Pattern developing process and apparatus therefor

A resist is coated on a photomask and a predetermined pattern is exposed on the resist. The photomask is dipped in a developing solution together with an electrode which exhibits a stable potential in the developing solution, so that a change in current flowing between the photomask and the electrode is detected on the basis of a change in capacitance between the photomask and the developing solution, while developing the pattern formed on the resist. The current abruptly changes (e.g., exhibits its peak) around the time at which the resist is removed and a chromium underlying layer of the photomask is exposed. The time obtained by multiplying the time until the change appears by a predetermined coefficient is regarded as the time corresponding to the end of the developing step.

BACKGROUND OF THE INVENTION 
The present invention relates to a pattern developing process and an 
apparatus therefor, which can detect completion of resist development. 
In recent years, many highly integrated, high-speed semiconductor devices 
have been developed. This has required high-precision micropatterning of 
various circuits formed on semiconductor wafers. 
In order to satisfy such a requirement, various improvements have been 
made. For example, as regards the lithography technique, extensive studies 
have been made about use of short wavelength X-rays instead of 
conventional ultraviolte ray as a light source when a resist is exposed 
through a mask. In a method of manufacturing a mask, the conventional 
method of exposing a pattern with ultraviolet ray is being replaced with a 
method of exposing a pattern with electron beams which allows 
micropatterning. 
A method of manufacturing a photomask or an X-ray mask by electron-beam 
lithography will be described. A metal film is formed by deposition or 
sputtering on a substrate which is transparent in a wavelength range of an 
exposure light source. Next, an electron-beam resist is coated on the 
metal film, and a desired pattern is exposed with electron beam. 
Thereafter, the drawn pattern is developed to selectively remove the 
electron-beam resist, thus forming a resist pattern. The metal film is 
etched using the remaining resist pattern as a mask to form a desired mask 
pattern. Thereafter, the resist pattern is removed to form a mask. 
An electron-beam resist coated on a semiconductor wafer can be directly 
exposed with electron beam without using a lithography technique, thus 
obtaining a still finer pattern. In this electron-beam exposure technique, 
the electron-beam resist is coated on the semiconductor wafer and a 
desired pattern is exposed thereon by use of electron beam. Next, the 
exposed pattern is developed to selectively remove the electron-beam 
resist, thus forming a resist pattern. A semiconductor layer or metal film 
on a semiconductor substrate is etched or doped using the remaining resist 
pattern as a mask to form a desired circuit pattern and element. 
Thereafter, the resist pattern is removed. 
However, when a micro mask pattern is formed on the electron-beam resist as 
described above, the developing temperature greatly influences the 
developing speed, and therefore, the period of the developing step. The 
developing period is set based on experience, but the period thus set is 
not always the optimum. This is because the developer contains an 
inorganic solvent such as ketone or alcohol, which evaporates from the 
surface of the developer in a developing tank and deprives heat, thus 
making the temperature distribution of the developer nonuniform. Hence, 
the developing step must be repeated to accurately determine the actual 
developing time. Even though a proper time can be determined through 
repeated tests, if the developer temperature varies widely during such 
tests, this renders the test results inaccurate. The developing rate is 
also influenced by the dose of electron beam, variations among 
manufacturing lots of resist, degradation in developer, baking conditions 
after coating the resist, and the like. Therefore, although the developing 
step is performed for a predetermined period of time, a wafer or a mask is 
often underdeveloped or overdeveloped, and the size of the formed pattern 
may be greatly differnt from design values and cannot therefore meet the 
required level of precision. 
In order to solve this problem, the developing time is gradually changed by 
an operator while repeating the developing step. However, since the 
variation factors (e.g., the temperature of the developer) are not always 
constant, this method has low reliability and poor reproducibility, and 
does not allow formation of patterns with high precision. 
In addition, a technique for determining completion of development, which 
utilizes a change in reflectance of laser beams radiated on a resist 
pattern during development, has been studied. However, such an optical 
method is influenced by the refractive index of the developer and 
scattering of the laser beam in the developer, thus resulting in poor 
reliability. 
