JPWO2004097925A1 - Manufacturing method of semiconductor device - Google Patents

Abstract

Provided is a method for manufacturing a semiconductor device, in which boron ions ion-implanted into a gate electrode can be prevented from penetrating and a decrease in mobility of a channel region can be suppressed. A method for manufacturing a semiconductor device includes a step of forming a gate insulating layer on an active region of a semiconductor substrate, a step of introducing nitrogen from the surface side of the gate insulating layer with active nitrogen, and a gate insulating layer into which nitrogen is introduced, And an annealing process in an NO gas atmosphere so as to maintain a nitrogen concentration distribution that is high on the surface side and low at the interface with the semiconductor substrate.

Description

  The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for manufacturing a semiconductor device having a gate insulating film containing nitrogen.

In order to improve the integration degree and the operation speed of the semiconductor integrated circuit device, the MOSFET as a component is reduced in size and the gate insulating film is reduced in thickness. The gate electrode formed on the gate insulating film is usually formed of a polysilicon layer or a stacked layer of a polysilicon layer and a silicide layer. The polysilicon layer is usually ion-implanted with impurities simultaneously with the source / drain regions. N-type impurities are ion-implanted into the gate electrode and source / drain regions of the surface channel n-channel MOSFET. A p-type impurity is ion-implanted into the gate electrode and source / drain regions of the surface channel p-channel MOSFET.
When the gate insulating film becomes thin, a phenomenon that boron, which is a p-type impurity ion-implanted into the gate electrode of the surface channel type p-channel MOSFET, penetrates the gate insulating film and reaches the channel region. When boron is implanted into the channel region which is an n-type region, not only the threshold value is changed, but also the mobility is deteriorated.
It is known that introduction of nitrogen into the gate insulating film is effective for suppressing boron penetration. In order to introduce nitrogen into a silicon oxide film, a method of heating a silicon substrate by resistance heating or lamp heating in a nitride gas atmosphere such as NH ₃ gas, NO gas, or N ₂ O gas is known. A method of introducing a higher concentration of nitrogen into the surface of the silicon oxide film using nitrogen plasma is also known.
It is also known that when the gate insulating film becomes thinner, a tunnel current flows between the gate electrode and the channel region, and the gate leakage current increases. If a high dielectric constant insulating film with a higher dielectric constant is used instead of (a part of) the silicon oxide gate insulating film, the physical film thickness is increased while the gate capacitance is reduced while the inversion capacitance equivalent film thickness is kept thin. Can be suppressed. Silicon nitride oxide generally has a higher dielectric constant than silicon oxide, and is effective in increasing the physical film thickness while suppressing the inversion capacitance equivalent film thickness.
Japanese Patent Laid-Open No. 2002-198531 introduces nitrogen into a silicon oxide gate insulating film formed on a silicon substrate by remote plasma nitriding, and then oxynitrides the gate insulating film in an N ₂ O atmosphere at 800 ° C. to 1100 ° C. It has been proposed to redistribute nitrogen and form a gate insulating film having a uniform nitrogen concentration by annealing. It is stated that a transistor having a long lifetime and high reliability can be obtained by forming a gate insulating film having a uniform nitrogen concentration of 6 at% or more, for example, 8 at% or 10 at%.
Here, remote plasma nitridation is a process in which nitrogen plasma is generated by a microwave or the like in a plasma generation chamber different from the processing chamber containing the substrate, and active nitrogen is transferred to the processing chamber to perform nitriding.
When annealing is performed in an N ₂ O atmosphere, a part of the N ₂ O gas may be decomposed into N ₂ , O ₂ , NO, etc. Problems can arise in controlling the uniformity and uniformity between wafers.
In Japanese Patent Laid-Open No. 2002-110673, when nitrogen enters the vicinity of the interface on the Si substrate side, the mobility of the MOS transistor is reduced. It is proposed to introduce a lot of nitrogen. By performing radical nitridation using nitrogen gas on the silicon oxynitride film previously introduced with nitrogen, the nitrogen flow diffusing from the surface is suppressed, the amount of nitrogen introduced near the silicon substrate interface is suppressed, and the film surface It proposes to increase the nitrogen concentration.

An object of the present invention is to provide a method for manufacturing a semiconductor device having a thin gate insulating film and a MOSFET having excellent characteristics.
Another object of the present invention is to provide a method of manufacturing a semiconductor device that can suppress boron ion penetration through a gate electrode and suppress a decrease in mobility of a channel region. .
According to one aspect of the present invention, a step of forming a gate insulating layer on an active region of a semiconductor substrate, a step of introducing nitrogen with active nitrogen from the surface side of the gate insulating layer, and a gate insulating layer into which nitrogen is introduced And a step of performing an annealing process in a NO gas atmosphere so as to maintain a high nitrogen concentration distribution on the front surface side and a low nitrogen concentration distribution at the interface with the semiconductor substrate.

FIGs. 1A to 1F are cross-sectional views and graphs for explaining experiments conducted by the inventors and results thereof.
FIGs. 2A to 2D are cross-sectional views and graphs for explaining the experiment conducted by the inventor and the results thereof.
FIGs. 3A and 3B are a table and a graph showing the conditions and results of still another experiment conducted by the present inventors.
FIGs. 4A and 4B are a table and a graph showing the conditions and results of still another experiment conducted by the present inventors.
FIGs. 5A to 5D are cross-sectional views of a semiconductor substrate for explaining a method of manufacturing a semiconductor device according to an embodiment of the present invention.
FIGs. 6A and 6B are tables and graphs showing conditions and results of still another experiment conducted by the present inventors. FIGs. 7A, 7B, and 7C are a cross-sectional view schematically showing a configuration of a remote plasma nitriding apparatus and a decoupled RF nitrogen plasma apparatus, and a cross-sectional view schematically showing a configuration of a gate insulating layer using a high-k material.

