JP3338915B2 - Method for manufacturing semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of forming a thin gate oxide film of a MOS type semiconductor device.

[0002]

2. Description of the Related Art Conventionally, with the miniaturization and high integration of MOS type semiconductor integrated circuit devices, the thickness of a gate oxide film has been reduced, and a gate oxide film corresponding to the thinner gate oxide film has been developed. There is a demand for improved reliability.

As a method of forming a gate oxide film in this conventional MOS type semiconductor integrated circuit device, a dry O ₂ oxidation method, a wet oxidation method, and a hydrochloric acid (HCl) oxidation method are known.

As a method for improving the characteristics of the gate oxide film, it is known to improve the breakdown voltage of the oxide film by adding a halogen element such as Cl to an oxidizing agent atmosphere. ₂ After forming an oxide film in an atmosphere or a wet atmosphere, heat treatment is performed in an NH ₃ or N ₂ O atmosphere to reduce the interface state by nitriding the interface between the silicon semiconductor substrate and the oxide film and the oxide film. It is also known to prevent the impurity from penetrating into the silicon substrate when impurity ions are implanted into the gate electrode.

[0005]

However, if a halogen element such as Cl is introduced into the oxide film by adding a halogen element such as Cl into the oxidizing agent atmosphere, the positive fixed charge increases, and thereafter, further increase It is necessary to perform heat treatment in an active gas atmosphere, and although the withstand voltage of the obtained gate oxide film has been improved, the film prevents the impurity from penetrating into the silicon semiconductor substrate during the ion implantation of the impurity into the gate electrode. Was still a weak film, and sufficient characteristics were not necessarily obtained.

Also, dry O_TwoAtmosphere or wet atmosphere
After forming an oxide film in air, NH 3 _ThreeOr N_TwoO atmosphere
In the case of nitriding in air, Cl.
Inert gas on oxide films formed by adding halogen elements such as
Interface state compared to heat treatment in
MOS characteristics such as breakdown voltage are inferior,
After all, sufficient characteristics were not obtained.

[0007] Accordingly, the present invention provides an ultra-miniaturized M
A gate required as a gate oxide film of an OS type semiconductor integrated circuit device, which has a small fixed charge in the oxide film, a low interface state density, is strong against stress application, and has a function of preventing impurity penetration into a substrate. The purpose is to form an oxide film.

[0008]

SUMMARY OF THE INVENTION The present invention provides a method for forming a gate oxide film in an atmosphere in which a gas containing a halogen element such as Cl or F is added to an oxidizing agent such as dry O _{2 or} a wet atmosphere. Oxidizing the silicon semiconductor substrate, then heat treating in a nitriding atmosphere , followed by an inert
It is characterized by cooling in gas .

Further, the present invention is characterized in that a nitriding atmosphere containing neither hydrogen nor moisture is used as the nitriding atmosphere. Further, the present invention is characterized in that a nitriding atmosphere containing hydrogen or moisture is used as the nitriding atmosphere, and thereafter, a heat treatment is further performed in an inert gas atmosphere.

[0010]

[Action] By heat treatment in a nitriding atmosphere performed after oxidation,
By nitriding the interface between the silicon semiconductor substrate and the silicon dioxide film, the interface state density is reduced, and the effect of preventing impurities injected into the gate electrode from penetrating into the silicon semiconductor substrate is increased.

In addition, during the nitridation or during the heat treatment after the nitridation, the halogen element such as Cl or F taken in the silicon dioxide film fills the defects induced during the nitridation, The bond with the unbonded electron pair (dangling bond) that still remains after that makes it possible to reduce traps and fixed charges in the silicon dioxide film.

Further, when a nitriding atmosphere containing neither hydrogen nor moisture is used as the nitriding atmosphere, the subsequent heat treatment becomes unnecessary, and when a nitriding atmosphere containing hydrogen or moisture is used as the nitriding atmosphere. Requires a heat treatment in an inert gas atmosphere in order to expel hydrogen caused by ammonia present in the silicon dioxide film.

