JPH09266308A - Method of manufacturing semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the boundary level and to suppress the generation of electron trap, by performing heat treatment at a specified temperature range in the same furnace that an oxide film is formed. SOLUTION: After forming a gate oxide film on a silicon substrate, the heat treatment of it is performed in a fluoride gas atmosphere in the same furnace that an oxide film is formed. Activation energy that is obtained by a calculation is used and each reaction is assumed as an Arrhenius type. Upper limit temperature is approximately 80 deg.C where trap level density corresponds to Si-O density that is not bonded and the allowable upper limit of the density is 10<11> cm<-2> . Lower limit temperature is approximately 70 deg.C to suppress the density of an Si-H bond and an Si-OH bond that are not substituted by an Si-F bond to be 10<12> cm<-2> or less. When the setting temperature of the heat treatment is kept in the range of 700 to 800 deg.C and the heating is continued for 3 to 10 minutes, F is conducted into the boundary and the boundary level is terminated. Containment of F into an oxide film bulk is suppressed because of low temperature treatment. After that, N2 is introduced into the furnace and the substrate is taken out of the furnace.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for manufacturing a semiconductor device in which a gate oxide film is formed within a predetermined temperature range.

[0002]

2. Description of the Related Art Conventionally, a gate oxide film of a silicon MOS type field effect transistor (MOSFET) has been formed in a dry oxygen or mixed gas atmosphere of oxygen and hydrogen by 750 to 750.
It is performed by heating a silicon Si substrate at a temperature of 1200 ° C. At this time, heat treatment is performed in an atmosphere of argon gas or nitrogen N ₂ gas for the purpose of reducing the accumulation of fixed positive charges in the oxide film and the generation of interface states due to radiation irradiation.

However, even if such a process is performed, there is still a problem that an interface state or a charge trap in a film is generated due to stress such as irradiation of radiation, injection of hot carriers, and application of a high electric field. This is due to Si-H bonds existing in the interface or oxide film, desorption of hydrogen H from Si-OH bonds, and distortion of the oxide film structure near the interface between the gate oxide film and the Si substrate. Is believed to be. The existence of these interface states and charge traps
There is a problem that the threshold voltage of the transistor fluctuates, the insulation resistance of the device is reduced, and the like.

In order to prevent this, a method has been considered in which fluorine F which forms a stable bond with Si is introduced into the interface between the gate oxide film and the Si substrate, thereby terminating interface states and relaxing strain. One of the methods for introducing F into the interface between the oxide film and the Si substrate is as follows.
First, F is introduced into the gate electrode by an ion implantation method, and then heat treatment is performed at 900 to 1100 ° C. in an inert gas atmosphere to diffuse F in the gate oxide film and reach the interface. There is a method of terminating dangling bonds at the interface (“Journal of Appl.
ied Physics "(hereinafter J. Appl. Phys)
s. 61, 5102-5109, 1987
Year, JP-A-62-285470). According to this method, as shown in FIG. 13, the interface state density is significantly reduced with the introduction of F. As a result, it is reported that device characteristics such as hot carrier resistance of the device are improved.

As another method of introducing F into the interface, a method of forming a gate oxide film and then heating the lamp at a temperature of about 1000 to 1200 ° C. in a nitrogen trifluoride (NF ₃ ) gas atmosphere has been proposed. (JP-A-1-283873, JP-A-5-152323). According to this method, the Si—H bond existing at the interface and in the film is replaced with a more stable bond, the Si—F bond.
As shown in FIGS. 4A and 4B, the generation of the interface state due to the stress as described above is suppressed.

[0006]

In the above-described prior art, the interface state is reduced and the device characteristics are improved. However, when the density of introduced F increases, the shift of the flat band Vfb in the positive direction increases. Will happen. FIG. 15 is a characteristic diagram showing this state. The flat band V of a MOS capacitance device having a gate oxide film subjected to ion implantation of F and high temperature treatment is shown.
It shows that bf depends on the amount of F introduced (DDX
ie and D.E. R. J. Young. App
l. Phys. , 70 (1991), pp. 2755, the horizontal axis dose and the vertical axis Vfb shift. According to this figure, it is observed that the flat band Vfb shifts greatly in the positive direction with an increase in the density of the introduced F. This is because when the F is taken into the oxide film, It is considered that a level that becomes an electron trap is newly generated therein.

