JPH063721B2 - Scanning electron microscope - Google Patents

Description

The present invention relates to a scanning electron microscope, and more particularly to a scanning electron microscope suitable for observing a semiconductor wafer sample or the like.

[Background of the Invention]

As a sample stage of a conventional scanning electron microscope, usually,
It has a 5-axis (X, Y, Z, T (inclination), R (rotation)) mechanism so that various samples can be observed from various angle directions. When observing a sample in which patterns (chips) of the same type are arranged in order, such as a wafer, in a rotated or rotated / tilted state, the corresponding part of another chip corresponding to the currently observed part is moved to the sample stage. It was difficult to find it by moving X / Y, and this point was not taken into consideration.

Further, since a large field of view movement occurs with the rotation of the sample, when observing a certain sample position from another angle (assuming that the sample is tilted), the same portion is moved to the X / X axis of the sample stage.
It was difficult to search by Y movement, and no consideration was given to this point.

[Object of the Invention]

An object of the present invention is to observe a sample currently being observed when rotating or rotating / tilting a sample in which patterns (chips) of the same kind are regularly arranged, such as a semiconductor wafer having a pattern printed thereon. Another object of the present invention is to provide a scanning electron microscope which can quickly and easily find the corresponding portion of another chip corresponding to.

[Outline of Invention]

The present invention is a sample stage coordinate system (sample stage drive system)
The coordinate system x, y fixed to the sample is adopted for X, Y, and the stage drives X, Y are controlled so that the sample is always moved in the sample coordinate system x, y.

Example of Invention

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the basic concept of the sample stage 8 of the scanning electron microscope. The sample 2 is placed on the R (rotating) table 3 and can rotate (rotate). R stand 3 to Y move stand 4, Y
The moving table 4 is on the T (tilt) table 5, the T table 5 is on the X moving table 6, and
The moving table 6 is placed on the Z moving table 7. Normally, R stand 3
Since the center axis of rotation of is located at the mechanical center of the R table 3 itself, in the image observation of the scanning electron microscope by irradiation of the electron beam 1, a large field of view movement (image shift) occurs with respect to simple sample rotation. . On the other hand, since the tilt center axis of the T table 5 is placed so as to coincide with the irradiation point of the electron beam 1, in the image observation of the scanning electron microscope by the irradiation of the electron beam 1,
The visual field does not move (image shift) with respect to the sample tilt.
It should be noted that the sample stage with a small amount of X, Y movement is generally driven manually, but a sample stage with a large amount of movement for observing a large-diameter sample such as a semiconductor wafer over the entire sample area. In general, the drive is usually performed by a motor or the like. Recently, although a motor drive is possible for all five axes (X, Y, Z, T, R) for this type of sample stage, stage control is performed in the sample stage coordinate system. In FIG. 1, the drive motor system and the control system are omitted.

The semiconductor wafer sample 2 ′ is mounted on the sample stage 8, but it is usual to first set the orientation flat of the semiconductor wafer sample 2 ′ parallel to the moving direction of the X moving table 6. This is because when the chip array of the semiconductor wafer sample 2'is assigned, it is usually done in this way. Second
The figure shows the state of the semiconductor wafer sample 2'as seen from the arrow P in FIG. If the moving direction of the X-moving table 6 and the orientation flat (correctly, chip arrangement) completely match, the sample stage coordinate system X, Y and the sample coordinate system x, y match as shown in this figure. There is. In this case, if the stage is driven by X or Y of the sample stage coordinate system (sample stage drive system), the observation corresponding points on the chip of the semiconductor wafer sample 2'will appear one after another.

Next, consider the case where the sample 2 ′ is rotated by the angle θ. This is shown in FIG. Between the sample stage coordinate system X, Y and the sample coordinate system x, y The relationship is established. In this case, if it is attempted to move Δx or Δy in the sample coordinate system x, y so that the observation corresponding points on the chip of the semiconductor wafer sample 2 ′ appear one after another, the sample stage drive ΔX, ΔY is Respectively Or It should be done.

