JP2010041000A - Method of manufacturing nitrogen doped silicon wafer and nitrogen doped silicon wafer obtained by the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a nitrogen doped silicon wafer and a nitrogen doped silicon wafer obtained by the same, both of which facilitate manufacturing the nitrogen doped silicon wafer injected with high concentration nitrogen necessary for forming high density BMD. <P>SOLUTION: The method of manufacturing the nitrogen doped silicon wafer includes: a step in which any one of a surface and the backside or both thereof of a silicon wafer to which nitrogen is not doped are made to come in contact with HF solution, thereby silicon in a surface layer portion of a contact face is made to terminate by hydrogen; and a step in which the wafer after hydrogen termination step is held in a nitrogen contained atmosphere at a temperature of 1,100 to 1,300°C for 1 to 100 sec, and nitrogen is injected from a surface layer of a hydrogen termination step face to a depth of 20 μm and with a concentration of 5×10<SP>14</SP>to 1×10<SP>16</SP>atoms/cm<SP>3</SP>. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention provides a method for producing a nitrogen-doped silicon wafer capable of easily producing a nitrogen-doped silicon wafer into which nitrogen of a concentration necessary for forming a high-density BMD is introduced inside the silicon wafer, and the method This relates to a nitrogen-doped silicon wafer obtained by the following.

  In general, in the manufacture of a semiconductor device element, a silicon wafer cut out from a silicon single crystal ingot grown by the Czochralski method (hereinafter referred to as CZ method) as a substrate is used. . In recent semiconductor device elements, the degree of integration of devices has increased remarkably, and accordingly, a higher quality silicon wafer has been required. For this reason, efforts are being made to clean the manufacturing process in the device manufacturing process, and efforts are made to improve the integrity of the surface of the silicon wafer, which is the electrically active region of the device, that is, to make the vicinity of the wafer surface defect-free. ing. In order to make the vicinity of the surface of the silicon wafer defect-free, it is important to reduce the density of oxygen precipitates (Bulk Micro Defect, hereinafter referred to as BMD) in the vicinity of the surface of the silicon wafer as much as possible. This BMD becomes apparent in the silicon wafer by the heat treatment. If this BMD exists in the vicinity of the wafer surface, it adversely affects the reliability and yield of the device.

  In the device manufacturing process, there are several processes in which metal impurities such as Fe, Cu, and Ni are mixed. If these metal impurities are present in the vicinity of the wafer surface, the device characteristics may be deteriorated and the product yield may be reduced. Therefore, metal impurities are prevented from being taken into the wafer surface, which is an electrically active region. There is a need to.

  Therefore, a gettering technique is employed as one technique for controlling the BMD density and removing metal impurity contamination from the device formation region. The gettering technique is classified into an internal gettering (Intrinsic Gettering, hereinafter referred to as IG) method, an external gettering (Extrinsic Gettering, hereinafter referred to as EG) method, and the like.

  In the IG method, the oxygen concentration in the vicinity of the wafer surface is reduced by high-temperature heat treatment to form a BMD-free layer (hereinafter referred to as a DZ layer) near the wafer surface, and a high-density BMD in a deeper position than the DZ layer. This BMD defect is used as a metal impurity capture source.

In the EG method, SiO ₂ abrasive grains are artificially sprayed from the jet nozzle onto the back surface of the wafer by air pressure, and mechanical damage is applied to the back surface of the wafer. Crystal defects generated from the mechanical damage are caused by metal impurities. A method using a capture source (BSD method) or a method of growing a polysilicon layer of about 0.5 to 1.5 μm on the back side of a silicon wafer and using this polysilicon layer as a metal impurity capture source (PBS method) and so on.

  On the other hand, an epitaxial silicon wafer in which an epitaxial layer is deposited on a silicon wafer is widely used as a wafer for manufacturing individual semiconductors, bipolar ICs and the like because of its excellent characteristics, and the demand for it is increasing.

  However, in general, an epitaxial silicon wafer is subjected to a high-temperature heat treatment to deposit an epitaxial layer on the silicon wafer. Therefore, oxygen precipitate nuclei that have grown to some extent in the thermal environment during crystal growth disappear due to the high-temperature heat treatment in this epitaxial growth process. Therefore, there is a problem that BMD is difficult to be formed.

