JP7203542B2 - Machining system and method - Google Patents

Description

The present invention relates to a machining system and method for flattening the surface of a workpiece (surface to be machined).

In the field of semiconductor manufacturing, there is a polishing apparatus that applies a chemical mechanical polishing (CMP) technique for polishing the surface of a semiconductor wafer such as a silicon wafer (hereinafter referred to as a "wafer") as an object to be processed to a smooth surface. known (see, for example, Patent Document 1).

The polishing apparatus described in Patent Document 1 smoothes the surface of the wafer by rotating the wafer and platen against each other and pressing the wafer against a polishing pad on the platen while supplying slurry containing abrasive grains.

JP 2016-159385 A

However, since the polishing apparatus described in Patent Document 1 as described above processes the wafer surface uniformly over the entire surface, if the wafer surface before polishing is uneven, there is a risk that the unevenness of the wafer surface will remain as it is. was there.

Therefore, there arises a technical problem to be solved, that is, to process the surface of the workpiece (surface to be processed) flat with high accuracy. An object of the present invention is to solve this problem.

In order to achieve the above object, a processing system according to the present invention is a processing system for processing a surface of a wafer flat, comprising: a grinding device for grinding the surface of the wafer; and a polishing head attached to the polishing head. a CMP apparatus for polishing the entire surface of the wafer ground by the grinding apparatus by pressing the wafer rotating with the rotating polishing pad against the rotating polishing pad; and the wafer polished by the CMP apparatus through a hole penetrating the polishing pad. a measuring device for measuring the height of the surface of the wafer over the entire surface of the wafer, and extracting a region of the wafer where the height of the surface of the wafer is equal to or higher than a threshold value from the measurement result measured by the measuring device, and A controller for setting irradiation conditions according to the height of the surface of the wafer, and a trimming for trimming the region by irradiating the region with a gas cluster ion beam in which only gas cluster ions in the center are selected under the irradiation conditions. and a device.

According to this configuration, after the entire surface of the workpiece is polished by CMP, a relatively high region of the workpiece surface is irradiated with a gas cluster ion beam to locally trim the workpiece. By making the unevenness of the surface moderate, the surface of the workpiece can be processed flat with high efficiency and high accuracy as compared with the case where the surface of the workpiece is only uniformly polished by CMP. In addition, by measuring the height of the surface of the workpiece after polishing with a measuring device, it is possible to accurately detect a relatively high area on the surface of the workpiece. can be processed. Furthermore, by continuously performing grinding, CMP polishing, and trimming on a composite substrate or the like, the surface of the workpiece can be efficiently processed flat.

Moreover, in the processing system according to the present invention, it is preferable that the irradiation conditions include the type of gas, the amount of irradiation, and the irradiation time .

Further, in the processing system according to the present invention, the CMP device polishes the surface of the wafer ground by the grinding device to ⅓ of the thickness of the wafer, and the trimming device polishes the wafer in the region. It is preferable to trim several percent to twenty-odd percent of the thickness .

Further, in the processing system according to the present invention, it is preferable that the trimming device changes paths of gas cluster ions smaller than gas cluster ions in the central portion by a magnetic field.

Further, in order to achieve the above object, a processing method according to the present invention is a processing method for processing the surface of a wafer flat, wherein the surface of the wafer is ground, and a polishing head is attached to the polishing head to form a polishing apparatus. The entire surface of the ground wafer is polished by pressing the rotating wafer against the rotating polishing pad, and the height of the polished surface of the wafer is measured over the entire surface of the wafer through holes penetrating the polishing pad. and extracting a region where the height of the surface of the wafer is equal to or higher than a threshold value from the measurement results of the height of the surface of the wafer, setting irradiation conditions according to the height of the surface of the wafer in the region, The region is trimmed by irradiating the region with a gas cluster ion beam in which only gas cluster ions in the center are selected under the irradiation conditions.

According to this configuration, after the entire surface of the workpiece is polished by CMP, a relatively high region of the workpiece surface is irradiated with a gas cluster ion beam to locally trim the workpiece. By making the unevenness of the surface moderate, the surface of the workpiece can be processed flat with high efficiency and high accuracy as compared with the case where the surface of the workpiece is only uniformly polished by CMP. In addition, by measuring the height of the surface of the workpiece after polishing with a measuring device, it is possible to accurately detect a relatively high area on the surface of the workpiece. can be processed. Furthermore, by continuously performing grinding, CMP polishing, and trimming on a composite substrate or the like, the surface of the workpiece can be efficiently processed flat.