[0013]

FIG. 1 is an explanatory view of a manufacturing process according to a first embodiment of the present invention. First, in an ordinary heat treatment furnace such as a heat diffusion furnace, the substrate temperature was raised to 950 ° C. in an atmosphere in which HCl was added to an oxidizing agent composed of dry O ₂ diluted with N ₂ gas as an inert gas.
In this state, an oxidation process is performed to form an oxide film having a thickness of 6 nm.

Next, the silicon semiconductor substrate is transferred to a lamp annealing apparatus and subjected to a heat treatment for 60 seconds at a substrate temperature of 950 ° C. in an N ₂ O atmosphere which is a nitriding gas atmosphere containing no hydrogen and moisture. Then, the interface between the silicon semiconductor substrate and the silicon dioxide film is nitrided. In this case, the surface of the silicon dioxide film is not completely nitrided.

Thereafter, the temperature is lowered to room temperature in an inert gas atmosphere to complete the gate oxide film forming step. Normally, thereafter, a gate electrode is deposited and patterned, and impurities are ion-implanted using the gate electrode (sidewall if necessary) as a mask to form a source and a drain, thereby completing the MOSFET. .

Next, the characteristics of the silicon dioxide film obtained by the first embodiment will be described with reference to FIGS. First, FIG. 2 explains the principle of the QS-CV method, and FIG. 3 shows the state of the interface state density measured by the QS-CV method. The effect of reducing the interface state density will be described.

Referring to FIG. 2 (a), the QS (quasi-static) -CV method is a method using a very low frequency (quasi-static) C
V measurement method. When the substrate applies a positive bias (+ V _G ) to a p-type MOS capacitor, majority carriers in the semiconductor substrate respond very quickly to the change in the bias voltage,
Minority carriers only respond very slowly,
In high frequency measurements, only the majority carrier responds and the majority carrier is repelled from the interface, reducing the capacitance.

On the other hand, very low frequency (quasi-stati)
c) In measurement, minority carriers (electrons in this case) are attracted to the substrate side to increase the capacity, but when the bias is small, a region where neither majority carriers nor minority carriers exist is formed near the surface. . FIG. 2A shows these measurement results.

FIG. 2 (b) and (c) an equivalent circuit of the MOS capacitor in the reference frequency measurements will series circuit of a capacitance C _ox and substrate capacitance C _S of the gate oxide film as shown in FIG. 2 (b) In addition, in an ultra-low frequency (quasi-static) measurement, electric charges flow into and out of the interface state, so that the equivalent circuit of the MOS capacitor has a capacitance of the gate oxide film as shown in FIG. and C _ox, is made of a series circuit of a parallel circuit of an equivalent capacitance C _it of substrate capacitance C _S and the interface state.

As is apparent from this equivalent circuit, QS-
The capacitance C _LF by CV measurement is as shown in the following equation (1).
The interface state density D _it is as shown in equation (2).

[0021]

(Equation 1)

It should be noted that the ideal MOS substrate capacitance C _s in this equation is obtained from the measurement result of the high frequency measurement. This interface state density D _it is a value near the Fermi level, and if the Fermi level changes according to the gate voltage, this value also changes. Therefore, a plot of the interface state density according to the interface potential is shown in FIG. You can draw like 3.

FIG. 3 is a graph showing the interface state density of a MOS capacitor in a 250 μm square with a polycrystalline Si gate after a gate oxide film was formed on p-type Si having a specific resistance of 10 Ω · cm under various conditions. It is the result of having measured. As is apparent from the figure, 950 ° C.
O ₂ oxidation at 950 ° C., N ₂ / O ₂ / HCl at 950 ° C.
Oxidation, dry O ₂ oxidation at 950 ° C. + N ₂ at 950 ° C.
O-nitriding, the first embodiment of the present invention, N ₂ at 950 ° C.
It can be confirmed that the interface state density is reduced in the order of / O ₂ / HCl oxidation + N ₂ O nitridation at 950 ° C., and the remarkable effect of the present invention is clear.