Another method for determining the developing end point has been described 
in PCT application No. WO81/00646. In this technique, a wafer and an 
electrode which is kept at a constant potential by a bias means and is 
connected to the wafer, are dipped in a conductive developer, and an 
insulating resist is removed by the developer. Then, the completion of 
pattern development is determined from a change in voltage when the 
electrode and the wafer are electrically connected and a circuit is 
formed. More specifically, electrical connection is detected when the 
voltage exceeds a predetermined threshold value. However, this technique 
simply utilizes the Ohm's law where, when electrical resistance of the 
resist is decreased and the circuit is formed, a current flows, and which 
is converted into voltage. The voltage rises abruptly when the electrode 
and the wafer are electrically connected. However, this change in voltage 
depends on types of wafer, and it is difficult to determine the completion 
of development, regardless of the type of the wafer. In this technique, 
when the voltage exceeds a predetermined threshold value, the completion 
of development is detected. However, such a method can hardly set an 
optimal developing time for each wafer. For this reason, in this 
technique, the developing time for each different type of wafer to be 
mass-produced is corrected using test wafers. This results in a 
time-consuming process and it is difficult to obtain a desired patteren 
size with high precision. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a pattern developing 
process and an apparatus therefor, which can form a resist pattern with 
high precision. 
According to an aspect of the present invention, there is provided a 
pattern developing process, comprising a resist forming step of forming a 
resist film on a surface of a conductor, a pattern forming step of forming 
a predetermined pattern on the resist film, a developing step of 
developing the pattern, such that the conductor on which the resist 
pattern is formed is dipped in a developer containing an organic solvent 
to selectively remove the resist film, a detecting step in which an 
electrode exhibiting a stable potential in the developer is dipped in the 
developer to detect a change in an electrochemical parameter between the 
electrode and the conductor, based on a change in capacitance between the 
conductor and the developer, and an end-determining step for determining 
the end point of said developing step, with reference to a reference time 
between the time preceding a changing point of the electrochemical 
parameter by a predetermined period and the time following the changing 
point of the parameter by another predetermined period. 
According to another aspect of the present invention, there is provided a 
pattern developing apparatus which develops a conductor on which a resist 
film and a predetermined pattern are successively formed, comprising a 
developing bath in which a developing solution containing an organic 
solvent is stored and in which the conductor is dipped, an electrode which 
is dipped in the developing solution in the developing bath and which 
exhibits a stable potential in the developing solution, and detecting 
means for detecting the changing point of an electrochemical parameter 
between the conductor and the electrode, thereby determining the end point 
of said developing step, with reference to a reference time between the 
time preceding a changing point of the electrochemical parameter by a 
predetermined period and the time following the changing point of the 
parameter by another predetermined period. 
According to the present invention, the capacitance between a conductor and 
a developer changes largely around the time at which a resist pattern on 
the conductor is removed by the developer and the conductor is exposed. 
Thus, the changing point of an electrochemical parameter between the 
conductor and the electrode is detected on the basis of the change in 
capacitance. 
For this reason, an appropriate developing time or the time to the end of 
the developing step can be determined with reference to the time until the 
changing point appears or a given time interval therearound. Unlike the 
conventional method wherein a voltage exceeding a threshold value is 
detected to determine the end of development, completion of development is 
determined with reference to the changing point based on a change in 
capacitance. Therefore, a reference point for determining the end of the 
developing step becomes apparent, regardless of the object to be measured, 
and an optimal reference point can be uniquely determined by the same 
determination method. 
Therefore, the size precision of the pattern can be significantly improved.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A first embodiment of the present invention will now be described with 
reference to the accompanying drawings. 
FIG. 1 is a block diagram showing an apparatus embodying a pattern 
developing method according to this embodiment. Reference numeral 1 
denotes a developing bath, which contains developer 2. Photomask 3 as an 
object to be developed and electrode 4 are dipped in developer 2. 
Photomask 3 is prepared such that a chromium film is deposited on a glass 
substrate, an electron-beam resist is coated thereon, and a desired 
pattern is exposed on the resist by use of electron beam. One end of lead 
wire 8 is connected to the chromium underlying layer of photomask 3, and 
the other end thereof is connected to inverting input terminal 14 of 
operational amplifier 5. Output terminal 16 of operational amplifier 5 is 
connected to recorder 7, through signal line 11. One end of feedback 
resistor 6 is connected to signal line 12, and the other end thereof is 
connected to signal line 13. Signal lines 12 and 13 are connected to lead 
wire 8 and signal line 11, respectively. More specifically, inverting 
input terminal 14 and output terminal 16 of operational amplifier 5 are 
connected through feedback resistor 6. One end of lead wire 9 is connected 
to electrode 4, and the other end thereof is connected to noninverting 
input terminal 15 of operational amplifier 5. Lead wire 9 and recorder 7 
are connected through signal line 10. In this way, operational amplifier 5 
and feedback resistor 6 constitute a zero-shunt ammeter, and recorder 7 
records a current value flowing between photomask 3 and electrode 4 when 
the potential difference between photomask 3 and electrode 4 is zero. 
