JPH03133039A - Electron beam optical axis adjusting method - Google Patents

Abstract

PURPOSE:To measure pattern size highly precisely while setting an optical axis to be rectangular to a sample by detecting inclination of an electron beam optical axis based on relative transfering volume of a first and a second electron beam detecting means against the electron beam optical axis and correcting the inclination of the electron beam optical axis by driving a deflecting means based on the detected value. CONSTITUTION:Since inclination of an electron beam optical axis 20 in x- direction (y-direction) against a transfering plane of a stage 4 is known based on electric current supplied to an auxiliary deflecting coil 6 and deflecting magnification of the auxiliary deflecting coil 6, the volume of inclination is corrected by a second deflecting coil installed in an electron optical lens-barrel. Ideally, the electron beam should cross rectangularly to a stage transfering plane when it is observed from x-direction of y-direction at the time of correction, but considering errors of deflecting magnification, etc. the correction procedure is repeated 2-3 times and in both x- and y-directions. As a result, the electron beam is injected rectangularly against the sample stage 4 and right information of pattern shape and size is obtained. In this way, precise measuring of a pattern is achieved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention uses an electron beam to accurately measure the dimensions of a fine pattern on a mask that serves as an original when printing circuits such as ICs and LSIs onto a wafer using lithography. It relates to a device for.

[Prior Art] Conventionally, the electron beam optical axis in this type of length measuring machine was set as shown in FIG. 1 is an electron gun, 2 is a condenser lens, 4 is a sample stage, 4a is a sample, 5a and 5b are a first deflection system, 6 is a second deflection system, 7 is a sensor that detects secondary electrons and reflected electrons, 8 is a deflection voltage generator, 9 is a display, 10 is a voltmeter to know the amount of deflection, 11.12 is A
/D converter and display element, R1 to R5 are voltage dividing resistors. The electron beam generated from the electron gun 1 is focused by a condenser lens 2, the electron beam is deflected in two stages by first deflection systems 5a and 5b so that it passes through the center of the objective lens 3, and then the electron beam is focused by a second deflection system so as to pass through the center of the objective lens 3. The beam is deflected perpendicular to the surface and irradiated onto the sample, allowing the shape and dimensions of the sample to be measured from changes in the amount of secondary electrons and reflected electrons generated.

The ratio between the two-stage deflection of the first deflection system and the deflection amount of the second deflection system is determined by resistors R1 to R5, and these values are determined based on ideal design values.

[Problems to be Solved by the Invention] However, in reality, the optical axis of the electron optical column and the plane in which the sample stage moves are not always perpendicular to each other, and various assembly errors, mechanical changes over time, and problems with the electron optical column may occur. Due to beam drift caused by contamination within the sample stage, the moving surface of the sample stage and the electron beam have a certain angle with respect to the perpendicular, and this angle is not constant and detection is difficult. If the beam and the sample surface are not perpendicular to each other in this way, there is a problem that when measuring the line width of a pattern, the pattern appears thicker by the inclination angle Δ, as shown in FIG. In addition, in order to obtain information on the cross-sectional shape, for example, if the inclination angle of the edge of a pattern is measured from the amount of deflection when the electron beam is deflected so that the optical axis of the electron beam is parallel to the edge surface of the pattern, As shown in FIG. 7, although the actual edge inclination angle is φ, it is detected as if it were φ1 and φ2. In other words, there was a problem in that the pattern appeared to be tilted. Furthermore, since the inclination of the beam optical axis varies arbitrarily depending on the measurement time, the measurement conditions are no longer constant and there is a problem that the measured values are not reproducible.

The present invention has been made in view of the above-mentioned drawbacks of the prior art, and an object of the present invention is to provide an electron beam dimension measuring instrument that enables highly accurate measurement by keeping the optical axis orthogonal to the sample surface during measurement. .

[Means and Effects for Solving the Problems] According to the invention, at least three sets of reference planes are arranged shifted in the direction of the electron beam optical axis from a reference plane perpendicular to the plane on which the sample stage moves (reference plane). an electron beam detection element divided into at least two parts; a reference provided within these elements at a known distance from the vertical reference; means for aligning the reference with the electron beam optical axis; A means for measuring the inclination of the electron beam optical axis with respect to the stage movement plane when the reference is aligned with the electron beam optical axis, and a means for rotating the relative position of the electron beam optical axis and the sample stage at least around the X axis or Y@. By providing this, the electron beam optical axis is always perpendicular to the plane of movement of the sample stage.