Next, the breakdown voltage characteristics of the gate oxide film in the MOS capacitor obtained by the voltage sweep method will be described with reference to FIG. This voltage sweep method measures an IV characteristic when a voltage is swept and applied at a certain time interval at a certain fixed time, and the voltage at the time when a certain appropriately determined determination current is reached, A Mode (initial destruction), B mode (2 to 8 MV / cm), C mode (intrinsic destruction), and the like.

Referring to FIG. 4, in FIG. 4, a voltage of 0.2 MV is swept at 0.1 second intervals, and the judgment current is set to 1 × 10 ⁻⁴ A, that is, 100 μm.
The results at the time of μA are shown.
FIG. 7 is a -V characteristic diagram, and the diagram on the right is a histogram for mode division.

N ₂ / O ₂ at 950 ° C. shown in FIG.
In the case of / HCl oxidation, except that a slight A-mode failure is observed, the current flowing at 100 μA is not less than 8 MV / cm.
Most of the modes, that is, non-defective products. FIG.
In the case of dry O ₂ oxidation at 950 ° C. and N ₂ O nitridation at 950 ° C. shown in (b), a considerable A-mode failure is observed, and a 100 μA flowing voltage of 2 to 8 MV / cm B
Mode failures are also considerably observed, and it can be understood that this method cannot manufacture a gate insulating film having excellent withstand voltage with good yield.

In the case of N ₂ / O ₂ / HCl oxidation at 950 ° C. + N ₂ O nitridation at 950 ° C., which is the first embodiment of the present invention shown in FIG. Is hardly seen, and it can be understood that the highest withstand voltage is obtained among the three examples.

Next, with reference to FIG. 5, a state of a failure with respect to time when a constant current stress is applied will be described. FIG. 5 shows the cumulative failure rate (Cumulative Fa) over time when a constant current of 1 mA / cm ² is applied.
ilure).

In this case as well, dry O ₂ oxidation at 950 ° C., N ₂ / O ₂ / HCl oxidation at 950 ° C., dry O ₂ oxidation at 950 ° C. + N ₂ O nitridation at 100 ° C. Example 1 N ₂ / O ₂ / HCl at 950 ° C.
It can be seen that the cumulative failure rate is greatly reduced in the order of oxidation and N ₂ O nitridation at 1100 ° C. In this case, the nitriding temperature in the first embodiment of the present invention was changed from 950 ° C. to 1100 ° C. in order to shorten the processing speed.

Therefore, by employing the structure of the embodiment of the present invention, the interface state density is reduced and the dielectric breakdown voltage of the gate oxide film is improved as compared with the conventional method of manufacturing a gate insulating film. More than that, the effect that the cumulative failure rate is reduced by several times or more, that is, the reliability is remarkably improved, can be confirmed, and the remarkable effect of the present invention is clear.

Next, a second embodiment of the present invention will be described with reference to FIG. First, as in the first embodiment, in an ordinary heat treatment furnace such as a heat diffusion furnace, an atmosphere in which HCl is added to an oxidizing agent composed of dry O ₂ diluted with N ₂ gas as an inert gas is used. Then, oxidation treatment is performed in a state where the substrate temperature is 950 ° C.,
An oxide film having a thickness of 6 nm is formed.

Next, the silicon semiconductor substrate is transferred to a lamp annealing apparatus and subjected to a heat treatment for 60 seconds in a NH ₃ atmosphere, which is a nitriding gas atmosphere containing hydrogen or water, at a substrate temperature of 850 ° C. for 60 seconds. The interface between the semiconductor substrate and the silicon dioxide film is nitrided. Also in this case, the surface of the silicon dioxide film is not completely nitrided.

