Method of monitoring ion-implantation process using photothermal response from ion-implanted sample, and monitoring apparatus of ion-implantation process

A method and apparatus of monitoring an ion-implantation process include a precise analysis for the process conditions of the ion-implantation process by processing the detected signals by using frequency response characteristics of plasma and thermal waves generated by irradiating an ion-implanted surface with a laser beam. The monitoring includes: counting a complex conversion coefficient from the each result value measured for the photo-thermal response by irradiating a laser beam on the sample into which ions are implanted by changing a specific process condition of the ion-implantation process; linearizing a specific parameter of complex conversion coefficient for each value of the complex conversion coefficient according to the changes of the specific process condition; and monitoring a value of the specific process condition of the ion-implantation process based on a detected value of the specific parameter which is linearized according to the changes of the specific process condition.

CROSS-REFERENCES TO RELATED APPLICATIONS 
The present application claims priority under 35 U.S.C. .sctn.119 to Korean 
Patent Application No. 97-74377 filed on Dec. 26, 1997, the entire 
contents of which are hereby incorporated by reference. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method of monitoring ion-implantation 
process, and a monitoring apparatus using the same. More particularly, the 
present invention is directed to a method of monitoring an 
ion-implantation process using photo-thermal response from an 
ion-implanted sample in order to improve the analysis for process 
conditions of ion-implantation process, such as ion-dose or 
ion-implantation energy, by using the frequency response characteristics 
of the plasma and thermal waves generated by the excitation of the 
ion-implanted portion, and a monitoring apparatus using the same. 
2. Description of Related Art 
Generally, in the semiconductor device fabrication process, 
ion-implantation is carried out in order to implant impurities on a 
certain active area or insulating area, and change the electrical 
characteristics of the corresponding areas. 
The ion-implantation requires precise setting of process conditions and 
controls therefor in order to achieve desired electrical characteristics 
on a semiconductor wafer. In general, the dose on the ion-implanted sample 
and the uniformity of the ion-implantation are the main factors for 
setting the process conditions and the controls therefor exactly. 
Conventionally, the ion-dose and the uniformity are detected by measuring 
sheet resistivity. This method requires the performance of an annealing 
process after implanting ions on the wafer. However, the annealing process 
takes lots of time, and the above measurement method cannot be applied on 
the wafer having a specific pattern formed thereon. 
In order to address these problems, the inspection method for the ion-dose 
and the uniformity using a photo-thermal response technology was newly 
introduced, and the U.S. Pat. No. 4,632,562 and the U.S. Pat. No. 
5,408,327 disclose the analysis of a sample using photo-thermal response 
technology, both of which are hereby incorporated by reference in their 
entirety. 
In the photo-thermal response technology, if a modulated laser beam is 
absorbed on the ion-implanted sample, plasma and thermal waves are 
generated by excitation of the sample. At this time, frequency differences 
between the two waves occur, which is used in the analysis for the 
ion-implantation process. 
In other words, during the ion-implantation, damage often occurs on the 
surface of the sample according to the dose of the impurities and the 
energy. If a modulated laser beam is irradiated on the surface of the 
sample for the analysis of the ion-implantation process, a modulated laser 
beam is absorbed on the damaged portion, and plasma and thermal waves are 
generated by excitation. The generated plasma and thermal waves change the 
reflectivity of the surface of the wafer, and the detected results, i.e., 
the response characteristics, have phase shifts representing a time delay 
between the amplitude of the changed reflectivity and the excitation. 
The response characteristics are measurement parameters for analyzing the 
dose for the sample and the uniformity, with "K" as the plasma wave 
parameter, and "R" as the reflectivity parameter are derived from the 
response characteristics, which are used for the analysis. The thermal 
wave parameter is K (complex conversion coefficient), which is used for 
the analysis of ion-dose. 
In the analysis using the K (complex conversion coefficient), the amplitude 
and the phase shift of the K (complex conversion coefficient) according to 
the variance of the ion dose show a certain range which can be seen as 
curve-shape as a second-order function graph. However, it is difficult to 
judge the process conditions for controlling the ion dose precisely just 
by means of the above graph for K (Complex Conversion Coefficient) with 
the curve-shape as described above. Fine variations in the signal 
corresponding to the imaginary part of the curve may cause a great 
difference in the variance of the ion dose corresponding to the real part 
thereby making it difficult to precisely analyze. 
