Controlling method of forming thin film, system for said controlling method, exposure method and system for said exposure method

A method for irradiating a substrate such as a semiconductor substrate, coated with a photoresist, with light to measure variations in optical properties, such as reflectivity, refractive index, transmittance, polarization, spectral transmittance, for determining an optimum photoresist coating condition, an optimum photoresist baking condition, an optimum developing condition or an optimum exposure energy quantity, and forming a photoresist pattern according to the optimum condition. A system for the exposure method, a controlling method of forming a photoresist film by use of the exposure method, and a system for the controlling method, are useful for stabilization of the formation or treatment of the photoresist film, and ensure less variations in the pattern size. Furthermore, even in the case of a thin film other than a photoresist film, the formation or treatment of the thin film can be stabilized by measuring the optical property before and during or after the formation of the thin film and using the measurement results to control the condition for forming the thin film, the etching condition or the coating condition.

BACKGROUND OF THE INVENTION 
The present invention relates to the production of a semiconductor device 
or the like, and more particularly to a controlling method for forming a 
thin film suitable for stabilization of formation or treatment of a thin 
film of a semiconductor, a system for controlling the method, an exposure 
method and a system for the exposure method. 
With the progress of high integration of semiconductor devices, pattern 
size has become finer, the device structure has become three-dimensional, 
and the manufacturing processes of semiconductor devices have become more 
complicated. It is therefore necessary to pay more attention than before 
to the stabilization of production process conditions in the manufacturing 
steps of semiconductor devices. 
For instance, in projecting a pattern drawn on a reticle onto a wafer by a 
projection aligner, exposing light of a single wavelength in a 
comparatively narrow wavelength bandwidth is used. Therefore, as shown in 
FIG. 2a, the exposure light 71 undergoes multiple reflection in a 
photoresist film 72 or in a light-transmitting undercoat forming film 74. 
As a result, mutual interference of light occurs and the intensity of 
light varies in the depth direction inside the photoresist film 72. 
Accordingly, the exposure energy is varied in the depth direction and, 
upon development, the cross section of the photoresist film appears 
rugged, as shown in FIG. 2b. When the process conditions in various 
manufacturing apparatuses are varied, the thickness of photoresist film t 
or the formed condition of the light-transmitting undercoat 74 is varied. 
Consequently, upon exposing a photoresist under the same exposure energy, 
the width W of the photoresist in contact with the uppermost layer of the 
undercoat 73 is varied under the effect of stationary waves, resulting in 
varied pattern size. In order to stabilize the pattern size W, an optimum 
exposure energy according to the variation in the thickness of photoresist 
film t and the formed condition of the undercoat 74 should be set. 
When the optical property or thickness of the photoresist film is varied 
due to variations in the photoresist coating or baking conditions in a 
photoresist coating machine, the pattern size varies even if the formed 
condition of the undercoat on the wafer or exposure and developing 
conditions are the same. It is therefore necessary, even in the 
photoresist coating machine, to keep monitoring the variation in coating 
and baking conditions, the major causes of variations in the thickness and 
optical properties of the photoresist film. 
In thin film forming and treating steps such as the film forming step and 
etching step before or after the exposure step, as shown in FIG. 4, due to 
the increase in the diameter of the wafer formed and treated and the 
decrease in the thickness of film, the thickness and optical properties of 
the thin film formed and treated are varied with slight variations in the 
production process conditions. In a thin film forming and treating 
apparatus, therefore, it is necessary to constantly monitor the thickness 
and optical properties of the thin film being formed or treated, and to 
control the process conditions so as to keep constant the thickness and 
optical properties of the thin film. 
A preliminary operation method of maintaining a constant pattern size in, 
for example, an exposure step in the presence of variations been performed 
in which exposure and development of one or several sheets of wafer are 
conducted on a trial basis. The pattern size is measured by a measuring 
instrument to judge the acceptability of exposure energy. The judgment is 
fed back to the opening and closing times for shutters in an optical 
system for illumination, or the like. 
In the manufacture of small volumes of many types of products such as ASIC 
(Application Specific Integrated Circuit), however, the preliminary 
operation is required every time the type of product is changed. The 
requirement has increased the number of working steps and has been the 
major cause of lowering the operating efficiency of an exposure apparatus. 
With the trend towards higher integration, the method of correcting 
variations in the process conditions by such preliminary operations is 
unable to give sufficient accuracy. 
In order to eliminate the preliminary operations, a method has been 
devised, as disclosed in Japanese Patent Application Laid-Open (KOKAI) No. 
63-31116 (1988). In the method, assuming that the relationship between the 
thickness of a photoresist film and pattern size and the relationship 
between exposure energy and pattern size are known, the thickness of a 
photoresist film on a wafer to be exposed is measured by a photoresist 
film thickness measuring apparatus incorporated in a reduction projection 
aligner. The measurement result is fed back to the exposure energy so as 
to reduce variations in the pattern size and to stabilize the pattern 
size. 
In a thin film-forming and treating step, also, a method has been used in 
which the thickness of a photoresist film is measured for the preceding 
wafer by an apparatus for forming and treating a thin film. The process 
conditions for fabrication of the intended product is set based on the 
film thickness thus measured. 
