JP2006093240A - Method of forming film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of forming a film by which a hafnium silicate gate insulating film which can be raised in the temperature of crystallization without deteriorating interfacial characteristics can be formed by a MOCVD method by introducing nitrogen. <P>SOLUTION: At the time of forming a metallic silicate film on a silicon substrate by the MOCVD method by supplying a first vapor phase raw material containing a metallic element and a second vapor phase raw material containing Si, a step of forming the metallic silicate film is executed at treating pressure set within a pressure range, in which the depositing speed of an oxide component containing the metallic element contained in the metallic silicate constituting the metallic silicate film is lowered when the flow rate of the second vapor phase raw material is increased. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

    The present invention relates to a semiconductor device, and more particularly to a method for manufacturing an ultrafine high-speed semiconductor device having a high dielectric film.

  In today's ultra-high-speed semiconductor devices, gate lengths of 0.1 μm or less are becoming possible as the miniaturization process advances. In general, the operation speed of a semiconductor device increases with miniaturization. However, in such a semiconductor device that is extremely miniaturized, the thickness of the gate insulating film is reduced according to the scaling law as the gate length is shortened by miniaturization. It is necessary to let

  However, when the gate length is 0.1 μm or less, the thickness of the gate insulating film needs to be set to 1 to 2 nm or less when the conventional thermal oxide film is used. In the insulating film, the tunnel current increases, and as a result, the problem that the gate leakage current increases cannot be avoided.

Under such circumstances, the relative dielectric constant is much larger than that of the thermal oxide film so far, so that even if the actual film thickness is large, the converted film thickness Tox (the film thickness when converted to the SiO ₂ film) is large. It is proposed to apply a small dielectric material such as Ta ₂ O ₅ , Al ₂ O ₃ , ZrO ₂ , HfO ₂ , or ZrSiO ₄ or HfSiO ₄ (so-called high-K material) to the gate insulating film. Has been. By using such a high dielectric material, it is possible to use a gate insulating film having a physical film thickness of about 10 nm even in an extremely short ultrahigh-speed semiconductor device having a gate length of 0.1 μm or less. Gate leakage current can be suppressed.

In particular, a metal silicate material such as ZrSiO ₄ or HfSiO ₄ has a slightly lower relative dielectric constant than an oxide material such as ZrO ₂ or HfO ₂ , but the crystallization temperature is remarkably increased, so that it is used in the manufacturing process of semiconductor devices. Even when heat treatment is performed, the occurrence of crystallization in the film can be effectively suppressed. Therefore, it is considered to be extremely suitable as a high dielectric gate insulating film material for a high-speed semiconductor device. Conventionally, nitrogen is introduced into the high dielectric gate insulating film to suppress crystallization and suppress diffusion of a dopant such as B having a large diffusion coefficient from the gate electrode to the channel region. . When nitrogen is introduced to increase the crystallization temperature, nitrogen atoms are preferably bonded to Si atoms in the film, and thus the high dielectric gate insulating film has a sufficient amount of Si in the film. Must contain atoms.
JP 2001-284344 A WO03 / 049173 US Pat. No. 6,551,948

Conventionally, it is known that such a high dielectric gate insulating film can be formed by atomic layer deposition (ALD) method or MO (organometallic) CVD method. In particular, when an ALD method for forming a film by depositing one atomic layer at a time is used, an arbitrary composition gradient can be formed in the film. For example, in Japanese Patent Laid-Open No. 2001-284344, an ALD technique is used in a ZrSiO ₄ gate insulating film so that the vicinity of the interface with the silicon substrate becomes Si-rich and becomes Zr-rich as the distance from the interface increases. It is described to form a composition gradient. On the other hand, the ALD method has a problem that it takes time because the source gas is switched one atomic layer at a time and deposition is performed while a purge process is sandwiched therebetween, and the manufacturing throughput of the semiconductor device is reduced.

  On the other hand, in the MOCVD method, since the deposition is performed using the organometallic compound raw material, the manufacturing throughput of the semiconductor device can be greatly improved. On the other hand, when the MOCVD method is used, particularly when a very thin film having a maximum thickness of about 1 nm, such as a high-dielectric gate insulating film, is to be formed, a method of changing the material supply amount during film formation, etc. Thus, it was difficult to form a desired composition gradient. Conventionally, when a high dielectric gate insulating film is formed using the MOCVD method, it has been assumed to form a film having a substantially uniform composition in the thickness direction.

  However, for example, when nitrogen atoms are introduced into the film in order to increase the crystallization temperature of the high dielectric gate insulating film or to solve problems such as penetration of a dopant passing through the film, In order not to reach the vicinity of the surface of the silicon substrate where the channel is formed and form defects such as interface states, a concentration gradient is formed such that the nitrogen concentration is low at the bottom surface of the gate insulating film and high at the top surface. desirable.