When a pattern is to be formed by the pattern developing apparatus as 
described above, photomask 3 and electrode 4 are dipped in developer 2 in 
developing bath 1, and a current value flowing therebetween is measured 
while developing a pattern formed on the resist on photomask 3. A current 
peak appears around the time at which the chromium underlying layer of 
photomask 3 is exposed, and is recorded in recorder 7. In this case, when 
an electrolyte is added to developer 2, a current peak appears more 
clearly. Next, the developing time is changed while observing the current 
waveform recorded in recorder 7, and the developed pattern width is 
measured. Thus, the developed pattern can have an appropriate width after 
a time, obtained by multiplying the time until the current peak appears or 
a time therearound by a predetermined coefficient (herein after called 
developing coefficient), has passed. 
In the developing step, the time until the current peak appears depends on 
the developing rate of the resist. Parameters which influence the 
developing rate include the temperature of the developer, in addition to 
resist coating and electron beam exposure conditions, although they exert 
only a small influence. However, even if the developing rate is changed by 
the above parameter, the period until the current peak appears corresponds 
to the developing rate, and accordingly, the appropriate developing time 
obtained through multiplying the time until the current peak appears by 
the predetermined coefficient remains can changed since the changes of the 
developing rate have been compensated. Even if the temperature of the 
developer varies during a single developing step, the variation in 
developing rate can be compensated for as described above, during the time 
until the current peak appears. Therefore, the pattern width is influenced 
only by variations in temperature from the time the current peak appears 
until the time the developing ends. However, since this time is short with 
respect to the total developing time, the variations in temperature during 
the single developing step can only slightly influence the pattern width. 
According to this embodiment, since the completion of development is 
determined with reference to the current peak, a clear reference point for 
determination can be obtained for each object to be measured. For this 
reason, an optimal reference point for determining the completion of 
development can be determined for each object. The completion of 
development is determined such that the current peak is detected and the 
time until the current peak appears is simply multiplied with a 
predetermined coefficient, resulting in a simple arrangement. In addition, 
variations in developing rate caused by variations in parameters (e.g., 
temperture of the developer) can be compensated for, and variations in 
temperature of the developer during the single developing step exert only 
a small influence. Therefore, variations in pattern width caused by 
variations in developing rate can be suppressed. For this reason, the 
precision in the size of the developed pattern can be significantly 
improved. 
The reason why the current peak appears will be explained below. When 
photomask 3 is in a nondeveloped state, since the entire surface of the 
mask is normally covered with a resist having a thickness of several 
thousands of angstroms, the chromium underlying layer of the mask and the 
developer constitute a capacitor using the resist as a dielectric. In this 
case, the capacitance of the capacitor is normally a very small value 
(i.e., several tens of nF/cm.sup.2). As development of the pattern exposed 
on the mask progresses, the resist corresponding to the portion exposed 
with the electron beam is dissolved, and the chromium underlying layer 
directly contacts the developer. Under this condition, a capacitor (a 
so-called electric double layer) is formed on the surface of the chromium 
underlying layer, and has a high capacitance of several .mu.F/cm.sup.2 to 
several tens of .mu.F/cm.sup.2, when compared with the capacitor including 
the resist. For this reason, when the development progresses and the 
developer reaches the chromium underlying layer, the capacitance between 
the chromium underlying layer and the developer abruptly increases, as 
shown in FIG. 2. During the development, since the chromium underlying 
layer of mask 3 and electrode 4 are short-circuited, a voltage is applied 
across the two ends of the capacitor formed by the chromium underlying 
layer and the developer. Assuming that the voltage in this case is given 
by V and the capacitance is given by C, current is flowing between 
photomask 3 and electrode 4 can be expressed by relation (1): 
EQU i=VdC/dt (1) 
In this way, current i is proportional to a value obtained by 
differentiating capacitance C over time t. Therefore, as shown in FIG. 3, 
when the capacitance abruptly changes, a current peak appears. 
Next, examples wherein patterns are developed in accordance with the above 
embodiment will be described. 
EXAMPLE 1 
An EBR-9 (trade name; available from TORAY INDUSTRIES, INC.: 
poly-2,2,2-trifluoroethyl-.alpha.-chloroacrylate) was used as an 
electron-beam resist, an MIBK (methyl isobutyl ketone) was used as 
developer 2, and a platinum plate was used as electrode 4, and a current 
flowing between photomask 3 and electrode 4 was measured using the 
apparatus shown in FIG. 1. As a result, as shown in FIG. 4, a small 
current peak of about 9 nA appeared after about five minutes had passed 
from the beginning of the developing step. It was confirmed that the 
current peak appeared around the time at which the chromium underlying 
layer of photomask 3 was exposed. 
