JP4506056B2 - Method of nitriding object and semiconductor element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for nitriding a workpiece, by which a nitride film (insulating layer) of good characteristics can be formed in a state to highly hold the controllability of a film thickness. SOLUTION: In the nitriding method for nitriding the surface of the workpiece W that is made at a prescribed temperature in a treating vessel 2, the nitriding is performed by using H2 and NH3 under a reduced pressure atmosphere to form nitride films 76, 82. As a result, the nitride film (insulating layer) of good characteristics is formed in a state to highly hold the controllability of the film thickness.

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for nitriding an object to be processed, which performs a nitriding process on the surface of an object to be processed such as a semiconductor wafer, and a semiconductor element.
[0002]
[Prior art]
In general, in order to manufacture a semiconductor integrated circuit, various processes such as a film formation process, an etching process, an oxidation process, a diffusion process, a modification process, and a nitriding process are performed on a semiconductor wafer made of a silicon substrate or the like. Among the various processes described above, for example, when an oxidation process is taken as an example, this oxidation process is known to oxidize the surface of a single crystal or a polysilicon film, or to oxidize a metal film, etc. In particular, it is mainly used when forming an insulating film such as a gate insulating film or a capacitor.
[0003]
From the viewpoint of pressure, the oxidation treatment method includes a normal pressure oxidation treatment method performed in a treatment vessel under an atmosphere substantially equal to atmospheric pressure and a reduced pressure oxidation treatment method carried out in a treatment vessel under a vacuum atmosphere. In addition, from the viewpoint of the type of gas used for oxidation, for example, a wet oxidation method (for example, a special method) in which water vapor is generated by burning hydrogen and oxygen in an external combustion apparatus and oxidation is performed using the water vapor. (Kaihei 3-140453, etc.) and a dry oxidation treatment method in which oxidation is carried out without using water vapor by flowing only oxygen or a gas obtained by adding an inert gas to oxygen into the treatment vessel (for example, Japanese Patent Laid-Open No. Sho-sho). 57-1232 etc.).
[0004]
[Problems to be solved by the invention]
By the way, in consideration of film quality characteristics such as pressure resistance, corrosion resistance, and reliability, an insulating film is generally formed by a wet evolution process rather than a dry oxidation process. It is relatively good. Further, from the viewpoint of the film formation rate of the oxide film (insulating film) to be formed and the uniformity within the wafer surface, in general, an object formed by normal-pressure wet oxidation treatment has a high oxidation rate. In addition, the in-plane uniformity of the film thickness is inferior, and the product formed by the wet oxidation treatment under reduced pressure has the characteristic that the oxidation rate is small but the in-plane uniformity of the film thickness is excellent.
[0005]
Conventionally, since the design rule of the semiconductor integrated circuit was not so strict, various oxidation methods as described above were used in consideration of the application, process conditions, equipment cost, etc. to which the oxide film is applied. It was done. However, as line width and film thickness become smaller and design rules become stricter as recently, higher quality and in-plane uniformity of film quality are required accordingly. However, in the oxidation method, there has been a problem that an insulating film that sufficiently meets this requirement cannot be formed. For example, it is generally said that the higher the temperature is, the better the quality of the insulating film can be formed. However, an insulating film having a thickness of 1 nm or more can be formed in the temperature raising process, the temperature lowering process, and the process of stabilizing the temperature in the processing vessel. In some cases, it is difficult to form an insulating film of 1.5 nm or less with good controllability.
[0006]
In addition, as an example of forming an insulating film by a wet oxidation method, for example, as shown in JP-A-4-18727, H ₂ gas and O ₂ gas are separately introduced into the lower end of a vertical quartz reaction tube, Proposal is also made for an oxidizer that burns this in a combustion section provided in the quartz cap to generate water vapor, and raises the water vapor along the wafer arrangement direction to perform an oxidation process to form an insulating film. Has been.
However, in this case, since the H ₂ gas is burned in the above-described combustion section, for example, the lower end of the processing vessel becomes water vapor rich, and as the water vapor rises, it is consumed and consumed. On the contrary, since the water vapor tends to be insufficient at the upper end, the thickness of the insulating film formed on the wafer surface may vary greatly depending on the support position of the wafer, and the inter-surface uniformity of this insulating film thickness deteriorates. There was a case.
[0007]
As another example of the apparatus, as disclosed in, for example, Japanese Patent Application Laid-Open No. 57-1232, a plurality of semiconductor wafers are arranged side by side in a horizontal batch type reaction tube. _There has also been proposed an oxidizer in which an insulating film is generated in a reduced pressure atmosphere by introducing _two gases or introducing O ₂ gas and H ₂ gas simultaneously.
