JPH1038805A - Cathode luminescence device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To determine existence of a residual film by means of non-destructive inspection by arranging a photo-detector on the back face of a wafer for detecting luminescence on the back face when the wafer is scanned by means of an electron beam and detecting secondary electron at the same time for displaying images in coordination. SOLUTION: When an electron beam is radiated on the front face of a wafer 3, the light radiated from the back face of the wafer 3 is detected by means of a photo-detector 5. The wafer 3, which is a semiconductor crystal, transmits a light beam with a wavelength longer than that corresponding to its band gap energy. If luminescence is generated when the surface of the wafer 3 is scanned by means of the electron beam, in this luminescence, the light with a wavelength longer than that corresponding to the band gap energy is transmitted so as to be detected by means of the photo detector 5. When the wafer 3 is scanned by means of the electron beam, a secondary electron is detected and a secondary electron image is displayed, and at the same time, a luminescence image detected by means of the photo detector 5 can be also displayed, so that existence of a residual film can be detected non-destructively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cathosoluminescence device for detecting luminescence generated by irradiating a surface of a sample with an electron beam.

[0002]

2. Description of the Related Art With the recent development of semiconductor technology, semiconductor devices, such as transistors, are formed in finer patterns. Circuit function such as a memory element.

With the miniaturization of semiconductor elements such as transistors, the line width measurement of patterns has shifted from a method using an optical microscope to a method using an electron microscope. In the case of a semiconductor sample, when the sample is irradiated with an electron beam having a high acceleration voltage, the sample may be damaged due to charge-up or the like. Therefore, a scanning electron microscope (SEM) having a low acceleration voltage is mainly used for length measurement.

[0004] In addition, with the miniaturization of semiconductor elements, a structure having a large aspect ratio (pattern depth / width ratio) has been formed along with miniaturization and three-dimensionalization of contact holes and trenches, and processing is difficult. If there is a processing residue (residual film) such as a Si oxide film or a resist film on the bottom surface of the fine portion, device failure such as conduction failure occurs, which causes a reduction in process yield. In order to prevent this device failure, it is necessary to determine the presence or absence of a residual film in the middle of the manufacturing process and to provide feedback to the manufacturing process so that the residual film does not occur.

Conventionally, the mainstream method for determining the presence or absence of a residual film is to split a semiconductor wafer and observe the cross section of the semiconductor wafer with an electron microscope. There is also a method of taking a secondary electron image of a contact hole, a trench, or the like using an SEM to determine the presence or absence of a residual film, but the size of the contact hole is 0.2 μm in diameter and 2 μm in depth. small,
When the aspect ratio is large, it is difficult for a measurer with considerable skill and experience to determine whether a residual film exists at the bottom of the contact hole.

As a method of analyzing and evaluating materials of semiconductors and ceramic thin films, there is a method called a cathodoluminescence method as one of surface analysis methods. This method measures the luminescence generated by irradiating the sample surface with an electron beam, and analyzes the luminescence.
It analyzes crystal defects and the like. This method is mainly used for analyzing a sample surface.

[0007]

SUMMARY OF THE INVENTION Currently used S
The secondary electron resolution at low acceleration voltage of EM is several nm /
Although it is about IKv, the pattern width of transistors, semiconductor elements, etc. is approaching the order of secondary electron resolution,
When the aspect ratio is large, such as in a contact hole or a trench, it is difficult to observe the bottom of the contact hole with a low-acceleration SEM. It is difficult to determine the presence or absence of a residual film by SEM observation, as described above, without considerable skill and experience. Since it is necessary, there is a problem that it is difficult to apply in a manufacturing process.

Although the resolution can be increased by increasing the accelerating voltage, the charge-up of the sample becomes intense, so that not only the accurate measurement cannot be performed but also the sample is damaged, and other than the method of increasing the accelerating voltage. We have to think about the means.

