JPS59178739A - Device for measuring carrier mobility - Google Patents

Abstract

PURPOSE:To make it possible to perform measurement at a surface resolution of several hundred mum non-destructively without contact, when the carrier mobility in a semiconductor sample is measured, by utilizing photovoltaic effect. CONSTITUTION:A semiconductor sample to be measured 5 is mounted on a metallic sample table 4, which also serves a role of an electrode. A transparent electrode is provided at the lower surface of a glass plate 7, and the glass plate 7 is arranged over the sample 5 with an interval of 100mum or less being provided. Thus, electric capacity coupling is formed between the surface of the sample 5 and the plate 7. Output light from a variable wavelength laser 8 such as a coloring matter laser is inputted to a light detector 14 through beam splitters 10 and 10'. The output signal from the detector 14 is inputted to a microcomputer 22 through an amplifier 14' and interface 21. At the same time, the output light, which is transmitted through the splitter 10, is projected on the surface of the sample 5 through a reflecting mirror 11 and a lens 12. The value the yielded electric capacity coupling is amplified by a lock in amplifier 17 and inputted to the microcomputer 22 by way of an A/D converter 18 and the interface 21. By using the capacity by optical coupling, mobility is measured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a device for measuring carrier mobility in a semiconductor sample, and particularly to a device for measuring semiconductor characteristics suitable for non-destructive measurement that does not require the formation of electrodes on the sample. .

[Background technology]

Conventionally, there is a para method as a standard method for measuring the mobility of carriers in a semiconductor. In this method, a sample is made into the shape shown in FIG. 1(a). The circular part in the middle is the area to be measured, and four pads for attaching ridge poles are formed around it. A direct current (2) is caused to flow through the wiring shown in FIG. 1(a), and a magnetic field B is applied. By determining the voltage change amount ΔV that occurs at that time, the hole mobility μH can be determined. However, this method requires the application of an external magnetic field, restricts the sample to a special shape, requires electrode formation, and is a completely destructive test. Therefore, it is impossible to measure the mobility distribution of a wafer-shaped sample.

Next, there is the eddy current method as a non-contact measurement method.

As shown in FIG. 1(b), a direct current magnetic field is applied perpendicularly to the sample surface, and an eddy current is caused to flow through the sample using an inductively coupled coil 2 connected to an oscillator 1. At this time, the Hall electromotive force generated in the radial direction is extracted by the annular electrode 3 using electrostatic coupling. Since this Hall voltage is proportional to the mobility, the mobility can be determined by performing calibration using a conventional technique such as the para method. However, this method requires placing the sample in a magnetic field, which tends to increase the size of the equipment.
Operability also decreases. Moreover, the surface resolution of the measurement is
Since it is limited by the size of the electrostatic coupling electrode 3, the practical limit is around 10 mm even if it is made small.

That is, the actual situation is that it is extremely difficult to improve the surface resolution because the S/N ratio decreases when the electrode dimensions are made smaller.

Moreover, since this method is a relative measurement, there is a problem in that it requires calibration using a known method.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a measuring device that is particularly useful in semiconductor manufacturing processes to improve yields, has good surface resolution of carrier mobility, and can measure carrier mobility non-contact and non-destructively.

[Summary of the invention]

In order to achieve all of the above objects, the present invention is characterized in that the measuring device is constructed using all four photovoltaic effects.

[Embodiments of the invention]

Hereinafter, the present invention will be explained using figures.

First, the basics of the present invention will be described. Although the photovoltaic effect is a phenomenon that is generally measured on a semi-exclusive basis, a pn junction having an n-type coating layer on a p-type SI substrate will be explained here as an example. The principle explained below is based on the S! It can be similarly applied to other semiconductors and to surface photovoltaic effects other than p-n junctions. In order to measure the photovoltage generated during normal observation of the photovoltaic effect, a metal electrode for detecting the photovoltage is required on the semiconductor. However, in the present invention, the light beam irradiated to the sample is chopped, and the sample is applied with an AC photovoltage (AC photovoltage).
to occur. Therefore, the capacitive coupling makes it possible to measure AC photovoltage without directly forming electrodes on the sample. In other words, the photovoltage can be measured non-contact and non-destructively.