  In order to solve such problems, it has been proposed to use a silicon wafer doped with nitrogen as a substrate on which an epitaxial layer is formed. This is because, by doping nitrogen, oxygen precipitate nuclei that do not disappear in the epitaxial growth process are formed, and thus an epitaxial silicon wafer having high gettering ability can be produced.

Moreover, not only when producing an epitaxial silicon wafer, in order to form a high-density BMD inside the silicon wafer, nitrogen may be contained therein. As a method for incorporating nitrogen into such a wafer, a method of introducing nitrogen as a raw material at the stage of crystal growth is known. For example, a silicon raw material with a nitride film is added to a silicon raw material for pulling up a single crystal to form a silicon melt doped with nitrogen, and a silicon single crystal ingot is pulled from the silicon melt and cut out from the pulled ingot. Discloses a method for obtaining a nitrogen-doped silicon wafer (see, for example, Patent Documents 1 to 3).
JP 2000-109396 A (Claim 7) JP 2000-272959 A (paragraphs [0029], [0031]) JP 2001-199794 A (Claim 2)

  However, since the segregation coefficient of nitrogen is very small, and the concentration of doped nitrogen is greatly different between the top and bottom portions of the pulled silicon single crystal ingot, the silicon single crystal lifted by the method described in Patent Documents 1 to 3 above. From the crystal ingot, since only a small amount of nitrogen-doped silicon wafer doped with nitrogen of a concentration necessary for forming the high-density BMD can be obtained, there is a problem that the production efficiency is inferior. The nitrogen concentration distribution in the radial direction inside the nitrogen-doped silicon wafer could not be controlled, resulting in variations in the nitrogen concentration.

  An object of the present invention is to provide a method for producing a nitrogen-doped silicon wafer capable of easily producing a nitrogen-doped silicon wafer into which a high concentration of nitrogen necessary for forming a high-density BMD is introduced, and to obtain the method. It is an object of the present invention to provide a nitrogen-doped silicon wafer.

  Another object of the present invention is to provide a method for producing a nitrogen-doped silicon wafer which can make the nitrogen concentration in the radial direction inside the wafer uniform, and a nitrogen-doped silicon wafer obtained by the method.

  As a result of earnestly examining experiments and theoretical considerations back to the device manufacturing process, and further to the silicon wafer manufacturing process, the present inventors obtained new knowledge about the BMD defect generated in the silicon semiconductor substrate, and obtained the present invention. It has been completed.

That is, the invention according to claim 1 is a step of terminating the silicon in the surface layer portion of the contact surface with hydrogen by bringing either or both of the front surface and the back surface of the silicon wafer not doped with nitrogen into contact with the HF aqueous solution. Then, the wafer after the hydrogen termination treatment is held in a nitrogen-containing atmosphere at a temperature of 1100 to 1300 ° C. for 1 to 100 seconds to a depth of 5 × 10 ¹⁴ to 1 × 10 ¹⁶ from the surface layer of the hydrogen termination treatment surface to 20 μm. and a step of introducing nitrogen at a concentration of atoms / cm ³ .

The invention according to claim 2 is a nitrogen-doped silicon wafer obtained by the method according to claim 1, wherein either or both of the front surface and the back surface of the silicon wafer not doped with nitrogen are brought into contact with the HF aqueous solution. The silicon of the surface layer portion of the contact surface is terminated with hydrogen, and the wafer after the hydrogen termination treatment is held in a nitrogen-containing atmosphere at a temperature of 1100 to 1300 ° C. for 1 to 100 seconds to 20 μm from the surface layer of the hydrogen termination surface. This is a nitrogen-doped silicon wafer in which nitrogen is introduced at a depth of 5 × 10 ¹⁴ to 1 × 10 ¹⁶ atoms / cm ³ .

  In the method for producing a nitrogen-doped silicon wafer of the present invention and the nitrogen-doped silicon wafer obtained by the method, it is not necessary to introduce nitrogen at the stage of crystal growth as in the conventional nitrogen-doped silicon wafer. Since the high concentration of nitrogen necessary for forming the high-density BMD can be easily introduced later, the production efficiency is improved. Further, since nitrogen is introduced into the wafer, the nitrogen concentration distribution in the radial direction inside the wafer can be made uniform. In addition, high-concentration nitrogen can be obtained by treating silicon in the surface layer portion of either or both of the front and back surfaces of a silicon wafer not doped with nitrogen in a highly reactive ammonia-containing atmosphere after hydrogen termination. It can be efficiently introduced into the wafer.