Introducing nitrogen into the silicon oxide film is effective in preventing boron from penetrating through the gate insulating film in the ion implantation of boron into the gate electrode. However, as the gate insulating film becomes thinner, it becomes difficult to prevent boron from penetrating, and boron reaches the interface between the gate insulating film and the silicon substrate. When boron reaches the channel region, the mobility is lowered. Also, the boron concentration at the interface tends to be non-uniform.
By introducing active nitrogen generated by plasma into a silicon oxide film or a silicon oxynitride film, a nitrogen concentration distribution having a peak in the surface of the insulating film or in the film can be obtained. By using such plasma nitriding, it is possible to introduce more nitrogen while suppressing the nitrogen concentration at the interface with the substrate. A high nitrogen concentration is effective in suppressing boron penetration.
In addition, the dielectric constant of the insulating film can be increased by introducing more nitrogen. Increasing the physical film thickness while suppressing the inversion capacitance equivalent film thickness (Teff) is effective in suppressing gate leakage current.
By reducing the nitrogen concentration at the interface between the insulating film and the silicon substrate, the mobility in the channel region can be prevented from lowering. Further, it is effective for suppressing deterioration of NBTI (negative bias temperature instability) characteristics. The NBTI characteristic is a deterioration characteristic when the temperature is increased by applying stress.
The technique of generating nitrogen plasma at a location away from the substrate and introducing active nitrogen into the substrate is said to be a damage-free process that does not damage the substrate.
The present inventor has considered that even if active nitrogen generated in plasma is introduced into an insulating film of a silicon substrate arranged away from plasma, there is a possibility of causing some damage to the substrate. In order to recover this damage, annealing at a higher temperature than the nitrogen introduction process will be effective. Therefore, the influence of annealing treatment was examined.
FIGs. 1A to 1E are cross-sectional views showing a sample preparation process of an experiment conducted by the present inventors.
FIG. As shown to 1A, the mask which covers the active region 4 is formed in the surface of the silicon substrate 1, and anisotropic etching is performed to the silicon substrate 1, and the element isolation trench 2 is formed. An insulating layer such as silicon oxide is deposited so as to fill the element isolation trench 2, and an unnecessary insulating layer on the surface of the silicon substrate 1 is removed by chemical mechanical polishing (CMP) to embed an insulating film in the trench. An element isolation region 3 was formed by shallow trench isolation (STI).
FIG. As shown in FIG. 1B, a gate oxide film 5 having a thickness of 1.0 nm was formed on the surface of the active region 4 of the silicon substrate 1 in an oxygen atmosphere at 965 ° C.
FIG. As shown in FIG. 1C, nitrogen was introduced into the gate insulating film 5 in an atmosphere at 450 ° C. by active nitrogen derived from nitrogen plasma excited by a 1.5 kW microwave. Nitrogen is introduced into the surface of the silicon oxide film to form a silicon nitride oxide film 5x. For the introduction of active nitrogen, a remote plasma nitriding apparatus available from Applied Materials of Santa Clara, California, USA was used.
FIG. 7A schematically shows the configuration of the remote plasma nitriding apparatus. The plasma generation chamber 21 has N ₂ Gas is introduced and nitrogen plasma is generated. Active nitrogen (radicals) is generated from the nitrogen plasma and supplied into the reaction chamber 22. The reaction chamber 2 includes a lamp heating device 23 including a number of lamps, and can heat the wafer 24.
FIG. As shown in FIG. 1D, annealing treatment was performed in a nitrogen atmosphere at 1050 ° C. to recover the substrate damage caused by the introduction of active nitrogen. The silicon nitride oxide film 5x becomes a silicon nitride oxide film 5y by annealing.
FIG. As shown in FIG. 1E, a polycrystalline silicon layer having a thickness of 100 nm is deposited on the gate insulating film by CVD, and patterned using a resist pattern, thereby forming a gate electrode 6 having a gate length of about 0.5 μm to 1.0 μm. Formed. The gate insulating film 5y was also patterned to form the gate insulating film 5z.
After patterning the gate electrode, B, which is a p-type impurity, was ion-implanted to form an extension region 7. Thereafter, a silicon oxide film having a thickness of about 60 nm is deposited on the substrate so as to cover the gate electrode by chemical vapor deposition (CVD), reactive ion etching is performed, the silicon oxide film on the flat surface is removed, and the gate is removed. Sidewall spacers 8 were left only on the electrode sidewalls.
After the side wall spacer 8 was formed, p-type impurity B was further ion-implanted to form a high concentration source / drain region 9. In the ion implantation process, the p-type impurity B is also ion-implanted into the gate electrode 6. Thereafter, an interlayer insulating film was formed, an opening exposing the source / drain region and the gate electrode was formed, and an electrode was formed. A sample S1 was thus obtained.
For comparison, FIG. After the active nitrogen introduction step shown in FIG. 1D is not performed, and FIG. As shown in 1E, a comparative sample S2 in which a MOSFET was formed was also prepared.
FIG. 1F is a graph showing the characteristics of the two types of MOSFETs created. In the figure, the horizontal axis indicates Vg−Vth, which is obtained by subtracting the threshold value Vth from the gate voltage Vg, in the unit V. The vertical axis represents the normalized transconductance in units of mS × nm, which is obtained by multiplying the transconductance Gm by the inversion capacitance equivalent film thickness Teff and further multiplying the ratio W / L of the width W and the length L of the channel region. The transconductance is normalized regardless of the thickness of the gate insulating film and the size of the channel region.
The characteristic s1 of the sample S1 annealed at 1050 ° C. in the nitrogen atmosphere after the introduction of active nitrogen has higher transconductance in almost the entire region than the characteristic s2 of the sample S2 not annealed in the nitrogen atmosphere. Show. It is clear that the MOSFET characteristics are improved by the annealing treatment. It is considered that the carrier mobility is improved and the saturation current is improved.
Thus, it has been found that the transistor characteristics are improved by performing the annealing process after the introduction of active nitrogen. However, it was further investigated how the characteristics improvement changes depending on the conditions of the annealing process. Nitrogen (N ₂ ), Nitric oxide (NO), oxygen (O ₂ ) Was used.
First, FIG. The element isolation region 3 was formed on the silicon substrate by the same process as shown in 1A. FIG. By a process similar to that shown in 1B, O at a temperature of 965 ° C. ₂ The surface of the silicon substrate was thermally oxidized in an atmosphere to form a gate oxide film 5 having a thickness of 1.2 nm.
Then, FIG. A nitriding step similar to the step shown in 1C was performed at a substrate temperature of 550 ° C. At the stage where nitrogen was introduced, the thickness of the gate insulating film was 1.457 nm as measured by an ellipsometer.
FIG. As shown in 2A, the third sample S3 was annealed at 1050 ° C. in a nitrogen atmosphere after introducing nitrogen. This annealing process is an annealing process in an inert gas.
FIG. As shown in 2B, the fourth sample S4 was annealed at 950 ° C. in a NO atmosphere after introducing nitrogen. This annealing process is an annealing process involving oxidation and nitridation. Thereafter, annealing was performed at 1050 ° C. in a nitrogen atmosphere. At this stage, the thickness of the gate insulating film measured with an ellipsometer was 1.538 nm. Compared to the third sample, an annealing treatment in NO is added to the fourth sample. The film thickness increased by the annealing treatment in NO was 0.081 nm.
FIG. As shown in 2C, for the fifth sample S5, oxygen (O ₂ ) Annealing treatment at 1000 ° C. was performed in the atmosphere. This annealing process is an annealing process accompanied by oxidation. Thereafter, annealing was performed at 1050 ° C. in a nitrogen atmosphere. Compared to the third sample, O for the fifth sample ₂ An annealing process inside has been added.
Each annealing process is performed by rapid thermal annealing RTA and is very short. Thereafter, an insulated gate electrode and source / drain regions were formed as in the first and second samples.
FIG. 2D is a graph showing the characteristics of the created third, fourth, and fifth samples. The horizontal and vertical axes are FIG. Same as 1F.
The characteristic s3 of the third sample S3, which is slightly different from the first sample in the thickness of the gate insulating film and the temperature when active nitrogen is introduced, is shown in FIG. It was almost the same as the characteristic s1 of 1F. The characteristic s4 of the sample S4 subjected to the annealing treatment (nitriding, oxidizing) at 950 ° C. in the NO atmosphere after introducing the active nitrogen showed a clear improvement. The characteristic s5 of the sample S5 that was subjected to (oxidation) annealing at 1000 ° C. in an oxygen atmosphere after the introduction of active nitrogen was an intermediate characteristic between the two.
Summarizing these results, it is clear that the mutual conductance is improved by annealing after the introduction of active nitrogen. Even if the annealing process is performed in an oxygen atmosphere, the mutual conductance is improved as compared with the annealing process in a nitrogen atmosphere, but the mutual conductance is the highest when the annealing process is performed by nitriding oxidation annealing in an NO atmosphere. .
The inventors think that this is because silicon-oxygen-nitrogen (Si-O-N) bonds are efficiently formed in the vicinity of the interface on the substrate side by annealing in an NO atmosphere.
