JP2024086012A - Inspection Equipment - Google Patents

Abstract

To provide an inspection device that can improve the detection accuracy of a characteristic of an MRAM element.SOLUTION: An inspection device 1 includes: a stage 10 that has a magnetoresistive memory element fixed on a stage surface 13; a plurality of electromagnets 20 that generate a first magnetic field in which a direction of a magnetic field component in a vertical direction perpendicular to the stage surface 13 changes from a first direction to a second direction depending on a position on the stage surface 13 and a second magnetic field in which a direction of the magnetic field component in an in-plane direction parallel to the stage surface 13 changes from a third direction to a fourth direction depending on the position on the stage surface 13; an optical system 30 that irradiates the magnetoresistive memory element with illumination light including polarized light and condenses reflection light of the illumination light reflected by the magnetoresistive memory element; and a detector 40 that detects the reflection light in a case where a position of the magnetoresistive memory element in the first magnetic field is changed and the reflection light in a case where the position of the magnetoresistive memory element in the second magnetic field is changed.SELECTED DRAWING: Figure 1

Description

This disclosure relates to an inspection device, for example, an inspection device that inspects the magnetic properties of magnetoresistive memory elements.

A semiconductor memory element called a magnetoresistive random access memory element (hereinafter referred to as an MRAM element) is a non-volatile memory that uses a magnetic tunnel junction (MTJ) as a component. In a semiconductor production line, early inspection of anomalies in MRAM elements formed on a wafer before the completion of a magnetoresistive memory device (hereinafter referred to as an MRAM device) is important for improving the production yield of MRAM devices. In order to inspect MRAM devices before their completion, it is necessary to understand the magnetic field characteristics as well as non-destructive appearance inspection using an optical microscope or electron beam. As a high-speed measurement method for magnetic field measurement, optical measurement using a magneto-optical effect called the magneto-optical Kerr effect (MOKE) is known. According to this method, an external magnetic field is applied to each MRAM element in an MRAM device, and while changing the strength of the magnetic field, the magnetic hysteresis loop at the measurement point can be obtained by measuring the change in polarization of the reflected light.

Patent Document 1 describes an inspection device that uses a gradient magnetic field generated between the yoke of an electromagnet having two coils to scan an MRAM device on a stage and detects defects in the MRAM element with a TDI (TDI Delay Integration) camera.

JP 2022-072599 A

In the inspection device of Patent Document 1, the horizontal magnetic field is almost constant before and after magnetic field reversal of the vertical magnetic field (easy axis direction), so it is possible to detect the characteristics of the vertical magnetic field. However, the inspection device of Patent Document 1 has difficulty detecting changes in the characteristics of the MRAM element due to changes in the horizontal magnetic field, and is unable to improve the detection accuracy of the magnetic characteristics of the MRAM element.

This disclosure has been made to solve these problems, and aims to provide an inspection device that can improve the detection accuracy of the magnetic properties of MRAM elements.

An inspection apparatus according to an embodiment includes:
a stage having a stage surface on which a magnetoresistive memory element is fixed;
a plurality of electromagnets that generate a first magnetic field, the orientation of a magnetic field component in a vertical direction perpendicular to the stage surface changes from a first orientation to a second orientation opposite to the first orientation depending on a position on the stage surface, and a second magnetic field, the orientation of a magnetic field component in an in-plane direction parallel to the stage surface changes from a third orientation to a fourth orientation opposite to the third orientation depending on the position on the stage surface;
an optical system that illuminates the magnetoresistive memory element with illumination light including polarized light and collects light reflected by the magnetoresistive memory element from the illumination light;
a detector for detecting the reflected light when the position of the magnetoresistive memory element is changed in the first magnetic field and the reflected light when the position of the magnetoresistive memory element is changed in the second magnetic field;
Equipped with.

In the above inspection device,
When the position of the magnetoresistive memory element is changed so as to change from the first orientation to the second orientation within the first magnetic field, the magnetic field component perpendicular to the first scanning direction and the perpendicular direction may be zero.

In the above inspection device,
When the position of the magnetoresistive memory element is changed so as to change from the third orientation to the fourth orientation within the second magnetic field, the magnetic field component in the second scanning direction and the magnetic field component in the perpendicular direction may be zero.

In the above inspection device,
the plurality of electromagnets includes at least four electromagnets including a first electromagnet, a second electromagnet, a third electromagnet, and a fourth electromagnet;
the first electromagnet includes a first coil wound in a predetermined direction around a first vertical portion of an L-shaped first yoke having a first vertical portion extending in the vertical direction and a first in-plane portion extending in the in-plane direction,
the second electromagnet includes a second coil wound in the predetermined direction on a second vertical portion of an L-shaped second yoke having a second vertical portion extending in the vertical direction and a second in-plane portion extending in the in-plane direction,
the third electromagnet includes a third coil wound in the predetermined direction around a third vertical portion of an L-shaped third yoke having a third vertical portion extending in the vertical direction and a third in-plane portion extending in the in-plane direction,
the fourth electromagnet includes a fourth coil wound in the predetermined direction on a fourth vertical portion of an L-shaped fourth yoke having a fourth vertical portion extending in the vertical direction and a fourth in-plane portion extending in the in-plane direction,
The first in-plane portion and the second in-plane portion extend in one direction, and an end portion of the first in-plane portion and an end portion of the second in-plane portion face each other in the one direction,
The third in-plane portion and the fourth in-plane portion extend in another direction perpendicular to the one direction, and the end portion of the third in-plane portion and the end portion of the fourth in-plane portion face each other in the other direction,
the first magnetic field is generated by passing a current in a fifth direction through the first coil, passing the current in a sixth direction opposite to the fifth direction through the second coil, and setting the current flowing through the third coil and the fourth coil to zero;
The second magnetic field may be generated by passing the current in the fifth direction through the first coil and the second coil, and passing the current in the sixth direction through the third coil and the fourth coil.

In the above inspection device, the detector includes:
Detecting the reflected light when the position of the magnetoresistive memory element in the first magnetic field is scanned in the one direction;
The reflected light may be detected when the position of the magnetoresistive memory element in the second magnetic field is scanned in a direction at an angle of 45° to the one direction and the other direction.

In the above inspection device,
An information processing unit that processes an image of the reflected light detected by the detector is further provided.
The information processing unit includes:
The magnetoresistive memory element may be inspected for defects caused by the magnetic field component in the perpendicular direction from a difference image between the image in the magnetic field component in the first orientation and the image in the magnetic field component in the second orientation.

