JP2867410B2 - Small size measuring instrument - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a micro-size measuring device for measuring a micro-size of a sample from a signal due to charged particles from the sample obtained by scanning the sample with a charged particle beam. Things.

(Prior Art) In a conventional micro dimensional measuring device using an electron beam, a primary electron beam with a low accelerating voltage was used in order to prevent the sample from being charged.

(Problems to be Solved by the Invention) In the conventional technology as described above, since a high accelerating voltage cannot be used, a large detection signal cannot be obtained, and the S / N is poor. Was.

Attempts have been made to prevent the sample from being charged in order to increase the S / N, but there is a problem that the apparatus becomes complicated.

(Means for Solving the Problems) In view of the above, the present invention relates to a micro-size measuring instrument for measuring a pattern size on a sample from a signal emitted from the sample by injecting a charged particle beam into the sample. A micro-size measuring device characterized by introducing a gas containing oxygen atoms such as water vapor and oxygen, and a charged particle beam for scanning a sample is provided with a pressure limit provided only by its focal length above the objective lens. A micrometer that is deflected around the aperture as the center of deflection, and detects separately positive and negative charged particles created by the interaction between low-pressure gas and charged particles from the sample. This is a micro dimensional measuring device characterized by having a detector and performing signal processing of a difference signal from each detector or a single signal.

(Operation) A low-pressure gas such as water vapor or oxygen (for example, 20
rr), these gases are ionized by charged particles from the sample and become conductive,
The charging of the sample can be prevented, and the radiation damage of the sample can be greatly reduced.

In addition, since oxygen and carbon, in which water vapor is decomposed, react with carbon to evaporate into carbon monoxide and carbon dioxide, carbon is not deposited on the sample.

Therefore, since a higher accelerating voltage (for example, 2 Kev or more) can be used as compared with the conventional one, the S / N can be increased in combination with ionization of the low-pressure gas by the charged particles from the sample, and Since the chromatic aberration is small and the diffraction is small due to the acceleration voltage, the charged particle beam can be narrowed down, and the dimension measurement accuracy is improved.

Further, since the charged particle beam is deflected around the minute aperture as the center of deflection, a wide area can be scanned.

In addition, the detector collects positive and negative charged particles,
The detection sensitivity can be improved. If a large signal current flows through the detector, the amplification factor of the amplifier can be reduced, and the frequency characteristics are improved.

〔Example〕

FIG. 1 is an explanatory view showing an electron optical lens barrel of a micro-size measuring instrument according to the present invention. The primary electron beam emitted from the electron gun 1 in the electron gun chamber 2 is applied to a pressure limiting aperture 28 of the electron gun chamber 2 "hereinafter,
Exits the sample chamber 21 and exits the target 27
Hit. In this process, the primary electron beam is controlled so as to be focused on the target 27 by the condenser lens 4 and the objective lens 26, and is scanned two-dimensionally on the sample by the deflection coils 6, 7. At this time, any astigmatism is corrected by the astigmatism correction coil 5. Gas 23 such as water vapor or oxygen is introduced into the sample chamber 21 through a valve 22. Secondary electrons are emitted from the target 27 scanned by the primary electron beam, and ionize the gas by interacting with the gas introduced from the valve 22 to form a large number of pairs of electrons and ions. As shown in FIG. 2, these charged particles are a positive group of electrodes formed by alternately connecting a plurality of electrodes arranged at the center of the axis.
The light enters the detector 15 composed of 15A and the negative electrode group 15B, is taken out of the vacuum through the lead wires 11A, 11B and hermetic seals 10A, 10B, respectively, is amplified by the amplifiers 11, 12, respectively, and the signal on one side has a sign. The signal is inverted and processed by the signal processing circuit 14 into an amount necessary for dimension measurement. In the signal processing circuit 14,
The signal from the amplifier 11 and the signal from the amplifier 12 can be processed independently, or the sum signal of the two (the signal is almost doubled)
Can also be produced. Which signal to use depends on the optimal S / N and required response speed depending on the sample to be measured. The electron gun chamber 2 is evacuated through a valve 3 and kept at a high vacuum.

The gas in the sample chamber 21 is exhausted through the valves 9A and 9B, and the gas that has come out to the electron gun chamber 2 through the minute holes 28 is exhausted by the valve 3 '. Will be kept. As shown by a trajectory 8 in which the trajectory of the electron beam deflected by the deflectors 6 and 7 is expanded in the lateral direction, the scanning is deflected around the microhole 28,
A large area can be scanned despite the small hole diameter. Since the minute hole 28 is located at a position apart from the lens main surface by the focal length of the objective lens 26, the orbit 8 enters the sample almost perpendicularly after exiting the objective lens 26.