However, annealing treatment in an oxidizing or nitriding oxidizing atmosphere causes oxidation or nitridation oxidation of the substrate, and the gate insulating film becomes thick. When a transistor having an effective gate insulating film thickness of 2 nm or less is formed, an annealing process in an NO atmosphere in which the film thickness increase is small is more preferable. The increase in the insulating film thickness due to the annealing process in the NO gas atmosphere is preferably 0.2 nm or less. When a gate insulating film having a thickness of 1.7 nm or less is obtained, the initial oxide film thickness is preferably 1.5 nm or less.
As described in the prior art, it has been proposed to introduce active nitrogen (radical) into the silicon oxynitride film. The present inventor measured TDDB (time dependent dielectric breakdown), which is a reliability evaluation, in a semiconductor device having a gate insulating film formed by the following two types of manufacturing methods. In the manufacturing methods of (1) and (2), oxide film thickness, introduction of active nitrogen, NO heat treatment, N ₂ Although the order of the heat treatment is different, the contents of each treatment are the same.
(1) After forming a thermal oxide film, after heat treatment in an NO gas atmosphere, nitrogen is introduced by active nitrogen, and then N ₂ A gate insulating film heat-treated in a gas atmosphere, and
(2) After forming the thermal oxide film, nitrogen is introduced by active nitrogen, and then heat treatment is performed in an NO gas atmosphere. ₂ Gate insulation film heat-treated in a gas atmosphere.
Comparing yields that were below the fracture criterion after applying stress in the above measurement, it was 0% for the sample (1), but 88% for the sample (2), showing a large difference between the two.
That is, the sample of (2) has a nitrogen distribution in the insulating film almost the same as the sample of (1), but the difference in the effect on reliability is large. The present inventor believes that this is because a silicon-oxygen-nitrogen (Si-O-N) bond is efficiently formed in the vicinity of the interface on the substrate side by heat treatment in an NO atmosphere performed after the active nitrogen introduction treatment. Yes.
Note that after annealing in a NO gas atmosphere, the N ₂ The reason for performing the heat treatment in the gas atmosphere is to improve the NBTI characteristics, and is not an essential process.
As a plasma nitriding apparatus, in addition to a remote plasma nitriding apparatus, a decoupled RF nitrogen plasma apparatus available from Applied Materials, Inc. of Santa Clara, California is also known.
FIG. 7B schematically shows the configuration of a decoupled RF nitrogen plasma apparatus. In this apparatus, nitrogen plasma is generated by RF excitation of a coil 26 provided on the top of a reaction chamber 25 that houses a sample 27 in the lower part. Nitrogen plasma is generated only in the region away from the sample 27 along the upper wall of the reaction chamber. This device is hereinafter abbreviated as DPN.
Two types of samples were formed using a DPN nitriding apparatus.
FIG. 3A shows conditions for creating two types of samples S6 and S7 and a sample S8 for comparison.
First, FIG. A silicon oxide film having a thickness of 0.85 nm was formed with a lamp annealing apparatus in an oxygen atmosphere at 900 ° C. by a process similar to the process shown in 1A and 1B. Thereafter, nitrogen plasma was excited with 700 W of RF power in the DPN apparatus, and active nitrogen was introduced into the silicon oxide film of the substrate disposed below in the room temperature atmosphere.
The sixth sample S6 was subjected to oxidation annealing (RTO) in a reduced pressure oxygen atmosphere at 1000 ° C. after introduction of active nitrogen and then annealing (RTA) in a nitrogen atmosphere at 1050 ° C.
For the seventh sample S7, after introducing active nitrogen, nitriding oxidation annealing (RTNO) was performed in a NO gas atmosphere at 950 ° C., followed by annealing (RTA) in a nitrogen atmosphere at 1050 ° C. . For comparison, two types of sample S8 in which a gate electrode is formed only with a silicon oxide film were also prepared.
FIG. 3B shows the measurement results of these samples. The horizontal axis represents the inversion capacitance equivalent film thickness Teff in the unit of nm, and the vertical axis represents the gate leakage current Ig in the unit (A / cm ² ). The characteristic s8 of the sample in which the gate insulating film is formed of only the silicon oxide film is the two points indicated by x, and when extrapolated, it becomes a straight line.
The characteristic s6 of the sixth sample S6 is below the characteristic s8 of the comparative sample S8, and indicates that the gate leakage current can be reduced.
The measurement point s7 of the seventh sample S7 is a nitridation oxidation annealing process in NO, oxidation is suppressed, and the effective gate insulating film thickness is thinner than the measurement point s6. In addition, it exists below the characteristic s8, and shows that the gate leakage current can be reduced as in the case of the sample S6.
FIG. In the characteristics of 3B, the reduction degree of the gate leakage current is almost equal between the two samples S6 and S7. In sample S7, the effective gate insulating film thickness is reduced by 0.013 nm. Also, the mutual conductance Gm is excellent. As a characteristic of the semiconductor device, a saturation current can be improved by 3.6% in a MOS transistor having a gate length of 40 nm.
Further, the distribution of nitrogen in the gate insulating film into which active nitrogen was introduced was examined by secondary ion mass spectrometry (SIMS). As the active nitrogen introducing device, DPN was used, and the annealing treatment after the introduction of active nitrogen was performed in two kinds of atmospheres of oxygen and NO.
FIG. The table of 4A schematically shows the production process of two types of samples. In the ninth sample S9, a silicon oxide film having a thickness of 0.8 nm was formed by a lamp annealing apparatus in an oxygen atmosphere at 900 ° C., and active nitrogen was formed in the gate oxide film in a room temperature atmosphere by 700 W decoupled RF nitrogen plasma. Was introduced (DPN). Thereafter, annealing RTO was performed in a reduced pressure oxygen atmosphere at 1000 ° C., followed by annealing (RTA) in a nitrogen atmosphere at 1050 ° C.
In the tenth sample S10, a silicon oxide film having a thickness of 0.8 nm is formed as in the ninth sample S9. After introducing active nitrogen using a DPN device, an annealing process (RTNO) in a NO gas atmosphere at 950 ° C. is performed. Then, annealing treatment (RTA) in a nitrogen atmosphere at 1050 ° C. was further performed.
FIG. 4B is a graph showing the measurement results of these two types of samples. The horizontal axis indicates the depth from the surface in the unit of nm, and the vertical axis indicates the measured nitrogen concentration in the unit (atoms / cc). The characteristic s9 of the sample annealed in the oxygen atmosphere has a higher peak value near the surface, and the nitrogen concentration gradually decreases with the depth. The change in nitrogen concentration by one digit or more within the measurement range is shown, but the interface between the gate insulating film and the silicon substrate exists in the middle.
The thickness of the nitrided oxide film was 1.324 nm, the peak of nitrogen concentration was 8.6 at%, and the nitrogen concentration at the interface with the substrate was 3.6 at%. The nitrogen concentration at the interface is ½ or less of the peak nitrogen concentration.
The characteristic s10 of the sample S10 annealed in the NO atmosphere after the introduction of active nitrogen appears to have a somewhat flat peak on the surface side, but the nitrogen distribution by the introduction of active nitrogen and the annealing treatment in the NO atmosphere Should be included. After that, it shows a tendency to decrease with the depth while showing a slightly higher nitrogen concentration than the characteristic s9, and the distribution is substantially the same as the characteristic s9 from a certain depth.
The thickness of the nitrided oxide film was 1.174 nm, the peak of nitrogen concentration was 7.6 at%, and the nitrogen concentration at the interface with the substrate was 4.9 at%. If the thickness of the nitrided oxide film is increased, the nitrogen concentration at the substrate interface may be reduced to ½ or less of the peak nitrogen concentration. The nitrogen concentration at the interface with the substrate is 5 at% or less.
From the viewpoint of increasing the nitrogen concentration on the surface side and lowering the nitrogen concentration at the interface with the substrate, O ₂ Annealing in an oxidizing atmosphere such as However, the increase in the film thickness is larger than the annealing in the nitriding and oxidizing atmosphere. From the viewpoint of reducing the thickness of the nitrided oxide film and forming a transistor having an excellent driving capability, annealing in a nitrided oxidizing atmosphere such as NO may be suitable.
In any measurement result, the nitrogen concentration has a peak on the gate insulating film surface side, and continues to decrease toward the interface with the silicon substrate along with the depth. Therefore, a large amount of nitrogen can be introduced into the gate insulating film, and boron penetration can be effectively suppressed, and the nitrogen concentration at the interface with the silicon substrate is preferably suppressed to 5 at% or less, and the mobility in the channel region is reduced. It turns out that a fall can be suppressed.
Furthermore, the experiment was conducted under the condition that the excitation energy of the decoupled RF plasma was lowered from 700 W to 500 W, expecting that active nitrogen was introduced only near the surface of the silicon oxide film.
FIG. The table of 6A schematically shows the production process of three types of samples. In an eleventh sample S11, a silicon oxide film having a thickness of 0.8 nm is formed by a lamp annealing apparatus in an oxygen atmosphere at 900 ° C., and a gate oxide film is formed in a room temperature atmosphere by a 500 W decoupled RF nitrogen plasma without a bias electric field. Active nitrogen was introduced therein (DPN). Thereafter, annealing (RTO) was performed in a reduced pressure oxygen atmosphere at 1000 ° C., followed by annealing (RTA) in a nitrogen atmosphere at 1050 ° C.
In the twelfth sample S12, as in the eleventh sample, a silicon oxide film having a thickness of 0.8 nm is formed by a lamp annealing apparatus in an oxygen atmosphere at 900 ° C., and gated in a room temperature atmosphere by a 500 W decoupled RF nitrogen plasma. Active nitrogen was introduced into the oxide film (DPN). Thereafter, annealing (RTNO) was performed in a reduced pressure NO atmosphere at 950 ° C., followed by annealing (RTA) in a nitrogen atmosphere at 1050 ° C.
