JPH0982771A - Method and apparatus for evaluating semiconductor material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to detect the luminescence due caused by dielectric breakdown, leakage or other defect in the infinitesimal area of a semiconductor or an IC material with the accuracy of 1μm or less by detecting a near field light generated from an electrified semiconductor material. SOLUTION: A semiconductor material 1 is electrified, and a near field light generated from the electrified material 1 is detected. For example, the surface of a sample 1 is scanned while vibrating a probe 7 in the mode that a high-frequency vibration having small amplitude is superposed on a low-frequency vibration having an amplitude equivalent to the light wavelength in the state that the sample 1 is electrified. When the end of the probe 7 is brought into contact with the surface of the sample 1, the amplitude or frequency of the vibration of the probe 7 is varied, and hence the change of the high-frequency vibration component is detected by displacement detecting mechanism 13 to 15, and the height regulation of the Z-axis of the sample 1 is fed back. The light captured by the probe 7 is divided to be detected corresponding to the low-frequency vibration of the probe 7, and the precise distribution of the luminescence from the infinitesimal position is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for detecting fine defects in a semiconductor material to evaluate its quality.

[0002]

2. Description of the Related Art Semiconductors and ICs often have fine defects due to dielectric breakdown and electrical leakage inside the material. Dielectric breakdown and electrical leakage are
It is caused by various factors such as the thickness and material of the insulating film used for C, the flatness of the surface, contamination by impurities, pinholes, fine particles or foreign substances / inclusions, and changes in internal structure due to stress. Therefore, detecting defects and their positions in the semiconductor material with high accuracy and further clarifying their causes are guidelines for reviewing the design specifications of the semiconductor element and improving the manufacturing process, and thus improve the reliability of the semiconductor element. That is extremely important above.

By the way, when a semiconductor / IC element is energized to operate, a light emission phenomenon is sometimes observed. This light emission includes not only light emission based on the above defects but also high energy electrons (hot electrons or hot electrons). There is light emission by the carrier). In the case of a field effect transistor (FET), the high-energy electrons enter the insulating film and damage the insulating film, thus deteriorating the electrical characteristics.

Therefore, it is important to elucidate where in the IC and under what kind of energization conditions hot carriers are generated in order to estimate changes in the IC over time and to evaluate reliability. That's right. Therefore, capturing and analyzing the light emission from the semiconductor / IC element is a very useful method for clarifying the defect of the semiconductor material and its cause.

[0005]

Conventionally, this kind of light emission observation has been carried out by energizing a semiconductor element to operate it, enlarging the light emission generated in the element with a microscope, and then dispersing it with a monochromator to increase photoelectron enhancement. A method of measuring the amount of light by a double tube or CCD has been used.

However, in semiconductors and ICs, the degree of integration has been increasing year by year, beginning with LSI (large-scale integrated circuits), and miniaturization has been progressing. For example, in a 16 Mbit random access memory (DRAM), the wiring width and the size of an electrical operation area are 1 μm or less, and in a 1 Gbit memory, the size is 0.1 μm. Therefore, when evaluating the above-mentioned dielectric breakdown, leakage, and hot carriers, it is necessary to observe and evaluate in a minute region of 0.1 μm or less.

However, in the conventional method of observing with a microscope, in principle, the wavelength is less than the wavelength of visible light, that is, 0.5 to
Since it is impossible to observe a minute portion of 1 μm or less and it is difficult to evaluate a high density element such as an LSI, a new method that enables highly accurate observation in such a minute area has been demanded.

[0008]

The present invention is a semiconductor, IC
Focusing on the near-field light of the light emitted from the defect portion when the device is energized and operated, the method and apparatus described later for accurately detecting the position achieves the intended purpose.
By the way, this near-field light is a light wave that exists only in the vicinity of the material surface because of the property of exponentially decaying with the distance from the material surface, and the existing area (distance from the material surface) is the wavelength of light. The degree, that is, usually several hundreds nm or less. Therefore, the detection of near-field light means that a defect or the like exists at that position.

Therefore, the first invention of the present application relates to a method for evaluating a semiconductor material, which has a step of energizing the semiconductor material and a step of detecting near-field light generated from the energized semiconductor material. Is characterized by.

The second invention of the present application relates to a semiconductor material evaluation apparatus, including a sample table on which a sample to be tested is mounted, means for energizing the sample, a probe for capturing near-field light generated from the sample, A vibration mechanism that vibrates the probe in the direction perpendicular to the sample surface, a displacement detection mechanism that detects changes in the amplitude or frequency of the probe vibration and controls the gap between the sample surface, and the light captured by the probe It is characterized by having a photodetection system that detects the light by dividing it according to the vibration of the.