Of the prior arts mentioned above, the stabilization of pattern size has 
been carried out by measuring variations of the thickness of a photoresist 
film formed by coating, determining an optimum exposure energy based on 
the measurement results, and controlling the pattern size. With the recent 
increasingly higher integration of semiconductor devices, however, it has 
become impossible to ignore the effects of variations in the manufacturing 
process conditions, such as variations of the formed state of an undercoat 
due to variations in forming and treating conditions in the thin film 
forming and treating step, variations of the optical properties of a 
photoresist film due to variations in coating and baking conditions in the 
photoresist coating step, etc. 
Furthermore, in the thin film forming and treating step according to the 
prior art, the operation with the current film thickness measuring 
apparatus is affected directly by variations in the state of an undercoat 
formed in the precedent step resulting in errors in the measured values of 
the film thickness. It is therefore difficult to set accurately the 
optimum process conditions based on the measurements of the film 
thickness. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a controlling method of 
forming a thin film, and a system for the method, which reduces variations 
in the settings of process conditions for the above-mentioned 
manufacturing processes and to ensure stability in the formation and 
treatment of a thin film. 
It is another object of the present invention to provide an exposure method 
and system therefor to constantly a pattern size irrespective of 
variations in the process conditions. 
The above objects can be attained by measuring an optical property of an 
undercoat prior to formation and treatment of a desired thin film, and 
correcting the measurements of the optical property obtained during or 
after the formation or treatment of the thin film, thereby controlling the 
process conditions accurately. 
For instance, in an exposure step for projecting a pattern onto a 
photoresist, which is a light-transmitting thin film with a complex 
refraction index (the optical property of interest here) varied during 
formation and treatment of the thin film, an optimum exposure energy for 
obtaining a required pattern size is obtainable by measuring the optical 
property of an undercoat before application of the photoresist, measuring 
the variation in the optical property due to exposure of a wafer coated 
with the photoresist, and determining the variation in the optical 
property of the photoresist. 
As exposure of a photoresist proceeds, the optical properties of the 
photoresist, such as absorption coefficient (.kappa.) and refractive index 
(n), are varied as shown in FIGS. 5a and 5b. The manner by which the 
optical properties are varied with time depend on, for instance, 
variations in the reflectivity of the undercoat arising from variations in 
process conditions of the manufacturing apparatus in the step preceding 
the exposure step. However, the optical properties, such as absorption 
coefficient and refractive index, of the photoresist upon completion of 
the projection of the pattern on the wafer are substantially constant. As 
seen in FIGS. 5a and 5b, though the optimum time to finish exposure varies 
from T.sub.1 through T.sub.2 to T.sub.3 under the influence of variations 
in the process conditions, the absorption coefficient .kappa..sub.1 and 
refractive index n.sub.1 upon completion of the exposure are substantially 
constant. In view of this fact, the variations of the optical properties, 
such as absorption coefficient (.kappa.) and refractive index (n), of the 
photoresist with time during exposure can be determined by measuring the 
variations in these optical properties during provisional exposure 
conducted over part of a photoresist-coated wafer prior to the pattern 
projecting step. 
The optical properties of the photoresist cannot be measured directly. The 
values of these properties are obtained by measuring the optical 
properties of the undercoat before application of the photoresist. Based 
on the measurement results, the complex index of refraction N 
(=n-i.multidot..kappa.) of the photoresist derived from the variation in 
the reflectivity R of the wafer upon coating with the photoresist is 
corrected, and the corrected complex index of refraction N into the 
absorption coefficient (.kappa.) and the refractive index (n) is reduced. 
Based on the optical property values thus obtained, art exposure energy T, 
photoresist coating conditions (the rotational frequency of a spinner for 
applying the photoresist, the temperature, humidity or gas pressure in the 
spinner, or the like) or photoresist baking conditions (baking temperature 
or baking time for baking the applied photoresist) necessary for the 
photoresist on the wafer to fulfill the pattern size accuracy requirements 
are calculated. The results of the calculation are fed back to an 
illumination system in a projection aligner used for actual pattern 
projection, a photoresist coating machine, or the like, whereby 
stabilization of control of the pattern size is achievable. 
Similarly, a method may be adopted in which an exposure energy T, 
photoresist coating conditions or photoresist baking conditions necessary 
for a photoresist formed on a wafer to fulfill the pattern size accuracy 
requirements are determined by measuring both the spectral transmittance 
of an undercoat before coating with the photoresist and the variation with 
time of the spectral transmittance due to exposure of the wafer after 
coating with the photoresist, and calculating the variation of the 
spectral transmittance of the photoresist with time based on the 
measurement results. 
Furthermore, in a step of forming a thin film having a light-transmitting 
property, for instance, an optimum film forming condition for obtaining 
the required formed film thickness is achievable through determining the 
manner in which an optical property of the film being formed varies, based 
on both the optical properties of the undercoat before film formation and 
variations in the optical properties of the wafer during the film 
formation. 