One mM of tetrabutyl ammonium perchlorate acting as an electrolyte was 
added to the MIBK, and the current flowing between photomask 3 and 
electrode 4 was measured. In this case, as shown in FIG. 5, one apparent 
current peak appeared after about five minutes had passed from the 
beginning of the developing step. It was found that the current peak was 
about 1 .mu.A, which was about 100 times or more the current peak obtained 
when no electrolyte was added, and it had a good S/N ratio. It was also 
confirmed that this current peak appeared around the time at which the 
chromium underlying layer of photomask 3 was exposed. 
Next, a pattern having a width of 4 .mu.m was exposed on the EBR-9 coated 
on photomask 3, with electron beam, and was developed using the MIBK as 
developer 2 in the same manner as described above. In this case, the 
current was measured by the apparatus shown in FIG. 1, the resist pattern 
was developed while observing the current waveform recorded in recorder 7, 
and the actually developed pattern width was measured. Note that in the 
measuring of the pattern width, the developing coefficient was set between 
1.2 to 2.0, to be changed stepwise in units of 0.2, and measurement was 
conducted twice for each developing coefficient. FIG. 6 is a graph showing 
the relationship between the developing coefficient and the pattern width, 
wherein the developing coefficient is plotted along the abscissa, and the 
pattern width after development is plotted along the ordinate. As can be 
seen from this graph, the developing coefficient and the pattern width 
have a linear relationship therebetween. When the developing coefficient 
in the case wherein the pattern width after development is 4 .mu.m, 
corresponding to the width exposed by the electron beam, is obtained from 
this line, said coefficient is about 1.3. More specifically, when the 
resist and the developer of this embodiment are used, the completion of 
development can be determined to correspond to a value obtained by 
multiplying the time until the current peak appears, by about 1.3. 
EXAMPLE 2 
In this example, a photomask was prepared and was subjected to 
electron-beam exposure in the same manner as in Example 1, except that a 
PMMA (polymethyl methacrylate) was used as an electron-beam resist. 
Thereafter, a current flowing between the chromium underlying layer of 
photomask 3 and platinum electrode 4 was measured, while developing the 
resist pattern using the apparatus shown in FIG. 1. In this case, the MIBK 
to which 1 mM of tetrabutyl ammonium perchlorate was added, was used as 
the developer. FIG. 7 shows a change in current. As can be seen from FIG. 
7, when the PMMA was used as the electron-beam resist, one apparent 
current peak appeared. Although not shown in this example, there was also 
confirmation of the relationship between the developing coefficient and 
the pattern width shown in FIG. 6. 
EXAMPLE 3 
In this example, the MIBK was used as the developer, as in Examples 1 and 
2, and an inorgainc material, for example, cerium (IV) ammonium nitrate, 
was added to the developer, unlike the organic material used in Examples 1 
and 2. The photomask was prepared and was subjected to electron-beam 
exposure under the same conditions as in Example 1, except for the above. 
Thereafter, a current value flowing between photomask 3 and platinum 
electrode 4 was measured while developing the resist pattern using the 
apparatus shown in FIG. 1. FIG. 8 shows a change in current in this 
example. As can be seen from FIG. 8, when the inorganic material was added 
to the developer, one clear current peak appeared, as in Examples 1 and 2. 
When the current value was measured under the same conditions as in 
Example 1, the time until the currnt peak appeared was substantially the 
same as that in the case shown in FIG. 5. In this case, the current peak 
was 10 times or more that shown in FIG. 5. although not shown in this 
example, there was also confirmation of the relationship between the 
developing coefficient and the pattern width shown in FIG. 6. 
When inorganic materials which have differnt valencies (e.g., cerium salt, 
iron salt, and the like) were used as an additive for the developer and 
were mixed to constitute a rdox system (e.g., a mixture of cerium (III) 
ammonium nitrate and cerium (IV) ammonium nitrate), a potential across the 
chromium underlying layer of photomask 3 and electrode 4 was stabilized. 
For this reason, the waveform of the measured current was stabilized, and 
this made determination of the completion of development easier. 
EXAMPLE 4 
In this example, the photomask was prepared and was subjected to 
electron-beam exposure in the same manner as in Example 1, except that 
electrode 4 comprised a silver/silver chloride electrode. Thereafter, a 
current value flowing between the chromium film of photomask 3 and the 
silver/silver chloride electrode was measured while developing the resist 
pattern using the apparatus shown in FIG. 1. FIG. 9 shows a change in 
current in this example. As is apparent from FIG. 9, one noticeable 
current peak appeared after about five minutes had passed from the 
beginning of the developing step, and was about 10 .mu.A, which was 10 
times or more that in the case wherein electrode 4 comprised the platinum 
electrode as in Example 1, and it has a good S/N ratio. In this example, 
it was confirmed that the developing step progressed and the current peak 
then appeared around the time at which the chromium underlying layer of 
photomask 3 was exposed. In addition, when the current value was measured 
under the same conditions as in Example 1, the time until the current peak 
appeared was substantially the same as that in the case shown in FIG. 5. 
