JP7207970B2 - Wafer processing method - Google Patents

Description

The present invention relates to a wafer processing method, particularly plasma dicing.

In general, dicing with a cutting blade or laser processing with a laser beam is used to divide a wafer made of silicon, gallium arsenide, SiC, sapphire, etc. on which semiconductor devices are formed into individual device chips. Since the cutting blade is crushed, chipping occurs at the edge of the chip, and the bending strength of the chip is limited (upper limit). In addition, even if the modified layer formed inside the wafer with a laser beam is used as a fracture starting point to split into device chips, cracks will occur on the sides of the chips, albeit only slightly, so the die strength of the chips will have a limit (upper limit). .

In particular, semiconductor device chips are processed smaller and thinner year by year along with technological innovation. Therefore, chipping of the edge of the chip and cracking of the side surface of the chip greatly reduce the bending strength. Therefore, techniques for dicing wafers by plasma processing (plasma dicing) have been developed (see, for example, Patent Documents 1 and 2).

Japanese Patent No. 4447325 Japanese Patent No. 6188589

In this type of technology, it is necessary to cover the surface of the device with a mask in order to prevent the device from being etched during plasma processing of the wafer. However, since the mask is also removed by plasma processing, albeit at a low rate, the device may be damaged if the mask disappears during plasma processing.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a wafer processing method capable of easily detecting whether or not a mask layer covers a device.

In order to solve the above-described problems and achieve the object, the present invention provides a wafer processing method in which devices are formed in a plurality of regions partitioned by grid-like dividing lines, wherein the devices are covered with a wafer. A mask layer coating step of coating the surface of the wafer with a mask layer of a predetermined color that exposes the area of the line to be divided, and after performing the mask layer coating step, supplying an etching gas in a plasma state to the surface side of the wafer. and a plasma processing step of etching the lines to be divided exposed from the mask layer , after the plasma processing step, checking the presence or absence of the mask layer on the surface of the wafer and applying the predetermined color to the surface of the wafer. is detected, further comprising a mask layer detection step.

In this configuration, in the mask layer covering step, two or more mask layers having different colors are laminated, and in the mask layer detecting step, the number of mask layers on the surface of the wafer is estimated from the detected colors. If the number of layers is less than a preset number, continuation of subsequent steps may be stopped.

According to the present invention, by providing at least a mask layer of a predetermined color different from the surface of the wafer, whether or not the mask layer covers the device can be easily detected based on the presence or absence of detection of the predetermined color. can do. Therefore, there is an effect that it is possible to prevent a situation in which the device is erroneously etched and damaged. Further, by detecting a predetermined color, it can be used as a guideline when selecting mask layer coating conditions such as the thickness of the mask layer required for plasma processing.

FIG. 1 is a perspective view showing an example of a wafer to be processed by a wafer processing method according to a first embodiment. FIG. 2 is a flow chart showing the procedure of the wafer processing method. FIG. 3 is a perspective view showing a frame supporting step. FIG. 4 is a side sectional view showing the resin coating step. FIG. 5 is a side sectional view showing the laser processing steps. FIG. 6 is a perspective view schematically showing the wafer after the laser processing step. FIG. 7 is a cross-sectional view of the essential parts of the wafer after the laser processing step. FIG. 8 is a cross-sectional view showing the configuration of an etching apparatus used in the plasma processing step. FIG. 9 is a cross-sectional view of the main portion of the wafer after the plasma processing step. FIG. 10 is a side sectional view showing the mask layer detection step. FIG. 11 is a side sectional view showing the mask layer removal step. FIG. 12 is a side sectional view showing the resin film coating step of the wafer processing method according to the second embodiment. FIG. 13 is a cross-sectional view of the main part of the wafer after the laser processing step.

A form (embodiment) for carrying out the present invention will be described in detail with reference to the drawings. The present invention is not limited by the contents described in the following embodiments. In addition, the components described below include those that can be easily assumed by those skilled in the art and those that are substantially the same. Furthermore, the configurations described below can be combined as appropriate. In addition, various omissions, substitutions, or changes in configuration can be made without departing from the gist of the present invention.

[Embodiment 1]
A wafer processing method according to the first embodiment will be described with reference to the drawings. FIG. 1 is a perspective view showing an example of a wafer to be processed by a wafer processing method according to a first embodiment. FIG. 2 is a flow chart showing the procedure of the wafer processing method.

