JPH0574937B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an apparatus for evaluating electrical characteristics of semiconductor wafers, and particularly to a configuration suitable for non-destructive measurement of carrier trap levels within a semiconductor.

[Background of the invention]

As a method to measure the carrier life of semiconductors,
There is a method of measuring the phenomenon of transient attenuation of the number of free carriers due to light or electron beam excitation by measuring the change in microwave absorption rate accompanying the change in the number of free carriers.
(Reference 1: Akira Usami, “Silicon wafer lifetime measurement technology using non-contact method”, Electronic Materials (1981, 2nd issue) p. 67, Reference 2: Japanese Patent Application Laid-Open No. 1983-1999-
(No. 55013) This measurement of the microwave absorption rate using a wafer semiconductor crystal as a sample involves detecting reflected microwaves from the wafer, which is practical as there is no restriction on the wafer shape. An example of using this method is described in "Embodiments of the Invention" in Reference 2, but conventional measuring devices such as this known example are intended to measure only the value of carrier life at room temperature. Therefore, the precise measurement of the carrier capture level, which is the purpose of the present invention, is not considered.Therefore, the characteristics of the present invention are 1. Mechanism for controlling the temperature of the sample wafer 2. Water vapor on the sample surface in a low temperature range There are no examples that have a mechanism to prevent the adhesion of.

[Purpose of the invention]

An object of the present invention is to provide a crystal evaluation device for non-destructively measuring carrier trap levels within a semiconductor wafer.

[Summary of the invention]

A feature of the present invention is that the light beam or electron beam and the microwave are applied to the same area on the surface of a wafer-like semiconductor crystal (the irradiation area of the light or electron beam may be completely included within the microwave irradiation area, or vice versa). (The microwave irradiation area may be completely included in the light or electron beam irradiation area.) and (2) a function to keep the sample wafer in a vacuum state and prevent water vapor from adhering to the wafer surface. First, the function (2) makes it possible to measure the reflected microwave intensity at low temperatures with high accuracy. In addition, function (1) is a new function that has not been considered in the past, and this function makes it possible to measure the carrier capture level with high accuracy.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.
First, as shown in FIG. 1, a sample stage 8, which has the ability to store liquid nitrogen and cool the sample, consists of a lid 1 provided with a microwave waveguide 4 and a window material 5 at the tip, a main body 3,
It is installed in a vacuum container consisting of an O-ring 2 and a vacuum pump 13, and keeps the sample wafer in a vacuum state. For this reason, the spaces between the waveguide 4 and the lid 1, and between the tip of the waveguide and the window material 5 are designed to maintain vacuum tightness.

The sample stage 8 is also provided with a cooling system consisting of a liquid nitrogen tank 6, a liquid nitrogen supply pipe 11, a vaporized nitrogen exhaust pipe 12, and a cooling fin 7, and a heater 9, which controls the current value and liquid nitrogen supply to the heater. By adjusting the amount, the temperature of the sample 14 can be kept constant in the temperature range from liquid nitrogen temperature to room temperature or higher.

After the sample 14 is stabilized at a predetermined temperature by the temperature control mechanism, a light or electron beam 15 is irradiated through the window material 5 to generate free carriers within the sample wafer. Furthermore, microwaves are irradiated through the waveguide 4 in a manner that includes the irradiation area of the beam 15, and the reflected wave from the wafer passes through the wafer 4 again and is converted into an electrical signal by a detector.

FIG. 2 represents the entire measurement system for measuring Chiaria lifespan. Reference numeral 23 schematically represents the vacuum vessel described using FIG. 1, and similarly, 24 schematically represents the sample stage portion shown in FIG. The configuration of the measurement system will be explained below using FIG. 2. First, the microwave 19 generated by the microwave generator 16 passes through the circulator 17 and is constantly irradiated onto the wafer-shaped sample 25 through 20 routes. A pulsed electron or light beam is also directed into the microwave irradiation region on the sample to periodically excite free carriers within the wafer sample. As a result, the reflected microwaves 20 and 21 from the wafer sample surface pass through the circulator 17 to the microwave detector 18.
This signal is converted into an electrical signal, but this signal is modulated by the modulation period of the beam used for carrier excitation.
Therefore, when the signal from the signal amplifier 27 is synchronized with the periodic signal from the beam generator 28 and observed with an oscilloscope 30, the waveform immediately after the beam is cut off becomes an exponential decay waveform, and the key carrier life τ can be determined from its time constant. Oscilloscope 30 signal and
Signals from the temperature detectors 26 and 29 are transmitted to a computer 31 to determine the temperature dependence of the carrier life τ.

According to this embodiment, it is possible to bring the relative positions of the microwave waveguide 4 and the wafer-shaped sample 14 in FIG. 1 close to about 1 mm. Therefore, since the microwave is irradiated without spreading the surface of the wafer sample, the intensity of the reflected microwave increases, which has the effect of increasing signal detection sensitivity. Furthermore, by integrating the vacuum container and the waveguide, the relative position between the wafer-shaped sample and the end face of the waveguide can always be kept constant, making it possible to perform highly reproducible measurements.
In addition, since the signal is detected using microwaves, it is difficult to detect electric signals using high-resistance materials (for example, 10 ^S
This method has the effect of making it easy to measure the carrier lifetime and carrier trapping level in semi-insulating GaAs (semi-insulating GaAs, which has a resistivity of about Ωcm).

〔Effect of the invention〕

According to the present invention, it is possible to perform highly accurate non-destructive measurement of the carrier trapping level of a wafer-shaped crystal, which has been difficult in the past.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a sample stage portion, and FIG. 2 is an apparatus configuration diagram showing the configuration of a carrier life measurement system. 1...Lid of vacuum container, 2...O ring, 3...
Vacuum container body, 4...Microwave waveguide, 5...
Vacuum sealing window material, 6...Liquid nitrogen tank, 7...
Cooling fin, 8...Sample stand, 9...Heater, 1
0... Liquid nitrogen, 11... Liquid nitrogen supply pipe, 12... Nitrogen gas exhaust pipe, 13... Vacuum pump, 14... Sample wafer, 15... Electron beam or light beam, 16... Microwave generation Vessel, 17...
...Circulator, 18...Microwave detector,
19...Incoming microwave, 20...Incoming and reflected microwave, 21...Reflected microwave, 22...
Electron beam or light beam, 23...vacuum container, 2
4... Sample stage, 25... Sample wafer, 26... Temperature detector, 27... Signal amplifier, 28... Beam generator, 29... Temperature measuring device, 30... Oscilloscope, 31... System control and Computer for signal processing.

Claims (1)

[Scope of Claims] 1. A wafer stage, a means for controlling the temperature of a semiconductor wafer placed on the wafer stage, a means for preventing water vapor from adhering to the surface of the semiconductor wafer, and a means for controlling the temperature of a semiconductor wafer placed on the wafer stage. means for irradiating a microwave irradiation area on the semiconductor wafer with a light beam or an electron beam; and means for detecting reflected waves of the microwave from the surface of the semiconductor wafer. A semiconductor evaluation device comprising: 2. The means for preventing water vapor from adhering to the surface of the semiconductor wafer is a vacuum container, and the vacuum container includes a waveguide that serves as a means for irradiating the microwave and a means for detecting the reflected microwave. A window material, which is a means for irradiating the light beam or electron beam, is provided at the tip of the waveguide, and the wafer stage is provided within the vacuum container. A semiconductor evaluation device according to claim 1. 3. The semiconductor evaluation device according to claim 1 or 2, wherein the means for controlling the temperature has a function of keeping the temperature constant in a temperature range from liquid nitrogen temperature to room temperature or higher.