JPS60227347A - Scanning type electron microscope - Google Patents

Abstract

PURPOSE:To maintain a high vacuum condition by setting almost all lead wires to a sample and circuit elements to the outside of vacuum condition and sealing the inlet port of signal line to the vacuum chamber. CONSTITUTION:A sample 3 is placed above a sealed body 6 provided just below the sample. The sealing body 6 is mounted in such a manner that a flange 11 is removably mounted with hermetically sealed structure to an upper receptor 22 through a vacuum sealing material 12 and allows many signal lines to pass therethrough while keeping a highly vacuum sealing structure. The lines passing through the sealing body are connected to the connection end 28 of power supply in the side of atmospheric condition. Thereby, signal lines 7 and circut elements 8 to the sample 8 are all set outside the vacuum condition and influence by gas released from these signal lines 7 and circuit elements 8 can be eliminated perfectly.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a scanning electron microscope, and particularly to a scanning electron microscope suitable for observing the operating state of a semiconductor sample having a large number of signal introduction lines.

[Background of the invention]

In recent years, methods have been used to analyze the operating state of semiconductor samples, especially LSIs, using electron beams. Such a technique can be realized with a scanning electron microscope. That is, the electron microscope chops the electron beam (beam) in synchronization with the operation cycle of the signal inside the r-sr,
It is configured to use this to observe the operating state of the LSI. Such an electron microscope is what is called a strobe type electron microscope.

Such an electron microscope (hereinafter referred to as SEM) uses an objective lens to irradiate a sample such as an LSI mounted on a sample table in a sample chamber with a primary electron beam emitted from an electron gun and focused by an electron lens. (2) It is constructed so that the state of the sample such as LST can be observed by detecting the secondary electrons emitted from the sample such as -1SI with a secondary electron detector.

Therefore, in order to observe the operating state of an LSI sample using the SEM, the LSI must first be mounted on the sample stage of the strobe SEM, and a signal line from the outside must be connected to the LSI sample on the sample stage. Then, the LSI is operated by a voltage supplied from an external drive power supply through a part of the signal line, and under that operating state, the - main and child lines are connected to the operating cycle of the internal signal of the LSI. All you have to do is chop it in synchronization with , and observe the resulting secondary electron image.

By the way, in the case of such a SEM, more than 100 signal lines from the outside are brought into the vacuum inside the sample chamber, and in addition, the signal lines are shielded with a double-sided structure to prevent them from being influenced by the outside. Since wires had to be used, a large amount of gas was released from the signal wires, and the configuration had to be extremely poor in terms of vacuum.

In addition, the strobe SEM has an acceleration voltage of 0.5 to 1[
On the contrary, it is required that the degree of vacuum be maintained at a very high level because it is necessary to use it at a very low voltage state such as KV).

Therefore, it is not preferable to introduce a large number of signal lines as described above in order to maintain a high vacuum state.

Furthermore, unlike general SEM samples, the LSI used for m-detection belongs to large samples, so the sample chamber and sample stage must be large, and the entire sample chamber must be exposed to the atmosphere every time the sample is replaced. However, there are also problems such as the need for a long time for evacuation.

In addition, in the actual operating state of the sample, it is necessary to easily incorporate rotating elements (resistance, etc.) in the close vicinity of the sample, but it is necessary to easily incorporate rotating elements (such as resistors) in the close vicinity of the sample. If the line is brought into the air, gas will be emitted like the signal line, which violates the requirement to maintain the high vacuum necessary for low-acceleration observation.

[Purpose of the invention]

An object of the present invention is to provide a scanning electron microscope that can maintain a high vacuum state.

[Summary of the invention]

In order to achieve the above object, the present invention employs a method in which most of the lead-in wires to the sample and the circuit elements are outside the vacuum, and the lead-in port of the signal wire to the vacuum chamber is hermetically sealed (hermetic seal method).
This allows the seal and the sample to be connected over the shortest distance.

Furthermore, the present invention has the following advantages: - An air lock means provided on one side of the sample stage is added to the above structure, and only the minimum volume created between the air lock means and the sample stage is brought to atmospheric pressure. This allows samples to be exchanged.

[Embodiments of the invention]

Embodiments of the present invention will be described below based on the drawings.

