JP3492482B2 - Minority carrier lifetime measurement device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a minority carrier lifetime measuring device, and more particularly to a minority carrier lifetime measuring device used for quality control of semiconductor wafers by a photoconductive microwave attenuation method. .

[0002]

2. Description of the Related Art With the recent trend toward ultra-precision semiconductor devices represented by VLSI, semiconductor wafers used therefor are required to undergo more strict quality control. For this quality control, a non-contact type evaluation method that is free from the risk of contamination or damage to the semiconductor wafer is desirable. For example, a lifetime measuring device for a minority carrier of a semiconductor wafer disclosed in Japanese Patent Publication No. 61-60576 is known. Has been. FIG. 5 is a diagram showing a schematic configuration of an example A01 of a conventional minority carrier lifetime measuring apparatus. As shown in FIG. 5, a conventional minority carrier lifetime measuring apparatus A01 irradiates an optical pulse on the surface of a sample holder / carrying mechanism 51 and a sample 52 (semiconductor wafer) supported by the sample holder / carrying mechanism 51. Optical pulse generator 5
3, a gun oscillator 54 that generates microwaves to the surface of the sample 52, an impedance matching device 55 that adjusts microwaves emitted from the gun oscillator 54, E-H tuners 56 and 57, a magic T58, and a reflectionless termination. The adjustment mechanism 60 composed of 59, the detector 62 for detecting the microwave adjusted by the adjustment mechanism 60 by passing through the waveguide 61 and the adjustment mechanism 60 again, and the change of the microwave detected by the detector 62 It is composed of a synchroscope 63 for displaying.

The measurement principle will be described below. The sample 5 is irradiated with the light pulse emitted from the light pulse generator 53 to the sample 52.
Carriers, which are free electron-hole pairs, are excited at 2. This carrier is in excess of the carrier concentration of the sample 52 in the thermal equilibrium state, and increases the electric conductivity of the surface of the sample 52. Then, excess carriers are recombined between the light pulses at which the light irradiation is interrupted and gradually disappear, so that the carrier concentration is lowered. Such a change in carrier concentration, that is, a change in electric conductivity is remarkable on the minority carrier side. The reflectance of the microwave incident on the sample 52 in this state changes due to the above-described electrical conductivity.
The changed microwave becomes a reflected wave and is transmitted to the wave detector 62 through the waveguide 61 and the E-H tuner 57.
The reflected wave of the microwave detected here is displayed as an attenuation curve by the synchroscope 63. The lifetime of the minority carrier, which represents the physical properties of the sample 52, can be measured from this attenuation curve. However, there are unnecessary reflected waves such as multiple reflected waves between the open end of the waveguide 61 of the device A01 and the sample 52, and the amount thereof changes depending on the electrical conductivity of the sample 52. Therefore, it is difficult for the device A01 to accurately measure the minority carrier lifetime of a semiconductor wafer having a wide range of electrical conductivity. Therefore, the present inventors have developed the following devices A02 and A03 in order to remove the unnecessary reflected waves (Japanese Patent Laid-Open Nos. 6-27048 and 7-5122).
issue).

FIG. 6 shows a conventional device A02, in which the waveguide 61 in the device A01 is divided into two parts (61a, 61b), and the microwave radiated by the gun oscillator 54 is magic T58 '. Divide into two. The two-divided microwaves are radiated to the sample 52 through the two waveguides 61a and 61b, respectively, and the reflected light here is again passed through the waveguides 61a and 61b to the magic T58 '. Guide and interfere here. Laser 53 is irradiated with laser pulse light on the side of the waveguide 61a. The output RF corresponding to the change in the microwave interfered by the magic T58 'at this time is amplified by the amplifier 65 and input to the detector 62. On the other hand, the gun oscillator 54
A part of the microwave generated by is extracted by the demultiplexer 67 and is input to the detector 62 as the reference signal LO, where it is mixed with the output RF for detection. Output IF from the detector 62
Is processed by the waveform processing circuit 66 and displayed by the lifetime display device 63 '. In addition, the waveguides 61a, 61
Antennas 64a and 64b are provided on the opening side of b.