  In recent years, the correlation between the roughness of the high dielectric gate insulating film and the gate leakage current has been investigated, and it has been found that the leakage current tends to increase as the roughness increases. In the metal silicate film formed by the MOCVD method, the metal oxide phase becomes dominant as the content ratio of the metal element increases, and the roughness of the film increases. In addition, when the composition distribution is formed in the film thickness direction of the metal silicate film, there is a problem that the roughness increases with a base portion where the metal element ratio is large.

In an actual semiconductor device manufacturing process, an extremely thin interface layer (SiO ₂ or SiON) is interposed between the high dielectric insulating film and the silicon substrate in order to improve the carrier mobility in the channel region. When a high dielectric insulating film is formed on the silicon oxide film of such an interface layer by MOCVD, the roughness may be further increased depending on the selection of a film forming material such as a metal amide compound.

  SUMMARY OF THE INVENTION Accordingly, it is a general object of the present invention to provide a novel and useful film forming method that solves the above problems.

  A more specific problem of the present invention is that a metal silicate film containing nitrogen atoms is formed on a silicon substrate by MOCVD, and the concentration of the nitrogen atoms is small in the vicinity of the interface with the silicon substrate and increases as the distance from the interface is increased. It is an object of the present invention to provide a film forming method that can be formed so as to be included in such a profile.

  Still another object of the present invention is to provide a film forming method capable of reducing the roughness of the formed metal silicate film when the metal silicate film is formed on the silicon substrate by MOCVD.

The present invention solves the above problems.
As described in claim 1,
A method for forming a metal silicate film on a silicon substrate by an organic metal CVD method,
Supplying a first vapor phase material made of an organometallic compound containing a metal element constituting the metal silicate film and a second vapor phase material made of an organic silicon compound to the silicon substrate surface;
Decomposing the first vapor phase raw material and the second vapor phase raw material on the silicon substrate surface to form a metal silicate film;
A step of introducing nitrogen atoms into the metal silicate film,
The step of forming the metal silicate film includes forming a composition gradient layer in a film thickness direction of the metal silicate film under a single film formation condition, or according to claim 2. like,
The film formation method according to claim 1, wherein the composition gradient layer has a composition gradient in which a metal element concentration increases from the surface of the metal silicate film toward the silicon substrate side. Like
3. The film forming method according to claim 1, wherein the first raw material is a metal alkoxide raw material having a tertiary riboxyl group as a ligand, and the second raw material is a silicon alkoxide raw material. Or as described in claim 4
The single film forming condition is set within a pressure range in which the deposition rate of the oxide component of the metal element in the metal silicate decreases when the flow rate of the second vapor phase raw material is increased. According to any one of claims 1 to 3, or as described in claim 5,
The film forming method according to any one of claims 1 to 4, wherein the composition gradient is controlled by a flow rate of the second raw material, or as described in claim 6.
2. The composition according to claim 1, wherein the first vapor phase raw material is made of tertiary butyl hafnium, the second vapor phase raw material is made of tetraethyl orthosilicate, and the metal silicate film is made of hafnium silicate. By membrane method or as described in claim 7
The process pressure is 40 Pa or more and 133 Pa or less by the film forming method according to claim 6, or as described in claim 8.
The film forming method according to claim 6 or 7, wherein, in the film forming step, the second vapor phase raw material is supplied at a flow rate in a range of 0.05 SCCM to 1.0 SCCM. As described in 9,
9. The film forming step, wherein the first and second vapor phase raw materials are formed so that the hafnium silicate film contains Si at a concentration exceeding 50 atomic%. Among them, according to any one of the film forming methods, or as described in claim 10,
The step of introducing a nitrogen atom is a radical nitridation step with a nitrogen radical, or, as described in claim 11,
The nitrogen radical is formed by high-frequency plasma excitation of nitrogen gas, by the film forming method according to claim 1, or as described in claim 12,
Prior to the step of forming the metal silicate film, the method further includes a step of forming a silicon oxide film on the silicon substrate by radical oxidation using an ultraviolet photoexcited oxygen radical. , By the film forming method according to any one of the above, or as described in claim 13,
The film forming method according to claim 12, further comprising a step of nitriding the silicon oxide film with nitrogen radicals prior to forming the metal silicate film, or as described in claim 14.
The nitrogen radical is formed by the film forming method according to claim 13, wherein the nitrogen radical is formed by high-frequency plasma excitation of nitrogen gas.