In the above inspection device,
An information processing unit that processes an image of the reflected light detected by the detector is further provided.
The information processing unit includes:
The magnetoresistive memory element may be inspected for defects caused by the magnetic field component in the in-plane direction from a difference image between the image in the magnetic field component in the third orientation and the image in the magnetic field component in the fourth orientation.

The inspection device disclosed herein can provide an inspection device that can improve the detection accuracy of the magnetic properties of MRAM.

1 is a cross-sectional view illustrating an inspection device according to a first embodiment. FIG. 2 is a perspective view illustrating an electromagnet of the inspection device according to the first embodiment. 4 is a graph illustrating magnetic properties in an easy axis direction of an MRAM element using the VSM according to the first embodiment, in which the horizontal axis indicates an external magnetic field and the vertical axis indicates magnetization. 4 is a graph illustrating magnetic properties in the hard axis direction of the MRAM element using the VSM according to the first embodiment, where the horizontal axis indicates an external magnetic field and the vertical axis indicates magnetization. 5A and 5B are diagrams illustrating current flow through a coil when a magnetic field having a magnetic field component perpendicular to a stage surface is applied to an MRAM element according to the first embodiment. 1 is a graph illustrating magnetic flux density in the α-axis direction along the first scan axis, and in the β-axis and γ-axis directions perpendicular to the first scan axis in embodiment 1, where the horizontal axis indicates position along the α-axis and the vertical axis indicates magnetic flux density. FIG. 4 is a diagram illustrating magnetic flux density vectors in an αγ plane according to the first embodiment. 5A and 5B are diagrams illustrating current flow through a coil when a magnetic field having a magnetic field component parallel to a stage surface is applied to an MRAM element according to the first embodiment. 1 is a graph illustrating magnetic flux density in the α-axis direction along the second scan axis, and in the β-axis and γ-axis directions perpendicular to the second scan axis in embodiment 1, where the horizontal axis indicates position along the α-axis and the vertical axis indicates magnetic flux density. FIG. 4 is a diagram illustrating magnetic flux density vectors in an αβ plane according to the first embodiment. 1 is a diagram illustrating the magnetic characteristics of an MRAM element, in which the horizontal axis indicates an external magnetic field and the vertical axis indicates the Kerr rotation angle. 1 is a diagram illustrating the magnetic characteristics of an MRAM element, in which the horizontal axis indicates an external magnetic field and the vertical axis indicates the Kerr rotation angle. FIG. 2 is a plan view illustrating a wafer according to the first embodiment. FIG. 2 is a configuration diagram illustrating details of an inspection device according to the first embodiment. FIG. 2 is a flow chart illustrating a method for inspecting a wafer including MRAM elements according to the first embodiment. 4 is a flow chart illustrating a method for inspecting magnetic properties in a perpendicular direction of the MRAM element according to the first embodiment; FIG. 4 is a flow chart illustrating a method for inspecting magnetic characteristics in an in-plane direction of the MRAM element according to the first embodiment. FIG. FIG. 11 is a flow chart illustrating a method for inspecting magnetic properties in the perpendicular direction of an MRAM element according to the second embodiment. FIG. 11 is a flow chart illustrating a method for inspecting the magnetic characteristics in the in-plane direction of an MRAM element according to the second embodiment.

For clarity of explanation, the following description and drawings have been omitted and simplified as appropriate. In addition, the same elements in each drawing are given the same reference numerals, and duplicate explanations have been omitted as necessary.

(Embodiment 1)
An inspection device according to the first embodiment will be described. FIG. 1 is a cross-sectional view illustrating the inspection device according to the first embodiment. FIG. 2 is a perspective view illustrating an electromagnet of the inspection device according to the first embodiment. In FIG. 1, in order to avoid the diagram from becoming complicated, hatching of some members is omitted, and some reference numerals are omitted. The same applies to the following figures. As shown in FIG. 1 and FIG. 2, the inspection device 1 includes a stage 10, a plurality of electromagnets 20, an optical system 30, a detector 40, and an information processing unit 50. Below, <1. Stage>, <2. Multiple electromagnets>, <3. Optical system>, <4. Detector>, and <5. Information processing unit> will be described. After that, <6. Details of the inspection device> and <7. Inspection method> will be described. In addition, in <2. Multiple electromagnets>, <2-1. Magnetic properties of MRAM element>, <2-2. Application of magnetic field perpendicular to stage surface>, and <2-3. Application of magnetic field parallel to stage surface> will be described.

＜1. Stage＞
The stage 10 includes a moving part 11 and a main body part 12. The upper surface of the moving part 11 is called a stage surface 13. Thus, the stage 10 has the stage surface 13. The stage 10 fixes a magnetoresistive memory element (hereinafter referred to as an MRAM element) on the stage surface 13. For example, the stage 10 places a sample such as a wafer WF including an MRAM element on the stage surface 13. In the following, the sample will be described as a wafer WF. Note that the sample is not limited to a wafer WF, and may be a semiconductor device or the like, so long as it includes an MRAM element.

The moving part 11 in the stage 10 may have a wafer chuck for fixing the wafer WF. The wafer WF is fixed on the stage surface 13 by the wafer chuck using vacuum or static electricity. The stage 10 may have an XYZθ drive axis having an actuator such as a linear motor, ball screw, VCM, or piezoelectric to move the wafer WF. The moving part 11 moves relative to the main body part 12 based on the XYZθ drive axis. An inspection surface W0 is introduced as a surface parallel to the stage surface 13.

Here, for convenience of explanation of the inspection device 1, an XYZ Cartesian coordinate system is introduced. For example, the direction perpendicular to the inspection surface W0 is the Z-axis direction, and the plane parallel to the inspection surface W0 is the XY plane. For convenience, the Z-axis direction is called the vertical direction or the vertical direction, the +Z-axis direction is called the upward direction, and the -Z-axis direction is called the downward direction. The XY plane is called the horizontal plane, and the direction parallel to the XY plane is called the horizontal direction or the in-plane direction. Note that the vertical direction, vertical direction, upward, downward, horizontal plane, horizontal direction, and in-plane direction are for convenience only, and do not indicate the direction in which the actual inspection device 1 is disposed. The stage 10 inspects the MRAM elements included in the wafer WF by scanning in a predetermined direction in the XY plane.

