JP2005174599A - Wafer holder and electron microscope device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce wafer vibration causing image vibration, in an electron microscope for carrying out inclined observation of a semiconductor wafer. <P>SOLUTION: A damping seat is mounted at the center part of this wafer holder. The damping seat is so structured as to support a contact part to the back face of a wafer by a thin plate of a resin material; and a longitudinal spring constant is set in a range 1-5 times as much as that at the center part of the wafer with a periphery fixed. Thereby, vibration of the wafer can efficiently be reduced while avoiding adhesion of foreign matter, and high-resolution observation is enabled. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an inspection electron microscope suitable for use in the field of manufacturing semiconductor devices, and more particularly to an electron microscope wafer holder.

  Since the electron microscope apparatus has a higher magnification than the optical microscope, if the sample vibrates during observation, the image is blurred and the resolution is lowered. In particular, in an electron microscope apparatus for inspection and observation used in the semiconductor element manufacturing field, a thin disk-shaped wafer having a thickness of about several hundred micrometers is an object to be observed. Since the semiconductor wafer is thinner than the area, it is easily deformed and vibrated in a direction perpendicular to the surface.

In recent years, the diameter of semiconductor wafers has been increasing in order to improve production efficiency, and wafers having a diameter of 300 mm are used in the latest production lines. Even in the case of a wafer having such a large diameter, the thickness has not increased much. For this reason, the wafer tends to bend, that is, bend-induced vibrations easily.
As examples of the wafer holder, examples described in Patent Documents 1 and 2 below are known.

  When it is intended to closely observe a pattern side wall of a semiconductor element with an electron microscope, it is necessary to make an electron beam incident on the wafer from an inclined direction. For this purpose, an electron microscope having an inclination observation function such as an inclination stage and an inclination beam is used. In an electron microscope having a tilt observation function, the image is disturbed by the vibration of the wafer.

  The relationship between wafer bend vibration and image disturbance will be described with reference to FIG. As shown in FIG. 3A, when the electron beam 31 is incident perpendicularly to the surface of the wafer, image vibration does not occur directly due to wafer vibration, but as shown in FIG. When the electron beam 31 is incident from a direction inclined with respect to the surface of the wafer, image vibration is caused by the vibration of the wafer. Since the image resolution of an electron microscope for observing a semiconductor wafer is usually on the order of a few nanometers, harmful image distortion occurs even with very slight wafer vibration. This is a problem in an electron microscope having a tilt observation function.

  In an electron microscope for wafer observation, a wafer holder for preventing wafer vibration has been proposed. For example, Japanese Patent Application Laid-Open No. 2002-42708 describes a method using an electrostatic chuck. In the electrostatic chuck, since the back surface of the wafer is in close contact with the entire surface of the chuck surface by electrostatic attraction force, the curvature or vibration of the wafer can be effectively reduced.

Japanese Patent Laid-Open No. 3-95845 Japanese Patent No. 3197220 JP 2002-42708 A

  However, when the electrostatic chuck is used, the foreign matter attached to the back surface of the wafer is held by the chuck and is carried into the next manufacturing process. It is considered that the foreign matter adhering to the back surface of the wafer may wrap around the surface in the next manufacturing process, causing a product defect. Therefore, in recent years, it has been necessary to avoid as much as possible foreign matter adhering to the back surface of the wafer.

  An object of the present invention is to realize a wafer holder that effectively reduces the vibration of the wafer and has no problems such as adhesion of foreign matter.

  According to the present invention, at least three of the support seats that support the wafer are fixed rigid seats, and the other support seats are damping seats using a high damping material.

  Further, in the present invention, a thin plate made of a resin material is used as the damping seat, and a structure that supports the contact portion with the back surface of the wafer so as to be elastically movable in the vertical direction is used.

  According to the present invention, since the attenuation can be increased while holding the wafer in an accurate position, the vibration of the wafer is effectively prevented. The contact area to the back surface of the wafer can be made as small as possible to avoid adhesion of foreign matters.

  FIG. 1 is a perspective view showing an example of a wafer holder 20 of the present invention, and FIG. 2 is a perspective view showing a state in which the wafer 1 is mounted on the wafer holder 20 shown in FIG. The wafer holder 20 of this example is suitable for use in a sample moving plate of an electron microscope. The wafer holder 20 of this example includes a plate 2, two fixed pins 3 provided on the plate 2, one movable pin 4, and six fixed seats 5-1, 5-2, 5-3, 5-4. , 5-5, 5-6 and three damping seats 6. As shown in FIG. 2, the wafer 1 is prevented from moving in the lateral direction by two fixed pins 3 and one movable pin 4, and six fixed seats 5-1, 5-2, 5-3, 5 -4, 5-5, and 5-6 determine the support position in the thickness direction. Further, the bend vibration of the wafer 1 is damped by the three damping seats 6.