  According to the present invention, the formation of the metal silicate film on the silicon substrate by the organic metal CVD method is performed on the surface of the silicon substrate by the first vapor phase comprising the organometallic compound containing the metal element constituting the metal silicate film. A raw material and a second vapor phase raw material made of an organic silicon compound are supplied, and the first vapor phase raw material and the second vapor phase raw material are decomposed on the silicon substrate surface to form a metal silicate film. Performing the step of forming the metal silicate film by introducing nitrogen atoms into the metal silicate film, and the step of forming the metal silicate film by decomposing the first vapor phase raw material and generating a metal oxide A composition gradient layer is formed in the thickness direction of the metal silicate film by setting and executing a single film forming condition in which a difference in incubation time for decomposing the second vapor phase raw material is increased. Formation to. Since the incubation time of the second vapor phase raw material is longer than the incubation time of the first vapor phase raw material, the metal element can be taken into the film at a high concentration at the initial stage of film formation. On the other hand, after the initial stage of film formation, the second gas phase raw material suppresses the incorporation of the metal element into the film, and the resulting metal silicate film has a composition rich in Si in the upper layer portion. . For example, according to the present invention, particularly when tertiary butyl hafnium (HTB) is used as the first gas phase raw material and tetraethyl orthosilicate (TEOS) is used as the second gas phase raw material, the processing pressure is set to 40 Pa. As described above, by setting the pressure to 133 Pa or less, it is possible to form a hafnium silicate film having a composition gradient with a high hafnium concentration in the lower layer portion and a high Si concentration in the upper layer portion. In this way, when nitrogen atoms are introduced into the metal silicate film having a high Si concentration in the upper layer portion to increase the crystallization temperature of the film, the nitrogen atoms are concentrated in the upper layer portion of the film having a high Si concentration, and the silicon substrate and Few things reach the vicinity of the interface. Thus, the crystallization temperature of the metal silicate film can be increased by introducing nitrogen atoms into the film without deteriorating the electrical characteristics of the semiconductor device such as the formation of interface states. When such a metal silicate film is used as a gate insulating film, the gate insulating film does not crystallize even when heat treatment associated with the semiconductor process is performed. Factors that change the electrical characteristics of the device can be further eliminated.

  In particular, an oxide film formed by ultraviolet light-excited oxygen radicals is interposed between the silicon substrate and the metal silicate film, and this oxide film is nitrided with nitrogen radicals, so that the composition of the metal silicate film is affected. Therefore, the roughness of the surface of the metal silicate film can be reduced.

  In particular, when the concentration of Si atoms in the metal silicate film is set to 50 atomic% or more, crystallization of the metal silicate film can be avoided even after heat treatment.

[principle]
FIG. 1 shows the configuration of an MOCVD apparatus used in the present invention.

  Referring to FIG. 1, the MOCVD apparatus 20 includes a processing container 22 that is evacuated by a pump 21, and a holding table 22 </ b> A that holds a substrate W to be processed is provided in the processing container 22.

  Further, a shower head 22S is provided in the processing container 22 so as to face the substrate W to be processed, and a line 22a for supplying oxygen gas is not shown in the shower head 22S. And is connected via a valve V1.

  The MOCVD apparatus 20 includes a container 23B for holding an organic metal compound raw material such as tertiary butyl hafnium (HTB), and the organic metal compound raw material in the container 23B is a fluid flow controller by a pressurized gas such as He gas. The organometallic compound source gas supplied to the vaporizer 22e via 22d and vaporized with the aid of a carrier gas such as Ar in the vaporizer 22e is supplied to the shower head 22S via the valve V3.

  Further, the MOCVD apparatus 20 is provided with a heating vessel 23A for holding an organic silicon compound material such as TEOS, and the organic silicon compound material gas evaporated in the heating vessel 23A is supplied to the shower head through the MFC 22b and the valve V2. 22S.

  In the shower head 22S, the oxygen gas, the organic silicon compound source gas, and the organometallic compound source gas pass through their respective paths, and through an opening 22s formed on the surface of the shower head 22S that faces the silicon substrate W. , And discharged into the process space in the processing vessel 22.

  2 shows that the substrate temperature is set to 550 ° C. in the MOCVD apparatus 20 of FIG. 1, and the TEOS gas flow rate is gradually increased from 0 (zero) SCCM while supplying HTB gas at a flow rate of 0.33 SCCM and oxygen gas at a flow rate of 300 SCCM. In this case, the deposition rate of the Hf silicate film formed on the silicon substrate W was set such that the process pressure in the processing vessel 22 was 40 Pa (0.3 Torr), 133 Pa (1 Torr), and 399 Pa (3 Torr). The result obtained for the case is shown. However, in FIG. 2, the deposition rate of the Hf silicate film is expressed by the film thickness measured after deposition for 300 seconds.

Referring to FIG. 2, Si that when TEOS flow rate is 0SCCM whereas HfO ₂ film is on the silicon substrate W contains no Si is deposited, contained in the HfO ₂ film and TEOS flow rate is increased As the concentration of Hf increases, the film has a composition of Hf silicate.

  At this time, when the process pressure is set to 399 Pa (3 Torr), as shown in FIG. 2, the film thickness increases as the TEOS concentration increases, whereas the process pressure is 133 Pa (1 Torr) or 40 Pa (0 Torr). .3 Torr), it can be seen that the deposition rate initially increases with an increase in TEOS concentration, but then begins to decrease.

  FIG. 3 is a diagram showing the refractive index of the Hf silicate film thus obtained as a function of the TEOS flow rate.

Referring to FIG. 3, when the TEOS flow rate is 0 SCCM, the obtained film has a refractive index of 2.05 to 2.1, which closely matches the refractive index value of HfO ₂ . From this, it is considered that the film formed with the TEOS flow rate set to 0 SCCM is actually an HfO ₂ film.

