JPH0478021B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a semiconductor device in which the density of mobile ions contained in an insulating film is reduced.

In recent years, a so-called self-aligned element formation method has come to be used in order to integrate elements and their electrodes and wiring at high density inside a semiconductor device. In this method, for example, in a MOS type integrated circuit, a film made of a high-melting point metal such as molybdenum (MO) is used as a mask for implanting impurity ions into a semiconductor substrate, and is also left as is for use as electrodes and wiring. This process will be explained using the drawings using a MOS transistor as an example. First, as shown in FIG. 1A, an Si oxide film 2 for element isolation is formed on a Si substrate 1, and then a gate oxide film 3 is formed. after that,
As shown in FIG. 1B, a high melting point metal film for the electrode is deposited, for example, Mo, and processed by photolithography to form the gate electrode 4. Next, as shown in FIG. 1c, impurity ions having a conductivity type opposite to that of the substrate 1 are implanted using the gate electrode 4 as a mask to form a source region 5 and a drain region 6 of the MOS transistor. Thereafter, the impurities are activated by heating to about 1000° C. in a nitrogen gas atmosphere.

In this process, self-alignment is performed using the gate electrode as a mask for ion implantation, which is different from conventional techniques that do not use self-alignment. Doesn't require leeway. Therefore, the area occupied by the elements is reduced, and more elements can be formed within a limited pellet area. Currently, in order to produce high-density integrated circuits,
Such a self-aligned element formation method has become an essential technology.

When using this self-aligned element formation method,
The thin film that becomes the gate electrode acts as a mask for the impurity ions being implanted, and
It is necessary that the material has properties that can withstand heating up to a certain degree.

In MOS type integrated circuits, impurity-doped polycrystalline Si has traditionally been used for such gate electrodes and wiring. However, the specific resistance is about 5×
Since the resistance is high at 10 ^-4 Ωcm or more, signal propagation delays due to increased resistance in the wiring have become a problem due to the finer structure of electrodes and wiring. For this reason, technology that uses high melting point metals such as Mo, which have even lower specific resistance, for gate electrodes and wiring has recently been attracting attention.

For example, when Mo is formed into a thin film, its resistivity is approximately two orders of magnitude lower than that of doped polycrystalline Si, and its crystal grain size is also smaller, so it is being considered to use Mo for gate electrodes to increase the density and speed of integrated circuits. has been done. Also, the atomic number is 42 and the bulk density is 10.2 g cm _U-3
Because of its large size, its blocking ability against ion implantation is also high.

However, in reality, Mo is used for electrodes and wiring to create MOS
When a transistor is manufactured, it is observed that its threshold voltage fluctuates over a long period of use. This phenomenon is particularly noticeable when a bias-temperature acceleration test is performed as a negative change in the threshold voltage. In general, the stability of the threshold voltage of a MOS transistor in a MOS type integrated circuit is the most important issue in terms of reliability of the integrated circuit, and the above fluctuations are unacceptable. Many studies have been conducted on the causes of this threshold voltage variation, mainly due to
It is known that this is caused by the movement of alkali metal ions such as Na in the gate oxide film. It is also believed that these mobile ions are initially contained as impurities in the metal material of the gate electrode, and enter the gate oxide film through diffusion due to heat treatment or the like.

Conventionally, various methods have been studied for reducing the number of mobile ions in the gate oxide film. The first method uses chemical vapor deposition (CVD),
It forms a high-purity metal film. High-melting point metal materials such as Mo and W used in general sputtering and vapor deposition methods are mainly refined by physical methods such as vacuum melting, and targets for sputtering are then processed by hot pressing, etc. is also added,
The purity is about 99.9-99.9%. In contrast to this,
When using the CVD method, the metal is first converted into a gas such as a halide, and then purified and reduced by a chemical method, which further improves the purity. However, compared to sputtering and vapor deposition methods, metal
The CVD method has not been established as a film-forming technology,
The disadvantage is that the film formation itself is difficult.

The second method is to introduce phosphorus P into the gate oxide film and utilize the gettering effect of Na due to P.
This is an attempt to fix Na in the gate oxide film. In this case, a method is generally used in which a P-containing silicate glass is deposited on the patterned gate electrode and the P in the silicate glass is diffused into the gate oxide film through subsequent heat treatment. In this method, since P is introduced by thermal diffusion, it is not easy to accurately limit and control the region into which P is introduced into the gate oxide film. In particular, in high-density MOS type semiconductor devices, the gate oxide film thickness becomes as thin as 300 mm or less, making it even more difficult to control P diffusion.