Also in this example, there was confirmation of the relationship between 
the developing coefficient and the pattern width shown in FIG. 6. 
EXAMPLE 5 
In this example, the time during which the current value reached X% of the 
current peak before it reached the current peak, or the time during which 
the current value fell back to X% of the currnt peak after it had reached 
the current peak, was used as a reference for optimally determining 
completion of development, in place of the current peak appearance time. 
The same measurement apparatus and the same object to be measured as in 
Example 4 were used, and a detailed description thereof is omitted. A 
change in current in this example was substantially the same as that 
obtained in Example 4 shown in FIG. 9, as shown in FIG. 10. In FIG. 10, 
reference symbol A represents a point at which the current value reached 
75% of the current peak value before it reached the current peak; and B, a 
point at which the current value fell back to 75% of the current peak 
value after it had reached the current peak. 
FIG. 11 shows the relationship between the developing coefficient and the 
pattern width determined with reference to these points. In this manner, 
it was found that the developing coefficient and the pattern width has a 
linear relationship therebetween, as in that of FIG. 6 which was obtained 
when the developing coefficient was determined with refernce to the 
current peak appearance time. 
The same test was conducted for various patterns, and analysis was made 
using various values of X other than 75. As a result, when the value of X 
falling within the range of 10 to 100 (before the current value reached 
the current peak) was used, or when the value of X falling within the 
range of 40 to 100 (after the current value had reached the current peak) 
was used, it was found that the same relationship shown in FIG. 11 could 
be obtained, although the resultant values varied widely when the value of 
X was small. 
As described above, it was found that if the relationship between the 
developing coefficient and the pattern width was predetermined, a time 
other than the current peak appearance time, which was determined with 
reference to the current peak, could be used as a reference for 
determining the appropriate developing time. 
EXAMPLE 6 
In this example, a time at which a differential value of the measured 
current represented its maximum or minimum value was used as a reference 
for optimally determining completion of development. The same measurement 
apparatus and the same object to be measured as in Example 4 were used, 
and a detailed description thereof is omitted. FIG. 12 shows a change in 
differential value of the current in this example. In FIG. 12, two points 
indicated by A and B represent, respectively, a point at which the 
differential value is at maximum, and at which it is at minimum. 
FIG. 13 shows the relationship between the developing coefficients and the 
pattern widths determined with reference to these points. The same test 
was conducted for various patterns. As a result, it was found that the 
developing coefficient and the pattern width had a linear relationship 
therebetween as that in FIG. 6, obtained when the developing coefficient 
was determined with reference to the peak current appearance time. 
As described above, it was found that if the relationship between the 
developing coefficient and the pattern width was predetermined, the 
developing time could be appropriately determined with reference to the 
time representing the maximum or minimum differential value of the 
current. 
EXAMPLE 7 
In this example, the PMMA as the electron-beam resist was coated on the 
photomask substrate having a quartz plate on which chromium was deposited, 
and 20 pairs of 2-.mu.m lines and 2-.mu.m spaces were formed thereon by 
electron-beam exposure and a pair of a 100-.mu.m line and a 100-.mu.m 
space was formed thereon by electron-beam exposure, thus preparing a 
photomask. The thus obtained photomask was dipped in the MIBK containing 1 
mM of tetrabutyl ammonium perchlorate, to be developed, and a current 
value flowing between a silver/silver chloride electrode dipped in the 
developer and the underlying chromium film of the photomask was measured 
using the apparatus shown in FIG. 1. As a result, two current peaks 
appeared as shown in FIG. 14. Two photomasks for which the developing step 
was terminated respectively after time periods, 1.4 times those until the 
two current peaks appeared, had passed, were prepared, and were rinsed and 
etched. Next, the distance between lines and spaces formed on each of the 
two photomasks was measured. As a result, when the appearance time of the 
first current peak was used as a reference, the distance was 2.02 .mu.m 
substantially equal to the distance in the pattern formed on the photomask 
by electron-beam exposusre. In contrast to this, when the second current 
peak was used as a reference, the distance was 2.18 .mu.m. Thus, an 
appropriate pattern width can be obtained with reference to the first 
current peak. Similarly, the present inventors examined cases wherein a 
plurality of current peaks appeared. In any case, it was found that when 
the developing time was calculated with reference to the time until the 
first current peak appeared, an appropriate pattern width could be 
obtained. 
