JP5040385B2 - Polishing method - Google Patents

Description

  The present invention relates to a polishing apparatus and method for polishing a sample to form a thin film, and is suitably applied to a case where a part of a semiconductor chip on which a fine device is formed is used as a sample.

  Conventionally, for example, AFM (Atomic Force Microscope), TEM (Transmission Electron Microscope), SIMS (Secondary Ion Mass) are used to accurately evaluate electrical characteristics and element distribution of semiconductor devices. A physical analysis technique such as Spectrometry (secondary ion mass spectrometry) is used. In order to perform such a physical analysis technique and perform an accurate analysis, it is necessary to thin a semiconductor chip or the like as a sample into an extremely thin state.

  Usually, in order to produce the thin film sample as described above, a polishing apparatus that polishes the sample surface to form a thin film is used. This polishing apparatus includes a polishing unit including a polishing plate for polishing a sample, and a sample holding unit that holds the sample fixedly and brings the sample into contact with the polishing surface of the polishing plate. At the time of polishing, for example, the back surface of a semiconductor chip as a sample is brought into contact with the surface of a rotating polishing plate, and the target position is exposed while leaving the device structure of the semiconductor chip. In this case, it is necessary to reduce the thickness of the entire sample to about 1 μm or less. As described above, when a semiconductor chip having a size on the order of millimeters is cut to a thickness of about 1 μm or less, extremely high flatness is required on the surface of the sample that has been polished.

JP-A-9-189649 JP 2006-84484 A

  However, the conventional polishing apparatus employs a configuration in which both the polishing unit and the sample holding unit rotate during polishing and the sample supported by the sample holding unit is polished relative to the polishing unit. Polishing direction, contact angle and polishing rate are not always constant. For this reason, polishing marks and stress unevenness are likely to occur on the polished surface of the sample. In particular, a sample made of a brittle material such as silicon is easily cleaved, resulting in cracks. Moreover, even if a thinned sample is obtained, a polishing flaw occurs on the polished surface of the sample, and sufficient surface flatness cannot be obtained. There is a problem of becoming.

The present invention has been made in view of the above problems, suppresses the occurrence of polishing marks and stress unevenness on the polished surface of the sample, and can provide sufficient flatness over an extremely wide range of the sample surface for analysis evaluation. It is an object of the present invention to provide a polishing method that can realize a large enlargement of such a region and obtain a highly reliable thin film sample.

  The polishing method of the present invention is a polishing method for polishing a sample to form a thin film, wherein the sample stage is fixed and is movable within a polishing surface for polishing the sample. The sample is polished and thinned in a state where the position is fixed at a predetermined portion of the sample and the polishing direction at an arbitrary contact point with the polishing surface of the sample is kept constant.

  According to the present invention, the generation of polishing marks and stress unevenness on the polished surface of the sample is suppressed, and sufficient flatness is obtained over a very wide range of the sample surface, thereby realizing a large enlargement of the area that can be analyzed and evaluated. A highly reliable thin film sample can be obtained.

-Basic outline of the present invention-
The present inventor uses a polishing unit having a polishing surface for polishing a sample, and a sample holding unit for bringing the sample into contact with the polishing surface. However, the present inventors have found that this is due to the difference in speed between the polishing speed in the polishing surface and the sample stage on which the sample is fixed, and the variation in the friction force caused by local irregularities on the polishing surface on the sample surface. Furthermore, since the sample holder moves randomly relative to the polishing surface during polishing, the polishing direction may be parallel to the cleaved surface of the sample (including momentary cases). At this time, the sample is cleaved. And found that cracking occurs.

  In the present invention, based on the above consideration, the sample holder is provided with a sample stage installation mechanism that allows the sample stage to move with respect to the polishing surface and fixes the sample stage at an arbitrary position within the polishing surface. In this case, at the time of polishing, the polishing direction of the polishing part (in the case where the polishing part is a rotationally driven polishing plate, the rotational tangent direction at the contact point with the polishing surface of the sample), the contact angle with respect to the polishing direction, and the polishing rate are Always kept constant. In this configuration, the polishing direction and the contact angle on the polishing surface of the sample, the polishing angle, and the polishing rate are appropriately adjusted to suppress the occurrence of polishing marks and stress unevenness on the polishing surface of the sample. Accordingly, sufficient flatness can be obtained in a very wide range of the sample surface, and the region where analysis and evaluation can be performed can be greatly enlarged, and a highly reliable thin sample can be obtained.

