JP2007292623A - Material evaluation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To quantitatively measure the charge flaw in the material that is a target of evaluation, by analyzing the charge phenomenon of X-ray photoelectric spectroscopy. <P>SOLUTION: In a process 1, a plurality of operation diaphragms, having different pore sizes, are provided to the front of a sample, in order to vary the irradiation area of X rays applied to the sample; in a process 2, the operation diaphragm are used so as to uniformize the intensity distribution of the X rays, applied to the sample, to perform measurements; and in a process 3, the start and completion of the irradiation of the sample with X rays are performed by a high-speed shutter provided between the X-ray source and the sample using X rays radiated from the X-ray source, in a steady state. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an apparatus for evaluating hole traps and electron traps in materials having a band gap (semiconductor material, phosphor material, functional insulator material, etc.) having a significant effect on the characteristics of the material.

  Semiconductor materials, phosphor materials, and functional insulator materials are structurally sensitive materials, and very few impurities and defects determine their characteristics. Various evaluation methods have been developed to evaluate the defect concentration, the trapping relaxation time for the defect, and the energy level of the defect.

  In the Si-MOS type semiconductor device, a method of measuring the relationship between the capacitance of the MOS structure and the applied voltage, called CV (electric capacity / voltage) method, has been widely used. This method can evaluate interface traps in Si-MOS structures and defects in oxide films. However, although the CV method is simpler than making an actual device, it is necessary to form a device for evaluation and attach an electrode.

Further, an x-ray topography technique is often used for observing crystal defects in a Si single crystal or a GaAs single crystal. This method can observe crystal defects without breaking or scraping the Si wafer or GaAs wafer without breaking it. However, it is limited to a single crystal substrate.
DLTS is a technique for measuring the transient process of capacitance by thermal excitation, and is used for trap analysis in various semiconductors such as Si, GaAs, InP, etc. This technique also needs to form a simple device structure and electrodes. .

  Development of a technique that can easily evaluate traps in various materials without forming electrodes or element structures has been desired. As one of such techniques, the present inventor has proposed time-resolved x-ray photoelectron spectroscopy. First, the difference between normal x-ray photoelectron spectroscopy and time-resolved x-ray photoelectron spectroscopy will be described.

  X-ray photoelectron spectroscopy, which evaluates a photoelectron spectrum generated by irradiating a sample with x-rays, is widely used as a composition analysis on the surface of various materials and an analysis method of chemical bonding states. In the case where the material is a semiconductor or an insulator, it is also well known that a charging phenomenon occurs in a sample due to emission of photoelectrons. This charging phenomenon changes the energy value of the photoelectron spectrum, making it difficult to evaluate the chemical bonding state. Until now, in order to suppress the charging phenomenon during measurement by x-ray photoelectron spectroscopy, it has been mainly performed to perform neutralization treatment to compensate the charge amount by irradiating the sample with electrons or ions during the measurement.

  On the other hand, the present inventor has proposed that the charging phenomenon is also a physical phenomenon, and that the charging phenomenon is used for evaluating charge defects in semiconductors and insulators. That is, the gist of the present invention. It has already been reported by the present inventor in Journal Applied Physics (Applied Physics Reviews), 79 (1996), pp.6653-6713 that the charging phenomenon is due to charge trapping on defects in semiconductors and insulators. Reference 1]. That is, charges such as electrons and holes can be generated in the material by x-ray irradiation on the material having a band gap. Charges generated by irradiation are trapped by defects in the material. This charge trapping phenomenon is affected by the density of defects, the ease of trapping (capturing cross section or 1 / capture relaxation time), and the energy state of the defects. Accordingly, by observing the charge trapping process, that is, the charging process, various defects in the material having the band gap can be evaluated (Patent Document 1). Since metal does not have a band gap, charging does not occur even if there is a defect.

  In the evaluation of various defects inside a material having a band gap using the charging phenomenon of this x-ray photoelectron spectroscopy, it is necessary to form an element structure for evaluation as compared with various electrical methods in the previous period. There is an advantage that electrode formation is unnecessary.

  However, from the viewpoint of quantitative analysis, in the conventional methods, the uniformity of the intensity of the irradiated x-ray, the uncertainty of the irradiation area, the temporal stability of the x-ray intensity, particularly the x-ray intensity immediately after the start of irradiation. There was a problem with stability.

JP-A-9-162253 S. Iwata & A. Ishizaka; Journal Applied Physics (Applied Physics Reviews), 79 (1996), pp.6653-6713

  The first problem to be solved is to control the x-ray irradiation area when evaluating charge defects in the material to be evaluated by analyzing the charging phenomenon of x-ray photoelectron spectroscopy, thereby enabling quantitative analysis. thing. For that purpose, it is possible to irradiate a desired irradiation area with x-rays of uniform intensity. The second problem to be solved is to make it possible to measure the initial stage of the trapping phenomenon of the electric charge trap defect that has the greatest influence on the physical properties of the electronic material, that is, the initial stage of the charging phenomenon. If the intensity of x-rays fluctuates in the early stage of x-ray generation, the effect of fluctuations in the x-ray intensity and changes due to the trapping process in the charge traps in the sample overlap, making quantitative analysis difficult. The challenge is to be able to irradiate x-rays with a constant intensity with little time fluctuation from the very beginning of measurement. To measure the initial stage of charging phenomenon at high speed, measure the sample current.