  An appropriate number of fixed pins 3 and movable pins 4 are provided at positions on the outer peripheral portion of the wafer 1. In the illustrated example, two fixed pins 3 and one movable pin 4 are provided, but a larger number may be used.

  Of the six fixed seats, three fixed seats 5-4, 5-5, and 5-6 are provided at the outer peripheral portion of the wafer 1, and the other three fixed seats 5-1, 5-2, 5-3 are arranged on the same circumference radially inward from the fixed pin 3 and the movable pin 4. There may be at least three fixed seats 5.

  The damping seat 6 is preferably arranged on the same circumference radially inward from the fixed seats 5-1 to 5-6. There may be at least one damping seat 6. However, if only one damping seat 6 is provided at the center, it is effective in reducing the lowest-order resonance mode mainly consisting of vertical movement of the wafer center, but higher-order bend resonance without vertical movement of the wafer center. Is less effective. For this reason, in this example, three damping seats 6 are provided slightly apart from the center of the wafer so as to effectively attenuate higher-order resonance of the wafer.

  The six fixed seats 5-1 to 5-6 are mounted such that their upper surfaces are all at the same height. Similarly, the three damping seats 6 are mounted so that their upper ends are all at the same height. However, the upper end of the damping seat 6 is disposed at a position slightly higher than the upper surfaces of the fixed seats 5-1 to 5-6. When the wafer is supported by the fixed seats 5-1 to 5-6, the damping seat 6 supports the wafer in an elastically deformed state.

  In order to stably support the wafer 1, the number of fixed support seats such as the fixed pins 3, the movable pins 4, and the fixed seats 5-1 to 5-6 may be increased. In order to effectively prevent the vibration of the wafer 1, the number of damping seats 6 may be increased. However, wafers that have undergone various processes may have warpage due to residual stress. Therefore, even if the number of support seats and damping seats is increased, not all of the support seats and damping seats contact the wafer. Therefore, it is meaningless to increase the number of support seats and damping seats too much.

  Hereinafter, the damping characteristic of the damping seat 6 will be described in detail. In general, it is known that damping is effective for reducing vibration. In order to reduce the vibration of the wafer, a high damping characteristic may be given to the support seat that supports the wafer. However, damping in the first place is a phenomenon in which vibration energy is converted into thermal energy due to internal friction of the material. Therefore, in order to give a high damping characteristic to the support seat, the material or structure of the support seat may be selected so as to be low in rigidity and easily deformed. However, if the support seat is easily deformed, the wafer cannot be stably supported.

  In this example, the wafer is supported in the thickness direction by the fixed seat 5, and the bend vibration of the wafer is damped by the damping seat 6. The optimum damping characteristics of the damping seat when the wafer is supported using the fixed seat and the damping seat as in this example will be discussed below.

  FIG. 4 is a graph showing the result of calculating the variation of the damping coefficient of the wafer vibration when the damping seat is applied to the central portion of the wafer whose periphery is fixed. In the figure, η is the damping coefficient of the entire vibration system of the wafer vibration, ηc is the damping coefficient of the damping seat, kc is the vertical spring constant of the wafer support portion of the damping seat, and kw is up and down at the center of the wafer with the periphery fixed. This is a spring constant related to the displacement of the central portion due to the bend of the wafer when a directional force is applied. The vertical axis of the graph 51 is the damping coefficient ratio η / ηc, and the horizontal axis is the spring constant ratio kc / kw. The damping coefficient ratio η / ηc increases as the spring constant ratio kc / kw increases, reaches a maximum, and then decreases.