In Embodiment 1, the wafer 1 is a disk-shaped semiconductor wafer or optical device wafer having a substrate 2 made of silicon, sapphire, SiC (silicon carbide), gallium arsenide, or the like. As shown in FIG. 1, the wafer 1 has dividing lines 6 provided in a grid pattern on the surface 3 of the substrate 2. A plurality of areas partitioned by these dividing lines 6 contain ICs, LSIs, etc., respectively. A device 5 is formed comprising: The circuit constituting the device 5 is, for example, an inorganic film such as SiOF or BSG (SiOB), or an organic film such as a polyimide or parylene polymer film. membrane). A back surface 4 is the surface of the substrate 2 opposite to the surface 3 on which the device 5 is formed.

The wafer processing method according to the first embodiment is a method of dividing the wafer 1 into individual devices 5 along dividing lines 6 . The wafer processing method includes, as shown in FIG. 2, a frame supporting step ST1, a mask layer covering step ST2, a plasma processing step ST3, a mask layer detecting step ST4, and a mask layer removing step ST5.

(frame support step)
FIG. 3 is a perspective view showing a frame supporting step. The frame supporting step ST1 is a step of supporting the above-described wafer 1 on the annular frame 201 via the adhesive tape 200. As shown in FIG. In Embodiment 1, as shown in FIG. 3, the annular frame 201 has an opening 201A larger in diameter than the wafer 1, and the outer peripheral portion 200A of the adhesive tape 200 is placed on the lower surface of the annular frame 201 so as to cover the opening 201A. Affix (wear). Then, the rear surface 4 side of the wafer 1 is adhered to the adhesive tape 200 exposed in the opening 201A of the annular frame 201. As shown in FIG. In this frame supporting step ST1, the wafer 1 is supported by the annular frame 201 via the adhesive tape 200 with the surface 3 (device 5) side of the substrate 2 exposed.

(Mask layer covering step)
The mask layer covering step ST2 is a step of covering the surface 3 of the wafer 1 with a mask layer 10 that covers the devices 5 and exposes the regions of the dividing lines 6 . In the present embodiment, the mask layer coating step ST2 includes a step of coating the entire surface 3 of the substrate 2 with the resin film 11 (referred to as a resin film coating step) and a step of irradiating a laser beam along the dividing lines 6 to divide the substrate. The process is performed in two stages: a step of removing the resin film 11 in the region of the line 6 to form a mask layer 10 (referred to as a laser processing step). FIG. 4 is a side sectional view showing the resin film coating step. FIG. 5 is a side sectional view showing the laser processing steps. FIG. 6 is a perspective view schematically showing the wafer after the mask layer coating step. FIG. 7 is a cross-sectional view of the main part of the wafer after the mask layer coating step.

The resin film coating step is a step of coating the surface 3 of the wafer 1 with a resin film 11 resistant to plasma etching before performing the laser processing step. In the resin film coating step, as shown in FIG. 4, the back surface 4 side of the wafer 1 is held by suction on the spinner table 21 of the spin coater 20 via the adhesive tape 200, and the annular frame 201 is clamped by the clamper 22. FIG. In this state, the liquid resin 24 is dropped onto the surface 3 (device 5) of the wafer 1 from the coating nozzle 23 while rotating the spinner table 21 about its axis. At this time, the coating nozzle 23 reciprocates in the diameter direction of the wafer 1 . The dropped liquid resin 24 flows on the surface 3 of the wafer 1 from the center side toward the outer circumference side due to the centrifugal force generated by the rotation of the spinner table 21, and is applied to the entire surface 3 of the wafer 1. Cover the device 5.