  In order to adjust the contact angle as appropriate, an angle adjusting mechanism for adjusting the installation angle with respect to the polishing direction in the polishing surface of the sample fixed to the sample table may be added to the sample holding unit. In this case, it is preferable that the angle adjusting mechanism is provided with an angle scale adjacent to the sample stage so that the installation angle is visible. With this angle adjustment mechanism, the operator can easily and accurately set the contact angle to an arbitrary value, and reliably prevent the occurrence of cleaving of the sample. When the sample is made of a brittle material such as silicon, cleavage easily occurs, resulting in cracking. However, the adjustment of the contact angle eliminates the concern of the sample cracker.

  Patent Document 1 discloses a technique in which a dummy sample is attached around a sample and the polishing angle is adjusted based on the difference in thickness between the two. Patent Document 2 discloses a technique for processing a minute sample piece into a planar shape using an energy beam. However, in the former technique, it is necessary to provide a dummy sample in addition to the sample in order to polish the sample. Therefore, it is an invention different from the present invention, and it takes undue effort and inevitably complicates the sample configuration. Further, the latter technique is an invention different from the present invention in which an energy beam is used for flattening the sample surface, and can be said to adopt a detour structure as compared with the present invention.

-Preferred embodiment to which the present invention is applied-
DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments to which the present invention is applied will be described in detail with reference to the drawings.

(Configuration of polishing equipment)
FIG. 1 is a perspective view showing a schematic configuration of the polishing apparatus according to the present embodiment together with its operation. FIG. 2 is a plan view showing a schematic configuration of a sample holder which is a component of the polishing apparatus. In addition, about the sample stand installation mechanism 12 which is a structural member of the sample holding part 2, illustration is abbreviate | omitted in FIG. 1 for convenience.
As shown in FIG. 1 (a), this polishing apparatus includes a polishing unit 1 having a polishing plate for polishing a sample 10, and a sample holding unit 2 for bringing the sample 10 into contact with the polishing surface 1a of the polishing plate. It is prepared for.

The polishing unit 1 has a polishing plate that is a disk-shaped plate member, and is rotated by bringing the sample 10 into contact with the polishing surface 1a of the polishing plate (for example, the rotation of the polishing surface 1a in FIG. 1). The direction is indicated by an arrow A1), whereby the sample 10 is thinned to a desired thickness. In addition, as a grinding | polishing part, it replaces with a disk-shaped thing, for example, it may be set as the rectangular plate-shaped member, and this may be rock | fluctuated in a predetermined direction and the sample 10 may be grind | polished.
As the sample 10, a semiconductor chip or the like is mainly assumed. Silicon, which is a main material constituting the semiconductor chip, is a relatively brittle material and is likely to be cleaved.

  The sample holder 2 includes a sample table 11 on which the sample 10 is fixed, a sample table setting mechanism that allows the sample table 11 to move with respect to the polishing surface 1a, and fixes the sample table 11 at an arbitrary position within the polishing surface 1a. 12, an angle adjusting mechanism 13 for adjusting the installation angle of the sample 10 fixed to the sample table 11 in the polishing surface 1 a with respect to the polishing direction, and a horizontal level for adjusting the sample table 11 so as to be horizontal with respect to the polishing surface 1 a. And an adjustment mechanism 14. Here, the sample stage 11, the angle adjustment mechanism 13, and the horizontal adjustment mechanism 14 are provided in the main body 2 a of the sample holder 2.

For example, as shown in FIG. 2, the sample stage setting mechanism 12 translates the chucking member 12a for gripping the main body 2a and the chucking member 12a freely in a plane, and fixes the chucking member 12a at a predetermined position. And an arm member 12b.
During polishing, the main body 2a is gripped from the side by the chucking member 12a, and the main body 2a is translated by the arm member 12b within the polishing surface 1a of the polishing unit 1 (in the radial direction of the polishing surface 1a as an example in FIG. 1). Is indicated by an arrow A2) and fixed at a predetermined position on the polishing surface 1a.