For example, the stage 10 can move the wafer WF in a predetermined direction, including the X-axis direction and the Y-axis direction, within a plane parallel to the inspection surface W0. The stage 10 can also rotate the wafer WF on the stage surface 13 around a rotation axis extending in a direction perpendicular to the inspection surface W0. The stage 10 can also move the wafer WF on the stage surface 13 in a direction perpendicular to the inspection surface W0.

<2. Multiple electromagnets>
The multiple electromagnets 20 may include at least four electromagnets 20a to 20d including electromagnets 20a to 20d. The at least four electromagnets 20a to 20d are collectively referred to as electromagnets 20. Electromagnets 20a and 20b are disposed facing each other in the X-axis direction. Electromagnets 20c and 20d are disposed facing each other in the Y-axis direction. Note that the electromagnets 20 may be five or more as long as they include at least four electromagnets 20a to 20d. In this case, the electromagnets 20 are not limited to being disposed facing each other in the X-axis and Y-axis directions.

The electromagnets 20a to 20d may each include a coil 21a to 21d. Coils 21a to 21d are collectively referred to as coil 21. By controlling the direction of the current flowing through coil 21, the direction of the magnetic field generated by electromagnet 20 can be controlled.

The electromagnets 20a to 20d may be fixed to yokes 22a to 22d, respectively. The yokes 22a to 22d are collectively referred to as yoke 22. The yoke 22 has, for example, an L-shape. The yoke 22 is L-shaped with a vertical portion 23 extending in a direction perpendicular to the stage surface 13 and an in-plane portion 24 extending in a direction parallel to the stage surface 13. The coil 21 is wound in a predetermined direction around the vertical portion 23.

Specifically, the electromagnet 20a includes a coil 21a wound in a predetermined direction on a vertical portion 23a of an L-shaped yoke 22a having a vertical portion 23a extending in a direction perpendicular to the stage surface 13 and an in-plane portion 24a extending in a direction parallel to the stage surface 13. The electromagnet 20b includes a coil 21b wound in a predetermined direction on a vertical portion 23b of an L-shaped yoke 22b having a vertical portion 23b extending in a direction perpendicular to the stage surface 13 and an in-plane portion 24b extending in a direction parallel to the stage surface 13. The electromagnet 20c includes a coil 21c wound in a predetermined direction on a vertical portion 23c of an L-shaped yoke 22c having a vertical portion 23c extending in a direction perpendicular to the stage surface 13 and an in-plane portion 24c extending in a direction parallel to the stage surface 13. The electromagnet 20d includes a coil 21d wound in a predetermined direction on the vertical portion 23d of an L-shaped yoke 22d having a vertical portion 23d extending in a direction perpendicular to the stage surface 13 and an in-plane portion 24d extending in a direction parallel to the stage surface 13.

The vertical portions 23a to 23d are collectively referred to as the vertical portions 23, and the in-plane portions 24a to 24d are collectively referred to as the in-plane portions 24. The coils 21a to 21d are wound in the same predetermined direction on the vertical portions 23a to 23d, respectively. The vertical portions 23a to 23d extend in the Z-axis direction. The vertical portions 23a to 23d pass through the central axes of the electromagnets 20a to 20d, respectively. The upper ends of the yokes 22a to 22d, i.e., the upper ends of the vertical portions 23a to 23d, are connected to the connecting plate 25. The lower ends of the vertical portions 23a to 23d are connected to one end of the in-plane portions 24a to 24d, respectively.

The in-plane portion 24a of the yoke 22a and the in-plane portion 24b of the yoke 22b extend in the X-axis direction. One end of the in-plane portion 24a is connected to the lower end of the vertical portion 23a that passes through the center of the electromagnet 20a. Thus, the in-plane portion 24a extends in the +X-axis direction from the lower end of the vertical portion 23a. One end of the in-plane portion 24b is connected to the lower end of the vertical portion 23b that passes through the center of the electromagnet 20b. Thus, the in-plane portion 24b extends in the -X-axis direction from the lower end of the vertical portion 23b. The end of the in-plane portion 24a and the end of the in-plane portion 24b face each other in the X-axis direction.

The in-plane portion 24c of the yoke 22c and the in-plane portion 24d of the yoke 22d extend in the Y-axis direction. One end of the in-plane portion 24c is connected to the lower end of the vertical portion 23c that passes through the center of the electromagnet 20c. Thus, the in-plane portion 24c extends in the +Y-axis direction from the lower end of the vertical portion 23c. One end of the in-plane portion 24d is connected to the lower end of the vertical portion 23d that passes through the center of the electromagnet 20d. Thus, the in-plane portion 24d extends in the -Y-axis direction from the lower end of the vertical portion 23d. The end of the in-plane portion 24c and the end of the in-plane portion 24d face each other in the Y-axis direction.

<2-1. Magnetic properties of MRAM elements>
Next, the magnetic characteristics of the MRAM measured by a vibrating sample magnetometer (hereinafter referred to as VSM) will be described. Fig. 3 is a graph illustrating the magnetic characteristics in the easy axis direction of the MRAM element measured by the VSM according to the first embodiment, where the horizontal axis indicates the external magnetic field and the vertical axis indicates the magnetization. Fig. 4 is a graph illustrating the magnetic characteristics in the hard axis direction of the MRAM element measured by the VSM according to the first embodiment, where the horizontal axis indicates the external magnetic field and the vertical axis indicates the magnetization.

As shown in FIG. 3, the magnetization of the MRAM element perpendicular to the top surface of the wafer WF is easily reversed by changing the external magnetic field. The direction perpendicular to the top surface of the wafer WF, i.e., the direction perpendicular to the stage surface 13, is called the easy axis direction. On the other hand, as shown in FIG. 4, the magnetization of the MRAM element parallel to the top surface of the wafer WF is difficult to reverse by changing the external magnetic field. The direction parallel to the top surface of the wafer WF, i.e., the direction parallel to the stage surface 13, is called the hard axis direction. Thus, the easy axis direction perpendicular to the top surface of the wafer WF and the hard axis direction parallel to the top surface of the wafer WF have different magnetic properties. For this reason, it is necessary to inspect the magnetic properties in two directions, the easy axis direction and the hard axis direction, to inspect defects in the MRAM element.