In the conventional device A02, the reflected waves of the microwaves which have passed through the waveguides 61a and 61b divided into two parts have the same phase by making the effective lengths of the waveguides 61a and 61b equal. Becomes However, since the level change occurs only on the irradiation side of the excitation light (laser 53),
By interfering the reflected waves of the microwaves that have respectively passed through the waveguides 61a and 61b, only the level change (modulation component) of the reflected wave of the microwaves is detected. By thus removing unnecessary reflected waves, the minority carrier lifetime can be accurately measured even if the semiconductor wafer has a wide range of electrical conductivity. However, in the conventional device A02, the microwaves are incident on different positions of the semiconductor wafer 52 in order to remove the unnecessary reflected waves, and therefore, when the semiconductor wafer 52 and the support base 51 are tilted, the waveguides 61a and 61b are removed. There is a phase difference between the microwaves that have passed through each, causing imbalance in the microwave circuit. When the microwave circuit is unbalanced, even if the semiconductor wafer 52 is not irradiated with the excitation light, the power does not become completely zero at the stage of the microwave synthetic interference, and the amplifier 65, the detector 62, and the like do not operate. There was a risk that the power of the microwave circuit components would saturate and the sensitivity of the device would decrease. In order to correct this imbalance, the conventional device A03 has a mechanism for controlling and adjusting the microwave oscillation frequency.

FIG. 7 shows a schematic structure of the conventional device A03, and the basic structure is the same as that of the conventional device A02. The difference from the conventional device A02 is that the waveguide 61b has an electrical length (effective length) different from that of the waveguide 61a by an integral multiple of a half wavelength in one way of microwave, and a laser pulse is generated by a laser 53. The point is that a microwave frequency adjuster 68 is provided to adjust the frequency of the microwave generated by the gun oscillator 54 so that the interference wave detected by the detector 67 is reduced when light is not irradiated. In the conventional device A03, even if the semiconductor wafer or the like is tilted, the electric length is adjusted by changing the oscillation frequency of the microwave so that the phase difference of the reflected wave input to the magic T58 approaches 0. can do. Therefore, the error due to the inclination of the semiconductor wafer or the like can be absorbed and the carrier lifetime of the semiconductor wafer can be accurately measured.

[0007]

However, the conventional device A0
In No. 3, the microwave is divided into two in order to irradiate the semiconductor wafer in order to remove the influence of multiple reflection, and the drawback that the structure of the antenna part becomes complicated and large has not been solved. Moreover, in order to absorb the error due to the tilt of the semiconductor wafer, a complicated control mechanism for constantly adjusting the oscillation frequency of the microwave was required. In order to solve the problems in the conventional art, the present invention improves a minority carrier lifetime measuring device and uses a wide range without using a complicated control mechanism for constantly adjusting the microwave oscillation frequency. It is an object of the present invention to provide a minority carrier lifetime measuring device capable of accurately measuring the minority carrier lifetime of a semiconductor wafer having the electric conductivity of 1.

[0008]