First and second electron beam detection means are provided at a predetermined distance apart along the electron beam irradiation direction, and after the first detection means and the electron beam are aligned, the second detection means and the electron beam are aligned. let The inclination of the electron beam is detected based on the amount of movement in this alignment operation. The electron beam irradiation direction is corrected based on this detected value.

[Example] 1 and 2 show an embodiment of the invention.

1 is an electron gun, 2 is a condenser lens, 3 is an objective lens,
4a is a sample, 4 is a sample stage, 5x, 5y are deflection coils, 6 is an auxiliary deflection coil, 7ax, 7bX is a first electron beam detection element for adjusting the optical axis in the X direction, 8ax, 8b
x is a second electron beam detection element for adjusting the optical axis in the X direction.

The electron beam detection element is similarly provided in the X direction. 1
0 is a mirror for measuring the position of the sample stage; 11 is a half mirror; 12 is a laser light source; these constitute a laser interferometer. When the sample stage 4 has two vertical axes, it can move in the xyx directions to measure pattern dimensions in the xy plane. The sample stage 4 is provided with references 4vx and 4vy perpendicular to the sample moving direction. The vertical reference 4vx is a plane perpendicular to the xy plane of the sample stage and also perpendicular to the X axis of the sample stage, and the vertical reference 4vy is a plane perpendicular to the xy plane of the sample stage and also perpendicular to the y axis of the sample stage. It is. The perpendicularity of these surfaces is guaranteed by machining accuracy with reference to the X or X-direction guide surface of the sample stage. First electron beam detection element 7a
x.

7bx is a plane electrode, and an ammeter is connected to it so that the current when irradiated with an electron beam can be detected. Second
As shown in the figure, the edges of the electrodes on both hands 7axe and 7bx
e (or 7aye, 7bye) constitutes a slit perpendicular to the X glaze (or y axis). Also 7a
x, lower surface of 7bx 7axb, 7bxb (7ay
b.

7byb) is installed so that it is almost flush with the sample surface. 7axe, 7bxe (or 7aye,
7bya) is the vertical reference 4vx (or 4vy)
The 7axe and 7bxe are installed at a known distance with an accuracy of 0.01 mm or less, and the gap between the 7axe and 7bxe is set to about 0.1 mm. The second electron beam detection element 8 is disposed offset by about 60 mm in the direction of the electron beam optical axis. 8ax, 8b
x is a plane electrode, to which an ammeter is connected so that the current can be detected when the electron beam is irradiated. Both edges 8axe, 8bxe (or 8aye, 13b
ye) constitutes a slit perpendicular to the X axis (or y@). Edge 8axe, 8bxe (or 8aye, 8bye) is vertical reference 4vx (or 4v
7axe7bxe with an accuracy of 0.01mm or less from
The gap between 8axe and 8bxe is set to about 0.1 mm. Further, the auxiliary deflection coil can scan the electron beam in the X direction (X direction) with a known deflection magnification (sensitivity).

In the above configuration, when power is supplied to the electron gun 1, condenser lens 2, deflection coil 5, and objective lens 3 to focus the electron beam on the sample surface, the electron beam optical axis 20 is perpendicular to the moving plane of the sample stage. Suppose it wasn't. First, in order to make the electron beam optical axis 20 perpendicular to the X glaze, the stage is moved in the X direction, and the X coordinate of the electron beam optical axis and the X coordinate of the center of the first electron beam detection element are roughly matched. Next, move the stage in the X direction and set the X coordinates of the electron beam optical axis and 7ax and 7bx.
(or 7ay, 7bY), the X coordinates of the centers of the first electron beam detecting elements are made to roughly match. Then 7ax, 7bx (or 7ay, 7by
) so that both become zero, that is, the electron beam is 7ax, 7bx (or 7ay, 7
The stage is moved in the X direction so as to pass through the slit between

In other words, by dividing the first electron beam detection element into two and measuring the current irradiated to each element, the reference or slit in the element can be aligned with the electron beam optical axis. . Next, check the currents from 8ax, 8bx (or 8ay, 8by) and make sure that both are zero, that is, the electron beam is 8ax, 8bx
(or 8ay, 8by), an alternating current is supplied to the auxiliary deflection coil 6 so as to pass through the slit I.