Note that the relationship shown in FIG. 6 can be accomplished when a 
micropattern in the order of submicrons is to be obtained. When a ratio of 
the developing time to the peak appearance time is appropriately selected, 
the pattern width after development can be increased or decreased with 
respect to the width of a pattern formed on a photomask by electron-beam 
exposure. 
When the developing coefficient was 1.1 in FIG. 6, a nondevelopd portion 
still remained, and the resist was left on the pattern portion, thus 
preventing pattern width measurement. In addition, the same effect as 
described above could be obtained when an organic material which was 
dissolved and ionized in the developer, such as tetralkyl ammonium 
perchlorate (e.g., tetraethyl ammonium perchlorate) tetrafluoroborate, or 
hexafluorophosphate, was added to the developer. 
Next, a second embodiment of the prsent invention will be described. 
A current flowing between electrode 4 and photomask 3 is measured while 
developing a pattern formed on photomask 3, using the apparatus shown in 
FIG. 1, in the same manner as in the first embodiment. In this case, the 
developing time until the pattern has a given width, i.e., an appropriate 
developing coefficient, changes in accordance with the pattern area ratio, 
and the smaller the pattern area ratio, the smaller the developing 
coefficient. The current peak value also changes in accordance with the 
pattern area ratio, and the larger the pattern area ratio, the higher the 
current peak value. For this reason, when the relationship therebetwen is 
predetermined, a pattern area ratio of the photomask after development can 
be obtained from the current peak value, and an appropriate developing 
coefficient can be determined from the obtained pattern area ratio. 
Therefore, even if the pattern area ratio varies widely, a pattern can be 
developed with high size precision. 
Examples wherein patterns were developed in accordance with this embodiment 
will be described below. 
EXAMPLE 8 
The EBR-9 as the electron-beam resist was coated on a photomask substrate 
having a quartz plate on which chromium was deposited, and was exposed by 
an electron-beam exposure apparatus to form a predetermined pattern 
thereon. In this case, patterns having pattern area ratios of 95% and 50% 
were chosen from various test patterns, and a 2-.mu.m width pattern was 
formed thereon. The pattern having the 95% pattern area ratio was reversed 
to prepare a pattern having a 5% pattern area ratio. Using the photomasks 
having the pattern area ratios of 5%, 50%, and 95%, the current flowing 
between the photomask and the electrode was measured while developing the 
pattern, using the apparatus shown in FIG. 1. As a result, data shown in 
FIGS. 15 and 16 could be obtained. In this case, 5" square photomasks were 
used. 
FIG. 15 is a graph showing the relationship between the developing 
coefficient and the pattern width for each pattern area ratio, wherein the 
developing coefficient is plotted along the abscissa, and the pattern 
width of the photomask after development is plotted along the ordinate. As 
can be seen from FIG. 15, the developing coefficients and the pattern 
widths have a linear relationship therebetween at any pattern area ratio, 
and inclinations thereof are substantially equal to each other. However, 
the positions of the lines are shifted, and the smaller the pattern area 
ratio, the larger the pattern width after development, regardless of the 
value of the developing coefficient. More specifically, the smaller the 
pattern area ratio, the smaller the developing coefficient for obtaining 
an appropriate pattern width. In this manner, since the appropriate 
developing coefficient differs in accordance with the pattern area ratios, 
when a developed pattern requires high precision, the developing 
coefficient is determined based on the pattern area ratio. 
FIG. 16 is a graph showing the relationship between the pattern area ratio 
and the current peak value, wherein the pattern area ratio is plotted 
along the abscissa and the current peak value is plotted along the 
ordinate. As can be seen from FIG. 16, the current peak value increases 
linearly upon increase in the pattern area ratio of the photomask. 
Therefore, the pattern area ratio can be obtained in accordance with the 
current peak value. 
Next, the width of the pattern developed in accordance with this example 
will be described in comparison with that of a pattern which is developed 
by fixing the developing coefficient to be 1.4. Two groups of 5" square 
substrates having the above three pattern area ratios were prepared. One 
group of substrates was developed while fixing the developing coefficient 
to be 1.4, and the other group of substrates was developed by the 
apparatus shown in FIG. 1, after the developing coefficients were 
determined in accordance with their pattern area ratios. These groups are 
named A and B groups. Table 1 shows the pattern widths after development 
in the A and B groups. 