FIG. 2 shows the details of the detection unit. Detector 15 is a positive group of electrodes formed by alternately connecting a plurality of electrodes arranged at the axis center.
15A and a negative electrode group 15B. A bias of the opposite sign is applied to the electrodes 15A and 15B. That is, the electrode
A negative bias is applied to 15A and a positive bias is applied to the electrode 15B. Since gas and electrons and ions created by the interaction with secondary electrons are immediately collected by one of the electrodes (electrons and negative ions are collected by the electrode 15B and positive ions are collected by the electrode 15A). The ions do not accumulate in space for a long time, and the response speed of the detection unit is increased. When negative ions or electrons enter the electrode 15B, the signal generated at both ends of the high resistance 31 connected to the positive electrode of the power supply 30 and the electrode 15B whose negative electrode is grounded is amplified by the amplifier 32 and input to the signal processing circuit 14. Is done. Here, the resistor 33 is a potentiometer for adjusting the amplification factor. On the other hand, when positive ions are incident on the electrode 15A, a signal generated at both ends of the high resistance 35 connected to the negative electrode of the power supply 34 whose positive electrode is grounded and the electrode 15A is amplified by the amplifier 36,
Thereafter, the signal is inverted by the inverting circuit 13 and input to the signal processing circuit 14.

Accordingly, the signal detection circuit 14 obtains not only the secondary electrons from the sample but also the ionized positive ions and negative ions as signals, so that a large signal can be obtained.

In FIG. 1, the electrode 15 is connected to the electrodes 15A and 15A for simplicity.
Although not shown separately in FIG. 5B, the electrode 15 in FIG.
Although the drawing is different from the electrode 15 in the figure, it is substantially the same. The electrode 17 is also axially symmetric with two types of electrodes 17.
A, 17B (not shown) is provided, and the electrodes 15A, 1B
5B, each of which is connected to 5B and is in the exhaust path, so that a gas passage hole is provided, which is represented by a broken line.

In addition, since at least the surface of the electrodes 15A and 15B is coated with a low atomic weight metal such as _Be , C, etc., when particles are incident, re-emission of various particles from here is suppressed to a small extent, thereby increasing noise. Can be prevented.

Further, as shown in the figure, the objective lens 26 moves the magnetic field distribution toward the sample 27 by making the upper pole 18 sufficiently thick so that the magnetic flux density does not saturate, and making the lower pole 19 thin so as to saturate the reverse pole. Aberration characteristics similar to those of an in-lens type lens are provided. Then, by bringing the lower pole 19 of the objective lens 26 closer to the sample 27, the above-described in-lens system is approached, and by increasing the solid angle at which the objective lens hole is viewed from the sample 27 sufficiently large, a large angle from the sample to the optical axis is obtained. The secondary electrons emitted in the direction having the above can also be effectively directed toward the detector (they are not shaken by the objective lens).

A detector is provided above the objective lens 26 (on the side of the electron gun chamber 2).
Since the 15 is provided, the moving distance until the secondary electrons reach the detector 15 becomes longer, sufficient interaction between the gas and the secondary electrons becomes possible, and a large signal current can be obtained from the detector.

 Reference numerals 20, 24 and 25 in FIG. 1 denote vacuum seals.

(Effects of the Invention) As described above, according to the present invention, a large detection signal can be obtained, and as a result, a signal waveform with a good S / N can be obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an embodiment of the electron optical column of the micro-size measuring instrument according to the present invention, and FIG. 2 is an explanatory view showing a specific configuration of a detecting section. (Explanation of reference numerals of main parts) 15 (15A, 15B) ... electrode, 22 ... valve, 23 ... gas, 28 ... pressure limiting aperture

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kenji Morita 1-6-3 Nishioi, Shinagawa-ku, Tokyo Nikon Oi Works Co., Ltd. (56) References JP-A-63-12146 (JP, A) 61-162936 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01B 15/00-15/08

Claims (3)

(57) [Claims] A micrometer for measuring a pattern dimension on a sample from a signal emitted from the sample by injecting a charged particle beam into the sample, wherein the sample chamber contains low-pressure oxygen atoms such as water vapor and oxygen. A micro-size measuring device characterized by introducing gas. 2. The microscopic measuring device according to claim 1, wherein the charged particle beam for scanning the sample is deflected around a pressure limiting aperture provided above the objective lens by a focal length thereof as a deflection center. A small size measuring device characterized by the following. 3. The micrometer according to claim 1, further comprising a detector for separately collecting positive and negative charged particles produced by the interaction between the low-pressure gas and the charged particles from the sample,
A minute dimension measuring device characterized by measuring a dimension of a pattern on a sample by processing a difference signal from each detector or a single signal processing.