1 In order to make the irradiation area of x-rays applied to the sample variable, an operating aperture having a different hole diameter is provided between the x-ray source and the sample.
2. A method of measuring with an optimum aperture diameter using the operating aperture of 1 above so that the intensity distribution of the x-rays hitting the sample can be measured uniformly.
3 After generating x-rays and keeping them in a steady state, the start and end of irradiation of the x-ray sample are performed with a high-speed shutter provided between the x-ray source and the sample.
4 In order to measure the initial stage of the charging phenomenon at high speed, the high speed shutter is opened and the sample current is measured at high speed in synchronization with the start of x-ray irradiation.

  Since the sample can be irradiated with a uniform area of x-rays with a fixed area, quantitative x-ray photoelectron spectroscopy is possible. In addition, it is possible to analyze an initial process with the most drastic change in the charge accumulation process, which has been difficult with time-resolved x-ray photoelectron spectroscopy. The evaluation apparatus of the present invention can be applied to the evaluation of a material having a band gap.

  A squeezed mask and a high-speed shutter are installed between the x-ray source of the x-ray photoelectron spectrometer and the sample.

FIG. 1 is a cross-sectional view of one embodiment of the apparatus of the present invention.
This is an evaluation apparatus in which a conventional aperture mechanism and a high-speed shutter mechanism having different hole diameters are installed in a conventional x-ray photoelectron spectrometer.

FIG. 2 shows the x-ray irradiation area when the aperture mask area is changed and the sample current flowing from the sample to the ground in order to compensate for the photoelectron intensity emitted from the sample with the x-ray irradiation. It shows the relationship with the measurement results. By changing the diameter of the aperture, the irradiation area of x-rays was changed to 20, 40, 60, 75, 85, 100 mm ² . This hole diameter can be set arbitrarily. In general, when the sample is a metal, it is known that the charging phenomenon does not occur, the intensity of the emitted photoelectrons is proportional to the x-ray intensity, and the sample current is proportional to the photoelectron intensity. As a sample, Au subjected to a clean surface treatment was used. If the sample is a metal with a clean surface such as Au, the charge will not accumulate in the sample and will not be charged, so we will investigate the performance of the high-speed shutter and operating aperture of the x-ray photoelectron spectrometer in the present invention. Is suitable. When the aperture area is large, the intensity of x-rays is reduced in the peripheral area as compared with the central area of x-ray irradiation, so that the relationship between the sample current and the aperture area deviates from the straight line. Therefore, in the quantitative analysis of the x-ray photoelectron spectroscopy, evaluation was performed in the portion maintaining the linear relationship in FIG. 1 (in this figure, the area of x-ray irradiation is 75 mm ² or less).

  FIG. 3 shows the time variation of the sample current at the initial stage of x-ray irradiation. Reference numeral 11 in FIG. 3 represents the initial time change of the change in the sample current when the x-ray power supply is turned on. Reference numeral 12 in FIG. 3 represents an initial time change of the change in the sample current when the x-ray is generated and kept in a steady state, and the shutter is opened and the sample is irradiated with the x-ray. The time required to open and close the shutter was 4ms (1 / 250s). The opening / closing of the shutter may be performed by a control unit of the apparatus, or may be manually performed by an operator. Comparing 11 and 12 in FIG. 3, it was shown that 12 was irradiated with x-rays at a constant intensity from the beginning of x-ray irradiation start.

  The time-dependent x-ray photoelectron spectroscopy shown in Example 1 was evaluated in order to clarify the temporal deterioration phenomenon of luminance during use of a green phosphor in which 200 ppm of Al and 100 ppm of Cu were added to ZnS. As a result, it was found that the amount of charge during the measurement of the x-ray photoelectron spectroscopy was larger for a sample that was irradiated with an electron beam to the phosphor and the luminance change with time was large and the luminance was greatly deteriorated. In particular, it was found that a phosphor sample whose luminance was deteriorated at the beginning of measurement of x-ray photoelectron spectroscopy was extremely large as compared with a sample before luminance deterioration. FIG. 4 shows the time dependence of the sample current. 4 in FIG. 4 shows the case of the phosphor sample before the luminance deterioration, and 14 shows the case of the phosphor sample whose luminance is deteriorated by 45%. It can be seen from FIG. 4 that positive charges are trapped in the hole traps in the phosphor sample. FIG. 5 shows the result of rearranging FIG. 4 according to the time dependence of the number of positive charge traps. From FIG. 5, the saturation value of the hole trap concentration is almost the same for the phosphor with degraded luminance and the phosphor before luminance degradation, but the trapping time in the trap is equal to the usage time of the phosphor (= electron beam irradiation). It has been found that the traps in the phosphor sample having deteriorated brightness changed to traps that are easily captured by electron beam irradiation. That is, in the case of the phosphor with deteriorated luminance (16), as compared with the case of the phosphor sample before the luminance deterioration (15), the charges are rapidly captured by the holes with the start of the x-ray irradiation. In trap evaluation in a Si semiconductor, after processing into an element shape, an electrode is attached and electrical evaluation is performed by avalanche charge injection or the like. However, with a powder sample such as a phosphor, it is extremely difficult to process into an element shape and to form an electrode. In the time-dependent x-ray photoelectron spectroscopy shown in the present invention, processing into an element shape is unnecessary and it is not necessary to form an electrode. In addition, the present invention enables quantitative examination as compared with the conventional time-dependent x-ray photoelectron spectroscopy.