TABLE 1 
______________________________________ 
(.mu.m) 
Group 
Area Ratio A B 
______________________________________ 
5% 2.09 2.01 
50% 2.04 1.99 
95% 1.94 1.98 
______________________________________ 
In this manner, according to this example, even when the pattern area 
ratios are considerably different, patterns can be developed with high 
precision. 
A third embodiment of the present invention will now be described with 
reference to the accompanying drawings. 
FIG. 17 is a block diagram showing an apparatus for carrying out the 
pattern developing method of this embodiment. The same reference numerals 
in FIG. 17 denote the same parts as in FIG. 1, and a detailed description 
thereof will be omitted. Reference numeral 21 denotes a capacitance meter 
for measuring a capacitance between photomask 3 and electrode 4. 
Capacitance meter 21 is connected to photomask 3 and electrode 4 
respectively through lead wires 8 and 9. Capacitance meter 21 is connected 
to the input terminal of recorder 7 through operational device 22, and the 
value of the capacitance output from capacitance meter 21 is 
differentiated by device 22 and is then recorded in recorder 7. A value 
obtained by differentiating a capacitance between photomask 3 and 
electrode 4 measured by capacitance meter 21, i.e., a value proportional 
to a current value flowing between photomask 3 and electrode 4, is 
recorded in recorder 7. 
In order to form a pattern by the pattern developing apparatus, photomask 3 
and electrode 4 are dipped in developer 2 in developing bath 1, and a 
capacitance therebetween is measured. The capacitance abruptly changes 
around the time at which the chromium underlying layer of photomask 3 is 
exposed. Next, in order to detect the point at which the capacitance 
changes, the value of the capacitance detected by capacitance meter 21 is 
inputed to device 22, and is differentiated thereby to output a value 
proportional to a current value between photomask 3 and electrode 4, to 
recorder 7. The changing point of the capacitance coincides with the peak 
which appears when the chromium underlying layer of photomask 3 is exposed 
and therearound, as where the current detected by the apparatus of FIG. 1. 
The developing time is determined with refernce to this peak, in the same 
manner as in the first embodiment, when the peak current value is 
measured. For this reason, a clear reference point for determining the 
completion of development can be obtained regardless of the object to be 
measured. 
Examples wherein patterns were developed in accordance with this embodiment 
will be described below. 
EXAMPLE 9 
In this example, photomask 3, in which chromium was deposited on a quartz 
plate, and an EBR-9 as an electron-beam resist was coated thereon, was 
used. For a pattern to be formed on photomask 3, a pattern having a 
pattern area ratio of 30% was selected from 64K Bit D-RAM patterns, and 
was formed on photomask 3 by an electron-beam exposure apparatus. The thus 
prepared photomask was dipped in an MIBK containing 100 .mu.m of 
tetraethyl ammonium perchlorate, to be developed, and a capacitance 
between photomask 3 and electrode 4 at 10 Hz, i.e., a capacitance between 
the chromium undercoat of photomask 3 and developer 2, was measured using 
a capacitance meter 21 (available from Hewlett-Packard Co., 4192A). The 
measured value was differentiated by device 22, and was recorded in 
recorder 7. In this case, a silver/silver chloride electrode was used as 
electrode 4. 
FIG. 18 is a graph showing a change over time in capacitance between 
photomask 3 and electrode 4 detected by capacitance 21, wherein the 
developing time is plotted along the abscissa, and the capacitance is 
plotted along the ordinate. As can be seen from this graph, the 
capacitance abruptly changes after three minutes have passed from the 
beginning of the developing step. In practice, since the curve shown in 
FIG. 18 is differentiated and recorded in recorder 7, an apparent peak 
appears to correspond with the time until the capacitance abruptly 
changes, as described previously. When the operation described in the 
above embodiments is performed with reference to the peak appearance time, 
an appropriate developing time can be obtained. 
EXAMPLE 10 
In this example, by paying close attention to a stepwise increase in the 
capacitance in Example 9 shown in FIG. 18, a reference for optimally 
determining completion of development was determined. 
A measurement apparatus used in Example 9 was used, except that operational 
device 22 was omitted therefrom, as shown in FIG. 19. The same objects to 
be measured as in Example 9 were used, and a detailed description thereof 
is omitted. The change in capacitance is substantially the same as that 
obtained in Example 9 shown in FIG. 18, as shown in FIG. 20. In FIG. 20, 
three points indicated by A, B, and C represent, respectively, a point at 
which a capacitance begins to increase, a point at which an increase in 
capacitance is stopped, and a point which indicates an intermediate 
capacitance between those points A and B. 
When the relationship between the pattern widths and the developing 
coefficients determined with reference to these points was examined, it 
was found that they had the same linear relationship therebetween as in 
FIG. 6, obtained when the developing coefficient was determined with 
reference to the current peak appearance time. 
