JPH11200072A - Concentration control method for phosphoric acid bath for semiconductor treatment and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for controlling the concn. of a phosphoric acid bath for a semiconductor wafer etching treatment by replenishment of DIW and an apparatus therefor. SOLUTION: The output of a system heater is fixed by initial setting in such a manner the set temp. most adequate for the boiling state of the phosphoric acid bath is attained. The present temp. and the set temp. are thereafter compared and the replenishing rate of DIW is automatically controlled according to the result thereof. The replenishment of the DIW is started at the timing before the phosphoric acid bath attains the set temp. after the start of heating of the etching treatment system. The DIW is dropped in a water drop form on the surface of the phosphoric acid bath. A plurality of nozzles 25 for dropping the DIW having cruciform cross members in apertures are arrayed and arranged above the surface of the phosphoric acid bath.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for controlling the concentration of a phosphoric acid bath for semiconductor processing, and more particularly to a method for controlling the concentration of a phosphoric acid bath for etching semiconductor wafers. The present invention relates to an improvement in technology performed by replenishing DIW to a surface.

[0002] In this specification, "DIW" means
Deion commonly used for etching semiconductors
sized water, that is, ultrapure water,
The ionic component is completely removed from ordinary water to make its conductivity substantially zero.

[0003]

2. Description of the Related Art In the manufacture of a semiconductor wafer, an etching process is generally performed to form a circuit or the like on a surface of the semiconductor wafer. At this time, a nitride (oxide) and an oxide (oxide) are mixed. Selective etching is performed, and the ratio between the two etching rates becomes a problem. This point is shown in FIG.
This will be described with reference to FIG.

FIG. 10 shows a state before etching, in which an oxide mask 103 is provided on a silicon substrate 101 of a semiconductor wafer, and a nitride mask 105 is further provided thereon. FIG. 11 shows dry etching, in which the nitride mask 105 is partially removed and the oxide mask 103 is partially exposed.

[0005] Then, as shown in FIG. 12, an exposed portion of the oxide mask 103 grows by thermal oxidation, and fills the removed portion of the nitride mask 105. The growth portion of the oxide mask 103 is a portion which becomes a circuit line, for example, in the finished product. Finally, the nitride mask 10 is finally etched as shown in FIG.
5 is completely removed, leaving only the oxide growth portion on the wafer.

By the way, the above-described etching process of a semiconductor wafer is usually performed in a phosphoric acid bath. A general configuration of such a processing system is shown in FIG. In the figure, an etching bath 200 containing a phosphoric acid bath is composed of a process tank 201 and an overflow tank 203, and further has a tank heater 213 for heating the phosphoric acid bath. For example, a quartz tank is used as the etching tank 200. Tank heater 2
The power and temperature of 13 are, for example, 3 KW and 300 c or less.

In the etching tank 200, the phosphoric acid bath overflowing from the process tank 201 is circulated from the overflow tank 203 to the process tank 201 via the circulation line 215. This circulation amount is usually set to about 1/2 of the tank capacity. For example, for an 81-inch tank, it is set to 250 / min or more.

The circulation line 215 is provided with a circulation pump 205, a pump damper 207, a filter 209, and an in-line heater 211 in order from the upstream side. To give a specific example, IWKIFH-4
0RT, IWAKI for the pump damper 207, NITTO DENKI for the filter 209, and a lamp heater or the like for the in-line heater (lamp heater) 211. In-line heater (lamp heater) 211
For example, a power and color temperature of 4 KW, 2350 K, and a length of 75 cm or more are used. In order to prevent deterioration of the phosphoric acid bath, part of the phosphoric acid bath in the process tank 201 is discharged out of the system via the discharge line 217 at an appropriate cycle.

By the way, in the selective etching of the nitride and the oxide shown in FIGS. 10 to 13, it is desirable to set the process conditions so that the etching rate of the nitride is as high as possible and the etching rate of the oxide is as low as possible. That is, the removal of the nitride in the dry etching shown in FIG. 11 and the final etching shown in FIG. 13 is performed as quickly as possible (that is, in a state where the etching is easy), and the removal of the oxide in the final etching is as slow as possible (that is, in the state where the etching is difficult). It is desirable to do it.

FIG. 15 shows the relationship between the phosphoric acid bath concentration (%) and the nitride etching rate (A / min). The solid line in the figure shows the relationship between the concentration at each phosphoric acid bath temperature and the etching rate, and the broken line shows the relationship between the concentration at the boiling point of the phosphoric acid bath and the etching rate. As is clear from the figure, in the case of nitride, the etching rate is highest at the boiling point at any phosphoric acid bath temperature.