That is, the operator of the scanning electron microscope uses the sample coordinate system x,
It is extremely easy to observe the semiconductor wafer sample by instructing the sample movement with y. In this case, the actual movement of the sample stage should satisfy the formula (2) or (3) with respect to the Δx and Δy drive commands. It is only necessary to be controlled automatically.

The actual operation of driving the sample stages X and Y in searching for the observation corresponding point on the chip of the semiconductor wafer sample by the sample coordinate system x and y commands has been described above, but the sample coordinate system x and y should be adopted. As a result, another important point comes out. This is described below.

The operator of the scanning electron microscope usually manages the coordinates of five axes, but it is extremely convenient to manage the movement within the sample plane in the sample coordinate system as described above. In this case, if the visual field movement (image shift) occurs when the sample rotation is executed, it means that the observation point of the sample is shifted, that is, the observation point is moved by the sample rotation, for example, the coordinate point (in the sample coordinate system). Since x ₁ , y ₁ ) is changed to (x ₂ , y ₂ ), the observation coordinate point (x, y) in the sample coordinate system is also changed by a simple R (rotation) control command. This means that the independence of each axis is lost, which is very inconvenient for coordinate management. In other words, in the management of the five axes, the x and y coordinate values change with a simple R control command, which is a problem from the standpoint of maintaining the independence of each axis. In this case, if the sample stage coordinate system X, Y and the sample coordinate system x, y are rotated by the angle θ, and if it is attempted to rotate by Δθ by the R control, the observation point in the current sample coordinate system ( x, y),
The correction drive ΔX and ΔY of the sample stage are It should be done.

That is, in response to the Δθ (rotation) command from the operator of the scanning electron microscope, not only the actual movement of the sample stage is Δθ rotation, but also the X and Y drives are automatically controlled so as to satisfy equation (4). That's a good translation. As a result, the coordinate value of the sample coordinate system does not change due to the R control command, that is, the observation of the center of the visual field can be observed in the observation of the scanning electron microscope.

FIG. 4 shows the control of the sample coordinate system according to the embodiment of the present invention. It is a sample stage control system. 5 axes (x, y, Z, T, R)
A command from the operation panel 9 for giving a control command is given to the computer 10, and this computer 10 performs X, Y drive according to the equation (2) or (3) for x or y drive, and R drive for R control. Besides, X, Y drive by formula (4), T
The commands for T and Z driving are read as they are and the commands for T and Z driving are issued. This command causes the driver circuit 1
1, the output is supplied to the drive system (for example, a motor) of the sample stage 8 and the sample 2 mounted on the sample stage 8 is driven. Of course, this maintains the independence of the five axes.

The above is the case where the semiconductor wafer sample 2'is ideally mounted on the sample stage. Actually, the chip arrangement of the semiconductor wafer sample 2'is completely parallel (or perpendicular) to the X and Y directions of the sample stage. ) Is usually not. Further, the rotation center axis of the sample stage does not always coincide with the center of the semiconductor wafer sample 2 '. This is shown in FIG. 5 (since the P-view views in FIGS. 2 and 3 are difficult to understand, they are drawn so that X and Y of the sample stage are horizontal and vertical). First, the preset angle error φ of the chip arrangement of the semiconductor wafer sample 2'with respect to the X movement direction of the sample stage is obtained. From the chips of the semiconductor wafer sample 2 ', select those that are parallel to the orientation flat and are as far apart as possible. Chips 12 and 13 are shown in the figure.
Image observation of a certain part of the chip 12 by driving the sample stage,
Its coordinate point is (X ₁ , Y ₁ ). On the other hand, chip 1
An image of a portion corresponding to 3 is observed by driving the sample stage, and its coordinate point is (X ₂ , Y ₂ ). As a result, the rotation angle of the sample coordinate system x, y with respect to the sample stage coordinate system X, Y Is required. Next, the origin of the sample coordinate system, that is, the center of rotation,
The amount of deviation (a, b) from the origin of the sample stage coordinate system is obtained. First, since the angle error φ of the preset is found from the equation (5), the sample 2 ′ is rotated in the opposite direction by the angle φ so that the sample coordinate system x, y and the sample stage coordinate system X, Y become parallel. To do. At this time, certain points on the sample 2 ', for example, chips coordinate points of a certain point of 12 _(X 3, _{Y 3)} and (X
₀ , Y ₀ ). Since the two coordinate systems are parallel, the origin misalignment of the two axes is a and b. Becomes Next, the sample is rotated 90 ° counterclockwise.
The coordinate points of the point of interest are (X ₄ , Y ₄ ) and (x ₁ ,
y ₁ ). At this time, note that x ₁ = x ₀ , y ₁ = y ₀ because the sample coordinate system x, y is multiplied on the sample itself, and the formula for coordinate rotation including the origin deviation At θ = 90 ° To get The equation (6) can also be obtained by setting θ = 0 ° in the equation (7).