<2-2. Application of a magnetic field perpendicular to the stage surface>
5 is a diagram illustrating the current flow through the coil 21 when a magnetic field having a magnetic field component perpendicular to the stage surface 13 according to the first embodiment is applied to the MRAM element. As shown in FIG. 5, when a magnetic field having a magnetic field component perpendicular to the stage surface 13 is applied to the MRAM element, currents in opposite directions are applied to the coils 21a and 21b of the electromagnets 20a and 20b that face each other in the X-axis direction. On the other hand, no current is applied to the coils 21c and 21d of the electromagnets 20c and 20d that face each other in the Y-axis direction.

In other words, a magnetic field having a magnetic field component perpendicular to the stage surface 13 is generated by passing a current in a predetermined direction through coil 21a, passing a current in the opposite direction to the predetermined direction through coil 21b, and setting the current flowing through coils 21c and 21d to zero. A magnetic field having a magnetic field component perpendicular to the stage surface 13 is called the first magnetic field. The direction perpendicular to the stage surface 13 is called the vertical direction. In the case of the first magnetic field, the α-axis direction parallel to the X-axis direction is the scan axis. The scan axis in the case of the first magnetic field is called the first scan axis. The direction perpendicular to the α-axis direction in the XY plane is the β-axis direction. The β-axis is in the same direction as the Y-axis. The direction perpendicular to the α-axis direction and the β-axis direction is the γ-axis. The γ-axis is in the same direction as the Z-axis. The β-axis and γ-axis are perpendicular to the first scan axis.

Figure 6 is a graph illustrating magnetic flux density in the α-axis direction along the first scan axis, and in the β-axis direction and γ-axis direction perpendicular to the first scan axis according to embodiment 1, where the horizontal axis indicates position along the α-axis and the vertical axis indicates magnetic flux density. Figure 7 is a diagram illustrating magnetic flux density vectors in the αγ plane according to embodiment 1.

As shown in Figures 6 and 7, the first magnetic field has a vertical magnetic field component whose orientation changes from one direction to the opposite direction depending on the position on the stage surface 13. The magnetic field component parallel to the stage surface 13 is constant. In other words, between the end of the in-plane portion 24a of the yoke 22a and the end of the in-plane portion 24b of the yoke 22b, the magnetic field component in the γ-axis direction is reversed, the magnetic field component in the α-axis direction is constant at a predetermined value, and the magnetic field component in the β-axis direction is zero. In this way, when the position of the MRAM element is changed so that the orientation of the magnetic field component in the γ-axis direction in the first magnetic field changes from one direction to the opposite direction, the magnetic field components perpendicular to the α-axis and γ-axis directions are zero. Here, a magnetic field component of zero means not only strictly zero, but also zero within a range that includes unavoidable measurement errors.

By moving the wafer WF along the first scan axis, the sign of the vertical magnetic field component applied to the MRAM elements contained in the wafer WF can be changed while the magnetic field component in the β-axis direction can be kept at zero.

In this way, the multiple electromagnets 20 generate a magnetic field that includes a magnetic field component in the easy axis direction. The easy axis direction is, for example, the Z-axis direction perpendicular to the stage surface 13. The multiple electromagnets 20 generate a first magnetic field in which the orientation of the perpendicular magnetic field component changes from a first orientation to a second orientation opposite to the first orientation depending on the position on the stage surface 13.

<2-3. Application of a magnetic field in a plane parallel to the stage surface>
8 is a diagram illustrating the current flow through the coil 21 when a magnetic field having a magnetic field component parallel to the stage surface 13 according to the first embodiment is applied to the MRAM element. As shown in FIG. 8, when a magnetic field having a magnetic field component parallel to the stage surface 13 is applied to the MRAM element, currents of the same predetermined direction are applied to the coils 21a and 21b of the electromagnets 20a and 20b that face each other in the X-axis direction. On the other hand, currents of the opposite direction to that of the coils 21a and 21b are applied to the coils 21c and 21d of the electromagnets 20c and 20d that face each other in the Y-axis direction.

In other words, a magnetic field having a magnetic field component parallel to the stage surface 13 is generated by passing a current in a predetermined direction through coils 21a and 21b, and passing a current in the opposite direction to the predetermined direction through coils 21c and 21d. A magnetic field having a magnetic field component parallel to the stage surface 13 is called the second magnetic field. The direction parallel to the stage surface 13 is called the in-plane direction. When the XYZ orthogonal coordinate axis system is fixed to the multiple electromagnets 20, in the case of the second magnetic field, the α-axis direction having an angle of 45° with the X-axis and Y-axis is the scan axis. The scan axis in the case of the second magnetic field is called the second scan axis. The direction perpendicular to the α-axis direction in the XY plane is the β-axis direction. The direction perpendicular to the α-axis direction and the β-axis direction is the γ-axis. The γ-axis is in the same direction as the Z-axis.

Figure 9 is a graph illustrating magnetic flux density in the α-axis direction along the second scan axis, and in the β-axis and γ-axis directions perpendicular to the second scan axis according to embodiment 1, where the horizontal axis indicates position along the α-axis and the vertical axis indicates magnetic flux density. Figure 10 is a diagram illustrating magnetic flux density vectors in the αβ plane according to embodiment 1.

9 and 10, the second magnetic field has an in-plane magnetic field component whose direction changes from one direction to the opposite direction depending on the position on the stage surface 13. The magnetic field component in the vertical direction perpendicular to the stage surface 13 is 0. That is, in the space surrounded by the end of the in-plane portion 24a of the yoke 22a, the end of the in-plane portion 24b of the yoke 22b, the end of the in-plane portion 24c of the yoke 22c, and the end of the in-plane portion 24d of the yoke 22d, the magnetic field component in the β-axis direction is reversed, and the magnetic field components in the α-axis direction and the γ-axis direction are 0. In this way, when the position of the MRAM element is changed so that the direction of the magnetic field component in the β-axis direction changes from one direction to the opposite direction in the second magnetic field, the magnetic field components in the α-axis direction and the γ-axis direction are 0. Here, the magnetic field component being 0 means not only strictly 0, but also 0 within a range including unavoidable measurement errors.

By moving the wafer WF along the second scan axis, the sign of the magnetic field component in the β-axis direction applied to the MRAM element contained in the wafer WF can be changed, while the magnetic field components in the α-axis direction and the γ-axis direction can be kept at zero.