The third method includes F. Yanagawa et al. deposited Mo
There is a high-temperature hydrogen heat treatment method that has been reported (F. Yanagawa, K. Kiuchti, T. Hosoya, T.
Tsuchiya, T. Amazawa, and T. Mano: IEEE
Trans.Electron Devices, VOl.ED−27,
pp.1602-1606, 1980.) In this method, the Mo gate electrode after patterning is exposed to H ₂ −N ₂ (10%−90
%) Heat treatment at 1000°C in mixed gas, or heat treatment at 1000°C in _N2 gas followed by heat treatment at 1000°C in _H2 - _N2 mixed gas. As a result, the mobile ion density in the gate oxide film is reduced to about 1×10 ¹¹ cm ⁻² . However, when this method is applied to a sputtered Mo film, the impurity concentration in the sputtered metal film is higher than that in the vapor-deposited film, so the effect of reducing the mobile ion density by this heat treatment alone is insufficient.

The present invention aims to eliminate these drawbacks and reduce the number of mobile ions, by estimating the metal film in an atmosphere containing hydrogen gas, and then performing high-temperature heat treatment in an atmosphere containing hydrogen gas. It is characterized by this.

In order to achieve the above object, the present invention comprises a step of forming an insulating film on the surface of a semiconductor substrate, a step of depositing a high melting point metal film on the insulating film in an atmosphere containing hydrogen gas, and a step of depositing a high melting point metal film on the insulating film in an atmosphere containing hydrogen gas. The gist of the invention is a method for manufacturing a semiconductor device characterized by including a step of patterning a film to form electrodes and wiring, and a step of performing high temperature heat treatment in an atmosphere containing hydrogen gas.

Next, embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that the embodiments are merely illustrative, and it goes without saying that various changes and improvements can be made without departing from the spirit of the present invention.

FIG. 2 is an explanatory diagram of the manufacturing process of the gate electrode of the MOS type semiconductor device according to the present invention, showing the cross-sectional shape of the main part of the MOS type semiconductor device at key points in the process. First, as shown in FIG. 2a, a Si oxide film 2 for element isolation and a gate oxide film 3 are formed on the surface of a Si substrate 1. In the present invention, the following process shown in FIG. 2b is different from the conventional process. In other words, conventionally 10 ^-3 ~
Mo for the gate electrode is prepared by sputtering a high melting point metal such as Mo in an Ar gas atmosphere at a pressure of about 10 ^-2 Torr, or by electron beam evaporation of Mo in a vacuum at a pressure of about 10 ^-6 Torr. A film was formed. In the present invention, instead of this, Ar gas partial pressure 7.5 ×
10 ^-3 Torr, _H2 gas partial pressure 2×10 ^-4 ~2×10 ^-3 Torr
A Mo target is sputtered in an Ar--H ₂ mixed gas atmosphere to deposit a Mo gate electrode film 7 with a thickness of 3300 Å. In this example, we used the spatuta method,
The Mo film may be deposited by vapor deposition in an H ₂ gas atmosphere at a pressure of about 10 ⁻⁵ to ^{10 −3} Torr.

After this, as in the conventional process, as shown in FIG. 2c, a masking material such as photoresist is applied directly onto the Mo gate electrode film 7, and processed by photolithography.
A Mo gate electrode 8 is formed. Next, as shown in FIG. 2d, impurity ions having a conductivity type opposite to that of the Si substrate 1 are implanted using the Mo gate electrode 8 as a mask.
A source region 5 and a drain region 6 of a MOS transistor are formed.

In the present invention, the subsequent steps are also different from the conventional method. That is, conventionally, in order to activate impurities implanted into the source/drain regions, heat treatment was performed at about 1000° C. in an N ₂ gas atmosphere. However, in the present invention, this heat treatment is performed in an atmosphere containing H ₂ gas. i.e. 10% _H2 gas, 90% _H2 gas
Heat at 1000°C for 30 minutes in a H ₂ -N ₂ mixed gas containing 1 atm. Additionally, this heat treatment is performed using N ₂
Heat treatment at 1000° C. may be performed in a gas atmosphere, followed by heat treatment at 1000° C. in an N ₂ -N ₂ mixed gas atmosphere.

As explained above, the present invention is characterized in that both the step of depositing the metal film for electrodes and the subsequent high-temperature heat treatment step of about 1000° C. are performed in an atmosphere containing H ₂ gas.