In the 13th sample S13, a silicon oxide film having a thickness of 0.8 nm is formed by a lamp annealing apparatus in a 900 ° C. oxygen atmosphere and is gated in a room temperature atmosphere by a 500 W decoupled RF nitrogen plasma. Active nitrogen was introduced into the oxide film (DPN). Thereafter, annealing treatment (RTO) is performed in a reduced pressure oxygen atmosphere at 1000 ° C., followed by annealing treatment (RTNO) in a reduced pressure NO atmosphere at 950 ° C., and further annealing treatment (RTA) in a nitrogen atmosphere at 1050 ° C. I did it. The reason why RTA is performed at a higher temperature after annealing in a NO atmosphere is to improve the NBTI characteristics and is not an essential process.
FIG. 6B is a graph showing the measurement results of these three types of samples. The horizontal axis indicates the depth from the surface in the unit of nm, and the vertical axis indicates the measured nitrogen concentration in the unit (atoms / cc).
The characteristic s11 of the eleventh sample S11 annealed in an oxygen atmosphere has a higher peak value near the surface, and the nitrogen concentration gradually decreases with depth. Nitrogen concentration change of one digit or more is shown in the measurement range. An interface between the gate insulating film and the silicon substrate exists in the middle.
The thickness of the nitrided oxide film was 1.189 nm, the nitrogen concentration peak was 7.5 at%, and the nitrogen concentration at the interface with the substrate was 2.2 at%. The nitrogen concentration at the interface is ½ or less of the peak nitrogen concentration.
The characteristic s12 of the twelfth sample S12 that has been annealed in an NO atmosphere after the introduction of active nitrogen has a broadened peak in the vicinity of the surface. Thereafter, while showing a nitrogen concentration slightly higher than the characteristic S11, it shows a tendency to decrease with the depth, but the nitrogen amount increases when approaching the interface, and has a characteristic distribution having two peaks at the surface and in the vicinity of the interface. Indicates. Annealing in an NO atmosphere seems to tend to introduce nitrogen near the interface with the substrate.
The thickness of the nitrided oxide film was 1.170 nm, the peak of the nitrogen concentration was 7.8 at%, and the nitrogen concentration at the interface with the substrate was 4.8 at%.
The characteristic s13 of the thirteenth sample S13 in which the nitrogen atmosphere is annealed after the introduction of active nitrogen and the NO atmosphere annealing is the same as the characteristic s11 of the oxygen annealing sample. Although it seems that there is a difference from the characteristic of s11, it is a difference within the measurement error of secondary ion mass spectrometry (SIMS). When approaching the interface, the amount of nitrogen increases and it can be confirmed that the interface is effectively nitrided in the NO atmosphere.
The thickness of the nitrided oxide film was 1.157 nm, the nitrogen concentration peak was 7.4 at%, and the nitrogen concentration at the interface with the substrate was 2.4 at%.
Even if the annealing is performed in an NO atmosphere after the introduction of active nitrogen to improve the characteristics, the nitrogen concentration at the interface with the substrate can be suppressed to 5 at% or less. By selecting the conditions, the nitrogen concentration at the interface can be made ½ or less of the nitrogen concentration at the surface. From the characteristics s12 and s13 of the samples S12 and S13, it can be seen that various nitrogen distributions can be realized by controlling the nitrogen distribution by the introduction of active nitrogen and the nitrogen distribution by the annealing treatment in the NO atmosphere. It is also possible to introduce nitrogen in the vicinity of the interface by annealing in a NO atmosphere without significantly destroying the sharp distribution shape due to the introduction of active nitrogen. It becomes easy to realize different nitrogen concentrations according to different requirements at the interface between the gate insulating film surface and the substrate.
FIG. 5A to 5D are cross-sectional views illustrating a method of manufacturing a semiconductor device according to an embodiment of the present invention based on the above experimental results.
FIG. As shown in FIG. 5A, an element isolation region 3 by STI is formed on a silicon substrate 1. Desired ion implantation is performed in the active region defined by the STI element isolation region to form an n-type well 4n and a p-type well 4p. Although only two wells are shown, a plurality of wells are formed simultaneously.
The exposed silicon substrate surface is subjected to pyrogenic oxidation at 800 ° C. to form a silicon oxide film 11 having a thickness of 7 nm. Pyrojec oxidation is a method in which oxidation is performed in an atmosphere in which hydrogen is burned in oxygen. The gate oxide film having a thickness of 7 nm serves as a gate insulating film for forming a MOSFET having an operating voltage of about 3V.
In the active region where a MOSFET for low voltage operation is formed, the grown silicon oxide film 11 is removed by etching. Dry oxidation is performed in an oxygen atmosphere at 965 ° C. to form a silicon oxide film 12 having a thickness of 1.2 nm. The gate oxide film having a thickness of 1.2 nm serves as a gate insulating film for forming a MOSFET having an operating voltage of about 1 to 1.2 V, for example. When a natural oxide film is present on the silicon substrate surface, the natural oxide film may be removed in a reducing atmosphere such as hydrogen radicals. A good quality silicon oxide film can be formed by oxidizing a clean silicon surface.
Although the case where a gate insulating layer having two types of thicknesses is formed has been described, a gate insulating layer having three or more types of thicknesses may be formed.
The thick silicon oxide film 11 previously formed by this oxidation also grows slightly. N-type and p-type wells having a thin gate insulating film 12 are also formed.
FIG. As shown in FIG. 5B, active nitrogen is introduced into the gate insulating films 11 and 12 in an atmosphere at 550 ° C. by RPN nitrogen plasma obtained by microwave of 1.5 kW. Active nitrogen is introduced, and the gate insulating films become silicon nitride oxide films 11x and 12x.
FIG. As shown in FIG. 5C, annealing is performed in a NO gas atmosphere at 950.degree. Due to the NO gas, the gate insulating film is further oxynitrided to recover the damage. In this way, gate insulating films 11y and 12y are formed. Subsequently, in order to suppress the deterioration of the NBTI characteristics, annealing at a higher temperature may be performed in a nitrogen atmosphere.
Thereafter, a polycrystalline silicon layer having a thickness of 100 nm is formed on the gate insulating film and patterned to a desired gate length using a resist pattern. A gate electrode having a gate length of 40 nm is formed on the thin gate insulating film 12y.
As shown in FIG. 5D, extension regions 7p and 7n are formed by ion implantation of n-type impurities and p-type impurities using a patterned gate electrode and a resist mask for selecting an n-channel region and a p-channel region as a mask. Thereafter, a silicon oxide film having a thickness of about 60 nm is deposited, and sidewall spacers 8 are formed by performing RIE. Source / drain regions 9n and 9p are formed by ion implantation of n-type impurities and p-type impurities using a gate electrode having sidewall spacers and a resist mask for separating the n-channel region and the p-channel region.
Thereafter, if necessary, the exposed silicon surface is silicided and covered with an interlayer insulating film. Openings are formed in the interlayer insulating film 2, lead plugs are formed, and further necessary wirings and interlayer insulating films are formed.
In this manner, a CMOS integrated circuit having a thin gate insulating layer and a thick gate insulating layer, which suppresses boron penetration even in the thin gate insulating layer and suppresses a decrease in mobility of the channel region is formed.
By such a process, a semiconductor device having a thin effective gate insulating film thickness of 2 nm or less, particularly 1.7 nm or less, capable of preventing boron penetration and suppressing reduction in mobility of the channel region is formed. .
As described above, according to the above-described embodiment, a nitrogen concentration that is high on the surface side and low at the interface with the silicon substrate is introduced into the gate insulating film, and boron penetration through the gate insulating film is suppressed and movement in the channel region is performed. Degree reduction can be suppressed.
Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. For example, depending on the purpose, annealing in NO diluted with an inert gas may be used instead of nitridation oxidation annealing in NO. Instead of the silicon oxide film, a silicon nitride oxide film containing 3 at% or less of nitrogen may be formed at the interface with the substrate as the insulating film formed first over the semiconductor substrate. A high-k material film having a high dielectric constant may be stacked over the silicon nitride oxide film.
FIG. 7C shows a configuration in which films of high-k (high dielectric constant) material are stacked. The high-k material has a significantly higher dielectric constant than silicon oxide. For example, a silicon oxide film 31 having a thickness of 0.58 nm is formed on the surface of the silicon substrate 30 in a 750 ° C. oxygen atmosphere by a lamp annealing apparatus, and the gate oxide film is formed in a room temperature atmosphere by a 500 W decoupled RF nitrogen plasma. Active nitrogen was introduced (DPN). Thereafter, annealing treatment (RTNO) in an NO gas atmosphere at 900 ° C. was performed, and further annealing treatment (RTA) in a nitrogen atmosphere at 1050 ° C. was performed. The nitrided oxide film thickness was 0.80 nm. It may be possible to further reduce the film thickness by adjusting the base oxide film thickness, plasma nitriding strength, NO gas annealing temperature, time, and the like. On this oxynitride film, an oxide film such as Al, Hf, Zr, or the like, and a high-k material film 32 such as an oxide silicate film thereof are formed, thereby preventing a reaction between the semiconductor substrate and the high-k material and ensuring reliability. A gate insulating film having excellent performance and driving capability can be provided.
It will be apparent to those skilled in the art that other various changes, modifications, combinations, and the like can be made.

