JP2817072B2 - Scanning electron microscope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning electron microscope,
In particular, the present invention relates to a scanning electron microscope suitable for efficiently detecting secondary electrons generated from the bottom of a concave portion such as a trench or a contact hole having a high aspect ratio.

[0002]

2. Description of the Related Art Conventionally, it has been used for observing or measuring a contact hole or a line pattern of a submicron order (1 μm or less) in a semiconductor device sample.
A scanning electron microscope is used.

In recent years, with the advance of semiconductor integrated circuit technology, circuit elements have been formed in three-dimensional directions. For example, contact holes, capacitive capacitors and isolation between elements have been formed on the surface of a sample. Deeper holes and grooves (hereinafter, represented by contact holes) are being formed.

However, when it is attempted to irradiate an electron beam into such a contact hole and observe its bottom, most of the secondary electrons emitted from the bottom of the contact hole are recognized as conventionally recognized. The secondary electrons collide with the side wall of the contact hole and are trapped, so that secondary electrons cannot escape from the contact hole.

A sample for a semiconductor device is generally A
An electrical insulator such as SiO2 or SiN is laminated on a conductor such as 1 or Si. When such a semiconductor device sample is irradiated with an electron beam, the surface of the electrical insulator is positively or negatively charged. .

Whether the insulator surface is charged positively or negatively depends on the energy of the irradiated electron beam, that is, the electron dose. The electron charge is positively charged when the electron dose is small, and negatively charged when the electron dose is large. Has been confirmed to be.

There is no problem if the insulator surface is positively charged, but if it is negatively charged, the rise of secondary electrons generated from the bottom of the contact hole is hindered by the negatively charged charge on the sample surface. It has been confirmed by the inventors of the present invention that secondary electrons are hardly detected.

A method for efficiently detecting secondary electrons in a contact hole is disclosed in, for example, Japanese Patent Application Laid-Open No. Sho 62-9724.
In Japanese Patent Application Publication No. 6 (1994) -1994, an electrode for extracting secondary electrons from a contact hole is provided between an objective lens and a sample surface to generate a positive electric field near the sample surface.
Techniques for extracting secondary electrons have been proposed.

In Japanese Patent Application Laid-Open No. 63-274049, a positive voltage is applied to a cylindrical electrode provided in a magnetic pole of an objective lens to generate a positive electric field in the vicinity of a sample surface. A technique has been proposed in which secondary electrons are efficiently extracted and guided to the electron source side of the objective lens.

[0010]

In the prior art described above, a positive electric field for efficiently extracting secondary electrons from the inside of the contact hole is formed near the sample surface, and this positive electric field is applied to the radiation emitted from the electron source. Since the electron beam is accelerated in the vicinity of the objective lens, various observation conditions are different depending on whether the observation is performed by generating a positive electric field or not.

That is, if the irradiation electron beam is accelerated in the vicinity of the objective lens, the amount of deflection of the electron beam by each electron lens and deflector changes, so that the focus, magnification, axial position, field of view, astigmatism, and contrast Etc. will change.

Whether or not it is better to generate a positive electric field depends on the sample and observation conditions. Therefore, when observation is first made without generating a positive electric field, and then observation is made by generating a positive electric field. However, there is a problem that operability is poor because each observation condition must be reset.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and to provide various observation conditions when a positive electric field for efficiently extracting secondary electrons from the inside of the contact hole is formed near the sample surface. Is automatically performed to improve the operability.

[0014]

In order to achieve the above object, according to the present invention, an electron beam spot is scanned in an observation area on a sample, and a signal generated secondarily from the area is acquired to obtain an observation image. An electrode for generating a positive electric field in the observation region on the sample, a first control data used when the positive electric field is not generated, and a second control data used when the positive electric field is generated. A storage unit for storing control data and a control unit for controlling each unit based on any of the control data are provided.

[0015]

According to the above configuration, the optimum control data is automatically selected according to whether or not a positive electric field is generated on the sample surface, so that the operability is greatly improved.

[0016]

FIG. 1 is a diagram showing a configuration of a scanning electron microscope according to one embodiment of the present invention. Although the actual apparatus is provided with an exhaust unit for evacuating the inside of the apparatus, which serves as an electron beam path, here, only the configuration necessary for the description of the present invention is shown.

The electron beam 21 emitted from the electron source 1 is converged by the condenser lens 2, and the axis is adjusted by the axis adjustment coil 3. The stigma coil 4 corrects the astigmatism of the electron beam 21, and the deflection coil 5 deflects and scans the electron beam 21.

On the upper magnetic pole 9a of the objective lens 9, there is provided a cylindrical bias electrode 7 which penetrates the inside of the magnetic pole opening, has a flange portion 7f at the sample facing end, and has an electron beam passage opening therein. ing.

