JP3619795B2 - Manufacturing method of semiconductor device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for forming a silicon oxynitride film used as a gate insulating film of a semiconductor element having a MOS (Metal Oxide Semiconductor) structure.
[0002]
[Prior art]
With the miniaturization of silicon semiconductor integrated circuits, the dimensions of MOS type semiconductor elements are miniaturized. According to the 2000 update version of ITRS (International Technology Roadmap for Semiconductors), a silicon oxide equivalent film thickness (Equivalent Physical Oxide Thickness; hereinafter referred to as EOT-1.5) is a 90 nm technology node. A gate insulating film is needed. In order to realize a gate insulating film in which leakage current is suppressed with this film thickness, SiO 2 ₂ A silicon oxynitride film (hereinafter referred to as a SiON film) having a low nitrogen concentration (<20 at.%) Is insufficient, and a SiON film having a high dielectric constant, that is, a SiON film having a high nitrogen concentration in the film is required. ing. Furthermore, since MOS transistors of logic integrated circuits are required to have high current driving capability in addition to suppressing leakage current, it is essential to increase the mobility of the MOS transistors. For the SiON film used as a gate insulating film, Therefore, it is required to reduce the interface state density and the fixed charge density.
[0003]
As a method of forming a SiON film used as a gate insulating film, conventionally, a SiON film is used. ₂ N ₂ O oxynitriding and NO oxynitriding have been used. For an ultra-thin gate insulating film, NO oxynitriding has been mainly used because nitrogen can be introduced without increasing the film thickness and hydrogen-free. However, in NO oxynitriding, since nitrogen enters near the interface on the Si substrate side, there is a problem in that interface states and fixed charges are generated, mobility is lowered, and current driving capability of the MOS transistor is reduced.
[0004]
Therefore, in recent years, SiO ₂ After forming the film, nitriding with active nitrogen (plasma nitriding or radical nitriding) is performed to form SiO ₂ A method of introducing nitrogen into the surface side of the membrane has been proposed (M. Togo, K. Watanabe, T. Yamamoto, N. Ikarashi, K. Shiba, T. Tatsumi, H. Ono, and T. Momami, 2000). Symp.on VLSI Tech.p.116; S.V. Hattagandy, R. Kraft, D.T. Grider, M.A. Douglas, G.A. Brown, P.A.Tiner, J.H. P. E. Nichollian, and MF Pas, IEDM Tech. Dig. 96-495). In this method, since the nitrogen concentration near the silicon substrate interface can be kept low, the mobility of the MOS transistor can be prevented from deteriorating and high driving force can be obtained.
[0005]
However, SiO ₂ Nitriding of the film with active nitrogen has a problem that the concentration of nitrogen that can be introduced into the film is saturated. In our study, plasma nitriding can introduce more nitrogen into the film than radical nitriding, but the surface density of nitrogen that can be introduced into the film is 3 × even if the process conditions are changed by plasma nitriding. 10 ¹⁵ cm ^-2 It has been experimentally shown that the degree is the upper limit. This introduced nitrogen surface density is insufficient as a gate insulating film for the next generation logic circuit capable of exhibiting sufficient performance. We have EOT = 1.2-1.3 nm and nitrogen areal density 4.5-4.8 × 10 ¹⁵ cm ^-2 It is estimated that (relative dielectric constant 6) is essential from the viewpoint of leakage current suppression. Therefore, the base insulating film is made of SiO. ₂ It is difficult to realize a gate insulating film with EOT = 1.2-1.3 nm by the method of performing plasma nitriding as a film.
[0006]
Base SiO ₂ Another problem with plasma nitridation of films is that the active species of nitrogen with charge is ion-implanted in the form of ion implantation. ₂ Since it is driven into the film, the base SiO ₂ When the film thickness is reduced, the introduced nitrogen penetrates into the Si substrate and the nitriding of the substrate proceeds. This causes the Si substrate interface to deteriorate. We use plasma nitridation for SiO ₂ It was confirmed that the SIMS profile of nitrogen introduced into the film and the simulation result of ion implantation quantitatively matched. That is, the profile in the film thickness direction of nitrogen introduced into the film is the base SiO. ₂ Regardless of the film thickness, it can be expressed as a function of depth from the film surface. Under typical plasma nitriding process conditions, the maximum value of the nitrogen concentration is located at a depth of about 0.7 nm from the film surface, and the full width at half maximum is about 0.7 nm. Therefore, base SiO ₂ When the film thickness is 1.4 nm or less, nitrogen introduced by plasma nitriding penetrates to the Si substrate, and nitriding proceeds in the vicinity of the interface with the Si substrate, so that interface states and interface fixed charges are generated. In order to suppress the deterioration of the Si substrate interface, the base insulating film needs to have a film thickness of 1.5 nm or more. ₂ As long as is used, increasing the film thickness is incompatible with the requirement to reduce EOT.
