Apparatus for measuring the life time of minority carriers of a semiconductor wafer

An apparatus for measuring the life time of minority carriers includes a light source for irradiating a first region of a semiconductor wafer, a microwave generator for generating microwaves, a transmission line for transmitting a first part of the generated mark raised to the region of the semiconductor wafer that is radiated by the excitation light and a second portion of the generated microwave to a region of the semiconductor wafer that is not radiated by the excitation light. The intensity of the microwave signals reflected from the semiconductor wafer are detected and the life time of the minority carriers is calculated based upon the detected intensities.

BACKGROUND OF THE INVENTION 
1. Field of the invention 
The present invention relates to a life time measuring apparatus for 
minority carriers of semiconductor wafers used for quality control of 
semiconductor wafers. 
2. Description of the Prior Art 
Along with an ultrahigh precision tendency in semiconductor devices 
represented by VLSI in recent years, severer quality control has come to 
be required for semiconductor wafers used in semiconductor devices. For 
such control, a noncontact type evaluation method is desirable which is 
free from contamination or damage to semiconductor wafers. As an example 
of a noncontact type evaluation method, a semiconductor characteristics 
measuring method using microwaves is well known (Japanese Patent 
Publication Sho-61-60576). 
FIG. 8 is a typical view showing the schematic circuit configuration in an 
example of prior semiconductor characteristics measuring apparatus A0. 
FIG. 9 is a graph showing results from the semiconductor characteristics 
measuring apparatus A0. 
As shown in FIG. 8, a prior semiconductor characteristics measuring 
apparatus consists of a specimen retention/transfer mechanism 47 (support 
base), an optical pulse generator 49 to irradiate optical pulses on the 
surface of the specimen 7 (semiconductor wafer) supported and transferred 
by the specimen retention/transfer mechanism 47, a gun oscillator 40 to 
generate microwaves to be radiated on the surface of the specimen 7, an 
impedance matching box 41 to regulate microwaves radiated from gun 
oscillator 40, a regulating mechanism 46 consisting of E-H tuners 42 and 
44, magic T 3 and reflection-free terminal 43, waveguide 11 to radiate 
microwaves regulated by regulating mechanism 46 on the surface of the 
specimen 7, detector 45 to detect microwaves deflected on the surface of 
the specimen 7 by allowing it to pass again through waveguide 11 and 
regulating mechanism 46, and synchroscope 48 to display the change in the 
microwave detected by detector 45. 
The measuring principle of said apparatus A0 is as follows: 
In the specimen 7, majority carriers and minority carriers, free 
electron--positive hole pairs, are excited by optical pulse irradiated 
from optical pulse generator 49 the carrier concentration increases during 
light irradiation. On the other hand, between optical pulses where light 
irradiation is interrupted, excessive carriers (i.e., carrier 
concentration in excess of the carrier concentration at thermal 
equilibrium) gradually disappear due to recombination, decreasing carrier 
concentration. Such change in carrier concentration is remarkable on the 
minority carrier side. Since electric conductivity (specific resistance) 
of the specimen 7 changes according to change in carrier concentration, 
level change is caused in the microwave incident on the specimen 7. The 
microwave where level change is caused becomes a reflected wave to be 
transmitted to detector 45 through waveguide 11 and regulating mechanism 
46. The reflected wave of the microwave detected here is displayed by 
synchroscope 48 as a damping curve. The life time of minority carriers of 
the specimen 7 can be measured from this damping curve. 
In measuring the life time of minority carriers of the specimen 7 
consisting of semiconductor wafers, it is necessary to carry out 
measurement without the effects of wafer thickness and wafer vibration in 
order to improve precision and to shorten measuring time. In other words, 
it is desired to conduct measurement without depending upon the distance 
between the opening end 6 of waveguide 11, a radiating end of microwaves, 
and the specimen 7. 
FIG. 9 shows results of measuring the life time of minority carriers of 
silicon single crystal wafers (P and N types), specimen 7, with distance d 
between the opening end 6 of waveguide 11 and the specimen 7 as 
parameters. It is found that change in distance d has virtually no effect 
on measured results. 
