JPS60241633A - Method for detecting automatic focusing of electron beam apparatus - Google Patents

Abstract

PURPOSE:To realize automatic focusing with a high accuracy even for a sample which generates lesser amount of secondary electrons by adding the function to sequentially move the center point of circular scanning on the sample and detect automatically the position of sample which generates the maximum information signal. CONSTITUTION:A sample 5 is scanned in circular with the primary electron beam of a scanning type electron microscope by adding the signal sent from a circular scanning generator 7 and the signal of a stair case wave deflection signal part 11 in an addition circuit part 12 and giving it to the X and Y deflection coils 2, the secondary electrons generated are detected, it is processed by a control circuit 10 having a signal detecting part 9 and a memory in order to control an objective lens coil 4. Thereby automatic focusing and automatic astigmatism correction are carried out. Accordingly, the automatic focusing with good S/N can be realized by sequentially moving the center point of circular scanning on the sample 5 in the X and Y directions and searching the maximum value of detected signal. As a result, it can be utilized adequately for IC and LSI, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to
Focusing and especially ICs that generate a small amount of secondary electrons.
The present invention relates to an automatic pointless detection method when semiconductor materials such as or LSI are used as a sample.

[Background of the invention]

Conventional automatic focusing will be explained with reference to FIG. The primary electron beam emitted from the J cathode is deflected in the X and Y directions by an X-Y deflection coil 2, and subjected to astigmatism correction by an astigmatism correction coil 3.

The objective lens coil 4 focuses the beam onto the sample surface 5 to obtain an optimum beam spot diameter. The X-Y deflection coil 2 receives a cosine wave current from the circular scanning generator 7 to the X intra-wound coil, and a sine wave current to the Y deflection coil.

Supplied with any amplitude and any period. Then, the primary electron beam scans the sample surface 5 in a circular manner. When a sample is irradiated with a primary electron beam, secondary electrons are generated from the sample, captured by a secondary electron detector 6, and manually inputted to a signal detection section 9. The signal detection unit 9 is a primary beam that irradiates the sample surface.
This is a circuit that detects the minimum random circle of the child beam. Generally, the smaller the diameter of the primary electron beam spot, the higher the frequency component of the generated secondary electron signal. Differential value comparison method, which integrates the signal and compares its value,
A peak value comparison method that utilizes the fact that the peak value of the generated secondary electron signal waveform changes depending on the primary electron beam spot diameter is used. An arbitrary current of 0 (A) is supplied to the objective lens coil 4 by the focal current supply section 8, and after circular scanning is performed once or several times, the output voltage of the signal detection section 9 obtained is input to the control circuit 10. Store in some memory.

Next, the current supplied to the objective lens coil 4 is increased (or decreased) by .DELTA. to perform a similar circular scan. Then, the obtained output voltage of the signal detection section 9 is compared with the previous memory contents, and the larger one is stored in the memory again. The flow of the objective lens coil 'Mt is sequentially increased by Δt and the series of operations is repeated. When the value at which the content of the memory becomes maximum and the current value supplied to the objective lens coil at that time are found and supplied to the coil, the primary electron beam spot diameter is minimized and a small circle of confusion is obtained.

That's right! However, this method was effective only when there were factors that changed the secondary electron generation efficiency, such as changes in the shape of the sample or differences in materials, on the circular scanning line used for primary electron beam irradiation. . For example, in semiconductor samples such as ICs and LSIs, patterns exist only in a certain area, and there are often no factors that change the amount of secondary electron generation on a circular scanning line.

- For example, a semiconductor sample as shown in FIG. 3(a).

A pattern of lines and spaces is formed from the same material. Even if the circular scan indicated by the arrow shown in the figure is executed, there is no change in the signal voltage detected in response to the change in the objective lens current, or the change is lost in noise. This results in the inability to automate focusing.

[Purpose of the invention]

An object of the present invention is to automatically detect a sample position where the amount of secondary electrons generated from the sample is the largest with respect to a sample with a small amount of secondary electrons generated with respect to the primary electron beam,
An object of the present invention is to provide an automatic thermal immersion detection method for an electron beam device that enables automatic focusing and automatic astigmatism correction.