However, in the case of this conventional apparatus example, since the film formation is performed under a relatively high pressure atmosphere using the hydrogen combustion oxidation method, the water vapor component becomes the main component of the reaction, and as described above, The difference in water vapor concentration between the upstream side and the downstream side of the gas flow becomes too large, and the inter-surface uniformity of the thickness of the insulating film may be deteriorated.
As another example of the apparatus, as disclosed in, for example, US Pat. No. 6,037,273, oxygen gas and hydrogen gas are supplied into a single-wafer process chamber by lamp heating, and both these gases are supplied to the process chamber. An apparatus is shown in which water vapor is generated by reacting in the vicinity of the surface of a semiconductor wafer placed inside, and an insulating film is formed by oxidizing silicon on the wafer surface with this water vapor.
[0008]
However, in the case of this apparatus example, oxygen gas and hydrogen gas are introduced into the process chamber from a gas inlet separated from the wafer by about 20 to 30 mm, and these oxygen gas and hydrogen gas are introduced in the vicinity of the semiconductor wafer surface. Is generated in a region where the process pressure is relatively high, and there is a problem that the in-plane uniformity of the film thickness may be inferior.
Therefore, the applicant of the present application proposes a method of forming an insulating film with good characteristics by using mainly hydrogen radical active species and oxygen active species in Japanese Patent Application No. 2001-128350, and can achieve some improvement. However, there was room for further improvement in characteristics.
The present invention has been devised to pay attention to the above problems and to effectively solve them. An object of the present invention is to provide a method for nitriding an object to be processed and a semiconductor element capable of forming a nitride film (insulating layer) having good characteristics while maintaining high controllability of the film thickness.
[0009]
[Means for Solving the Problems]
As a result of intensive studies on the formation of the insulating layer, the present inventors have conducted a nitriding treatment on a silicon substrate or a silicon oxide film (SiO ₂ ) using H ₂ gas and NH ₃ gas, thereby achieving a relatively low temperature, for example 600 By obtaining the knowledge that a nitride film having good characteristics can be formed as an insulating layer even at a moderate degree, the present invention has been achieved.
Invention, polycrystalline surface of the object has been made to a predetermined temperature in the processing vessel, or a single crystal silicon layer in the nitride method of nitriding, and H ₂ under a reduced pressure atmosphere NH prescribed in claim 1 ₃ is used to form a nitride film by performing the nitriding process.
This makes it possible to form a nitride film (insulating layer) with good electrical characteristics with good controllability of film thickness.
[0010]
In this case, for example, as defined in claim 2, an inert carrier gas may be used to supply the H ₂ and / or NH ₃ .
Further, for example, as defined in claim 3, the temperature of the nitriding treatment is in the range of 400 to 1000 ° C..
Defined in claim 4 invention relates to a semiconductor device using the insulating layer formed by the above method, i.e., in the semiconductor device of a multilayer structure having a gate insulating layer, as a pre-Symbol gate insulation layer, the present invention A semiconductor element characterized by using a nitride film formed by the method.
[0011]
Defined in claim 5 invention is a semiconductor device of a multilayer structure having a base layer under the gate insulation layer of a high dielectric material, as the underlying layer, a nitride film formed by the above process of this invention This is a semiconductor element characterized by the above.
As defined in this case, for example, in claim 6, wherein the metal oxide film _is one of the _{Al 2 O 3, Ta 2 O} 5, HfO 2, ZrO 2, La 2 O 3 and _Ln 2 _{O 3} is there.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of a method for nitriding a target object and a semiconductor element according to the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a cross-sectional view showing an example of a semiconductor device according to a first embodiment of the present invention, FIG. 2 is a cross-sectional view showing a semiconductor device according to a second embodiment of the present invention, and FIG. It is a block diagram which shows an example of the heat processing apparatus used in order to implement a method. First, an application in which a nitride film formed by the nitriding method of the present invention is used will be described.
[0013]
In FIG. 1, W is a semiconductor wafer made of a silicon substrate or the like as an object to be processed, and is doped with, for example, P-type or N-type impurities. For example, a semiconductor element 70 is formed on the upper surface of the semiconductor wafer W. The semiconductor element 70 is a gate element, and has a multilayer structure in which a gate insulating layer 74 is interposed between the surface of the wafer W and a gate electrode 72 made of, for example, polysilicon. In the first embodiment, a nitride film 76 formed by the method of the present invention described later is used as the gate insulating layer 74. The nitride film 76 is formed by nitriding a silicon film or a silicon oxide film (SiO ₂ ) by the method of the present invention. At this time, the thickness of the gate insulating layer 74 made of the nitride film 76 is, for example, 1.5 nm or less, depending on the specifications of the device.