[0007]
[Problems to be solved by the invention]
As mentioned above, SiO which is considered to be the best in the conventional method ₂ Even in the plasma nitridation of the film, when an attempt is made to realize a gate insulating film of a generation with a small EOT, (a) the upper limit of the nitrogen surface density that can be introduced is limited, and (b) the introduced nitrogen penetrates into the Si substrate There were two problems that the interface deteriorated due to the above.
[0008]
The present invention has been made to solve these problems, and an object of the present invention is to provide a method for manufacturing a semiconductor device having a gate insulating film using a SiON base insulating film having a small EOT and good interface characteristics. It is to provide.
[0009]
[Means for Solving the Problems]
The present invention provides a method of manufacturing a semiconductor device in which a semiconductor element including a gate insulating film is formed on a silicon substrate, wherein the step of forming the gate insulating film includes a base insulating film containing silicon, oxygen and nitrogen on the silicon substrate. A step of forming the base insulating film, an oxidizing step of exposing the base insulating film to an atmosphere containing oxygen, and a nitriding step of nitriding the base insulating film using active nitrogen after the oxidizing step. .
[0010]
In the present invention, the base insulating film (SiON film) is formed by thermal oxynitridation of a silicon substrate or by physical / chemical deposition. In the case of thermal oxynitridation of a silicon substrate, there is an advantage that a film having a relatively low interface state density can be formed. On the other hand, physical / chemical deposition has an advantage that a film having a high nitrogen concentration can be formed. These films may be used alone, but a laminated film combining both may be used from the viewpoint of achieving both good interface characteristics and a high dielectric constant.
[0011]
In the present invention, for the SiON base insulating film thus formed, oxygen (O ₂ Alternatively, after performing an oxidation step in an atmosphere containing active oxygen), nitridation using active nitrogen is subsequently performed. In this case, it is important that the oxidation step and the nitridation step are not simultaneous and the oxidation step is first. In the oxidation process, the interface state density can be reduced by introducing oxygen into the silicon substrate interface, and the film density can be increased by introducing oxygen into the SiON bulk portion to increase the film density. If the film is densified, it is possible to suppress diffusion of nitrogen introduced in the subsequent nitridation step using active nitrogen to the silicon substrate interface. This makes it possible to obtain a gate insulating film made of a SiON film having a high nitrogen density and good interface characteristics.
[0012]
That is, according to the present invention, the base insulating film is made of SiO. ₂ By changing from to SiON, an excellent gate insulating film having an EOT as small as 1.5 nm or less and an actual film thickness (physical film thickness) of 1.5 nm or more can be obtained. The nitrogen surface density in the SiON film finally formed after nitridation with active nitrogen is the sum of the nitrogen in the base SiON film and the nitrogen surface density introduced by nitridation with active nitrogen. The concentration is the desired value required for EOT = 1.2-1.3 nm (4.5 × 10 ¹⁵ cm ^-2 ) Or even larger. When the nitrogen concentration in the film increases, the dielectric constant of the film increases, and the leakage current can be suppressed without increasing the EOT.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[First embodiment]
FIG. 1 is a cross-sectional view of a SiON film manufacturing apparatus. This apparatus has a chamber 11 that can be evacuated. Chamber 11 is O ₂ , SiH ₄ , NO / N ₂ O, N ₂ Gas supply ports 12, 13, 14, 15 and a gas exhaust port 16. O ₂ , N ₂ Microwave cavities 17 and 18 are installed outside the gas pipe, respectively, and active oxygen O is generated by microwave discharge. ^* And active nitrogen N ^* Can be supplied into the chamber 11. The gas pipe where the microwave cavities 17 and 18 are installed is O ₂ Piping made of quartz, N ₂ The piping is made of boron nitride.
[0014]
A heater 20 is mounted in the chamber 11 on which a silicon wafer 19 can be placed. The background pressure of the chamber 11 of this manufacturing apparatus is 1 × 10 ^-8 The total pressure during the manufacturing process of the SiON film is about 0.1-10 Torr.
[0015]
The outline of the present invention including the process of forming the SiON film using the apparatus of FIG. 1 will be described taking MOS transistor formation as an example. As shown in FIG. 2, an element isolation trench is formed on the surface of a single crystal p-type silicon substrate 21 and is filled with a silicon oxide film by a CVD method to form an element isolation region 22. Next, as shown in FIG. 3, a gate insulating film 23 made of a SiON film is formed. A detailed method for forming the gate insulating film 23 will be described later.