In the present invention, after the entire surface of the workpiece is polished by CMP, a relatively high region of the workpiece surface is irradiated with a gas cluster ion beam to locally trim the surface of the workpiece. By smoothing the unevenness, the surface of the workpiece can be processed flat with high efficiency and high accuracy.

1 is a schematic diagram showing the configuration of a processing system according to an embodiment of the present invention; FIG. The schematic diagram which shows the structure of a grinding apparatus. The perspective view which shows a CMP apparatus typically. FIG. 2 is a schematic diagram showing the configuration of a trimming device; The schematic diagram which shows the procedure which processes a composite substrate. An AFM image of the wafer surface before trimming. An AFM image of the wafer surface after trimming.

An embodiment of the present invention will be described based on the drawings. In addition, hereinafter, when referring to the number, numerical value, amount, range, etc. of the constituent elements, unless otherwise specified or clearly limited to a specific number in principle, it is limited to the specific number It does not matter if the number is greater than or less than a certain number.

In addition, when referring to the shape or positional relationship of components, etc., unless otherwise specified or in principle clearly considered otherwise, etc. include.

In addition, the drawings may exaggerate characteristic parts by enlarging them in order to make the characteristics easier to understand. In addition, in cross-sectional views, hatching of some components may be omitted in order to facilitate understanding of the cross-sectional structure of the components.

FIG. 1 is a schematic diagram showing the basic configuration of a processing system 1. As shown in FIG. The processing system 1 is for processing the surface of a workpiece (surface to be processed), specifically processing a wafer to be thin and flat, or processing an oxide film or the like formed on the wafer surface to be flat. It is.

In the following, a composite substrate (hereinafter simply referred to as "wafer W") in which a supporting substrate (base layer) such as single crystal, polycrystalline ceramic or amorphous is bonded to a functional layer such as a semiconductor crystal or piezoelectric crystal as a work piece. will be described as an example, but the workpiece is not limited to this, and may be, for example, a single-layer substrate.

The processing system 1 performs grinding processing, trimming processing and polishing processing of the wafer W continuously. The processing system 1 includes a grinding device 10 , a CMP device 20 , a trimming device 30 and a control device 40 .

The processing system 1 also includes a transfer device (not shown) that transfers the wafer W between the grinding device 10 , the CMP device 20 and the trimming device 30 . The processing system 1 may be configured by housing various devices in a single housing, or may be configured by interconnecting devices each housed in a housing one by one. Absent.

FIG. 2 is a schematic diagram showing the configuration of the grinding device 10. As shown in FIG. The grinding apparatus 10 includes an index table 11 and a wafer chuck 12 arranged on the index table 11 to hold the back surface of the wafer W by suction.

The wafer chuck 12 has an adsorbent (not shown) made of a porous material such as alumina embedded in its upper surface. Wafer chuck 12 has a conduit (not shown) that extends through the interior to the surface. The pipeline is connected to a vacuum source, a compressed air source, or a water supply source via a rotary joint (not shown). When the vacuum source is activated, the wafer W placed on the wafer chuck 12 is held by the wafer chuck 12 by suction. Further, when the compressed air source or the water supply source is activated, the adsorption between the wafer W and the wafer chuck 12 is released.

A wafer chuck 12 is provided on the index table 11 via an air bearing 13 . The wafer chuck 12 is connected to a rotary joint (not shown) through the rotor of the air bearing 13, and the wafer chuck 12 is rotatable around the rotation axis a1.

The grinding device 10 also includes a grinding wheel 14 , a spindle 15 and a spindle feed mechanism 16 . For the grinding wheel 14, for example, a cup-shaped grindstone is used. A grinding wheel 14 is attached to the lower end of the spindle 15 . The spindle 15 supports the grinding wheel 14 so as to be rotatable around the rotation axis a2. The spindle feed mechanism 16 is configured to move the spindle 15 up and down in the vertical direction (vertical direction on the paper surface of FIG. 2). The spindle feed mechanism 16 includes two linear guides 16a that connect the spindle 15 and a column (not shown), and a known ball screw slider mechanism (not shown) that vertically moves the spindle 15 up and down.