In said prior measuring apparatus A0, measurement not depending upon 
distance d between the opening end 6 of waveguide 11 and the specimen 7 
may necessitate the following operations: removing unnecessary reflection 
from waveguide 11 having the opening end 6 with the use of two E-H tuners 
of regulating mechanism 46 and regulating the reflection quantity of 
microwaves from the specimen 7 variable depending upon a specific 
resistance of the specimen 7. In addition to what are respondable by said 
operations, however, there exist a multiple reflected wave between the 
opening end 6 and the specimen 7 and a reflected wave by a support base 47 
for microwaves passing through the specimen 7. The quantity of these 
reflected waves vary depending upon specific resistance of the specimen 7. 
Therefore, in the specific resistance range of around twice that shown in 
FIG. 9, prior measuring system A0 is respondable, while for semiconductor 
wafers with a wide range of specific resistance, it is difficult to obtain 
constant measured results without depending upon distance d between the 
opening end 6 and the specimen 7. 
In other words, specific resistance to measure semiconductor wafers usually 
covering a wide range from 1 to 100 .OMEGA.cm results in microwave 
amplitude reflectance from semiconductor wafers of a wide range of from 
0.5 to 1.0. Since microwave reflectance variations due to carriers 
generated in semiconductor wafers when light is irradiated is extremely 
small, it is necessary to normally use tens of mW microwave power to 
radiate semiconductor wafers in order to catch signals to find the life 
time at high precision. On the other hand, unless input power to detector 
45 is made below about 0.1 mW where the detection diode used for detector 
45 has square-law characteristics, errors are caused in the measured 
values of life time due to nonlinear effect of the detection diode. In the 
microwave circuit configuration of said prior measuring apparatus A0, it 
was difficult to meet said detection diode input power range for 
semiconductor wafers with said wide-range specific resistance. 
Furthermore, for measuring the intrinsic life time of semiconductor wafers 
at high precision, it is necessary to sufficiently reduce the quantity of 
minority carriers generated compared to originally existing majority 
carriers by reducing the quantity of light irradiated. However, reduced 
light quantity not only diminishes change in microwave reflectance in 
semiconductor wafers but also diminishes life time measuring signals 
obtained by detector 45. This made it difficult to measure by prior 
apparatus A0 semiconductor wafers with low specific resistance of below 
about 1 .OMEGA.cm. 
SUMMARY OF THE INVENTION 
The present invention has been made to solve said problem of prior art. 
Accordingly, it is an object of the present invention to provide a life 
time measuring apparatus for minority carriers of semiconductor wafers 
which is capable of measuring the life time of minority carriers of 
semiconductor wafers with a wide range of specific resistance at high 
precision and not sensitive to distance between said wafers and the 
radiating end of microwaves. 
In order to achieve said object, in a life time measuring apparatus for 
minority carriers of semiconductor wafers including irradiating means for 
irradiating excitation light on said semiconductor wafers, radiating means 
for radiating microwaves on said semiconductor wafers, detecting means for 
detecting reflected waves or transmitted waves of microwaves radiated by 
said radiating means, and measuring means for measuring the life time of 
minority carriers of said semiconductor wafers corresponding to change in 
microwaves detected by said detecting means. The first invention is 
characterized in that a life time measuring apparatus for minority 
carriers of semiconductor wafers comprises branching means for halving 
microwaves radiated by said radiating means, first wave directing means 
for directing one of the microwave halved by said branching means to the 
irradiated portion by excitation light by said irradiating means for said 
semiconductor wafers, second wave directing means for directing the other 
half of the microwave branch to the nonirradiated portion of said 
semiconductor wafers, and having effective length different due to round 
trip of microwaves from said first wave directing means by as much as a 
half wavelength or the sum of a half wavelength and a factor integer of 
wavelength, and interfering means for allowing reflected waves or 
transmitted waves made incident by said first and second wave directing 
means to interfere with one another, and the change in reflected waves or 
transmitted waves of microwaves made to interfere by said interfering 
means is detected by said detecting means. 
Two said detecting means may be established for comparing change signals 
detected by each said detecting means of reflected waves or transmitted 
waves of microwaves incident on said first and second wave directing 
means. 