At this time, the inclination of the electron beam optical axis in the X direction (X direction) with respect to the moving surface of the stage can be determined from the current value supplied to the auxiliary deflection coil 6 and the deflection magnification of the auxiliary deflection coil 6. This amount is now corrected by a second deflection coil provided in the electron optical lens barrel. Ideally, at this point, the electron beam should be perpendicular to the stage movement plane when viewed from the X direction or from the X direction. However, considering the error in deflection magnification, etc., the above procedure 2.
Repeat ~3 times. This is done in both the X direction and the X direction. As a result, the electron beam will be incident perpendicularly to the sample stage, making it possible to obtain accurate information regarding the shape and dimensions of the pattern.

Further, as a modification of this embodiment, the function of the auxiliary deflection coil 6 can be mechanically realized. In other words, after making the electron beam pass through the slit made up of 7axe and 7bxe, we mechanically move 8ax and 8bx so that the electron beam passes between 8ax and 8bx, and the amount of movement and From the tangent to the distance in the optical axis direction of 7ax and 8ax, the X direction of the electron beam optical axis (
(X direction) is detected and corrected by a second deflection coil provided in the electron optical lens barrel.

3 and 4 show other embodiments of the invention. 1 is an electron gun, 2 is a condenser lens, 3 is an objective lens, 4a
is the sample, 4 is the sample stage, 5x, 5y are the deflection coils,
6 is an auxiliary deflection coil, 7ax and 7bx are first electron beam detection elements for adjusting the optical axis in the X direction, 8x is a second electron beam detection element for adjusting the optical axis in the X direction, 9ax is an electrode, and 9bx is an insulating layer. It is. The electron beam detection element is similarly provided in the X direction. 10 is a mirror for measuring the position of the sample stage; 11
The half mirror 12 is a laser light source, and these constitute a laser interferometer. When the vertical axis is the Z axis, the sample stage can be moved in the xyx directions '8 to measure pattern dimensions in the xy plane. Sample stage 4
References 4νx and 4vy are provided perpendicular to the sample movement direction. The vertical reference 4vx is the xy of the X sample stage.
The vertical reference 4vy is a plane perpendicular to the xy plane of the sample stage and also perpendicular to the y axis of the sample stage. The perpendicularity of these surfaces is guaranteed by machining accuracy with reference to the X or X-direction guide surface of the sample stage.

The first electron beam detection elements 7ax and 7bx are planar electrodes, and an ammeter is connected thereto so that the current can be detected when the electron beam is irradiated. As shown in Figure 4, the X axis (or y
It forms a slit perpendicular to the axis). Also 7ax,
The lower surfaces 7axb and 7bxb of 7bx are installed so that they are almost flush with the sample surface. Edge 7axe, 7b
xe is 0.0 from the vertical reference 4VX (or 4vy).
Installed at a known distance with an accuracy of less than 0.01mm, 7axe
, 7be is set to about 0.1 mm. Second
The electron beam detection element 8 is arranged to be shifted by about 60 mm in the direction of the electron beam optical axis, and is composed of a multilayer electrode layer and an insulating layer including single layers 9a and 9b. 9a and 9b also have a slit-like shape perpendicular to the X glaze (or y@) as shown in FIG. It is known to have an accuracy of 0.01 mm or less. The thickness of each of 9a and 9b is approximately 0.
1 mm and 0.01 mm. The number of layers is also known.

Each electrode 9a is provided with a buffer (not shown), and the output of the buffer is connected to a multi-point switch (not shown), and by sequentially examining the output from each electrode, the area of the electrode 9a of the second electron beam detection element 8 It is possible to know which electrode 9a is irradiated with the electron beam, that is, the irradiation position in the X direction (or in the X direction).

In the above configuration, when power is supplied to the electron gun 1, condenser lens 2, deflection coil 5, and objective lens 3 to focus the deuteron beam on the sample surface, the electron beam optical axis 20 or the +g ff11 plane of the sample stage Suppose it wasn't vertical. First, in order to make the electron beam optical axis 20 perpendicular to +b in X, the stage is moved in the X direction, and the y coordinate of the electron beam optical axis and the y coordinate of the center of the first electron beam detection element are roughly matched. Next, move the stage in the X direction and set the X coordinate of the electron beam optical axis and 7ax.
, 7bx (or 7ay, 7by). Then 7ax, 7bx (or 7ay
, 7by) so that both become zero, that is, the electron beam passes through the slit between 7ax and 7bx (or 7ay, 7by).
Move the stage in the X direction.