A secondary electron 2 is provided in an upper opening of the first electrode 7.
A grid mesh (not shown) is drawn to pull out 2 to the detector 6 side. An opening is provided at the center of the grid mesh so as not to obstruct the deflection path of the electron beam 21.

A ring-shaped control electrode 8 is arranged above the bias electrode 7, and, like the bias electrode 7, the lower opening has a grid mesh (shown in the figure) having an opening at the center. Zu) is stretched.

The electron beam 21 that has passed through the control electrode 8 and the bias electrode 7 is converged by the objective lens 9 and irradiates the sample 20 placed in the sample chamber 10. Secondary electrons 22 generated from the sample 20 are detected by the detector 6.

The electron source 1 is connected to an electron source power supply 11, the condenser lens 2 is connected to a condenser lens power supply 12, the axis adjustment coil 3 is connected to an axis adjustment coil power supply 13, and the stigma coil 4 is connected to a stigma coil power supply 14. Connected, the deflection coil 5 is connected to a deflection coil power supply 15, the bias electrode 7 is connected to a bias electrode power supply 17, the control electrode 8 is connected to a control electrode power supply 18, and the objective lens 9 is connected to an objective lens power supply 19. ing. The detector 6 is connected to a detector power supply 16, which supplies power to the detector 6 and mediates a detection signal from the detector 6.

Each of the above-mentioned power supplies has an interface (I
/ F) 23 via a signal from a central processing unit (CPU) 24. Input of various data to the central processing unit 24 is performed from the keyboard 25. The detection signal from the detector 6 is sent to the central processing unit 24 via the interface 23, and is sent as an image to the image display means 2
6 is displayed.

The central processing unit 24 is connected to memories 30a and 30b in which the following data is stored in advance. (1) Data group A: Control data when the output voltages of the bias electrode power supply 17 and the control electrode power supply 18 are both 0 V. (a) Coil current supplied to the axial adjustment coil 3 (b) Stigma coil 4 Coil current to be supplied (c) Coil current to be supplied to deflection coil 5 at an arbitrary magnification. (2) Data group B: the output voltages of the bias electrode power supply 17 and the control electrode power supply 18 are the predetermined voltages V1 and V2, respectively.
(A) a coil current supplied to the axial adjustment coil 3 (b) a coil current supplied to the stigma coil 4 (c) a coil current supplied to the deflection coil 5 at an arbitrary magnification (d) DC current superimposed on deflection coil current to correct the field of view deviation (e) Increase in lens current supplied to objective lens 9 (f) Change in background level required for correction of image data.

Since the control data output to each power supply registered in the data group A differs depending on the magnification, the control data output to each power supply is registered in a data table format using the magnification as a parameter.

Since the control data output to each power supply registered in the data group B differs depending on the magnification and the voltages V1 and V2, the control data output to each power supply includes the magnification and the voltages V1 and V2 as parameters. It is registered in the data table format.

In such a configuration, the output voltages of the bias electrode power supply 17 and the control electrode power supply 18 are set to 0 V in a normal pattern observation or the like. The central processing unit 24 selects the data group A and controls each power supply accordingly.

When observing the inside of the contact hole, the bias electrode power supply 17 and the control electrode power supply 18 are used.
Are output voltages V1 (for example, +300 V),
V2 (for example, +30 V). The central processing unit 24 selects the data group B, and controls each power supply accordingly.

According to this embodiment, the control data of each part for obtaining the best scanning image is automatically selected according to whether or not the bias electrode 7 generates a positive electric field on the sample surface. Operability is dramatically improved.

In the above embodiment, when a positive electric field is generated on the sample surface, the bias electrode 7 and the control electrode 8
However, the present invention is not limited to this, and the control electrode 8 may be constantly grounded (0 V) and the voltage may be applied only to the bias electrode 7. .

In this case, the influence of the electric field generated by the bias electrode 7 on the electron beam 21 is suppressed up to the control electrode 8. Therefore, the data group B includes the coil current ( (a)), an additional DC current to be superimposed on the deflection coil current in order to correct the field of view deviation (see above).
(d) It is not necessary to register the control data for (1).

FIG. 2 is a diagram showing another configuration of the bias electrode 7, and the same reference numerals as those described above denote the same or equivalent parts.

In the present embodiment, the bias electrode 7 is divided into four parts (X1, X2, Y1, Y2) in the direction of the optical axis of the electron beam.
It is characterized in that the positive electric field generated by X2, Y1, Y2 can be made different.