  By fixing the polishing direction with respect to the polishing surface 1a of the sample 10, the polishing speed or torque at the contact portion (contact point) with the polishing surface 1a of the sample 10 becomes constant. Further, since the contact angle between the polishing surface 1a and the sample 10 is constant, the frictional force accompanying the polishing is constant on the surface of the sample 10. Therefore, the occurrence of polishing marks and stress unevenness on the surface of the sample 10 is suppressed, sufficient flatness is obtained in a very wide range of the surface of the sample 10, and the area capable of analysis and evaluation is greatly enlarged. A highly reliable thinned sample can be obtained. In this embodiment, for example, the sample 10 can be processed and polished flat while preventing cracking until the 1 mm square sample 10 has a thickness of 1 μm or less.

  The sample stage 11 is a rod-shaped member and is configured such that the sample 10 is installed at the tip portion. As shown in FIG. 1 (b), a grid 11a for attaching one side of the sample 10 together is formed at the tip portion. Further, a notch 11b serving as an installation marker corresponding to the grid 11a is formed on the side surface of the sample stage 11.

The angle adjusting mechanism 13 is provided adjacent to the sample stage 11 and has an angle scale 13a that allows the installation angle with respect to the polishing direction to be visible. The sample stage 11 is appropriately rotated with respect to the angle scale 13a. By moving it, the installation angle can be set to a desired value.
At the time of polishing, the sample 10 is stuck so that one side thereof is appropriately overlapped with the grid 11a, and the notch 11b is adjusted to the reference position (0 °) of the installation angle on the angle scale 13a. In this state, the installation angle may be set to a desired value.

  The angle adjustment in the angle adjustment mechanism 13 may be performed manually by the operator. However, in order to accurately adjust the minute angle, for example, as shown in FIG. It is also preferable that an automatic adjustment mechanism 21 is connected, the sample stage 11 is appropriately rotated by the automatic adjustment mechanism 21, and the installation angle is set to a desired value. Further, instead of providing the angle scale 13a (or in addition to the angle scale 13a), for example, a monitor 22 is connected to the automatic adjustment mechanism 22, and the monitor 22 instructs the automatic adjustment mechanism 21 to specify a desired value of the installation angle. You may comprise so that the installation angle of the sample stand 11 may be set by the drive of the adjustment mechanism 21. FIG.

  The horizontal adjustment mechanism 14 includes a pair of support bars 14a and 14b that support and adjust the sample table 11 with respect to the polishing surface 1a, and a micrometer 14c that adjusts the height of each support bar 14a and 14b from the polishing surface 1a. It is prepared for. By appropriately adjusting the heights of the support rods 14a and 14b with the micrometer 14c, the contact state of the sample 10 fixed to the sample table 11 with the polishing surface 1a is controlled.

  In the present embodiment, when the sample 10 is made of a material that is relatively brittle and easily cleaved, such as a semiconductor chip, the angle adjusting mechanism 13 cleaves the sample 10 with respect to the polishing direction when the sample 10 is polished. Set the surface to be inclined. In this state, the sample 10 is fixedly held on the polishing surface 1a by the sample stage setting mechanism 12, and polishing is started.

  As shown in FIG. 4A, when the installation angle is 0 °, the polishing direction and the cleavage surface of the sample 10 are parallel to each other, and the sample 10 is likely to be cleaved. This is because when the sample 10 is polished while being movable with respect to the polishing surface 1a as in the prior art, the sample 10 is randomly moved on the polishing surface 1a, so that the polishing direction is the cleavage plane of the sample 10. Corresponds to the case of being parallel to (perpendicular to one side 10a of the sample 10).

On the other hand, when the sample 10 is fixedly held with respect to the polishing surface 1a with the cleavage surface of the sample 10 inclined with respect to the polishing direction and polished, the polishing direction and the cleavage surface of the sample 10 are not parallel. Thus, the sample 10 is less likely to be cleaved.
As shown in FIG. 4B, specifically, in the present embodiment, the angle adjusting mechanism 13 sets the installation angle (the vertical state with respect to the polishing direction of the one side 10a of the sample 10 is 0 °) from 10 ° to 45 °. Set the value within the following range. By polishing the sample 10 by adjusting the installation angle as described above, the sample 10 can be thinned to 1 μm or less without causing cracking to a thickness of about several μm even in the case of the brittle material 10.

  As shown in FIG. 5A, for example, in order to prevent cleavage of the (110) plane of silicon, the sample 10 may be tilted by about 7 ° or more from the reference position (the position of the cleavage plane (0 °)). I know from experience. This direction is a random direction close to the (110) direction in crystallographic terms. If a margin is added in consideration of the accuracy of attaching the sample 10 to the sample stage 11, the lower limit value of the installation angle that can prevent the sample 10 from being cleaved during polishing is recognized to be about 10 °. In the above description, the cleaving of the (110) plane of silicon has been described as an example, but the same argument holds for other materials and other crystal planes.