FIG. 16 shows the relationship between the concentration of the phosphoric acid bath (%) and the oxide etching rate (A / min). The solid line in the figure shows the relationship between the concentration at each phosphoric acid bath temperature and the etching rate, and the broken line shows the relationship between the concentration at the boiling point of the phosphoric acid bath and the etching rate. As is clear from the figure, in the case of oxide,
The etching rate is lowest at the boiling point at any phosphoric acid bath temperature.

From the relationship between the phosphoric acid bath concentration and the etching rate, it is most desirable that the etching rate of the nitride be the highest and the etching rate of the oxide be the lowest. Therefore, it can be seen that the etching rate ratio between nitride and oxide is most desirable at the boiling point.

This is thought to be due to the following mechanism. In a hot phosphoric acid bath, phosphoric pentoxide P ₂ O ₅ is hydrated to various degrees to form a series of acids P ₂ O ₅ nH _2.
O is generated, and among them, the presence of pyrophosphate H ₄ P ₂ O ₇ or orthophosphate H ₃ PO ₄ promotes the etching of the oxide, and the oxide is more easily removed. In other words, when the nitride mask is removed in the etching process, if the concentration of the phosphoric acid bath is not appropriate, not only the nitride but also the oxide is shaved off. However, when the phosphoric acid bath is in a boiling state, the pyrophosphoric acid and the orthophosphoric acid are hardly generated, so that the oxide is not removed.

Specifically, when the etching rate of the phosphoric acid bath with respect to the nitride is set to 30 to 40 times or more the etching rate with respect to the oxide, it is considered that the oxide is not removed in the final etching.

That is, in order to perform the etching process in a good condition, the phosphoric acid bath must be maintained at a concentration that allows the high-temperature phosphoric acid bath to be kept in a boiling state at all times. Usually, the boiling temperature of the phosphoric acid bath is 155 ± 0.5 ° C., so that the temperature is set to this temperature, and the appropriate concentration of the phosphoric acid bath is 85%. That is, 85% of the phosphoric acid bath is phosphoric acid, and the remaining 15% is water.

By the way, with the progress of the etching process, the water in the phosphoric acid bath evaporates instantaneously due to the high temperature to become steam gas and leaves the phosphoric acid bath. For this reason, the concentration of the phosphoric acid bath gradually approaches 100% as the etching process proceeds. In other words, the density is not the appropriate density apart from the appropriate density of 85%. To prevent this, an appropriate amount of DIW is replenished to the phosphoric acid bath and the concentration is adjusted to an appropriate value of 85.
%, And the replenishment of the phosphoric acid bath with DIW during such an etching process has conventionally been generally performed. That is, according to the conventional method, the replenishment rate of DIW is set in three stages such as a value corresponding to the set temperature, a value corresponding to the temperature lower than the set temperature, and a value corresponding to the temperature exceeding the set temperature. (Tank heater and in-line heater) to control the temperature.

When DIW is replenished to a high-temperature phosphoric acid bath, two kinds of steam gas are generated in the entire system.
That is, even when DIW is replenished in the phosphoric acid bath, there is steam gas that escapes from the phosphoric acid bath without being dissolved.
In addition, there is a water vapor gas formed by evaporating moisture originally present in the phosphoric acid bath by a thermal reaction.

At the same time, in the phosphoric acid bath, three types of water mass groups are mixed. That is, the first group of water masses composed of DIW as replenished in the phosphoric acid bath, the second group of water masses composed of DIW slightly dissolved in the phosphoric acid bath, and The third water mass group constituted by the existing water is mixed. These three types of water mass groups have different concentrations and different temperatures.

As described above, in the conventional concentration control of a phosphoric acid bath, so-called binary control in which a change in heater power is combined with a DIW replenishment rate is generally performed. Each of these values is set by calculation based on experience before the etching process.

Further, in the prior art, DIW replenishment is started after the current temperature of the phosphoric acid bath reaches a set temperature.

FIG. 17 shows an example of a conventional phosphoric acid bath concentration control system, which is called an in-line replenishment system, in which DIW is replenished to the system in a circulating line of the phosphoric acid bath. There is a DIW replenishment system adopted by Nisso Engineering.

