JP2890840B2 - Evaluation method of semiconductor device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating a semiconductor device, and more particularly, to a method for analyzing a failure of a semiconductor device and a method for evaluating reliability.

2. Description of the Related Art Conventionally, an EB (Electron Beam) tester has been used for analyzing the operation of a semiconductor device. In this method, first, the chamber in which the sample is placed is evacuated to vacuum, the sample is actually operated, an electron beam of several to several tens keV is irradiated while the sample is operating, and the sample is emitted by secondary electrons emitted from the sample. Of the semiconductor device is normally operated by evaluating the voltage in the operating state of the semiconductor device.

Problems to be Solved by the Invention According to the above-described method, it is necessary to evacuate the chamber in which the sample is placed, so that there is a problem that it takes a long time for the evaluation. Furthermore, the surface of the sample must be made conductive to prevent charge-up due to irradiation electrons,
Since the process of removing the protective oxide film must be performed, there is also a problem that the evaluation cannot be performed easily.

The present invention has been made to solve the above-described problem, and has as its object to provide a method for evaluating a semiconductor device in a short time and easily.

Means for Solving the Problems The present invention is a semiconductor device evaluation method for examining the voltage of a semiconductor element constituting the device by performing wavelength analysis of light emission from the semiconductor device during operation using a weak light measuring device. is there.

Using a weak light measuring device and examining the spectrum of light emission from a semiconductor device in an operating state using a wavelength filter or a spectroscope, the relationship between the energy E corresponding to each wavelength and the light emission amount N per unit energy was found. Empirical formula N = Ce
xp (−E / k * Te)) (where C is a constant and k is Boltzmann's constant), where the electron temperature Te obtained as a constant is
It has been found that the voltage varies depending on the voltage applied to the semiconductor element. Therefore, each semiconductor element (eg, transistor, diode, etc.) that constitutes the semiconductor device to be evaluated
After examining the relationship between the electron temperature and the applied voltage by emission analysis, if the electron temperature of the operating semiconductor device is examined, the voltage applied to each component can be obtained.

First Embodiment First, a method for measuring the electron temperature of a semiconductor element in operation using a weak light measurement device will be described. FIG. 1 shows a diagram of an apparatus for evaluating a semiconductor device according to a first embodiment of the present invention. In FIG. 1, an evaluation sample 3 is set on a microscope 2 in a dark room 1, a light source 4 and light from the outside are shut off, a voltage is applied to the evaluation sample 3 from a power supply 9, and the light emission is enlarged by a microscope. Further, the light is input to the photomultiplier 5 through the wavelength filter 10, and the highly multiplied light emission is digitized and stored in the internal memory of the controller 8 for a certain period, and the light emission amount of the wavelength corresponding to the wavelength filter 10 is detected. According to this method, the emission amount is measured for at least two different wavelengths (for example, 500 nm and 700 nm). Next, from the measured data, the relationship between the energy E corresponding to each wavelength and the light emission amount N per unit energy is an empirical formula N = Cexp (−E / k * Te)) (C is a constant, k is a Boltzmann constant) ), This relational expression is
We used the one reported by Mr. Toriumi of Toshiba. I E
EE Transaction Electron Devices (IEEE, Trans. Electron Devices), vol. ED-34, pp.15
01 to 1508, 1987) The electron temperature Te can be obtained by calculation.