In order to achieve the above object, the present invention provides pulse excitation light irradiation means for intermittently irradiating a semiconductor wafer with excitation light, and irradiation with the excitation light by the pulse excitation light irradiation means. A microwave radiating means for radiating a microwave to the region of the semiconductor wafer and a detecting means for detecting a reflected wave of the microwave reflected by the semiconductor wafer or a transmitted wave of the microwave transmitted through the semiconductor wafer. In the minority carrier lifetime measuring device for measuring the minority carrier lifetime of a semiconductor wafer based on a change in the reflected wave or the transmitted wave before and after irradiation with the pulsed excitation light, the reflected wave or the transmitted wave is divided into two. And a reflected wave or a transmitted wave, which is divided into two by the above-mentioned two-dividing means, is guided to the above-mentioned detecting means. And a second wave guide means for delaying the reflected wave or the transmitted wave on the other side by a predetermined time to guide it to the detection means, and the first and second wave guide means. And a synthesizing means for synthesizing the reflected waves or the transmitted waves guided to each other and inputting to the detecting means,
A minority carrier lifetime measuring apparatus is characterized in that the minority carrier lifetime of the semiconductor wafer is measured based on the reflected wave or the transmitted wave detected by the detecting means. Therefore, it becomes possible to combine reflected or transmitted waves when the semiconductor wafer is irradiated with the excitation light or not irradiated with the excitation light with a time difference. Therefore, the influence of unnecessary microwaves other than the modulation component of microwaves can be canceled by a simpler structure than in the past, the carrier change can be accurately measured, and the device can be downsized.

Further, if adjusting means for adjusting the amplitude and / or the phase of the reflected wave or the transmitted wave passing through the second waveguide means is provided, the above-mentioned method can be used when the excitation light is not applied to the semiconductor wafer. The output of the synthesizing means can be set so as to be close to 0, and the influence of offset or the like, which appears due to device characteristics or the like, can be removed from the lifetime measurement. Further, if the microwave focusing means is provided at the radiating end of the microwave radiating means, the microwave intensity can be concentrated in the region of the semiconductor wafer irradiated with the excitation light, and the device sensitivity can be improved. . Further, if the length and / or the shape of the second waveguide means are set so that the reflected wave or the transmitted wave combined by the combining means becomes zero, most of the unnecessary microwaves are removed in advance. be able to. Furthermore, if the delay time of the reflected wave or the transmitted wave by the second waveguide means can be adjusted, the delay time can be adjusted according to the characteristics of the reflected wave or the transmitted wave, so that the life of the minority carrier is more accurate. Time measurement can be performed.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings to provide an understanding of the present invention.
The following embodiments are examples of embodying the present invention and are not of the nature to limit the technical scope of the present invention. 1 is a diagram showing a schematic configuration of a minority carrier lifetime measuring apparatus according to an embodiment of the present invention, FIG. 2 is a schematic diagram of an opening end shape of microwave radiating means, and FIG. 3 is a microwave intensity. 3 is a time chart showing an example of a time series change of. As shown in FIG. 1, a minority carrier lifetime measuring apparatus according to an embodiment of the present invention includes a microwave oscillator 1 that oscillates microwaves, and a microwave oscillator 1
The directional coupler 2 for distributing the microwave oscillated by the measuring microwave a to the local signal microwave b 2, the waveguide 3 for guiding the measuring microwave a to the semiconductor wafer 0, and the circulator 4 , Waveguide 5, Semiconductor wafer 0
A moving stage 6 for holding and transporting a laser beam, a pulse laser oscillator 7 for making a laser beam incident on the semiconductor wafer 0, a magic T8 for dividing the microwave c reflected by the semiconductor wafer 0 into two, and a magic T8 for dividing the microwave c into two. A waveguide 9 for guiding one of the microwaves e, a delay circuit 10 for time-delaying the other microwave d, an amplifier 11 and a phase shifter 12 for adjusting the amplitude and phase of the time-delayed microwave d ′ are provided. The waveguide 13 provided, a magic T14 for synthesizing the microwaves e and d'divided into two, a detector 15 for detecting the microwave f synthesized by the magic T14, and a microwave detected by the detector 15. A / D converter 16 that converts the intensity into a digital signal, calculates the lifetime from the digitized microwave intensity, and displays the calculation result And it is configured from the operation and display unit 17 that.