For the liquid resin 24, for example, a water-soluble liquid resin having resistance to plasma etching such as polyvinyl alcohol (PVA) or polyvinyl pyrrolidone (PVP) is used. Since this type of liquid resin is generally colorless and transparent, even when it is applied to the surface 3 of the wafer 1, it is difficult to determine whether the surface 3 is uniformly applied. Therefore, in the first embodiment, the liquid resin 24 is colored with a predetermined color (for example, white) by mixing water-soluble pigment (including carbon, pigment, ink, etc.). For this predetermined color, at least a color different from the color of the substrate 2 (including the device 5) of the wafer 1 is selected so that whether or not the liquid resin 24 is coated on the substrate 2 can be determined from the color difference. It's becoming

By applying the liquid resin 24 to the surface 3 of the wafer 1 and then curing the liquid resin 24 , the entire surface 3 of the wafer 1 can be covered with the resin film 11 obtained by curing the liquid resin 24 . The resin film 11 retains the colored tint even after being cured. In addition, the liquid resin 24 (resin film 11) varies in shade depending on the coating amount (thickness). For example, as the coating amount increases, the color becomes darker. In this configuration, a plurality of color densities and thicknesses of the resin film 11 are registered in advance, and the thickness of the resin film 11 can be estimated from the detected densities.

In the laser processing step, the wafer 1 having the resin film 11 formed on the entire surface 3 is irradiated with a laser beam from the surface 3 side along the planned division lines 6 , thereby removing the resin film 11 in the regions along the planned division lines 6 . This is the step of removing. In the laser processing step, as shown in FIG. 5, the back surface 4 side of the wafer 1 is held by suction on the chuck table 31 of the laser processing apparatus 30 via the adhesive tape 200, and the annular frame 201 is clamped by the clamper 32. FIG. In this state, an infrared camera (not shown) of the laser processing device 30 picks up an image of the wafer 1 through the resin film 11 to determine the position of the line 6 to be divided. While relatively moving along the line 6, the laser beam 33A is irradiated from the laser beam irradiation means 33 along the dividing line 6 (ablation processing).

In the laser processing step, for example, ablation processing is performed under the following processing conditions. As for the wavelength of the laser beam 33A, a wavelength that is absorptive to the wafer 1 and the liquid resin 24 (resin film 11) is adopted. This processing condition is an example and is not limited to this.
[Processing conditions]
Laser beam: YAG/YVO4
Wavelength: 355nm
Average output: 2W
Repetition frequency: 50kHz
Irradiation spot diameter: φ30 μm
Feeding speed of chuck table: 100mm/s

When the ablation process is performed under these processing conditions, the resin film 11 in the region corresponding to the dividing line 6 is removed to form a processed groove (dividing groove) 12, as shown in FIG. Thereby, a mask layer 10 for plasma etching is formed on the surface 3 of the wafer 1 . As shown in FIG. 7, the processed groove 12 is formed by removing the resin film 11 and the surface layer portion of the surface 3 of the substrate 2 (for example, a functional layer such as a low dielectric constant insulating film) to expose the surface 3 of the substrate 2. ing.

(Plasma processing step)
FIG. 8 is a cross-sectional view showing the configuration of an etching apparatus used in the plasma processing step. FIG. 9 is a cross-sectional view of the main portion of the wafer after the plasma processing step. In the plasma processing step ST3, the wafer 1 holding the adhesive tape 200 side by the chuck table 44 of the etching apparatus 40 shown in FIG. In this step, the substrate 2 is divided along the dividing line 6 by advancing toward the substrate 2 .

In the plasma processing step ST3, the wafer 1 supported by the annular frame 201 enters the chamber 43 through the opening 42 while the shutter 41 of the etching apparatus 40 shown in FIG. 8 is lowered to open the opening 42. Then, the surface 3 is electrostatically attracted to the chuck table 44 with the exposed surface facing upward in FIG. In this state, the opening 42 is closed by the shutter 41, and the inside of the chamber 43 is evacuated by the operation of the gas exhaust part 45. FIG.

Next, the etching gas supply means 46 is lowered to supply a fluorine-based stable gas as an etching gas from the gas supply part 47 to the gas flow hole 48, and the etching gas is ejected from the ejection part 49 on the lower surface of the etching gas supply means 46. . Then, a high frequency voltage is applied between the etching gas supply means 46 and the chuck table 44 from the high frequency power source 50 to turn the etching gas into plasma. Also, a bias voltage is applied to the wafer 1 to draw ions in the plasma to the surface 3 of the wafer 1 to etch the groove bottom of the processed groove 12 . As a result, as shown in FIG. 9, the groove bottom of the processed groove 12 is etched from the front surface 3 to the rear surface 4 by the thickness of the wafer 1, and the processed groove 12 reaches the adhesive tape 200. Then, as shown in FIG. Wafer 1 is divided into individual devices 5 by machined grooves 12 .