  Next, the best mode for carrying out the present invention will be described with reference to the drawings.

  In the method for producing a nitrogen-doped silicon wafer according to the present invention, first, a silicon wafer 11 not doped with nitrogen as shown in FIGS. 1A and 2A is prepared, and an arbitrary surface of the silicon wafer is prepared. Is brought into contact with an aqueous HF solution to terminate the silicon in the surface layer portion of the contact surface with hydrogen.

  The silicon located on the surface layer of the prepared silicon wafer before processing is in a state where oxygen is bonded, that is, a state in which the natural oxide film 12 is formed on the surface layer of the wafer. Oxygen bonded to a portion of silicon is replaced with hydrogen, and silicon on the wafer surface layer is terminated with hydrogen. By this hydrogen termination treatment, the contact surface with the HF aqueous solution is in a state where it is difficult to form a natural oxide film on the surface. Note that the contact surface is also terminated with hydrogen by bringing the HF aqueous solution into contact with the silicon wafer from which the natural oxide film has been removed.

  The contact of the silicon wafer with the HF aqueous solution may be contact of only the front surface of the wafer 11 as shown in FIG. 1B, contact of only the back surface of the wafer, or contact to both surfaces as shown in FIG. 2B. Good. FIG. 2B shows a case where the HF aqueous solution is brought into contact with not only both surfaces of the silicon wafer 11 but also the front and back surfaces, and the end surface, and all of the natural oxide film covering the silicon wafer 11 is removed. It is in the state.

  The HF aqueous solution used in this step is preferably 0.5 to 5% by mass in concentration for the following reason. That is, in an HF aqueous solution having a concentration of less than 0.5% by mass, it takes a long time to remove the natural oxide film, and the productivity is lowered. In an HF aqueous solution having a concentration of more than 5% by mass, the member used for the treatment tank is used. Therefore, the frequency of replacement of the treatment tank is increased.

  In addition, when an SC-1 cleaning liquid (mixed liquid of hydrogen peroxide and ammonium hydroxide) used for wafer cleaning is brought into contact with the wafer instead of the HF aqueous solution, a natural oxide film is formed on the wafer surface after the contact. Will be. Then, even if the wafer in which this natural oxide film exists is subjected to a heat treatment in a nitrogen-containing atmosphere as in the subsequent process, this natural oxide film becomes a barrier film, Nitrogen is not introduced uniformly.

Next, rapid thermal annealing (hereinafter referred to as RTA heat treatment) is performed in which the wafer after the hydrogen termination treatment is held in a nitrogen-containing atmosphere at a temperature of 1100 to 1300 ° C. for 1 to 100 seconds. By performing the RTA heat treatment under the above specific conditions in a nitrogen-containing atmosphere, as shown in FIG. 1 (c) and FIG. 2 (c), a high density is obtained at a depth 13 from the surface layer of the hydrogen-terminated surface to 20 μm. Nitrogen having a concentration of 5 × 10 ¹⁴ to 1 × 10 ¹⁶ atoms / cm ³ required for forming BMD can be introduced. The introduction of nitrogen in the above concentration range from the surface layer to a depth of 20 μm here does not mean that nitrogen is not introduced at a depth exceeding 20 μm. The RTA heat treatment here can be performed by a heat treatment apparatus 21 as shown in FIG. 3, for example. In this heat treatment apparatus 21, the silicon wafer 11 is placed in a state of being separated from the inner surface of the quartz tube 22 by using a support or the like, and an infrared lamp 23 is supplied from the outside while supplying the atmospheric gas G into the quartz tube 22. Heat treatment is performed by irradiating with infrared rays by lamp heating using the like.