As a film is formed on a wafer, the reflectivity Rd of the wafer varies as 
shown in FIG. 6. The manner by which the reflectivity varies is influenced 
by variations in the process conditions of an apparatus used in the step 
precedent to the film forming step. When the film forming time is 
controlled based on the variation in the reflectivity of the wafer, 
therefore, the film forming time varies in the range from T.sub.0 to 
T.sub.1. That is, under varying process conditions, the reflectivity Rd 
varies in the range from curve R.sub.0 to curve R.sub.0 ' and, therefore, 
control of the film forming time to a time point when a certain 
reflectivity is obtained will lead to variation in the film forming time 
from T.sub.0 to T.sub.1, resulting in the corresponding variation in the 
thickness of the film formed. When the optical property of the undercoat 
before film formation (the optical property is a cause of variations in 
the process conditions) is measured, the relationship between the 
reflectivity Rd of the wafer and the thickness d of the film formed is as 
shown in FIG. 7; therefore, when the variation in the reflectivity of the 
wafer during film formation is reduced to the variation in the thickness 
of the film being formed, by use of the reflectivity of the undercoat 
measured before the film formation, the relationship between the 
reflectivity of the wafer and the film forming time shown in FIG. 6 can be 
reduced to the relationship between the thickness of the film being formed 
and the film forming time. Thus, it is possible by use of the 
relationships to determine, on a real-time basis, the thickness of the 
film being formed. Accordingly, by converting the film forming rate and 
the formed film thickness thus obtained into process condition variables 
it is possible to stabilize the operation of the apparatus. The upper and 
lower curves in FIG. 7 correspond to curve R.sub.0 and curve R.sub.0 ' in 
FIG. 6, respectively. 
As described above, it is possible, by preliminarily measuring an optical 
property before formation and treatment of a desired thin film and 
correcting the optical property values measured during or after the 
formation or treatment of the thin film, to control accurately and 
stabilize the process conditions. 
The optical properties of a thin film in a thin film forming and treating 
step will now be explained below, taking reflectivity as an example. 
Determination of the optical properties of the thin film in the thin film 
forming and treating step is performed by measuring the reflectivity R of 
the wafer, before, during and after the formation or treatment of the thin 
film on the wafer at the same position. Based on parameters which are 
given beforehand, such as the complex index of refraction n' of the 
uppermost layer of an undercoat, etc., variations in the optical 
properties of the thin film being formed or treated (the thickness d, 
absorption coefficient .kappa., or refractive index n of the thin film) 
are determined from the reflectivity R of the wafer using the measurement 
results of the reflectivity R' of the undercoat. Variations in the process 
conditions can be determined accurately therefrom. 
According to Hiroshi Kubota, Hadoh-Kohgaku (Wave Optics), Iwanami Shoten 
Publishers, Tokyo, the reflectivity R of a light-transmitting thin film is 
given by 
EQU R=f(N, n', R', I.sub.2, d) (1) 
where N: complex index of refraction of thin film being formed and treated 
EQU N=n-i.multidot..kappa. 
n: refractive index of thin film being formed and treated 
.kappa.: absorption coefficient of thin film being formed and treated 
n': complex index of refraction of uppermost layer of undercoat beneath 
thin film being formed and treated 
R': reflectivity of undercoat beneath thin film being formed and treated 
I.sub.2 : irradiation illumination 
d: thickness of thin film being formed and treated 
Therefore, if n' and I.sub.2 are measured beforehand, variations with time 
of the optical properties of the thin film being formed and treated can be 
determined accurately, by measuring R' before the formation or treatment 
of the thin film and correcting the measurements of variation in 
reflectivity R with time. 
For instance, because the thickness of a photoresist being irradiated with 
exposure light is not changed by the irradiation, preliminary measurement 
of n', I.sub.2 and d in equation (1) and correction of measurements of 
variation in the reflectivity R make it possible to determine accurately 
the variation in the complex index of refraction N 
(N=n`i.multidot..kappa.) of the photoresist with time, even if the 
reflectivity of the undercoat is varied due to variations in the process 
conditions. Therefore, if an exposure energy E.sub.1 =I.sub.2 
(illuminance).times.T.sub.2 (time) corresponding to such a complex index 
of refraction N.sub.1 (=n.sub.1 -i.multidot..kappa..sub.1) of the 
photoresist as to give the required pattern size is determined, the 
exposure energy E.sub.1 is the optimum exposure energy. 
Besides, the optical properties such as absorption coefficient and 
refractive index, of the photoresist eventually converge at known, fixed 
values as shown in FIGS. 5a and 5b. Therefore, when the eventually 
converging reflectivity R is measured for variation in the thickness d of 
the photoresist film in this condition, based on the relationship 
represented by equation (1), the film thickness d can be calculated 
accurately from the reflectivity by use of the relationship shown in FIG. 
11, without preliminary measurement as mentioned above regardless of 
variations in the reflectivity of the undercoat due to variations in the 
process conditions. 
Meanwhile, the spectral transmittance of a photoresist, before and after 
exposure, is generally as shown in FIG. 12. The curvature varies as the 
reflectivity of the undercoat varies with the process conditions. 
Therefore, preliminary measurement of the spectral transmittance of the 
undercoat before coating with the photoresist and correction of the 
measurements of the spectral transmittance during the exposure give 
variation in the spectral transmittance of the photoresist with time. When 
the data on a standard pattern of the spectral transmittance to be 
obtained at the end of exposure is stored beforehand, then the data on a 
standard pattern of the spectral transmittance actually measured at the 
end of exposure is compared with the prestored data and the time required 
for the two kinds of data to agree with each other is measured, the 
optimum exposure energy E [I (illuminance).times.T (time)] can be 
determined accurately. 
By feedback of the optimum exposure energy thus obtained to a shutter 
opening and closing circuit in an illumination system for exposing in a 
projection aligner, an accurate and stable control of pattern size in the 
projection of the pattern intended can be achieved even if the 
reflectivity of the undercoat is varied due to variations in the process 
conditions. 
It is known that the thickness of a photoresist film, the initial 
absorption coefficient thereof and the like vary from wafer to wafer or 
from lot to lot due to the instability of process conditions. It is 
possible, however, to stabilize the photoresist coating step if correction 
of the measurements of variations in the optical properties is carried out 
through partial exposure of the photoresist at a location on a scribed 
line or the like of the wafer by the above-mentioned method and the 
corrected values are fed back to a spinning step or a baking step so as to 
yield a constant result. This procedure enables a further reduction of 
variations in the pattern size arising from variations in the process 
conditions. 
