JP2008060412A - Method for manufacturing semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a semiconductor device which can thin electrical film thickness by reducing the physical film thickness of a gate insulating film. <P>SOLUTION: Plasma nitriding treatment is applied to a ground silicon oxide film of a substrate, while maintaining the temperature of the substrate at ≥400°C in a mixed gas atmosphere having a hydrogen concentration of 50% or less, and containing N<SB>2</SB>and H<SB>2</SB>to form an oxynitrided insulating film on the ground silicon oxide film as a gate insulating film. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a thinning of a gate insulating film.

In general, when a semiconductor device such as an LSI is manufactured, a gate insulating film (also referred to as a gate oxide film) made of a silicon oxide film is formed on the surface of a silicon substrate or a glass substrate, and a gate electrode is formed thereon. For gate insulating films, thin films are more advantageous for improving LSI characteristics and performance, but there is a tendency that the limit of thin films is determined due to leakage current and reliability problems, and boron (B) is doped in the gate electrode. Then, there is a tendency that boron (B) passes through the gate insulating film and diffuses into the silicon substrate by heat treatment, and shifts the transistor characteristics. For this reason, conventionally, introduction of a silicon oxynitride film (SiON film) obtained by thermally nitriding a HIGH-K insulating film or a SiO ₂ film has been attempted. HIGH-K insulating film, it is possible to increase the physical thickness even higher dielectric constant of the same SiO ₂ film equivalent thickness, it is advantageous film to suppress the leakage current, the nitrogen added hafnium silicate film (HfSiON A high dielectric constant film typified by a film) has a problem that a threshold voltage (Vth) for determining a power supply voltage is greatly shifted and exceeds a design allowable value, so that the transition is difficult.
For this reason, the mainstream is to increase the nitrogen (N) concentration of the SiON film and increase the dielectric constant, and after forming a base silicon oxide film on a semiconductor substrate such as a silicon substrate in advance, a nitrogen gas atmosphere In particular, a method for forming an oxynitride film as a gate oxide film on at least the surface of a base silicon oxide film by mixing nitrogen into the base silicon oxide film by plasma nitriding is being studied (Patent Document 1).
JP 2003-282567 A (Regarding Plasma Nitriding of Oxide Film)

However, when the gate insulating film is formed by the plasma nitriding process, the physical film thickness of the gate insulating film increases and the electrical film thickness increases when nitrogen is mixed into the underlying silicon oxide film. There is a problem.
FIG. 6 shows a model of a conventional plasma nitriding process.
As shown in FIG. 6A, the thickness of the SiO ₂ film 14 that is the underlying silicon oxide film is 2.0 nm before the plasma nitriding treatment. As shown in FIG. 6B, when only nitrogen is introduced as a process gas and the plasma nitriding process is performed on the SiO ₂ film 14 in an atmosphere containing only nitrogen gas, quartz constituting a processing chamber (also called a reaction chamber) is formed. Since the oxygen contained in a minute amount in the outgas from the member is activated and turned into plasma, the reduction of the SiO ₂ film 14 is difficult to proceed. Thus, in such process conditions, the film thickness from the interface of the Si film 10 and the SiO ₂ film 14 although SiON film 20 as a gate insulating film by the incorporation of nitrogen in the SiO ₂ film 14 is formed to the surface of the SiON film 20 As shown in FIG. 6C, there is a problem that the physical and electrical film thickness as the gate insulating film increases.

  Accordingly, an object of the present invention is to reduce the physical film thickness of the gate insulating film and to make it electrically thin.

In order to achieve the above object, the present invention provides a substrate silicon oxide film on a substrate while maintaining the substrate temperature at 400 ° C. or higher in a mixed gas atmosphere containing N ₂ and H ₂ having a hydrogen concentration of 50% or less. Plasma nitriding is performed to form an oxynitride insulating film as a gate insulating film on the base silicon oxide film.

  According to the present invention, the physical and electrical film thickness of the gate insulating film is reduced, so that the performance of the semiconductor device is greatly improved.