A third invention of the present application relates to a method for evaluating a semiconductor material, wherein a probe for detecting near-field light in the first invention is provided with a periodic vibration having a high frequency and a small amplitude and a periodic vibration having a low frequency and a large amplitude. It is characterized in that it is detected while being overlaid with vibration.

A fourth invention of the present application relates to a method for evaluating a semiconductor material, wherein the frequency of periodic vibration with high frequency and small amplitude, which is excited by the probe in the third invention, is 1 k.
It is characterized in that the amplitude is 500 nm or less at Hz or more, and the frequency of periodic vibration having a low frequency and a large amplitude is 10 kHz or less and the amplitude is 400 nm or more.

A fifth invention of the present application relates to a semiconductor material evaluation apparatus, wherein the displacement detecting mechanism of the probe in the second invention is such that the high frequency vibration of the probe changes in frequency and amplitude and the low frequency vibration changes in frequency and amplitude. The feature is that it is a displacement detection mechanism capable of distinguishing and detecting.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION A semiconductor / IC evaluation apparatus according to the present invention has the following outline. A sample table for fixing semiconductor / IC test samples that enables precise movement / positioning in the horizontal direction (X axis, Y axis) and height direction (Z axis). A small probe that captures near-field light. The probe may be formed by processing the tip of a transparent material such as thin quartz glass fiber into a needle shape, or may be a fine light receiving material such as a photodiode. The probe is provided with a vibrating mechanism for vibrating in the direction perpendicular to the sample surface and its control system. A displacement detection mechanism and control system for detecting a change in amplitude or frequency of vibration of a probe to control the distance between the tip of the probe and the sample surface. A light detection system that allows the light captured by the probe to be split and detected by a detector such as a lock-in amplifier according to the vibration of the probe. A control system that controls near-field light imaging by controlling the vibration of the probe, movement of the sample stage, detection of light captured by the probe, and displacement detection of probe vibration.

The outline of the measuring method according to the present invention is as follows. While the sample is energized, the sample surface is scanned while vibrating the probe in a mode in which low-frequency vibration having an amplitude of about the wavelength of light and high-frequency vibration having a small amplitude are superimposed. Scanning is performed by XY movement of the sample with the probe fixed. When the tip of the probe comes into contact with the sample surface, the amplitude or frequency of the vibration of the probe changes, so the change in the high-frequency vibration component is detected by the displacement detection mechanism, and feedback is applied to the height adjustment of the Z axis of the sample. This allows the probe to detect minute changes in the shape of the sample surface,
It is controlled so that it always vibrates at a constant interval from the sample surface.

The light captured by the probe is divided and detected according to the frequency of the low frequency component of the probe, and the intensity (S) of the near-field light mainly when the probe is closest to the sample surface and the sample surface. By plotting the difference from the intensity (B) of the scattered light mainly at the farthest from the scanning region, a precise distribution of the light emission from a minute portion is obtained. Near-field light is mostly attenuated from the surface to 400 to 500 nm. Therefore, by obtaining the S / B ratio (signal / background ratio) in this way, the location where near-field light is generated, that is, the location where defects are present is determined. To be

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an element-related diagram for explaining the essential structure of an apparatus for evaluating semiconductors and IC materials according to the present invention.
Reference numeral (1) is a semiconductor or IC sample, which is placed on a sample table (2) equipped with a piezo actuator (3) and a step motor (5) and is tested by being energized by an external power source. (4) is the XYZ of the piezo actuator
3-axis controller, (6) is a step motor 3-axis controller. The step motor has an accuracy of the order of μm, and the piezo actuator has an XYZ 3
Both axes have an accuracy of the order of 0.1 nm.

The probe (7) made of an optical fiber made of quartz glass is made by bending a fiber having a diameter of 50 μm at a substantially right angle to squeeze the tip and then etching with hydrofluoric acid to form a needle. The radius of curvature of the tip is 2 nm or less. In addition, a flat surface is provided on the bent portion of the fiber to reflect the light from the laser diode (13). The fiber is coated with a metal film, leaving a few tens of nanometers at the tip, to prevent light from entering from other than the tip. (8) is a photomultiplier tube that detects the light beam captured by the probe, and (9) is a lock-in amplifier that detects and amplifies the photoelectron flow in synchronization with the low-frequency vibration of the probe. (1
0) is the same as (1)
1) is a piezo actuator for vibrating low frequency vibration, and the frequency and amplitude are adjusted by the modulator (12). The probe has its horizontal portion fixed to (10) and (11) by adhesion. However, it is also possible to generate high-frequency vibration and low-frequency vibration with one piezo actuator.