[0016]
Next, as shown in FIG. 4, a polysilicon film 24 is formed on the gate insulating film 23 by a CVD method. Next, a photoresist pattern (not shown) is formed on the polysilicon film 24 through a lithography process, and the polysilicon film 24 is subjected to reactive ion etching to form a gate electrode 25 as shown in FIG. Next, arsenic ion implantation is performed, for example, at an acceleration voltage of 40 keV and a dose of 2 × 10. ¹⁵ cm ^-2 N of high impurity concentration ⁺ Type gate electrode 25, n ⁺ Type source region 26, n ⁺ A type drain region 27 is formed simultaneously.
[0017]
Next, as shown in FIG. 6, a 300 nm silicon oxide film is deposited on the entire surface by the CVD method to form an interlayer insulating film 28. Thereafter, a photoresist pattern (not shown) for forming a contact hole is formed on the interlayer insulating film 28, and the interlayer insulating film 28 is etched by reactive ion etching using this as a mask to open a contact hole. . Finally, after an Al film is formed on the entire surface by sputtering, this is patterned to form an electrode wiring 29 to complete an n-type MOS transistor. In this embodiment, the manufacturing process of the n-type MOS transistor is shown. However, the p-type MOS transistor is different in that the conductivity type is switched between the n-type and the p-type, and the basic manufacturing process is exactly the same. is there.
[0018]
Details of the step of forming the gate insulating film 23 will be described next. FIG. 7 shows a gate insulating film forming step in the first embodiment. First, dilute hydrofluoric acid treatment is performed on the silicon wafer as pretreatment. Other pretreatments such as hydrochloric acid and ozone water may be used to effectively remove wafer contamination, but the final treatment is preferably dilute hydrofluoric acid. Next, the wafer for which the pretreatment has been completed is transferred into the chamber 11 of the manufacturing apparatus shown in FIG. The heater 20 is heated so that the temperature of the wafer 19 is 750 ° C., and NO / N ₂ 400 Torr of NO gas was supplied from the O gas inlet 14 and heated for 3 minutes. Thereby, a SiON base insulating film is formed.
[0019]
Next, the supply of NO gas was stopped, the output of the heater was adjusted, and the temperature of the wafer 19 was set to 500 ° C. O from the gas inlet 12 ₂ While supplying gas, plasma oxygen was generated by setting the output of the microwave cavity 17 to 2.45 GHz and 200 W. The amount of oxygen introduced into the chamber 11 was controlled so that the total pressure was 0.5 Torr, and plasma oxidation was performed at 500 ° C. for 1 minute. In this oxidation process, instead of plasma oxidation, 1000 ° C., 0.5 Torr, 1 minute O ₂ Similar effects can be obtained by oxidation.
[0020]
Next, the output of the microwave cavity 17 and O ₂ After stopping the gas supply, nitrogen gas was supplied from the gas inlet 15 and the output of the microwave cavity 18 was set to 2.45 GHz and 100 W to generate plasma nitrogen. Plasma nitridation was performed at 500 ° C. for 10 minutes with the total pressure in the chamber 11 being 10 Torr. As described above, a gate insulating film made of a silicon oxynitride film (SiON film) having an EOT of 1.5 nm or less and an actual film thickness (physical film thickness) of 1.5 nm or more (for example, 1.8 nm) is obtained. It is done.
[0021]
Next, the temperature of the wafer is raised to 1000 ° C., and N Torr of 0.1 Torr from the gas supply port 14. ₂ O gas was supplied to perform post-annealing for 20 seconds. Note that the subsequent annealing is performed as described above for N ₂ Instead of O annealing, 1000 ° C, 0.5 Torr, 20 sec O ₂ Similar effects can be obtained by oxidation.
[0022]
The operation of each step in the film forming process will be described. First, when dilute hydrofluoric acid is used for the pretreatment (the last), SiO at the end of the pretreatment ₂ Compared with the case where the film is left (for example, the case where the last pretreatment is treated with hydrochloric acid / ozone water), the nitrogen concentration in the film due to NO oxynitriding can be increased. In a gate insulating film having a small EOT, it is necessary to increase the nitrogen concentration. However, performing the NO oxynitriding step immediately after the pretreatment with diluted hydrofluoric acid meets this requirement. Of course, after diluted hydrofluoric acid treatment, NH ₃ When strong nitriding such as nitriding is performed, the nitrogen concentration is further increased. In this case, however, a large amount of interface states and fixed charges are generated, which is not preferable as a film used as a CMOS gate insulating film.