FIG. 16 is a characteristic diagram of mass analysis of secondary emission ions of a MOS capacitor device having a gate oxide film subjected to high-temperature treatment by ion implantation of F, showing an atomic concentration with respect to depth. (Y. Sioya et.
al. Appl. Phys. , 61 (198
7), p. 5102). As shown in this figure, 8
From the temperature exceeding 00 ° C., it can be seen that F is taken in not only at the interface of the gate oxide film / Si substrate but also in the bulk of the gate oxide film.

[0008] As described above, the reason why F is taken into the bulk of the gate oxide film is as follows: termination of dangling bonds in the film;
Alternatively, Si—OH and Si—H bonds in the film
Substitution to a -F bond is contemplated. Further, as can be seen from FIG. 16, the density (10 ¹⁵ cm ⁻² ) of F in the film after the heat treatment at 1000 ° C. is intrinsic (int) in the film.
linsic), the charge trap density (存在 10 ¹²
cm ^-2 ) or Si-OH, Si-H density (10 ¹³
~ 10 ¹⁴ ~ cm ^-2 ). Therefore, the incorporation of F into the oxide film is not limited to the above-described termination and substitution reaction, but a reaction in which F breaks the Si—O—Si bond in the oxide film to form a new Si—F bond occurs. It is expected that

Further, as shown in FIG. 16, as the heat treatment temperature at the time of introducing F is increased, the F density in the bulk of the oxide film is increased. In addition, the flat band shift increases as the density of F in the bulk of the oxide film increases. Therefore, when the oxide film is exposed to a high temperature in an atmosphere containing F or in a state where F can diffuse in the oxide film, trap levels are generated in the oxide film, and characteristics as a gate oxide film, There is a risk that reliability will be reduced.

In this connection, in the method using ion implantation of F into the gate electrode described in the prior art, a high-temperature heat treatment at 900 ° C. or more is required to sufficiently diffuse F through the gate electrode to the interface. In the case of lamp heating in an NF ₃ gas atmosphere, heat treatment is performed at a high temperature of 1000 ° C. or higher in order to introduce F to the interface in a short time. Therefore, in the conventional method, trap levels are inevitably generated in the film with the introduction of F.

[0011] Trapping of charges to the level in the gate oxide film causes a problem that the threshold voltage of the transistor fluctuates and the insulation resistance of the device deteriorates. In addition, Elec
Trially Programmable Read-
When the conventional technique is applied to the formation of a tunnel oxide film of an only-memory (EPROM), trapping of electrons to a level in the film and a change in an electric field due to the trapped electrons are caused by EPR.
This is a more serious problem since the write / erase current of the OM is greatly changed.

An object of the present invention is to provide a method of manufacturing a semiconductor device which eliminates these problems, reduces the interface state, and forms a gate oxide film in which the generation of electron traps in the film is suppressed. Is to do.

[0013]

According to the structure of the present invention, in the method of manufacturing a semiconductor device in which a silicon substrate gate oxide film is formed and then heat treatment is performed in a fluorinated gas atmosphere, the heat treatment is the same as the oxide film formation. It is characterized in that it is carried out in a furnace and that the temperature range of the heat treatment is specified.

In the present invention, the temperature range of the heat treatment is that the fluorinated gas is Si--H, Si--O on the gate oxide film.
The activation energies and reaction energies of the respective reactions of substitution of H for Si-F and destruction of Si-O-Si by F are theoretically calculated, and the substitution reaction and the trap level generation reaction of the reaction are calculated from the activation energy values. The reaction coefficient is calculated, and from the calculated reaction coefficient, the temperature dependence of the density of Si—H and Si—OH bonds remaining in the film without being replaced and the density of the species of the trap level generated by the reaction of F are calculated. It is possible to determine the temperature condition in which the density is within a predetermined allowable range, and the activation energy of each reaction of substitution of Si-H and Si-OH with Si-F and destruction of Si-O-Si by F. The calculation of the reaction energy and the reaction energy can be performed by the ab initio molecular orbital method.

Further, in the present invention, the trap level density in the gate oxide film is made to correspond to the unbonded Si—O, and this density is set to 1/100 or less of the Si—O—Si density.
The temperature range can be set by setting the density of H bonds not replaced by Si-F bonds to 1/100 or less, and the temperature range of the heat treatment in the fluorinated gas atmosphere obtained from the results of theoretical calculation is 700 ° C to 800 ° C. It can be ° C.