  As the nitrogen-containing atmosphere in this RTA heat treatment, nitrogen gas, a gas having higher reactivity than nitrogen, such as ammonia gas or hydrazine gas, or a mixed gas of these nitrogen-containing gas and inert gas can be used. When the nitrogen-containing atmosphere is a mixed gas, it is preferable to set the partial pressure of the nitrogen-containing gas to 5% or more from the viewpoint that the gas needs to be supplied to the entire wafer surface during the heat treatment.

  In addition, the heat treatment temperature in the RTA heat treatment is defined as 1100 to 1300 ° C. The reason is that when the heat treatment temperature is less than 1100 ° C., the concentration required to promote the formation of high density BMD from the surface layer of the wafer to a predetermined depth. If nitrogen is not uniformly introduced in the radial direction and the heat treatment temperature exceeds 1300 ° C., the wafer slips due to the difference in thermal expansion coefficient between the support and the wafer supporting the wafer in the heat treatment furnace. This is because the yield in the device manufacturing process in the subsequent process is reduced. A preferable heat treatment temperature is 1150 to 1200 ° C.

  In addition, the retention time in the RTA heat treatment is defined to be 1 to 100 seconds because the concentration of nitrogen required to promote the formation of high density BMD to a desired depth when the retention time is less than 1 second. This is because the amount of nitrogen introduced into the wafer does not change even when the holding time exceeds 100 seconds, and there is a problem that productivity is lowered when the time is increased. A preferable holding time is 1 to 10 seconds.

  Thus, in the manufacturing method of the present invention, unlike the conventional nitrogen-doped silicon wafer, it is not necessary to introduce nitrogen at the stage of crystal growth, and it is necessary to form a high-density BMD later on an arbitrary wafer. Since it is possible to simply introduce nitrogen at a simple concentration, production efficiency is improved. Further, since nitrogen is introduced into the wafer hydrogen termination surface, the nitrogen concentration distribution in the radial direction inside the wafer can be made uniform.

In the nitrogen-doped silicon wafer of the present invention obtained by the above method, nitrogen was introduced at a concentration of 5 × 10 ¹⁴ to 1 × 10 ¹⁶ atoms / cm ³ from the surface layer of the hydrogen-terminated surface to 20 μm. It is characterized by.

  When a BMD revealing heat treatment is applied to a silicon wafer having nitrogen introduced at the above concentration in the vicinity of the surface, a DZ layer can be formed in the vicinity of the wafer surface, and a high-density BMD can be formed at a position deeper than the DZ layer. .

  Specifically, after holding for 4 hours at a temperature of 800 ° C. in an atmosphere of 80% nitrogen and 20% oxygen, a two-step heat treatment is performed for 16 hours at a temperature of 1000 ° C. By reducing the oxygen concentration, a DZ layer is formed in the vicinity of the wafer surface, and a BMD is formed at a position deeper than the DZ layer. This two-stage heat treatment is a heat treatment for oxygen precipitation performed at a temperature lower than that of the RTA heat treatment, and stabilizes oxygen precipitation nuclei and grows precipitates.

  Usually, during this two-step heat treatment, a DZ layer is formed by the out-diffusion of oxygen and nitrogen from the front and back surfaces, and the annihilation of silicon and vacancies between lattices injected by oxidation of the surface layer. BMD having a high density is formed at a deep position.

Here, since nitrogen is introduced into the nitrogen-doped silicon wafer of the present invention at a concentration of 5 × 10 ¹⁴ to 1 × 10 ¹⁶ atoms / cm ³ at a depth from the surface layer to 20 μm, during the two-stage heat treatment, The presence of nitrogen in the above concentration range lowers the mobility of vacancies and prevents vacancies from diffusing outward. As a result, BMD formation can be promoted and higher density BMD can be formed. .

  Note that the nitrogen near the wafer surface after the two-step heat treatment diffuses outward from the surface layer, but the role of preventing the outward diffusion of vacancies is performed during the heat treatment before the nitrogen is diffused outward. As a result, formation of high-density BMD is promoted.

  The technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, in the above embodiment, when the RTA heat treatment is performed on the silicon wafer 11, the infrared ray 23 is used to irradiate the silicon wafer 11 with infrared rays, and the silicon wafer 11 is heated by other means (heater heating). I do not care. In addition, the BMD revealing heat treatment is not particularly performed before the device fabrication process, and may be performed by a heat treatment performed in the subsequent device fabrication process.