In a life time measuring apparatus for minority carriers of said 
semiconductor wafers including irradiating means for irradiating 
excitation light on semiconductor wafers, radiating means for radiating 
microwaves on said semiconductor wafers, detecting means for detecting 
reflected waves or transmitted waves of microwaves radiated by said 
radiating means, and measuring means for measuring the life time of 
minority carriers of said semiconductor wafers corresponding to change in 
microwaves detected by said detecting means. The second invention is 
characterized in that a life time measuring apparatus for minority 
carriers of semiconductor wafers comprises branching interfering means for 
halving microwaves radiated by said radiating means and allowing reflected 
waves or transmitted waves of said halved microwave to electromagnetically 
interfere with one another, and a pair of wave directing means for 
directing microwaves halved by said branching interfering means with the 
same effective length, and change in reflected waves or transmitted waves 
of the microwaves made to interfere by said branching interfering means 
when excitation light is irradiated by said irradiating means on either of 
portions on semiconductor wafers radiated by the microwave respectively 
directed by said pair of wave directing means is detected by said 
detecting means. 
Amplifying means for amplifying change in reflected waves or transmitted 
waves of microwaves made to interfere by said branching interfering means 
may be established between said branching interfering means and said 
detecting means. 
In addition, the effective lengths of both said wave directing means may be 
made to agree with each other by inserting thin metal plates having an 
opening of the same shape as that of said wave directing means into either 
one of said pair of wave directing means. 
Furthermore, it is also possible to irradiate excitation light by shifting 
both irradiating means by establishing said irradiating means for each of 
said pair of wave directing means and making different from one another 
wavelengths of excitation light irradiated by each irradiating means. 
According to the first invention, microwaves radiated by radiating means is 
halved by branching means. When one of the microwave halved by said 
branching means is directed by the first wave directing means to the 
portion irradiated by excitation light by irradiating means for 
semiconductor wafers, level change is caused. On the other hand, when the 
other half of the microwave is directed to the nonirradiated portion of 
excitation light by irradiating means for said semiconductor wafers by 
second wave directing means having effective length different due to round 
trip of microwaves from said first wave directing means by as much as a 
half wavelength or the sum of a half wavelength and a factor integer of 
wavelength, no level change is caused. Reflected waves or transmitted 
waves of microwaves incident on said first and second wave directing means 
are made to interfere with one another by interfering means. This 
interference enables unnecessary waves other than reflected waves or 
transmitted waves in which level change is caused by the irradiation of 
said excitation light to be eliminated. Said unnecessary waves are 
multiple reflected waves between a radiating end of microwaves and said 
semiconductor wafers, reflected waves by the supporting base of microwaves 
passing through said semiconductor wafers, etc. Their quantity varies 
depending upon specific resistance of semiconductor wafers and distance 
between said wafers and the radiating end of microwaves. Only change in 
reflected waves or transmitted waves of microwaves in which level change 
is caused by the irradiation of said excitation light is detected by 
detecting means. In this way, when excitation light is irradiated on the 
surfaces of semiconductor wafers, signals of change in reflected waves or 
transmitted waves of microwaves caused by this irradiation can be detected 
with high S/N ratios. 
Since these signals of change correspond to the life time of minority 
carriers of semiconductor wafers, said life time will be measured by 
processing said signals by said measuring means. 
As a result, the life time of minority carriers of semiconductor wafers 
having a wide range of specific range of specific resistance can be 
measured with high precision. 
In addition, when two said detecting means may be established and each of 
them may detect change in reflected waves or transmitted waves of 
microwaves incident on said first and second wave directing means, output 
signals of each said detecting means are compared with each other by 
comparing means instead of said interfering means and the life time of 
minority carriers of semiconductor wafers can be measured by said 
comparing means as well as said interfering means. 