On the other hand, in the case of a film formed by adding TEOS to the source gas, the refractive index is lowered to around 1.8, but considering that the refractive index of the SiO ₂ film is about 1.4, The film formed by adding TEOS to the source gas in this way is considered to be a hafnium silicate film.

  FIG. 4 shows the relationship between the Si concentration Si (Si / (Si + Hf)) and the refractive index in the obtained hafnium silicate film. However, in FIG. 4, the Si concentration is indicated by atomic percent of Si. In the present invention, the Si concentration and Hf concentration in the film are measured by the XPS method.

  As can be seen from FIG. 4, there is a clear correspondence between the Si concentration in the film and the refractive index. Therefore, in the relationship shown in FIG. 3, in the hafnium silicate film obtained along with the TEOS flow rate. It can be seen that the Si concentration is changed.

5 calculates the ratio of the SiO ₂ component contained in the hafnium silicate film using the relationship of FIGS. 3 and 4 from the relationship of FIG. 2 described above, and the calculated ratio of the SiO ₂ component. based on, shows the result of calculating the virtual deposition rate of the SiO ₂ component in the hafnium silicate film with a specific volume of the SiO _2. Similarly, FIG. 6, FIG. 2, FIG. 3, and calculates the ratio of HfO ₂ component contained in the hafnium silicate film from the relationship of FIG. 4, HfO ₂ the percentage of the calculated HfO ₂ component based on The result of having calculated the virtual deposition rate of the HfO ₂ component using the specific volume of is shown.

Referring to FIGS. 5 and 6, when the process pressure is 40 Pa (0.3 Torr), it can be seen that the deposition rate of the HfO ₂ component sharply decreases when the SiO ₂ component is introduced into the film by supplying TEOS. It can be seen that a similar decrease in the deposition rate of the HfO ₂ component occurs even when the process pressure is 133 Pa (1 Torr), but does not occur when the process pressure is 399 Pa (3 Torr). The phenomenon of FIGS. 5 and 6 suggests that the deposition of Hf atoms is prevented by TEOS introduced into the processing vessel 22 during the deposition of the hafnium silicate film.

  FIG. 7 shows the deposition rate of the hafnium silicate film (left vertical axis) and the Hf concentration in the film (right vertical axis) when the TEOS flow rate in FIG. 2 is further increased and changed in the range of 5 to 20 SCCM. .

  Referring to FIG. 7, as the TEOS flow rate increases, the deposition rate slightly decreases, and correspondingly, the Hf concentration in the film is 20 atomic%, that is, the ratio of Hf atoms to Si atoms is 1: 4. You can see that they are converging. However, in FIG. 7, the substrate temperature is set to 550 ° C., oxygen gas is supplied into the processing vessel 22 at a flow rate of 300 SCCM, and HTB is introduced at a rate of 0.1 mol% with respect to TEOS.

  FIG. 8 shows a model of the MOCVD process occurring in the MOCVD apparatus of FIG.

Referring to FIG. 8, when HTB is introduced from the shower head 22S into the process space in the processing vessel 22, the ligand (CH ₃ ) ₃ C is desorbed and the very active precursor Hf (OH) ₄ ( (Hereinafter referred to as HTB ′). If the HTB 'is transported to the surface of the surface or the shower head of the the substrate W, the deposition HfO ₂ occurs by surface reaction H ₂ O is eliminated. Further, the desorbed H ₂ O is bonded to the desorbed ligand (CH ₃ ) ₃ C and discharged to the outside of the processing vessel 22 in the form of (CH ₃ ) ₃ C—OH.

  On the other hand, when TEOS is introduced into a low-pressure system in which such a reaction occurs, a part of active HTB 'and TEOS are combined as shown in FIG.

A precursor (HTB′-TEOS) ′ is formed. When this precursor (HTB′-TEOS) ′ is transported to the surface of the silicon substrate W, a Hf-rich hafnium silicate (referred to as HfSiO) film is deposited. Meanwhile, a part of the precursor (HTB′-TEOS) ′ is transported to the showerhead 22S, and Hf-rich hafnium silicate is deposited.

In this way, the low pressure of the reaction, 'the deposition reaction of the HfO ₂ film by (HTB'-TEOS)' HTB has deposition reaction and conflicts, is HfO ₂ deposition reaction by the TEOS is introduced HTB ' This is considered to be suppressed rapidly and cause a rapid decrease in the deposition rate of the HfO ₂ component described above with reference to FIGS.

  On the other hand, when the flow rate of TEOS supplied to the shower head 22S is further increased, the reaction formula in which TEOS is further bonded to the precursor (HTB'-TEOS) '.

Is formed, and when this precursor (HTB '-(TEOS)) "is transported to the surface of the silicon substrate W, the Si-rich hafnium silicate ( HfSiO) is deposited. At this time, a part of the precursor (HTB ′-(TEOS)) ”is transported to the surface of the showerhead 22S to cause the deposition of a Si-rich hafnium silicate film. This precursor (HTB ′-( The reaction involving TEOS)) "is the dominant reaction in the normal MOCVD process above 133 Pa (1 Torr).