A similar test was conducted for various patterns, and analysis was made 
regarding point C as an arbitrary point between points A and B. As a 
result, a linear relationship was confirmed between the developing 
coefficients and the pattern widths for all the patterns tested. However, 
no significant difference was found between the developing coefficients 
and the pattern widths, even though any of points A, B, and C was used as 
a reference point for determining the developing coefficient. 
It is considered that any difference in time between points A and B is at 
most several seconds, under normal developing conditions, and its 
influence vis-a-vis the pattern width is negligible in terms of current 
pattern size measurement precision. 
As described above, it has been confirmed that if the relationship between 
the developing coefficient and the pattern width is predetermined, the 
point at which the capacitance abruptly changes can be used as a reference 
for determining an appropriate developing time. 
Next, a fourth embodiment of the present invention will be described in 
detail. 
A current flowing electrode 4 and photomask 3 is measured while developing 
a pattern formed on photomask 3 using the apparatus shown FIG. 1, in the 
same manner as in the first embodiment. In this case, if the pattern area 
ratio of the photomask is small, a peak will not clearly appear. For 
example, if the pattern area ratio is smaller than 5%, it is difficult to 
accurately determine the position of the current peak. For this reason, 
when the pattern area ratio is smaller than 5%, a pattern for determining 
the completion of development is formed on the photomask, to increase the 
pattern area ratio to be larger than 5%. Then, a current peak clearly 
appears, and the end of the pattern developing step can be determined with 
reference to this peak. Note that the pattern for determining the end of 
the developing step is used to increase the pattern area ratio, and need 
not be a special pattern. For example, in the manufacture of photomasks, 
an arbitrary pattern can be formed on a peripheral portion which is not 
used for circuit pattern formation in the shadow of an exposure apparatus 
during exposure. Similarly, in the direct exposure process, an arbitrary 
pattern can be formed on the peripheral portion of a semiconductor wafer 
on which a semiconductor chip cannot be mounted. Alternatively, the widths 
of the letters (e.g., a mask number) printed on the periphery of the mask 
can be increased, or their black-and-white portion can be locally 
reversed. 
Next, an example wherein a pattern was developed in accordance with this 
embodiment will be described. 
EXAMPLE 11 
After a chromium film was deposited on a 125 mm.times.125 mm glass 
substrate, an EBR-9 as an electron-beam resist was coated thereon, and a 
pattern shown in FIG. 21 was formed thereon by electron-beam exposure, 
thus preparing a photomask. As shown in FIG. 21, 5-.mu.m wide evaluation 
patterns 41 were formed at 5-mm intervals on the central portion of the 
photomask, and 5-mm wide strips patterns 42 for determining the completion 
of the developing step were formed on the periphery thereof. As a 
comparative example, a photomask on which only patterns 41 were formed was 
prepared, as shown in FIG. 22. In this case, the pattern area ratio of the 
photomask of this example is 13%, and the photomask of the comparative 
example is 0.1%. 
The thus prepared photomasks were developed by the apparatus shown in FIG. 
1, and a change in current value flowing between photomask 3 and electrode 
4 was detected. As a result, in the comparative example, the current value 
to be measured was small, as indicated by the broken curve in FIG. 23, and 
a clear current peak could not be detected. However, when the pattern area 
ratio was increased using the development completion determination pattern 
as in this example, a clear current peak appeared, as indicated by the 
solid curve in FIG. 23. 
When a pattern having a size (e.g., 100 .mu.m.times.100 .mu.m), larger than 
the standard size, is used as the development completion determination 
pattern, the first current peak of a pattern which generates a plurality 
of current peaks, shown in Example 7, can be enhanced. This is effective 
when the pattern area ratio is large. 
In all the above embodiments, the photomask is used as the object to be 
developed. The present invention is not limited to this, however. For 
example, the present invention can be applied to an X-ray mask, a 
semiconductor wafer on which a pattern is formed directly thereon, and the 
like. The method of measuring an electrochemical parameter between an 
object to be developed and an electrode is not limited to the 
above-mentioned methods, but can be a method which can reliably detect a 
change in parameter (e.g., using a normal ammeter, a current detector, and 
the like). In the above embodiments, various materials which are ionized 
in the developer are used, but are not limited to those described above. 
They can be materials which can enhance a change in an electrochemical 
parameter. The electron-beam resist is not limited to that used in the 
above embodiments, but can be, for example, polymethyl methacrylate. 
Note that the developing coefficient differs in accordance with the 
combination of electron-beam resist and developer, and can be determined 
accordingly.