Next, the first embodiment of the present invention will be described in detail with reference to experimental data. As an evaluation sample, a semiconductor device whose operation is to be analyzed and each semiconductor element constituting the semiconductor device are individually prepared. First, in order to analyze the operation of a CMOS semiconductor circuit, a single Nc
An hMOS transistor (hereinafter referred to as N-MOSFET) and a PchMOS transistor (P-MOSFET) were prepared. Next, according to the method described above, the relationship between the applied voltage and the electron temperature of each semiconductor element is examined using a weak light measuring device. The relationship between the applied voltage of the N-MOSFET and the electron temperature is shown in FIGS. FIG. 2 shows N
-Changes in electron temperature when the drain voltage is changed while keeping the gate voltage applied to the MOSFET constant, and FIG. 3 shows changes in the electron temperature when the gate voltage is changed while the drain voltage is constant. . From FIGS. 2 and 3, it can be seen that the electron temperature of the N-MOSFET does not depend much on the gate voltage but changes greatly with the drain voltage. This relationship is the same for the P-MOSFET. Therefore, if the semiconductor device to be analyzed is operated and the electron temperatures of the N and P-MOSFETs are checked,
The drain voltage of the MOSFET in the device is obtained from the experimental data shown in FIGS. In other words, the operating voltage of the constituent elements of the semiconductor device at any location can be checked by light emission analysis, eliminating the need to make the sample surface conductive and the sample evaluation atmosphere to be a vacuum, unlike the conventional EB tester. Can be easily evaluated.

(Embodiment 2) FIG. 4 is a diagram showing an apparatus for evaluating a semiconductor device according to a second embodiment of the present invention. The difference from the first embodiment is that a spectroscope 20 is used instead of the wavelength filter 10. The measuring method is almost the same as in the first embodiment. Spectrometer
The light emission amount of the semiconductor element and the semiconductor device is measured for at least two different wavelengths (for example, 500 nm and 700 nm) using 20 and the electron temperature is obtained from the light emission amount. The method of obtaining the operating voltage of each semiconductor element from the relationship between the electron temperature and the applied voltage is the same as in the first embodiment. Further, since the spectroscope 20 can be automated by providing the controller 8 with the control function of the spectroscope 20, faster and more accurate data can be obtained.

(Embodiment 3) FIG. 5 shows a semiconductor device evaluation apparatus diagram in a third embodiment of the present invention. The difference from the first embodiment is that the spectroscope 20 is used in place of the wavelength filter 10, the power supply 9 is a pattern generator 30, and the photomultiplier 5 is provided with a gate function that operates at high speed. And the controller 8 is provided with a control function of the spectroscope 20, the pattern generator 30, and the photomultiplier 5. According to the pattern of the pattern generator 30 input to the semiconductor device to be evaluated, the gate of the photomultiplier 5 is operated in synchronization with the timing to be measured, and the light emission of at least two wavelengths or more is measured using a spectroscope. The electron temperature of each semiconductor element is obtained, and the operating voltage of each semiconductor element at the timing to be measured can be checked from the relationship between the electron temperature and the applied voltage. According to this measuring method, it is also possible to perform a timing analysis for checking an instantaneous AC operation of a complicated semiconductor integrated circuit.

(Example 4) A fourth example of the present invention will be described. The same evaluation device as that of the first or second embodiment is used. First, an appearance image of a semiconductor device to be evaluated is measured by the following procedure. In the dark room 1, the evaluation sample 3 is placed on the microscope 2
Is set, the external appearance image of the evaluation sample 3 is magnified in a state where the light is irradiated from the light source 4 of the microscope 2, input to the photomultiplier 5 and the video camera 6, and the image of the controller 8 is stored in the internal memory. Next, in accordance with the first or second embodiment, a voltage is applied from the power supply 9 to the evaluation sample 3 to measure a two-dimensional distribution of light emission amounts of at least two different wavelengths or more (for example, 500 nm and 700 nm). 8 to store and store data. FIG. 6 is a schematic view of an appearance image of the semiconductor device. Although only the Al wiring 40 is schematically shown,
Here, a transistor A; 41 and a transistor B; 42 are formed. FIG. 7 is a schematic view of a stored image of a two-dimensional distribution of light emission using a bandpass filter having a center wavelength of 700 nm and a half-value width of 10 nm. 43 and 44 are 70 transistors of transistors A and B, respectively.
It is an emission image at 0 nm. An accumulated image of a two-dimensional distribution of light emission using a band-pass filter having a center wavelength of 500 nm and a half-value width of 10 nm is measured in the same manner. The controller 8 stores the light emission amount as a numerical value for each pixel of the screen with respect to the accumulated image of the two-dimensional distribution of the light emission. Next, the empirical formula N =
Using Cexp (−E / k * Te)) (C is a constant, k is a Boltzmann constant), 50
From the accumulated data of the two-dimensional distribution of light emission at 0 nm and 700 nm, the electron temperature for each pixel on the screen is calculated. In FIG.
A schematic diagram of a two-dimensional distribution of electron temperatures obtained by the calculation is shown. 45 and 46 are distribution diagrams of the electron temperatures of the transistors A and B, respectively. The electron temperature is classified into several levels according to the temperature. FIG. 9 shows a diagram in which the two-dimensional distribution of the electron temperature (FIG. 8) is superimposed on the appearance image of the semiconductor device (FIG. 6) stored in the controller 8. Referring to FIG. 9, it is possible to see at which part of the semiconductor device the electron temperature is high. Since the two-dimensional distribution of the electron temperature shows the operating state of the semiconductor element and the internal energy state of the element caused by voltage application, it is very useful for the operation analysis of semiconductor devices, failure analysis, and reliability evaluation of hot carriers and the like. Give valid information.