In this way, the multiple electromagnets 20 generate a magnetic field that includes a magnetic field component in the hard axis direction. The hard axis direction is, for example, a direction perpendicular to the easy axis direction. The multiple electromagnets 20 generate a second magnetic field in which the direction of the magnetic field component in the in-plane direction parallel to the stage surface 13 changes from a third orientation to a fourth orientation opposite to the third orientation depending on the position on the stage surface 13.

3. Optical System
The optical system 30 may include an optical microscope. The optical microscope forms an image of the surface of the wafer WF. The optical system 30 illuminates the MRAM element with illumination light including polarized light, and collects light reflected from the MRAM element by the illumination light. The optical system 30 includes a light source 31, lenses L1 to L3, a polarizer 32, a mirror M1, an objective lens 33, and an analyzer 34. The optical system 30 may include other optical elements.

The light source 31 emits illumination light. The illumination light is, for example, laser light. The illumination light emitted from the light source 31 is converted by the polarizer 32 to include linearly polarized light. The illumination light including linearly polarized light is reflected by the mirror M1 and focused on the wafer WF by the objective lens 33. The mirror M1 is, for example, a non-polarizing beam splitter.

The objective lens 33 is used to image the pattern on the wafer WF, and is generally non-magnetic. If the wafer WF contains an MRAM element, the polarization angle of the linearly polarized light changes due to the magneto-optical Kerr effect.

Figure 11 is a diagram illustrating the magnetic characteristics of an MRAM element, where the horizontal axis indicates the external magnetic field and the vertical axis indicates the Kerr rotation angle. As shown in Figure 11, when the external magnetic field is increased from 0, the Kerr rotation angle increases. However, the Kerr rotation angle saturates when it reaches a certain value and does not change even if the external magnetic field is increased. Next, when the external magnetic field is decreased from the saturated state, the Kerr rotation angle decreases. Then, even if the external magnetic field is reduced to 0, the Kerr rotation angle remains. When the external magnetic field is further reduced, the Kerr rotation angle reaches a certain value and saturates. Therefore, it does not change even if the external magnetic field is reduced. When the external magnetic field is increased from the saturated state, the Kerr rotation angle increases. When the external magnetic field is increased and when the external magnetic field is reduced, the path of the Kerr rotation angle value is different. In this way, the Kerr rotation angle forms a hysteresis curve that follows a different route when the external magnetic field is increased and when the external magnetic field is reduced.

Figure 12 is a diagram illustrating the magnetic properties of an MRAM element, with the horizontal axis indicating the external magnetic field and the vertical axis indicating the Kerr rotation angle. Figure 12 also shows a schematic image including the polarization state of the MRAM element when the external magnetic field H is H1, H2, and H3. As shown in Figure 12, the image captured when the external magnetic field is gradually increased shows the brightness due to the different Kerr rotation angles for the external magnetic field H = H1, H2, and H3. There is a correlation between the Kerr rotation angle and the brightness detected by the detector 40. Therefore, the coercive force of each MRAM element (the magnetic field of the image of H2 in the above example) and its variation can be obtained from the image obtained by the detector 40. If the size of the MRAM element is smaller than the camera resolution or optical resolution, the average magnetic properties of the observation area are obtained.

The light reflected by the wafer WF passes through the objective lens 33 and mirror M1 and enters the analyzer 34. The analyzer 34 detects the change in the polarization angle of the linearly polarized light contained in the reflected light. The reflected light that passes through the analyzer 34 enters the detector 40.

4. Detector
The detector 40 detects the reflected light to obtain the pattern of the wafer WF. The detector 40 may include a line sensor 41. The line sensor 41 may include, for example, a TDI (Time Delay Integration). The detector 40 detects the reflected light when the position of the MRAM element in the first magnetic field is changed, and the reflected light when the position of the MRAM element in the second magnetic field is changed. For example, the detector 40 detects the reflected light when the position of the MRAM element in the first magnetic field is scanned in the first scan axis direction. The detector 40 also detects the reflected light when the position of the MRAM element in the second magnetic field is scanned in the second scan axis direction.

The inspection device 1 irradiates the wafer WF with illumination light that has been linearly polarized by the polarizer 32, and causes the reflected light to enter the detector 40 through the analyzer 34. The amount of light that enters the detector 40 through the analyzer 34 changes according to the polarization angle, so the magnetization distribution is imaged. By changing the magnetic field applied to the MRAM element, the magnetic characteristics of the MRAM element in the wafer WF can be measured from the distribution of polarization angles according to the magnetic field.

FIG. 13 is a plan view illustrating a wafer WF according to the first embodiment. As shown in FIG. 13, the wafer WF includes a plurality of die DIEs. Only the solid film of the perpendicular magnetization film before the die DIEs are formed may be inspected. The die DIE is, for example, a rectangle having short and long sides in the X-axis and Y-axis directions. The plurality of die DIEs are arranged on the wafer WF so as to have a spatially repeated periodicity in the X-axis and Y-axis directions. The die DIE includes a plurality of MRAM elements. The MRAM elements have storage areas arranged in an array with a repeated periodicity. The line sensor 41 acquires images in the forward direction while moving, for example, in the X-axis direction, across the plurality of die DIEs. After acquiring one row of images along the X-axis direction, the line sensor 41 moves in the Y-axis direction and again acquires one row of images along the X-axis direction from the reverse direction. When inspecting all the dies DIE on a wafer WF, images can be acquired in both the reverse and forward directions without gaps, including a few pixels for filtering and scan correction.

<5. Information Processing Section>
The information processing unit 50 processes the image of the reflected light detected by the detector 40. For example, the information processing unit 50 may be an information processing device such as a server device or a personal computer. The information processing unit 50 inspects the MRAM element for defects due to the magnetic field component in the vertical direction from a difference image between an image in the magnetic field component in one direction in the vertical direction in the first magnetic field and an image in the magnetic field component in the opposite direction. The information processing unit 50 also inspects the MRAM element for defects due to the magnetic field component in the in-plane direction from a difference image between an image in the magnetic field component in one direction in the in-plane direction in the second magnetic field and an image in the magnetic field component in the opposite direction.

<6. Details of the inspection device>
Next, details of the inspection device of embodiment 1 will be described. Fig. 14 is a configuration diagram illustrating details of the inspection device according to embodiment 1. As shown in Fig. 14, the inspection device 1 may further include devices W1 to W3 related to the transport of the wafer WF, members B1 to B4 related to the base of the inspection device 1, and a power source and control unit 60.