According to the second invention, branching interfering means for halving 
microwaves radiated by radiating means and for allowing reflected waves or 
transmitted waves of said halved microwave to electromagnetically 
interfere with one another and a pair of wave directing means for 
directing the microwave halved by said branching interfering means having 
the same effective length may be established. When excitation light is 
irradiated by said irradiating means on either of portions on 
semiconductor wafers radiated by microwaves respectively directed by said 
pair of wave directing means, level change is caused only in the microwave 
radiated on the irradiated portion. Unnecessary waves other than reflected 
waves or transmitted waves of the microwave in which level change is 
caused by the irradiation of said excitation light are eliminated from 
reflected waves or transmitted waves of microwaves incident on said pair 
of wave directing means by electromagnetically interfering with one 
another by said branching interfering means. In other words, in the second 
invention, since said pair of wave directing means have the same effective 
length, reflected waves or transmitted waves of microwaves incident on 
said branching interfering means via respective wave directing means have 
the same phase, generating electric fields corresponding to respective 
levels of reflected waves or transmitted waves of microwaves. Output waves 
fetched from the output side where acting direction of these electric 
fields is totally reverse become proportional only to level change in 
microwaves by the irradiation of said excitation light, thereby 
eliminating said unnecessary waves. 
As a result, as is the case with said first invention, life time of 
minority carriers of semiconductor wafers having a wide range of specific 
resistance can be measured with high precision without being affected by 
distance between said wafers and the radiating end of microwaves. 
In addition, when amplifying means for amplifying said output waves 
corresponding to change in reflected waves or transmitted waves of 
microwaves made to interfere by said branching interfering means is 
established between said branching interfering means and detecting means, 
detection precision of small output waves can be improved, further 
improving measuring precision of life time of minority carriers. Thus, 
measuring life time of minority carriers of semiconductor wafers having 
low specific resistance of 1 .OMEGA.cm which has been difficult so far 
becomes possible. 
Furthermore, effective lengths of said wave directing means can be made to 
agree by inserting thin metal plates having an opening of the same shape 
as that of said wave directing means into either of said pair of wave 
directing means. Because of the ease of adjusting effective length of wave 
directing means, processing precision of the apparatus is not required 
very much, thereby enabling the apparatus to be simplified. 
In addition, when said irradiating means is established in each of said 
pair of wave directing means and excitation light is irradiated by 
shifting both irradiating means by making different wavelengths of 
excitation light irradiated by each irradiating means, the need for 
transferring or replacing irradiating means is eliminated when the life 
time of minority carriers of semiconductor wafers is measured separately 
from a recoupling phenomenon caused in the surface of semiconductor 
wafers, thus enabling high-speed measurement. 
While the specifications concludes with a claim particularly pointing out 
and distinctly claiming the subject-matter of the invention, it is 
believed that the invention will be better understood from the following 
description taken in connection with the accompanying drawings herewith:

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
While only certain preferred embodiments of the present invention have been 
described, it will be apparent to those skilled in the art that various 
changes and modifications may be made therein without departing from the 
spirits and scope of the present invention. 
As shown in FIG. 1, semiconductor characteristics measuring apparatus A1 
according to the first preferred embodiment of the first invention mainly 
consists of support base 17, laser 9 for irradiating a laser pulse beam on 
the surface of the specimen 7 (semiconductor wafer) supported by support 
base 17 (corresponding to irradiating means), microwave generator 1 for 
generating microwaves to radiate on the surface of the specimen 7 
(corresponding to radiating means), branching separator 2 for halving 
microwaves radiated by microwave generator 1 (corresponding to branching 
means), a first transmission line 11a for directing one of the microwaves 
halved by branching separator 2 to the portion of the specimen 7 
irradiated by a laser pulse beam (corresponding to first wave directing 
means), second transmission line 11b for directing the other half of the 
microwave to the portion of the specimen 7 not irradiated by a laser pulse 
beam (corresponding to second wave directing means), line length variable 
mechanism 14 for changing the length of the second transmission line, 
mixer 8 having the function to allow reflected waves of microwaves 
respectively incident on the first and second transmission lines to 
interfere with one another (corresponding to interfering means) and the 
function to detect change in these interference waves (corresponding to 
detecting means), waveform processing circuit 12 for processing detection 
signals by mixer 8 (corresponding to measuring means), and life time 
display 13 for displaying the life time of minority carriers of the 
specimen 7, output of waveform processing circuit 12. 