Next, examples of the present invention will be described in detail together with comparative examples.
<Example 1>
First, a silicon wafer having a diameter of 300 mm that was not doped with nitrogen was prepared. This wafer is cut from a silicon single crystal ingot grown by the CZ method and the surface damage is removed by lapping, chamfering, chemical etching, etc., and a natural oxide film is formed on the surface. It was.

  Next, this silicon wafer was immersed in a liquid tank in which a 0.5 mass% HF aqueous solution was stored for 5 minutes to perform hydrogen termination on the entire surface of the silicon wafer. The wafer after the hydrogen termination treatment was in a state where the natural oxide film formed on the entire surface was removed.

Next, the hydrogen-terminated wafer is placed in the quartz tube 22 of the heat treatment apparatus 21 shown in FIG. 3 using a support, and then the infrared gas is supplied to the quartz tube 22 at a concentration of 15% while the infrared gas is supplied. The lamp 23 was irradiated with infrared rays, and RTA heat treatment was performed at a temperature of 1100 ° C. for 10 seconds. By this RTA heat treatment, nitrogen was introduced to a predetermined depth from the surface layer of the hydrogen-terminated surface. The wafer which passed through the said process was used as the nitrogen dope silicon wafer sample.
<Example 2>
A nitrogen-doped silicon wafer sample was obtained in the same manner as in Example 1 except that the heat treatment temperature of the RTA heat treatment was changed to 1150 ° C.
<Comparative Example 1>
As a silicon wafer, a wafer doped with nitrogen at a concentration of about 4 × 10 ¹⁴ atoms / cm ³ obtained by slicing a silicon single crystal ingot pulled from a silicon melt to which a predetermined amount of silicon nitride is added is used. The wafer was used as a nitrogen-doped silicon wafer sample without being subjected to hydrogen termination treatment and RTA heat treatment.
<Comparative example 2>
Instead of hydrogen termination treatment with HF aqueous solution, the silicon wafer was immersed for 5 minutes in the liquid tank where the SC-1 cleaning solution was stored to clean the front and back surfaces of the silicon wafer, and the RTA heat treatment temperature was changed to 1150 ° C. A nitrogen-doped silicon wafer sample was obtained in the same manner as in Example 1.
<Comparative Example 3>
A nitrogen-doped silicon wafer sample was obtained in the same manner as in Example 1 except that the heat treatment atmosphere of the RTA heat treatment was changed from an ammonia gas atmosphere to a nitrogen gas atmosphere and the heat treatment temperature was changed to 750 ° C.
<Comparison test 1>
For each sample of Examples 1 and 2 and Comparative Examples 1 to 3, the nitrogen concentration from the surface layer to a predetermined depth was measured by secondary ion mass spectroscopy (SIMS). The results are shown in FIGS. In these drawings, 1E + 14 means 1 × 10 ¹⁴ and 1E + 18 means 1 × 10 ¹⁸ .

In addition, each sample of Examples 1 and 2 and Comparative Examples 1 to 3 was subjected to BMD revealing heat treatment. This BMD revealing heat treatment is a first stage heat treatment at 800 ° C. for 4 hours in an atmosphere of 80% nitrogen and 20% oxygen, and further a second stage heat treatment at 1000 ° C. for 16 hours. Subsequently, the BMD density inside the wafer after the BMD revealing heat treatment was applied to each sample was measured by SIMS. The results are shown in Table 1 below. In Table 1, “ND” indicates the detection limit (3 × 10 ⁻¹⁴ atoms / cm ³ ) or less.

表１及び図４〜図８から明らかなように、予め窒素ドープされた単結晶インゴットから切出した比較例１のウェーハは、導入された窒素の濃度が約４×１０¹⁴ａｔｏｍｓ／ｃｍ³程度であり、また、ＢＭＤ顕在化熱処理後のＢＭＤ密度は約１×１０⁶ａｔｏｍｓ／ｃｍ²程度と高密度となったが、上記濃度範囲内の窒素ドープシリコンウェーハは、単結晶インゴットから僅かしか得ることができないため、生産効率が劣る。

As is apparent from Table 1 and FIGS. 4 to 8, the wafer of Comparative Example 1 cut out from a nitrogen-doped single crystal ingot has a concentration of introduced nitrogen of about 4 × 10 ¹⁴ atoms / cm ³ . In addition, the BMD density after the BMD revealing heat treatment was as high as about 1 × 10 ⁶ atoms / cm ² , but the nitrogen-doped silicon wafer within the above concentration range can be obtained from a single crystal ingot only slightly. Production efficiency is inferior.