  The another precursor (HTB ′-(TEOS)) ”has a structure in which four Si atoms are bonded to one Hf atom via each oxygen atom. In the hafnium silicate film formed by the reaction involved, the ratio of Hf atoms to Si atoms in the film tends to be 1: 4 as shown in FIG.

  FIG. 9 shows the relationship between the film thickness of the hafnium silicate film formed under the pressure of 40 Pa (0.3 Torr) in the MOCVD apparatus 20 of FIG. 1 and the Si concentration (Si / (Si + Hf)) expressed in atomic%. Show.

  Referring to FIG. 9, the film formation experiment was performed while changing the TEOS flow rate at various substrate temperatures of 550 ° C., but there was a minimum point indicated by an arrow in the Si concentration in the formed hafnium silicate film. When the film thickness of the hafnium silicate film is large, the Si concentration in the film is high. On the other hand, when the film thickness of the formed hafnium silicate film decreases, the Hf concentration in the film tends to increase. .

In FIG. 9, when the thickness of the hafnium silicate film further decreases, the Si concentration in the film increases again. This is an interface film mainly composed of SiO ₂ formed at the interface between the hafnium silicate film and the silicon substrate W. 10A and 10B are estimated to be 39.9 Pa (0.3 Torr) on the silicon substrate 41 derived from the result of FIG. The model of the hafnium silicate film | membrane 42 formed under pressure is shown. However, FIG. 10A shows the case where the TEOS flow rate is set to 0.05 SCCM, and FIG. 10B shows the case where the TEOS flow rate is set to 1.0 SCCM.

Referring to FIGS. 10A and 10B, an interface layer 41A mainly composed of SiO ₂ is formed between the silicon substrate 41 and the hafnium silicate film 42. When set to 05 SCCM, a hafnium silicate composition gradient in which the Hf concentration increases toward the interface layer 41A in the portion of the hafnium silicate film 42 in contact with the interface layer 41A as shown in FIG. It can be seen that the layer 42A is formed over a substantial portion of the thickness of the hafnium silicate film 42.

  On the other hand, when the TEOS flow rate is increased to 1.0 SCCM as shown in FIG. 10B, the thickness of the composition gradient layer 42A is remarkably reduced.

5 and 6 with reference to the relationship of FIG. 2, the incubation time of the precursor (HTB′-TEOS) ′ is low in the low-pressure MOCVD process using HTB and TEOS as raw materials. , 'longer than that of, the initial deposition HTB precursor (HTB)' HfO ₂ film is grown from, considered then (HTB'-TEOS) 'hafnium silicate film grows from. As a result, it is considered that a film having a high Si concentration is formed on a film having a high Hf concentration, and a film having a composition gradient is naturally formed.

A similar relationship is that when the MOCVD process is performed at a process pressure of 133 Pa (1 Torr), in other words, the process pressure is set within a pressure range in which the film formation rate decreases when the TEOS flow rate is increased. It is considered that this is true even when the film is formed.

[First embodiment]
FIG. 11 is a flowchart showing a method of forming a gate insulating film using a hafnium silicate film on the silicon substrate 41 according to the first embodiment of the present invention, and FIGS. 12A and 12B show the process of FIG. It is a figure which shows the structure of the semiconductor device formed by these. However, FIG. 12B shows the concentration distribution of nitrogen atoms in the hafnium silicate film 42 of FIG.

  Referring to FIG. 11, first, the silicon substrate 41 subjected to the HF treatment in step 1 is introduced as the substrate W to be processed into the processing container 22 of the MOCVD apparatus 20 in FIG. 1, and in step 2, the processing container 22 is set to 40 Pa (0 .. 3 Torr) to 133 Pa (1 Torr) or less. Further, by supplying HTB and TEOS, the silicon substrate 41 and the hafnium silicate film are simultaneously deposited on the surface of the silicon substrate 41, including a hafnium silicate film 42 including a composition gradient layer 42A rich in Hf at the bottom and rich in Si at the top. An interface layer 41 A is formed at the interface with 42.

  In Step 2 of FIG. 11, the Hf concentration in the composition gradient layer 42A can be appropriately set by setting the TEOS flow rate in the range of 0.05 SCCM to 1.0 SCCM.

  Further, in the process of FIG. 11, after step 2, in step 3, nitrogen atoms are introduced into the hafnium silicate film 42 by, for example, plasma nitriding, and then in step 4, the hafnium silicate film 42 is formed on the hafnium silicate film 42. 12A, a gate electrode 43 such as polysilicon is formed. 12A is a diagram showing a configuration of the semiconductor device 40 according to the first embodiment of the present invention.