The operation of the minority carrier lifetime measuring apparatus according to this embodiment will be described in detail below. The laser oscillated by the pulse laser oscillator 7 is intermittently applied to the semiconductor wafer 0 through the light guide hole 20 provided in the waveguide 5. This laser is a few mm in terms of spatial resolution
It converges to the following. In the irradiation region of the semiconductor wafer 0 irradiated with the laser, carriers are generated by photoexcitation,
The electric conductivity of the surface of the semiconductor wafer increases. The excited carriers diffuse to the periphery and recombine with holes or free electrons, and exponentially decrease in the absence of laser irradiation to return to a thermal equilibrium state. On the other hand, the microwave oscillated by the microwave oscillator 1 is distributed by the directional coupler 2 to the measurement microwave a and the local oscillation signal microwave b. The measurement microwave a passes through the waveguide 3, the circulator 4, and the waveguide 5, and is applied to the region of the semiconductor wafer 0 irradiated with the laser. By the way, the reflectance of microwaves changes depending on the electrical conductivity of the semiconductor wafer. Therefore, it becomes possible to measure the change in electric conductivity, that is, the change in carrier as described above, by microwave.

By the way, from the viewpoint of detection sensitivity in a microwave system, easiness of adjustment, and miniaturization of a device, a microwave of several tens GHz is generally used as a microwave frequency, but this microwave is efficiently guided. For this purpose, a waveguide of several millimeters to several centimeters square is used. However, since it is not possible to concentrate microwaves in the region excited by the laser with a simple waveguide opening, the opening end of the waveguide 5 has, for example, an opening end having a ridge structure as shown in FIG. To use. If the opening end is formed in a ridge shape that narrows down the microwave, the microwave intensity can be concentrated in the laser irradiation area, and the change in the reflected microwave can be detected with high sensitivity. Semiconductor wafer 0
The reflected wave c of the microwave modulated by the change of the electric conductivity of is divided into two by the magic T8. One of the two divided microwaves e is magic T1 by the waveguide.
It is guided to 4. The other microwave d is the delay circuit 1
A microwave d ′ is guided to the magic T 14 through a waveguide 13 including 0, an amplifier 11, and a phase shifter 12. Microwaves d ', e synthesized by Magic T14
The difference output f is input to the mixer 15 and detected. still,
The amplifier 11 and the phase shifter 12 are for making the differential output f smaller than a predetermined value in a state where the semiconductor wafer 0 is not irradiated with the laser. Fig. 3 shows microwave d
Is a diagram showing the microwave intensities (absolute values) of the microwaves d ′ and e and the difference output f thereof when the signal is delayed by about 100 ns from the microwave e. Microwave d ',
Although the influences of the above-described multiple reflection and the like are included before and after the incidence of both laser pulses, the influences are canceled out because a difference between the microwaves having the same influence is taken. Therefore, carrier generation / annihilation can be accurately measured from the difference output f between the delay times. In the minority carrier lifetime measuring apparatus according to the present embodiment, the waveguides 9 and 1 are used.
The length, shape, etc. of 3 are set on the basis of the characteristics of the magic T14, etc., and most of the unnecessary microwaves other than the modulated wave contained in the microwave f can be removed.
In addition, the delay circuit 10, the amplifier 11, the phase shifter 1 described above
2 can be adjusted to further remove the unnecessary microwave.

The difference output f detected by the mixer 15 is
It is digitized by the A / D converter 16 and input to the operation display unit 17. The arithmetic display unit 17 calculates the minority carrier lifetime based on the input signal and displays the result. The calculation by the calculation display unit 17 is performed based on the initial attenuation amount of the microwave generated during the delay time (100 ns), for example. This initial attenuation information is effective for the surface layer evaluation required for the evaluation of epitaxial wafers. It is also possible to calculate the microwave attenuation process after 100 ns by the calculation display unit 17.
When the detection output level is low and the S / N ratio of the signal is low, the arithmetic / display unit 17 performs the averaging process in synchronization with the excitation by the pulse laser in order to increase the S / N ratio. As described above, in the minority carrier lifetime measuring apparatus according to the present embodiment, the influence of the unnecessary reflected wave can be canceled by synthesizing the reflected waves of the two-divided microwaves while shifting them temporally. Since only one waveguide is required for making the microwave incident on the semiconductor wafer and an error due to the inclination of the semiconductor wafer or the like is eliminated, a complicated control mechanism for correcting the error is unnecessary. Further, since the structure of the antenna part is simplified, the device can be downsized.