In setting the temperature range in the heat treatment of the present invention, it is necessary to grasp the temperature at which the following process occurs. 1) Thermal decomposition of NF ³ 2) Diffusion of F into the oxide film 3) Termination of dangling bonds in the film and at the interface 4) Substitution of Si-H or Si-OH with Si-F 5) By F Si—O—Si destruction 6) Trap level generation Among them, 1) Regarding thermal decomposition of NF ³ , 500
It is already known that decomposition proceeds at or above ° C. 2) Regarding the diffusion of F in the oxide film, it is known that at 600 ° C. or more, F sufficiently passes through the oxide film and reaches the interface. 3) Regarding the termination of dangling bonds existing at the interface and the film, under conditions where F can diffuse sufficiently in the film and reach the interface, F terminates dangling bonds and stabilizes. . Therefore, what is necessary for specifying the temperature range is a temperature at which the reactions 4) and 5) occur.

In the present invention, the determination of the temperature is performed using theoretical calculations. First, the activation energy and reaction energy of each reaction are calculated by an ab initio molecular orbital method. From the energy values, the reaction coefficients of the substitution reaction and the trap level generation reaction are calculated. Using the obtained reaction coefficient, the temperature dependence of the density of the remaining Si—H and Si—OH bonds in the film and the density of the species that become trap levels generated by the reaction of F without being replaced is calculated. The temperature conditions under which these densities fall below the allowable range are found, and the optimum temperature range is determined.

First, the activation energy and reaction energy of each reaction are calculated by the ab initio molecular orbital method. First, the reaction that can occur between the F atoms and the gated film is calculated. The molecular orbital method is a method of obtaining a wave function Φ that minimizes the energy E obtained from the following Schrodinger equation for a molecule having a certain structure, and determining an optimal structure and electronic state. Here, H is Hamiltonian.

HΦ = EΦ In this calculation, a certain molecular structure is first assumed, and approximated by the wave function of this molecule. This is generally approximated by a linear combination of the following Gaussian function f _i : A method is used. Here, a _i is a coefficient.

Φ = Σa _i f _i This approximated wave function Φ is substituted into the above equation to calculate the total energy. Next, the hypothesized structure is slightly displaced and the same calculation is performed. The calculation is repeated until the structure with the minimum total energy is obtained by this operation, and the molecular structure is determined. In this wave function calculation process, to simplify the calculation, the method using the parameters obtained from the experiment is called the empirical molecular orbital method, and the method without using the empirical parameters is called the ab initio molecular orbital method. Is an effective method for systems that are difficult to identify by experiment. As the calculation of the ab initio molecular orbital method, as an existing calculation program, an ab initio molecular orbital calculation program Gaussian 92 (Gausss) developed by MS Gordon et al.
ian, Pittsfurg, PA, 1992).

In the calculation of the reaction system, the above-described optimization calculation is performed for all the atoms and molecules included in the system. Here, the substitution reaction of the Si—H bond to the Si—F bond will be described. A cluster model for simulating the Si—H bond in the film is set, and here, H shown in the schematic diagram of FIG.
It is assumed that Si (OH) ₃ is used. This F and HSi (O
It is assumed that there is a reaction of the following formula (1) in which FSi (OH) ₃ and H are formed by the reaction with H) ₃ .

F + HSi (OH) ₃ → FSi (OH) ₃ + H (1) The left side of this equation is called a reaction system, and the right side is called a generation system. First, for F and HSi (OH) _{3 on} the left side of the equation and each of the molecules, the optimum structure and total energy are calculated by the above-described method (hereinafter, this calculation is referred to as structure optimization).

Next, as shown in FIG.
Consider a system at a distance from (OH) ₃ . The distance between F and the molecule is the distance between F and Si at the center of the molecule, and the position of F is the Si— of _three molecules of HSi (OH).
On the extension of the H bond, it is placed on the opposite side to H with respect to Si.
In this case, the distance between F and Si (hereinafter referred to as R (F-Si)) is kept constant, and the structure is optimized to determine the molecular structure of other parts. The same calculation is performed using R (FS
i) is gradually reduced and the calculation is continued.