The devices W1 to W3 involved in transporting the wafer WF include a wafer transport robot W1, a pre-wafer alignment device W2, and a wafer supply cassette W3. The wafer transport robot W1 transports the wafer WF to be inspected from the wafer supply cassette W3 into the interior of the inspection device 1. The pre-wafer alignment device W2 corrects the rotation angle and shift of the wafer WF. After being adjusted by the pre-wafer alignment device PWA, the wafer WF is transported to the stage 10 of the inspection device 1.

The components B1 to B4 related to the base of the inspection device 1 include a stone base B1, an active vibration isolation table (Isolator) B2, a wedge B3, and a dispersion plate B4. The stone base B1 serves as a base on which components such as the stage 10 and the optical system 30 are placed. The active vibration isolation table B2 suppresses vibrations of components on the stone base B1. The wedge B3 adjusts the level of the stone base B1 and the active vibration isolation table B2. The dispersion plate B4 distributes the device load on the floor. The power supply and control unit 60 supplies power to the inspection device 1 and controls each part of the inspection device 1.

The optical system 30 may further include lenses L4 to L9, mirrors M2 to M4, and filters 35 to 36. The illumination light emitted from the light source 31 passes through the filter 35 via the lens L4, so that it contains a predetermined wavelength band. The illumination light that passes through the filter 35 is reflected by the mirror M2 via the lens L5. The illumination light reflected by the mirror M2 passes through the polarizer 32 via the lenses L1 and L2. The polarizer 32 converts the illumination light so that it contains linearly polarized light. The illumination light containing linearly polarized light is reflected by the mirror M1 and is focused on the wafer WF by the objective lens 33 via the lens L6. The mirror M2 is, for example, a non-polarizing beam splitter.

The reflected light reflected by the wafer WF passes through the objective lens 33, lens L6, and mirror M1, and enters the analyzer 34. The analyzer 34 functions as an analyzer that detects changes in the polarization angle of the linearly polarized light contained in the reflected light. The reflected light that passes through the analyzer 34 and lens L7 contains a predetermined wavelength band through the filter 36. The reflected light that passes through the filter 36 is reflected by the mirror M3 via the lens L8. The reflected light reflected by the mirror M3 enters the line sensor 41 via the lens L3. The AF sensor 37 is a member for focusing the wafer WF surface. The AF sensor 37 irradiates light onto the wafer WF through the mirror M4, captures the reflected light, and performs focus adjustment. The AF sensor 37 uses laser light that is longer or shorter than the wavelength of the illumination light and reflected light used in the optical system 30.

The detector 40 acquires the pattern of the wafer WF. The detector 40 may have multiple line sensors A1 and A2, and a review monitor 42. The multiple line sensors A1 and A2 are not limited to two, and may be three or more. The detector 40 may include, for example, a TDI (Time Delay Integration) sensor. The review monitor 42 detects the reflected light that has passed through the mirror M3 via the lens L9. The review monitor 42 may include a CCD (Charge-Coupled Device) sensor. The CCD sensor may be used for review. The optical path between the line sensors L1 and L2 and the review monitor 42 is switched by inserting the mirror M3.

<7. Testing Method>
Next, an inspection method will be described. Fig. 15 is a flow chart illustrating an inspection method for a wafer WF including an MRAM element according to the first embodiment. As shown in step S11 of Fig. 15, first, the wafer WF is placed on the inspection device 1. Specifically, the wafer transport robot W1 transports the wafer WF to be inspected from the wafer supply cassette W3 into the interior of the inspection device 1.

Next, as shown in step S12, the pre-wafer alignment device W2 corrects the rotation angle and shift of the wafer WF. After the wafer WF is adjusted by the pre-wafer alignment device W2, it is transferred to the stage 10 of the inspection device 1. Next, as shown in step S13, the wafer WF is aligned on the stage 10. For example, the wafer WF is aligned using a laser interferometer 14.

Next, as shown in step S14, the magnetic properties in the vertical direction of the MRAM element are inspected. Also, as shown in step S15, the magnetic properties in the in-plane direction of the MRAM element are inspected. Note that the order of steps S14 and S15 is not limited to this. After inspecting the magnetic properties in the in-plane direction of the MRAM element in step S14, the magnetic properties in the vertical direction of the MRAM element may be inspected in step S15. Next, as shown in step S16, after the inspection, the wafer WF is removed from the stage 10.

Figure 16 is a flow chart illustrating a method for inspecting the magnetic properties in the vertical direction of an MRAM element according to the first embodiment. As shown in step S21 of Figure 16, a first magnetic field having a magnetic field component in the vertical direction is formed. For example, currents in opposite directions are applied to the coils 21a and 21b of the electromagnets 20a and 20b that face each other in the X-axis direction. On the other hand, no current is applied to the two coils 21c and 21d of the electromagnets 20c and 20d that face each other in the Y-axis direction. In this way, a first magnetic field having a magnetic field component in a direction perpendicular to the stage surface 13 is generated using multiple electromagnets 20.

Next, as shown in step S22, the wafer WF on the stage 10 is moved. Specifically, the wafer WF is scanned along the α-axis, which is the first scan axis. When moving within the first magnetic field, the α-axis direction, which is the first scan axis, is the X-axis direction. In this way, the MRAM element is scanned within the first magnetic field.

Next, as shown in step S23, the detector 40 acquires an image of the magneto-optical effect in the MRAM element of the wafer WF. Specifically, the polarization angle due to the magneto-optical effect of the MRAM element is measured. Then, from the difference images before and after the magnetic polarity change during the scan, a defect inspection is performed using a first magnetic field having a vertical magnetic field component. In this manner, the MRAM element is inspected.

Next, as shown in step S24, it is determined whether to end the process. If there are still MRAM elements to be tested (No), the process returns to step S21 and steps S21 to S24 are repeated. On the other hand, if there are no MRAM elements to be tested (Yes), the process ends.

17 is a flow chart illustrating an example of a method for inspecting the in-plane magnetic properties of an MRAM element according to the first embodiment. As shown in step S31 of FIG. 17, a second magnetic field having an in-plane magnetic field component is formed. For example, when an XYZ orthogonal coordinate system is fixed to the electromagnets 20, the coils 21a and 21b of the electromagnets 20a and 20b facing each other in the X-axis direction are applied with a current having the same predetermined direction. On the other hand, the coils 21c and 21d of the electromagnets 20c and 20d facing each other in the Y-axis direction are applied with a current having an opposite direction to that of the coils 21a and 21b. In this way, a second magnetic field having an in-plane magnetic field component parallel to the stage surface 13 is generated. In this embodiment, the electromagnets 20 are rotated 45° in a horizontal plane, and the second scan axis is aligned with the X-axis of the XYZ orthogonal coordinate system fixed to the stage 10.