Therefore, the measurement of the dose of the implanted ions using the 
above method cannot be accurately applied in the analysis for the 
ion-implantation and the facility. 
SUMMARY OF THE INVENTION 
The present invention is therefore directed to a method of and an apparatus 
for monitoring the ion-implantation process which substantially overcomes 
one or more of the problems due to the limitations and disadvantages of 
the related art. 
The present invention is directed to providing a method of monitoring 
ion-implantation process by linearizing a specific parameter of a thermal 
wave parameter (the complex conversion coefficient, K) derived for the 
response characteristics by the frequency difference between the plasma 
and thermal waves generated by excitation from a modulated laser 
beam-absorbed sample, and converting the specific parameter to a 
first-order function relation which is in one-to-one correspondence with 
the process conditions of the ion-implantation process, such as a dose, 
etc. 
Another object of the present invention is directed to provide a monitoring 
apparatus of ion-implantation process based on the linearization of a 
specific parameter of a thermal wave parameter (the complex conversion 
coefficient, K) derived as the response characteristics by the frequency 
difference between the plasma and thermal wave generated by excitation 
according to the absorption of a modulated laser beam to a sample. 
To achieve these and other advantages and in accordance with purpose of the 
present invention, the method of monitoring ion-implantation process using 
photo-thermal response from an ion-implanted sample includes: counting a 
complex conversion coefficient from each of the result values measured for 
the photo-thermal response by irradiating a laser beam on the sample into 
which ions are implanted changing specific process conditions of the 
ion-implantation process; linearizing a specific parameter of complex 
conversion coefficient for each value of the complex conversion 
coefficient according to the changes of the process conditions; and 
monitoring the changes of the specific process conditions of the 
ion-implantation process based on the specific parameter which is 
linearized according to the changes of the process conditions. 
The specific process condition of the ion-implantation process, which is 
changed, may be a dose of ions or an energy of ions. The specific 
parameter of the complex conversion coefficient, which is linearized, 
maybe a distance between each indicating point of each of the complex 
conversion coefficient in a complex coordinates. 
The linearizing a specific parameter of each of the complex conversion 
coefficient according to the changes of the process conditions includes: 
designating each of the complex conversion coefficients in complex 
coordinates; detecting the traces between each of the indicating points of 
the complex conversion coefficients on the complex coordinates; counting 
the moving distance of the traces between each of indicating points 
responsive to the changes of the process conditions; and designating the 
moving distance of the traces between each of indicating points responsive 
to the changes of the process conditions on a graph. 
The detecting of the traces between each of the indicating points of the 
complex conversion coefficients may be carried out by converting the 
indicating point (real part, imaginary part) of each of the complex 
conversion coefficients designated in complex coordinates into a 
rectangular coordinate value (X,Y) in rectangular coordinates. 
The counting of the moving distance of the traces may be performed by 
setting an initial value corresponding to an initial condition of the 
process condition, which is changed, counting the moving distance of the 
traces according to the changes of each of the process conditions, and 
summing the initial value and the increase of the moving distance. 
The moving distances of the traces, which are shown as a graph, are 
designated as a first order function, which is in a one-to-one 
correspondence with the changes of the process conditions. 
In another aspect of the present invention, a monitoring apparatus of an 
ion-implantation process using photo-thermal response from an 
ion-implanted sample, wherein the ion-implanted sample is irradiated with 
a laser beam, the monitoring apparatus includes: a detector for measuring 
a photo-thermal response from the ion-implanted sample; a complex 
conversion coefficient counter which counts a complex conversion 
coefficient from a plurality of result values measured from the detector; 
and a linearizer which linearizes a specific parameter of the complex 
conversion coefficient for each of the complex conversion coefficients 
according to the variance of the process conditions of the 
ion-implantation process. The apparatus may include a display which 
displays the changes of a specific process condition of the 
ion-implantation process based on a specific parameter which is linearized 
by the linearizer. 
The linearizer may include a processor which designates each of the complex 
conversion coefficients in complex coordinates; detects the traces of each 
indicating point of the complex conversion coefficient in complex 
coordinates; and counts the moving distance of the indicating point of the 
complex conversion coefficient on the traces according to the variance of 
the process condition. The processor may also make a graphical 
representation of the moving distance of the indicating points on the 
traces according to the variance of the process condition. 