  In this embodiment, when nitrogen atoms are introduced into the hafnium silicate film 42 in the step 3 of FIG. 11, the composition gradient layer 42A rich in Si in the upper part and rich in Hf in the lower part in the hafnium silicate film 42. Therefore, most of the introduced nitrogen atoms are bonded to Si atoms in the upper part of the hafnium silicate film 42. As a result, the hafnium silicate film 42 has a structure as shown in FIG. A nitrogen profile is formed such that the concentration is high in the upper part of the film and lower in the lower part of the film. In the hafnium silicate film 42 having such a nitrogen profile, the number of nitrogen atoms reaching the lower part of the film is small.

Even if nitrogen atoms reach the lower part of the hafnium silicate film 42, most of the nitrogen atoms are mainly composed of SiO ₂ formed at the interface between the hafnium silicate film 42 and the silicon substrate 41. As a result, the formation of defects such as interface states on the surface of the silicon substrate due to the nitrogen atoms reaching the surface of the silicon substrate 41 is effectively suppressed.

  As described above, according to this embodiment, since the upper portion of the hafnium silicate film 42 contains nitrogen atoms at a high concentration, the crystallization of the film 42 is suppressed in this portion, and the hafnium silicate film 42 is formed on the upper portion of the hafnium silicate film 42. Diffusion of a dopant element or generation of a leak current from a formed gate electrode (not shown) such as polysilicon to the silicon substrate 41 via a crystal grain boundary formed in the hafnium silicate film 42 is effective. Is suppressed. Further, by introducing nitrogen atoms into the hafnium silicate film 42 in this way, the relative dielectric constant of the film 42 is improved, and the equivalent film thickness Tox is further reduced.

Note that the nitriding treatment in Step 3 of FIG. 11 is a nitriding treatment using a high-frequency remote plasma source as described in WO 03/049173, or a microwave plasma substrate processing apparatus described in US Pat. No. 6,551,948. Can be used. In addition, the nitriding treatment in Step 3 of FIG. 11 can be performed by exposing the hafnium silicate film 42 to a nitrogen atmosphere such as NO gas or N ₂ O gas, for example.

FIG. 13 shows an X-ray diffraction pattern immediately after the formation of the hafnium silicate film and the HfO ₂ film according to this example formed as described above, and FIG. 14 shows the rapid growth of the same hafnium silicate film and the HfO ₂ film at 1000 ° C. 2 shows an X-ray diffraction pattern after a heat treatment (RTP) step.

Referring to FIG. 13, it can be seen that in the case of the HfO ₂ film, the film is crystallized even in the state immediately after the deposition, and further, the crystallization is slightly generated even in the hafnium silicate film having the Si concentration of about 17 atomic%. . Further, FIG. 14 shows that when such a film is subjected to heat treatment, crystallization occurs even in a film containing Si at a concentration of about 50 atomic%.

On the other hand, by introducing nitrogen atoms into the hafnium silicate film in the step 3 of FIG. 11 described above, the crystallization temperature of the film rises, and it becomes possible to suppress crystallization of such a film. .

[Second Embodiment]
In the previous embodiment, the hafnium silicate film was directly formed on the HF-treated silicon substrate by the MOCVD method to form the composition gradient layer. However, the inventor of the present invention applied the silicon substrate surface on the silicon substrate. An interfacial oxide film or interfacial oxynitride film is formed in advance so as to cover, and even when the hafnium silicate film is deposited thereon by the MOCVD method, a verification experiment is conducted to confirm whether a similar composition gradient layer is formed. This was carried out as a second embodiment of the invention.

  FIG. 15 shows the configuration of the semiconductor device 60 created in the second embodiment of the present embodiment. However, in the figure, the same reference numerals are assigned to portions corresponding to the portions described above, and description thereof is omitted.

  Referring to FIG. 15, in this embodiment, an oxide film is formed to a thickness of about 0.4 nm on the silicon substrate 41 by ultraviolet light excited oxygen radicals, and this is further processed by nitrogen radicals excited by remote plasma, An oxynitride film 41B having a thickness of about 0.5 nm is formed. The formation of an oxide film by ultraviolet light-excited oxygen radicals on the surface of the silicon substrate is typically performed at a wavelength of 2.66 Pa (0.02 Torr) while supplying oxygen gas to the substrate surface at a substrate temperature of 450 ° C. It is executed by exciting with ultraviolet light of 172 nm. The nitriding treatment of the oxide film is performed using, for example, a nitrogen radical formed by using a toroidal type remote plasma source, supplying Ar gas and nitrogen gas thereto, and performing high frequency excitation of about 400 kHz. See WO03 / 049173.

  On the other hand, the hafnium silicate film 42 is deposited on the oxynitride film 41B using the MOCVD apparatus 20 of FIG.

  FIG. 16 shows the relationship between the film thickness and the Si concentration in the film obtained for the hafnium silicate film 42 formed on the oxynitride film 41B in this way, and the hafnium silicate film formed directly on the silicon substrate 41. FIG. However, the relationship of FIG. 16 is the case where the deposition of the hafnium silicate film is performed at a substrate temperature of 550 ° C. under a pressure of 40 Pa (0.3 Torr).