The figure is a schematic cross-sectional view showing an embodiment of a scanning electron microscope according to the present invention. In the figure, a primary electron beam 1 emitted from an electron gun (not shown) and converged by an electron lens (not shown) is directed onto a sample 3 mounted on a sample stage by a final converging (objective) lens 5 provided at the upper part of the sample 3. is focused and irradiated. At this time, the secondary electrons 2 generated from the surface of the sample 3 are guided upward as shown in the figure by the action of the hole of the objective lens 5 and the electric field of the accelerating electrode 4A covering the front surface thereof and the magnetic field of the objective lens 5. , can be detected by the secondary electron detector 4B provided above the objective lens 5 in the figure. Here, the configuration of the sample stage on which the sample 3 is mounted will be described.

The sample 3 is mounted on a hermetic seal 6 placed directly below it.

This airtight body 6 has a flange 11 with a vacuum sealing material 12
It is detachably attached to the upper receiver 22 via a structure that is airtightly sealed. Although this airtight body 6 has a structure in which a large number of signal lines pass through it while maintaining vacuum airtightness, it has a structure that sufficiently maintains their airtightness, and the sample 3 is attached to the penetrated wires on the vacuum side. Terminals are connected. On the other hand, a lead wire 7 whose terminal is treated with a certain resistance value on the atmospheric pressure side is connected to the wire passing through the airtight body 6,
Alternatively, circuit elements 8 are connected, and these are connected to a connection end 28 to a power source. Furthermore, Reed, I
It is preferable that i7 has a flexible structure so that no force is applied to the movement of the sample stage. The airtight body 6 that holds the sample 3 and the upper supporter 22 of the sample stage that holds the flange 11 are integrated with a Y moving table 23 that moves in the Y direction (perpendicular to the plane of the drawing), and the Ys moving body It is supported by a Y guide 25 via a Y rail 24 so as to be movable in the Y direction. In addition, the Y guide 25 is
It is mounted and fixed on top. The X moving table 26 is supported by an X guide 27 so as to be movable in the X direction (horizontal direction in the drawing).

The sample stage described above is provided on the high vacuum side within the sample chamber 15. Therefore, the lower chamber wall 14 of the sample chamber ■5
The bottomed end of the sample stage and one end of the upper receiver 22 of the sample stage are connected by a bellows 13, thereby maintaining airtightness.

According to the above structure, the signal line 7 to the sample 3 and the circuit element 8 can all be installed outside the vacuum, so the influence of the gas released from the signal line 7 and the circuit element 8 can be completely eliminated. can.

The structure of the air lock means for taking out the sample 3 outside the SEM and mounting it on the sample stage inside the SEM, that is, for exchanging the sample, will be described below.

A thin valve body 19 that can be taken in and out from a part of the sample chamber 15 and a sealing material 20 provided on this valve body 19 can be driven by a valve drive shaft 21 that can be operated from the left side of the atmosphere in the directions of arrows A and B in the figure. It has become. The state shown in the figure shows the usage state in which the sample 3 is installed, but when the valve body 19 is moved in the direction of the arrow A in the figure and stopped at the position where one end of the valve body 19 comes into contact with the valve receiver 18, the upper cradle 22. Sealing material 20. A space surrounded by the valve body 19 and the airtight body 6 is formed, and this space is isolated from the sample chamber 15.

Of course, when a new sample N3 is mounted on the upper part of the airtight body 6 and installed as shown in the figure, the shaft 21 may be moved in the direction of the arrow B in the figure to obtain the state shown in the figure.

In the above-described configuration, the shaft 21 is moved in the direction of arrow A in the figure, fitted into the valve receiver 18 provided in a part of the upper receiver 22 of the sample stage, and the valve body is moved by strongly pressing the drive shaft 21. 19 is pressed against the upper surface of the upper receiver 22 of the stage to form an air lock. By doing this, −
A minimum space surrounded by the valve body 19, the upper receiver 22, and the airtight body 6 is air-locked. Then, air is introduced through the exhaust pipe 9 provided on a part of the flange 11 and the valve 10 attached to the tip thereof, and the airtight body 6 is removed, and the sample 3 on the airtight body 6 is replaced with a new one. , airtight body 6 again
is attached to the upper receiver 22.