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.
First, a plasma processing furnace used in a method for manufacturing a semiconductor device according to an embodiment of the present invention will be described. In the present embodiment, as a plasma processing furnace, a substrate processing furnace (hereinafter, referred to as a plasma processing furnace) that plasma-treats a substrate such as a wafer using a modified magnetron type plasma source that can generate high-density plasma by an electric field and a magnetic field. Called MMT device).
In this MMT apparatus, a substrate is installed in a processing chamber that ensures airtightness, a reaction gas is introduced into the processing chamber via a shower head, the processing chamber is maintained at a certain pressure, and high-frequency power is supplied to the discharge electrode. As a result, an electric field and a magnetic field are formed, causing magnetron discharge. Since the electrons emitted from the discharge electrode continue to circulate while continuing the cycloid motion while drifting, the lifetime becomes longer and the ionization generation rate is increased, so that high-density plasma can be generated.
In this way, the MMT apparatus performs various plasma treatments on the substrate, such as diffusing treatment such as oxidizing or nitriding the substrate surface by exciting and decomposing the reaction gas, or forming a thin film on the substrate surface or etching the substrate surface. It is configured to be able to.

FIG. 1 is a schematic configuration diagram showing an example of the MMT apparatus. As shown in the figure, the MMT apparatus has a processing container 203, which is composed of a dome-shaped upper container 210 as a first container and a bowl-shaped lower container 211 as a second container. The upper container 210 is formed on the lower container 211.
The upper container 210 is made of a non-metallic material such as aluminum oxide or quartz, and the lower container 211 is made of aluminum.
Further, by forming a susceptor 217 which is a heater-integrated substrate holder (substrate holding means), which will be described later, with a non-metallic material such as aluminum nitride, ceramics, or quartz, metal contamination taken into the film during processing. Can be reduced.

The shower head 236 is provided in the upper part of the processing chamber 201, and includes a cap-shaped lid 233, a gas inlet 234, a buffer chamber 237, an opening 238, a shielding plate 240, and a gas outlet 239. Yes.
The buffer chamber 237 is provided as a dispersion space for dispersing the gas introduced from the gas introduction port 234.

A gas supply pipe 232 for supplying gas is connected to the gas inlet 234. The gas supply pipe 232 is connected via a valve 243a as an on-off valve and a mass flow controller 241 as a flow rate controller (flow rate control means). It is connected to the gas cylinder of the reaction gas 230 not shown in the figure. A reaction gas 230 is supplied from the shower head 236 to the processing chamber 201.
In addition, a gas exhaust port 235 for exhausting gas to the side wall of the lower container 211 is provided so that the gas after substrate processing flows from the periphery of the susceptor 217 toward the bottom of the processing chamber 201.
A gas exhaust pipe 231 for exhausting gas is connected to the gas exhaust port 235. The gas exhaust pipe 231 is connected to a vacuum pump 246 which is an exhaust device via an APC 242 which is a pressure regulator and a valve 243b which is an on-off valve. It is connected.

As a discharge mechanism (discharge means) for exciting the supplied reaction gas 230, a cylindrical electrode 215, which is a first electrode formed in a cylindrical shape, for example, a cylindrical shape, is provided.
The cylindrical electrode 215 is installed on the outer periphery of the processing vessel 203 (upper vessel 210) and surrounds the plasma generation region 224 in the processing chamber 201.
The cylindrical electrode 215 is connected to a high frequency power source 273 that applies high frequency power via a matching unit 272 that performs impedance matching.

Moreover, the cylindrical magnet 216 which is a cylinder, for example, the magnetic field formation mechanism (magnetic field formation means) formed in the shape of a cylinder is a cylindrical permanent magnet.
The cylindrical magnet 216 is disposed near the upper and lower ends of the outer surface of the cylindrical electrode 215.
The upper and lower cylindrical magnets 216 and 216 have magnetic poles at both ends (inner and outer peripheral ends) along the radial direction of the processing chamber 201, and the magnetic poles of the upper and lower cylindrical magnets 216 and 216 are set in opposite directions. Has been. Therefore, the magnetic poles in the inner peripheral portion are different from each other, and thereby magnetic lines of force are formed in the cylindrical axis direction along the inner peripheral surface of the cylindrical electrode 215.