On the other hand, where the thin film to be formed and treated is one 
which is formed and treated by a film forming apparatus, an etching 
apparatus or a thin film forming apparatus other than the photoresist 
coating machine, the complex index of refraction N (=n-i.multidot..kappa.) 
of the thin film is varied during the formation or treatment. Therefore, 
it is possible to determine the variation with time of the thickness d of 
the thin film being formed and treated from equation (1) by preliminarily 
measuring n' I.sub.2 and N, measuring the reflectivity R' of the wafer 
before the formation and treatment of the thin film, and correcting the 
measurements of variation of the reflectivity R with time during the 
formation and treatment of the thin film. Accordingly, a feedback control 
of the process conditions of the forming and treating apparatus such as to 
make constant the film thickness determined in the above-mentioned manner 
ensures stabilization of the forming and treating apparatus, even if the 
reflectivity of the wafer before the formation and treatment of the thin 
film is varied due to variations in the process conditions. 
The optical property measuring method is applicable further to 
transmittance, polarization property, or the like. With the method it is 
also possible to determine the variations in the process conditions 
accurately through correction similar to the above-mentioned correction of 
reflectivity values. Moreover, it is possible to stabilize the forming and 
treating apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Some preferred embodiments of the present invention will now be explained 
while referring to the accompanying drawings. 
EXAMPLE 1 
FIG. 1 is a block diagram showing a controlling system for forming a thin 
film according to a first embodiment of the present invention. In the 
figure, a wafer fed along a path for transferring wafers 104 to an optical 
property measuring system 108 is subjected to measurement of optical 
property before a thin film is formed and treated thereon. The result of 
the measurement is sent through an interface 103 to a process controlling 
system 45. The wafer to an apparatus for forming and treating a thin film 
107. The wafer is then fed to an optical property measuring system 56. The 
optical property is measured at the same position as that measured by the 
optical property measuring system 108. The result of the measurement is 
sent through an interface 101 to the process controlling system 45, where 
the measurement result is corrected according to data sent from the 
optical property measuring system 108. From the data thus obtained through 
correction, variations in process conditions are calculated. The 
calculated variations in process conditions are fed back through an 
interface 102 to the apparatus for forming and treating a thin film 107, 
thereby stabilizing of the apparatus for forming and treating a thin film. 
In this embodiment, the optical property measuring system 108 and the 
optical property measuring system 56 can be connected to a plurality of 
apparatuses for forming a thin film for which stabilization of thin film 
forming and treating conditions is contrived. 
The apparatus for forming and treating a thin film 107 in this embodiment 
may be a photoresist coating machine. The variations in process conditions 
to be calculated by the process controlling system 45 may be variations in 
the photoresist coating and baking conditions. The apparatus for forming 
and treating a thin film 107 may be an etching apparatus. Furthermore, the 
apparatus for forming and treating a thin film in this embodiment may be a 
thin film coating apparatus which is not varied in optical property even 
when irradiated with light. 
EXAMPLE 2 
Referring to FIG. 8, there is shown an embodiment in which the apparatus 
for forming and treating a thin film is a photoresist coating machine 49 
and the apparatus to be controlled is a projection aligner. Data obtained 
by an optical property measuring system 108 is used by a process 
controlling system 45 for correcting data obtained through measurement by 
an optical property measuring system 56. The optical property of only the 
photoresist is extracted from the corrected data, and an optimum exposure 
energy value for forming a required pattern is established based on the 
extracted optical property data. The exposure energy value is fed back 
through an interface 57 to a projection aligner 58. When a wafer of which 
the optical property has been measured by the optical property measuring 
systems 108 and 56 is fed into the projection aligner 58, exposure is 
carried out with the exposure energy value for the wafer, so as to 
stabilize the size of a pattern formed by the projection aligner 58. 
EXAMPLE 3 
FIG. 9 shows an embodiment in which the apparatus for forming and treating 
a thin film is a photoresist coating machine and the apparatus to be 
controlled is a developing apparatus. By using data obtained by an optical 
property measuring system 108, data obtained on measurement by an optical 
property measuring system 56 is corrected by a process controlling system 
45. The optical property of the photoresist only is extracted from the 
corrected data, and an optimum developing condition for forming a required 
pattern is established according to the extracted data. The developing 
condition is fed back to the developing apparatus 109 through an interface 
110. When a wafer of which the optical property has been measured by the 
optical property measuring systems 108 and 56 is fed into the developing 
apparatus 109, development is conducted under the developing condition 
established for that wafer, thereby stabilizing the size of a pattern 
formed by the developing apparatus 109. 