[0014]
FIG. 2 shows a semiconductor element 78 of the second embodiment, and this semiconductor element 78 is also a gate element. Here, a nitride film is not used as the gate insulating layer 74, and for example, a high dielectric material is used. Note that the present invention is not limited to this, and a normal oxide film or the like may be used as the insulating layer. A lower layer of the gate insulating layer 74 is provided as a boundary layer with the wafer surface, that is, an underlayer 80 is provided to form a multilayer structure. In the second embodiment, a nitride film 82 formed by the method of the present invention, which will be described later, is used as the base layer 80. At this time, the thickness of the base layer 80 made of the nitride film 82 is, for example, about several mm.
The present invention can also be applied to a multilayer structure in which an oxide film, a thin film of a high dielectric material, and a gate electrode are sequentially stacked on a silicon substrate.
Further, when the gate insulating layer 74 includes a thin film of a high dielectric material made of a metal oxide film as will be described later, the metal oxide film can be subjected to nitriding as shown below. According to this, a peak of nitrogen element exists in the thin film of the high dielectric material on the side close to the gate electrode, and the electrical characteristics of this element can be further improved.
[0015]
Next, the structure of the heat treatment apparatus for forming the nitride films 76 and 82 as described above will be described with reference to FIG.
The heat treatment apparatus 2 includes a vertical processing container 8 having a predetermined length of a double tube structure made of quartz made of an inner cylinder 4 and an outer cylinder 6. The processing space S in the inner cylinder 4 accommodates a quartz wafer boat 10 as a supporting means for holding the object to be processed. The wafer boat 10 includes a semiconductor wafer W as the object to be processed. Are held in multiple stages at a predetermined pitch. This pitch may be constant or may vary depending on the wafer position.
[0016]
A cap 12 is provided to open and close the lower portion of the processing container 8, and a rotating shaft 16 is provided through the cap 12 via a magnetic fluid seal 14. A rotary table 18 is provided at the upper end of the rotary shaft 16, a heat insulating cylinder 20 is provided on the table 18, and the wafer boat 10 is placed on the heat insulating cylinder 20. The rotating shaft 16 is attached to an arm 24 of a boat elevator 22 that can be moved up and down, and can be moved up and down integrally with the cap 12, the wafer boat 10 and the like. It can be inserted and removed from below. The wafer boat 10 may be fixed without rotating.
For example, a stainless steel manifold 26 is joined to the lower end opening of the processing vessel 8, and the flow rate controlled NH ₃ gas and H ₂ gas are introduced into the manifold 26 into the processing vessel 8. An NH ₃ gas supply system 28 and an H ₂ gas supply system 30 are individually provided.
[0017]
Specifically, first, the NH ₃ gas supply system 28 has a gas nozzle 32 provided through the manifold 26, and a flow rate controller 34 such as a mass flow controller is provided in the nozzle 32 on the way. A gas supply path 36 is connected. Then, this gas supply channel 36, the NH ₃ gas source 38 that stores the NH ₃ gas is connected.
Similarly, the H ₂ gas supply source 30 has a gas nozzle 40 provided through the manifold 26, and a flow rate controller 42 such as a mass flow controller is provided in the nozzle 40 in the middle. The gas supply path 44 is connected. Then, this gas supply path 44, the H ₂ gas source 46 that stores the H ₂ gas is connected.
[0018]
Accordingly, the gases supplied from the nozzles 32 and 40 ascend the wafer storage area, which is the processing space S in the inner cylinder 4, and turn downward at the ceiling, and the inner cylinder 4 and the outer cylinder 6. Then, it flows down in the gap of the gas and is discharged. Further, an exhaust port 50 is provided on the bottom side wall of the outer cylinder 6, and a vacuum exhaust system 56 formed by connecting a vacuum pump 54 to an exhaust path 52 is connected to the exhaust port 50. The inside of the processing container 8 is evacuated. Here, the distance H1 between the wafer storage area as the processing space S and the introduction position of each gas, specifically, the lower end of the wafer storage area, that is, the lower end of the wafer boat 10 and the nozzles 32, 40. The distance H1 between the gas outlet at the tip is separated by a predetermined distance. The first reason why the distance H1 is provided in this way is that heat from the processing container 8 heated by the heater 62 and brought into a hot wall state while each gas ascends the length of the distance H1. This is because the above gases are preliminarily heated. That is, in general, the temperature of the processing space S along the length direction of the wafer boat 10 is maintained substantially constant with high accuracy. For example, each gas at room temperature is introduced near the lower portion of the wafer boat 10. This is because the temperature in this portion is lowered and adversely affects the temperature distribution in the entire processing space S. The second reason is that when both gases rise over the length of the distance H1, these two gases are mixed well.