In the drawing, an etching bath 300 containing a phosphoric acid bath is composed of a process tank 301 and an overflow tank 303, and further provided with a tank heater 313 for heating the phosphoric acid bath.

In the etching bath 300, the phosphoric acid bath overflowing from the process tank 301 is circulated from the overflow tank 303 to the process tank 301 via the circulation line 315. The circulation line 315 is provided with a circulation pump 305, a filter 309, and an in-line heater 311 in order from the upstream side. In order to prevent deterioration of the phosphoric acid bath, part of the phosphoric acid bath in the process tank 201 is discharged out of the system via the discharge line 317 at an appropriate cycle.

In the above configuration, DIW is replenished from the DIW replenishing tank 306 through the replenishment line 319 into the system at a replenishment point 316 in the circulation line 315 downstream of the in-line heater 311.

FIG. 17 shows an example of a conventional phosphoric acid bath concentration control system, which is called a processing tank replenishment system, in which DIW is replenished into a phosphoric acid bath etching processing tank by rod-shaped water injection. Has a DIW replenishment system manufactured by Dainippon Screen.

In the figure, an etching tank 400 containing a phosphoric acid bath is composed of a process tank 401 and an overflow tank 403, and further provided with a tank heater 413 for heating the phosphoric acid bath.

In the etching tank 400, the phosphoric acid bath overflowing from the process tank 401 is circulated from the overflow tank 403 to the process tank 401 via the circulation line 415. The circulation line 415 is provided with a circulation pump 405, a filter 409, and an in-line heater 411 in order from the upstream side. In order to prevent deterioration of the phosphoric acid bath, part of the phosphoric acid bath in the process tank 401 is discharged out of the system via the discharge line 417 at an appropriate cycle.

In the above configuration, DIW is replenished from the DIW replenishment tank 406 through the replenishment line 419 into the process tank 401 by rod-shaped water injection. Note that rod-shaped water injection refers to a water injection state in which water flows out continuously from a water tap.

[0029]

As described above, when the concentration of the phosphoric acid bath is controlled by using two values, that is, the heater power and the DIW replenishment rate, there are the following problems. In general, since the specific heat of the phosphoric acid bath is small and about 0.5, the range of the boiling temperature is very small at about ± 0.5 ° C. Therefore, even if the power of the heater is changed even a little, the effect is large, and if the amount of the change is somewhat inadequate, the phosphoric acid bath tends to run out of control and a stable etching process is performed. It becomes difficult. Further, since the replenished DIW evaporates, the concentration of the phosphoric acid bath changes every moment, and it is not possible to follow the change in the concentration only by changing the replenishment rate of the DIW in three stages calculated and set in advance. That is, it is practically impossible to maintain the phosphoric acid bath at an appropriate concentration.

As described above, there is also a problem when DIW replenishment is started after the phosphoric acid bath reaches the set temperature. At a timing before the temperature of the phosphoric acid bath reaches the set temperature, that is, near the temperature of the phosphoric acid bath reaching 95 ° C., the water in the phosphoric acid bath has already started to evaporate. As a result, at the timing when the phosphoric acid bath reaches the set temperature, the concentration of the phosphoric acid bath is higher than the above-mentioned appropriate concentration of 85%. Therefore, even if replenishment of DIW is started at this timing, it is already too late to be in a boiling state. That is, the etching process cannot be performed in a good state.

Further, in the case of the above-described DIW in-line replenishment method, the in-line heater 3 is provided in the circulation line 315.
The high-temperature circulating phosphoric acid bath immediately after being heated by 11 reacts with the replenished DIW to generate a large amount of steam gas in the circulating line. This steam gas is accelerated by the reaction, and together with the phosphoric acid bath, the process tank 30 has a considerable strength.
As shown in FIG. 18, the inside of the tank is bumped, and a large amount of relatively large bubbles are disturbed in the phosphoric acid bath of the tank. Thus, the process tank 306
When the phosphoric acid bath in the inside becomes bumpy, not only cannot it be distinguished from the so-called normal boiling state, but also the semiconductor wafer in the phosphoric acid bath is greatly disturbed in its posture and jumps out of the Teflon carrier, and The unnecessary etching process is not performed.

On the other hand, if the DIW replenishment point 306 is set upstream of the in-line heater 311, the DIW evaporates in the in-line heater, and as a result, steam gas accumulates, and the heat generated by the heater at that point becomes empty. Is easy to invite.