[0023]
On the other hand, in NO oxynitriding, nitriding and oxidation occur simultaneously, and interface characteristics are not extremely deteriorated. ₃ It is preferable to use NO oxynitriding rather than nitriding. NH ₃ Even in the case of using nitriding, it is considered possible to advance oxynitriding while simultaneously flowing a small amount of oxygen or active oxygen.
[0024]
Next, plasma oxidation (or high temperature O 2) is applied to the formed SiON base insulating film. ₂ Oxidation) has the function of reducing the interface state density of the as-grown SiON film by introducing oxygen into the film. This oxidation step is not essential for high performance logic circuit MOS transistors, but this step should be included in digital / analog mixed circuit MOS transistors that strictly require good interface characteristics. In the first embodiment, plasma oxidation is used for this oxidation step, but we have experimentally found that the reduction of the interface state density correlates with the amount of oxygen introduced into the film. Therefore, if an equivalent oxygen introduction amount can be secured, O in addition to plasma oxidation. ₂ Oxidation, N ₂ O oxynitriding may be used. For example, 1000 ° C., 0.5 Torr, 1 minute O ₂ Even with oxidation, the same effect of reducing the interface state density can be obtained.
[0025]
In order to reduce the interface state density, it is desirable to adopt a method of accelerating oxygen diffusion to the Si substrate interface as much as possible. As one means, NO oxynitridation and plasma oxidation are performed in a plurality of times. There is a way. For example, in the above film forming process, NO oxynitridation is performed at 750 ° C. and 400 Torr for 3 minutes, and then plasma oxidation is performed at 500 ° C. and 0.5 Torr for 1 minute. On the other hand, for example, a process of NO oxynitridation at 750 ° C., 400 Torr, 1 minute 30 seconds, and subsequent plasma oxidation at 500 ° C., 0.5 Torr, 30 seconds may be repeated twice. Alternatively, each shorter process may be repeated more times. In this way, the process becomes complicated, but extremely good interface characteristics can be obtained.
[0026]
In the plasma nitridation for the SiON base insulating film subjected to plasma oxidation, nitrogen is introduced into the surface side of the base SiON film. A base SiON film formed by NO oxynitridation and subsequent plasma oxidation has a relatively high nitrogen concentration on the interface side and a low nitrogen concentration on the film surface side. In the plasma nitridation, nitrogen is newly introduced into the region having a low nitrogen concentration. Therefore, nitrogen in the already-introduced base SiON film does not hinder the introduction of new nitrogen during plasma nitridation. The amount of nitrogen introduced into the film is the sum of the amounts of nitrogen introduced in each process, and the maximum nitrogen surface density that can be introduced into the film can be increased. Base SiO ₂ It becomes larger than the saturated nitrogen surface density in the plasma nitriding of the film.
[0027]
As can be seen from the above, the nitrogen in the final film after plasma nitriding has a relatively uniform profile in the film thickness direction. This is extremely effective for reducing the leakage current. In our study, the more uniform the nitrogen profile in the film, the lower the leakage current reduction rate (vs. SiO ₂ ) (Yasuda, Muraoka, Koike, Satake "Nonlinearity between film composition and dielectric constant in ultrathin silicon oxynitride film" 2001 (Heisei 13), 48th Joint Lecture on Applied Physics Meeting, 29aYF4). In addition, when the base SiON film is plasma-nitrided, in order to realize an equal EOT, SiO ₂ Since a base insulating film having a larger actual film thickness than that of plasma nitridation of the film can be used, penetration of nitrogen introduced by the ion implantation mechanism into the Si substrate during plasma nitridation can be suppressed, and the interface of the Si substrate can be suppressed. Deterioration is suppressed.
[0028]
Further, since nitrogen is already present in the base SiON film at the time of plasma nitriding, diffusion from the nitrogen in the film and diffusion of Si from the Si substrate interface into the film are caused by the base insulating film film being SiO. ₂ It is suppressed compared with the case of. Therefore, the ratio of N and O substitution reaction during plasma nitridation is relatively increased, and the reaction between N and Si is suppressed, so that an increase in actual film thickness during plasma nitridation (leading to an increase in EOT) is suppressed. The advantage that Furthermore, an increase in the ratio of N and O substitution reactions is expected to improve the interface characteristics by diffusing part of the oxygen released during the substitution reaction to the interface.