A susceptor 217 is disposed at the bottom center of the processing chamber 201 as a substrate holder (substrate holding means) for holding the wafer 200 as a substrate.
The susceptor 217 is made of, for example, a non-metallic material such as aluminum nitride, ceramics, or quartz, and a heater (not shown) as a heating mechanism (heating means) is integrally embedded in the susceptor 217. The wafer 200 can be heated.
The heater is adapted to heat the wafer 200 to about 500 ° C. by applying electric power.

The susceptor 217 is also equipped with a second electrode that is an electrode for changing the impedance, and the second electrode is grounded via the impedance variable mechanism 274.
The impedance variable mechanism 274 is composed of a coil and a variable capacitor, and the potential of the wafer 200 can be controlled via the electrode and the susceptor 217 by controlling the number of coil patterns and the capacitance value of the variable capacitor. .

  A processing furnace 202 for processing the wafer 200 by magnetron discharge with a magnetron plasma source includes at least a processing chamber 201, a processing vessel 203, a susceptor 217, a cylindrical electrode 215, a cylindrical magnet 216, a shower head 236, and a gas exhaust. The opening 235 is configured so that the wafer 200 can be subjected to plasma processing in the processing chamber 201.

  Around the cylindrical electrode 215 and the cylindrical magnet 216, an electric field and magnetic field formed by the cylindrical electrode 215 and the cylindrical magnet 216 are arranged so as not to adversely affect the external environment and other processing furnaces. And a shielding plate 223 that effectively shields the magnetic field.

The susceptor 217 is insulated from the lower container 211 and is provided with a susceptor elevating mechanism (elevating means) 268 for elevating and lowering the susceptor 217.
The susceptor 217 is provided with through holes 217a, and at the bottom of the lower container 211, wafer push-up pins 266 for pushing up the wafer 200 are provided in at least three places.
Then, when the susceptor 217 is lowered by the susceptor elevating mechanism 268, the through hole 217 a and the wafer up pin are arranged such that the wafer push-up pin 266 penetrates the through-hole 217 a in a non-contact state with the susceptor 217. 266 is arranged.

  Further, a gate valve 244 serving as a gate valve is provided on the side wall of the lower container 211. When the gate valve 244 is opened, the wafer 200 is loaded into or unloaded from the processing chamber 201 by a transfer mechanism (transfer means) not shown in the drawing. The process chamber 201 can be hermetically closed when closed.

  Further, the controller 121 as a control unit (control means) includes the APC 242, the valve 243b and the vacuum pump 246 through the signal line A, the susceptor lifting mechanism 268 through the signal line B, the gate valve 244 through the signal line C, and the signal line D. The matching device 272, the high-frequency power source 273, the mass flow controller 241 and the valve 243a are controlled through the signal line E, and the heater and the impedance variable mechanism 274 embedded in the susceptor 217 through the signal line (not shown).

  Next, using the processing furnace 202 having the above-described configuration, a predetermined plasma process is performed on the surface of the wafer 200 or on the surface of the base film formed on the wafer 200 as one step of the semiconductor device manufacturing process. The method of applying will be described. In the following description, it is assumed that the operation of each part constituting the substrate processing apparatus is controlled by the controller 121.

The wafer 200 is loaded into the processing chamber 201 by a transfer mechanism (not shown) that transfers the wafer 200 from the outside of the processing chamber 201 constituting the processing furnace 202, and is transferred onto the susceptor 217. The details of this transport operation are as follows.
The susceptor 217 is lowered to the substrate transfer position, and the tip of the wafer push-up pin 266 passes through the through hole 217a of the susceptor 217. At this time, the push-up pin 266 is protruded by a predetermined height from the surface of the susceptor 217.
Next, the gate valve 244 provided in the lower container 211 is opened, and the wafer 200 is placed on the tip of the wafer push-up pin 266 by a transfer mechanism (not shown).
When the transfer mechanism is retracted out of the processing chamber 201, the gate valve 244 is closed.
When the susceptor 217 is raised by the susceptor lifting mechanism 268, the wafer 200 can be placed on the upper surface of the susceptor 217, and further raised to a position where the wafer 200 is processed.

The heater embedded in the susceptor 217 is preheated, and heats the loaded wafer 200 to a predetermined wafer processing temperature within a range of room temperature to 500 ° C.
The pressure of the processing chamber 201 is maintained at a predetermined pressure within the range of 0.1 to 100 Pa using the vacuum pump 246 and the APC 242.