EXAMPLE 4 
FIG. 10 is a schematic illustration of the optical property measuring 
system 56 in Example 1 and an interface 57. In the figure, illuminating 
light emitted from a light source 26 such as a mercury vapor lamp is 
guided by a lens 81 to an optical fiber or the like, and is branched into 
two beams of light. The beams of light are led by lenses 82 and 83 and 
pass through shutters 29 and 30. Interference filter 27 permits passage 
therethrough of the beam of light with an exposure wavelength. Sharp-cut 
filter 28 transmits light with a non-exposure wavelength. The beams of 
light are turned ON and OFF by switching the shutters 29 and 30. The two 
beams of light are led through a beamsplitter 31, by which the optical 
axes are combined. The combined beam of light is directed through a 
beamsplitter 85 to irradiate a wafer therewith. A lens 84 is an objective 
lens. A field stop 55 is provided for narrowing and limiting the region of 
irradiation of the wafer with the beam of light having an exposure 
wavelength. When the shutter 29 is closed and the shutter 30 opened, the 
wafer is irradiated with the beam of light with non-exposure wavelengths 
light is reflected back, transmitted through the beamsplitter 85, 
reflected by a beamsplitter 86 onto an alignment detecting system 37. By 
moving an X-Y stage 36 while under observation of the alignment detecting 
system (television camera) 32 it is possible to isolate a specified region 
on the wafer without exposing of the photoresist. When the stage is 
stationary and the shutter 29 is opened while the shutter 30 is closed, it 
is possible to irradiate the location isolated with exposure light. 
On the other hand, data on the complex index of refraction n' of an 
undercoat, irradiation illuminance I.sub.0 detected by an light quantity 
measuring system 35 (described later) and thickness of photoresist film d 
is preliminarily measured and inputted into an optimum exposure detecting 
system 37. The reflectivity R' of the undercoat is preliminarily 
determined by an optical property measuring system 108 and inputted into 
an optimum exposure detecting system 37. The optimum exposure detecting 
system 37 calculates the variation with time of the complex index of 
refraction N of the photoresist from the above-mentioned formula (1), 
based on the variation in the reflectivity R of the photoresist, which is 
a secondary optical property during exposure and measured by an optical 
property measuring system (photosensor) 33. An optimum exposure energy 
E.sub.1 (=exposure time T.sub.2 .times.irradiation illuminance I.sub.2) is 
obtainable based on the exposure time T.sub.2 necessary for the complex 
index of refraction N of the photoresist to reach a desired value N.sub.1 
(=n.sub.1 -i.multidot..kappa..sub.1) and the irradiation illuminance 
I.sub.2 detected by the light quantity measuring system 35, described 
hereinbelow. 
The optical properties of the photoresist eventually converges at fixed 
values .kappa..sub.28 and n.sub..infin., as shown in FIGS. 5a and 5b. On 
the basis of the relationship represented by the formula (1) (wherein 
N.sub..infin. =n.sub..infin. -i.multidot..kappa..sub..infin. has a known 
value), therefore, the variation in reflectivity R.sub..infin. with the 
thickness of photoresist film d in this condition is as shown in FIG. 11. 
Thus, by exposing a photoresist and measuring the reflectivity 
R.sub..infin. at the moment the optical property converges at a certain 
value, it is possible to determine the thickness of photoresist film d 
from the reflectivity according to the relationship shown in FIG. 11, 
without the above-mentioned preliminary measurement. It is accordingly 
possible to determine the thickness of photoresist film d from the 
variation in the reflectivity R of the photoresist, as mentioned above, 
without need for preliminary measurement of the thickness of photoresist 
film. The thickness of photoresist film d thus obtained can be used to 
calculate the variation with time of the complex index of refraction N of 
the photoresist, in an optimum exposure detecting system 37. 
An illuminance detecting apparatus 34 is a photo-electric transducer for 
measuring the illuminance at the wafer position. When the illuminance 
detecting apparatus 34 is moved to an exposure position (the position at 
which to detect the variation in the reflectivity R of the photoresist) by 
use of the X-Y stage, the light quantity measuring system 35 is capable of 
measure the illuminance of the exposure light (irradiation illuminance) 
based on a signal obtained from the illuminance detecting apparatus 34. 
Then, the optimum exposure detecting system 37 calculates the variation 
with time of the complex index of refraction N of the photoresist from the 
data on the complex index of refraction n' of the undercoat, the 
reflectivity R' of the undercoat, the irradiation illuminance I.sub.2, and 
the thickness of photoresist film d, and the variation in the reflectivity 
R of the photoresist, based on the relationship of the above-mentioned 
formula (1). The optimum exposure detecting system 37 determines the 
optimum exposure energy E.sub.1 (=exposure time T.sub.2 .times.irradiation 
illuminance I.sub.2) based on the exposure time T.sub.2 necessary for the 
complex index of refraction N of the photoresist to reach a desired value 
N.sub.1 (=n.sub.1 -i.multidot..kappa..sub.1) and the irradiation 
illuminance I.sub.2 detected by the illuminance detecting apparatus 34 
light quantity measuring system 35. The optimum exposure energy E.sub.1 is 
transferred as data to an illumination controlling system 38 in a 
projection aligner 58. 
