency between W and N is increased to form WN _x having excellent crystallinity.

The WN _x layer 13 having excellent crystallinity is formed by an in-situ nitriding process by RF plasma CVD.

That is, in the same chamber as the chamber for forming a WSi _x layer before depositing WSi _x layer forming write discharge because the WF ₆ gas and N ₂ by the high frequency plasma. The form of plasma used here is performed by supplying a high-efficiency high frequency wave having a waveform of 13.56 MHz, and the mixing ratio of WF ₆ and N ₂ is 1: 1.7 to 1: 2. The WN _x layer 13 formed under such conditions has a thickness of 40 to 100 kPa.

FIG. 1C is a cross-sectional view of a device after patterning a gate region after forming a tungsten silicide (WSi _x ) layer 14 over the entire structure. The WSi _x layer 14 is formed by CVD at a temperature of 500 to 650 ° C., and uses dichloroxylene (SiH ₂ Cl ₂ ) and WF ₆ as reaction gases. At this time, the mixing ratio of SiH ₂ Cl ₂ and WF ₆ is set to 2-3: 1 to 1.5, and the thickness of the WSi _x layer 14 formed under such conditions is 500 to 1000 kPa. In addition, in order to increase the adhesive strength between the doped polysilicon layer 12 and the WSi _x layer 14 and to improve oxidation characteristics, the chemical equivalent ratio (x) of silicon (Si) in the WSi _x is set to 2 to 2.8.

In this manner, after forming the WSi _x layer 14, the gate region is patterned, and then heat-treated at a temperature of 600 to 900 ° C. to form a gate of a tungsten-polyside structure that is changed from a hexagonal lattice structure to a square lattice structure.

The gate formed in this manner can prevent the F contained in the WSi _x layer 14 from being diffused toward the gate oxide layer by the WN _x layer 13, which is a conductive diffusion preventing layer, and the doped polysilicon layer 12. It is possible to prevent the diffusion of P in the surface to improve the interfacial properties of the WSi _x / WN _x / doped polysilicon.

As described above, according to the present invention, it is possible to prevent the phosphorus in the doped polysilicon layer from diffusing to the surface of the tungsten silicide layer, thereby increasing the adhesive strength between the doped polysilicon layer and the tungsten silicide layer and improving the oxidation characteristics. In addition, the chemical affinity between tungsten in the tungsten silicide layer and tungsten in the tungsten nitride layer improves the adhesive strength and secures a flat band voltage by securing an interface of tungsten silicide / tungsten nitride / doped polysilicon which exhibits a uniform energy band. Since the change in Vfb is reduced, the transistor characteristics can be improved, and the fluorine contained in the formation of the tungsten silicide layer can be prevented from diffusing toward the gate oxide layer, thereby improving GOI characteristics. In addition, the interfacial grooving phenomenon due to the consumption of the doped polysilicon layer at the tungsten silicide / doped polysilicon interface is excluded by the tungsten nitride layer, thereby ensuring the uniform interface to stabilize the electrical characteristics of the device. In the subsequent heat treatment process, the dopant redistribution in the doped polysilicon may be suppressed by the tungsten nitride layer to double the resistance uniformity of the doped polysilicon.

Claims (5)

Sequentially forming a gate oxide layer and a doped polysilicon layer on the semiconductor substrate, Forming a tungsten nitride layer on the doped polysilicon layer; Forming a tungsten silicide layer on the tungsten nitride layer; And patterning the layers, followed by heat treatment. The method of claim 1, The tungsten nitride layer is formed by an in-situ nitriding process by a high frequency plasma chemical vapor deposition method of 13.56MHz. The method of claim 1, The tungsten nitride layer is a gate electrode manufacturing method of a semiconductor device, characterized in that formed using the WF ₆ and N ₂ gas as the reducing gas. The method of claim 3, wherein The reducing gas is a gate electrode manufacturing method of a semiconductor device, characterized in that the mixing ratio of WF ₆ and N ₂ 1: 1.7 to 1: 2. The method of claim 1, The thickness of the tungsten nitride layer is formed so as to be 40 to 100 GPa gate electrode manufacturing method of a semiconductor device.