Further, there is a problem in the processing tank replenishment system described above. When DIW is replenished in the phosphoric acid bath, three kinds of water mass groups are mixed in the phosphoric acid bath as described above. Here, replenishing DIW by rod-shaped water injection means that a large-volume second water mass, that is, a mass of water composed of DIW slightly dissolved in a phosphoric acid bath is generated in a large-volume state. . The water mass has a lower concentration and a lower temperature than the phosphoric acid bath.
When such a large volume of water masses having different properties migrate in the process tank, the attitude of the semiconductor wafer is greatly disturbed. That is, the semiconductor wafer moves between slots in the Teflon carrier, or in the worst case, jumps out of the carrier. Furthermore, the concentration and temperature of the entire phosphoric acid bath become locally non-uniform, making it difficult to perform proper and uniform etching.

When such a group of water enters the in-line heater 411 through the circulation line, it rapidly becomes steam gas by heating, which causes an explosion. As a result, not only the in-line heater is damaged by the vibration, but also an excessive load is applied to other parts of the circulation line component.

In view of the state of the prior art, an object of the present invention is to provide a system for controlling the concentration of a phosphoric acid bath for etching a semiconductor wafer by replenishing DIW to control the system for maintaining the phosphoric acid bath at a boiling concentration. And to ensure that the phosphoric acid bath is brought to a boiling state at the set temperature.

Still another object of the present invention is to provide a system for controlling the concentration of a phosphoric acid bath for etching a semiconductor wafer by replenishing DIW in a bumping state of a phosphoric acid bath and a posture of a semiconductor wafer caused by replenishment of DIW. It is an object of the present invention to avoid turbulence, and to avoid the occurrence of low-concentration low-temperature large-sized water bodies when DIW is replenished and the accompanying problems.

[0037]

According to the first aspect of the present invention, the output of the system heater is fixed by initial setting so as to attain the set temperature most suitable for the boiling state of the phosphoric acid bath. And a set temperature, and automatically controls the DIW replenishment rate according to the result.

[0038] In the second aspect of the present invention, replenishment of DIW is started at a timing after the heating of the etching system is started and before the phosphoric acid bath reaches the set temperature. .

Further, the third invention is characterized in that DIW is dropped in the form of water droplets on the surface of the phosphoric acid bath.

Further, in the fourth invention, the gist is that a plurality of DIW dripping nozzles each having a cross cloth member at the opening are arranged above the surface of the phosphoric acid bath.

[0041]

According to the first aspect of the invention, the concentration of the phosphoric acid bath fluctuates finely in the vicinity of an appropriate concentration (85%) corresponding to the set temperature.

In the case of the second invention, DIW is replenished before the water in the phosphoric acid bath evaporates completely, so that the concentration value at the set temperature is substantially close to the appropriate concentration (85%).

In the case of the third invention, even if the total replenishment amount is the same as the conventional one, the total contact area of the phosphoric acid bath with DIW becomes large, and DIW dissolves well in the phosphoric acid bath.
Generation of water vapor gas due to escape of the IW is suppressed.

In the case of the fourth invention, DIW dropped due to the surface tension effect becomes small water droplets, and the total contact area with the phosphoric acid bath increases accordingly.

[0045]

As described above, in the present invention, the concentration of the phosphoric acid bath is controlled by one-value control. That is, the heater power is kept constant and only the DIW replenishment rate is automatically controlled, and the temperature is not controlled by the heater power. The power of the heater is fixed from the beginning so that the temperature is most suitable for the boiling state. DI instead
By changing the drive interval of the W replenishment pump, DI
The concentration of the phosphoric acid bath is kept constant by adjusting the replenishment rate of W. This configuration ensures that the heater is in a boiling state at a temperature obtained as a result of the power of the heater fixed at the beginning, and the concentration of the phosphoric acid bath is an appropriate value, that is, 85%.
It does not exceed.

In the present invention, replenishment of DIW is started before the temperature of the phosphoric acid bath reaches the set temperature. As a result, the concentration of the phosphoric acid bath was set at the set temperature of 155 ° C.
In the vicinity, the corresponding appropriate density is 85%. Further, during the heating of the phosphoric acid bath, the amount of evaporation of water is smaller than after the heating, so that the DIW replenishment rate is made smaller than that after the heating. After the current temperature of the phosphoric acid bath reaches the set temperature, the DIW replenishment rate is automatically controlled in small increments as described later.