As long as the substance has a band gap and causes a charging phenomenon, the time-dependent x-ray photoelectron spectroscopy shown in the present invention can be applied.
Si3N4, which is a material used as a charge retention film of a nonvolatile memory element, SiO2 film used as a gate insulating film of a Si-MOS type semiconductor element, ZnS; Al, Cu phosphor shown in Example 2, etc. The time-dependent x-ray photoelectron spectroscopy shown in the present invention was applied to various materials.
FIG. 6 shows the result of measuring the trap relaxation time of the hole trap of the above substances.

It is a block diagram of the basic composition of the present invention. Example 1 FIG. 6 is a relationship diagram between an x-ray irradiation area and a sample current. Example 1 It is a figure of the time dependence of the sample current at the beginning of x-ray irradiation. Example 1 It is a figure of x-ray irradiation time dependence of sample current. (Example 2) FIG. 6 is a relationship diagram between an x-ray irradiation area and a trapped hole concentration. (Example 2) It is the table | surface which showed the capture relaxation time to the hole trap of various substances. (Example 3)

Explanation of symbols

1 X-ray source.
2 Sample.
3 Sample holder.
4 Electron spectrometer.
5 Data collection and analysis equipment.
6 Ammeter.
7 Movable squeezing.
8 High-speed shutter.
9 Photoelectrons emitted from the sample by x-ray irradiation.
10 Vacuum chamber.
11 Initial time variation of sample current (∝ x-ray intensity) when the x-ray source is turned on.
12 Initial time fluctuation of sample current (∝ x-ray intensity) when using high-speed shutter.
13 Dependence of sample current on x-ray irradiation time during x-ray photoelectron spectroscopy measurement of phosphor (ZnS; Al, Cu) before luminance degradation.
14 Dependence of sample current on x-ray irradiation time during x-ray photoelectron spectroscopic measurement of a phosphor (ZnS; Al, Cu) whose luminance has been degraded by 45% due to aging with electron beam irradiation.
15 Dependence of trap concentration during x-ray photoelectron spectroscopy on hole traps in phosphor (ZnS; Al, Cu) before luminance degradation on x-ray irradiation time.
16 Dependence of trap concentration during x-ray photoelectron spectroscopic measurement on hole trap in phosphor (ZnS; Al, Cu) whose luminance has deteriorated by 45% due to time-dependent change due to electron beam irradiation.

Claims (6)

An X-ray irradiation unit for irradiating the sample with X-rays;
A diaphragm having a plurality of holes with different areas that limit the area irradiated with the sample by the X-ray,
Means for irradiating the X-ray with a limited irradiation area to the sample and measuring a sample current flowing from the sample to the ground;
A shutter for blocking the irradiation of the X-rays to the sample,
An evaluation apparatus comprising control means for controlling the operation of the shutter.   It has a mechanism to generate x-rays, and electrons and holes are generated in semiconductor materials, phosphor materials, and functional insulator materials by x-ray irradiation, and their generation amount changes over time or they are generated. Evaluation with the function to quantitatively evaluate defect traps in band gap materials (electronic materials such as semiconductor materials, phosphor materials, functional insulator materials, etc.) by changing the potential change of the sample surface due to time. apparatus.   3. The evaluation apparatus according to claim 2, wherein the area of the x-ray irradiation portion can be determined, and the x-ray intensity distribution can be irradiated in a uniform state.   3. The evaluation apparatus according to claim 2, wherein when irradiating the semiconductor material, the phosphor material, and the functional insulator material with x-rays, the x-rays with suppressed intensity fluctuation can be irradiated from the very initial stage of irradiation.   5. The sample current flowing from the sample to the ground in the charge trapping process in the charge defect in the sample when electrons and holes generated by x-ray irradiation are generated and photoelectrons are emitted. An evaluation device characterized by obtaining as a change. 5. The time change of the potential change of the sample surface when electrons and holes generated by x-ray irradiation are generated according to claims 2 to 4, wherein the time of the energy position of the photoelectron spectrum peak generated from the sample by x-ray irradiation. An evaluation device characterized by obtaining as a change.