In operation, first, a wafer 18 coated with a photoresist is fed into the 
apparatus. Then, the shutter 29 is closed. The shutter 30 is opened to 
irradiate the wafer 18 with non-exposure light. A region on the wafer, for 
instance, a part of a scribed line is searched with an alignment detecting 
system (television camera) 32 while the wafer 18 is moved by the X-Y stage 
36. At this position, an exposure region is limited by a field stop 55. 
The shutter 30 is closed. The shutter 29 is opened, and the wafer 18 is 
exposed to light with an exposure wavelength. The variation in the 
reflectivity R of the photoresist, which is the secondary optical property 
of the wafer during exposure, is measured by the optical property 
measuring system (photosensor) 33. The optimum exposure detecting system 
37 calculates the variation with time of the complex index of refraction N 
of the photoresist from the data on the complex index of refraction n' of 
the undercoat previously measured, the reflectivity R' of the undercoat, 
the irradiation illuminance I.sub.2, the thickness of photoresist film d, 
and the variation in the reflectivity R of the photoresist measured by the 
optical property measuring system (photosensor) 33, in accordance with the 
above-mentioned formula (1). Then, the optimum exposure time T.sub.2 for 
complex index of refraction N of the photoresist to reach the desired 
value N.sub.1 (=n.sub.1 - i.multidot..kappa..sub.1), namely, for exposure 
of the wafer 18 is obtained. Next, the illuminance detecting apparatus 34 
is moved to the exposure position by the X-Y 36. There the illuminance of 
the exposure light is obtained from the light quantity measuring system 35 
through detection by the illuminance detecting apparatus 34. Thus, the 
optimum exposure detecting system 37 determines the optimum exposure 
energy E.sub.1 (=exposure time T.sub.2 .times.irradiation illuminance 
I.sub.2) and transfers the optimum exposure energy E.sub.1 to the 
projection aligner 58. When the wafer 18, for which the optimum exposure 
energy E.sub.1 has been determined, is fed into the projection aligner 58, 
an exposure time T.sub.1 according to the energy is established by the 
illumination controlling system 38 based on the exposure light illuminance 
I.sub.1 detected by an exposure light illuminance detecting apparatus (not 
shown in FIG. 10, but denoted by 9 in FIG. 9) disposed in the projection 
aligner 58. The shutter in the illumination system for exposure 39 is then 
driven. 
In this embodiment, the optical property measuring system 56 can be 
connected to a plurality of projection aligner to be fed with the wafers 
18 for which the optimum exposure energy E.sub.1 has been determined, 
through an interface 57. 
EXAMPLE 5 
When a spectroscope is used in place of the photosensor 33 in Example 3, 
spectral transmittance during the exposure process can be measured as a 
secondary optical property. In this case, first the shutter 29 is closed 
and the shutter 30 opened. The wafer 18 is irradiated with non-exposure 
light. A region on the wafer, for instance a part of a scribed line is 
searched with an alignment detecting system (television camera) 32 while 
the wafer 18 is moved by the X-Y stage 36. The exposure region is limited 
by a field stop 55. The shutter 30 is opened. The shutter 29 is also 
opened, and the wafer 18 is exposed to light containing a variety of 
wavelength components including exposure light. Then, spectral 
transmittance is detected through the spectroscope, the spectral 
transmittance being varied with time from a value before exposure to a 
value after the exposure, as shown in FIG. 12. Data of the spectral 
transmittance after exposure which shows a fixed value (reference spectral 
transmittance) is preliminarily inputted to the optimum exposure detecting 
system 37, which compares the variation with time of the spectral 
transmittance detected through the spectroscope with the data of the 
spectral transmittance after exposure (reference spectral transmittance), 
and determines an optimum exposure time T.sub.2 for the varying spectral 
transmittance to accord with the reference spectral transmittance. Next, 
the illuminance detecting apparatus 34 is moved to the exposure position 
by the X-Y stage 36, and the illuminance of the exposue light is 
determined by the light quantity measuring system 35. Thus, the optimum 
exposure detecting system 37 determines the optimum exposure energy 
E.sub.1 (=exposure time T.sub.2 .times.irradiation illuminance I.sub.2) 
based on the irradiation illuminance I.sub.2 obtained from the light 
quantity measuring system 35 and the optimum exposure time T.sub.2. The 
optimum exposure time T.sub.2 is transferred to the illumination 
controlling system 38 in the projection aligner 58. Therefore, as in the 
above-mentioned example, when the optimum exposure energy E.sub.1 has been 
obtained and is fed into the projection aligner 58, an exposure time 
T.sub.1 according the energy is set by the illumination controlling system 
38 based on the irradiation illuminance I.sub.1 detected by an exposure 
light illuminance detecting apparatus (not shown in FIG. 10, but denoted 
by 9 in FIG. 16) disposed in the projection aligner 58, and the shutter in 
the illumination system for exposure 39 is driven. 
EXAMPLE 6 
Modifications of Example 4 are shown in FIGS. 13 and 14, in which the basic 
construction is the same as in FIG. 10. In FIG. 13, light with 
non-exposure wavelengths used for measurement of the secondary optical 
property is projected obliquely and is detected obliquely by a photosensor 
33'. By examining the polarization property, reflectivity or the like in 
this case, it is possible to measure the optical property under little 
influence of the undercoat on the measurement. In FIG. 14, the variations 
in the transmittance or spectral transmittance of the photoresist on the 
substrate due to exposure are capable of being measured by use of 
photosensors 33 and 33'. This process is effective in projecting a pattern 
onto a light-transmitting substance 90, such as a glass, of a TFT liquid 
crystal display or the like. 
EXAMPLE 7 
An embodiment in which, unlike the above embodiments, the apparatus 
controlled by an optical property measuring system 56 is a photoresist 
coating machine 49 is illustrated in FIG. 15. Data is sent from a process 
controlling system 45 to an interface 102 so that the variation in the 
optical property measured by the optical property measuring system 56 will 
be constant. The rotating frequency of a spinner 41, the temperature in a 
baking furnace 42 or baking time is controlled, whereby it is possible to 
stabilize a photoresist coating step. In this embodiment, the optical 
property measuring system 56 can be connected through an interface 57 to a 
plurality of photoresist coating machines of which the photoresist coating 
steps are to be stabilized. 40 is a wafer stocker. 