In this calculation, the distance R (F-Si) is about twice the F-Si bond distance, and the variation of R (F-Si) is 0.1 atomic unit or less. Is appropriate (1 atomic unit is the radius of the hydrogen atom). The total energy obtained by this calculation is R (F−
4 (a), and R (F−
As Si) approaches the length of the F-Si bond, the change in total energy gradually decreases, and as R (Si-H) increases, a certain energy maximum T is reached. After this maximum point T is obtained, structural optimization is performed while keeping the R (Si-H) distance constant. As a result, the change in the total energy of the reaction system is obtained as a function of R (F-Si) and R (Si-H) as shown in FIG. 4 (b).

In this figure, the energy difference between the production system and the maximum point T is the activation energy of this reaction, and the energy difference between the reaction system and the production system is the reaction energy. In the following reaction formula (1 ′) which is the reverse reaction of the reaction formula (1), the activation energy is obtained from the energy difference from the maximum point T using the left side as a reaction system. From this, the likelihood of a reaction occurring can be calculated. H + FSi (OH) ₃ → HSi (OH) ₃ + F (1 ′) In the calculation of the molecular orbital method, a reaction system of molecules / atoms can be handled, so if this calculation is applied to a solid system, the solid portion It is simulated with molecules (clusters) that are partially cut out from. Since the gate oxide film is composed of a Si—O—Si network, a part of the network is formed of (OH) ₃ SiOSi (OH) ₃ clusters as shown in FIG. , Si-OH bond is H-Si (O
H) ₃ , HO—Si (OH) _3, which can be simulated as shown in FIGS. The reaction in which the Si—H bond is replaced with the Si—F bond using these clusters can be determined in the same manner as in the reaction (1).

Similarly, the reaction of the following formula (2) in which the Si—OH bond is replaced by the Si—F bond can be obtained in the same manner as the above-mentioned reaction (1). Also in this case, R (FS
It can be obtained by changing the i) and R (Si—OH) and optimizing the structure.

F + OH—Si (OH) ₃ → FSi (OH) ₃ + OH (2) Further, regarding the destruction of the Si—O—Si bond by F, the following two reaction formulas (3) and (4) Can be considered.

F + (OH) ₃ Si—O—Si (OH) ₃ → FSi (OH) ₃ + OSi (OH) ₃ ... (3) F + (OH) ₃ Si—O—Si (OH) ₃ → Si (OH) ₃ + FOSi (OH) ₃ (4) In the case of reaction formula (3), as shown in FIG. 6 (a), when F approaches Si, at this time, R (F- Si) and R
Structural optimization is performed using (Si—O) as a parameter, and in the case of reaction formula (4), as shown in FIG.
In the case of approaching the O atom at the center of i-O-Si, at this time, F approaches O and Si (OH) ₃ separates, so that R (O
Structural optimization is performed using -F) and R (Si-F) as parameters.

Further, by the reaction between Si—O and F, S
The following reaction formulas (5) and (6) can be considered for the reactions that generate i-F and Si-OF, respectively, and the structure is similarly optimized.

F + OSi (OH) ₃ → O + FSi (OH) ₃ ... (5) F + OSi (OH) ₃ → FOSi (OH) ₃ ... (6) The obtained values of the reaction energy and the activation energy of each reaction are shown.

[0031]

[Table 1]

From Table 1, it can be seen from the reaction of the formula (4) that the formula (3)
It turns out that the reaction of is more dominant. Equation (1),
It is shown that the reactions (2) and (3) are accelerated as the temperature increases. Also, since the activation energy of the substitution of Si—H and Si—OH bonds into Si—F bonds is smaller than the reaction formula (3) for destruction of Si—O—Si bonds by F, the former reaction is lower in temperature than the latter. It is clear that this will happen.

Here, among the species generated by these reactions, the species that become the electron trap level are described in the above (1) to (4).
The stabilization energy when the species generated in the reaction process of (3) receives electrons is examined and examined. The generated Si-F
Part, Si—O part having unbonded O (hereinafter, unbonded Si—O part)
Using FSi (OH) ₃ and OFSi (OH) ₃ as the cluster model of the “part”, the stabilization energy when these receive one electron is calculated, and the calculation results are shown in Table 2 below.