Line length variable mechanism 14 consists of circulator 4 for changing the 
traveling direction of microwaves and short-circuit plate 5 for allowing 
microwaves entered by changing its traveling direction by circulator 4 to 
reflect at a given position, adjusting effective length of wave entered 
the second transmission line by short-circuit plate 5. A pore is provided 
in the first transmission line 11a, through which a laser pulse beam 
generated by laser 9 is irradiated on the surface of the specimen 7 from 
the first transmission line 11a. 
The basis measuring principle of said semiconductor characteristics 
measuring apparatus A1 being the same as prior examples, the description 
will be omitted. 
The operation procedure for apparatus A1 is described as follows, firstly 
on measuring preparations. 
During this time, a laser pulse beam from the laser 9 is not irradiated, 
and microwaves halved by branching separator 2 are respectively directed 
to the first and second transmission lines 11a and 11b via magic T 3 and 
radiated on the specimen 7 from the opening ends 6a and 6b of each line. 
Microwaves reflected on the surface of the specimen 7 are re-entered into 
corresponding transmission lines (i.e., entered into radiated transmission 
lines) to be directed to mixer 8. Microwaves directed to a mixer 8 are 
allowed to interfere one another. At this time, microwaves respectively 
entered into the first and second transmission lines 11a and 11b are 
adjusted by line length variable mechanism 14 to have effective length 
(round trip path length) different from each other by half a wavelength. 
When a laser pulse beam is not irradiated, microwaves respectively 
directed into mixer 8 via the first and second transmission lines 11a and 
11b are of the same level and different from each other by half a 
wavelength. Therefore, as a result of interference in mixer 8, microwaves 
completely disappear and are eliminated. The mixer receives a local 
oscillator signal (LO) from the separator 2. 
The next description is given of measuring time. During this time, a laser 
pulse beam by laser 9 is irradiated through a pore provided in 
transmission line 11a locally on the surface of the specimen 7 from the 
first transmission line 11a. As is the case with said measuring 
preparation time, halved microwaves are radiated respectively via the 
first and second transmission lines 11a and 11b. Reflected waves on the 
specimen 7 are respectively redirected to mixer 8 via the first and second 
transmission lines 11a and 11b to be allowed to interfere here. 
At this time, the level of microwaves via the first transmission line 11a 
in a laser pulse beam irradiation state is different from that of second 
transmission line 11b in a nonirradiation state. Therefore, microwaves do 
not disappear even if they are allowed to interfere in mixer 8. 
Here, the quantity of unnecessary reflected waves from the first and second 
transmission lines 11a and 11b and unnecessary reflected waves such as 
multiple reflected waves between the opening ends 6a and 6b of both lines 
11a and 11b and the specimen 7 transmitted to line 11a is equivalent to 
that transmitted to line 11b. This enables unnecessary reflected waves to 
be eliminated in mixer 8 like reflected waves of microwaves in said 
measuring preparation time. 
However, waves reflected on support base 17 of microwaves transmitted 
through the specimen 7 are not eliminated as stated before. In other 
words, since in a portion irradiated by a laser pulse beam, carriers are 
excited so that the surface of the specimen 7 becomes close to a state of 
metal, most of radiated microwaves are reflected on this surface and fail 
to reach support base 17. Therefore, reflected waves from support base 17 
at this portion are negligible. On the other hand, reflected waves by 
support base 17 exist in the laser pulse beam nonirradiated portion. For 
this reason, in mixer 8, reflected waves which have produced level change 
similar to reflected waves on the surface of the specimen 7 in said 
measuring time, and reflected waves which have produced no level change 
but have their phase dislocated by half wavelength of microwaves overlap 
with reflected waves which have produced no level change but have their 
phase dislocated from said half wavelength further by about twice the 
thickness of the specimen. However, since waves at this portion reflected 
on support base 17 produce no level change, it is unlikely to eliminate 
reflected waves from the laser pulse beam irradiated portion. Furthermore, 
effect by the dislocation of phase is actually negligible. Therefore, such 
effect by reflected waves from support base 17 is negligible. 
Thus, when a laser pulse beam is irradiated on the surface of the specimen 
7, signals of change in reflected waves caused only in transmission line 
11a (signals necessary for correctly measuring the life time) can be 
detected with high S/N ratios. 
As a result, the life time of minority carriers of semiconductor wafers 
having a wide range of specific resistance can be measured with high 
precision. 