The reason why such a central portion has high characteristics is as follows.
(1) In a region where the spring constant of the damping seat is smaller than the spring constant of the bend of the wafer (kc / kw = 0.1-1), the damping seat is deformed according to the wafer vibration, and vibration energy is generated by the deformation of the damping seat. Is absorbed and a damping action works. However, the smaller the spring constant of the damping seat, the smaller the force acting between the wafer and the damping seat, and the smaller the amount of vibration energy transmitted, the smaller the damping of the entire vibration system.
(2) In the region (kc / kw = 5 to 100) in which the spring constant of the damping seat is several times or more than the spring constant of the wafer bend, the force acting between the wafer and the damping seat is large due to wafer vibration. However, since the damping seat is hard, it is difficult to be deformed, and the wafer is greatly deformed at a portion not in contact with the damping seat. For this reason, the larger the spring constant of the damping seat, the smaller the absorption of vibration energy by the damping seat.
(3) Eventually, in the region where the spring constant of the damping seat is several times that of the wafer bend (kc / kw = 1-5: hatched region 52), the wafer vibration is effectively damped by the damping seat. Therefore, it is preferable to determine the spring constant of the damping seat so that the ratio of the spring constant is 1 to 5.

  In the case of a silicon wafer having a diameter of 300 mm and a fixed periphery, the above-described spring constant kw is about 16 Newton / mm. Therefore, the spring constant kc of the damping seat may be set to 16 Newton / mm to 80 Newton / mm. When a plurality of damping seats are provided, the value obtained by dividing this value by the number of damping seats is the spring constant of each damping seat. Thus, in this example, the optimum damping characteristic of the damping seat can be obtained by setting the ratio of the spring constant kc of the damping seat to the spring constant kw of the wafer bend to kc / kw = 1-5.

  FIG. 5 shows a first example of a damping seat according to the invention. The damping seat 6 of this example includes a thin plate 41 and a mounting block 42. The thin plate 41 is bent into a U shape, and both ends thereof are connected to both end surfaces of the mounting block 42. The U-shaped tip portion constitutes a wafer contact portion 11 in contact with the wafer. The mounting block 42 may be attached to the plate 2 by screws or bolts (not shown). The damping seat 6 may be disposed in a recess 2A provided in the plate 2 as shown.

  The thin plate 41 is made of a resin thin plate having a thickness of 0.1 mm to 0.2 mm. The material of the thin plate 41 may be any resin as long as it is a resin with less adhesion or generation of foreign matter, and may be nylon, polyethylene resin, polyimide resin, fluorine resin, or the like. However, preferably a fluororesin is used.

  Since a thin plate bent in a U shape is used in this way, a damping seat with a spring constant ratio of kc / kw = 1 to 5 can be easily realized as described above. For example, the dimensions are determined so that the spring constant when the wafer contact portion 11 of each damping seat is pushed downward is approximately 10 Newton / mm. The spring constant of the six damping seats is approximately 60 newtons / millimeter.

  In this example, the wafer contact portion 11 of the attenuation seat 6 has a cylindrical surface, and the contact area with the back surface of the wafer is small. As described above, the upper end of the damping seat 6 is disposed at a position slightly higher than the upper surface of the fixed seat 5, and when the wafer is supported by the wafer holder, the wafer bonding portion 11 of the damping seat 6 contacts the back surface of the wafer in an elastically deformed state. To do. Since this contact area is small, there is little possibility of foreign matter adhesion or contamination on the backside of the wafer.

  FIG. 6 shows another example of the damping seat 6 according to the present invention. The damping seat 6 of this example has a wafer contact portion 11, a thin plate 41, and two mounting blocks 42, which are formed in a substantially U-shaped integral structure. The material of the damping seat of this example may be the same as the material of the first example of the damping seat of FIG. Also in this example, the wafer contact portion 11 has a cylindrical surface. The two attachment blocks 42 may be attached to the plate 2 by screws or bolts (not shown). Similarly to the example shown in FIG. 5A, the damping seat 6 may be disposed in a recess provided in the plate 2.

  In the first and second examples of the damping seat described above, both ends of the thin plate 41 are fixed. However, a structure in which a thin plate is fixed in a cantilever manner may be used. In the case of the cantilever structure, there are advantages such as fewer manufacturing processes and less material to be used. However, when the thin plate 41 is deformed by a force from above, the wafer contact portion 11 may be displaced laterally at the same time. is there. Therefore, there is a drawback that the contact with the back surface of the wafer becomes unstable.