In Embodiment 1, a fluorine-based stable gas such as sulfur hexafluoride (SF6) or carbon tetrafluoride (CF4) is used as the etching gas. However, in addition to this, at least one fluorine-based stable gas among hexafluoroethane (C2F6), tetrafluoroethylene (C2F4), trifluoromethane (CHF3), and the like may be used. Also, as the etching apparatus, a so-called remote plasma type etching apparatus may be used in which an etching gas is turned into plasma outside the chamber and the plasmatized etching gas is supplied into the chamber.

(Mask layer detection step)
FIG. 10 is a side sectional view showing the mask layer detection step. The mask layer detection step ST4 is a step for determining the presence or absence of the mask layer 10 on the surface 3 of the wafer 1 based on whether or not the predetermined color is detected on the surface 3 of the wafer 1 . In the mask layer detection step ST4, as shown in FIG. 10, the back surface 4 side of the wafer 1 is placed on an inspection table 52 via an adhesive tape 200, and the mask layer 10 on the front surface 3 side of the wafer 1 is used for inspection. is imaged by the camera 51 of . This camera has an imaging element such as a CCD image sensor or a CMOS image sensor. The imaging target area may be an area covering the entire surface (devices 5) of the surface 3 of the wafer 1, or may be an area including a plurality of devices 5 at predetermined positions.

For example, when a predetermined color is detected in the entire region of one device 5 in the captured image, it is determined that the device 5 is covered with the mask layer 10 . On the other hand, when a color different from the predetermined color (the color of the device 5) is detected in at least part of the region of the one device 5, it is determined that part of the device 5 is not covered with the mask layer 10. be done. Specifically, the RGB values of the picked-up image (each pixel) of the region of one device 5 are acquired, and if all of these RGB values are within the range of a predetermined color, they are covered with the mask layer 10, and the image of the predetermined color is obtained. If there is something that exceeds the range, it is determined that at least a portion of it is not covered with the mask layer 10 . With this configuration, the presence or absence of the mask layer 10 can be simply determined based on whether or not a predetermined color is detected. It is possible to prevent a device etched (damaged) from being produced.

In addition to simply detecting a predetermined color, when using the mask layer 10 whose color becomes darker as the thickness increases, it is possible to detect a captured image and a registered image registered in advance in a storage device (not shown). The colors (RGB values) may be compared, and the thickness of the mask layer 10 corresponding to the captured image may be estimated from the registered image with the closest color. In this configuration, not only the presence or absence of the mask layer 10 but also the thickness of the mask layer 10 can be detected.

In the present embodiment, the detection of the predetermined color is performed based on the captured image captured by the camera 51. However, a light sensor (not shown) that receives the reflected light when the mask layer 10 is irradiated is used to detect the reflected light. The configuration may be such that the color or brightness of the mask layer is detected based on the light reflectance characteristics.

When it is determined in the mask layer detection step ST4 that the imaged device 5 is entirely covered with the mask layer 10, the process moves to the mask layer removal step ST5, and at least part of the imaged device 5 is covered with the mask layer 10. If it is determined that it is not covered with, discontinue the continuation of the subsequent work steps. As a result, the processing of the wafer 1 containing the device 5 that may have been erroneously etched is stopped, so that this type of device can be reliably prevented from being commercialized.

(Mask layer removal step)
FIG. 11 is a side sectional view showing the mask layer removal step. The mask layer removing step ST5 is a step of cleaning and removing the mask layer 10 . In the mask layer removing step ST5, the back surface of the wafer 1 (each device 5) is held by suction on the spinner table 61 of the cleaning device 60 shown in FIG. In this state, while rotating the spinner table 61 about its axis, the cleaning water 64 is supplied from the cleaning nozzle 63 toward the mask layer 10 on the surface 3 of the wafer 1 . At this time, the cleaning nozzle 63 reciprocates in the diameter direction of the wafer 1 . The supplied washing water 64 flows over the surface of each device 5 from the center side toward the outer circumference side due to the centrifugal force generated by the rotation of the spinner table 61, and the mask layer 10 covering the surface of each device 5 is formed. (including the pigment used for coloring) is dissolved, and the device 5 (chip) with its surface exposed remains. Pure water, for example, can be used as the cleaning water 64 . Finally, the remaining device 5 (chip) is picked up and finished.