It is to be understood that the both foregoing general description and the 
following detailed description are exemplary and explanatory and are 
intended to provide further explanation of the invention as claimed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Reference will now be made in detail to the preferred embodiments of the 
present invention, examples of which are illustrated in the accompanying 
drawings. 
In the embodiment of the present invention, when the dose of the 
ion-implanted sample is analyzed using an ion-implantation analysis 
facility, a necessary analysis standard as the complex conversion 
coefficient is set, and the ion-implanted wafer is irradiated with a laser 
beam according to the set analysis standard. As a result, a signal having 
a certain frequency is detected, and the ion-implantation process can be 
monitored based on the detected signals. 
First, the method of monitoring ion-implantation process according to the 
present invention will be described in detail referring to the process 
sequence of FIG. 4B. 
Ions are implanted on a sample in an ion-implantation facility (not shown) 
such that the ion-implanted sample is set to have a certain dose in 
advance (S2), and a certain signal is detected by irradiating the 
ion-implanted sample with a laser beam (S4). 
In the analysis facility (not shown) for the measurement according to the 
embodiment of the present invention, a photo-thermal response principle is 
used, and further, an analysis facility using a photo-thermal heterodyne 
principle having a complex conversion coefficient can be used. The 
analysis facility employing the photo-thermal response principle may have 
a different light source depending on its manufacturer, but in a specific 
example, an analysis facility having laser diode light source operating a 
wavelength of 785 nm, which generates one single beam with two excitation 
frequencies, may be used. 
In the measurement step (S4), a laser beam from a light source is focused 
through a collect lens 10 on an ion-implanted portion of the sample 
surface 12 as shown in FIG. 1, and the power of the laser beam is absorbed 
on the surface of the sample 12 which is damaged by the ion-implantation. 
In other words, the surface of the sample is damaged by the implanted ions, 
that is, when ions having electrical characteristics are implanted on the 
sample, the ions collide with the molecules of the sample. As a result, 
the distortion in the linkages of the sample molecules occurs, and 
electrons and holes are produced due to the changes of the linkages of the 
molecules. 
Then, the damaged sample surface absorbs power of the laser beam focused on 
the damaged portion, and as a result, plasma and thermal waves are 
produced by excitation because of the changes of the energy state of the 
molecules, or the combination of electrons and holes. 
Then, there occurs a known photo-thermal response for the plasma and 
thermal waves having a frequency identical to the excitation frequency 
difference of the plasma and thermal waves, and the photo-thermal response 
is modified-shown as thermal wave parameter, K (complex conversion 
coefficient). The complex conversion coefficient is shown as functional 
relation of the thermal and plasma waves(or charge-carrier wave) having 
complex components. The thermal wave is designated as complex function, 
F(T) and the charge-carrier wave is designated as complex function, F(C). 
Therefore, the complex conversion coefficient, K is designated as complex 
function by the vectorial superposition of the two functions, and the 
results are shown in the complex coordinates shown in FIG. 3 in which a 
real part axis and an imaginary part are perpendicular (S6). That is, 
K=F(T)+F(C). 
When the measurement for the ion-implanted sample is completed with a 
specifically-set dose of ions as described above, the above S2 to S6 are 
repeatedly carried out while varying the dose of ions, and from each 
measurement value acquired according to the variance of the dose of ions, 
a complex conversion coefficient is counted, which can be designated in 
complex coordinates. Alternatively, if the energy is the parameter of 
interest, the above calibration maybe performed by varying the energy at 
set levels. 
At this time, increasing the dose of the ions according to the set dose 
from the initial condition to the final condition, a plurality of complex 
conversion coefficients, K, are obtained and are designated in complex 
coordinates. As shown in FIG. 5, with the dose of ions varied from "a" to 
"f", the complex conversion coefficient values are changed from "Ka" to 
"Kf", and the magnitudes and phases of each complex conversion coefficient 
are gradually changed. 
Detecting the photo-thermal response for the ion-implanted sample with the 
variance of dose of ions as described above, graphs of phase (imaginary 
values), magnitude (.vertline.K.vertline.), and real values of the 
detected signals for the plurality of complex conversion coefficient 
values according to the variance of the dose of ions ranging from "a" to 
"f" are shown in FIG. 3 respectively. 