  Referring to FIG. 16, even when the hafnium silicate film 42 is formed on the oxynitride film 41B, when the film thickness is small, Hf is concentrated in the film, It can be seen that a composition gradient layer rich in Hf and rich in Si is formed in the upper part of the film.

  Similar to the previous embodiment, such a composition gradient layer is MOCVD at a processing pressure of 40 to 133 Pa (0.3 to 1 Torr) set within a pressure range in which the film formation rate is lowered when the TEOS flow rate is increased. It can be formed by executing a process. Also in this embodiment, by introducing nitrogen atoms into the hafnium silicate film 42, it is possible to form a nitrogen concentration distribution with a high nitrogen concentration on the film surface and a low nitrogen concentration on the film lower surface in the film 42. is there.

  17 shows the CV characteristics obtained for the structure of FIG. 15, and FIG. 18 shows the relative dielectric constant of the hafnium silicate film 42 obtained from the CV characteristics. However, in this measurement, a substrate having a specific resistance of 0.6 to 1.5 Ω · cm is used as the silicon substrate 41, and a film having a Si concentration of 50% is used as the hafnium silicate film 42.

  Referring to FIG. 17, CV characteristics are measured by changing the applied voltage from -4V to + 8V for three types of samples (24 nm, 16 nm, and 9.5 nm) having different physical film thicknesses measured by ellipsometry. However, as can be seen from FIG. 18, a good linear relationship is established between the actually measured film thickness and the equivalent oxide film thickness (Tox), and the relative dielectric constant k of the hafnium silicate film 42 is It is calculated to be 11.0.

FIG. 19 shows the surface roughness Ra of the hafnium silicate film 42 when the thickness of the interface film 41B is variously changed in the configuration of FIG. In the figure, “UVO ₂ ” indicates the case where the interface film 41 B is formed by ultraviolet photoexcited oxygen radicals, and “UVO ₂ + RFN” indicates that the interface film 41 B is a silicon oxide film formed by the ultraviolet photoexcited oxygen radicals as a high-frequency remote. The case of nitriding with nitrogen radicals formed by plasma excitation is shown. On the other hand, “HF-last” indicates a case where the hafnium silicate film 42 is deposited directly on the HF-treated silicon substrate 41 as in the first embodiment without providing the interface film 41B. However, the thickness of the interface film 41B on the horizontal axis is measured by the XPS method.

Referring to FIG. 19, when the interface film 41B is not provided, or when the film thickness of the interface film 41B is 0.4 nm or less, the surface roughness Ra of the hafnium silicate film 42 is about 0.3 to 0.4 nm. On the other hand, when the interface film 41B is a UVO ₂ film, the thickness of the interface film 41B is about 0.4 nm or more, and when the interface film 41B is a UVO ₂ + RFN film, the thickness of the interface film 41B is increased. Is about 0.6 nm or more, it can be seen that the surface roughness Ra of the film 41B is reduced to about 0.2 nm.

  FIG. 20 shows the results of determining the surface roughness Ra and Rms for hafnium silicate films and hafnium oxide films having various compositions formed on various bases.

Referring to FIG. 20, when the HfO ₂ film is directly deposited on the surface of the silicon substrate that has been subjected to HF treatment, the surface roughness Ra of the film exceeds 0.32 nm, and the root mean square roughness Rms exceeds 0.41 nm. On the other hand, when the hafnium silicate film is formed directly on the surface of the silicon substrate subjected to HF treatment, the surface roughness Ra is reduced to 0.30 nm, and the root mean square roughness Rms can also be reduced to 4.0 nm or less. I understand.

In FIG. 20, when a hafnium silicate film is formed on a silicon substrate on which a silicon oxide film (UVO ₂ ) having a thickness of 0.2 nm is formed by ultraviolet photoexcited oxygen radicals, the surface roughness Ra is about 0.33 nm. The mean square roughness Rms increases to about 0.416 nm, whereas an HfO ₂ film or a hafnium silicate film is formed on an oxynitride film (UVO ₂ + RFN) formed by remote plasma nitriding the UVO ₂ film. In this case, the surface roughness Ra is reduced to 0.287 nm at the maximum, and the root mean square roughness Rms is also reduced to the maximum 0.360 nm.

  Although the present invention has been described with reference to the preferred embodiments, the present invention is not limited to such specific embodiments, and various modifications and changes can be made within the scope described in the claims.