Next, preliminary evacuation is performed from the exhaust pipe 9, and the vacuum level of the space becomes the same as that of the sample chamber 15, and the shaft 21 is again moved in the direction of the arrow B in the figure to bring it into the state shown in the figure. In this way, only the minimum space surrounding the sample 3 needs to be preliminarily evacuated to atmospheric pressure and vacuum; the conventional method was to introduce air into the entire sample chamber 15, exchange the sample, and return to a vacuum state. Compared to the previous method, the sample exchange time was 50 to 100 times shorter, resulting in an advantage. In addition, the inside of the sample chamber 15 is 1.
A high vacuum of about 0.00 to 1000 is maintained.

Note that the sample 3 is taken out by taking out the integrated airtight body 6 and flange 11 downward through the inner diameter of the bellows 13. Further, the sample chamber 15 can be exhausted through an exhaust pipe 17 attached to a part of the chamber wall 16.

The sample chamber 15 has a structure that can be divided into two parts at a portion C into the chamber wall 16 and the lower chamber wall 14. Therefore, installation of the sample stage, maintenance and inspection, etc. can be easily performed. Furthermore, in the embodiment, the valve body 19 was a thin valve body of 5 (mm) or less.

The distance between the objective lens 5 and the sample 3, that is, the sliding distance, could be reduced, and even though the sample 3 was large, high-resolution observation could be facilitated.

〔Effect of the invention〕

As explained above, according to the present invention, the ultimate vacuum degree of the sample chamber is lower than that of the conventional method by adopting a structure in which items such as signal lines to the sample, circuit elements, etc. that emit large amounts of gas can be taken out of the vacuum. This is an improvement of 100 to 1000 times compared to that of the previous model, and as a result, the contamination of the sample is reduced by 1/100 to 1. /1000, and has the effect of preventing deterioration of resolution due to contamination and extending the maintenance period of the device itself.

In addition, according to the present invention, since the circuit elements connected to the sample are outside the vacuum, the selection and installation of the circuit elements is easy and is not subject to vacuum considerations or restrictions, and only the operation of the circuit is considered. There is also the effect that it is possible to select elements that are

Furthermore, according to the present invention, the upper surface of the upper receiver of the sample stage can be air-locked with a thin plate valve body.
Vacuum steam melting becomes extremely small, which has the effect of greatly shortening the time required for replacement.

[Brief explanation of the drawing]

The figure is a schematic sectional view showing an embodiment of the present invention. 3... Sample, 4A... Accelerating electrode, 4B... Secondary electron detector, 5... Objective lens, 6... Airtight body, 7...
... Shield wire, 8... Circuit element, 11... Plunge, 12... Vacuum sealing material, 13... Bellows, 1
4... Lower chamber wall, 15... Sample chamber, 16... Upper chamber wall, 18... Valve receiver, 19... Valve body, 20...
... Seal material, 21 ... Valve drive shaft, 22 ... Upper receiver.

Claims (1)

[Claims] (1) A primary electron beam emitted from an electron gun and focused by an electron lens is irradiated onto a sample mounted on a sample stage in a sample chamber using an objective lens, and various signals are sent from various parts to the sample on the sample stage. In a scanning electron microscope equipped with an electric wire that provides . A scanning electron microscope characterized in that the electric wire and circuit element are connected to the atmosphere side of the signal line of the airtight body. 2. A primary electron beam emitted from an electron gun and focused by an electron lens is irradiated onto a sample mounted on a sample stage in a sample chamber using an objective lens, and is equipped with electric wires that send various signals to the sample on the sample stage from the outside. In this scanning electron microscope, the sample stage uses an airtight body through which a signal line is passed through the sample mounting part, and the vacuum side of the signal line of the airtight body can be connected to the sample, and the signal line of the airtight body can be connected to the sample. The electric wire and circuit element are connected to the atmosphere side of the line, and an air lock means is provided above the sample stage, which is operable from the outside and isolates a small space containing the sample from the sample chamber. A scanning electron microscope featuring: 3. In claim 2, the air lock means includes a valve body provided with a sealing material that comes into contact with the upper receiver of the sample stage to produce a sealing effect, and a valve that operates and drives this valve body from the outside. A scanning electron microscope comprising a drive shaft and a valve receiver that abuts the valve body.