[0034]

[Table 2]

It can be seen from Table 2 that the Si--O portion is at the electron trap level. From the above calculation results, electron trap levels in the oxide film are generated by the introduction of F in a process as shown in the schematic diagram of FIG. That is, F (FIG. 7A) that diffuses the oxide film at high temperature is Si—O—Si
The bond is broken to generate a Si—F bond and unbonded Si—O (FIG. 7B). When electrons are injected into this portion, the electrons are trapped in the unbonded Si—O portion (FIG. 7).
(C)). This is considered to be the cause of the flat band shift observed by the conventional method.

From the above results, in order to prevent the generation of electron trap levels by the introduction of F, it is sufficient to introduce F at a low temperature at which Si—O—Si destruction does not occur. However,
Since Si—H bond and Si—OH bond can also easily desorb H to become a charge trap level, these bonds are
It is necessary to substitute as much as possible for the iF bond. Therefore, a high temperature higher than the temperature at which the substitution reaction can sufficiently occur is required.

Next, using the activation energy obtained by the calculation, it is assumed that each reaction is of the Arrhenius type, so that Si—H, Si—OH, unbonded Si—
Calculate how each density of O changes with temperature.

In this case, the density N of Si—H and Si—OH
_Si-H and N _Si-OH are experimentally measured values.
For example, it is shown on page 223 of Takuo Sugano, "Physics of Si Devices". The reaction coefficient K of each reaction at the temperature T
Is determined from the reaction shown in Table 1 and its activation energy Ea. Here, A is the reaction frequency (constant), and k is the Boltzmann coefficient.

K = Aexp (−Ea / kT) Therefore, for a certain F density [F], Si—H, Si—
The change in OH density is expressed by the following equation.

[0040]

Where K1 and K2 are represented by the reaction formula (1),
The reaction coefficient of (2), K1 'and K2', are the reaction coefficients of the inverse reaction of K1 and K2. Therefore, each change in density is caused by the reaction (3) ), Si-O and F
The formulas of reactions (5) and (6) in which Si—F and Si—OF are generated by the reaction with are calculated as follows. Here, K3 is the reaction coefficient of equation (3), K4 and K5 are the reaction coefficients of equations (5) and (6), and K4 'is the reaction coefficient of the inverse reaction of K4.

[0042]

Here, the dose of F is 10 ¹⁵ cm
⁻² , the density of Si—H in the film is 10 ¹³ cm ⁻² , the density of Si—OH in the film is 10 ¹² cm ⁻² , and the density of Si— ^{OS in} the film is
The density of i was 10 ¹³ cm ^-2 . The calculation result is shown in FIG. Here, the trap level density in the film is unbonded Si—O.
Corresponding to the density, the upper limit of the density is 10 ¹¹ cm
^{Assuming −2} , the upper limit temperature is about 800 ° C. as shown in the characteristic diagram of FIG. In addition, Si-H bond and Si-O
In order to suppress the density of H bonds not replaced by Si—F bonds to 10 ¹² cm ⁻² or less, the lower limit temperature is about 700 ° C.
It can be seen that it is.

In summary, the heat treatment temperature of the gate oxide film in the NF ₃ atmosphere for reducing the interface state and the trap state in the film is determined to be 700 to 800 ° C.

[0045]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, as an embodiment of the present invention, a procedure for forming a gate oxide film based on the present invention will be described with reference to the drawings. FIG. 1 is a timing chart showing a time change of a temperature and an introduced gas at the time of forming a gate oxide film according to an embodiment of the present invention. First, by the same operation as the conventional manufacturing method,
Using an oxidation furnace, in a dry oxygen atmosphere, 900 to 1100
The Si substrate is heated at a temperature of ° C. to form a gate oxide film. Next, the temperature in the furnace is lowered to 850 ° C. or lower while introducing N ₂ gas and exhausting O ₂ . At that time, NF ₃ gas diluted with O ₂ or N ₂ is introduced into the oxidation furnace. N at this time
The ratio of F ₃ is O ₂ /0.2 to 1.0 vol% NF ₃ ,
N ₂ /0.05 to 0.2 vol% NF ₃ is set. Maintain the temperature at the set temperature (700-800 ° C.) and heat for 3-10 minutes. This process introduces F into the interface and terminates the interface state. Further, since the treatment is performed at a lower temperature than in the conventional method, the incorporation of F into the bulk of the oxide film is suppressed. Thereafter, N ₂ is introduced into the furnace, and the substrate is discharged from the furnace.