[0014]

[Embodiment] In the above-described embodiment, an example in which a waveguide is used for microwave transmission is shown, but a coaxial line or a strip line may be used instead of the waveguide. Such a minority carrier lifetime measuring apparatus is also an example of the minority carrier lifetime measuring apparatus in the present invention. Further, in the above embodiment, the semiconductor wafer 0 is simply irradiated with microwaves via the waveguide 5, but in order to reduce unnecessary reflection as much as possible and increase the radiation efficiency to the semiconductor wafer, A stub, an E-H tuner, or the like may be inserted in the wave tube 5 or the like. Such a minority carrier lifetime measuring apparatus is also an example of the minority carrier lifetime measuring apparatus in the present invention. Further, in the above embodiment, a single mixer using a single local oscillator signal is used as a means for detecting microwaves, but the detection output is measured by the phase change of the local oscillator signal and shown in FIG. In this way, the local oscillator signals of different phases are generated by the phase shifters 21 and 22,
The quadrature detection measurement may be performed by the plurality of mixers 20a and 20b. By performing quadrature detection measurement, changes in the amplitude and phase of the modulated microwave can be measured, and the state of carrier diffusion can be evaluated in more detail. Such a minority carrier lifetime measuring apparatus is also an example of the minority carrier lifetime measuring apparatus in the present invention.

[0015]

INDUSTRIAL APPLICABILITY According to the present invention, a pulsed excitation light irradiating means for intermittently irradiating a semiconductor wafer with excitation light, and a microwave for irradiating a region of a semiconductor wafer irradiated with the excitation light by the pulsed excitation light irradiation means. And a detection means for detecting the reflected wave of the microwave reflected by the semiconductor wafer or the transmitted wave of the microwave transmitted through the semiconductor wafer. In a minority carrier lifetime measuring device that measures the minority carrier lifetime of a semiconductor wafer based on changes before and after irradiation with pulsed excitation light,
A dividing means for dividing the reflected wave or the transmitted wave into two,
A first wave guide means for guiding one reflected wave or transmitted wave divided by the two dividing means to the detecting means, and the other reflected wave or transmitted wave delayed by a predetermined time to the detecting means. The second detection means for guiding and the combination means for combining the reflected wave or the transmitted wave respectively guided by the first and second guiding means and inputting to the detection means, The minority carrier lifetime measuring device is characterized in that the minority carrier lifetime of the semiconductor wafer is measured based on the reflected wave or the transmitted wave detected by the means.
Therefore, it becomes possible to combine a reflected wave or a transmitted wave when the semiconductor wafer is irradiated with the excitation light or not irradiated with the excitation light with a time difference.

Here, in addition to the adjustment of the time difference, the second
If the adjusting means for adjusting the amplitude and / or the phase of the reflected wave or the transmitted wave passing through the waveguiding means is provided, the output of the synthesizing means is further reduced to 0 when the excitation light is not applied to the semiconductor wafer. The microwaves can be set to be close to each other, and stationary microwaves (unnecessary waves) other than the microwaves modulated by the excitation light irradiation can be removed with a simpler structure than before, and the device can be downsized. Further, if the microwave focusing means is provided at the radiating end of the microwave radiating means, the microwave intensity can be concentrated in the region of the semiconductor wafer irradiated with the excitation light, and the device sensitivity can be improved. . Further, by setting the length and / or shape of the second wave guiding means so that the reflected wave or the transmitted wave combined by the combining means becomes zero, a stationary microwave other than the modulated microwave is previously set. Most of the waves can be removed. Furthermore, if the delay time of the reflected wave or the transmitted wave by the second waveguide means can be adjusted, the delay time can be adjusted according to the characteristics of the reflected wave or the transmitted wave, and the lifetime of the minority carrier is reduced. Can be measured more accurately.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a minority carrier lifetime measuring apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of an open end shape of a waveguide for making a microwave incident on a semiconductor wafer.