When the temperature of the wafer 200 reaches the processing temperature and stabilizes, the upper surface (processing surface) of the wafer 200 disposed in the processing chamber 201 from the gas inlet 234 through the gas outlet 239 of the shielding plate 240. Introduce towards.
At the same time, high frequency power is applied to the cylindrical electrode 215 from the high frequency power supply 273 via the matching unit 272. The power to be applied is a predetermined output value within the range of 150 to 200W.
At this time, the impedance variable mechanism 274 is controlled in advance so as to have a desired impedance value.

Magnetron discharge is generated under the influence of the magnetic field of the cylindrical magnets 216 and 216, charges are trapped in the upper space of the wafer 200, and high-density plasma is generated in the plasma generation region 224. Then, the surface of the wafer 200 on the susceptor 217 is subjected to plasma processing by the generated high density plasma.
The wafer 200 that has been subjected to the plasma processing is transferred outside the processing chamber 201 using a transfer mechanism (not shown) in the reverse order of substrate loading.

Next, an example of a method for forming a gate oxide film using the NMT apparatus will be described with reference to FIG.
FIG. 2 shows an example of the manufacturing process of the gate insulating film.
First, a known method such as a LOCOS (Local Oxidation of Silicon) process or an STI (Shallow Trench Isolation) process is performed on a Si substrate (silicon substrate) 10 as a semiconductor substrate shown in FIG. The element isolation region 12 is formed as shown in FIG.

Next, after well ion implantation, channel stop ion implantation, threshold adjustment ion implantation, and the like are performed by a well-known method, an oxide film equivalent to a thermal oxide film is formed on the Si substrate 10 using the MMT apparatus. A SiO ₂ film 14 is formed.
In this case, a large amount of krypton (Kr) and oxygen are introduced into the processing chamber 201 of the MMT apparatus to generate Kr / O ₂ plasma, and the SiO ₂ film 14 is formed.
The reason why Kr is used is that the energy band for activating Kr is low and matches with the O ₂ radical excitation energy.

Next, as shown in FIG. 2C, plasma 18 is generated in the processing chamber 201 by a predetermined plasma nitriding process, as shown in FIG. 2C, and at least the surface of the SiO ₂ film 14 is nitrided. Then, a SION film (silicon oxynitride film) 20 as a gate insulating film is formed. In this case, in order to achieve the thinning of the SiON film 20 by eliminating the influence of oxygen as an outgas from the quartz material. As described above, the reduction of the SiO ₂ film 14 during the plasma nitriding process is important.
FIG. 3 shows an example of boundary conditions for oxidation and reduction of Si (silicon). In the figure, the abscissa temperature, the vertical axis represents the gas ratio of H _{2 O} and H _2.
From the results shown in FIG. 3, (1) Si (silicon) is reduced under the condition that even if oxygen is contained in the processing atmosphere, it is H ₂ rich with respect to oxygen and the temperature of silicon is high (about 900 ° C.). (2) When low-temperature plasma nitriding is performed in a mixed gas atmosphere of N ₂ and H ₂ using plasma with a high electron temperature, the hydrogen radicals activated by the plasma cause the reduction temperature shown in FIG. It can be seen that the SiO ₂ film 14 is reduced at a lower temperature.
For this reason, in this embodiment, in the MMT apparatus, after the SiO ₂ film 14 is formed, the Kr / O ₂ gas is exhausted from the processing chamber 201, and then the N ₂ gas (nitrogen gas) and the H ₂ gas (hydrogen gas) ), A mixed gas containing N ₂ gas (nitrogen gas) and NH ₃ gas (ammonia gas), or a mixed gas containing H ₂ gas and NH ₃ gas is introduced to perform gas replacement, A mixed gas atmosphere capable of generating hydrogen radicals was used, and the plasma nitriding treatment was performed on the SiO ₂ film 14 in the mixed gas atmosphere under the following plasma nitriding treatment conditions (1) and (2).
Plasma nitriding conditions ・ Hydrogen concentration in the mixed gas is 50% or less, preferably 5 to 50%
-Temperature of the Si substrate 10: 400 ° C or higher, preferably 500 ° C or higher