[0029]
Next, N ₂ Post-annealing in an O atmosphere reduces fixed charges in the film. In our study, in order to reduce the fixed charge, it is necessary to perform annealing in an atmosphere capable of exchanging charges with the sites in the film having the fixed charge. In other words, the fixed charge is reduced by annealing in an atmosphere that causes an oxidation or reduction reaction (reaction for exchanging electrons and holes) with the SiON film. At this time, the fixed charge reduction effect is determined by the process temperature, and the fixed charge reduction rate increases as the annealing temperature increases. N ₂ In an inert gas such as Ar, the reduction rate of the fixed charge is low. From the above, in this embodiment, the low-pressure N of such a degree that the thickness of the SiON film is hardly increased. ₂ Post annealing was performed in an O atmosphere. Of course, low pressure O ₂ The same fixed charge reduction effect can be obtained by annealing (1000 ° C, 0.5 Torr, 20 seconds, etc.), annealing in low-pressure active oxygen, annealing in low-pressure active nitrogen, and other annealing in a gas atmosphere that combines these. It is done. Depending on the plasma nitriding conditions, the amount of fixed charges generated may be small. In that case, the oxidation after the formation of the initial SiON film is O 2 at high temperature and low pressure. ₂ If it is oxidized (1000 ° C., 0.5 Torr, 1 minute), post-annealing can be omitted.
[0030]
In this embodiment, microwave discharge is used to generate active nitrogen / oxygen, but the same effect can be obtained by using high-frequency excitation (RF: 13.56 MHz) or an optical excitation source such as ultraviolet rays instead of microwave. . Moreover, plasma nitridation / oxidation containing charged active nitrogen / oxygen is used as the active nitrogen / oxygen, but the effect of improving the quality of the SiON film is also obtained by radical nitridation / oxidation, which is mostly neutral species. It is done. N as a source gas for forming active nitrogen and oxygen ₂ And O ₂ However, any gas containing nitrogen and oxygen atoms can be substituted with another gas. Furthermore, in order to increase the excitation efficiency of active nitrogen / oxygen, a rare gas such as He, Ne, Ar, or Kr may be added to the source gas. In this embodiment, a heater is used to heat the silicon wafer, but the same effect can be obtained by directly heating the wafer with a lamp.
[0031]
[Second Embodiment]
Since the element structure of the MOS transistor according to the second embodiment is the same as that of the first embodiment, detailed description thereof is omitted. FIG. 8 shows a manufacturing process of the gate insulating film in this embodiment.
[0032]
As shown in FIG. 8, the silicon wafer is pretreated with diluted hydrofluoric acid. Thereafter, the wafer was transferred into the chamber 11 of the oxynitride film manufacturing apparatus. The wafer temperature is set to 500 ° C., and O is introduced from the gas inlets 12, 13, 15. ₂ , SiH ₄ , N ₂ Supplied. The gas supply condition at this time is O ₂ / SiH ₄ / N ₂ = 0.1 Torr / 20 sccm / 120 sccm, and the total pressure in the chamber 11 was 1.2 Torr. An output of 2.45 GHz and 100 W was applied to the microwave cavity 18 to generate nitrogen plasma, and a SiON film serving as a base insulating film was deposited. A SiON film having an actual film thickness of 1.4 nm was formed by a process of 1 minute 30 seconds. According to XPS (X-ray photo-electron spectroscopy) evaluation, the composition of this SiON film has an oxygen concentration of 40 atomic% (a surface density of oxygen: 4.2 × 10 ¹⁵ cm ^-2 , Nitrogen areal density 2.4 × 10 ¹⁵ cm ^-2 )Met.
[0033]
Further, the relationship of 2 [O] +3 [N] = 4 [Si] is established among the concentrations of oxygen, nitrogen, and silicon, and a stoichiometric silicon acid that does not contain Si—H, N—H bonds, or the like. Nitride film ((SiO ₂ ) _x (Si ₃ N ₄ ) _1-x ) Was confirmed. In this embodiment, the SiON film is deposited by nitrogen-excited plasma CVD, but thermal CVD may be used as the SiON film deposition method in addition to plasma CVD. For example, SiH ₄ And NH ₃ (And low pressure O if necessary ₂ The SiON film can be deposited by thermal CVD in the temperature range of 600 ° C. to 750 ° C., using as a source gas.