  On the other hand, as shown in the left diagram of FIG. 5B, the upper limit of the installation angle that can prevent the cleavage of the sample 10 during the polishing process is about 45 °. This is a value obtained from symmetry in the crystal of the sample 10, that is, when the installation angle is set to a value larger than 45 ° (60 ° in the illustrated example) as shown in the right diagram of FIG. 5B. This is because the other angle of the installation angle with respect to the cleavage plane is less than 45 ° (30 ° in the illustrated example).

(Polishing method)
Hereinafter, a method for polishing the sample 10 using the above-described polishing apparatus will be described.
FIG. 6 is a flowchart showing the polishing method according to the present embodiment in the order of steps. FIG. 7 is a schematic view showing a state of polishing in the polishing method according to the present embodiment.

  First, as shown in FIG. 7A, the sample piece 3 is cut out to a size of about 1 mm square, for example, from the semiconductor substrate 30 on which the plurality of element patterns 20 are formed. And the sample piece 3 is affixed on the glass plate 39 using the predetermined | prescribed adhesive agent 38, and the sample 10 is produced. When the sample 10 is manufactured, the surface to be attached to the glass plate 39 differs depending on whether the polishing is front surface polishing or back surface polishing. FIG. 7B shows a case where surface polishing is performed, and FIG. 7C shows a case where rear surface polishing is performed. In the former case, the back surface of the sample 10 is the pasting surface, and in the latter case, the surface of the sample 10 is the pasting surface.

  In the sample 10, for example, a MOS transistor is formed as the element pattern 20. In this MOS transistor, an active region is defined by the STI element isolation structure 31, and a gate electrode 33 through a gate insulating film 32 and source / drain regions 34 are formed on both sides of the active region so as to cover them. An interlayer insulating film 35a is formed on the gate insulating film 35a. A wiring 37 electrically connected to the source / drain region 34 is formed through a contact hole 36 formed in the interlayer insulating film 35a. An interlayer insulating film 35b covering the wiring 37 is formed. It is formed and is roughly configured.

The glass plate 39 of the sample 10 produced as described above is attached to the grid 11a of the sample table 11 and attached using, for example, wax (step S1).
Subsequently, the sample table 11 to which the sample 10 is attached is placed on the main body 2a of the sample holding unit 2 (step S2).
Subsequently, the sample holder 2 on which the sample table 11 is installed is installed on the sample table installation mechanism 12, and the sample holder 2 is brought into contact with the polishing surface 1a of the polishing unit 1 and fixedly held (step S3).

Subsequently, the polishing section 1 drives the polishing plate to perform trial polishing of the sample 10 (step S4).
Subsequently, based on the result of the trial polishing, the polishing mark generated on the surface of the sample 10 is observed using, for example, an optical microscope or a scanning electron microscope (SEM), and the direction of the polishing mark (polishing direction) and the cleavage direction are determined. Is measured (step S5).

Subsequently, as a result of measuring the angle difference between the polishing direction and the cleavage direction in step S5, it is determined whether or not the angle difference is, for example, not less than 10 ° and not more than 45 ° (step S6).
In step S6, if it is determined that the angle difference is, for example, 10 ° or more and 45 ° or less, the installation angle of the sample 10 is within the specified range, and it is recognized that the sample 10 is not easily cleaved. Proceed to step S8.

  On the other hand, if it is determined in step S6 that the angle difference is smaller than, for example, 10 ° (or larger than 45 °), the installation angle of the sample 10 is out of the specified range, and the sample 10 is cleaved. Since it is recognized that the state is easy, the angle adjustment mechanism 13 rotates and adjusts the sample stage 11 so that the installation angle of the sample 10 becomes a desired value within a specified value (step S7). Then, trial polishing in step S4 is performed again.

Subsequently, in the sample 10 in which the installation angle is determined to be the specified value, the level adjustment mechanism 14 adjusts the contact state with the polishing surface 1a of the polishing unit 1, that is, the level (step S8).
Subsequently, the polishing plate 1 is rotationally driven by the polishing unit 1 using a polishing liquid and a polishing plate for rough finishing, and the sample 10 is roughly polished (step S9). In this rough polishing process, if necessary, the rough polishing process is performed while finely adjusting the level of the sample 10 by the leveling mechanism 14.