Next, the mobile ion density of the MOS capacitor manufactured in this example will be explained using the drawings.
Figure 3 shows a P-type Si manufactured using the process shown in this example.
(100) A MOS capacitor with a gate oxide film thickness of 400 Å and a Mo gate electrode shape of 500 μm square was formed on a substrate, and the mobile ion density was measured using the TVS method (Triangular Voltage Sweep Method). The horizontal axis shows the H ₂ gas partial pressure P _H2 in the sputtering gas, and the vertical axis shows the mobile ion density N _n in the gate oxide film. Before heat treatment, P _H2
Mobile ions are first detected when the temperature is increased to 2 × 10 ^-3 Torr, but when heat treatment is performed in N ₂ gas at 1000℃ for 30 minutes, N _n is about ~10 ¹² cm ^-2 regardless of P _H2 rapidly increasing. However, if heat treatment in _N2 gas (1000℃, 10 minutes) is followed by heat treatment in _H2 - _H2 mixed gas (1000℃, 10 minutes),
H _n decreases, and this decrease becomes particularly noticeable when P _H2 is 1×10 ⁻³ Torr or higher. On the other hand, when only heat treatment was performed in H ₂ - N ₂ mixed gas at 1000°C, the effect on N _n was even greater and decreased rapidly as P _H2 increased, P _H2 = 6 × 10 ^- At ⁴ Torr, mobile ions become undetectable. From these experimental results, the addition of _H2 gas into the sputtering gas is
It was confirmed that heat treatment in a H ₂ -N ₂ mixed gas further promoted the N _n reduction effect.

As shown in the above examples, in addition to the conventional heat treatment in an atmosphere containing N ₂ gas, the metal film for the electrode is also formed in an atmosphere containing N ₂ gas as in the present invention. Even in MOS semiconductor devices whose gate electrodes are made of high-melting point metal films that are relatively difficult to purify, it is possible to reduce the mobile ion density in the gate insulating film to the detection limit of ~10 ¹⁰ cm ^-2 . It became clear that it was possible.

Furthermore, this effect does not appear simply by forming the metal film for electrodes in an atmosphere containing _H2 gas, but
It became clear that combination with heat treatment in an atmosphere containing H ₂ gas was essential. Conventional heat treatment in an atmosphere containing _H2 gas reduces the mobile ion density by 1/13, but as shown in the present invention, a synergistic effect can be achieved by combining metal film formation in an atmosphere containing _H2 gas. The effect is obtained, and the mobile ion density is reduced by about 1/400.

In this example, Mo was used for the gate electrode, but
It is also possible to use other high melting point metals such as W, Ta, and Ti. Furthermore, heat treatment in a forming gas mainly composed of H ₂ gas has conventionally been carried out at a temperature of around 400°C in order to reduce the level density at the interface between Si and Sio ₂ . However, at such a relatively low temperature, the effect of reducing the mobile ion density, which is the objective of the present invention, cannot be obtained. Therefore, in the present invention, a high temperature of about 700° C. or higher is required as the heat treatment temperature. Although this example deals with a MOS type semiconductor device, the gate insulating film is not limited to Si oxide, and can be made of general MIS (Metal-
The present invention can be used for an insulator-semiconductor type semiconductor device. Also, MIS
It is clear that the present invention can be applied not only to type semiconductor devices but also to passivation insulating films for bipolar type semiconductor devices and the like.

As explained above, according to the present invention, both the process of depositing a high-melting point metal film for electrodes and wiring on the insulating film of a semiconductor device and the subsequent high-temperature heat treatment process are performed using H ₂
By carrying out the process in an atmosphere containing gas, the density of mobile ions contained in the insulating film can be significantly reduced.

As a result, the mobile ion density can be reduced to 1×10 ¹⁰ cm ⁻² or less, which is 1/400 or less compared to the case where the present invention is not used. Further, compared to the conventionally known effect of reducing the mobile ion density by heat treatment in an atmosphere containing H ₂ gas, the present invention can further reduce the density by one order of magnitude. This is a synergistic effect obtained by combining the heat treatment in an atmosphere containing H ₂ gas and the metal film deposition in an atmosphere containing H ₂ gas, which is the method of the present invention. Therefore, in the semiconductor device manufactured in this way, even if a bias temperature acceleration test is performed, the deterioration of the characteristics of the semiconductor device caused by the movement of mobile ions is significantly improved. Therefore, the present invention has the effect of significantly improving the reliability of semiconductor devices.

[Brief explanation of drawings]

FIGS. 1a to 1c are enlarged sectional views of main parts for explaining the conventional manufacturing process of a MOS transistor, and FIGS. 2a to 2d are main parts for explaining the manufacturing process of a MOS type semiconductor device according to the present invention. The enlarged sectional view, FIG. 3, is a characteristic diagram showing the relationship between H ₂ gas partial pressure and mobile ion density. 1...Si substrate, 2...Si oxide film for element isolation, 3
... Gate oxide film, 4 ... Gate electrode, 5 ... Source region, 6 ... Drain region, 7 ... Mo gate electrode film, 8 ... Mo gate electrode.

Claims (1)

[Claims] 1. A step of forming an insulating film on the surface of the semiconductor substrate,
A process of depositing a high melting point metal film on the insulating film in an atmosphere containing hydrogen gas, a process of patterning the high melting point metal film to form electrode wiring, and a high temperature heat treatment in an atmosphere containing hydrogen gas. 1. A method of manufacturing a semiconductor device, the method comprising: