JP2007012666A - Method for forming dielectric film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form a uniform and sharp SiN film having a high concentration and an arbitrary film thickness on the surface of an SiO<SB>2</SB>film. <P>SOLUTION: The SiN film 2 is deposited on a substrate 1 directly before the SiN film 2 is turned into a thin film using sputter etching by an oxygen ion 3. In this case, by controlling the irradiation energy of the oxygen ion 3, an incident angle to the surface of the SiN film 2, and a dose rate, nitrogen in the deposited SiN film 2 is substituted for oxygen injected by irradiation for forming a silicon oxide film 4 at an interface side with the substrate 1, thus forming an SiN/silicon oxide lamination structure with a surface side as the extremely thin SiN film 2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a method for forming a dielectric film, and particularly a dielectric film characterized by a technique for forming a very thin dielectric film having a SiN / SiO ₂ structure having a steep interface, particularly a gate insulating film. It is related with the formation method of this.

  In recent years, as the degree of integration of semiconductor integrated circuit devices has increased, the thickness of the gate insulating film has been reduced, and accordingly, it is necessary to reduce the leakage current through the gate insulating film.

Therefore, by trying to laminate a silicon nitride film (SiN film) having a dielectric constant higher than that of the SiO ₂ film on the silicon oxide film (SiO ₂ film), or by nitriding the surface of the SiO ₂ film by a remote plasma method, Attempts have been made to form a SiON film there (see, for example, Non-Patent Document 1).

In the case of laminating the SiN film on the former SiO ₂ film, dichlorosilane (DCS) or trichlorosilane (TCS) and NH ₃ are used as the source gas. When this source gas is used, There is a problem that the SiN film is not uniformly formed on the SiO ₂ film.

For this reason, before depositing the SiN film, the surface of the SiO ₂ film is thermally nitrided at about 700 ° C. to 850 ° C., thereby forming the SiON film there.

However, if the former method is used to obtain a gate insulating film having a thickness of about 1.2 nm, a large amount of N reaches not only the surface of the SiO ₂ film but also the Si substrate during thermal nitridation. As a result, the threshold value V _{th of} the MISFET fluctuates in the negative direction, and the hole mobility in the channel decreases.

On the other hand, in the latter method of nitriding by the remote plasma method, a SiON film is formed, and if the N concentration in the vicinity of the surface of the Si substrate is controlled so as to avoid the above-described problems, There is a problem that the nitriding of the SiO ₂ film becomes insufficient and the effect of reducing the leakage current cannot be obtained sufficiently.

  Further, if the leakage current is to be sufficiently reduced, there arises a problem that the threshold value fluctuates and the mobility is lowered as in the case of the former lamination.

Therefore, in order to solve such a problem, it is proposed that a SiN film is deposited on the SiO ₂ film by a CVD method, and then the deposited SiN film is modified by a remote plasma nitriding process to reduce a leakage current. (For example, refer to Patent Document 1).

On the other hand, SiN / Other methods of forming the SiO ₂ layered structure, in the SiN film by injecting O ₂ ions, SiN / SiO ₂ by converting the SiO ₂ film by oxidizing a part of the SiN film A method of forming a laminated structure has been proposed (see, for example, Patent Document 2).
VLSI Symposium 2001 Session, T7A-4 JP 2004-022902 A Japanese Patent Application Laid-Open No. 10-125813

  However, although the leakage current is reduced by modifying the SiN film by remote plasma nitriding treatment, the film thickness of the deposited SiN thin film is originally not uniform. It cannot be solved.

On the other hand, the method of oxidizing a part of the SiN film by ion implantation is a process for forming a charge trapping interface in the nonvolatile memory. Therefore, simply replacing a part of the SiN film with the SiO ₂ film, There is a problem that the film thickness cannot be controlled.

Accordingly, an object of the present invention is to form a uniform and steep SiN layer having a high concentration and an arbitrary film thickness on the SiO ₂ surface in order to obtain intended electrical characteristics.

FIG. 1 is a diagram illustrating the basic configuration of the present invention. Means for solving the problems in the present invention will be described with reference to FIG.
In order to solve the above-mentioned problem, in the dielectric film formation method of the present invention, after depositing the SiN film 2 directly on the substrate 1, the SiN film 2 is thinned by sputter etching with oxygen ions 3. At the same time, by controlling the irradiation energy of oxygen ions 3, the incident angle to the surface of the SiN film 2, and the dose amount, substitution of nitrogen in the deposited SiN film 2 and oxygen implanted by irradiation is caused. Then, by forming the silicon oxide film 4 on the interface side with the substrate 1, a SiN / silicon oxide layer having a very thin SiN film 2 on the surface side is formed.
The silicon oxide layer is ideally a SiO ₂ film.

  As described above, by utilizing the thinning and the oxidizing action by the sputter etching using the oxygen ions 3, the SiN / silicon oxide layer structure can be formed by the oxidizing action, and to a certain thickness by the thinning action. The thickness of the uniformly formed SiN film 2 can be arbitrarily reduced.

  At this time, the interface between the SiN film 2 and the silicon oxide film 4 can be made sharp by controlling the incident angle of the oxygen ions 3 to the surface of the SiN film 2, and the substrate can be controlled by controlling the irradiation energy. Nitrogen atoms in the vicinity of the surface of 1 can be removed by out-diffusion accompanying the oxidation of the SiN film 2, and the film thickness of the silicon oxide film 4 formed by controlling the dose amount and SiN etched by sputtering The amount of membrane 2 can be controlled.

  In this case, it is desirable that the irradiation energy of the oxygen ions 3 is 150 to 350 eV / Oatm, preferably 250 eV / Oatm, thereby more efficiently causing substitution of nitrogen and oxygen, and the surface of the silicon oxide film 4 is formed. A high-concentration uniform and steep SiN film 2 can be formed.

  The incident angle of the oxygen ions 3 is preferably 0 to 30 ° with respect to the normal line of the substrate 1, whereby the steep SiN film 2 can be formed.

Further, the dose amount of the oxygen ions 3 is desirably 1 × 10 ¹⁶ cm ⁻² or more, thereby causing more efficient sputter etching and supplying sufficient oxygen for replacement.

  By using the above-described SiN / silicon oxide layer, an increase in leakage current can be suppressed even if the gate insulating film is thinned.

When configuring a semiconductor device having such a gate insulating film, a nitrogen concentration gradient in the range of 1 nm in the vicinity of the center of the transition region at the interface between the SiN film 2 and the silicon oxide film 4 is represented by n and the nitrogen concentration is represented by n. When the film thickness in the vicinity of the center is t [nm],
log ₁₀ n = a × t
It is desirable that the nitrogen concentration gradient a as viewed from the SiN film 2 side expressed by the following formula has a steep nitrogen concentration gradient a where a <−0.8.

In the present invention, since a thermal process such as a thermal nitriding method is not used, a uniform and steep SiN film can be formed on the SiO ₂ film surface, and the thickness of the SiN film / SiO ₂ film can be increased. Since the thickness depends on the thickness of the SiN film serving as the base and the etching rate, the thickness of the SiN film serving as the base is reduced to some extent, so that the thickness of the current-generation gate insulating film is sufficiently 1.2 nm. It becomes possible.

In the present invention, after a SiN film is directly deposited on a silicon substrate by CVD or sputtering, the irradiation energy is 150 to 350 eV / Otom, the dose is 1 × 10 ¹⁶ cm ⁻² or more, and the incident angle with respect to the normal of the substrate The SiN film is thinned by performing sputter etching with oxygen ions under a condition of 0 to 30 °, and the substitution of nitrogen in the deposited SiN film with oxygen injected by irradiation causes an interface side with the substrate A silicon oxide film, ideally an SiO ₂ film, is formed.

Here, with reference to FIG. 2 thru | or FIG. 3, the formation method of the dielectric film of Example 1 of this invention is demonstrated.
See Figure 2
In FIG. 2, first, on the silicon substrate 11, the pressure in the chamber is set to 1 to 100 Pa, the substrate temperature is set to 600 to 800 ° C., and dichlorosilane (DCS) is set to 1 to 1 by low pressure chemical vapor deposition (LPCVD). The SiN film 12 having a thickness of, for example, 6 nm is formed by supplying 100 sccm and NH ₃ at a flow rate of 1 to 1000 sccm.