(13) and (14) are constituent elements of the displacement detection mechanism, which are a laser diode and a photodiode for detecting changes in the amplitude of the probe due to irregularities on the sample surface, respectively. The laser diode uses a red communication element, and the light reflected from the probe is reflected by the photodiode (1
Detected in 4). (15) is an amplitude detector including an analog / digital converter. (16) is the vibration of the probe,
A control system including a computer for controlling photocurrent detection and XYZ movement of a sample, (17)
Is a monitor that depicts the two-dimensional distribution of near-field light.

In the evaluation of semiconductors, ICs, etc. by this apparatus, first, the sample 1 fixed to the sample table is energized from an external power source through the lead frame to bring it into an operating state. next,
The sample table is moved so that a predetermined part of the sample is located directly below the probe 7, and the surface of the sample is brought close to the probe. A low-frequency vibration and a high-frequency vibration are applied to the probe 7, and the displacement is constantly monitored by a displacement detection mechanism using a laser beam by a change in the amplitude of the high-frequency vibration component.

When the sample is brought closer to the probe in this state and the surface of the sample comes into contact with the tip of the probe, the amplitude of the high frequency vibration component of the probe changes. Therefore, feedback is applied to the Z-axis piezo of the sample stage in response to the change in the amplitude, and the sample is moved in the XY directions while always maintaining a constant gap between the sample surface and the probe, and the sample surface is probed. To scan sequentially. The vibration applied to the probe has a frequency of 5 to 50 kHz, which is close to the resonance frequency of the probe, and an amplitude of 10 to 50 nm.
The low-frequency excitation has a frequency of 0.5 to 5 kHz and an amplitude of about the size of the region where near-field light exists, that is, 400 to 1000 n.
m is suitable. Outside this range, the visible light range is exceeded, and the sensitivity and accuracy of measurement deteriorate.

While scanning the surface of the sample in this manner,
The intensity of the light captured by the probe is continuously measured and the S /
B ratios are plotted sequentially. As described above, near-field light is mostly attenuated from the surface to 400 to 500 nm, so S /
A location where the B ratio changes greatly is detected with extremely high accuracy as a location of near-field light, that is, a location where a defect or the like exists.

Ten samples that had been previously tested by the method of the present invention were tested for the presence of defective points by the conventional method. As a result, 20 of the defective points detected by the method of the present invention were detected.
Only% was detected. The results show that the practice of the present invention significantly enhances the reliability of semiconductor materials.

[0024]

According to the present invention, it is possible to detect light emission due to dielectric breakdown, leakage or other defects in a minute area of a semiconductor or IC material, which has been difficult in the past, with an accuracy of 1 μm or less, and to identify a place where a defect has occurred. By becoming accurate, I
It has an extremely beneficial effect on C and LSI design, process development, manufacturing, and product management improvement.

[Brief description of drawings]

FIG. 1 is an element-related diagram illustrating a main part configuration of an embodiment of an evaluation device according to the present invention.

[Explanation of symbols]

 1 sample 2 sample stage 3,5 sample fine movement device 7 probe 8 photomultiplier tube 9 lock-in amplifier 10,11 exciter 13,14,15 displacement detection mechanism 16 control system 17 monitor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kiyozo Doi 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Toshiba Research & Development Center

Claims (5)

[Claims] 1. A method of evaluating a semiconductor material, comprising: a step of energizing a semiconductor material; and a step of detecting near-field light generated from the energized semiconductor material. 2. A sample table on which a sample to be tested is placed, a means for energizing the sample, a probe for capturing near-field light generated from the sample, and a probe for vibrating the probe in a direction perpendicular to the sample surface. A vibration mechanism, a displacement detection mechanism that detects changes in the vibration amplitude or frequency of the probe to control the gap with the sample surface, and a light detection system that detects the light captured by the probe by dividing it according to the vibration of the probe. An apparatus for evaluating a semiconductor material, comprising: 3. A probe for detecting near-field light is detected by superimposing a periodic vibration having a high frequency and a small amplitude and a periodic vibration having a low frequency and a large amplitude, while vibrating. The method for evaluating a semiconductor material described in. 4. The frequency of periodic vibration having a high frequency and a small amplitude is 1 kHz or more and the amplitude is 500 nm or less, and the frequency of a periodic vibration having a low frequency and a large amplitude is 10 kHz.
The method for evaluating a semiconductor material according to claim 3, wherein the amplitude is 400 nm or more. 5. The semiconductor according to claim 2, wherein the displacement detecting mechanism of the probe is a displacement detecting mechanism capable of separately detecting a change in frequency and amplitude of high frequency vibration of the probe and a change in frequency and amplitude of low frequency vibration of the probe. Material evaluation equipment.