FIG. 3 is a perspective view showing the configuration of the CMP apparatus 20. As shown in FIG. The CMP apparatus 20 processes the entire surface of the wafer W flat. The CMP apparatus 20 has a platen 21 , a polishing pad 22 and a polishing head 23 .

The platen 21 is disc-shaped and connected to a rotating shaft 24 arranged below the platen 21 . As the rotating shaft 24 is driven by the motor 25 to rotate, the platen 21 rotates in the direction of arrow D1 in FIG.

A polishing pad 22 is attached to the upper surface of the platen 21 . The polishing pad 22 is made of, for example, urethane, but is not limited to this. It should be noted that the polishing pad 22 is not limited to the one that is formed in a circular shape as shown in FIG. 3 and that rotates around the rotation axis at the center of the polishing pad 22. For example, the polishing pad 22 is formed in the shape of an endless belt that moves linearly. It doesn't matter if it is.

Slurry, which is a mixture of abrasives and chemicals, is supplied onto the polishing pad 22 from a nozzle (not shown). The slurry spreads on the polishing pad 22 as the platen 21 rotates and is supplied to the contact area between the wafer W and the polishing pad 22 . The slurry is, for example, one containing an oxidizing agent and an abrasive, silica slurry, or the like. Examples of the oxidizing agent include ceria slurry, alumina slurry and the like, but are not limited thereto. Also, a wetting agent that makes the surface of the wafer W hydrophilic may be added to the slurry.

The polishing head 23 is shaped like a disc with a smaller diameter than the platen 21 and is connected to a rotating shaft 26 arranged above the polishing head 23 . The polishing head 23 rotates in the direction of arrow D2 in FIG. 3 by rotating the rotary shaft 26 driven by a motor (not shown). The polishing head 23 can be vertically moved up and down by a lifting device (not shown). The polishing head 23 descends to press the wafer W against the polishing pad 22 when polishing the wafer W. As shown in FIG.

The CMP apparatus 20 includes a height sensor 27 that measures the thickness (height) of the functional layer within the wafer W. As shown in FIG. The height sensor 27 is, for example, a laser interferometer using laser light, but is not limited to this. The height sensor 27 is arranged below the platen 21 . The height sensor 27 projects a laser beam onto the surface of the wafer W through a transparent window 29 mounted in a hole 28 vertically penetrating the platen 21 and the polishing pad 22, and detects the light reflected by the wafer W. By receiving light, the thickness of the functional layer is measured.

FIG. 4 is a schematic diagram showing the configuration of the trimming device 30. As shown in FIG. The trimming device 30 locally irradiates the surface of the wafer W after grinding with a gas cluster ion beam (GCIB) to process the irradiated region of the wafer W flat.

Specifically describing the configuration of the trimming device 30, the trimming device 30 is mainly configured by connecting a source chamber 31A, an ion chamber 31B, and a process chamber 31C. decompressed.

A nozzle 33 made of glass is installed in the source chamber 31A, and when high-pressure gas is injected from the nozzle 33 into a vacuum, the molecules are cooled by rapid adiabatic expansion to generate gas clusters consisting of a large number of molecules. . The gas is, for example, nitrogen trifluoride, oxygen, nitrogen, argon, or the like, and can be arbitrarily selected depending on the type of wafer.

The gas cluster moves toward a skimmer 34 with a small hole diameter that is provided between the source chamber 31A and the ion chamber 31B perpendicularly to the traveling direction of the gas cluster (the direction of the arrow in FIG. 4). The skimmer 34 separates the central cluster and the peripheral monomer so that only the cluster enters the ion chamber 31B.

In the ion chamber 31B, an ionizer 35, an accelerator 36, an aperture plate 37, and an electrostatic lens 38 are provided in this order along the traveling direction of the clusters.

The ionizer 35 applies and accelerates thermal electrons emitted from a filament (not shown) to cause the thermal electrons to collide with the gas clusters, thereby ionizing the gas clusters.

The accelerator 36 applies and accelerates the ionized gas cluster ions.

The aperture plate 37 selects only central gas-cluster ions out of the gas-cluster ions, and the electrostatic lens 38 changes the course of relatively small gas-cluster ions by the magnetic field. As a result, the cluster size of the gas cluster ions is selected, and the GCIB is converged to irradiate the wafer W through the aperture hole 39 . Reference symbol S denotes a stage that holds the wafer W. FIG. The stage S is configured such that the wafer W can be moved relative to the irradiation position of the GCIB.