In other words, by dividing the first electron beam detection element into two and measuring the current irradiated to each element, the reference or slit in the element can be aligned with the electron beam optical axis. . Next, an alternating current is supplied to the auxiliary deflection coil 6 so that the deuteron beam swings slightly larger than the thickness of the insulating layer 9b on the second electron beam detection element 8. Then, since the electron beam is always irradiated to one of the electrodes 9a, each electrode 9a is
By sequentially checking the output from a with a multi-point switch (not shown), it can be determined whether the electron beam has been irradiated to the τ pole 9a, and the X direction 1 from the vertical reference 4VX (4vy) of each electrode 9a can be determined.
The distance in 'J (X direction) and the distance in the electron beam optical axis direction between the first electron beam detection element and the second electron beam detection element are 0.
Since it is known with an accuracy of about 0.1 mm, from the tangent of both,
The inclination of the electron beam optical axis in the X direction (X direction) with respect to the stage sliding surface can be seen. This amount is now corrected by a second deflection coil provided in the electron optical lens barrel. Ideally, at this point, the electron beam should be perpendicular to the stage movement plane when viewed from the X direction or from the X direction. However, taking into consideration errors in deflection magnification, etc., the above procedure is repeated two to three times. As a result, the electron beam will be incident perpendicularly to the sample stage, making it possible to obtain accurate information regarding the shape and dimensions of the pattern.

[Effects of the Invention] As explained above, the present invention allows the electron beam to enter the sample stage perpendicularly, making it possible to accurately measure the line width and cross-sectional shape of a pattern using an X-ray mask, etc. It is possible to reduce fluctuations caused by tilting of the electron beam optical axis.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of a first embodiment of an electron beam dimension measuring instrument according to the present invention, Fig. 2 is an explanatory diagram of main parts of the first embodiment, and Fig. 3 is a diagram of a second embodiment of the present invention. Configuration diagram, Figure 4 is the second
FIG. 5 is a diagram illustrating the configuration of a conventional length measuring device, and FIGS. 6 and 7 are diagrams each illustrating a decrease in pattern measurement accuracy when the optical axis is tilted. 1: 4: vx vy ax bx ay by ax bx electron gun, sample stage, : reference, reference, : first electron beam detection element, first electron beam detection element, : first electron beam detection element, first 1 electron beam detection element, 2nd electron beam detection element, : 2nd electron beam detection element, 8ay: 2nd electron beam detection element, aby: 2nd electron beam detection element.

Claims (6)

[Claims] (1) An electron beam irradiation means for irradiating the sample to be measured, a deflection means for the electron beam, a sample stage on which the sample is mounted and movable parallel to the mounting surface, and a position measuring means for the sample stage. A method for adjusting an electron beam optical axis of a dimension measuring device equipped with the above-mentioned method, wherein a vertical reference having a surface perpendicular to the moving direction of the sample stage is provided, and the step is arranged at a position at a predetermined distance from the vertical reference plane in the same direction as the sample stage. A movable first electron beam detection means is provided, and a second electron beam detection means movable in the same direction as the sample stage is provided at a position a predetermined distance from the first electron beam detection means along the electron beam irradiation direction. a predetermined position of the first electron beam detection means is aligned with the electron beam optical axis, a predetermined position of the second electron beam detection means is aligned with the electron beam optical axis, and the first and second electron beam detection means are aligned with the electron beam optical axis. The tilt of the electron beam optical axis is detected based on the amount of relative movement of the electron beam detection means with respect to the electron beam optical axis, and the tilt of the electron beam optical axis is corrected by driving the deflection means based on the detected value. A method for adjusting the electron beam optical axis. (2) The sample stage has X and Y directions perpendicular to each other.
direction, the first
2. The electron beam optical axis adjustment method according to claim 1, further comprising: and a second electron beam detection means. (3) The electron beam optical axis adjustment method according to claim 1, wherein the first and second electron beam detection means are comprised of two planar electrodes with a slit formed in the center. (4) The first electron beam detection means consists of two planar electrodes with a slit formed in the center, and the second electron beam detection means consists of a multi-segmented electrode provided on an insulating layer in the direction of movement. The electron beam optical axis adjustment method according to claim 1, characterized in that the method comprises an electrode layer. (5) An auxiliary deflection means is provided between the first and second electron beam detection means, and the alignment operation of the second electron beam detection means is performed by deflecting the electron beam with the auxiliary deflection means. An electron beam optical axis adjustment method according to claim 1. (6) The first and second electron beam detection means are mutually movable, and the second electron beam detection means is moved to perform an alignment operation with the electron beam. The method for adjusting the electron beam optical axis according to item 1.