Next, using an ion implantation apparatus, the surface of the SiN film 12 is irradiated with O ₂ ⁺ 13 accelerated to 300 to 700 eV, for example, 500 eV at a dose of 1 × 10 ¹⁶ cm ⁻² or more at room temperature. In addition to sputter etching, substitution of nitrogen in the SiN film 12 and oxygen implanted by irradiation causes the SiO ₂ film 14 to be formed on the interface side with the silicon substrate 11. Here, the situation of oxidation from the surface side is shown.

In this case, nitrogen substituted for oxygen is driven to the SiN film 12 side, and excess nitrogen is released from the surface of the SiN film 12.
By performing this oxygen ion irradiation for a predetermined time, for example, by irradiation with a dose of 1 × 10 ¹⁷ cm ⁻² , 2 nm of the surface is made into the SiN film 15 and the remaining 2 nm is made into the SiO ₂ film 14.

See Figure 3
FIG. 3 shows the result of measuring the nitrogen distribution in the depth direction of the sample irradiated by changing the incident angle of oxygen ions by the SIMS (secondary ion mass spectrometry) method, and the angle with respect to the normal line of the silicon substrate 11. It can be seen that at 0 to 30 °, the interface between the SiN film 15 and the SiO ₂ film 14 is steep due to sputter etching and substitution.

Further, as apparent from FIG. 3, the nitrogen concentration in the vicinity of the surface is almost the same as that during the formation of the SiN film 12, and the problem with the conventional nitriding method by the remote plasma method, If the N concentration in the vicinity is controlled to be low, the problem of insufficient nitridation of the SiO ₂ film has been solved.

When the incident angle is 40 °, the nitrogen concentration gradient in the range of 1 nm near the center of the transition region at the interface between the SiN film 15 and the SiO ₂ film 14 is n, the nitrogen concentration is n, and the film thickness near the center of the transition region. Is t [nm],
log ₁₀ n = a × t
The nitrogen concentration gradient a seen from the SiN film 15 side represented by
a≈ [−1.80 − (− 1.05)] / 1 nm = −0.75
Therefore, it can be said that the nitrogen concentration gradient a is sufficiently steep if a <−0.8.

In this way, O ₂ ⁺ 13 is formed to a certain thickness with an acceleration energy of 300 to 700 eV (150 to 350 eV per oxygen atom), an incident angle of 0 to 30 °, and a dose of 1 × 10 ¹⁶ cm ^−2. The SiN film deposited in a uniform film thickness is thinned by ion etching, and the interface side with the silicon substrate is replaced with a SiO ₂ film, so that the SiN / SiO ₂ structure with a steep nitrogen concentration at the interface is obtained. A dielectric film can be formed.

Here, the manufacturing process of the semiconductor device according to the second embodiment of the present invention will be described with reference to FIGS. 4 to 5. Here, the manufacturing process of the n-channel type MISFET in the CMOS semiconductor device is shown.
See Figure 4
An element isolation region 22 is formed on a p-type silicon substrate 21 using a STI (Shallow Trench Isolation) method, and then a p-type well 23 is formed by implanting B ions into the element formation region. Is implanted to form a channel doped region (not shown).

Next, after removing the natural oxide film on the surface of the p-type well region 23 by HF treatment, the pressure in the chamber is set to 1 to 100 Pa, for example, 20 Pa, and the substrate temperature is set to 600 to 800 ° C., for example, 650 ° C. by LPCVD. The SiN film 24 having a thickness of, for example, 4 nm is formed by supplying dichlorosilane (DCS) at a flow rate of 1 to 100 sccm, for example, 30 sccm and NH ₃ at a flow rate of 1 to 1000 sccm, for example, 150 sccm.

Next, using an ion implantation apparatus, O ₂ ⁺ 25 accelerated to 300 to 700 eV, for example, 500 eV, at room temperature at an incident angle of 0 to 30 °, for example, 0 °, 1 × 10 ¹⁶ cm. The surface of the SiN film 24 is sputter etched by irradiating at a dose of ⁻² or more, and at the interface side with the p-type well region 23 by causing substitution of nitrogen in the SiN film 24 and oxygen implanted by irradiation. A SiO ₂ film 26 is formed.
Here, the situation of oxidation from the surface side is shown.