Subsequently, the thickness of the sample 10 subjected to the rough polishing in step S9 is measured, and it is determined whether or not the thickness is, for example, 10 μm or less (step S10).
If it is determined in step S10 that the thickness is 10 μm or less, it is recognized that the level of the sample 10 with respect to the polished surface 1a is within an allowable range, and thus the process proceeds to step S11.
On the other hand, if it is determined in step S10 that the thickness is larger than 10 μm, it is recognized that the level of the sample 10 with respect to the polishing surface 1a is not within the allowable range and is insufficient, and therefore the sample 10 is again in step S8. Adjust the level.

  Subsequently, when it is recognized that the level of the sample 10 is within the allowable range, the polishing plate is rotated by the polishing unit 1 using a polishing liquid and a polishing plate for precision finishing, and the sample 10 is precisely polished. Is performed (step S11). During the precision polishing process, if necessary, the leveling mechanism 14 performs the precision polishing process while finely adjusting the level of the sample 10.

  Subsequently, the thickness of the sample 10 subjected to precision polishing in step S11 is measured, and whether the thickness is, for example, 1 μm or less, or whether an object (for example, part of the wiring 37) is exposed from the surface of the sample 1 It is determined whether or not (step S12).

If it is determined in step S12 that the thickness is 1 μm or less or the object is exposed from the surface of the sample 1, the polishing result of the sample 10 is recognized as good, and the polishing process is terminated.
On the other hand, if it is determined in step S12 that the thickness is greater than 1 μm, or the object is not yet exposed from the surface of the sample 1, it is recognized that the polishing result of the sample 10 is insufficient. The leveling mechanism 14 adjusts the level of the polishing unit 1 again (step S13). Then, the precision polishing process in step S11 is performed again.

  As described above, according to the present embodiment, generation of polishing marks and stress unevenness on the polished surface of the sample 10 can be suppressed, and sufficient flatness can be obtained over a very wide range of the surface of the sample 10 to enable analysis evaluation. Therefore, it is possible to obtain a highly reliable thin-film sample. With this configuration, a wide range and accurate evaluation of a miniaturized device by AFM, TEM, SIMS, or the like is possible, and a lot of information can be obtained by observation evaluation of one sample.

It is a perspective view which shows schematic structure of the grinding | polishing apparatus by this embodiment with the operation | movement. It is a top view which shows schematic structure of the sample holding part which is a component of a grinding | polishing apparatus. It is a perspective view which shows the other example of the periphery structure of the sample holding part in a grinding | polishing apparatus. It is a schematic diagram for demonstrating the appropriateness | suitability of the installation angle of the sample in this embodiment. It is a schematic diagram for demonstrating the appropriate range of the installation angle of the sample in this embodiment. It is a flowchart which shows the grinding | polishing method by this embodiment in process order. It is a schematic diagram which shows the mode of the grinding | polishing process in the grinding | polishing method by this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Polishing part 1a Polishing surface 2 Sample holding part 2a Main body 10 Sample 11 Sample stand 11a Notch 11b Grid 12 Sample stand installation mechanism 12a Chucking member 12b Arm member 13 Angle adjustment mechanism 13a Angle scale 14 Horizontal adjustment mechanisms 14a and 14b Support rod

Claims (4)

A polishing method for polishing a sample to form a thin film,
The sample is fixed, specimen table which is movable in a polishing surface for polishing the sample, at any point of contact with the fixed in position at a predetermined site within the polishing surface, the polishing surface of the sample A polishing method comprising polishing the sample to form a thin film in a state where the polishing direction is constant. An installation angle of the sample fixed to the sample stage with respect to the polishing direction in the polishing surface is adjusted so that the cleaved surface of the sample is not parallel to the polishing direction, and the sample stage is fixed in position. in polishing method according to claim 1, characterized in that thinned by polishing the sample. The sample stage is provided with a grid formed at a fixed portion of the sample and an installation marker formed corresponding to the grid, and the installation marker is adjusted to a reference position of the installation angle. The polishing method according to claim 2 , wherein the sample is polished to be a thin film in a state where the installation angle is adjusted with reference to a state. The polishing method according to claim 2 or 3, wherein the installation angle is set to a value in the range of 10 ° to 45 °.

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