[0034]
Next, while maintaining the wafer temperature at 500 ° C., O ₂ The pressure was set at 0.5 Torr, and an output of 2.45 GHz and 200 W was applied to the microwave cavity 17 to perform plasma oxidation for 1 minute. When the deposited film is an initial SiON film as in this embodiment, it is particularly important to include this oxidation step. This is because the deposited oxynitride film generally has many defects in the film, and interface defects and defects in the film can be greatly reduced by performing plasma oxidation. In addition, the deposited oxynitride film generally has a low density, but the film density increases through a plasma oxidation process. If the film density is increased by plasma oxidation, nitrogen introduced by subsequent plasma nitriding can be prevented from diffusing in the film, and there is an advantage that interface deterioration due to introduction of nitrogen into the Si substrate interface is reduced. In place of the above plasma oxidation, high temperature and low pressure O ₂ The same effect can be obtained by using oxidation (1000 ° C., 0.5 Torr, 1 minute).
[0035]
Next, the temperature of the wafer was kept at 500 ° C., nitrogen gas was supplied from the gas inlet 15, and at the same time, an output of 2.45 GHz and 100 W was applied to the microwave cavity 18 to perform plasma nitriding for 10 Torr for 10 minutes. According to XPS evaluation, 2.5 × 10 ¹⁵ cm ^-2 Is introduced, and the nitrogen surface density after plasma nitriding is 4.5 × 10 ¹⁵ cm ^-2 Became.
Next, the temperature of the wafer is raised to 1000 ° C., and N Torr of 0.1 Torr from the gas supply port 14. ₂ O gas was supplied to perform post-annealing for 20 seconds. This post-annealing is a low pressure O ₂ Annealing (1000 ° C., 0.5 Torr, 20 seconds, etc.) can be substituted, and any of them can reduce the fixed charge.
[0036]
The operation in the above series of steps is basically the same as in the first embodiment, and a gate insulating film having an EOT of 1.5 nm or less and a physical film thickness of 1.5 nm or more is obtained. Each process follows the same concept as described in the first embodiment, and can be appropriately replaced by other processes. The deposited oxynitride film has the feature that the nitrogen concentration in the film can be increased by controlling the flow rate ratio of the source gas, while the defect density is lower than that of the SiON film formed by thermal oxynitridation of the Si substrate. There is a disadvantage of being expensive. However, we have experimentally confirmed that the defects in the deposited SiON film can be sufficiently reduced in the plasma oxidation / plasma nitriding process after the film deposition. The deposited oxynitride film is added to the initial SiON film. There is no penalty for using it.
[0037]
The actions according to this embodiment are summarized as follows.
(1) The SiON film formed by the deposition method has a lower density than the heat-induced oxynitride film. For this reason, oxygen can be diffused to the silicon substrate interface by plasma oxidation after deposition, and a good interface can be obtained.
{Circle around (2)} Since the film density is improved by plasma oxidation, the subsequent plasma nitriding can prevent the diffusion of nitrogen to the silicon substrate interface, and the nitrogen enters the surface of the SiON film. Therefore, even if it is a deposited film, there is no interface deterioration due to nitrogen diffusion, and a SiON gate insulating film having a sufficiently high nitrogen density and a high dielectric constant can be obtained.
(3) Even if the initial deposited film contains defects, the defects can be eliminated or reduced by plasma oxidation and plasma nitridation.
[0038]
By the way, it is difficult to directly confirm from the electrical measurement that the film density of the deposited SiON film is increased by plasma oxidation. This is because the film thickness is increased by plasma oxidation. However, an increase in film density due to plasma oxidation can be confirmed from the following experiment. In the experiment, if the film density is increased by radical oxidation, the film density should be increased by radical nitriding as well, and the increase in film thickness (electrical film thickness) is small in radical nitridation compared to radical oxidation. Take advantage of the fact that
[0039]
FIG. 12 shows a process for manufacturing SiON films of two experimental samples. One is direct radical oxidation of the deposited SiON film (sample A). The other is radical oxidization (sample B) after plasma nitriding the deposited SiON film. FIG. 13 shows the result of measuring the electric film thickness of the SiON film after radical oxidation of these samples A and B. The lower the film density of the SiON film, the greater the degree of oxygen oxidation progressing through the film and the substrate oxidation, so the final film thickness should increase. The result of FIG. 13 shows that the increase in film thickness due to radical oxidation is suppressed as compared with the sample A as a result of the film density of the sample B being increased by radical nitridation.
[0040]
FIG. 14 shows the results of measuring the interface state density after radical oxidation for samples A and B. As described above, the smaller the film density before radical oxidation, the higher the degree of oxygen oxidation progressing through the film and the substrate oxidation, so the interface should be better and the interface quasi-density should be lower. The result of FIG. 14 shows that the film density of sample B is increased by radical nitridation, so that oxygen permeation during radical oxidation is suppressed and the interface state density is not reduced as compared with sample A. Yes.