Next, after performing a heat treatment for 60 seconds or more in a N ₂ gas atmosphere, which is an inert gas, at a substrate temperature of 950 ° C., the temperature is lowered to room temperature to complete the gate oxide film forming step. In this case, the heat treatment is performed for a time sufficient to drive out hydrogen in the silicon dioxide film, and the heat treatment time depends on the heat treatment temperature but has no particular upper limit. And also in this second embodiment,
As in the first embodiment, a remarkable improvement is obtained as compared with the conventional method for manufacturing a gate oxide film.

The processing temperature in each of the above embodiments is as follows.
The temperature is 950 ° C., 850 ° C., 1100 ° C., etc., but is not limited to these temperatures, and may be in the range of 800 ° C. to 1100 ° C., and it is not necessary to perform each step at the same temperature. It is good to go.

In each of the above embodiments, the heat treatment furnace and the lamp annealing apparatus are used in combination, but all the steps including the oxidation step may be performed using only the lamp annealing apparatus. Alternatively, all the steps may be performed in a normal heat treatment furnace.

In each of the above embodiments, Cl is used as the halogen element and HCl is used as the Cl source. However, the present invention is not limited to this, and another Cl source may be used. Other halogen elements such as F may be used.

In each of the above embodiments, the oxidizing agent was used.
Inert gas to dilute and NH_ThreeIn nitriding heat treatment
N as inert gas_TwoIs used, but argon
Other inert gas may be used.
O diluted with inert gas _TwoBesides, dry O_Twosingle
Germany, O_TwoAnd H_TwoWet O consisting of O_TwoAnd steamed
Ki (H_TwoO) or the latter two with an inert gas
A diluted oxidizing agent may be used.

[0038]

According to the present invention, a silicon semiconductor substrate is oxidized in an atmosphere in which a gas containing a halogen element such as Cl or F is added to an oxidizing agent such as dry O _{2 or} a wet atmosphere. By performing heat treatment in a nitriding atmosphere, it is possible to obtain a gate insulating film having a lower interface state density, a better withstand voltage due to hot carriers and the like, and a good resistance to current stress application, as a result. It is possible to obtain a semiconductor device with significantly improved reliability due to a significant decrease in the cumulative failure rate and the like.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of the principle of the QS-CV method.

FIG. 3 is a diagram showing a measurement result of an interface state density measured by a QS-CV method.

FIG. 4 is an explanatory diagram of a withstand voltage characteristic of a gate oxide film in a MOS capacitor obtained by a voltage sweep method.

FIG. 5 is a diagram showing a measurement result of a cumulative failure rate over time when a constant current stress is applied.

FIG. 6 is an explanatory diagram of a second embodiment of the present invention.

[Explanation of symbols]

 1 Capacitance of gate oxide film 2 Substrate capacitance 3 Equivalent capacitance of interface state

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-244125 (JP, A) JP-A-5-251428 (JP, A) JP-A-2-246334 (JP, A) JP-A-62-162 298115 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 29/78

Claims (4)

(57) [Claims] An oxidation treatment of a silicon semiconductor substrate in an atmosphere in which a gas containing a halogen element is added to an oxidizing agent,
Next, heat treatment is performed in a nitriding atmosphere , followed by an inert gas.
A method for manufacturing a semiconductor device, wherein the temperature is lowered in the semiconductor device. 2. The method according to claim 1, wherein a nitriding atmosphere containing neither hydrogen nor moisture is used as the nitriding atmosphere.
The manufacturing method of the semiconductor device described in the above. 3. The method of manufacturing a semiconductor device according to claim 1, wherein a nitriding atmosphere containing hydrogen or moisture is used as the nitriding atmosphere, and a heat treatment is further performed in an inert gas atmosphere. 4. The method according to claim 1, wherein the oxidizing agent is diluted with an inert gas.