If the two-dimensional distribution of the electron temperature is measured at a specific timing as in the third embodiment, the timing analysis of the AC operation of a complicated semiconductor integrated circuit can be performed two-dimensionally. It is possible to dramatically improve the operation analysis efficiency of the device.

EFFECT OF THE INVENTION By using the evaluation method of the present invention, there is no need to evacuate the atmosphere of the evaluation sample and the surface of the sample does not need to be conductive, so that the voltage state of the semiconductor element in the operating state can be easily checked. As a result, the evaluation efficiency of the semiconductor device can be greatly improved. Therefore, it can be said that the present invention is a very effective evaluation method in operation analysis, failure analysis, and reliability evaluation of a semiconductor device.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an evaluation device according to a first embodiment of the present invention,
FIG. 2 is a characteristic diagram showing the drain voltage dependence of the electron temperature of the N-MOSFET obtained by using the evaluation apparatus of the present invention, and FIG. 3 is a characteristic diagram showing the gate voltage dependence of the electron temperature of the N-MOSFET. FIG. 4 is a schematic configuration diagram of an evaluation device of a second embodiment of the present invention, FIG. 5 is a schematic configuration diagram of an evaluation device of the third embodiment of the present invention, and FIG. FIG. 7, FIG. 7 is a schematic diagram of an accumulated image of a two-dimensional distribution of light emission using a bandpass filter having a center wavelength of 700 nm and a half-value width of 10 nm, FIG. 8 is a schematic diagram of a two-dimensional distribution of electron temperatures obtained by calculation, FIG. 9 is a diagram showing a two-dimensional distribution of the electron temperature of the semiconductor device in which FIGS. 6 and 8 are overlapped. 2 ... microscope, 3 ... evaluation sample, 5 ... photomultiplier,
6 video camera, 7 display, 10 wavelength filter, 11 light emission, 20 spectroscope, 30 pattern generator.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 21/66 G01B 11/00

Claims (2)

(57) [Claims] 1. A method for measuring the amount of light emitted from a semiconductor device during operation using at least two different wavelengths using a faint light measuring device, wherein energy corresponding to each wavelength is E, and light emitted per unit energy is N. Then, the empirical formula N = Cexp
(−E / K * Te)) (C is a definition, K is a Boltzmann definition), an electron temperature Te is calculated, and a voltage of a semiconductor element constituting the semiconductor device is checked based on the electron temperature. Evaluation methods. 2. A two-dimensional distribution of light emission from a semiconductor device in an operating state is measured for at least two different wavelengths using a weak light measuring device, and energy corresponding to each wavelength is E, light emission per unit energy. When the quantity is N, a two-dimensional distribution of the electron temperature Te is calculated using an empirical formula N = Cexp (−E / K * Te)) (C is a definition, K is a Boltzmann definition), and the two-dimensional distribution is calculated. A method for evaluating the electron temperature distribution of a semiconductor element by superimposing the electron temperature distribution on a micrograph of the semiconductor device.