Industrial applicability

  It is suitable for the manufacture of MOS transistors with advanced miniaturization.

  The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for manufacturing a semiconductor device having a gate insulating film containing nitrogen.

  In order to improve the integration degree and the operation speed of the semiconductor integrated circuit device, the MOSFET as a component is reduced in size and the gate insulating film is reduced in thickness. The gate electrode formed on the gate insulating film is usually formed of a polysilicon layer or a stacked layer of a polysilicon layer and a silicide layer. The polysilicon layer is usually ion-implanted with impurities simultaneously with the source / drain regions. N-type impurities are ion-implanted into the gate electrode and source / drain regions of the surface channel n-channel MOSFET. A p-type impurity is ion-implanted into the gate electrode and source / drain regions of the surface channel p-channel MOSFET.

  When the gate insulating film becomes thin, a phenomenon that boron, which is a p-type impurity ion-implanted into the gate electrode of the surface channel type p-channel MOSFET, penetrates the gate insulating film and reaches the channel region. When boron is implanted into the channel region which is an n-type region, not only the threshold value is changed, but also the mobility is deteriorated.

  It is known that introduction of nitrogen into the gate insulating film is effective for suppressing boron penetration. In order to introduce nitrogen into a silicon oxide film, a method of heating a silicon substrate by resistance heating or lamp heating in a nitride gas atmosphere such as NH 3 gas, NO gas, N 2 O gas or the like is known. A method of introducing a higher concentration of nitrogen into the surface of the silicon oxide film using nitrogen plasma is also known.

  It is also known that when the gate insulating film becomes thinner, a tunnel current flows between the gate electrode and the channel region, and the gate leakage current increases. If a high dielectric constant insulating film with a higher dielectric constant is used instead of (a part of) the silicon oxide gate insulating film, the physical film thickness is increased while the gate capacitance is reduced while the inversion capacitance equivalent film thickness is kept thin. Can be suppressed. Silicon nitride oxide generally has a higher dielectric constant than silicon oxide, and is effective in increasing the physical film thickness while suppressing the inversion capacitance equivalent film thickness.

  In Japanese Patent Laid-Open No. 2002-198531, nitrogen is introduced into a silicon oxide gate insulating film formed on a silicon substrate by a remote plasma nitriding process, and then the gate insulating film is annealed by oxynitriding in an N 2 O atmosphere at 800 ° C. to 1100 ° C. Thus, it has been proposed to redistribute nitrogen and form a gate insulating film having a uniform nitrogen concentration. It is stated that a transistor having a long lifetime and high reliability can be obtained by forming a gate insulating film having a uniform nitrogen concentration of 6 at% or more, for example, 8 at% or 10 at%.

  Here, remote plasma nitridation is a process in which nitrogen plasma is generated by a microwave or the like in a plasma generation chamber different from the processing chamber containing the substrate, and active nitrogen is transferred to the processing chamber to perform nitriding.

  When annealing is performed in an N2O atmosphere, it is considered that a part of the N2O gas is decomposed into N2, O2, NO, etc., the uniformity of the oxide film thickness increase amount, the nitrogen concentration increase amount within the wafer surface, and uniformity between wafers Problems can arise in controlling sex.

In Japanese Patent Laid-Open No. 2002-110673, when nitrogen enters the vicinity of the interface on the Si substrate side, the mobility of the MOS transistor is reduced. It is proposed to introduce a lot of nitrogen. By performing radical nitridation using nitrogen gas on the silicon oxynitride film previously introduced with nitrogen, the nitrogen flow diffusing from the surface is suppressed, the amount of nitrogen introduced near the silicon substrate interface is suppressed, and the film surface It proposes to increase the nitrogen concentration.
JP 2002-198531 A Japanese Patent Laid-Open No. 2002-110474

  An object of the present invention is to provide a method for manufacturing a semiconductor device having a thin gate insulating film and a MOSFET having excellent characteristics.

  Another object of the present invention is to provide a method of manufacturing a semiconductor device that can suppress boron ion penetration through a gate electrode and suppress a decrease in mobility of a channel region. .

  According to one aspect of the present invention, a step of forming a gate insulating layer on an active region of a semiconductor substrate, a step of introducing nitrogen with active nitrogen from the surface side of the gate insulating layer, and a gate insulating layer into which nitrogen is introduced And a step of performing an annealing process in a NO gas atmosphere so as to maintain a high nitrogen concentration distribution on the front surface side and a low nitrogen concentration distribution at the interface with the semiconductor substrate.

  Introducing nitrogen into the silicon oxide film is effective in preventing boron from penetrating through the gate insulating film in the ion implantation of boron into the gate electrode. However, as the gate insulating film becomes thinner, it becomes difficult to prevent boron from penetrating, and boron reaches the interface between the gate insulating film and the silicon substrate. When boron reaches the channel region, the mobility is lowered. Also, the boron concentration at the interface tends to be non-uniform.

  By introducing active nitrogen generated by plasma into a silicon oxide film or a silicon oxynitride film, a nitrogen concentration distribution having a peak in the surface of the insulating film or in the film can be obtained. By using such plasma nitriding, it is possible to introduce more nitrogen while suppressing the nitrogen concentration at the interface with the substrate. A high nitrogen concentration is effective in suppressing boron penetration.

  In addition, the dielectric constant of the insulating film can be increased by introducing more nitrogen. Increasing the physical film thickness while suppressing the inversion capacitance equivalent film thickness (Teff) is effective in suppressing gate leakage current.

  By reducing the nitrogen concentration at the interface between the insulating film and the silicon substrate, the mobility in the channel region can be prevented from lowering. Further, it is effective for suppressing deterioration of NBTI (negative bias temperature instability) characteristics. The NBTI characteristic is a deterioration characteristic when the temperature is increased by applying stress.

  The technique of generating nitrogen plasma at a location away from the substrate and introducing active nitrogen into the substrate is said to be a damage-free process that does not damage the substrate.

  The present inventor has considered that even if active nitrogen generated in plasma is introduced into an insulating film of a silicon substrate arranged away from plasma, there is a possibility of causing some damage to the substrate. In order to recover this damage, annealing at a higher temperature than the nitrogen introduction process will be effective. Therefore, the influence of annealing treatment was examined.

  FIGs. 1A to 1E are cross-sectional views showing a sample preparation process of an experiment conducted by the present inventors.

  FIG. As shown to 1A, the mask which covers the active region 4 is formed in the surface of the silicon substrate 1, and anisotropic etching is performed to the silicon substrate 1, and the element isolation trench 2 is formed. An insulating layer such as silicon oxide is deposited so as to fill the element isolation trench 2, and an unnecessary insulating layer on the surface of the silicon substrate 1 is removed by chemical mechanical polishing (CMP) to embed an insulating film in the trench. An element isolation region 3 was formed by shallow trench isolation (STI).

  FIG. As shown in FIG. 1B, a gate oxide film 5 having a thickness of 1.0 nm was formed on the surface of the active region 4 of the silicon substrate 1 in an oxygen atmosphere at 965 ° C.

  FIG. As shown in FIG. 1C, nitrogen was introduced into the gate insulating film 5 in an atmosphere at 450 ° C. by active nitrogen derived from nitrogen plasma excited by a 1.5 kW microwave. Nitrogen is introduced into the surface of the silicon oxide film to form a silicon nitride oxide film 5x. For the introduction of active nitrogen, a remote plasma nitriding apparatus available from Applied Materials of Santa Clara, California, USA was used.

  FIG. 7A schematically shows the configuration of the remote plasma nitriding apparatus. N2 gas is introduced into the plasma generation chamber 21 to generate nitrogen plasma. Active nitrogen (radicals) is generated from the nitrogen plasma and supplied into the reaction chamber 22. The reaction chamber 2 is provided with a lamp heating device 23 including a number of lamps, and can heat the wafer 24.

  FIG. As shown in FIG. 1D, annealing treatment was performed in a nitrogen atmosphere at 1050 ° C. to recover the substrate damage caused by the introduction of active nitrogen. The silicon nitride oxide film 5x becomes a silicon nitride oxide film 5y by annealing.

  FIG. As shown in FIG. 1E, a polycrystalline silicon layer having a thickness of 100 nm is deposited on the gate insulating film by CVD, and patterned using a resist pattern, thereby forming a gate electrode 6 having a gate length of about 0.5 μm to 1.0 μm. Formed. The gate insulating film 5y was also patterned to form the gate insulating film 5z.

  After patterning the gate electrode, B, which is a p-type impurity, was ion-implanted to form an extension region 7. Thereafter, a silicon oxide film having a thickness of about 60 nm is deposited on the substrate so as to cover the gate electrode by chemical vapor deposition (CVD), reactive ion etching is performed, the silicon oxide film on the flat surface is removed, and the gate is removed. Sidewall spacers 8 were left only on the electrode sidewalls.

  After the side wall spacer 8 was formed, p-type impurity B was further ion-implanted to form a high concentration source / drain region 9. In the ion implantation process, the p-type impurity B is also ion-implanted into the gate electrode 6. Thereafter, an interlayer insulating film was formed, an opening exposing the source / drain region and the gate electrode was formed, and an electrode was formed. A sample S1 was thus obtained.

  For comparison, FIG. After the active nitrogen introduction step shown in FIG. 1D is not performed, and FIG. As shown in 1E, a comparative sample S2 in which a MOSFET was formed was also prepared.

  FIG. 1F is a graph showing the characteristics of the two types of MOSFETs created. In the figure, the horizontal axis indicates Vg−Vth, which is obtained by subtracting the threshold value Vth from the gate voltage Vg, in the unit V. The vertical axis represents the normalized transconductance in units of mS × nm, which is obtained by multiplying the transconductance Gm by the inversion capacitance equivalent film thickness Teff and further multiplying the ratio W / L of the width W and the length L of the channel region. The transconductance is normalized regardless of the thickness of the gate insulating film and the size of the channel region.