[0019]
Therefore, the distance H1 does not adversely affect the temperature distribution in the wafer storage area (processing space S), and is sufficiently long to sufficiently mix the introduced NH ₃ gas and H ₂ gas, for example, 100 mm. Above, preferably set to 300 mm or more. In this embodiment, the distance H1 is set to about 350 mm. In addition, a heat insulating layer 60 is provided on the outer periphery of the processing vessel 8, and a heater 62 is provided as a heating means on the inner side to heat the wafer W positioned inside to a predetermined temperature. ing.
Here, the overall size of the processing container 8 is, for example, the size of the wafer W to be processed is 8 inches, the number of wafers held in the wafer boat 10 is about 150 (about 130 product wafers, 20 dummy wafers, etc.). The diameter of the inner cylinder 4 is about 260 to 270 mm, the diameter of the outer cylinder 6 is about 275 to 285 mm, and the height of the processing container 8 is about 1280 mm.
[0020]
Further, when the size of the wafer W is 12 inches, the number of wafers held on the wafer boat 10 may be about 25 to 50. At this time, the diameter of the inner cylinder 4 is about 380 to 420 mm, The diameter of the cylinder 6 is about 440 to 500 mm, and the height of the processing container 8 is about 800 mm. The height H2 of the wafer boat 10 depends on the number of wafers and falls within a range of about 200 to 1000 mm, for example. These numerical values are merely examples.
In the figure, 64 is a seal member such as an O-ring that seals between the cap 12 and the manifold 26, and 66 is a seal member such as an O-ring that seals between the manifold 26 and the lower end of the outer cylinder 6. It is.
[0021]
Next, the method of the present invention performed using the heat treatment apparatus configured as described above will be described.
First, a large number of unprocessed semiconductor wafers W are held in multiple stages on the wafer boat 10 at a predetermined pitch, and in this state, the boat elevator 22 is lifted to drive the wafer boat 10 into the processing container 8 from below. Insert and seal the inside of the processing container 8. The inside of the processing container 8 is preheated in advance, and for example, a silicon oxide film or the like to be nitrided is formed on the surface of the semiconductor wafer W in the previous step. Further, the surface of the single crystal silicon wafer itself may be nitrided.
When the wafer W is inserted as described above, the supply voltage to the heater 62 is increased to raise the temperature of the wafer W to a predetermined process temperature, and the processing chamber 8 is evacuated by the vacuum exhaust system 56. .
[0022]
After reaching the predetermined temperature and pressure settings, the NH ₃ gas whose flow rate is controlled from the gas nozzle 32 of the NH ₃ gas supply system 28 is introduced into the processing vessel 8 and the flow rate is controlled from the gas nozzle 40 of the H ₂ gas supply system 30. The H ₂ gas thus introduced is introduced into the processing container 8.
In this way, NH ₃ gas and H ₂ gas separately introduced into the processing vessel 8 rise in the processing vessel 8 while the NH ₃ gas is decomposed and activated. At this time, this activation is H Promoted by _two gases, the active species will nitride the wafer surface. The active species generated at this time include NH, NH ₂ N, and the like. The nitriding process conditions at this time are as follows: the wafer temperature is in the range of 400 to 900 ° C., preferably in the range of 400 to 800 ° C. in consideration of the heat resistance of the underlying element, and the pressure is 133 Pa (1 Torr). Less, preferably in the range of 6.7 Pa (0.05 Torr) to 66.5 Pa (0.5 Torr) in consideration of the concentration distribution.
[0023]
Here, an inert gas such as N ₂ gas or Ar gas may be added as a carrier gas to one or both of H ₂ gas and NH ₃ gas.
In this way, by using only NH ₃ gas and H ₂ gas, which are reducing gases, without adding an oxidizing gas such as O ₂ , and by adding a small amount of H ₂ gas, the decomposition of NH ₃ gas is achieved. Activation is greatly promoted, and a nitride film can be formed by nitriding a silicon or silicon oxide film with sufficient controllability of film thickness even at a low temperature of about 600 ° C., for example.
