JPH0582066A - Flatness correcting function for electron microscope - Google Patents

Abstract

PURPOSE:To correct automatically out of focusing generated by projections/ recesses (flatness) of a specimen or a stage therefore using an electron microscope. CONSTITUTION:An encoder 8 for adjustment of focal point is installed to know the actual working distance at each stage prior to actual observation, and also a memory 10 is provided to store the objective lens current data of the encoder. The objective lens current 9 to achieve correction of the flatness is controlled by a lens controlling CPU 7 and permitted to flow to an objective current 5. A stage controlling CPU 11 is tied with the lens controlling CPU 7 and stores and controls the objective current data in correspondence to the stage position.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron microscope, and more particularly to a function suitable for correcting defocus when the working distance is constant.

[0002]

2. Description of the Related Art Conventionally, there are electron microscopes capable of intentionally changing the working distance, in which an appropriate lens current corresponding to the working distance is stored as fixed data and automatically set. When the stage moves in a constant state, depending on the flatness of the sample and sample stage,
Sometimes it deviated from the proper lens current.

[0003]

The above-mentioned prior art does not consider the change in the actual working distance caused by the flatness of the sample or the sample stage when the stage is moved while the working distance is constant. There is a problem that it is necessary to perform focus adjustment for each visual field depending on the position of the stage even if the working distance is apparently the same.

An object of the present invention is to minimize focus adjustment for each visual field at the same working distance and improve operability.

[0005]

The object of the present invention is to store the objective lens current value depending on the position of the sample or the sample stage at the same working distance in the memory as flatness data in advance for each electron microscope. This is achieved by obtaining the objective lens current corresponding to the actual working distance at the stage position for image observation from the flatness data and passing it through the objective lens.

[0006]

The data of the objective lens current at the time of the positive focus at the required number of points and the required positions are collected within the stage movement range where the working distance is constant. This objective lens current data is stored in the memory. Since the actual accurate working distance can be calculated from the data of the objective lens current, the information (for example, surface equation) representing the unevenness in the surface of the stage movement range can be obtained by using the position data of the sample stage as coordinates. ..
On the other hand, in the case of actually observing, based on the position data of the sample stage at that time, necessary surface irregularity information is automatically set in the objective lens through the D / A converter as the objective lens current.

As a result, the current of the objective lens when observing an image corresponds to a more actual working distance.
Focus adjustment in each viewing field is minimal.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. The objective lens 5 which has the XY stage 3 on which the sample 1 is placed and which can be moved while keeping the working distance 2 constant, and which adjusts the focus of the electron beam 4 is controlled by the lens control CPU 7 via the D / A converter 6. To be done.

The focus adjustment encoder 8 can manually adjust the focus by adjusting the objective lens current 9 via the lens control CPU 7. The memory 10 for storing the objective lens current data (flatness data) and the stage control CPU 11 are connected to the lens control CPU 7,
The lens control CPU 7 and the stage control CPU 11 can be controlled by the host CPU 12. For example, the observation points (1) to (6) shown in FIG. 2 are moved to below the beam axis 7 of FIG. 2 by using the XY stage 3 of FIG. Each observation point
In (1) to (6), the focal point is adjusted by the focus adjustment encoder 8 shown in FIG. 1 and the like, and the objective lens current data at that time is stored in the memory 10. At that time, each observation point is stored in association with stage position information from the stage control CPU 11 or the like.

Next, when observing the same type of sample, an objective lens current suitable for the stage position information of the observation point is passed through the objective lens 5 through the lens control CPU 7 and the D / A converter 6.

For example, in a semiconductor manufacturing line or the like, the same point on the same type of wafer is often routinely observed and dimensioned. Therefore, the stored objective lens current data is directly reproduced as the objective lens data for each observation point. By doing this, when the stage is moved, without adjusting the focus,
A well-focused image can be obtained. If a more general flatness correction is performed, the host CPU 12
It is also possible to create a surface equation or an interpolation formula representing the unevenness information of the surface within the stage movement range by using the stored flatness data. Based on this, by controlling the objective lens current 9 via the lens control CPU 7, it is possible to easily obtain a focused image to some extent even at a stage position where flatness data is not stored.

Further, by carrying out the function of the present invention before execution of the existing automatic focusing function, there is an effect that the accuracy and speed of automatic focusing are improved.

[0013]

According to the present invention, once the flatness data is sampled, the flatness correction can be performed faithfully any number of times.
Moreover, the correction can be made by reentering new flatness data. Since the flatness data can be collected for each actual device, there is an effect of eliminating a difference in defocus between devices. Compared to a reduction projection exposure apparatus, the electron microscope does not necessarily require mechanical flatness of the sample stage, so rather than mechanically ensuring flatness,
The present invention can obtain the required flatness at a lower cost.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a top view illustrating a sample observation example.

[Explanation of symbols]

2 ... Working distance, 5 ... Objective lens, 7 ... CP for lens control
U, 10 ... Memory, 11 ... Stage control CPU.

Claims (1)

[Claims] 1. An electron microscope comprising a CPU-controlled electron optical system and a CPU-controlled sample stage, wherein the flatness of the sample stage or sample when the distance (working distance) between the objective lens and the sample stage is constant. A memory space for storing the objective lens current data, the storage of the aforementioned data,
A flatness correction function for an electron microscope, which has software capable of automatically setting an appropriate objective lens current for each stage coordinate using the data.