In the above-described conventional method of dividing the wafer with respect to the remaining film at the bottom of the contact hole and observing the cross section with an electron microscope, it is not always possible to observe the cross section of the contact hole as intended. In addition, since the wafer is broken, the observed wafer cannot be returned to the manufacturing process, and the yield of the manufacturing process is greatly reduced. For this reason, there is a strong demand for the development of a method that can reliably determine the presence or absence of a residual film at the bottom of a contact hole or a trench without damaging the wafer.

In order to solve these problems, the present invention is provided with a photodetector for detecting light on the back surface of a sample, detecting cathodoluminescence on the back surface when the sample is scanned with an electron beam, and performing secondary light detection. Detects electrons, etc.
It is an object of the present invention to display a luminescence image of a semiconductor product or the like in association with the shape of a sample or the like and to enable the presence or absence and position of a remaining film to be detected.

[0011]

Means for solving the problem will be described with reference to FIG. In FIG. 1, the wafer 3
Is a sample for detecting a residual film and the like, which is held on the stage 4.

The stage 4 holds the wafer 3 and moves in the horizontal direction. The photodetector 5 is provided on the back surface of the wafer 3 and detects light emitted when the wafer 3 is irradiated with an electron beam.

Next, a detection method will be described. Holding the wafer 3 on the stage 4 and scanning the wafer 3 with an electron beam,
At this time, an image is displayed by amplifying a signal obtained by detecting light by the photodetector 5 provided on the back surface of the wafer 3.

Further, the wafer 3 is held on the stage 4 and scanned on the wafer 3 with an electron beam. At this time, a signal obtained by detecting light by a photodetector 5 provided on the back of the wafer 3 is amplified to form an image. In addition to the display, the signal detecting the secondary electrons emitted on the side irradiated with the electron beam is amplified, the image is displayed together, and the two images are associated with each other.

At this time, a line scan or surface scan is performed on the wafer 3 with an electron beam to display an image corresponding to the line scan or surface scan. Therefore, a photodetector 5 for detecting light is installed on the back surface of the wafer 3 as a sample, and the cathode luminescence on the back surface when the wafer 3 is scanned by the electron beam and the secondary electrons are detected and associated. By displaying the image, the luminescence image of the semiconductor product or the like can be displayed in association with the shape of the wafer 3 and the like, and the presence or absence and the position of the remaining film can be detected.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment and operation of the present invention will be sequentially described in detail with reference to FIGS.

FIG. 1 is a block diagram showing one embodiment of the present invention.
In FIG. 1, an SEM column 1 scans an electron beam while irradiating it onto a wafer 3 while narrowing the electron beam. Although not shown, an electron source that generates an electron beam, an electron beam emitted from the electron source, Lens for focusing the electron beam, and the electron beam focused by the condenser lens
It comprises an objective lens 11 that focuses finely upward, and a deflection system that scans the electron beam irradiated on the wafer 3 in the X direction and the Y direction. The inside of the SEM lens barrel 1 is evacuated to a vacuum. Further, when the wafer 3 is irradiated with the electron beam, secondary electrons are emitted, and the secondary electrons return to the direction in which the electron beam was irradiated, and the secondary electrons provided inside or above the objective lens 11 as shown in FIG. It is detected by the electronic detector 12. The secondary electron image of the surface of the wafer 3 is displayed on the screen by performing luminance modulation by the detected secondary electron signal.

The vacuum chamber 2 is a chamber for storing the wafer 3 and the like in a vacuum, and is evacuated to a vacuum by a vacuum exhaust system (not shown). The wafer 3 is a sample for irradiating an electron beam and detecting light from the back, and is fixed on the stage 4.

The stage 4 is for fixing the wafer 3 and moving it in the X and Y directions. Photodetector 5
Is to detect light emitted from the back surface of the wafer 3 when the surface is irradiated with an electron beam. Wafer 3
Is a semiconductor crystal and has a property of transmitting light having a wavelength longer than the wavelength corresponding to the band gap energy. Therefore, when luminescence occurs when the surface of the wafer 3 is scanned with an electron beam, , Light longer than the wavelength corresponding to the bandgap energy is transmitted and detected by the photodetector 5. For example, a wafer is subjected to various processes on a semiconductor crystal, and luminescence does not occur if a residual film (such as a silicon oxide film or a resist film) exists in a contact hole or a trench, but the semiconductor crystal itself is irradiated with an electron beam. Then, luminescence is generated, and of the generated light, light longer than the wavelength corresponding to the band gap energy of the wafer 3 is transmitted and detected by the photodetector 5 provided on the back surface. The luminance of the detected light signal is modulated, and an image of a residual film on the surface of the wafer 3 (such as a Si oxide film or a resist film that generates light by electron beam irradiation) is displayed on the screen.