[Embodiment 2]
The second embodiment differs from the first embodiment in the resin film coating step that precedes the mask layer coating step ST2. FIG. 12 is a side sectional view showing the resin film coating step of the wafer processing method according to the second embodiment. FIG. 13 is a cross-sectional view of the main part of the wafer after the laser processing step. The same reference numerals are assigned to the same configurations as in the first embodiment, and the description thereof is omitted.

In the second embodiment, the resin film coating step applies a plurality (two) of liquid resins of different colors to the entire surface 3 of the wafer 1 in layers to form a laminated resin film. Specifically, a predetermined first color (e.g., white) and a water-soluble pigment (carbon, pigment, ink, etc.) of a predetermined second color (e.g., gray) different from the first color are added to the above liquid resin. ) are mixed in, and a first liquid resin colored in a first color and a second liquid resin colored in a second color are prepared. These predetermined first and second colors are selected to be different from each other and different from the color of substrate 2 of wafer 1 (including devices 5).

As shown in FIG. 12, the back surface 4 side of the wafer 1 is held on the spinner table 21 via the adhesive tape 200 . In this state, while rotating the spinner table 21 about its axis, the first liquid resin is dropped onto the surface 3 (device 5) of the wafer 1 from the coating nozzle 23 . The dropped first liquid resin flows from the center to the outer circumference on the surface 3 of the wafer 1 due to the centrifugal force generated by the rotation of the spinner table 21, and is applied to the entire surface 3 of the wafer 1. to cover the device 5. By curing the first liquid resin, the entire surface 3 of the wafer 1 can be covered with the first resin film 11A obtained by curing the first liquid resin.

Next, while rotating the spinner table 21 about its axis, the second liquid resin 24B is dropped from the coating nozzle 23 onto the surface of the first resin film 11A. The dropped second liquid resin 24B flows on the surface of the first resin film 11A from the center side of the wafer 1 toward the outer circumference side due to the centrifugal force generated by the rotation of the spinner table 21. is applied to the entire surface of the resin film 11A. By curing the second liquid resin 24B, the first resin film 11A and the second resin film 11B can be laminated over the entire surface 3 of the wafer 1. FIG. The first resin film 11A and the second resin film 11B retain the tints of the first color and the second color even after being cured, and the first color and the second color are mixed. It does not discolor.

When the laser processing step is performed under the same processing conditions as in Embodiment 1, as shown in FIG. A groove (division groove) 12 is formed. As a result, a mask layer 10A for plasma etching, which is laminated in two layers, is formed on the surface 3 of the wafer 1. Next, as shown in FIG. In this embodiment, the mask layer 10A composed of the first resin film 11A and the second resin film 11B is formed, but three or more layers may be laminated as long as each resin film has a different color.

In the mask layer detection step ST4, for example, the color of the mask layer 10A in the area of one device 5 is detected based on the captured image, as in the first embodiment. Then, the number of layers of the mask layer 10A on the surface 3 of the wafer 1 is estimated from this detected color. Specifically, when the second color is detected, the mask layer 10A in the region of one device 5 is formed by laminating two layers of the first resin film 11A and the second resin film 11B. Presumed. On the other hand, when the first color is detected, it is estimated that the mask layer 10A in the area of one device 5 is a single layer of the first resin film 11A only.

If the estimated number of layers is less than the preset number, there is a possibility that the device 5 is not sufficiently protected, so continuation of the subsequent work steps is stopped. As a result, the processing of the wafer 1 containing the device 5 that may have been erroneously etched is stopped, so that this type of device can be reliably prevented from being commercialized. In the second embodiment, since the mask layer 10A is formed by laminating a plurality of resin films having different colors, the thickness of the mask layer 10A can be easily determined by whether or not the color of the uppermost resin film is detected. can. That is, when the second color is detected, the mask layer 10A is presumed to consist of at least two layers of the first resin film 11A and the second resin film 11B. It can be easily determined that the thickness is sufficient to protect the device 5 . With this configuration as well, the thickness of the mask layer 10A can be used as a guide when selecting the coating conditions for the mask layer 10A required in the plasma processing step ST3.