As shown in FIG. 3, since the variance of a phase, a magnitude, and a real 
value of the complex conversion coefficient shows a specific curve ranges 
of multiple functions respectively, the process conditions of the 
ion-implantation process, especially the changes of the dose of ions, 
cannot be analyzed exactly just with the detected signals as above. 
Then, referring to FIG. 4B, an indicating point (end point) of each of the 
complex conversion coefficient from "Ka" to "Kf", which can be designated 
as (real part, imaginary part) in complex coordinates, is converted into 
(X,Y) coordinate in rectangular coordinates (S8). Then, the traces of 
rectangular coordinate (X,Y) for each indicating point according to the 
sequential variance of the dose of the ions (a.fwdarw.b) are detected 
(S10). 
Then, an arbitrary value, e.g., "100", is set as the constant of the dose 
of the initial condition for the ion-implanted sample, a moving distance 
of the traces of the coordinate (X,Y) of each complex conversion 
coefficient is counted (S12). Then, the counted result and the arbitrary 
value set for the initial condition are added. That is, if the moving 
distance of the traces, which is counted according to the variance of the 
dose after the initial condition, is "20", and the arbitrary value is 
"100", the new value "120" comes out as result by summing the increase of 
the moving distance of the traces for the corresponding dose "20". 
When corresponding each of the doses set forth above to the magnitude of 
the moving distance of the traces, that is, a.fwdarw.f and A.fwdarw.F, a 
graphical representation can be achieved as shown in FIG. 6. Referring to 
FIG. 6, the moving distance of the traces is proportional to the gradual 
increase of the dose and the dose, and the moving distance of the traces 
counted from the detected signals have one-to-one correspondence, 
first-order functional relationship, which can be the analysis standard 
for the dose of the ion-implantation. 
Accordingly, the monitoring standard for the process analysis of the 
ion-implantation process can be set-up as described above, in such a 
manner that the complex conversion coefficient in complex coordinates is 
converted into the value in rectangular coordinates, the traces according 
to each dose are detected in the conversion state, the moving distance of 
the traces for the increase of the dose is counted, and a graphical 
representation for the counted distance values is made. 
As shown in FIG. 4A, in another aspect of the present invention, the 
monitoring apparatus of the ion-implantation process employs the above 
method of monitoring the ion-implantation process. The monitoring 
apparatus includes a detector 20 which measures a photo-thermal response 
from the ion-implanted sample which has been irradiated by a laser beam as 
shown in FIG. 1, and a complex conversion coefficient counter 22 for 
counting a complex conversion coefficient from the result value measured 
from the detector 20. In addition, the monitoring apparatus includes a 
linearizer 24 including a processor 25 for counting the moving distance of 
the traces of each complex conversion coefficient value on a complex 
coordinate, and linearizing it for the dose. The monitoring apparatus may 
also include a display 26 for displaying the changes of the dose of the 
ion-implantation process based on the linearized moving distance of the 
traces. 
Thus, the detector 20 performs step (S4), the counter 22 performs step 
(S6), the processor 25 performs steps (S8)-(S12) and the display 26 
display the graph from step (S14). Steps (S6)-(S14) may all be performed 
by a single processor. 
Therefore, based on the analysis standard of the above ion-implantation 
process referring to the graph in FIG. 6, signals are detected from the 
ion-implantation sample so that the dose of the ion-implantation process 
or the energy can be precisely analyzed. In other words, once calibration 
according to a variation of a parameter of interest, e.g. dose or energy, 
has been performed at set levels, additional measurements of unknown 
samples can precisely determine the value of the parameter of interest. 
Therefore, according to the present invention, process conditions of 
ion-implantation process can be exactly analyzed by processing signals 
detected from an ion-implanted sample during a specific ion-implantation 
process, and comparing with the results acquired as above, i.e. based on 
the correlation of the main process conditions of the ion-implantation 
process, such as dose or energy, and the linearized moving distance of the 
traces of complex conversion coefficient, thereby making it possible to 
precisely manage the process, and maximizing the production yield. 
Still further, while the present invention has been described in detail, it 
should be understood that various changes, substitutions and alterations 
can be made thereto without departing from the spirit and scope of the 
invention as defined by the appended claims.