As described above, the electron beam is scanned on the wafer 3 to detect secondary electrons generated at that time, and a secondary electron image is displayed on a screen. Light can be detected and a light image (luminescence image) can be displayed on the screen. This gives 2
The presence of a film that generates luminescence, such as a Si oxide film or a resist film, on the wafer 3 by recognizing the shape of the wafer 3 such as a contact hole or trench by the next electron image and displaying a luminescence image in a different color, for example. It is possible to recognize the location and its amount. In order to make it easy to see the place and the amount, the light signal detected by the photodetector 5 may be subjected to amplitude modulation (for example, amplitude modulation in the Y direction) to make the place and the quantity easy to see. Hereinafter, the configuration will be described in detail with reference to FIG. 2, and the system configuration will be described in detail with reference to FIG.

FIG. 2 is a block diagram showing a main part of the present invention. FIG.
In FIG. 1, the objective lens 11 constitutes the SEM lens barrel 1. The electron beam 21 generated and focused by an electron gun and a condenser lens located above and not shown in the figure.
Is focused on the wafer 3 and narrowed down.

The secondary electron detector 12 emits the electron beam 21 onto the wafer 3 while scanning the surface in the X and Y directions by a deflection system (not shown).
The secondary electrons are captured by the magnetic field of the objective lens 11, run on the axis spirally upward in the direction in which a positive voltage is applied, and are captured to detect secondary electrons.

The stage 4 is for fixing the wafer 3 and moving it to an arbitrary position in the X and Y directions to scan the surface with the electron beam 21. An image is displayed on the screen based on the secondary electron signal of the scanned portion and the optical signal detected from the back surface of the wafer 3, respectively.

The photodetector 5 detects light transmitted through the wafer 3 and emitted from the back, and here comprises an infrared detector 51, a cooling device 52 and the like. .

The infrared detector 51 detects light transmitted through the wafer 3 (for example, longer than the wavelength corresponding to the band gap energy of the wafer 3) out of the cathode luminescence generated when the surface of the wafer 3 is scanned with the electron beam. Wavelength light) and infrared light.

The cooling device 52 is for cooling the infrared detector 51 to increase the S / N ratio to increase the sensitivity. With the above configuration, the electron beam 21
The surface of the wafer 3 is surface-scanned (or line-scanned), secondary electrons emitted from the wafer 3 toward the surface at that time are detected, and a secondary electron image is displayed on a screen. Of the cathode luminescence generated by the semiconductor product on the bottom of the hole, the wafer 3
(Usually infrared light) transmitted through is detected by the high-sensitivity infrared detector 51 cooled by the cooling device 52, and a light image (luminescence image) is displayed on the screen in different colors. At this time, if the detector cannot be directly placed on the back surface due to the structure of the device, light may be guided to an appropriate position using an optical fiber and detected. By simultaneously observing these secondary electron images and luminescence images of different colors, it is possible to recognize which contact hole or trench is on the wafer 3 by the secondary electron image, and to expose the semiconductor crystal in the luminescence image. It is possible to easily recognize the position and amount of a semiconductor product that generates cathode luminescence such as the bottom of a contact hole or the bottom of a trench. This makes it possible to take out the wafer 3 flowing on the manufacturing line and easily detect the presence of a residual film such as a contact hole or the bottom of a trench without destruction by the apparatus of the present invention.

FIG. 3 shows a system configuration diagram of the present invention.
3, the secondary electron detector 12 is the secondary electron detector 12 shown in FIG. 2, and detects secondary electrons generated when a surface scan is performed while irradiating the wafer 3 with the electron beam 21. is there.