At this time, the dose amount is controlled by adjusting the oxygen ion irradiation time. For example, 1 nm of the surface is irradiated with a dose amount of 2 × 10 ¹⁷ cm ⁻² to form the SiN film 27 and the remaining 1 nm is SiO 2. _Two films 26 are formed.
In this case, the total thickness of the SiN film + SiO ₂ film and the thickness ratio of the SiN film / SiO ₂ film can be controlled by the incident angle of oxygen ions, acceleration energy, and dose.

See Figure 5
Then, again, the pressure in the chamber is set to 10 to 50 Pa, for example, 40 Pa, the substrate temperature is set to 600 to 650 ° C., for example, 620 ° C., and SiH ₄ gas is supplied at a flow rate of 50 to 300 sccm, for example, 200 sccm by LPCVD. As a result, a polycrystalline silicon film 28 having a thickness of, for example, 110 nm is formed.

Next, after patterning the polycrystalline silicon film 28 to the SiO ₂ film 26 to form a gate structure 30 using the polycrystalline silicon film as the gate electrode 29, n ions are implanted by using the gate structure 30 as a mask. A mold extension region 31 is formed.

Next, after depositing a SiO ₂ film on the entire surface, anisotropic etching is performed to form a sidewall 32, and then As ions are implanted using the sidewall 32 and the gate structure 30 as a mask. -The drain region 33 is formed.

Next, Co is deposited on the entire surface and then heat treatment is performed to form a silicide electrode 34 made of CoSi _{2 on} the surfaces of the n-type source / drain regions 33 and the gate electrode 29, and then hydrogen peroxide solution and ammonia solution Unreacted Co is removed by etching using a mixed solution of sulfuric acid or a mixed solution of sulfuric acid and hydrogen peroxide.

Next, after a SiN film 35 having a thickness of, for example, 20 nm is deposited on the entire surface by using the CVD method, an SiO ₂ film 36 is deposited on the entire surface.

Next, by sequentially etching the SiO ₂ film 36 and the SiN film 35 to expose the n-type source / drain regions 33, a doped polycrystalline silicon layer doped with P is deposited and then patterned. By forming the source / drain extraction electrode 37, the basic configuration of the n-channel MISFET is completed.

In the second embodiment, the gate insulating film has a SiN / SiO ₂ structure composed of a SiO ₂ film in which the substrate side of the SiN film is replaced by oxygen ion irradiation, so that the gate insulating film is made thinner and leakage current resistance is improved. Can be achieved.

  In addition, since the SiN film is deposited to a certain thickness at the deposition stage, the SiN film can be made to have a uniform thickness, and since it is thinned by sputter etching, the thickness of the thinned SiN film is also uniform. Can be kept in.

Although the embodiments of the present invention have been described above, the present invention is not limited to the configurations and conditions described in the embodiments, and various modifications are possible. For example, in the embodiments, oxygen ions Although using O ₂ ⁺ as, not limited to O ₂ ^+, it is those may be used O ^+, in which may be the acceleration energy of 150~350eV per oxygen atom.

  In each of the above embodiments, the SiN film to be deposited first is formed by LPCVD using dichlorosilane as a Si raw material. However, the SiN film can be formed by any method, for example, trichlorosilane. An LPCVD method using Si material may be used, or a plasma CVD method may be used.

  Further, in each of the above embodiments, sputter etching with oxygen ions is performed using an ion implantation apparatus. However, an oxygen ion gun is provided in a CVD apparatus for forming a SiN film to form a SiN film. Oxygen ion irradiation may be performed as a series of steps in the same chamber.

  In each of the above embodiments, a silicon substrate is used as the substrate. However, the substrate is not limited to a silicon substrate, and a SiGe substrate containing 50 atomic% or less of Ge may be used.