In practicing the present invention, DIW
It is assumed that the total replenishment amount (total volume) during a certain period of time does not change from the conventional one and that the total contact area between DIW and the phosphoric acid bath is made as large as possible. To this end, it is conceivable to replace the conventional rod-shaped water injection with layered water injection, that is, to replenish DIW in the form of a thin and wide layer. However, according to this method, a second mass of water in the above-mentioned triad mixed state, that is, a large mass of low-concentration and low-temperature mass composed of DIW slightly dissolved in the phosphoric acid bath is generated. However, it is not preferable from the viewpoint of the uniformity of the phosphoric acid bath. That is, it is also a premise of the invention that no second water mass group is generated.

In order to satisfy all of these three requirements, in the present invention, as shown in FIGS. 1 and 2, DIW is formed into water droplets and replenished by dropping them on the surface of a phosphoric acid bath. This dropping is preferably performed on the overflow tank of the etching processing tank, and may be performed on the process tank. In any case, the dropped water DIW once settles in the phosphoric acid bath and then slowly floats toward the surface, during which time it sufficiently dissolves in the phosphoric acid bath.

In this case, although the surface area of each water droplet (that is, the contact area with the surrounding phosphoric acid bath) is small, the total contact area becomes large as a whole because the number of water droplets is large. Moreover, even if the second water mass group is generated, the volume of each water mass becomes small because the water droplets on which the second water mass group is formed are small in the first place,
It does not substantially affect the uniformity of the concentration and temperature of the entire phosphoric acid bath.

It is desirable that the water droplet has a diameter of about 1.5 to 2.0 mm. The specific gravity of DIW is 1, while the specific gravity of the phosphoric acid bath is 1.5 to 1.6. Therefore, the water droplets are made too small. The water droplets do not settle in the phosphoric acid bath but float only on the surface, and cannot be dissolved in the phosphoric acid bath. Therefore, it is not preferable to spray in a so-called mist state.

The replenishment rate is 20 to 300 cc / mi.
Preferably, it is at the n-th position, and it is desirable to arrange at least about 10 nozzles. In order to form water droplets more reliably, it is desirable to provide a cross cloth member 27 at the opening of each nozzle 25 as shown in an example in FIGS. Due to the presence of such a cross cloth member 27, surface tension is generated in the DIW and water droplets are easily formed.

FIG. 3 shows an example of the configuration of a system embodying the present invention. In the figure, an etching tank containing a phosphoric acid bath, a process tank 1 and an overflow tank 3
And a tank heater 3 for heating the phosphoric acid bath.

In the etching tank, the phosphoric acid bath overflowing from the process tank 1 is circulated from the overflow tank 3 to the process tank 1 via the circulation line 5.
The circulation line 5 is provided with a circulation pump 5, a pump damper 7, a filter 9, and an in-line heater 11 in this order from the upstream side. In order to prevent the deterioration of the phosphoric acid bath, part of the phosphoric acid bath in the process tank 1 is discharged out of the system via the discharge line 7 at an appropriate cycle.

In the above configuration, DIW is replenished from the DIW replenishing pump 21 through the replenishing line 19 and the overflow meter 23 by the drip nozzle 25 into the system.

FIG. 4 shows a state in the phosphoric acid bath when DIW is replenished according to the present invention. The water droplets of DIW dropped from the nozzle 25 become small bubbles, and settle once in the phosphoric acid bath of the overflow tank 3 and then float on the surface. During this time, DIW dissolves in the phosphoric acid bath through the contact surface between the water droplet and the phosphoric acid bath. Even if some of the bubbles enter the circulation line 15 from the overflow tank 3 and are recirculated into the process tank 1 as shown in the figure, since the original water droplets are small, they do not become large bubbles. It does not disturb the posture of the semiconductor wafer in the acid bath.

As described above, in the present invention, the power of the heater is fixed, and the DIW replenishment rate is automatically controlled in small increments corresponding to the temperature of the phosphoric acid bath. FIG. 5 shows an example of the general procedure. In this case, the DIW16 replenishment pump used in this case has about 15 to 1 shot.
20 cc, and the control of the DIW replenishment rate is performed by changing the drive interval. The reference value of the replenishment rate is 8 shots / min = about 160 cc / min. The DIW replenishment rate can be linearly controlled in the range of 20 to 300 cc / min by changing the drive interval of the pump.