[0041]
In addition, SiO ₂ Regarding the film, it has already been reported that the thermal oxide film and radical oxide film formed on the silicon substrate have a higher density in the latter (M. Nagamine, H. Itoh, H. Satake, and A. Toriumi). "Radical Oxygen (O *) Process for Highly-Reliable SiO2 with High Film-Density and Smoother SiO2 / Si interface," in IEDM Technical 3 (98). Also from this, it can be easily estimated that the film density increases by performing radical oxidation on the SiON film.
Furthermore, if the film density is increased by radical oxidation, high-temperature O ₂ Even with annealing, the film density is thought to increase.
[0042]
[Third embodiment]
Since the element structure of the MOS transistor according to the third embodiment is the same as that of the first embodiment, detailed description thereof is omitted. FIG. 9 shows a manufacturing process of the gate insulating film in this embodiment.
[0043]
As shown in FIG. 9, the silicon wafer subjected to the diluted hydrofluoric acid treatment was transferred into the chamber 11 of the manufacturing apparatus of FIG. The wafer temperature was set to 750 ° C., and 400 Torr of NO gas was allowed to flow for 1 minute to perform oxynitriding. Thereafter, a SiON film was deposited at a wafer temperature of 500 ° C. The deposition conditions at this time are a total pressure of 1.2 Torr and SiH. ₄ / N ₂ / O ₂ = 20 sccm / 120 sccm / 0.1 Torr, and the process was performed for 1 minute. N supplied from the pipe 15 ₂ , Active nitrogen was generated by applying an output of 2.45 GHz and 100 W to the microwave cavity 18. Thus, a base insulating film made of a laminated SiON film having an actual film thickness (physical film thickness) of 1.3 nm was formed.
[0044]
Next, the temperature of the wafer was maintained at 500 ° C., and oxygen was supplied from the pipe 12 at a pressure of 0.5 Torr. At the same time, an output of 2.45 GHz and 200 W was applied to the microwave cavity 17 to generate active oxygen, and plasma oxidation was performed for 1 minute. This oxidation step is performed at 1000 ° C., 0.5 Torr, 1 minute O ₂ It can be replaced by oxidation. The actual film thickness (physical film thickness) of the SiON film after this step was 1.8 nm.
[0045]
Next, nitrogen gas is supplied from the gas inlet 15 while maintaining the wafer temperature at 500 ° C., and at the same time, an output of 2.45 GHz and 100 W is applied to the microwave cavity 18 to perform plasma nitriding for 10 Torr for 10 minutes. It was. As described above, a gate insulating film having an EOT of 1.5 nm or less and a physical film thickness of 1.5 nm or more is obtained.
In this example, no post-annealing was performed. ₂ O, O ₂ Annealing (1000 ° C., 0.5 Torr, 20 seconds) or the like can be appropriately performed following the plasma nitridation.
[0046]
FIG. 10 and FIG. 11 show the electrical characteristics of the SiON gate insulating film thus formed with respect to leakage current and interface state density. FIG. 10 shows the measurement result of the leakage current Jg (A / cm 2) at the power supply voltage (oxide film equivalent electric field 5 MV / cm). The data of this example is “O ^* 500 ℃ + N ^* As a comparative example, plasma nitridation was performed at 10 Torr and 10 minutes at 500 ° C. and 900 ° C., respectively, on the SiON base insulating film (the film after the deposition of NO oxynitride and oxynitride film). What I did ("N ^* 500 ℃ ”,“ N ^* 900 ° C ”) NH for 10 seconds at 1050 ° C ₃ Nitrided ("NH ₃ 1050 ° C ”), plasma oxidation for 1 minute at 500 ° C. and 0.5 Torr (“ O ” ^* “500 ° C.” is also shown for reference.
[0047]
As can be seen from FIG. 10, when the plasma oxidation step for the base SiON film is omitted and only the plasma nitridation at 500 ° C. is performed, the leakage current is not sufficiently reduced. If the base SiON film is modified only by plasma nitriding to reduce the leakage current, a temperature of about 900 ° C. is required. However, although the leakage current is reduced by plasma nitriding at 900 ° C., the interface state density is not reduced as shown in FIG.
[0048]
On the other hand, it is understood that when plasma oxidation (500 ° C., 0.5 Torr, 1 minute) is performed for a short time before plasma nitriding, the leakage current is reduced to a level expected by the tunnel current calculation. That is, it is extremely effective to reduce the leakage current of the laminated SiON film including the deposited film by inserting a short oxidation step before plasma nitriding. This is also true when the initial SiON film is a deposited film single layer (second embodiment). Although EOT increases in the oxidation process (plasma oxidation), the EOT can be reduced by performing plasma nitriding (10 Torr, 10 minutes) at 500 ° C., and in the example, finally, EOT = 1. It became 26 nm. In FIG. 10, for comparison, SiO ₂ The characteristics of the film are also shown. According to this example, EOT SiO of equal EOT ₂ Compared to the film, the leakage current was reduced by three orders of magnitude.