It is a figure which shows the structure of the MOCVD apparatus used by this invention. It is a figure which shows the relationship between the deposition rate of a hafnium silicate film | membrane formed with the MOCVD apparatus of FIG. 1, and a TEOS flow rate. It is a figure which shows the relationship between the refractive index of the hafnium silicate film | membrane obtained in FIG. 2, and TEOS flow volume. It is a figure which shows the relationship between the refractive index of the hafnium silicate film | membrane obtained in FIG. 2, and Si density | concentration in a film | membrane. Hafnium silicate film obtained in FIG. 2 is a diagram showing a relationship between a virtual deposition rate and TEOS flow rate of the SiO ₂ component. Hafnium silicate film obtained in FIG. 2 is a diagram showing a relationship between a virtual deposition rate and TEOS flow rate of HfO ₂ components. It is a figure which shows the relationship between the deposition rate of a hafnium silicate film | membrane when a TEOS flow rate is increased, a film composition, and a TEOS flow rate. It is a figure which shows the deposition reaction model of a hafnium silicate film | membrane. It is a figure which shows the relationship between the film thickness at the time of forming a hafnium silicate film | membrane in low pressure in the MOCVD apparatus of FIG. 1, and a film | membrane composition. (A), (B) is a figure which shows the composition gradient formed in a hafnium silicate film | membrane at the time of forming a hafnium silicate film | membrane with various TEOS flow volume in the MOCVD apparatus of FIG. 3 is a flowchart illustrating a film forming method according to a first embodiment of the present invention. (A), (B) is a figure which shows the structure of the semiconductor device formed by the film-forming method of 1st Example of this invention. It is a figure which shows the X-ray-diffraction figure immediately after film-forming of the hafnium silicate film | membrane formed by the film-forming method of 1st Example of this invention. It is a figure which shows the X-ray-diffraction figure after the heat processing of the hafnium silicate film | membrane formed with the film-forming method of 1st Example of this invention. It is a figure which shows the structure of the semiconductor device formed with the film-forming method of 2nd Example of this invention. It is a figure which shows Si concentration distribution in the hafnium silicate film | membrane obtained by the film-forming method of 2nd Example of this invention. It is a figure which shows the capacitor CV characteristic formed based on the structure of FIG. It is a figure which shows the dielectric constant of the hafnium silicate film | membrane obtained by the film-forming method of 2nd Example of this invention. FIG. 16 is a diagram showing the relationship between the surface roughness of the hafnium silicate film and the interface layer in the configuration of FIG. 15. It is a figure which shows the relationship between a base surface and surface roughness of various Hf containing films | membranes formed on various surfaces.

Explanation of symbols

20 MOCVD equipment 21 Exhaust system 22 Processing vessel 22A Substrate holder 22a Oxygen gas line 22b, 22d MFC
22c raw material gas line 22e vaporizer 22S shower head 22s opening 23A, 23B raw material container 41 silicon substrate 41A interface layer 41B interface oxynitride film 42 hafnium silicate film 42A composition gradient layer 42B, 42C Si rich layer 43 gate electrode

Claims (14)

A method for forming a metal silicate film on a silicon substrate by an organic metal CVD method,
Supplying a first vapor phase material made of an organometallic compound containing a metal element constituting the metal silicate film and a second vapor phase material made of an organic silicon compound to the silicon substrate surface;
Decomposing the first vapor phase raw material and the second vapor phase raw material on the silicon substrate surface to form a metal silicate film;
A step of introducing nitrogen atoms into the metal silicate film,
The step of forming the metal silicate film comprises forming a composition gradient layer in the film thickness direction of the metal silicate film under a single film formation condition.   2. The film forming method according to claim 1, wherein the composition gradient layer has a composition gradient in which a metal element concentration increases from the surface of the metal silicate film toward the silicon substrate side.   3. The film forming method according to claim 1, wherein the first raw material is a metal alkoxide raw material having a tertiary riboxyl group as a ligand, and the second raw material is a silicon alkoxide raw material. .   The single film forming condition is set within a pressure range in which the deposition rate of the oxide component of the metal element in the metal silicate decreases when the flow rate of the second vapor phase raw material is increased. The film forming method according to any one of claims 1 to 3.   The film forming method according to claim 1, wherein the composition gradient is controlled by a flow rate of the second raw material.   2. The composition according to claim 1, wherein the first vapor phase raw material is made of tertiary butyl hafnium, the second vapor phase raw material is made of tetraethyl orthosilicate, and the metal silicate film is made of hafnium silicate. Membrane method.   The film forming method according to claim 6, wherein the processing pressure is 40 Pa or more and 133 Pa or less.   8. The film forming method according to claim 6, wherein in the film forming step, the second vapor phase raw material is supplied at a flow rate in a range of 0.05 SCCM to 1.0 SCCM.   9. The film forming step, wherein the first and second vapor phase raw materials are formed so that the hafnium silicate film contains Si at a concentration exceeding 50 atomic%. The film-forming method as described in any one of them.   The film forming method according to claim 1, wherein the step of introducing the nitrogen atom is a radical nitridation step using nitrogen radicals.   The film forming method according to claim 1, wherein the nitrogen radical is formed by high frequency plasma excitation of nitrogen gas.   Prior to the step of forming the metal silicate film, the method further includes a step of forming a silicon oxide film on the silicon substrate by radical oxidation using an ultraviolet photoexcited oxygen radical. The film-forming method as described in any one.   13. The film forming method according to claim 12, further comprising a step of nitriding the silicon oxide film with nitrogen radicals prior to forming the metal silicate film.   The film forming method according to claim 13, wherein the nitrogen radical is formed by high frequency plasma excitation of nitrogen gas.