It is also possible to control both the projection aligner 58 and the 
photoresist coating machine 49 by use of the optical property measuring 
system 56. 
EXAMPLE 8 
FIG. 16 shows an embodiment in which a system for measuring the variation 
in optical property due to exposure of a wafer is mounted on a reduction 
projection aligner. In the figure, illuminating light from a mercury vapor 
lamp 1 is controlled to have a fixed illuminance by a power supply 
controlling system 2. On the other hand, the light from the mercury vapor 
lamp 1 is branched to an exposure system and a prealignment system by a 
beamsplitter 3. The light transmitted through the beamsplitter 3 is turned 
ON and OFF by controlling the opening and closing times of a shutter 5 by 
a shutter controlling system 4. In this system, only the exposure 
wavelength is extracted by an interference filter 59. The light 
transmitted through a condenser lens 6 is projected onto a reticle 7 
provided with a required pattern. An image of the reticle is focused on a 
wafer 18 by a reduction projection lens 8. On the other hand, the other 
light reflected by the beamsplitter 3 is guided to the prealignment system 
through a field stop 55 by use of an optical fiber 90 or the like means. 
The light is led to either a sharp-cut filter 12 which transmits only the 
light with non-exposure wavelengths or to an interference filter 13 which 
transmits light with exposure wavelengths, by switching the filters 12 and 
13. With the sharp-cut filter 12 selected, an alignment pattern on the 
wafer 18 can be detected by a prealignment detecting system 32, without 
exposing the pattern on the photoresist. A condensed beam of light with 
exposure wavelength can be set on a scribed line position on the wafer 18. 
Then, the filter is changed over from the sharp-cut filter 12 to the 
interference filter 13, whereby partial exposure of the wafer 18 can be 
performed, and the region of irradiation with the exposure light can be 
limited by a field stop 55. The variation with time of the reflectivity R 
of the photoresist during the exposure process is measured by a 
photosensor 33. The optimum exposure detecting system 37 calculates the 
variation with time of the complex index of refraction N of the 
photoresist from the complex index of refraction n' of the undercoat 
preliminarily measured and inputted, the thickness of photoresist film d, 
the reflectivity R' of the undercoat measured by the optical property 
measuring system 108, the reflectivity R of the photoresist measured by 
the photosensor 33 and the illuminance I.sub.2 detected through the light 
quantity measuring system 35 supplied with an output from an illuminance 
detecting apparatus 9, based on the above-mentioned formula (1). An 
optimum exposure time T.sub.2 for the complex index of refraction N of the 
photoresist to reach the desired value N.sub.1 (=n.sub.1 
-i.multidot..kappa..sub.1) is determined, and an optimum exposure energy 
E.sub.1 is determined based on the optimum exposure time T.sub.2 and the 
illuminance I.sub.2 detected through the light quantity measuring system 
35. An exposure light illuminance I.sub.2 at the time of actually 
projecting a circuit pattern in a reticle 7 through a reduction projection 
lens 8 onto the wafer 18 for which the optimum exposure energy E.sub.1 has 
been determined is measured by an illuminance detecting apparatus 9. Then, 
an exposure illuminance or exposure time T.sub.1 for obtaining the optimum 
exposure energy E.sub.1 is determined based on an exposure light 
illuminance I.sub.1. The thus obtained data is sent through an interface 
57 to a power supply controlling system 2, which is an illuminance 
controlling system, and to control the opening and closing times of 
shutters by a shutter controlling system 4, in the same manner as in the 
above embodiments. The illuminance detecting apparatus 9 is a 
photo-electric transducer for measuring the illuminance at the image 
forming position, and the illuminance is measured by the light quantity 
measuring system 35. The illuminance detecting apparatus 9 is capable of 
measure the illuminance in the prealignment system, by moving an X-Y stage 
11. 
In this embodiment, it is unnecessary to measure the absolute illuminance. 
That is, the illuminance at the exposure position for projecting a pattern 
drawn on the reticle 7 onto the wafer 18 is detected by the illuminance 
detecting apparatus 9, which is then moved to the position of 
prealignment, and the illuminance of the light led to the prealignment 
system is determined. Then, the optimum exposure time T.sub.1 at the 
exposure position for projecting the pattern drawn on the reticle 7 onto 
the wafer 18 is given by the following formula (2): 
EQU T.sub.1 =(I.sub.2 /I.sub.1).times.T.sub.2 (2) 
where I.sub.1 is the illuminance at the exposure position, I.sub.2 is the 
illuminance at the prealignment position, and T.sub.2 is the optimum 
exposure time for the light led to the prealignment system. 
Thus, the optimum exposure time T.sub.1 at the exposure position for 
projecting the pattern drawn on the reticle 7 onto the wafer 18 is 
obtainable from the optical property (reflectivity, spectral transmittance 
or the like) measured by the optical property measuring system 
(photosensor) 33 in the optimum exposure detecting system 37 and the 
illuminance measured by the illuminance detecting apparatus 9. In order to 
provide the exposure time thus determined, a controlling system 4 controls 
the illuminance of a mercury vapor lamp through power source control 2 in 
the illumination system and the opening and closing time of the shutter 5, 
whereby the pattern drawn on the reticle 7 is projected on the wafer 18 
for the optimum exposure time. Thus, the pattern on the reticle 7 can be 
projected in conformity with the demanded pattern. In this embodiment, 
furthermore, the optimum exposure energy for the wafer immediately before 
exposure is determined, and there is only a short time from the 
determination of the optimum exposure energy to the actual exposure; 
therefore, there are few variations in the process conditions. In FIG. 16, 
19 is a shutter. 