FIG. 3 is a time chart showing the microwave intensity in time series.

FIG. 4 is a diagram showing a schematic configuration of a minority carrier lifetime measuring apparatus according to an embodiment of the present invention.

FIG. 5: Conventional minority carrier lifetime measuring device A
The figure which shows the schematic structure of 01.

FIG. 6 A conventional minority carrier lifetime measuring device A
The figure which shows the schematic structure of 02.

FIG. 7: Conventional minority carrier lifetime measuring device A
The figure which shows schematic structure of 03.

[Explanation of symbols]

0 ... Semiconductor wafer 1. Microwave oscillator 2. Directional coupler 3, 5, 9, 13 ... Waveguide 4 ... Circulator 6 ... Movement stage 7 ... Pulse laser 8, 14 ... Magic T 10 ... Delay circuit 11 ... Amplifier 12 ... Phase shifter 15 ... Mixer 16 ... A / D converter 17 ... Calculation display

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Shingo Sumie Inoue 1-5-5 Takatsukadai, Nishi-ku, Kobe-shi, Hyogo Prefecture Kobe Steel Works, Ltd. Kobe Research Institute (72) Inventor Kunio Range Nishi-ku, Kobe-shi, Hyogo Prefecture Takatsukadai 1-5-5 Kobe Steel No. 5 Building in Genesis Technology Co., Ltd. (72) Inventor Futoshi Ojima 1-5 Takazukadai, Nishi-ku, Kobe City, Hyogo Prefecture Kobe Steel No. 5 Building in Genesis Technology Co., Ltd. (56) References JP-A-6-347423 (JP, A) JP-A-6-27048 (JP, A) JP-A-7-5122 (JP, A) (58) Fields investigated (Int. Cl. ⁷⁾ , DB name) H01L 21/66 G01N 22/00

Claims (5)

(57) [Claims] 1. A pulsed excitation light irradiation means for intermittently irradiating a semiconductor wafer with excitation light, and a microwave radiation for radiating a microwave to a region of the semiconductor wafer irradiated with the excitation light by the pulsed excitation light irradiation means. Means for detecting the reflected wave of the microwave reflected by the semiconductor wafer or the transmitted wave of the microwave transmitted through the semiconductor wafer, and the pulsed excitation light irradiation of the reflected wave or the transmitted wave. In a minority carrier lifetime measuring device for measuring the minority carrier lifetime of a semiconductor wafer based on the change in front and back, it is divided into two by the dividing means for dividing the reflected wave or the transmitted wave into two and the two dividing means. First wave guide means for guiding one reflected wave or transmitted wave to the detection means, and the other reflected wave or transmitted wave A second wave guide means for delaying by a predetermined time to guide to the detecting means and a reflected wave or a transmitted wave respectively guided by the first and second wave guiding means are combined and input to the detecting means. And a synthesizing means for
A minority carrier lifetime measuring device, characterized in that the minority carrier lifetime of a semiconductor wafer is measured based on a reflected wave or a transmitted wave detected by the detecting means. 2. The minority carrier lifetime measuring apparatus according to claim 1, further comprising adjusting means for adjusting the amplitude and / or phase of the reflected wave or the transmitted wave passing through the second waveguide means. 3. The minority carrier lifetime measuring device according to claim 1, wherein a microwave focusing means is provided at a radiation end of said microwave radiation means. 4. The length and / or shape of the second waveguide means is set such that the reflected wave or the transmitted wave combined by the combining means becomes zero.
Minority carrier lifetime measuring device according to any one of 1. 5. The minority carrier lifetime measuring device according to claim 1, wherein the delay time of the reflected wave or the transmitted wave by the second waveguide means can be adjusted.