In said measurement, in order to improve the precision, it is necessary to 
put close the opening ends 6a and 6b as if their carrier concentrations 
were equivalent. When this poses a problem of so-called cross talk where 
microwaves enter into the other side between the opening ends 6a and 6b, 
it is effective to establish a thin metal plate or a wave absorber for 
electromagnetic wave shielding between the opening ends 6a and 6b. 
Measuring apparatuses A2 to A4 according to the other preferred embodiments 
of the first invention will be described while making reference to FIGS. 2 
to 4. 
In said first preferred embodiment, measuring apparatus Al's circuit 
consists of two transmission lines, while a circuit can also be similarly 
composed with coaxial lines 11a and 11b. FIG. 2 shows measuring apparatus 
A2 in the second preferred embodiment, an example where coaxial lines are 
used. Here, coaxial lines where the opening ends 6a and 6b serving as rod 
antennas or loop antennas are closely located. The difference between both 
line lengths (lines between branching separator 2 and circulators 4a and 
4b) is adjusted so that unnecessary reflection from antennas and multiple 
reflected waves between antennas and the specimen 7 can be eliminated. 
However, with coaxial lines, magic T 3 is not used in circuit 
configuration as in measuring apparatus A1. Instead of line length 
variable mechanism 14, configuration may be made so that one line is 
looped to obtain effective length different from that of the other line. 
Measuring apparatus A2 enables transmission lines, round trip path for 
microwaves, to be thinner, resulting in the minimization of the entire 
circuits. 
In said first and second apparatuses, each circuit is located to eliminate 
unnecessary reflected waves on microwave circuits, their circuit lengths 
being different from each other by half a wavelength of microwaves. 
As shown in FIG. 3, on the other hand, in measuring apparatus A3 in the 
third preferred embodiment, detectors 8a and 8b are located respectively 
in the two circuits irrespective of the two microwave circuit lengths. In 
other words, two microwave electric signals detected by detectors 8a and 
8b are adjusted by amplifiers 22a and 22b so that levels thereof become 
the same, and then unnecessary power is canceled by differential amplifier 
23 (corresponding to comparing means). Thus, only change in reflected wave 
signals from the specimen 7 by a laser pulse beam is extracted. At this 
time, all signal power by unnecessary reflection from the opening ends 6a 
and 6b of the first and second transmission lines, reflected waves from 
the specimen 7, multiple reflected waves between the opening ends 6a and 
6b and the specimen 7 and reflected waves of microwaves from support base 
17 which has passed through the specimen 7 is canceled. 
Thus, when a laser pulse beam is irradiated on the surface of the specimen 
7, signals of change in reflected waves caused only in one of the two 
transmission lines (signals necessary for correctly measuring the life 
time) can be detected with high S/N ratios. 
As a result, the life time of semiconductor wafers having a wide range of 
specific resistance can also be measured with high precision like said 
measuring apparatuses A1 and A2. 
FIG. 4 shows measuring apparatus A2 according to the second preferred 
embodiment in which microwaves circuit is mounted on a strip line. While 
the circuit is equivalent to the one shown in FIG. 2, configuration by a 
strip line enables by far remarkable miniaturization of the apparatus 
compared with a circuit by waveguides and transmission lines. 
Furthermore, since no adjusting operations by an E-H tuner, etc. in prior 
examples are required, maintainability can be improved. In addition, 
miniaturization in the apparatus can be achieved because eliminated need 
for adjustment enables the circuit system to be expanded not only to 
previous waveguides and transmission lines but also to coaxial lines and 
strip lines shown in FIGS. 3 and 4. 
In said apparatuses A1 to A3, while the length between two transmission 
lines is varied by half a wavelength of effective length of microwaves 
traveling in each line, change to the sum of a half wavelength and a 
factor integer of wavelength will cause no trouble in actual use. 
In said apparatuses A1 to A3, while the effective length is varied in the 
second transmission line side, change in the first transmission line side 
will cause no trouble in actual use. 