Under such plasma nitriding conditions, when nitriding plasma 18 is generated in the processing chamber 201 and the SiO ₂ film 14 on the surface of the Si substrate 10 is subjected to nitriding, as shown in FIG. While oxygen in the SiO ₂ film 14 as a silicon film is reduced by hydrogen radicals activated by the plasma 18, nitrogen is introduced into the SiO ₂ film 14 to form an SiON film (silicon oxynitride film) 20. It was.
Then, as shown in FIG. 2E, a gate electrode 22 made of polysilicon is formed on the SiON film 20 by a known method such as CVD.
The gate electrode 22 contains B (boron atom) as an impurity. Thereafter, for example, lead wires and capacitors are formed, and an LSI such as a DRAM is formed.
When various heat treatment steps are performed after the gate electrode 22 is formed, diffusion of B (boron atoms) into the Si substrate 10 is prevented by the effect of preventing diffusion of B (boron atoms) in the SiON film 20 which is a gate insulating film. The

Next, examples of the present invention will be described.
First, as described in the above embodiment, the Si substrate 10 on which the SiO ₂ film 14 having a thickness of 2.0 nm is formed is placed in the processing chamber 201, and a mixed gas containing H ₂ gas and N ₂ gas is added to the MMT. The atmosphere in the processing chamber 201 was supplied to the processing chamber 201 of the apparatus, and the mixed gas atmosphere was replaced with Kr / O ₂ gas for forming an oxide film. At this time, the flow rate of H ₂ gas supplied to the processing chamber 201 was 50 sccm, the flow rate of N ₂ was 450 sccm, the hydrogen concentration in the mixed gas was 50% or less, and the pressure in the processing chamber 201 was 2.5 Pa.
Next, the temperature of the Si substrate 10 was heated to 700 ° C., and nitriding plasma was generated in the processing chamber 201 by the MMT apparatus. The high frequency power RF of the MMT apparatus was 250 W, and the plasma processing time was 90 sec.
During the nitriding plasma treatment, as shown in FIG. 4B, oxygen in the base silicon film is reduced by hydrogen radicals activated by the plasma 18, and oxygen in the base silicon film is replaced with nitrogen. Is done. For this reason, after the nitriding plasma treatment, as shown in FIG. 4C, the thinning from the interface between the Si substrate 10 and SiO2 to the surface of the SiON film 20 and the physical thinning of the SiON film 20 are achieved. It was done.

(Comparative example)
For comparison with Example 1, the Si substrate 10 on which the SiO ₂ film 14 having a thickness of 2.0 nm is formed is installed in the processing chamber 201, and only the N ₂ gas is supplied to the processing chamber 201 of the MMT apparatus. The atmosphere of 201 was replaced with a nitrogen gas atmosphere from Kr / O ₂ gas for forming an oxide film.
At this time, the flow rate of N ₂ gas supplied to the processing chamber 201 was 500 sccm. The pressure in the processing chamber 201 was 2.5 Pa. Next, the temperature of the Si substrate 10 was set to 700 ° C., and nitriding plasma was generated in the processing chamber 201 by the MMT apparatus. The high frequency power RF of the MMT apparatus was 250 W, and the plasma processing time was 90 sec.
When the plasma nitriding process the SiO ₂ film 14 in this condition is subjected, as shown in FIG. 6 (b), although the SiON film 20 is formed by the incorporation of nitrogen, in the SiO ₂ film 14 by activated oxygen It is difficult to reduce oxygen. For this reason, as shown in FIG. 6C, the film thickness of the SiON film 20 and the film thickness from the interface between the Si substrate 10 and the SiON film 20 to the surface of the SiON film 14 are larger than the film thickness before the processing. .
FIG. 5 shows the electrical thickness of the SiON film 20 after the plasma nitriding treatment as the gate insulating film in Example 1 and the comparative example.
As shown in FIG. 5, in Example 1, the film thickness of the SiO ₂ film 14 before the plasma nitriding treatment was 1.6 nm including the SiON film 20 after the plasma nitriding treatment. In the comparative example, The film thickness after the plasma nitriding treatment increased to 2.2 nm.
As is clear from this, when the plasma nitriding process is performed under the processing conditions of Example 1, the physical film thickness of the SION film 20 as the gate insulating film is decreased, and the electrical film thickness is decreased.
In Example 1, the same result was obtained when a mixed gas containing N ₂ gas (nitrogen gas) and NH ₃ gas (ammonia gas) or a mixed gas containing H ₂ gas and NH ₃ gas was used. It was.
Further, when the temperature condition of the Si substrate 10 on which the SiO ₂ film 14 is formed is 400 ° C., the electrical film thickness of the SiON film 20 becomes thin and good in practical use. Became possible.