  The characteristic s1 of the sample S1 annealed at 1050 ° C. in the nitrogen atmosphere after the introduction of active nitrogen has higher transconductance in almost the entire region than the characteristic s2 of the sample S2 not annealed in the nitrogen atmosphere. Show. It is clear that the MOSFET characteristics are improved by the annealing treatment. It is considered that the carrier mobility is improved and the saturation current is improved.

  Thus, it has been found that the transistor characteristics are improved by performing the annealing process after the introduction of active nitrogen. However, it was further investigated how the characteristics improvement changes depending on the conditions of the annealing process. Nitrogen (N2), nitric oxide (NO), and oxygen (O2) were used as the atmosphere for the annealing treatment.

  First, FIG. The element isolation region 3 was formed on the silicon substrate by the same process as shown in 1A. FIG. By the same process as shown in 1B, the surface of the silicon substrate was thermally oxidized in an O 2 atmosphere at a temperature of 965 ° C. to form a gate oxide film 5 having a thickness of 1.2 nm.

  Then, FIG. A nitriding step similar to the step shown in 1C was performed at a substrate temperature of 550 ° C. At the stage where nitrogen was introduced, the thickness of the gate insulating film was 1.457 nm as measured by an ellipsometer.

  FIG. As shown in 2A, the third sample S3 was annealed at 1050 ° C. in a nitrogen atmosphere after introducing nitrogen. This annealing process is an annealing process in an inert gas.

  FIG. As shown in 2B, the fourth sample S4 was annealed at 950 ° C. in a NO atmosphere after introducing nitrogen. This annealing process is an annealing process involving oxidation and nitridation. Thereafter, annealing was performed at 1050 ° C. in a nitrogen atmosphere. At this stage, the thickness of the gate insulating film measured with an ellipsometer was 1.538 nm. Compared to the third sample, an annealing treatment in NO is added to the fourth sample. The film thickness increased by the annealing treatment in NO was 0.081 nm.

  FIG. As shown in 2C, the fifth sample S5 was annealed at 1000 ° C. in an oxygen (O 2) atmosphere after introducing nitrogen. This annealing process is an annealing process accompanied by oxidation. Thereafter, annealing was performed at 1050 ° C. in a nitrogen atmosphere. Compared to the third sample, an annealing treatment in O 2 is added to the fifth sample.

  Each annealing process is performed by rapid thermal annealing RTA and is very short. Thereafter, an insulated gate electrode and source / drain regions were formed as in the first and second samples.

  FIG. 2D is a graph showing the characteristics of the created third, fourth, and fifth samples. The horizontal and vertical axes are FIG. Same as 1F.

  The characteristic s3 of the third sample S3, which is slightly different from the first sample in the thickness of the gate insulating film and the temperature when active nitrogen is introduced, is FIG. It was almost the same as the characteristic s1 of 1F. The characteristic s4 of the sample S4 subjected to the annealing treatment (nitriding, oxidizing) at 950 ° C. in the NO atmosphere after introducing the active nitrogen showed a clear improvement. The characteristic s5 of the sample S5 that was subjected to (oxidation) annealing at 1000 ° C. in an oxygen atmosphere after the introduction of active nitrogen was an intermediate characteristic between the two.

  Summarizing these results, it is clear that the mutual conductance is improved by annealing after the introduction of active nitrogen. Even if the annealing process is performed in an oxygen atmosphere, the mutual conductance is improved as compared with the annealing process in a nitrogen atmosphere, but the mutual conductance is the highest when the annealing process is performed by nitriding oxidation annealing in an NO atmosphere. .

  The inventors think that this is because silicon-oxygen-nitrogen (Si-O-N) bonds are efficiently formed in the vicinity of the interface on the substrate side by annealing in an NO atmosphere.

  However, annealing treatment in an oxidizing or nitriding oxidizing atmosphere causes oxidation or nitridation oxidation of the substrate, and the gate insulating film becomes thick. When a transistor having an effective gate insulating film thickness of 2 nm or less is formed, an annealing process in an NO atmosphere in which the film thickness increase is small is more preferable. The increase in the insulating film thickness due to the annealing process in the NO gas atmosphere is preferably 0.2 nm or less. When a gate insulating film having a thickness of 1.7 nm or less is obtained, the initial oxide film thickness is preferably 1.5 nm or less.

As described in the prior art, it has been proposed to introduce active nitrogen (radical) into the silicon oxynitride film. The present inventor measured TDDB (time dependent dielectric breakdown), which is a reliability evaluation, in a semiconductor device having a gate insulating film formed by the following two types of manufacturing methods. In the manufacturing methods (1) and (2), the oxide film thickness, active nitrogen introduction, NO heat treatment, and N2 heat treatment are different in order, but the contents of each treatment are the same.
(1) After forming the thermal oxide film, after heat-treating in an NO gas atmosphere, nitrogen is introduced by active nitrogen, and then heat-treated in an N2 gas atmosphere, and (2) after forming the thermal oxide film, A gate insulating film in which nitrogen is introduced by active nitrogen, heat-treated in an NO gas atmosphere, and then heat-treated in a higher temperature N 2 gas atmosphere.

  Comparing yields that were below the fracture criterion after applying stress in the above measurement, it was 0% for the sample (1), but 88% for the sample (2), showing a large difference between the two.

  That is, the sample of (2) has a nitrogen distribution in the insulating film almost the same as that of the sample of (1), but the difference in the effect in terms of reliability is large. The inventor believes that this is because silicon-oxygen-nitrogen (Si-O-N) bonds are efficiently formed in the vicinity of the interface on the substrate side by heat treatment in an NO atmosphere performed after the active nitrogen introduction treatment. Yes.

  Note that the annealing in the NO gas atmosphere and the heat treatment in the N 2 gas atmosphere at a higher temperature are performed in order to improve the NBTI characteristics, which is not an essential process.

  As a plasma nitriding apparatus, in addition to a remote plasma nitriding apparatus, a decoupled RF nitrogen plasma apparatus available from Applied Materials, Inc. of Santa Clara, California is also known.

  FIG. 7B schematically shows the configuration of a decoupled RF nitrogen plasma apparatus. In this apparatus, nitrogen plasma is generated by RF excitation of a coil 26 provided on the top of a reaction chamber 25 that houses a sample 27 in the lower part. Nitrogen plasma is generated only in the region away from the sample 27 along the upper wall of the reaction chamber. This device is hereinafter abbreviated as DPN.

  Two types of samples were formed using a DPN nitriding apparatus.

  FIG. 3A shows conditions for creating two types of samples S6 and S7 and a sample S8 for comparison.

  First, FIG. A silicon oxide film having a thickness of 0.85 nm was formed with a lamp annealing apparatus in an oxygen atmosphere at 900 ° C. by a process similar to the process shown in 1A and 1B. Thereafter, nitrogen plasma was excited with 700 W of RF power in the DPN apparatus, and active nitrogen was introduced into the silicon oxide film of the substrate disposed below in the room temperature atmosphere.

  The sixth sample S6 was subjected to oxidation annealing (RTO) in a reduced pressure oxygen atmosphere at 1000 ° C. after introduction of active nitrogen and then annealing (RTA) in a nitrogen atmosphere at 1050 ° C.

  For the seventh sample S7, after introducing active nitrogen, nitriding oxidation annealing (RTNO) was performed in a NO gas atmosphere at 950 ° C., followed by annealing (RTA) in a nitrogen atmosphere at 1050 ° C. . For comparison, two types of sample S8 in which a gate electrode is formed only with a silicon oxide film were also prepared.

  FIG. 3B shows the measurement results of these samples. The horizontal axis represents the inversion capacitance equivalent film thickness Teff in the unit of nm, and the vertical axis represents the gate leakage current Ig in the unit (A / cm 2). The characteristic s8 of the sample in which the gate insulating film is formed of only the silicon oxide film is the two points indicated by x, and when extrapolated, it becomes a straight line.

  The characteristic s6 of the sixth sample S6 is below the characteristic s8 of the comparative sample S8, and indicates that the gate leakage current can be reduced.

  The measurement point s7 of the seventh sample S7 is a nitridation oxidation annealing process in NO, oxidation is suppressed, and the effective gate insulating film thickness is thinner than the measurement point s6. In addition, it exists below the characteristic s8, and shows that the gate leakage current can be reduced as in the case of the sample S6.

  FIG. In the characteristics of 3B, the reduction degree of the gate leakage current is almost equal between the two samples S6 and S7. In sample S7, the effective gate insulating film thickness is reduced by 0.013 nm. Also, the mutual conductance Gm is excellent. As a characteristic of the semiconductor device, a saturation current can be improved by 3.6% in a MOS transistor having a gate length of 40 nm.

  Further, the distribution of nitrogen in the gate insulating film into which active nitrogen was introduced was examined by secondary ion mass spectrometry (SIMS). As the active nitrogen introducing device, DPN was used, and the annealing treatment after the introduction of active nitrogen was performed in two kinds of atmospheres of oxygen and NO.