In other words, in general, when nitriding is performed on an oxide film, when nitriding is performed using an oxidizing gas such as N ₂ O or NO, a large amount of nitrogen is distributed in the vicinity of the wafer interface. The current situation is that the nitrogen concentration distribution in the film cannot be controlled due to the occurrence of the nitrogen pile-up phenomenon, and the electron mobility of the device formed in such a state is extremely reduced. As described above, the nitrogen pile-up portion can be formed not at the interface with the wafer but at the interface with the gate electrode by nitriding the oxide film using NH ₃ gas and a slight amount of H ₂ gas. Devices can be obtained.
[0024]
By using the nitride film formed in this way as the nitride film 76 of the gate insulating layer 74 as shown in FIG. 1, a nitride film with high controllability of the film thickness can be formed, and the leakage current is small and good. A semiconductor element maintaining electrical characteristics can be obtained.
Further, by using the nitride film formed in this way as the nitride film 82 for forming the base layer 80 of the gate insulating layer 74 as shown in FIG. As a result, it is possible to significantly prevent impurities such as boron implanted into the gate electrode 72 from penetrating through the gate insulating layer 74 and penetrating to the wafer side. In particular, a high dielectric material such as Al ₂ O ₃ , Ta ₂ O ₅ , HfO ₂ , ZrO ₂ , La ₂ O ₃ , Ln ₂ O ₃ or the like may be used as the gate insulating layer 74. In such a case, the effects as described above can be remarkably expressed.
[0025]
Note that the gas flow rate, temperature, and the like described above are merely examples, and are not limited thereto. Although the case where the nitride film according to the method of the present invention is used for the gate insulating layer itself or the base layer of the gate insulating layer is described as an example here, the present invention is not limited to this, and may be used for an insulating film of a capacitor, for example.
In addition, the vertical heat treatment apparatus shown here is merely an example, and the present invention can be applied to a heat treatment apparatus of a type that supplies gas from the ceiling of the processing vessel, a single pipe heat treatment apparatus, and the like. Of course.
Although the method of the present invention has been described by taking a batch type vertical heat treatment apparatus as an example here, the present invention is not limited to this, and a lamp heating type or resistance heating type single wafer heat treatment apparatus may be used.
Further, the object to be processed is not limited to a semiconductor wafer, and can be applied to an LCD substrate, a glass substrate, and the like.
[0026]
【The invention's effect】
As described above, according to the method for nitriding an object to be processed and the semiconductor element of the present invention, the following excellent operational effects can be exhibited.
A nitride film (insulating layer) with good electrical characteristics can be formed with good controllability of film thickness.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing an example of a semiconductor device according to a first embodiment of the present invention.
FIG. 2 is a sectional view showing a semiconductor device according to a second embodiment of the present invention.
FIG. 3 is a configuration diagram showing an example of a heat treatment apparatus used for carrying out a method for nitriding an object according to the present invention.
[Explanation of symbols]
2 Heat treatment apparatus 4 Inner cylinder 6 Outer cylinder 8 Processing vessel 12 Support means (wafer boat)
28 NH ₃ gas supply system 30 H ₂ gas supply system 32 Gas nozzle 38 NH ₃ gas source 40 Gas nozzle 46 H ₂ gas source 56 Vacuum exhaust system 62 Heating heater (heating means)
70 Semiconductor element 72 Gate electrode 74 Gate insulating layer 76 Nitride film 78 Semiconductor element 80 Underlayer 82 Nitride film W Semiconductor wafer (object to be processed)

Claims (6)

Polycrystalline surface in the processing vessel was made to a predetermined temperature target object, or in the nitriding method for nitriding the single crystal silicon layer, the nitride by using H ₂ and NH ₃ at a reduced pressure atmosphere A method for nitriding an object to be processed, wherein a nitride film is formed by performing a treatment. _{2. The} method for nitriding a target object according to claim 1, wherein a carrier gas of an inert gas is used to supply the H ₂ and / or NH ₃ .   The method of nitriding an object to be processed according to claim 1 or 2, wherein a temperature of the nitriding treatment is in a range of 400 to 1000 ° C. In a semiconductor device having a multilayer structure having a gate insulating layer ,
As before Symbol gate insulation layer, a semiconductor element characterized in that a nitride film formed by the method described in any one of claims 1 to 3. In a semiconductor device having a multilayer structure having a base layer under a gate insulating layer made of a high dielectric material ,
Wherein as the base layer, a semiconductor element characterized in that a nitride film formed by the method described in one item of claims 1 to 3 Neu deviation. The gate insulating layer is made of Al. ₂  O ₃  , Ta ₂  O ₅  , HfO ₂  , ZrO ₂  , La ₂  O ₃  And Ln ₂  O ₃  6. The method for nitriding an object to be processed according to claim 5, wherein the method is one of the above.

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