By the way, when a p-n junction sample is irradiated with carrier excitation light of a chopping frequency f (angular frequency ω = 2πf), an optical tortoise current occurs when the carrier diffusion length is smaller than the thickness.
, is expressed by the following formula.

Here, q is the electron charge, ■ is the reflectance of the sample surface to light, α is the absorption coefficient to light, and ■0 is the light intensity. Further, L* is a factor related to the carrier diffusion length as follows.

Here, D represents the carrier diffusion coefficient, and τ represents the carrier lifetime.

Therefore, the alternating photovoltage Vph measured through the capacitance
is expressed by the following equation, where Z is the junction impedance.

R no Vph ”” Z jIph = ” I
ph・Mountain・(3)1+jωCJRj Here, RI is junction resistance and CI is junction capacitance. Normally, CIR > τ, so the frequency characteristic of Vph is αl
When L*l<1, it becomes as shown in Fig. 2 (a) and (b).

By the way, it has already been proposed that the absolute value of the carrier lifetime can be determined from the frequency characteristics of the photovoltage shown in FIG. That is, from the value ωb of ω at the point where Vpb changes from the ω-1 dependence to the ω-d dependence, the absolute value of the carrier lifetime can be determined by τ=1/ωbK.

On the other hand, from equations (1) and (3), Vp for absorption coefficient α
h has the following relationship.

Vph = J ((1+) ・Dan・
River(4)L* Here, K-fq(1(9)IoZ+)-'.

Therefore, when K is kept constant (ω and 0 are fixed) and α is changed (the wavelength of the irradiated light is changed), α″1 and ■ are shown in Figure 2 (b). It becomes a linear relationship. From this, from the value of the horizontal axis at the point where the straight line intersects the horizontal axis (the value of α-1 when V -0), lL"l = lα-11, and find IL*1. Can be done. Furthermore, ωku1
If the diffusion length is determined at a frequency of /τ, L''=L from equation (2)9, and the diffusion length of a normal carrier can be determined.

As explained above, the absolute value τ of the carrier lifetime can be determined from the frequency temporality of the photovoltage, and the carrier diffusion length can be determined from the absorption coefficient dependence characteristic.

As is well known, there is a relationship L=V'D T between diffusion length and carrier lifetime. Therefore, the carrier diffusion coefficient can be found by the following equation.

D=L2/τ ・・・・・・・・・(5
) Furthermore, it is well known that D has the following relationship with mobility μ.

Here, k is Boltzmann's constant and T is absolute temperature. (
From equations 5) and (6), it is possible to determine the mobility μ in a non-contact and non-destructive manner by measuring with an alternating current optical voltage. The sample temperature was measured using a radiation thermometer.
Easy to measure. In addition, the surface resolution of the measurement is determined in principle by the sum of the irradiation spot diameter of the light beam and the carrier diffusion length, and can be set to several hundred microns or less.

Next, one embodiment of the present invention will be explained using diagram g3. The semiconductor sample 5 is placed on a metal sample stand 4 which also serves as a magnetic pole. A glass flat plate 7 having a transparent electrode 6 attached to its lower surface is set on top of the glass plate 7 with a space of 100 μm or less to form an electric capacitive coupling with the surface of the sample 5. The output light of a variable wavelength laser 8 such as a dye laser is outputted by an optical modulator 9.
The signal is chopped at the oscillation frequency f of the oscillator 15. After a portion of the chopped light is reflected by the beam spitter 10, the chopped light is further reflected by another beam spitter 10.
It is partially reflected at ', and the wavelength is read by the spectrometer 13. The spectrometer 13 sends an electric signal corresponding to the read wavelength to the interface 21 and causes the microcomputer 22 to set the value of the absorption coefficient.

On the other hand, the light transmitted through the beam spiriter 10' is converted into an electric signal by the photodetector 14, amplified by the amplifier 14', and passed through the interface 21 as a code for controlling the output of the tunable laser 8. 22. The amplitude control signal from the microcomputer 22 issues a command to the controller 16 to control the output of the variable wavelength laser 8 to always be constant. Furthermore, the oscillation frequency of the oscillator 15 can be freely controlled as the optical chopping frequency fi f by commands from the microcomputer 22.

In the end, the intensity of the output light from the optical modulator 9 is kept constant, and the chopping frequency and wavelength of the light are controlled by the control terminal 2.
It will be controlled by commands from 3.

