JPH0217050B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus capable of extremely accurately detecting the height of a sample, for example, the height of a mask blank or wafer surface in a charged particle beam exposure apparatus.

For example, when drawing a fine circuit pattern on a semiconductor wafer etc. using an electron beam exposure device, if the wafer surface deviates from the set height, the position and size of the exposed circuit may differ from the predetermined one. In particular, in direct exposure in which multiple types of fine circuit patterns are layered and exposed on a semiconductor wafer (surface), the drawing accuracy is significantly reduced. Therefore, accurately measuring the height of the exposed material is extremely important for highly accurate drawing.

In conventional height measuring devices, an electrode is placed opposite the surface of the material to be exposed, and the capacitance of a capacitor formed between this surface and the electrode changes as the surface moves up and down. However, in such devices, an electrostatic field is generated by the electrodes, which adversely affects the electron beam during measurement. Therefore, the height measurement point must be located far away from the most important electron beam irradiation point, and high measurement accuracy cannot be expected.

On the other hand, there are methods that irradiate the surface of the material to be exposed with laser light and use interference fringes between the reflected light on the surface and the irradiated light, or irradiate the edge member with light from an arbitrary light source and create an image of the edge. It has also been proposed to reflect this on a material surface, project it onto the imaging plane of an image dissector tube, and detect the height displacement of the material as a positional shift of an edge image. Since these are optical measurements, it is possible to match the electron beam irradiation point with the measurement point, and therefore it is possible to measure height with higher precision than in the case of using capacitance.

However, in this measurement, in addition to the detection system, a light irradiation system must be installed in a narrow sample chamber space, which results in a complicated and expensive structure and may even be impossible to install.

The present invention aims to eliminate the above-mentioned drawbacks, and utilizes the primary charged particle beam itself used for processing and analysis as a height measurement tool.

The configuration of the present invention is such that in an apparatus that irradiates a sample surface with a charged particle beam and processes, analyzes or observes the sample, an axis that intersects the axis of the charged particle beam at a constant angle near the sample surface is used. at least one imaging lens is provided along the sample, and charged particles scattered from the sample are imaged by the lens;
Sample surface height measurement of a charged particle beam device configured to have a detector with at least one-dimensional position detection function installed on the imaging plane, and detect the height position of the sample based on the output signal of the detector. The device has features.

An embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram of an embodiment of the present invention, where 1 indicates a charged particle source, such as an electron gun. Electrons emitted from this electron gun are focused by a focusing lens 2 and projected onto a cross-sectional shaping slit 3. The electrons passing through the shaping slit are imaged by an imaging lens 4 and a reduced image of the slit 3 is projected onto a sample (wafer) 5. An X and Y deflector (only one direction is shown in the figure) 6 is placed along the path of the electron beam, so that the shaped electron beam can be scanned over the sample 5. A pattern signal is applied to this deflector from a computer 8 via an amplifier 7, and a desired IC pattern is drawn on a semiconductor wafer 5 as a sample. 9 is a blanking deflector placed between the electron gun 1 and the focusing lens 2;
In combination with 0, the electron beam passes through in a pulsed manner. An on-off signal is applied to the deflector 9 from the computer 8 via an amplifier 11 according to a pattern. Reference numeral 12 denotes a cylindrical electrostatic lens, which is composed of two cylinders 13a and 13b slightly spaced apart, and is arranged along an axis Z' that intersects at a constant angle near the sample surface with respect to the axis Z of the primary electron beam. It is located. A DC power supply 14 is connected to both cylinders 13a and 13b.
Different DC voltages are applied to each other, thereby generating a curved electric field in the gap between the two cylinders, focusing the backscattered electrons scattered from the sample 5, and forming an image of the backscattered electron scattering point (primary electron irradiation point). Form an image. A position detector 15 is placed on the imaging plane to detect the position of the imaging spot of the reflected electrons. As the position detector, a semiconductor position detector (PSD), a photodiode array sensor, a solid-state image sensor (CCD, etc.), an image dissector tube, etc. can be used. The signal from the detector is sent to a detection circuit 16, converted into a signal regarding the height position of the sample, and sent to a display device 17. As a result, the amount of deviation of the surface of the sample 5 from the reference position is displayed on the display device. A part of the output of the detection circuit 16 is also sent to the amplifier 7 of the deflector 6 to control the gain of the amplifier. That is, errors in the drawing pattern caused by the height deviation of the sample 5 are corrected. In this case, as shown by the dotted line, a signal from the detection circuit 16 may be sent to the computer 8 to correct the drawing pattern stored in the computer using software. Although not shown, it is desirable to supply the output of the detection circuit 16 to the power source of the imaging lens 4 and to control the focus position of the electron beam according to the height deviation of the sample 5.