For a MOS capacitor device having a gate oxide film formed using this process,
FIG. 9 shows a result obtained by performing Static CV measurement and calculating the interface state density in comparison with a conventional method (ion implantation of F + high-temperature annealing). Here, the oxide film thickness is 9n.
m, oxide film formation temperature 900 ° C., N ₂ /0.2 vol% N
In F _3, set temperature 700 ° C., was heated 3 min. It can be seen that even with the low-temperature treatment shown in the present invention, the interface state is reduced to the same extent as that by the conventional method. According to the conventional method, an oxide film is formed at the same oxide film thickness at 900 ° C., an F dose is 1 + 10 ¹⁵ cm ⁻² , 30 keV, and N ₂ atmosphere.
Annealing was performed at 00 ° C. for 30 minutes.

The results of measuring the flat band shift after applying a constant current of 0.1 A / cm ² to the MOS capacitor device manufactured in the same manner for 100 seconds are shown below.
As shown in FIG. The shift amount is about 2 V smaller than that in which F is introduced by the conventional method (ion implantation + high temperature annealing), and it is clear that the generation of electron trap levels in the film is suppressed. Therefore, it can be understood that the present invention can suppress the fluctuation of the threshold voltage of the MOS transistor.

Next, as a second embodiment of the present invention, EP
The result of the case where it is used for forming a tunnel oxide film for ROM will be described. In this case, the tunnel oxide film is formed at an oxidation temperature of 900 in a dry oxygen atmosphere with an oxide film thickness of 11 nm.
° C., was performed by 3 min heating F introduced in N ₂ /0.2vol%NF _3, 750 ℃.

FIG. 1 shows the repetition characteristics of the FN write / FN erase type flash memory having the tunnel oxide film.
It is shown in FIG. For comparison, the characteristics of a flash memory using a normal tunnel oxide film without the introduction of F are also shown. Looking at the variation of the threshold value (Vth) after the repetition of 10 ⁶ , in the case of the present embodiment, in particular, Vt at the time of erasing
It can be seen that the increase in h is suppressed. This is FN
This indicates that generation of electron traps generated when a current flows through the tunnel oxide film is suppressed. In the process of the present embodiment, the Si—H and Si—OH in the oxide film
Is replaced by Si—F, and thus generation of electron trap levels due to elimination of H from these bonds is considered to be suppressed.

Next, the same gate oxide film formed according to the present embodiment was subjected to a bottom current conduction stress (0.1 A /
FIG. 12 shows current-voltage (IV) characteristics before and after (cm ² , 100 seconds). According to this FIG. 12, the leakage current after stress is small in the low voltage region according to the present embodiment. This means that in the process according to the invention,
It is considered that the generation of the electron trap level in the film was suppressed, so that the leak current via the level was reduced. From these results, it is expected that the retention characteristics of the flash memory can be improved by using the tunnel oxide film according to the present invention. From the above, it can be seen that this method is also useful as a method for forming a tunnel oxide film for EPROM.

[0051]

As described above, according to the present invention,
By terminating the interface state with F, the density can be reduced by about one digit, and a device having much higher hot carrier resistance than that of the H terminator can be manufactured. With regard to the generation of the electron trap level, the generation amount is improved by about one digit or more. As a result, in the MOS field effect transistor, improvement in device characteristics such as improvement in hot carrier resistance and mobility and reduction in fluctuation of threshold voltage are expected, and in EEPROM, improvement in repetition characteristics and retention characteristics. Can be expected.

[Brief description of drawings]

FIG. 1 is a timing chart of temperature and gas flow for explaining a gate oxide film forming process according to an embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating a cluster model of a Si—H bond according to the present embodiment.

FIG. 3 is a schematic diagram illustrating the influence of F atoms on the cluster model of FIG. 2;

FIG. 4 is a schematic diagram illustrating the relationship between reaction energy, activation energy, and total energy in the present embodiment.

FIG. 5 shows a gate oxide film, a Si—H bond,
It is a schematic diagram explaining the solid structure of a Si-OH bond and a simulated cluster.

FIG. 6 is a schematic diagram illustrating a cluster when an F atom approaches Si and O in the present embodiment.

FIG. 7 is a schematic diagram illustrating an electron trap level generation model when F is introduced according to the present embodiment.