The processing system 1 is controlled in operation by a control device 40 . The control device 40 controls each of the components that make up the machining system 1 . The control device 40 is composed of, for example, a CPU, a memory, and the like. The functions of the control device 40 may be realized by controlling using software, or may be realized by operating using hardware.

Next, a procedure for planarizing the functional layer of the wafer W using the processing system 1 will be described with reference to FIG.

[Grinding process]
After the wafer W is sucked and held by the wafer chuck 12, the grinding wheel 14 is brought close to the wafer W. As shown in FIG. Next, the grinding wheel 14 is pressed against the surface of the wafer W while rotating the wafer chuck 12 and the grinding wheel 14 .

The grinding conditions of the grinding apparatus 10 are, for example, the rotation speed of the wafer chuck 12 is 300 rpm, the grinding wheel 14 is #6000, the spindle 15 is 2000 rpm, and the spindle feed mechanism 16 is 0.4 μm/s. be.

The grinding device 10 grinds the wafer W to a desired thickness (for example, 6 μm), as shown in FIG. 5(a). The grinding process may be performed using only a single grinding apparatus, or may be performed stepwise by preparing a plurality of grinding apparatuses having different processing conditions.

[CMP process]
After the wafer W is attached to the lower end of the polishing head 23 so that the surface of the wafer W faces the polishing pad 22 , the polishing head 23 is brought closer to the polishing pad 22 . Next, as shown in FIG. 5B, the polishing head 23 presses the wafer W against the polishing pad 22 while rotating the platen 21 and the polishing head 23 respectively. In addition, in FIG. 5B, the polishing pad 22, the polishing head 23, and the wafer W are shown upside down for convenience of explanation.

The polishing conditions of the CMP apparatus 20 are, for example, the rotation speed of the platen 21 is 80 rpm, the rotation speed of the polishing head 23 is 80 rpm, the pressure acting on the wafer W is 3 psi, and the polishing time is 60 sec.

The CMP apparatus 20 polishes the entire surface of the wafer W uniformly. The amount of polishing by the polishing pad 22 is set to about 2 μm from the surface of the wafer W, for example.

When the grinding by the grinding apparatus 10 is finished, as shown in FIG. 5C, the height sensor 27 detects the wafer W every time the window 29 of the platen 21 passes below the wafer W during the rinsing process after CMP polishing. The thickness of the functional layer is measured over the entire surface of W, and the height of fine irregularities on the surface of the wafer W after polishing is measured. The measurement point of the height sensor 27 can be arbitrarily set on the surface of the wafer W by rotating the polishing head 23 while moving horizontally with respect to the platen 21 . In addition, in FIG. 5C, the height sensor 27 and the wafer W are shown upside down for convenience of explanation.

The control device 40 generates a profile indicating the shape of the surface of the wafer W based on the coordinates and height of the measurement points measured by the height sensor 27 .

[Trimming process]
Based on the profile, the control device 40 extracts, as a trimming target region, a region including measurement points whose surface height is equal to or higher than a predetermined threshold, and irradiates the trimming target region with the GCIB. Set the irradiation conditions to be used.

The height threshold value of the surface of the wafer W to be trimmed can be arbitrarily changed, but for example, it can be set to several hundred nanometers with respect to the target height before CMP polishing.

The irradiation conditions of GCIB include the type of gas, irradiation amount, irradiation time, etc., and depending on the desired trimming amount (for example, several hundred nm), etc., a combination of irradiation conditions stored in advance in the control device 40 is called. .

After the wafer W is held on the stage S, the stage S moves the wafer W relative to the GCIB irradiation position so that the GCIB irradiation range includes the trimming target region.

After that, as shown in FIG. 5D , the trimming device 30 irradiates the surface of the wafer W with GCIB based on the irradiation conditions called from the control device 40 . The gas cluster ions with which the surface of the wafer W is irradiated sputter atoms on the surface of the wafer W, thereby flattening the surface of the wafer W as shown in FIG. 5(e).

In GCIB, since the energy per atom of cluster ion is inversely proportional to the number of atoms forming the cluster, damage to the surface of the wafer W can be reduced compared to monomer ions. Note that when a plurality of trimming regions are extracted, the trimming by the trimming device 30 is performed on each region.