From equations (6) and (8) And the origin deviation amount (a, b) is obtained.

Since the preset angle error φ and the preset origin deviation amount (a, b) were found, the sample 2 ′ was rotated in the opposite direction by the angle φ to make the sample coordinate system and the sample stage coordinate system parallel, and then the further amount The sample stage coordinate system is virtually translated by (a, b) to mathematically match the origin of the sample stage coordinate system with the origin of the sample coordinate system. Considering this as the initial setting, that is, as shown in FIG. 2, this is the case where the semiconductor wafer sample 2'is ideally mounted on the sample stage, and the detailed description of the present invention is valid.

According to one embodiment of the present invention, the movement command can be given by the sample coordinate system, and the observation corresponding point on the semiconductor wafer sample can be searched very easily, and the visual field center can be rotated.

〔The invention's effect〕

According to the present invention, since a sample driving command can be issued by the sample coordinate system, a sample in which patterns of the same type (chips) are arranged in an orderly manner is rotated or rotated / tilted like a semiconductor wafer having a pattern printed on it. When observing with, there is an effect that it is possible to quickly and easily find a corresponding portion of another chip corresponding to the portion currently being observed.

Further, according to the present invention, the visual field movement does not occur even if rotation is applied during observation of a portion other than the rotation center, so that it becomes possible to perform image observation of the visual field center rotation.

[Brief description of drawings]

FIG. 1 is a basic conceptual diagram of a sample stage of a scanning electron microscope, and FIG. 2 is a semiconductor wafer sample preset on the sample stage and a sample stage coordinate system (sample stage drive system) viewed from the arrow P of FIG. X, Y and sample coordinate system x, y
And FIG. 3 is a diagram showing the relationship between both coordinate systems when the sample of FIG. 2 is rotated by an angle φ, and FIG. 4 is a sample stage which is an embodiment of the present invention. FIG. 5 is a block diagram showing the control system, and FIG. 5 is a diagram showing the relationship between both coordinate systems when the sample is ideally not preset as shown in FIG. DESCRIPTION OF SYMBOLS 1 ... Electron beam, 2 ... Sample, 2 '... Semiconductor wafer sample, 8 ... Sample stage, 9 ... Operation panel, 10 ... Computer, 11 ... Driver circuit, 12, 13
… Chip.

Claims (1)

[Claims] 1. At least functions of X movement, Y movement, and rotation (R), the coordinates of the center of rotation on the sample stage coordinate system change with X movement and Y movement, and the rotation angle changes. In a scanning electron microscope equipped with a sample stage in which the relative angle between the sample coordinate system and the sample stage coordinate system changes accordingly, as a function of the rotation angle of the sample stage and the desired movement amount Δx, Δy of the sample on the sample coordinate system. The scanning electron microscope further comprises means for driving and controlling the sample stage so that the sample moves on the sample coordinate system by the desired movement amounts Δx and Δy.