Next, as shown in step S32, the wafer WF on the stage 10 is moved. Specifically, the wafer WF is moved along the α-axis, which is the second scan axis. In this way, the MRAM element is moved within the second magnetic field.

Next, as shown in step S33, the detector 40 acquires an image of the magneto-optical effect in the MRAM element of the wafer WF. Specifically, the polarization angle due to the magneto-optical effect of the MRAM element is measured. In this manner, the MRAM element is inspected.

Next, as shown in step S34, it is determined whether to end the process. If there are still MRAM elements to be tested (No), the process returns to step S31 and steps S31 to S34 are repeated. On the other hand, if there are no MRAM elements to be tested (Yes), the process ends.

Next, the effects of this embodiment will be described. In order to inspect defects in MRAM elements, the inspection device 1 of this embodiment can form a first magnetic field in which the orientation of the vertical magnetic field component changes from a first orientation to a second orientation depending on the position on the stage surface 13, and a second magnetic field in which the orientation of the in-plane magnetic field component changes from a third orientation to a fourth orientation depending on the position on the stage surface 13. Therefore, it is possible to detect magnetic characteristics not only in the easy axis direction but also in the hard axis direction, and the detection accuracy of the MRAM characteristics can be improved.

The inspection device of Patent Document 1 detects defects in MRAM elements by scanning the MRAM elements in a gradient magnetic field formed by an electromagnet including two coils. The inspection device of Patent Document 1 measures saturation magnetization characteristics by applying a magnetic field in the easy axis direction, which is a magnetic field component perpendicular to the gradient magnetic field. In this way, the inspection device of Patent Document 1 realizes wafer defect inspection. However, in order to grasp the characteristics of MRAM elements, it is necessary to inspect not only the characteristics in the easy axis direction, which is the direction in which magnetization is easy, but also the magnetization characteristics in the hard axis direction. In particular, the anisotropic magnetic field in the hard axis direction needs to be inspected without changing the magnetic characteristics in the easy axis direction, whose characteristics change with a small magnetic field. The inspection device of Patent Document 1 cannot detect the magnetic characteristics in the hard axis direction, and therefore cannot improve the detection accuracy of the MRAM characteristics.

In contrast, the inspection device 1 of this embodiment can detect the magnetization characteristics in the easy axis direction without changing the magnetization characteristics in the hard axis direction, and can detect the magnetization characteristics in the hard axis direction without changing the magnetization characteristics in the easy axis direction. This improves the detection accuracy of the MRAM characteristics.

The inspection device 1 of this embodiment performs inspection by moving the MRAM element within the first magnetic field and the second magnetic field. In contrast, a method in which the magnetic field is changed by fixing the stage 10 and changing the current flowing through the electromagnet requires time to change the current. Also, for highly sensitive detection, the exposure time of the camera needs to be long. In particular, when inspecting the entire surface of the wafer WF, it is necessary to repeat measurements in which each MRAM element on the wafer WF is moved to the inspection position and the current flowing through the electromagnet is changed. Therefore, an increase in inspection time becomes a problem.

In this embodiment, the current flowing through the coil 21 of the electromagnet 20 does not need to be changed during testing, so the time required to change the current can be reduced. In addition, the magnetic properties can be detected by moving the MRAM element, so the exposure time of the detector 40 can be reduced.

(Embodiment 2)
Next, an inspection device according to embodiment 2 will be described. The inspection device 1 of embodiment 1 described above rotates the multiple electromagnets 20 by 45° to scan the MRAM elements after inspecting the magnetic properties in the vertical direction. On the other hand, the inspection device of this embodiment rotates the stage 10 by 45° to scan the MRAM elements after inspecting the magnetic properties in the vertical direction.

Figure 18 is a flow chart illustrating a method for inspecting the magnetic properties in the vertical direction of an MRAM element according to the second embodiment. As shown in step S41 of Figure 18, a first magnetic field having a magnetic field component in the vertical direction is formed. For example, currents in opposite directions are applied to the coils 21a and 21b of the electromagnets 20a and 20b that face each other in the X-axis direction. On the other hand, no current is applied to the two coils 21c and 21d of the electromagnets 20c and 20d that face each other in the Y-axis direction. In this way, a first magnetic field having a magnetic field component in a direction perpendicular to the stage surface 13 is generated using multiple electromagnets 20.

Next, as shown in step S42, the wafer WF on the stage 10 is moved. Specifically, the wafer WF is scanned along the α-axis, which is the first scan axis. When moving within the first magnetic field, the α-axis direction, which is the first scan axis, is the X-axis direction. In this way, the MRAM element is scanned within the first magnetic field.

Next, as shown in step S43, the detector 40 acquires an image of the magneto-optical effect in the MRAM element of the wafer WF. Specifically, the polarization angle due to the magneto-optical effect of the MRAM element is measured. Then, from the difference images before and after the change in magnetic field polarity during the scan, a defect inspection is performed using a first magnetic field having a vertical magnetic field component. In this manner, the MRAM element is inspected.

Next, as shown in step S44, it is determined whether to end the process. If there are still MRAM elements to be tested (No), the process returns to step S41 and steps S41 to S44 are repeated. On the other hand, if there are no MRAM elements to be tested (Yes), the process ends.

19 is a flow chart illustrating an example of a method for inspecting the in-plane magnetic properties of an MRAM element according to the second embodiment. As shown in step S51 of FIG. 19, a second magnetic field having an in-plane magnetic field component is formed. For example, when an XYZ orthogonal coordinate system is fixed to a plurality of electromagnets 20, currents of the same predetermined direction are applied to the coils 21a and 21b of the electromagnets 20a and 20b facing each other in the X-axis direction. On the other hand, currents of the opposite direction to the coils 21a and 21b are applied to the coils 21c and 21d of the electromagnets 20c and 20d facing each other in the Y-axis direction. In this way, a second magnetic field having an in-plane magnetic field component parallel to the stage surface 13 is generated. In this embodiment, the stage 10 is rotated 45° in the horizontal plane, and the second scan axis is aligned with the X-axis of the XYZ orthogonal coordinate system fixed to the stage 10.