Next, the light transmitted through the beam spiriter 10 is reflected by a reflecting mirror 1.
The light is reflected by the lens 1 and focused onto the surface of the sample 5 by the lens 12. Then, an AC photovoltage is generated in sample 5, so
The optical voltage is amplified by the synchronous detection amplifier 17 through the capacitive coupling described above. The output of the synchronous detection amplifier 17 is an analog-digital (A/D) converter (-coupler 18).
The data is digitized and input to the microcomputer 22.

Now, when measuring the carrier life, the control terminal 23
By giving a command from
(around μm) and sweep the force and chopping frequency. As a result, the frequency characteristics of the optical voltage are stored in the memory section of the microcomputer 22. When the measurement is completed, the microcomputer 22 extracts ωb of the frequency characteristic of the photovoltage, calculates τ=1/ωb, and calculates τ=1/ωb.
τ will be output on the display 24. Next, according to a command from the control terminal 23, the chopping frequency is set to a value such that ω<1/CJR+ (~1
0H2 position) and sweep the wavelength of the light source 8. As a result, the relationship between α and Vph is stored in the memory of the microcomputer 22 in the form of equation (4).

When the measurement is completed, the microcomputer 22
(■ The value of α-1 that is -1-0 is obtained, and L is obtained and output to the display 24. Through the above measurements, τ and 1
4, the microcomputer 22 calculates the carrier mobility and outputs it to the display 24.

The above measurement was explained for one point on the sample 5, but it is also possible to determine the distribution d(11) by moving the sample stage 4 with the moving device 19. In this case, the command from the control terminal 23 Microcomputer-22
, may be provided to the controller 20 of the mobile device 19 through the entire interface 21.

〔Effect of the invention〕

According to the present invention, the carrier mobility distribution of a semiconductor can be measured with a surface resolution of several hundred microns in a non-contact, non-destructive manner, so it is not only effective as a monitoring device during the semiconductor manufacturing process to improve yield, but also useful for devices. It can also be a powerful device for characterizing the characteristics of

[Brief explanation of the drawings] Figure 1 (a), (b) fj: Diagrams explaining the prior art. Schematic diagram of the principle of mobility measurement, Figure 2 (a)
, (b) is a diagram explaining the present invention in detail, (a) is a diagram showing the frequency characteristics of the photovoltage in logarithm, and (b) is the 7ζth diagram explaining the method of determining the diffusion length. FIG. 3 is a basic configuration diagram showing a specific embodiment of a gear rear mobility measuring device according to an example of the present invention. 1... Oscillator, 2... Eddy current excitation coil, 3...
- Static coupling electrode for hole acid pressure detection, 4... Metal sample stand, 5... Semiconductor sample, 6... Transparent electrode, 7... Glass flat plate, 8... Variable wavelength laser, 9... ...Light modulator, 10°10'...Beam spitter, 11.
... Reflector, 12... Lens, 13... Spectrometer,
14...Photodetector, 14'...Amplifier, 15...
Frequency sweep type oscillator, 16... Laser wavelength and amplification controller, 17... Synchronous detection type amplifier, 18.
... Analog-digital comparator z (A/D converter), 19... Sample stage moving device, 20... Controller for moving device, 21... Interface, 22
... Microcomputer-123 ... Control terminal, 24 liters (Oh

Claims (1)

[Claims] 1. A metal sample stage for mounting a semiconductor sample having a potential barrier near the surface, and an absorption coefficient of the semiconductor sample from an extremely small value to an extremely large value when the semiconductor sample placed above is irradiated with light. means for generating a light beam with a wavelength that can vary up to 100 nm, means for converting said light beam into a pulsed light beam, and means for converting said light beam into a pulsed light beam with a variable wavelength; means for detecting by capacitive coupling;
means for detecting the amplitude of the fc optical pressure; means for obtaining the carrier lifetime of the semiconductor sample by sweeping the pulse frequency of the light beam; and means for obtaining the carrier lifetime of the semiconductor sample by sweeping the wavelength of the light beam; A carrier mobility measuring device comprising means for obtaining a diffusion length, and signal processing means for calculating carrier mobility in the semiconductor sample from the carrier lifetime and diffusion length obtained by both of the above means.