First, the heaters (tank heater and in-line heater) are turned on at the same time as the phosphoric acid bath circulation starts. The temperature of the phosphate bath gradually rises,
In this period, since the instantaneous current temperature of the phosphoric acid bath is lower than the set temperature, the evaporation of water is reduced accordingly, and the replenishment rate of DIW may be less than the reference value. For example, the drive interval of the refill pump is set to about 40 seconds, and the refill rate is set to 1.5 shots / min = 30 cc / min.

When DIW replenishment is continued at this replenishment rate and the current temperature of the phosphoric acid bath reaches the set temperature, the DIW replenishment rate is set to a reference value. That is, the driving interval of the replenishing pump is set to about 7.5 seconds, and the replenishing rate is set to 8 shots /.
min = 160 cc / min.

While the replenishment of DIW is continued at this replenishment rate, the temperature of the phosphoric acid bath is monitored, and if the current temperature exceeds the set temperature, the evaporation of water increases accordingly, so the replenishment rate of DIW exceeds the reference value. Value. For example, the drive interval of the refill pump is set to about 46.5 seconds, and the refill rate is set to 9.2 shots / min = 185 cc / min.

While the DIW replenishment is continued at this replenishment rate, the temperature of the phosphoric acid bath is monitored, and when the current temperature returns to the set temperature, the evaporation of water is reduced accordingly, so the DIW replenishment rate is returned to the reference value. That is, the drive interval of the refill pump is returned to about 7.5 seconds, and the refill rate is set to 8 shots / min = 160 cc / min.

While the replenishment of DIW is continued at this replenishment rate, the temperature of the phosphoric acid bath is monitored, and if the current temperature falls below the set temperature, the evaporation of water is further reduced. And For example, the driving interval of the replenishing pump is about 8 seconds, and the replenishing rate is 7.5 shots / min = 150 cc / min.

Hereinafter, the above procedure is repeated as appropriate to automatically control the concentration of the phosphoric acid bath. The details will be described below with reference to FIGS. 6 and 7. FIG. 6 shows the procedure during the temperature rise of the phosphoric acid bath (current temperature <set temperature), and FIG. 7 shows the procedure after the temperature rise (current temperature ≧ set temperature). As in the above case, the DIW replenishing pump has a shot of about 15 to 20 cc per shot, and the time (seconds) shown in the figure indicates the drive interval. The initial value and the control value are values of the drive interval of the DIW replenishment pump.

In FIG. 6 showing the control procedure during the temperature rise of the phosphoric acid bath, first, the circulation of the phosphoric acid bath is started and the power of the heater is turned on. Then, monitoring of the temperature of the phosphoric acid bath is started. If a monitoring result indicates that the current temperature is higher than the set temperature, it is due to a process error, for example, a sensor error or DIW replenishment error. This is because the fact that the current temperature becomes higher than the set temperature while the temperature is rising toward the set temperature is a phenomenon that cannot normally occur.

Therefore, the monitoring result usually indicates that the current temperature is lower than the set temperature. In this case, the correspondence differs at 100 ° C., which is the evaporation point of water. If the current temperature is 100 ° C. or higher, the replenishment rate needs to be increased because of the large evaporation of water, and 15 seconds is read into the system as a control value. When the temperature is 100 ° C. or lower, the replenishment rate may be low because the evaporation of water is small, and 30 seconds is read into the system as an initial value. When the replenishment of the phosphoric acid bath is started at each pump drive interval, the current temperature of the phosphoric acid bath eventually reaches the set temperature, and the two become equal.
Thus, the procedure during the temperature rise is completed.

Next, a control procedure after the temperature rise of the phosphoric acid bath shown in FIG. 7 is started. First, 7.5 seconds (D
The driving interval of the IW replenishing pump is read into the system, and DIW replenishment is performed at the replenishment rate of the reference value. During this time, monitoring of the temperature of the phosphoric acid bath is continued.

When the monitoring result that the current temperature of the phosphoric acid bath is higher than the set temperature is obtained, the temperature is continuously monitored for a certain period of time, for example, 60 seconds. 1 second shorter than the value. That is, since the evaporation of DIW increases in accordance with the replenishment amount of DIW, the replenishment rate is made higher than the reference value. The above loop control is repeated until the current temperature of the phosphoric acid bath becomes equal to the set temperature.

When the drive interval of the DIW replenishment pump has reached the minimum value as a result of the above loop control, error monitoring is continued for a certain period of time, and when a monitoring result indicating that the current temperature of the phosphoric acid bath is higher than the set temperature appears, Process error (DIW
The process is stopped because of a replenishment shortage error.