As described above, when the gate insulating film, that is, the SiON film 20 is formed by plasma nitriding the SiO ₂ film 14, a mixed gas containing N ₂ gas (nitrogen gas) and H ₂ gas (hydrogen gas), N ₂ Using a mixed gas containing a gas (nitrogen gas) and NH ₃ gas (ammonia gas) or a mixed gas containing H ₂ gas and NH ₃ gas, the plasma nitriding treatment conditions were set, and the hydrogen concentration in the mixed gas was 50 %, The temperature of the Si substrate 10 is 400 ° C. or higher, preferably 500 ° C. or higher, and the concentration of hydrogen contained in the mixed gas is 5% to 50%.
[Appendix]

Hereinafter, aspects of this embodiment will be additionally described.
[Embodiment 1]
In a semiconductor device manufacturing method, plasma nitriding treatment is performed on a base silicon oxide film of a substrate while maintaining the substrate temperature at 400 ° C. or higher in a mixed gas atmosphere containing N ₂ and H ₂ having a hydrogen concentration of 50% or less. When an oxynitride insulating film as a gate insulating film is formed on the base silicon oxide film, oxygen in the oxide film as the base silicon oxide film is reduced by activated hydrogen radicals by plasma nitriding (low temperature plasma nitriding). However, since nitrogen is introduced, the physical and electrical thickness of the oxynitride film as the gate insulating film is reduced.

Embodiment 2
Plasma nitriding treatment is performed on the base silicon oxide film of the substrate while maintaining the substrate temperature at 400 ° C. or higher in a mixed gas atmosphere containing NH ₃ and N ₂ having a hydrogen concentration of 50% or less, and the base silicon oxide film is gated When an oxynitride insulating film is formed as an insulating film, nitrogen is introduced while oxygen in the oxide film as a base silicon oxide film is reduced by activated hydrogen radicals by plasma nitriding treatment (low temperature plasma nitriding treatment). Therefore, the physical and electrical film thickness of the silicon oxynitride film as the gate insulating film is reduced.

[Embodiment 3]
Plasma nitriding is performed on the base silicon oxide film of the substrate while maintaining the substrate temperature at 400 ° C. or higher in a mixed gas atmosphere containing NH ₃ and H ₂ having a hydrogen concentration of 50% or less, and the base silicon oxide film is gated When an oxynitride insulating film is formed as an insulating film, nitrogen is introduced while oxygen in the oxide film as a base silicon oxide film is reduced by activated hydrogen radicals by plasma nitriding treatment (low temperature plasma nitriding treatment). Therefore, the physical and electrical film thickness of the silicon oxynitride film as the gate insulating film is reduced.

It is explanatory drawing which shows the substrate processing furnace used for the manufacturing method of the semiconductor substrate of this invention. It is process drawing which shows the manufacturing method of the semiconductor device which concerns on this invention. It is a figure which shows an example of the boundary condition of oxidation of Si (silicon) and reduction | restoration. It is process drawing which concerns on one Example of this invention and shows the manufacturing method of the semiconductor device by a plasma nitriding process. It is explanatory drawing which contrasted the electrical film thickness of the Example which concerns on this invention, and the electrical film thickness of a comparative example. It is process drawing which shows the manufacturing method of the semiconductor device by the conventional plasma nitriding process.

Explanation of symbols

10 Si substrate 14 SiO ₂ film (underlying silicon oxide film)
20 SiON film (silicon oxynitride film)

Claims (1)

Plasma nitriding is performed on the base silicon oxide film of the substrate while maintaining the substrate temperature at 400 ° C. or higher in a mixed gas atmosphere containing N ₂ and H ₂ having a hydrogen concentration of 50% or less, and the base silicon oxide film is gated A method of manufacturing a semiconductor device, wherein an oxynitride insulating film is formed as an insulating film.

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