FIG. 2 is an optical diagram showing the principle of height measurement according to the present invention, and shows a case where the height of the sample 5 has changed by h as indicated by 5'. When the sample is 5', the irradiation point p of the primary electron beam was imaged at p' on the detector 15, but when the sample is 5', the irradiation point is virtually q, and its image is q. ’. Therefore, the distance l between p and q is h cos θ (where θ is the angle between the sample surface and the axis Z')
The distance L between p' and q' is L=M·l=M·h cos θ, where M is the magnification of the lens 12. Here, M and θ
is known and constant, so if L on the detector 15 is known, the height h of the sample can be easily determined.

Now, in order to perform electron beam exposure, a primary electron beam is first irradiated onto a certain point on the sample 5 (a point that is not in the drawing area). Due to this irradiation, the electrons reflected from the sample 5 are imaged on the detector 15 by the lens 12,
The imaging position is detected. The signal regarding the image forming position is sent from the circuit 16 as a height signal to the display device 17.
The height position of the sample 5 is displayed. The height of the sample may be manually adjusted based on this display value, or the gain of the amplifier 7 of the deflector 6 may be controlled, but in practice, as shown in FIG. It is convenient to automatically adjust the amplifier 7 or to directly correct the drawing pattern written on the computer 8.

After the above height measurement is completed, the computer 8 sends signals such as the drawing pattern to each part, and the sample 5
A desired pattern with desired dimensions can be exposed thereon.

Although the above description has been made regarding an electron beam exposure apparatus, the present invention is not limited to this and can be similarly applied to an ion beam exposure apparatus, a length measuring apparatus, an analyzer, and other particle beam apparatuses. Also, in these devices,
If there is another charged particle beam source other than the charged particle beam used for drawing, it may be used. Furthermore, although a cylindrical electrostatic lens is used as the imaging lens for the reflected particle beam in the above description, other types or electromagnetic lenses can also be used.

As detailed above, the present invention irradiates a sample surface with a charged particle beam, captures the reflected particle beam, forms an image of the irradiated point on a detector using an electron lens, and Since the height of the sample is known, the height of the charged particle beam irradiation point itself can be measured, making it possible to measure with extremely high accuracy compared to conventional capacitance type, etc. Also, there is a lens in the exposure room. 1
2, the device is smaller and simpler than the conventional optical displacement-side determining device, and costs less, and there is almost no worry that it cannot be installed in the exposure room.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the invention, and FIG. 2 is a diagram explaining the principle of the invention. 1: Electron gun, 2: Focusing lens, 3: Shaping slit, 4: Imaging lens, 5: Sample, 6, 9: Deflector, 7, 11: Amplifier, 8: Computer, 1
0: Slit, 12: Electrostatic lens, 13a, 13
b: cylinder, 14: DC power supply, 15: position detector,
16: detection circuit, 17: display device.

Claims (1)

[Scope of Claims] 1. In an apparatus for irradiating a sample surface with a charged particle beam and processing, analyzing or observing the sample, the charged particle beam intersects the axis of the charged particle beam at a certain angle near the sample surface. At least one imaging lens is provided along the axis, the charged particles scattered from the sample are imaged by the lens, and a detector having at least one-dimensional position detection function is installed on the imaging plane. A sample surface height measuring device for a charged particle beam device, characterized in that the height position of the sample is detected by the output signal of the detector. 2. A sample surface height measuring device for a charged particle beam device according to claim 1, further comprising means for displaying the height of the sample based on the output of the detector. 3. A sample surface height measuring device for a charged particle beam device according to claim 1, wherein the deflection signal of the charged particle beam is corrected based on the output of the detector.