Secondly, as shown in FIG. 5, semiconductor measuring apparatus A4 
according to the first preferred embodiment of the second invention mainly 
consists of support base 17'laser 9a' for irradiating a laser pulse beam 
on the surface of the specimen 7' (semiconductor wafer) supported by 
support base 17' (corresponding to irradiating means), microwave generator 
1' for generating microwaves to radiate on the surface of the specimen 7' 
(corresponding to radiating means), magic T 3' which halves microwaves 
radiated by microwave generator 1' and allows reflected waves of halved 
microwaves to electromagnetically interfere each other (corresponding to 
branching interfering means), a pair of transmission lines 11a' and 11b' 
which direct microwaves halved by magic T 3' with the same effective 
length (corresponding to a pair of wave directing means), amplifier 10' 
for amplifying output waves corresponding to change in microwaves 
interfered by magic T 3' when a laser pulse beam is irradiated by laser 
9a' on transmission line 11a' in portions on the specimen 7' radiated by 
microwaves respectively directed by transmission lines 11a' and 11b' 
(corresponding to amplifying means), mixer 8' for detecting output waves 
amplified by amplifier 10' (corresponding to detecting means), waveform 
processing circuit 12' for processing detection signals by mixer 8' 
(corresponding to measuring means) and life time display 13' for 
displaying the life time of minority carriers of the specimen 7', output 
of waveform processing circuit 12'. 
In apparatus A4, circulator 2' for generating standard signals (LO signals) 
is located instead of branching separator 2 in said apparatus A1. In 
addition, antenna 6' is located on the opening side of transmission lines 
11a' and 11b'. 
The basic principle of said semiconductor characteristics measuring 
apparatus A4 is also the same as in prior examples. 
The operation procedure for apparatus A4 is described as follows while 
making reference to FIG. 5 and FIGS. 6(a) to (d). 
Firstly, during measuring preparation time, a laser pulse beam by laser 9a' 
is not irradiated, and microwaves generated by microwave generator 1' are 
directed to opening 01 of circulator 2' shown in FIG. 6(a). These 
microwaves are input from opening 02 of circulator 2' to H branch output 
opening 01 of magic T 3' shown in FIG. 6(b). The microwaves input to 
opening O1 of magic T 3' are halved in magic T 3'. Microwaves respectively 
fetched from two H surface T branch openings 02 and 03 of magic T 3' are 
directed to a pair of transmission lines 11a' and 11b', which are radiated 
on the specimen 7' from antenna 6' shown in FIG. 6(c). Reflected waves 
from the specimen 7' are redirected to magic T 3' via transmission lines 
11a' and 11b'. Microwaves directed to magic T 3' are allowed to interfere 
here electromagnetically. In other words, since in apparatus A4, a pair of 
transmission lines 11a' and 11b' have the same effective lengths, 
reflected waves of microwaves incident on magic T 3' via transmission 
lines 11a' and 11b' become of the same phase. Electric fields 
corresponding to respective levels of reflected waves of these microwaves 
are generated. Acting directions of electric fields viewed from E branch 
output opening 04 of magic T 3' are reverse to one another, and a combined 
wave (output wave) of both radiated waves of microwaves from this E branch 
output opening 04 is fetched. Here, in order to make effective lengths of 
transmission lines 11a' and 11b' equal, thin metal plates 14' having an 
opening the same in shape with the one in transmission line 11b' shown in 
FIG. 6(d) are inserted in transmission line 11b'. The insertion of the 
metal plates 14' enables the difference in effective length between both 
transmission lines resulting from processing errors to be adjusted. 
Various thicknesses are available for thin metal plates 14', and ones with 
adequate thickness are selected for insertion. In this way, said 
difference is correctly adjusted, thus making the phase difference of both 
said reflected waves zero. Then, as a result of interference in magic T 
3', both reflected waves are eliminated. In other words, output power of 
an output wave fetched from E branch output opening 04 of magic T 3' 
becomes zero. 
During the measuring time, a laser pulse beam by laser 9a' is locally 
irradiated on the surface of the specimen 7' from antenna 6' through a 
pore provided on transmission line 11a' side of antenna 6'. Microwaves 
halved in the same way as during said measuring time are radiated via a 
pair of transmission lines 11a' and 11b'. Reflected waves from the 
specimen 7' are directed to magic T 3' respectively via transmission lines 
11a' and 11b' and allowed to interfere here. 