Each of the electrodes 7 and 8 has an electron beam 21 at the center.
Are provided, and meshes 7b, 8b are provided around the passage holes 71, 72 so that secondary electrons can pass therethrough.
It is composed of

In this embodiment, four bias electrodes 7 are connected.
Although described as being divided, the present invention is not limited to this, and may be divided into two, six, or the like.

According to the present embodiment, the voltage applied to each of the plurality of divided electrodes can be controlled independently, so that the relative relationship between the voltages applied to each electrode and its absolute value can be adjusted. Thus, the axial tone ((a)) and the correction of the field deviation ((a)) set in the data group B can be omitted.

FIG. 3 is a diagram showing a configuration of a scanning electron microscope according to another embodiment of the present invention, wherein the same reference numerals as those described above denote the same or equivalent parts.

This embodiment is characterized in that a deflection correction coil 27 and a deflection correction coil power supply 28 are added to the configuration described with reference to FIG.

The deflection correction coil power supply 28 is connected to the interface 23, and the central processing unit 24 controls the output current. In the central processing unit 24,
Control data relating to the deflection amount and the deflection direction of the electron beam necessary for correcting the field deviation and the axis deviation generated when a positive voltage is applied to the bias electrode 7 and the control electrode 8 are registered in advance.

In such a configuration, the bias electrode 7
When no positive voltage is applied to the control electrode 8, the output current of the deflection correction coil power supply 28 is also set to zero.

When a positive voltage is applied to the bias electrode 7 and the control electrode 8, a deflection correction coil power supply 28 is supplied so that a current for correcting a visual field deviation and an axis deviation is supplied based on the control data. Control.

According to the present embodiment, the axial tone ((a)) and the visual field shift ((d)) set in the data group B are used.
Can be performed by the dedicated correction coil 27, so that the amount of control data can be reduced.

[0043]

As described above, according to the present invention, control data of each unit for obtaining a scanned image is automatically selected according to whether or not a positive electric field is generated on the sample surface. Operability is dramatically improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a scanning electron microscope according to an embodiment of the present invention.

FIG. 2 is a diagram showing another configuration of the bias electrode of the present invention.

FIG. 3 is a configuration diagram of a scanning electron microscope according to another embodiment of the present invention.

[Explanation of symbols]

1. Electron source, 2. Condenser lens, 3. Axial coil,
4: Stigma coil, 5: deflection coil, 6: detector,
7 bias electrode, 8 control electrode, 9 objective lens, 1
0: sample chamber, 11: electron source power, 12: condenser lens power, 13: axial adjustment coil power, 14: stigma coil power, 15: deflection coil power, 16: detector power, 1
7 ... Bias electrode power supply, 18 ... Control electrode power supply, 19 ... Objective lens power supply, 20 ... Sample, 21 ... Electron beam, 22 ... Secondary electron, 23 ... Interface, 24 ... Central processing unit, 25 ... Keyboard, 26 ... Image Display means, 27: deflection correction coil, 28: deflection correction coil power supply

Continuation of the front page (56) References JP-A-64-52370 (JP, A) JP-A-62-31931 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01J 37 / 28 H01J 37/153 H01J 37/21

Claims (8)

(57) [Claims] 1. A scanning electron microscope which scans an electron beam spot in an observation region on a sample and takes in a signal generated secondarily from the region to obtain a scanned image. An electrode for generating a positive electric field in the observation region, and various control data for obtaining a desired scanning image, first control data used when the positive electric field is not generated and used when the positive electric field is generated. A scanning electron microscope, comprising: storage means for storing second control data; and control means for controlling each unit based on any of the control data. 2. The apparatus according to claim 1, wherein the second control data is set so that a change in a scanned image caused by accelerating the electron beam by the positive electric field is corrected. The scanning electron microscope as described. 3. The second control data includes data for optical axis alignment, data for astigmatism correction, data for magnification setting, data for field setting, data for focusing, and data for background level setting of a scanned image. The scanning electron microscope according to claim 1, wherein the number is at least one. 4. The electrode according to claim 1, wherein the electrode is a cylindrical electrode provided so as to penetrate a magnetic pole hole of the objective lens and to which a positive voltage is applied to a sample. The scanning electron microscope according to any one of the above. 5. The scanning electron microscope according to claim 1, wherein a ring-shaped electrode is arranged on the cylindrical electrode with a predetermined gap. 6. The scanning electron microscope according to claim 1, wherein said ring-shaped electrode is grounded. 7. The cylindrical electrode is divided into a plurality of parts along the optical axis of an electron beam, and a voltage different from other parts is applied to at least one of the divided parts. The scanning electron microscope according to any one of claims 1 to 6, wherein 8. The scanning electron microscope according to claim 1, further comprising an electron beam deflecting unit between the electrode and the sample.