  FIG. The table of 4A schematically shows the production process of two types of samples. In the ninth sample S9, a silicon oxide film having a thickness of 0.8 nm was formed by a lamp annealing apparatus in an oxygen atmosphere at 900 ° C., and active nitrogen was formed in the gate oxide film in a room temperature atmosphere by 700 W decoupled RF nitrogen plasma. Was introduced (DPN). Thereafter, annealing RTO was performed in a reduced pressure oxygen atmosphere at 1000 ° C., followed by annealing (RTA) in a nitrogen atmosphere at 1050 ° C.

  In the tenth sample S10, a silicon oxide film having a thickness of 0.8 nm is formed as in the ninth sample S9. After introducing active nitrogen using a DPN device, an annealing process (RTNO) in a NO gas atmosphere at 950 ° C. is performed. Then, annealing treatment (RTA) in a nitrogen atmosphere at 1050 ° C. was further performed.

FIG. 4B is a graph showing the measurement results of these two types of samples.
The horizontal axis indicates the depth from the surface in the unit of nm, and the vertical axis indicates the measured nitrogen concentration in the unit (atoms / cc). The characteristic s9 of the sample annealed in the oxygen atmosphere has a higher peak value near the surface, and the nitrogen concentration gradually decreases with the depth. The change in nitrogen concentration by one digit or more within the measurement range is shown, but the interface between the gate insulating film and the silicon substrate exists in the middle.

  The thickness of the nitrided oxide film was 1.324 nm, the peak of nitrogen concentration was 8.6 at%, and the nitrogen concentration at the interface with the substrate was 3.6 at%. The nitrogen concentration at the interface is ½ or less of the peak nitrogen concentration.

  The characteristic s10 of the sample S10 annealed in the NO atmosphere after the introduction of active nitrogen appears to have a somewhat flat peak on the surface side, but the nitrogen distribution by the introduction of active nitrogen and the annealing treatment in the NO atmosphere Should be included. After that, it shows a tendency to decrease with the depth while showing a slightly higher nitrogen concentration than the characteristic s9, and the distribution is substantially the same as the characteristic s9 from a certain depth.

  The thickness of the nitrided oxide film was 1.174 nm, the peak of nitrogen concentration was 7.6 at%, and the nitrogen concentration at the interface with the substrate was 4.9 at%. If the thickness of the nitrided oxide film is increased, the nitrogen concentration at the substrate interface may be reduced to ½ or less of the peak nitrogen concentration. The nitrogen concentration at the interface with the substrate is 5 at% or less.

  From the viewpoint of increasing the nitrogen concentration on the surface side and lowering the nitrogen concentration at the interface with the substrate, annealing in an oxidizing atmosphere such as O 2 would be more suitable. However, the increase in the film thickness is larger than the annealing in the nitriding and oxidizing atmosphere. From the viewpoint of reducing the thickness of the nitrided oxide film and forming a transistor having an excellent driving capability, annealing in a nitrided oxidizing atmosphere such as NO may be suitable.

  In any measurement result, the nitrogen concentration has a peak on the gate insulating film surface side, and continues to decrease toward the interface with the silicon substrate along with the depth. Therefore, a large amount of nitrogen can be introduced into the gate insulating film, and boron penetration can be effectively suppressed, and the nitrogen concentration at the interface with the silicon substrate is preferably suppressed to 5 at% or less, and the mobility in the channel region is reduced. It turns out that a fall can be suppressed.

  Furthermore, the experiment was conducted under the condition that the excitation energy of the decoupled RF plasma was lowered from 700 W to 500 W, expecting that active nitrogen was introduced only near the surface of the silicon oxide film.

  FIG. The table of 6A schematically shows the production process of three types of samples. In an eleventh sample S11, a silicon oxide film having a thickness of 0.8 nm is formed by a lamp annealing apparatus in an oxygen atmosphere at 900 ° C., and a gate oxide film is formed in a room temperature atmosphere by a 500 W decoupled RF nitrogen plasma without a bias electric field. Active nitrogen was introduced therein (DPN). Thereafter, annealing (RTO) was performed in a reduced pressure oxygen atmosphere at 1000 ° C., followed by annealing (RTA) in a nitrogen atmosphere at 1050 ° C.

  In the twelfth sample S12, as in the eleventh sample, a silicon oxide film having a thickness of 0.8 nm is formed by a lamp annealing apparatus in an oxygen atmosphere at 900 ° C., and gated in a room temperature atmosphere by a 500 W decoupled RF nitrogen plasma. Active nitrogen was introduced into the oxide film (DPN). Thereafter, annealing (RTNO) was performed in a reduced pressure NO atmosphere at 950 ° C., followed by annealing (RTA) in a nitrogen atmosphere at 1050 ° C.

  In the 13th sample S13, a silicon oxide film having a thickness of 0.8 nm is formed by a lamp annealing apparatus in a 900 ° C. oxygen atmosphere and is gated in a room temperature atmosphere by a 500 W decoupled RF nitrogen plasma. Active nitrogen was introduced into the oxide film (DPN). Thereafter, annealing treatment (RTO) is performed in a reduced pressure oxygen atmosphere at 1000 ° C., followed by annealing treatment (RTNO) in a reduced pressure NO atmosphere at 950 ° C., and further annealing treatment (RTA) in a nitrogen atmosphere at 1050 ° C. I did it. The reason why RTA is performed at a higher temperature after annealing in a NO atmosphere is to improve the NBTI characteristics and is not an essential process.

  FIG. 6B is a graph showing the measurement results of these three types of samples. The horizontal axis indicates the depth from the surface in the unit of nm, and the vertical axis indicates the measured nitrogen concentration in the unit (atoms / cc).

  The characteristic s11 of the eleventh sample S11 annealed in an oxygen atmosphere has a higher peak value near the surface, and the nitrogen concentration gradually decreases with depth. Nitrogen concentration change of one digit or more is shown in the measurement range. An interface between the gate insulating film and the silicon substrate exists in the middle.

  The thickness of the nitrided oxide film was 1.189 nm, the nitrogen concentration peak was 7.5 at%, and the nitrogen concentration at the interface with the substrate was 2.2 at%. The nitrogen concentration at the interface is ½ or less of the peak nitrogen concentration.

  The characteristic s12 of the twelfth sample S12 that has been annealed in an NO atmosphere after the introduction of active nitrogen has a broadened peak in the vicinity of the surface. Thereafter, while showing a nitrogen concentration slightly higher than the characteristic S11, it shows a tendency to decrease with the depth, but the nitrogen amount increases when approaching the interface, and has a characteristic distribution having two peaks at the surface and in the vicinity of the interface. Indicates. Annealing in an NO atmosphere seems to tend to introduce nitrogen near the interface with the substrate.

  The thickness of the nitrided oxide film was 1.170 nm, the peak of the nitrogen concentration was 7.8 at%, and the nitrogen concentration at the interface with the substrate was 4.8 at%.

  The characteristic s13 of the thirteenth sample S13 in which the nitrogen atmosphere is annealed after the introduction of active nitrogen and the NO atmosphere annealing is the same as the characteristic s11 of the oxygen annealing sample. Although it seems that there is a difference from the characteristic of s11, it is a difference within the measurement error of secondary ion mass spectrometry (SIMS). When approaching the interface, the amount of nitrogen increases and it can be confirmed that the interface is effectively nitrided in the NO atmosphere.

  The thickness of the nitrided oxide film was 1.157 nm, the nitrogen concentration peak was 7.4 at%, and the nitrogen concentration at the interface with the substrate was 2.4 at%.

  Even if the annealing is performed in an NO atmosphere after the introduction of active nitrogen to improve the characteristics, the nitrogen concentration at the interface with the substrate can be suppressed to 5 at% or less. By selecting the conditions, the nitrogen concentration at the interface can be made ½ or less of the nitrogen concentration at the surface. From the characteristics s12 and s13 of the samples S12 and S13, it can be seen that various nitrogen distributions can be realized by controlling the nitrogen distribution by the introduction of active nitrogen and the nitrogen distribution by the annealing treatment in the NO atmosphere. It is also possible to introduce nitrogen in the vicinity of the interface by annealing in a NO atmosphere without significantly destroying the sharp distribution shape due to the introduction of active nitrogen. It becomes easy to realize different nitrogen concentrations according to different requirements at the interface between the gate insulating film surface and the substrate.

  FIG. 5A to 5D are cross-sectional views illustrating a method of manufacturing a semiconductor device according to an embodiment of the present invention based on the above experimental results.

  FIG. As shown in FIG. 5A, an element isolation region 3 by STI is formed on a silicon substrate 1. Desired ion implantation is performed in the active region defined by the STI element isolation region to form an n-type well 4n and a p-type well 4p. Although only two wells are shown, a plurality of wells are formed simultaneously.