FIG. 8 is a temperature characteristic diagram of each reaction coefficient obtained by the theoretical calculation of the present embodiment.

FIG. 9 is a characteristic diagram showing an interface state density of a MOS capacitor device manufactured according to the present invention and a conventional example.

FIG. 10 is a characteristic diagram showing a flat band shift of a MOS capacitance device made according to the present invention and a conventional example.

FIG. 11 is a characteristic diagram showing the repetitive storage characteristics of a flash memory having a tunnel oxide film formed according to the present invention and a conventional example.

FIG. 12 is a voltage-current characteristic diagram of a MOS capacitance device manufactured according to the present invention and a conventional example.

FIG. 13 is a characteristic diagram showing an interface state density Dit of a conventional MOS capacitor device having a gate oxide film subjected to F ion implantation and high-temperature treatment.

FIG. 14 is a characteristic diagram showing an interface state generation due to radiation irradiation stress of a conventional MOS capacitor device having a gate oxide film heat-treated in NF3.

FIG. 15 is a characteristic diagram showing the dependence of the flat band shift on the amount of F introduced in a conventional MOS capacitor device having a gate oxide film subjected to F ion implantation and high-temperature treatment.

FIG. 16 is a characteristic diagram showing secondary emission ion mass spectrometry results of a conventional MOS capacitor device having a gate oxide film subjected to F ion implantation and high temperature treatment.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication location H01L 27/115 H01L 27/10 434 21/336 29/78 301Z

Claims (8)

[Claims] 1. A method of manufacturing a semiconductor device, comprising forming a gate oxide film on a silicon substrate and then performing heat treatment in a fluorinated gas atmosphere, wherein the heat treatment is performed in the same furnace as the oxide film formation, and A method for manufacturing a semiconductor device, characterized in that a temperature range of heat treatment is specified and treated. 2. The temperature range of the heat treatment is such that the activity of each reaction of the replacement of Si—H and Si—OH with Si—F by the fluorinated gas on the gate oxide film and the destruction of Si—O—Si by F. Theoretical calculation of reaction energy and reaction energy,
The reaction coefficients of the substitution reaction and the trap level generation reaction are calculated from the activation energy values, and the reaction coefficients of the Si—H and Si—OH bonds remaining in the film without substitution and the F reaction are calculated from the calculated reaction coefficients. 2. The method for manufacturing a semiconductor device according to claim 1, wherein the temperature dependence of the density of the species that will become the trap level is calculated, and the temperature condition in which these densities are within a predetermined allowable range is determined. 3. The activation energy and reaction energy of each reaction of substitution of Si—H and Si—OH with Si—F and destruction of Si—O—Si by F are calculated by an ab initio molecular orbital method. The method for manufacturing a semiconductor device according to claim 2, which is performed. 4. A cluster model for simulating Si—H and Si—OH bonds is HSi (OH) ₃ and HOS, respectively.
4. The method of manufacturing a semiconductor device according to claim 3, wherein i (OH) ₃ is used to calculate the activation energy and reaction energy of the reaction in which these bonds are replaced by Si—F bonds. 5. The reaction of breaking the Si-O-Si by F, F + (OH) ₃ SiOSi (OH) ₃ is (OH) ₃
SiF + Si (OH) ₃ and (OH) ₃ SiOF + S
4. The method of manufacturing a semiconductor device according to claim 3, wherein the activation energy and the reaction energy are calculated by simulating as i (OH) ₃ . 6. The reaction coefficient K of each reaction at the temperature T is:
Activation energy Ea of each reaction, reaction frequency (constant) A,
K = Aexp (-EA) where k is the Boltzmann coefficient
3. The method for manufacturing a semiconductor device according to claim 2, wherein the value is calculated as / kT). 7. The trap level density in the gate oxide film is made to correspond to unbonded Si—O, and this density is set to 1/100 or less of the Si—O—Si density, and Si—F of Si—H bonds is bonded.
3. The method of manufacturing a semiconductor device according to claim 2, wherein the temperature range is set such that the density of those not replaced by bonds is 1/100 or less. 8. The method of manufacturing a semiconductor device according to claim 2, wherein the temperature range of the heat treatment in the fluorinated gas atmosphere determined from the result of theoretical calculation is 700 ° C. to 800 ° C.