[Summary of the invention]

In order to achieve the above object, the present invention includes means for narrowly converging an electron beam using an electron lens and irradiating the sample onto the sample;
an electron beam deflection means for circularly scanning the electron beam on the sample; a signal processing means for detecting an information signal generated from the sample to determine the spot shape of the electron beam; In an electronic edge device equipped with means for automatic focusing by controlling the excitation current of the lens, the center point of the circular scan is sequentially moved over the sample, and the sample position that produces the maximum information signal is automatically detected. It is characterized by the addition of functions.

[Example of invention]

Hereinafter, one embodiment of the invention will be described with reference to FIG. In addition to the conventional configuration, one staircase wave deflection value unit 11 and an adder circuit unit 1 are added.
2 is newly installed, and the signal from the conventional circular scan generating section 7 and the signal from the staircase wave deflection signal section 11 are added to each of X and Y in an adder circuit section 12 and supplied to the XY deflection coil 2. FIG. 4 shows signal waveforms at each part. The X deflection coil receives a cosine wave signal Xc
and the waveform Xs from the staircase wave deflection signal section are added and supplied, and the sine wave signal Yc and the waveform Y8 from the staircase wave deflection signal section are added and supplied to the Y deflection coil.

Now, before performing the autofocusing series, supply an arbitrary current Io to the objective lens coil. In this state, the sample is scanned circularly with an arbitrary amplitude, and the secondary electron signals generated therefrom are stored in a memory using a detection system similar to automatic focusing. Next, the center point of one circular scan is moved in the 'ThX direction, and a circular scan is performed. For example, Fig. 3(b)
As shown in , the sample surface is moved sequentially from the left end to the right, the detected signal voltage values are compared, and the larger one is stored in the memory. After moving in the X direction any number of times, for example 0 times,
Return the X direction to the origin, move it to the Y direction, compare the detection signals in the same way, and store the larger one in the memory. This is carried out sequentially and repeatedly over the entire surface of the sample to search for the maximum value of the detection signal and the X8·YmO value that gives the maximum value.

In this way, by searching for the position on the sample where the signal is greatest and performing automatic focusing, automatic focusing can be reliably achieved even for semiconductor materials.

〔Effect of the invention〕

As explained above, according to the present invention, automatic focusing with good S/N and automatic astigmatism correction can be performed in order to automatically search for patterns with many signals, and secondary electron Highly accurate automatic focusing and astigmatism correction can be achieved even for samples with a small amount of generation, such as semiconductor materials.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a conventional automatic focusing system, Fig. 2 is a block diagram showing an embodiment of the present invention, and Fig. 3 is a schematic diagram showing the trajectory of an electron beam circularly scanning over a sample surface. 4A is a diagram showing a conventional method, FIG. 4B is a schematic diagram according to the present invention, and FIG. 4 is a diagram showing a current waveform supplied to an XY deflection coil. l...Cathode, 2...X-Y deflection coil, 3...Stigma coil, 4...Objective lens coil, 5...
E material, 6... Secondary electron detector, 7... Circular scanning generating section, 8... Focus current supplying section, 9... Signal detecting section, 10
. . . Control circuit section, 11 . . . Staircase wave deflection signal section, 12
...Addition circuit section. %; l Figure Zz diagram ■ 3 Figure (L) (b) Figure 4

Claims (1)

[Claims] ゛Means for narrowly converging the single beam using an electron lens and irradiating it onto the sample; electron beam deflection means for circularly scanning the electron beam on the sample; detecting information signals generated from the sample to spot the electron beam; signal processing means for determining the shape;
In an electron beam apparatus equipped with means for automatic focusing by controlling the excitation current of the electron lens according to the result of the signal processing, the center point of the circular scan is sequentially moved on the sample to obtain the maximum information signal. 1. An automatic focus detection method for an electron beam device, characterized by having a function of automatically detecting a sample position that causes .