If a monitoring result indicating that the current temperature of the phosphoric acid bath is lower than the set temperature is obtained, the temperature is continuously monitored for a certain period of time, for example, 150 seconds, and after confirming the temperature, the drive interval of the DIW replenishing pump is set to the above-mentioned initial control. 0.5 seconds longer than the value.
That is, since the DIW is less evaporated, the replenishment rate is set lower than the reference value. The above loop control is repeated until the current temperature of the phosphoric acid bath becomes equal to the set temperature.

When the drive interval of the DIW replenishing pump reaches the maximum value as a result of the above loop control, error monitoring is continued for a certain period of time, and if a monitoring result indicating that the current temperature of the phosphoric acid bath is lower than the set temperature appears, The process is stopped because of a process error (DIW excess replenishment error and / or heater power drop error).

If the result of the above two loop controls and the result of monitoring that the current temperature of the phosphoric acid bath is equal to the set temperature after reading the initial control value are obtained, the drive interval of the DIW replenishment pump is set to the initial control value ( 7.5 seconds), that is, the replenishment rate is returned to the reference value. Thereafter, the process returns to the control phase before the reading of the initial control value.

[0071]

According to the present invention, the concentration of the phosphoric acid bath fluctuates finely in the vicinity of the appropriate concentration (85%) corresponding to the set temperature. Therefore, the phosphoric acid bath is kept at the boiling concentration, the nitride and the oxide have a preferable etching ratio, and a clean etching process can be performed.

Further, the power of the heater is initially fixed and the DIW
, The control is much easier and more accurate than the conventional binary control method in which the heater power and the replenishment rate are changed.

Further, since DIW is replenished before the water in the phosphoric acid bath evaporates completely, the concentration value becomes substantially close to the appropriate concentration (85%) at the set temperature. Therefore, the phosphoric acid bath can be reliably brought into a boiling state at the set temperature.

Furthermore, according to the present invention, even if the total replenishment amount is the same as the conventional one, the DIW dripped due to the surface tension effect becomes small water droplets, enters the phosphoric acid bath, and the total contact area with DIW becomes large. Dissolves well in the phosphoric acid bath, and as a result, generation of water vapor gas due to escape of DIW is suppressed. In addition, since the large second water mass group does not occur, the temperature and the concentration of the phosphoric acid bath become uniform as a whole.
That is, troubles caused by the occurrence of the water mass group are drastically reduced.

According to the present invention, by the above synergistic effect,
The etching of the semiconductor wafer is performed in a very favorable condition.

[Brief description of the drawings]

FIG. 1 is a front view showing the principle configuration of the present invention.

FIG. 2 is a side view of the same.

FIG. 3 is a block diagram showing an example of a configuration of a system for implementing the present invention.

FIG. 4 is an enlarged view of a main part showing a state of a bubble in an etching processing tank according to the present invention.

FIG. 5 is a schematic flowchart showing an example of a procedure of automatic control of the concentration of a phosphoric acid bath according to the present invention.

FIG. 6 is a detailed flowchart showing an example of a procedure during the temperature rise of the phosphate bath for automatic control of the phosphate bath concentration according to the present invention.

FIG. 7 is a detailed flowchart showing an example of a procedure after the temperature rise of the phosphoric acid bath.

FIG. 8 is a bottom view showing an example of a DIW dropping nozzle used in the apparatus of the present invention.

FIG. 9 is a sectional side view of the same.

FIG. 10 is a side view showing a state before an etching process of the semiconductor wafer.

FIG. 11 is a side view showing a state after dry etching.

FIG. 12 is a side view showing a state after thermal oxidation.

FIG. 13 is a side view showing a state after the completion of the final etching.

FIG. 14 is a block diagram showing a general configuration of a semiconductor wafer etching processing system.

FIG. 15 is a graph showing the relationship between the concentration of a phosphoric acid bath and the etching rate of a nitride in a semiconductor etching process.

FIG. 16 is a graph showing the relationship between the concentration of a phosphoric acid bath and the etching rate of an oxide in a semiconductor etching process.

FIG. 17 is a block diagram showing a system configuration of a conventional DIW in-line replenishment system.

FIG. 18 is an enlarged side view of a main part showing a bumping state of the phosphoric acid bath in the system.

FIG. 19 is a block diagram showing a system configuration of a conventional DIW processing tank HK system.