The detailed features of the present invention will be described again with reference to FIG. 1 again.
Again see Figure 1
(Appendix 1) After depositing the SiN film 2 directly on the substrate 1, the SiN film 2 is thinned by sputter etching with oxygen ions 3, and the irradiation energy of the oxygen ions 3 at that time, to the surface of the SiN film 2 By controlling the incident angle and the dose amount, the nitrogen in the deposited SiN film 2 is replaced with the oxygen implanted by the irradiation, and the silicon oxide film 4 is formed on the interface side with the substrate 1. A method of forming a dielectric film, comprising forming a SiN / silicon oxide layer having a very thin SiN film 2 on the surface side.
(Additional remark 2) The formation method of the dielectric film of Additional remark 1 characterized by making irradiation energy of the said oxygen ion 3 into 150-350 eV / Otom.
(Additional remark 3) The incident angle of the said oxygen ion 3 shall be 0-30 degrees with respect to the normal line of the said board | substrate 1, The formation method of the dielectric film of Additional remark 1 or 2 characterized by the above-mentioned.
(Additional remark 4) The dosage amount of the said oxygen ion 3 shall be 1 * 10 ^{< 16} > cm ^<-2 > or more, The formation method of the dielectric film of any one of Additional remark 1 thru | or 3 characterized by the above-mentioned.
(Supplementary note 5) The method for forming a dielectric film according to any one of supplementary notes 1 to 4, wherein the substrate 1 is a semiconductor substrate, and the SiN / silicon oxide layer is a gate insulating film. (Supplementary Note 6) mainly of the silicon oxide layer is, the method of forming the dielectric film according to any one of Appendices 1 to 5, characterized in that of SiO _2.
(Supplementary Note 7) The semiconductor substrate side includes a silicon oxide film 4 in which N in the SiN film 2 is replaced with O, and the surface side includes a gate insulating film made of a SiN / silicon oxide layer, which is the SiN film 2. A semiconductor device.
(Supplementary Note 8) The nitrogen concentration gradient in the range of 1 nm near the center of the transition region at the interface between the SiN film 2 and the silicon oxide film 4 is n, and the film thickness near the center of the transition region is t [nm]. If
log ₁₀ n = a × t
8. The semiconductor device according to appendix 7, wherein the nitrogen concentration gradient “a” as viewed from the SiN film 2 side represented by the formula is a <−0.8.

As a practical example of the present invention, a gate insulating film forming process in a semiconductor integrated circuit device is typical, but it is also applied to a gate structure forming process in a nonvolatile memory using charge trapping at the SiN / SiO ₂ interface. Furthermore, the present invention is also applied to the case where a capacitor as an LCR is directly formed on a semiconductor substrate.

It is explanatory drawing of the fundamental structure of this invention. It is explanatory drawing of the formation process of the dielectric film of Example 1 of this invention. It is explanatory drawing of the incident angle dependence of the oxygen ion of depth direction nitrogen distribution. It is explanatory drawing of the manufacturing process to the middle of the semiconductor device of Example 2 of this invention. FIG. 5 is an explanatory diagram of the manufacturing process of FIG.

1 Substrate 2 SiN film 3 Oxygen ion 4 Silicon oxide film 11 Silicon substrate 12 SiN film 13 O ₂ ⁺
14 SiO ₂ film 15 SiN film 21 p-type silicon substrate 22 element isolation region 23 p-type well 24 SiN film 25 O ₂ ⁺
26 SiO ₂ film 27 SiN film 28 Polycrystalline silicon film 29 Gate electrode 30 Gate structure 31 n-type extension region 32 Side wall 33 n-type source / drain region 34 Silicide electrode 35 SiN film 36 SiO ₂ film 37 Source / drain extraction electrode

Claims (5)

After depositing the SiN film directly on the substrate, the SiN film is thinned by sputter etching with oxygen ions, and the irradiation energy of oxygen ions, the incident angle on the SiN film surface, and the dose are controlled at that time. Thus, by replacing the nitrogen in the deposited SiN film with the oxygen implanted by irradiation, a silicon oxide film is formed on the interface side with the substrate, so that the SiN / oxidation with a very thin SiN film on the surface side is formed. A method for forming a dielectric film, comprising forming a silicon laminated structure. 2. The method of forming a dielectric film according to claim 1, wherein the irradiation energy of the oxygen ions is 150 to 350 eV / Otom. 3. The method of forming a dielectric film according to claim 1, wherein an incident angle of the oxygen ions is set to 0 to 30 degrees with respect to a normal line of the substrate. 4. The method for forming a dielectric film according to claim 1, wherein a dose amount of the oxygen ions is set to 1 × 10 ¹⁶ cm ⁻² or more. 5. The method for forming a dielectric film according to claim 1, wherein the substrate is a semiconductor substrate, and the SiN / silicon oxide stacked structure is a gate insulating film.

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