The amplifier 13 amplifies the secondary electron signal detected by the secondary electron detector 12, and amplifies the signal.
5, for amplifying to an appropriate level and amplitude for luminance modulation or the like.

The photodetector 5 applies the electron beam 21 to the wafer 3
Is a detector that detects light from the back surface of the wafer 3 when scanning the surface while irradiating the wafer 3. The amplifier 14 includes the photodetector 5
Amplifies the signal of light detected by the image display device 1
5, for amplifying to an appropriate level and amplitude for luminance modulation or the like.

The image display device 15 displays a secondary electron image and a luminescence image. In this case, the two images are superimposed and different colors to be a secondary electron image or a luminescence image. Are displayed so that they can be distinguished and recognized. At this time, the surface of the wafer 3 is scanned with an electron beam, and the secondary electron signal and the luminescence signal detected at that time are subjected to luminance modulation to display the secondary electron image and the luminescence image in different colors. The secondary electron signal and the luminescence signal detected at that time by line scanning with an electron beam are both amplitude-modulated and correspond to the brightness and shape of the secondary electron image on the line of the wafer 3 scanned by the electron beam 21 with different colors. In addition, the brightness and the shape of the luminescence image may be displayed in an easily viewable manner. Further, the wafer 3 is linearly scanned by the electron beam on the wafer 3 at a predetermined interval, and based on the secondary electron signal and the luminescence signal detected at that time, the amplitude is modulated at the predetermined interval and the wafer scanned with the electron beam 21 in a different color. The brightness and shape of the luminescence image may be displayed in a three-dimensional manner so that the brightness and shape of the luminescence image are easily associated with the brightness and shape of the secondary electron image on line 3.

[0031]

As described above, according to the present invention,
A photodetector 5 for detecting light is installed on the back surface of the wafer 3, which is a sample, and the cathode luminescence on the back surface when the wafer 3 is scanned with an electron beam is detected, and secondary electrons and the like are detected and associated with each other. Is displayed, the luminescence image of the semiconductor crystal can be displayed in association with the shape of the wafer 3 and the like, and the presence or absence and position of the remaining film can be detected. As a result, contact holes and trenches on a semiconductor wafer with a large aspect ratio can be measured at the same time as the length measurement using a low-acceleration voltage electron beam used for length measurement by SEM, and the conventional wafer can be broken. It is possible to determine the remaining film without destruction without performing, and it is possible to take out an arbitrary wafer on the manufacturing line, perform length measurement and determine the remaining film, and return to the original manufacturing line, thereby improving the yield. Can be.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of one embodiment of the present invention.

FIG. 2 is a configuration diagram of a main part of the present invention.

FIG. 3 is a system configuration diagram of the present invention.

[Explanation of symbols]

 1: SEM lens barrel 11: Objective lens 12: Secondary electron detector 13, 14: Amplifier 15: Image display 2: Vacuum chamber 21: Electron beam 22: Secondary electron 3: Wafer 4: Stage 5: Photodetector 51: Infrared detector 52: Cooling device

Claims (4)

[Claims] 1. A catholyte luminescence device for detecting luminescence generated by irradiating an electron beam onto a surface of a sample, comprising: a stage for holding the sample to be irradiated with the electron beam; A photodetector for detecting the light to be emitted, and a means for displaying an image based on a signal detected by the photodetector. 2. A catholyte luminescence device for detecting luminescence generated by irradiating an electron beam on a surface of a sample, comprising: a stage for holding the sample to be irradiated with the electron beam; A photodetector for detecting light to be emitted, a detector for detecting charged particles emitted on the sample irradiated with the electron beam or a current absorbed by the sample, and a signal detected by the photodetector. And a means for displaying an image and displaying the image based on the signal detected by the detector. 3. The cathode luminescence device according to claim 2, wherein both images are displayed in association with each other. 4. The cathode according to claim 1, wherein said electron beam is line-scanned or surface-scanned on a sample to display an image corresponding to said line-scanning or surface-scanning. Luminescence device.