Next, as shown in step S52, the wafer WF on the stage 10 is moved. Specifically, the wafer WF is moved along the α-axis, which is the second scan axis. In this way, the MRAM element is moved within the magnetic field.

Next, as shown in step S53, the detector 40 acquires an image of the magneto-optical effect in the MRAM element of the wafer WF. Specifically, the polarization angle due to the magneto-optical effect of the MRAM element is measured. In this manner, the MRAM element is inspected.

Next, as shown in step S54, it is determined whether to end the process. If there are still MRAM elements to be tested (No), the process returns to step S51 and steps S51 to S54 are repeated. On the other hand, if there are no MRAM elements to be tested (Yes), the process ends.

According to this embodiment, the moving part 11 of the stage 10 is rotated instead of the multiple electromagnets 20. This makes it possible to detect the magnetization characteristics of the MRAM element when a magnetic field is applied in the in-plane direction. Therefore, it is possible to suppress positional deviations caused by the movement of the multiple electromagnets 20 and the optical system 30.

The present invention is not limited to the above-described embodiments, and can be modified as appropriate without departing from the spirit of the invention. For example, combinations of the configurations of embodiments 1 to 4 are also within the scope of the technical concept of the present invention.

1 Inspection apparatus 10 Stage 11 Moving part 12 Main body part 13 Stage surface 14 Laser interferometer 20, 20a, 20b, 20c, 20d Electromagnet 21, 21a, 21b, 21c, 21d Coil 22, 22a, 22b, 22c, 22d Yoke 23, 23a, 23b, 23c, 23d Vertical part 24, 24a, 24b, 24c, 24d In-plane part 25 Connection plate 30 Optical system 31 Light source 32 Polarizer 33 Objective lens 34 Analyzer 35, 36 Filter 37 AF sensor 40 Detector 41 Line sensor 42 Review monitor 50 Information processing unit 60 Power supply and control unit A1, A2 Line sensor B1 Stone surface plate B2 Active vibration isolation table B3 Wedge B4 Dispersion plates L1, L2, L3, L4, L5, L6, L7, L8, L9 Lenses M1, M2, M3, M4 Mirror W0 Inspection surface W1 Wafer transport robot W2 Pre-wafer alignment device W3 Wafer supply cassette WF Wafer

Claims (7)

a stage having a stage surface on which a magnetoresistive memory element is fixed;
a plurality of electromagnets that generate a first magnetic field, the orientation of a magnetic field component in a vertical direction perpendicular to the stage surface changes from a first orientation to a second orientation opposite to the first orientation depending on a position on the stage surface, and a second magnetic field, the orientation of a magnetic field component in an in-plane direction parallel to the stage surface changes from a third orientation to a fourth orientation opposite to the third orientation depending on the position on the stage surface;
an optical system that illuminates the magnetoresistive memory element with illumination light including polarized light and collects light reflected by the magnetoresistive memory element from the illumination light;
a detector for detecting the reflected light when the position of the magnetoresistive memory element is changed in the first magnetic field and the reflected light when the position of the magnetoresistive memory element is changed in the second magnetic field;
An inspection device equipped with When the position of the magnetoresistive memory element is changed so as to change from the first orientation to the second orientation within the first magnetic field, the magnetic field component perpendicular to the first scanning direction and the perpendicular direction is 0.
2. The inspection device according to claim 1. When the position of the magnetoresistive memory element is changed so as to change from the third orientation to the fourth orientation within the second magnetic field, the magnetic field component in the second scanning direction and the magnetic field component in the perpendicular direction are zero.
2. The inspection device according to claim 1. the plurality of electromagnets includes at least four electromagnets including a first electromagnet, a second electromagnet, a third electromagnet, and a fourth electromagnet;
the first electromagnet includes a first coil wound in a predetermined direction around a first vertical portion of an L-shaped first yoke having a first vertical portion extending in the vertical direction and a first in-plane portion extending in the in-plane direction,
the second electromagnet includes a second coil wound in the predetermined direction on a second vertical portion of an L-shaped second yoke having a second vertical portion extending in the vertical direction and a second in-plane portion extending in the in-plane direction,
the third electromagnet includes a third coil wound in the predetermined direction around a third vertical portion of an L-shaped third yoke having a third vertical portion extending in the vertical direction and a third in-plane portion extending in the in-plane direction,
the fourth electromagnet includes a fourth coil wound in the predetermined direction on a fourth vertical portion of an L-shaped fourth yoke having a fourth vertical portion extending in the vertical direction and a fourth in-plane portion extending in the in-plane direction,
The first in-plane portion and the second in-plane portion extend in one direction, and an end portion of the first in-plane portion and an end portion of the second in-plane portion face each other in the one direction,
The third in-plane portion and the fourth in-plane portion extend in another direction perpendicular to the one direction, and the end portion of the third in-plane portion and the end portion of the fourth in-plane portion face each other in the other direction,
the first magnetic field is generated by passing a current in a fifth direction through the first coil, passing the current in a sixth direction opposite to the fifth direction through the second coil, and setting the current flowing through the third coil and the fourth coil to zero;
The second magnetic field is generated by passing the current in the fifth direction through the first coil and the second coil and passing the current in the sixth direction through the third coil and the fourth coil.
2. The inspection device according to claim 1. The detector comprises:
Detecting the reflected light when the position of the magnetoresistive memory element in the first magnetic field is scanned in the one direction;
detecting the reflected light when the position of the magnetoresistive memory element in the second magnetic field is scanned in a direction at an angle of 45° to the one direction and the other direction;
5. The inspection apparatus according to claim 4. An information processing unit that processes an image of the reflected light detected by the detector is further provided.
The information processing unit includes:
inspecting the magnetoresistive memory element for defects caused by the magnetic field component in the perpendicular direction from a difference image between the image in the magnetic field component in the first direction and the image in the magnetic field component in the second direction;
2. The inspection device according to claim 1. An information processing unit that processes an image of the reflected light detected by the detector is further provided.
The information processing unit includes:
inspecting the magnetoresistive memory element for defects caused by the magnetic field component in the in-plane direction from a difference image between the image in the magnetic field component in the third orientation and the image in the magnetic field component in the fourth orientation;
2. The inspection device according to claim 1.

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