[0049]
As shown in FIG. 11, the interface state is not significantly reduced only by nitridation of the base SiON film, but the interface state density is greatly reduced by introducing a short-time oxidation step before that. It can be seen that no increase in interface state density is observed.
From the above, in order to achieve both reduction of leakage current and reduction of interface state, the base SiON film (laminated film of NO oxynitride film and deposited oxynitride film) is oxidized for a short period of time, followed by plasma. It can be seen that nitriding is good. Such a process step configuration is particularly effective when the initial base SiON film includes a deposited (acid) nitride film.
[0050]
【The invention's effect】
According to the present invention, a conventional SiON film is used as a base insulating film, and this is combined with an oxidation process and a subsequent nitridation process, thereby forming a conventional SiON film. ₂ A gate insulating film can be obtained in which a larger amount of nitrogen is introduced than plasma nitridation of the base film to reduce leakage current and to suppress deterioration of the Si substrate interface.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a film forming apparatus used in an embodiment of the present invention.
FIG. 2 is a sectional view showing an element isolation process according to an embodiment of the present invention.
FIG. 3 is a cross-sectional view showing a step of forming a gate insulating film according to the same embodiment.
FIG. 4 is a cross-sectional view showing a polycrystalline silicon film deposition step according to the same embodiment.
FIG. 5 is a cross-sectional view showing a gate electrode forming step and a diffusion layer forming step according to the same embodiment.
6 is a cross-sectional view showing an interlayer insulating film formation step and a wiring formation step in the same example. FIG.
FIG. 7 is a diagram showing a gate insulating film forming step in the first embodiment.
FIG. 8 is a diagram showing a gate insulating film forming step in the second embodiment.
FIG. 9 is a diagram showing a gate insulating film forming step in the third embodiment.
FIG. 10 is a diagram showing leakage characteristics of a gate insulating film obtained by the third embodiment together with a comparative example.
FIG. 11 is a diagram showing interface characteristics of a gate insulating film obtained by the third embodiment together with a comparative example.
FIG. 12 is a diagram showing an experimental sample manufacturing process to prove the increase in film density due to plasma oxidation.
FIG. 13 is a view showing an electric film thickness of the experimental sample.
FIG. 14 is a diagram showing an interface quasi-density of the experimental sample.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... Chamber, 12, 13, 14, 15 ... Gas supply port, 16 ... Gas exhaust port, 17, 18 ... Microwave cavity, 19 ... Silicon wafer, 20 ... Heater, 21 ... Silicon wafer, 22 ... Element isolation region, 23 ... Gate insulating film, 24 ... Polysilicon film, 25 ... Gate electrode, 26, 27 ... n ⁺ Mold diffusion layer, 28... Interlayer insulating film, 29.

Claims (6)

In the method of manufacturing a semiconductor device for forming a semiconductor element including a gate insulating film on a silicon substrate, the step of forming the gate insulating film includes:
Forming a base insulating film containing silicon, oxygen and nitrogen on a silicon substrate;
An oxidation step of exposing the base insulating film to an atmosphere containing oxygen;
A nitriding step of nitriding the base insulating film with active nitrogen after the oxidation step;
A method for manufacturing a semiconductor device, comprising: 2. The method of manufacturing a semiconductor device according to claim 1, wherein the gate insulating film has a silicon oxide equivalent film thickness of 1.5 nm or less and a physical film thickness of 1.5 nm or more. 2. The method of manufacturing a semiconductor device according to claim 1, wherein the base insulating film is formed by thermal oxynitridation of the silicon substrate. 2. The method of manufacturing a semiconductor device according to claim 1, wherein the base insulating film is formed by physical or chemical deposition on the silicon substrate. The base insulating film includes an oxide film or oxynitride film formed by thermal oxidation or oxynitridation of the silicon substrate, and an oxynitride film or nitride film formed thereon by a physical or chemical film deposition method. 2. The method of manufacturing a semiconductor device according to claim 1, wherein the semiconductor device is a laminated film. 2. The method of manufacturing a semiconductor device according to claim 1, further comprising a step of performing post-annealing on the formed gate insulating film in a reactive gas capable of transferring and receiving charges.

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