  Pyrogenic oxidation is performed on the exposed silicon substrate surface at 800 ° C. to form a silicon oxide film 11 having a thickness of 7 nm. Pyrojec oxidation is a method in which oxidation is performed in an atmosphere in which hydrogen is burned in oxygen. The gate oxide film having a thickness of 7 nm serves as a gate insulating film for forming a MOSFET having an operating voltage of about 3V.

  In the active region where a MOSFET for low voltage operation is formed, the grown silicon oxide film 11 is removed by etching. Dry oxidation is performed in an oxygen atmosphere at 965 ° C. to form a silicon oxide film 12 having a thickness of 1.2 nm. The gate oxide film having a thickness of 1.2 nm serves as a gate insulating film for forming a MOSFET having an operating voltage of about 1 to 1.2 V, for example. When a natural oxide film is present on the silicon substrate surface, the natural oxide film may be removed in a reducing atmosphere such as hydrogen radicals. A good quality silicon oxide film can be formed by oxidizing a clean silicon surface.

  Although the case where a gate insulating layer having two types of thicknesses is formed has been described, a gate insulating layer having three or more types of thicknesses may be formed.

  The thick silicon oxide film 11 previously formed by this oxidation also grows slightly. N-type and p-type wells having a thin gate insulating film 12 are also formed.

  FIG. As shown in FIG. 5B, active nitrogen is introduced into the gate insulating films 11 and 12 in an atmosphere at 550 ° C. by RPN nitrogen plasma obtained by microwave of 1.5 kW. Active nitrogen is introduced, and the gate insulating films become silicon nitride oxide films 11x and 12x.

  FIG. As shown in FIG. 5C, annealing is performed in a NO gas atmosphere at 950.degree. Due to the NO gas, the gate insulating film is further oxynitrided to recover the damage. In this way, gate insulating films 11y and 12y are formed. Subsequently, in order to suppress the deterioration of the NBTI characteristics, annealing at a higher temperature may be performed in a nitrogen atmosphere.

  Thereafter, a polycrystalline silicon layer having a thickness of 100 nm is formed on the gate insulating film and patterned to a desired gate length using a resist pattern. A gate electrode having a gate length of 40 nm is formed on the thin gate insulating film 12y.

  As shown in FIG. 5D, extension regions 7p and 7n are formed by ion implantation of n-type impurities and p-type impurities using a patterned gate electrode and a resist mask for selecting an n-channel region and a p-channel region as a mask. Thereafter, a silicon oxide film having a thickness of about 60 nm is deposited, and sidewall spacers 8 are formed by performing RIE. Source / drain regions 9n and 9p are formed by ion implantation of n-type impurities and p-type impurities using a gate electrode having sidewall spacers and a resist mask for separating the n-channel region and the p-channel region.

  Thereafter, if necessary, the exposed silicon surface is silicided and covered with an interlayer insulating film. Openings are formed in the interlayer insulating film 2, lead plugs are formed, and further necessary wirings and interlayer insulating films are formed.

  In this manner, a CMOS integrated circuit having a thin gate insulating layer and a thick gate insulating layer, which suppresses boron penetration even in the thin gate insulating layer and suppresses a decrease in mobility of the channel region is formed.

  By such a process, a semiconductor device having a thin effective gate insulating film thickness of 2 nm or less, particularly 1.7 nm or less, capable of preventing boron penetration and suppressing reduction in mobility of the channel region is formed. .

  As described above, according to the above-described embodiment, a nitrogen concentration that is high on the surface side and low at the interface with the silicon substrate is introduced into the gate insulating film, and boron penetration through the gate insulating film is suppressed and movement in the channel region is performed. Degree reduction can be suppressed.

  Although the present invention has been described with reference to the embodiments, the present invention is not limited thereto. For example, depending on the purpose, annealing in NO diluted with an inert gas may be used instead of nitridation oxidation annealing in NO. Instead of the silicon oxide film, a silicon nitride oxide film containing 3 at% or less of nitrogen may be formed at the interface with the substrate as the insulating film formed first over the semiconductor substrate. A high-k material film having a high dielectric constant may be stacked over the silicon nitride oxide film.

  FIG. 7C shows a configuration in which films of high-k (high dielectric constant) material are stacked. The high-k material has a significantly higher dielectric constant than silicon oxide. For example, a silicon oxide film 31 having a thickness of 0.58 nm is formed on the surface of the silicon substrate 30 in a 750 ° C. oxygen atmosphere by a lamp annealing apparatus, and the gate oxide film is formed in a room temperature atmosphere by a 500 W decoupled RF nitrogen plasma. Active nitrogen was introduced (DPN). Thereafter, annealing treatment (RTNO) in an NO gas atmosphere at 900 ° C. was performed, and further annealing treatment (RTA) in a nitrogen atmosphere at 1050 ° C. was performed. The nitrided oxide film thickness was 0.80 nm. It may be possible to further reduce the film thickness by adjusting the base oxide film thickness, plasma nitriding strength, NO gas annealing temperature, time, and the like. On this oxynitride film, an oxide film such as Al, Hf, Zr, or the like, and a high-k material film 32 such as an oxide silicate film thereof are formed, thereby preventing a reaction between the semiconductor substrate and the high-k material and ensuring reliability. A gate insulating film having excellent performance and driving capability can be provided.

  It will be apparent to those skilled in the art that other various changes, modifications, combinations, and the like can be made.

  It is suitable for the manufacture of MOS transistors with advanced miniaturization.

FIGs. 1A to 1F are cross-sectional views and graphs for explaining experiments conducted by the inventors and results thereof. FIGs. 2A to 2D are cross-sectional views and graphs for explaining the experiment conducted by the inventor and the results thereof. FIGs. 3A and 3B are a table and a graph showing the conditions and results of still another experiment conducted by the present inventors. FIGs. 4A and 4B are a table and a graph showing the conditions and results of still another experiment conducted by the present inventors. FIGs. 5A to 5D are cross-sectional views of a semiconductor substrate for explaining a method of manufacturing a semiconductor device according to an embodiment of the present invention. FIGs. 6A and 6B are tables and graphs showing conditions and results of still another experiment conducted by the present inventors. FIGs. 7A, 7B, and 7C are a cross-sectional view schematically showing a configuration of a remote plasma nitriding apparatus and a decoupled RF nitrogen plasma apparatus, and a cross-sectional view schematically showing a configuration of a gate insulating layer using a high-k material.

Claims (12)

Forming a gate insulating layer on the active region of the semiconductor substrate;
Introducing nitrogen from the surface side of the gate insulating layer with active nitrogen;
Next, a step of annealing the semiconductor substrate in a NO gas atmosphere;
A method of manufacturing a semiconductor device including: 2. The method of manufacturing a semiconductor device according to claim 1, wherein the active nitrogen is radical nitrogen or nitrogen generated from plasma. The method for manufacturing a semiconductor device according to claim 1, further comprising a step of performing an annealing process in an inert gas at a higher temperature after the annealing process in the NO gas atmosphere. 2. The method of manufacturing a semiconductor device according to claim 1, wherein an increase in film thickness of the gate insulating film by the annealing process in the NO gas atmosphere is 0.2 nm or less. 2. The method of manufacturing a semiconductor device according to claim 1, wherein the annealing treatment in the NO gas atmosphere is performed in an NO gas atmosphere at a temperature higher than the substrate temperature in the step of introducing nitrogen by active nitrogen. _{2. The} method of manufacturing a semiconductor device according to claim 1, wherein the annealing treatment in the NO gas atmosphere is performed in an NO gas atmosphere diluted with an inert gas containing any of N ₂ , Ar, and He. The method of manufacturing a semiconductor device according to claim 1, further comprising a step of performing annealing in an oxygen atmosphere or an oxygen atmosphere diluted with an inert gas before the annealing treatment in the NO gas atmosphere. 2. The method of manufacturing a semiconductor device according to claim 1, wherein the gate insulating layer formed on the active region is an insulating layer formed by thermally oxidizing the surface of the semiconductor substrate and has a thickness of 1.5 nm or less. 2. The method of manufacturing a semiconductor device according to claim 1, wherein the gate insulating layer is an oxynitride layer containing a trace amount of nitrogen of 3 at% or less at the interface with the semiconductor substrate. 2. The method of manufacturing a semiconductor device according to claim 1, wherein the nitrogen concentration at the interface between the gate insulating layer and the semiconductor substrate after annealing in the NO gas atmosphere is 5 at% or less. The method of manufacturing a semiconductor device according to claim 1, further comprising a step of annealing the semiconductor substrate in a reducing atmosphere and removing a natural oxide film before the step of thermally oxidizing the surface of the semiconductor substrate. 2. The method of manufacturing a semiconductor device according to claim 1, wherein the step of forming a gate insulating layer on the active region of the semiconductor substrate forms an insulating layer having a different thickness depending on the region.

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