EXAMPLE 9 
FIG. 17 shows an embodiment in which an optical property measuring system 
56 is mounted on a photoresist coating machine 49. The optical property 10 
of an undercoat of a wafer 18 is measured by an optical property measuring 
system 108, and the wafer 18 is fed from a wafer stocker 40 through a 
spinner 41 for applying a photoresist and through a baking furnace 42. 
Thereafter, variations in the reflectivity of the photoresist during an 
exposure process is measured by an optical property measuring system 56. 
The measurement result obtained from the optical property measuring system 
56 and the measurement result obtained from the optical property measuring 
system 108 are inputted through interfaces 57 and 103 to a process 
controlling system 45, which controls variations in process conditions 
(e.g., coating weight at the spinner 41, baking conditions in the baking 
furnace 42, etc.). 
According to this embodiment, variations in the thickness of photoresist 
film and variations in optical property, such as absorption coefficient, 
due to variations in the process conditions in the photoresist coating 
process can be reduced, and the photoresist coating process can be 
stabilized. Consequently, uniform exposure can be achieved for wafers 
stabilized in the photoresist coating process. 
Though in the above embodiment the complex index of refraction N of the 
photoresist is calculated from the reflectivity R of the photoresist, it 
is apparent that direct measurement of the complex index of refraction N 
of the photoresist suffices. 
EXAMPLE 10 
FIG. 18 is a schematic illustration of a system for stabilizing photoresist 
coating, baking and exposure processes, in which the apparatuses for which 
variations in process conditions are corrected are a photoresist coating 
machine 49 and a projection aligner 58. In the figure, the wafer is fed to 
an optical property measuring system 108, whereby the optical property of 
the wafer uncoated with the photoresist is measured. The resultant data is 
sent through an interface 103 to a process controlling system 45. After 
the measurement of the optical property, the wafer is fed along a path for 
transferring wafers 104 into the photoresist coating machine 49, whereby 
the photoresist is applied to the wafer and baked. The wafer coated with 
the photoresist is fed into an optical property measuring system 56, where 
the optical property of the wafer is measured by the optical property 
measuring system 108 before the wafer is coated with the photoresist. The 
thus obtained data is sent through an interface 101 to the process 
controlling system 45. The data sent from the optical property measuring 
system 108 is used to correct the data sent from the optical property 
measuring system 56. Based on the results of correction, the process 
controlling system 45 calculates the optimum exposure energy as a process 
variable for the exposure step and also calculate variations in process 
conditions for the photoresist coating step. When the wafer of which the 
optical property has been measured is fed along the path for transferring 
wafers 104 into the projection aligner 58, the optimum exposure energy 
corresponding to the wafer is inputted from the process controlling system 
45 into the projection aligner 58 through an interface 57. Then, exposure 
is carried out for the optimum exposure time, whereby stabilization of 
pattern size is contrived. The variations in process conditions for the 
photoresist coating step obtained by the process controlling system 45 are 
fed back through an interface 102 to the photoresist coating machine 49, 
in order to stabilize the photoresist coating and baking conditions. 
In this embodiment, the optical property measuring system 108 and the 
optical property measuring system 56 can be connected to a plurality of 
photoresist coating machines to stabilize the photoresist coating and 
baking conditions constituting the production process conditions, and to a 
plurality of projection aligners fed with wafers for which the optimum 
exposure energy has been determined. 
When the exposure, coating and baking conditions are controlled once for a 
few wafers, an effect on automation of the conventional preliminary 
operation is obtained. Where process conditions in the same manufacturing 
apparatus vary on a wafer basis, it is possible to control the exposure, 
coating and baking conditions on wafer basis. Furthermore, where 
variations in the process conditions within a wafer are important, it is 
possible to control the exposure condition on a chip basis and to control 
the coating and baking conditions within the wafer. 
In the above embodiment, the optical property measuring system 108 can be 
incorporated in the photoresist coating machine 49, and the optical 
property measuring system 56 can be incorporated in the photoresist 
coating machine 49 or the projection aligner 58. When the optical property 
measuring system 56 is incorporated in the projection aligner 58, the 
optimum exposure energy for a wafer can be set immediately before 
projecting a pattern onto the wafer by the projection aligner 58. Thus, 
the period of time from the determination of the optimum exposure energy 
to the exposure is so short that there arise no influence of variations in 
the process conditions in the period from the photoresist coating to the 
exposure. Moreover, the path for transferring wafers is short, which has 
the merits of enhancing the efficiency of the step and suppressing 
deposition of foreign matter on the wafer during feeding. 
Besides, if the optical property measuring system 56 incorporated in the 
photoresist coating machine 49 is the embodiment above, it is possible to 
measure the optical property of the photoresist immediately upon baking 
and after coating. It is therefore possible to control the variations in 
process conditions for the photoresist coating machine 49 on a real-time 
basis. 
Throughout the drawings, identical reference numerals indicate 
substantially the same portions. 
As has been explained hereinabove, according to the present invention, in a 
step for forming and treating a light-transmitting thin film on a wafer, 
the optical property of the wafer before the formation and treatment of 
the thin film is measured, then the measurement data on the optical 
property of the formed and treated thin film is corrected to extract only 
the data on the thin film formed and treated. Based on the measurement 
results, the variations in the variations in process conditions for the 
forming and treating apparatus are determined and controlled, whereby 
stabilization of the forming and treating apparatus can be contrived.