[Explanation of symbols]

 1, 201, 301, 401: Process tank 3, 203, 303, 403: Overflow tank 5, 205, 305, 405: Circulation pump 9, 209, 309, 409: Filter 11, 211, 311, 411: In-line heater 13 213, 313, 413: tank heater 15, 215, 315, 415: circulation line 17, 217, 317, 417: discharge line 19, 319, 419: DIW replenishment line 21: DIW replenishment pump 25: DIW drop nozzle 27 : Cross cloth member 101: Silicon substrate 103: Oxide mask 105: Nitride mask

Claims (12)

[Claims] 1. A method for controlling the concentration of a phosphoric acid bath for etching a semiconductor wafer by replenishing DIW, wherein an output of a system heater is initially set so as to be a set temperature most suitable for a boiling state of the phosphoric acid bath. A method of controlling the concentration of a phosphoric acid bath for semiconductor processing, comprising fixing the temperature by setting, thereafter comparing the current temperature with the set temperature, and automatically controlling the DIW replenishment rate according to the result. 2. A method for controlling the concentration of a phosphoric acid bath for etching a semiconductor wafer by replenishing DIW, wherein timing after the heating of the etching system is started and before the phosphoric acid bath reaches a set temperature. Wherein the replenishment of DIW is started in the step (a). 3. A method for controlling the concentration of a phosphoric acid bath for etching a semiconductor wafer by replenishing the phosphoric acid bath with DIW, wherein the DIW is dropped on the surface of the phosphoric acid bath in the form of water droplets. Of controlling the concentration of a phosphoric acid bath for semiconductor processing. 4. The method according to claim 3, wherein said DIW is dropped in the form of water droplets having a diameter of 1.5 to 2.0 mm. 5. The method according to claim 5, wherein the water drop of DIW is 20 to 300 cc / m.
4. The method of claim 3, wherein the method is performed at an in rate. 6. A method of controlling the concentration of a phosphoric acid bath for etching a semiconductor wafer by replenishing DIW, wherein an output of a system heater is initially set so as to be a set temperature most suitable for a boiling state of the phosphoric acid bath. The temperature is fixed by setting, then the current temperature is compared with the set temperature, the DIW replenishment rate is automatically controlled according to the result, and the phosphoric acid bath reaches the set temperature after the heating of the etching processing system is started. A method for controlling the concentration of a phosphoric acid bath for semiconductor processing, wherein replenishment of DIW is started at a previous timing. 7. A method for controlling the concentration of a phosphoric acid bath for etching a semiconductor wafer by replenishing DIW, wherein an output of a system heater is initially set so as to be a set temperature most suitable for a boiling state of the phosphoric acid bath. The temperature is fixed by setting, then the current temperature is compared with the set temperature, the replenishment rate of DIW is automatically controlled according to the result, and DIW is added to the surface of the phosphate bath.
A method for controlling the concentration of a phosphoric acid bath for semiconductor processing, characterized by dropping water in the form of water drops. 8. A method for controlling the concentration of a phosphoric acid bath for etching a semiconductor wafer by replenishing DIW, wherein an output of a system heater is initially set so as to be a set temperature most suitable for a boiling state of the phosphoric acid bath. The temperature is fixed by setting, then the current temperature is compared with the set temperature, the replenishment rate of DIW is automatically controlled according to the result, and the heating of the etching processing system is started and before the phosphoric acid bath reaches the set temperature. Wherein the replenishment of DIW is started at the timing of (1) and DIW is dropped on the surface of the phosphoric acid bath in the form of water droplets. 9. A method for controlling the concentration of a phosphoric acid bath for etching a semiconductor wafer by replenishing DIW, wherein timing after the heating of the etching system is started and before the phosphoric acid bath reaches a set temperature. Wherein the replenishment of DIW is started and DIW is dropped in the form of water drops on the surface of the phosphoric acid bath. 10. A type in which the concentration of a phosphoric acid bath for etching a semiconductor wafer is controlled by replenishing the phosphoric acid bath with DIW, wherein the DIW having a cross cloth member in an opening.
A concentration control device for a phosphoric acid bath for semiconductor processing, wherein a plurality of dropping nozzles are arranged above the surface of the phosphoric acid bath. 11. The apparatus according to claim 10, wherein said DIW dropping nozzle is disposed above a surface of a phosphoric acid bath in an overflow tank of the phosphoric acid bath. 12. The apparatus according to claim 10, wherein at least ten DIW dropping nozzles are arranged.