  Another example of the wafer holder of the present invention will be described with reference to FIG. Compared with the first example shown in FIG. 1, the wafer holder of this example has three damping seats 6-1, 6-6 instead of the three fixing seats 5-4, 5-5, 5-6. 2 and 6-3 are different, and other configurations may be the same. That is, the wafer holder of this example includes a plate 2, two fixed pins 3 provided on the plate 2, one movable pin 4, three fixed seats 5-1, 5-2, 5-3 and 6. It has the damping seats 6-1, 6-2, 6-3, 6, 6, 6. Two fixed pins 3 and one movable pin 4 are provided at a position of the outer peripheral portion of the wafer 1. The three attenuation seats 6-1, 6-2 and 6-3 are provided on the same circumference at the position of the outer peripheral portion of the wafer 1. The three fixed seats 5-1, 5-2, and 5-3 are provided on the same circumference radially inward from the fixed pin 3 and the movable pin 4 as in the example of FIG. 1. The three damping seats 6 are provided on the same circumference further radially inward as in the example of FIG.

  The wafer holder of this example basically has the same functions and effects as those of the example shown in FIG. 1, but a larger attenuation can be obtained because of the large number of attenuation seats. Even if the wafer is warped, it can be stably supported, but since the rigidity in the vertical direction of the wafer is lowered, the lowest-order resonance frequency is also slightly lowered.

  In this example, compared to the first example shown in FIG. 1, three damping seats 6-1, 6-2, instead of the three fixing seats 5-4, 5-5, 5-6, 6-3 is provided, the total number of fixed support seats and damping seats has not increased. Therefore, as described above, even if the wafer 1 is warped, there is little possibility that there is a support seat or a damping seat that does not contact the wafer.

  FIG. 8 shows an example of an electron microscope with a tilt function equipped with a wafer holder according to the present invention. The electron microscope of this example includes an electron optical system column 21, a vacuum chamber 22, a loader 23, an inclined plate 24, an X moving plate 25, and a Y moving plate 26. A wafer holder 20 that supports the wafer 1 is provided on the Y moving plate 26. As shown, the wafer 1 is inclined with respect to the optical axis of the electron optical system column 21.

  According to the electron microscope of the present invention, since the vibration of the wafer can be reduced, tilt observation with high resolution can be realized, which is suitable for observation of a semiconductor fine pattern.

  The example of the present invention has been described above, but the present invention is not limited to the above-described example, and it will be understood by those skilled in the art that various modifications can be made within the scope of the invention described in the claims. Like.

It is a perspective view which shows the 1st example of the wafer holder of this invention. It is a perspective view which shows the state which mounted | wore the wafer holder of FIG. It is a figure which shows the relationship between the vibration of a wafer, and an electron beam. It is explanatory drawing for demonstrating the relationship between the ratio of a damping coefficient, and a spring constant. It is a figure which shows an example of the structure of the damping seat by this invention. It is a perspective view which shows the other example of the structure of the damping seat by this invention. It is a perspective view which shows the 2nd example of the wafer holder of this invention. It is a figure which shows the outline of the electron microscope which has the tilt observation function provided with the wafer holder by this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Wafer, 2 ... Plate, 3 ... Fixed pin, 4 ... Movable pin, 5-1 to 5-6 ... Fixed seat, 6, 6-1 to 6-3 ... Damping seat, 11 ... Wafer contact part, 20 ... Wafer holder, 21 ... electro-optic system column, 22 ... vacuum chamber, 23 ... loader, 24 ... tilt plate, 25 ... X moving plate, 26 ... Y moving plate, 31 ... electron beam, 41 ... thin plate, 42 ... mounting block

Claims (7)

Three or more fixed seats for supporting the wafer and at least one damping seat for elastically supporting the wafer, the damping seat comprising a wafer contact portion that contacts the back surface of the wafer, and the wafer contact A wafer holder comprising: a support portion that elastically moves the portion. 2. The wafer holder according to claim 1, wherein the spring constant of the damping seat is selected so that the ratio of the spring constant kc of the damping seat to the spring constant kw of the central portion of the wafer supporting the periphery is kc / kw = 1-5. A wafer holder characterized by that. 2. The wafer holder according to claim 1, wherein an overall spring constant kc of the damping seat is 16 to 80 newtons / millimeter. 2. The wafer holder according to claim 1, wherein the wafer contact portion of the damping seat is a cylindrical surface formed by bending a thin plate. 2. The wafer holder according to claim 1, wherein an upper end of the damping seat is disposed so as to protrude from an upper surface of the fixed seat. 2. The wafer holder according to claim 1, wherein the fixed seat is disposed at a position corresponding to a peripheral portion of the wafer, and the damping seat is disposed radially inward from the fixed seat. An electron microscope apparatus comprising the wafer holder according to claim 1.

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