Here, an example of trimming by GCIB is shown. FIGS. 6(a)-(d) are AFM images showing four irradiation spots on the wafer surface before GCIB irradiation on a sample wafer (8-inch Si wafer). FIGS. 7(a)-(d) are AFM images showing four irradiation spots on the wafer surface after GCIB irradiation on a sample wafer. The irradiation points 1 to 4 were set at four points spaced apart from each other at equal intervals on concentric circles around the center of the wafer. Also, the sample wafers were previously ground using a grinding wheel 14 of #6000.

Table 1 shows the GCIB irradiation conditions when the sample wafer is trimmed by the trimming device 30 .

Table 2 shows the surface roughness Ra in the AFM image before GCIB irradiation and the surface roughness Ra in the AFM image after GCIB irradiation at four irradiation points.

According to Table 2, it can be seen that the surface roughness Ra is lowered at all the irradiation points 1 to 4, and the wafer surface is flattened.

In this manner, the above-described processing system 1 polishes the entire surface of the wafer W by CMP, and then locally trims the trimming target region of the surface of the wafer W whose height is equal to or greater than a predetermined threshold using GCIB. By smoothing the unevenness of the surface of the wafer W, the surface of the wafer W can be processed flat with high efficiency and high accuracy.

It should be noted that the present invention can be modified in various ways without departing from the spirit of the present invention, and it is a matter of course that the present invention extends to the modified ones.

In the above-described embodiment, the case where the wafer is processed to be thin and flat through the grinding process, the CMP process, and the trimming process has been described as an example. be.

Reference Signs List 1 ... Machining system 10 ... Grinding device 11 ... Index table 12 ... Wafer chuck 13 ... Air bearing 14 ... Grinding wheel 15 ... Spindle 16 ... Spindle feeding mechanism 20 CMP device 21 Platen 22 Polishing pad 23 Polishing head 24 Rotary shaft 25 Motor 26 Rotary shaft 27 Height sensor 28 Hole 29 ... window 30 ... trimming device 31A, 31B, 31C ... source chamber 32 ... turbomolecular pump 33 ... nozzle 34 ... skimmer 35 ... ionizer 36 ... accelerator 37 Aperture plate 38 Electrostatic lens 39 Aperture hole 40 Controller S Stage W Wafer

Claims (5)

A processing system for processing a flat surface of a wafer,
a grinding device for grinding the surface of the wafer;
a CMP device that polishes the entire surface of the wafer ground by the grinding device by pressing the wafer attached to a polishing head and rotating together with the polishing head against a rotating polishing pad ;
a measuring device for measuring the height of the surface of the wafer polished by the CMP device over the entire surface of the wafer through a hole penetrating the polishing pad ;
a control device that extracts a region of the wafer whose surface height is equal to or higher than a threshold value from the measurement result obtained by the measurement device, and sets irradiation conditions according to the height of the wafer surface of the region;
a trimming device for irradiating the region under the irradiation conditions with a gas cluster ion beam in which only central gas cluster ions are selected to trim the region;
A processing system comprising: 2. The processing system according to claim 1, wherein said irradiation conditions include a type of gas, an irradiation amount and an irradiation time. The CMP device polishes the surface of the wafer ground by the grinding device to 1/3 of the thickness of the wafer,
3. The processing system according to claim 1, wherein said trimming device trims several percent to twenty-odd percent of the thickness of said wafer in said region. 4. The processing system according to claim 3, wherein the trimming device changes paths of gas cluster ions smaller than gas cluster ions at the central portion by a magnetic field. A processing method for flattening the surface of a wafer, comprising:
grinding the surface of the wafer;
polishing the entire surface of the ground wafer by pressing the wafer attached to a polishing head and rotating with the polishing head against a rotating polishing pad ;
measuring the height of the surface of the wafer polished through holes penetrating the polishing pad over the entire surface of the wafer;
Extracting a region where the height of the surface of the wafer is a threshold value or more from the measurement result of the surface height of the wafer,
setting irradiation conditions according to the height of the surface of the wafer in the region;
A processing method comprising: irradiating said region with a gas cluster ion beam in which only central gas cluster ions are selected under said irradiation conditions to trim said region.

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