At this time, the level of microwaves directed via transmission line 11a' 
in a laser pulse beam irradiation state is different from the level of 
microwaves directed via transmission line 11b' in a nonirradiation state. 
Therefore, microwaves which are allowed to interfere in magic T 3' are 
unlikely to disappear. In other words, since microwave reflectance is 
changed by carriers generated in the laser pulse beam irradiated portion 
of the specimen 7', an output wave signal corresponding to carrier change 
by optical excitation due to lost balance is generated. This signal is 
amplified by amplifier 10' and input to RF terminal 01 of mixer 8' as an 
RF signal. The sum of reflected waves from antenna 6' is constantly 
generated in H branch output opening 01 of magic T 3'. This sum is input 
as an LO signal to LO terminal 02 of mixer 8' from opening 02 of 
circulator 2' via 03. The microwave amplitude changed by carriers excited 
by a laser pulse beam can be observed in output opening 03 of mixer 8' by 
overlapping an RF signal with an LO signal in mixer 8'. Output signals of 
mixer 8' are fetched into waveform processing circuit 12. The data is 
processed, whose results are displayed on the life time display 13'. 
Here, unnecessary reflected waves from transmission lines 11a' and 11b', 
multiple reflected waves between the antenna 6' and the specimen 7' and 
unnecessary reflected waves such as those from support base 17' can be 
completely eliminated or ignored for the same reason as for said apparatus 
A1. 
Thus, change in reflected waves caused only in transmission line 11a' can 
also be detected by apparatus A4 with high S/N ratios when a laser pulse 
bean is irradiated on the surface of the specimen 7', the life time of 
minority carriers of semiconductor wafers having a wide range of specific 
resistance can be measured with high precision. 
As a result, it is also possible to measure the life time of minority 
carriers of the specimen 7' having a low specific resistance of below 1 
.OMEGA.cm which has so far been difficult to measure. 
In addition, since effective lengths of a pair of transmission lines 11a' 
and 11b' can be made to agree by inserting into transmission line 11b' 
thin metal plates 14' having an opening the same in shape as the one in 
transmission line 11b', processing precision of the apparatus is not 
required very much, leading to the simplification thereof. 
Now, an apparatus A5 according to the second preferred embodiment of the 
second invention will be described while making reference to FIG. 7. 
It is well known that the difference in wavelength of excitation light 
results in a difference in penetration depth by excitation light into 
semiconductor wafers, causing the difference in distribution of generated 
carriers in depth direction. Therefore, the use of data of different 
excitation light wavelength leads to an advantage that the life time of 
wafer bulk can be separated from the recoupling life time on the wafer 
surfaces. Since said apparatus A4 provided only one laser 9a', laser 9a' 
was mechanically transferred to the upper part of the pore provided on 
transmission line 11a' side or replaced when the life time is measured. In 
the apparatus A5, lasers 9a' and 9b' which generate laser pulse beams 
different in wavelength from each other are located on both sides 
(transmission line 11a' side and transmission line 11b' side) of antenna 
6' as shown in FIG. 7. The configuration other than the periphery of 
antenna 6' is the same as that of said apparatus A4. Data can be collected 
without replacing or transferring lasers themselves when lasers 9a' and 
9b' of apparatus A5 are shifted and laser pulse beams are irradiated on 
the specimen 7'. 
Therefore, the life time at each measuring point of the specimen 7' can be 
measured at high speed. However, since there are two positions on which 
microwaves are radiated from antenna 6' and there is some distance between 
them, it is necessary to separately conduct coordinate operation for data 
and microwave radiating positions after collecting data. 
While in said apparatus A4, laser 9a' was located on the transmission line 
11a' side of antenna 6', no trouble will be caused when laser 9a' is 
located on transmission line 11b' side in actual use. 
While in said apparatus A4, the effective length was adjusted by inserting 
thin metal plate 14' into transmission line 11b', no trouble will be 
caused when thin metal plate 14' is inserted into transmission line 11a' 
in actual use. 
While in said apparatuses A1 to A5, the life time of minority carriers of 
the specimen 7(7') is measured using reflected waves of microwaves, no 
trouble will be caused when transmitted waves of microwaves are used in 
actual use.