On the other hand, if the color of the lowermost resin film (first color) is detected, the thickness of the mask layer 10A is simply not sufficient to protect the device 5. I can judge. Therefore, after stopping the continuation of the work process, it is possible to confirm whether or not the plasma processing conditions and the resin film coating conditions are appropriate as an emergency situation.

The wafer processing method according to this embodiment is a method for processing a wafer 1 in which devices 5 are formed in a plurality of regions partitioned by grid-like division lines 6, and the devices 5 are covered with the division lines 6. After performing the mask layer coating step ST2 of coating the surface 3 of the wafer 1 with a mask layer 10 made of a resin film 11 of a predetermined color that exposes a region, and the mask layer coating step ST2, plasma is applied to the surface 3 side of the wafer 1. and a plasma processing step ST3 of supplying an etching gas in a state to etch the dividing lines 6 exposed from the mask layer 10, and after the plasma processing step, checking the presence or absence of the mask layer 10 on the surface 3 of the wafer 1. Since the mask layer detection step ST4 is further provided based on whether or not a predetermined color is detected on the surface 3 of the wafer 1, the mask layer 10 made of the liquid resin 24 of a predetermined color different from that of the wafer 1 is used. , it is possible to easily detect whether or not the mask layer 10 covers the device 5 during the plasma processing step ST3 based on the presence or absence of detection of a predetermined color. Therefore, in the plasma processing step ST3, it is possible to prevent the device 5 from being erroneously etched and damaged. Further, by detecting the predetermined color, it can be used as a guideline when selecting the mask layer 10 covering conditions such as the thickness of the mask layer 10 required in the plasma processing step ST3.

Further, according to this embodiment, in the mask layer coating step ST2, two or more mask layers 10A made of liquid resins having different colors are laminated, and in the mask layer detection step ST4, the surface 3 of the wafer 1 is detected from the detected color. The number of layers of the mask layer 10A on the side is estimated, and if the number of layers is less than the preset number, the continuation of the subsequent steps is stopped, so that the device 5 is erroneously etched and damaged. There is an effect that it can be prevented.

Further, according to this embodiment, in order to divide the substrate 2 along the dividing lines 6 in the plasma processing step ST3, the side surfaces of the divided devices 5 are the surfaces removed by plasma etching. For this reason, the wafer processing method has the effect that chipping due to cutting does not remain on the side surfaces of the individually divided devices 5, and devices 5 with high bending strength can be manufactured.

It should be noted that the present invention is not limited to the above embodiments. That is, various modifications can be made without departing from the gist of the present invention. For example, although the mask layer detection step ST4 is performed after the plasma processing step ST3 in the above embodiment, it may be performed before the plasma processing step ST3. When performing the mask layer detection step ST4 before the plasma processing step ST3, it is taken into consideration that the thickness of the mask layers 10 and 10A is reduced by the etching of the plasma processing. Then, the minimum thickness of the mask layers 10 and 10A, which takes into account this decrease, is defined in advance, and it is determined in the mask layer detection step ST4 whether or not the remaining thickness exceeds the minimum thickness.

REFERENCE SIGNS LIST 1 wafer 3 front surface 4 rear surface 5 device 6 planned division line 10, 10A mask layer 11 resin film 11A first resin film 11B second resin film 12 processing groove 24 liquid resin 30 laser processing device 40 etching device 51 camera 60 cleaning device 200 adhesive tape 201 annular frame

Claims (2)

A method for processing a wafer in which devices are formed in a plurality of regions partitioned by grid-like division lines,
a mask layer coating step of coating the surface of the wafer with a mask layer of a predetermined color that covers the devices and exposes the regions of the dividing lines;
a plasma processing step of supplying etching gas in a plasma state to the surface side of the wafer after performing the mask layer covering step to etch the lines to be divided exposed from the mask layer;
A wafer processing method further comprising , after the plasma processing step, a mask layer detection step of determining whether or not the mask layer exists on the surface of the wafer based on whether the predetermined color is detected on the surface of the wafer. . In the mask layer covering step, two or more mask layers having different colors are laminated, and in the mask layer detecting step, the number of mask layers on the surface of the wafer is estimated from the detected colors, and the number of layers is estimated. 2. The method of processing a wafer according to claim 1, wherein the continuation of subsequent steps is stopped when is less than a preset number.

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