In the wafer of Comparative Example 2 in which SC-1 cleaning was performed as a pre-treatment before the heat treatment, the concentration of nitrogen introduced by the RTA heat treatment was low and became below the detection limit (about 3 × 10 ¹⁴ atoms / cm ³ ), and the apparent heat treatment The later BMD density was about 1 × 10 ⁵ atoms / cm ^2, which was insufficient. This is presumably because a natural oxide film was formed on the pre-processed wafer, and this natural oxide film became a barrier film and nitrogen introduction was inhibited.

Even in the wafer of Comparative Example 3 where the heat treatment temperature is lower than the RTA heat treatment temperature of the present invention, the concentration of nitrogen introduced by the RTA heat treatment is low and below the detection limit (about 3 × 10 ¹⁴ atoms / cm ³ ). Thus, the BMD density after the precipitation heat treatment was about 1 × 10 ⁴ atoms / cm ^2, which was insufficient. From this result, it can be seen that the temperature condition of the RTA heat treatment affects the introduction of nitrogen.

On the other hand, in the case of the wafer of Example 1 where the temperature of the RTA heat treatment is 1100 ° C., the BMD density is about 1 × 10 ⁶ atoms / cm ^{2 and} the temperature of the RTA heat treatment is 1150 ° C. In the case of the wafer of Example 2, the BMD density is about 2 × 10 ⁶ atoms / cm ^2, which is about the same as that of Comparative Example 1, and higher BMD density than Comparative Examples 2 and 3 could be obtained. .

  From the above results, it was confirmed that the high concentration of nitrogen required for the formation of high density BMD can be easily introduced by the production method of the present invention.

It is process drawing which shows the manufacturing method of this invention. It is process drawing which shows another manufacturing method of this invention. It is the schematic of the heat processing apparatus used at a nitrogen introduction | transduction process. It is a figure which shows the nitrogen concentration profile in the depth direction from the surface layer of the wafer obtained in Example 1. FIG. It is a figure which shows the nitrogen concentration profile in the depth direction from the surface layer of the wafer obtained in Example 2. FIG. It is a figure which shows the nitrogen concentration profile in the depth direction from the surface layer of the wafer obtained by the comparative example 1. FIG. It is a figure which shows the nitrogen concentration profile in the depth direction from the surface layer of the wafer obtained by the comparative example 2. FIG. It is a figure which shows the nitrogen concentration profile in the depth direction from the surface layer of the wafer obtained by the comparative example 3. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Silicon wafer 12 Natural oxide film 13 Nitrogen introduction area | region 21 Heat processing apparatus 22 Quartz tube 23 Infrared lamp G Atmospheric gas

Claims (2)

A step of terminating the silicon in the surface layer portion of the contact surface with hydrogen by bringing either or both of the front surface and the back surface of the silicon wafer not doped with nitrogen into contact with an HF aqueous solution;
The wafer after hydrogen termination is held in a nitrogen-containing atmosphere at a temperature of 1100 to 1300 ° C. for 1 to 100 seconds to a depth of 20 μm from the surface layer of the hydrogen termination surface to 5 × 10 ¹⁴ to 1 × 10 ^16. and a step of introducing nitrogen at a concentration of atoms / cm ³ . A nitrogen-doped silicon wafer obtained by the method according to claim 1,
The silicon of the surface layer portion of the contact surface is terminated with hydrogen by bringing either or both of the front surface and the back surface of the silicon wafer not doped with nitrogen into contact with an HF aqueous solution,
The wafer after hydrogen termination is held in a nitrogen-containing atmosphere at a temperature of 1100 to 1300 ° C. for 1 to 100 seconds to a depth of 20 μm from the surface layer of the hydrogen termination surface to 5 × 10 ¹⁴ to 1 × 10 ^16. A nitrogen-doped silicon wafer, wherein nitrogen is introduced at a concentration of atoms / cm ³ .

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