JPH10163167A - Etching apparatus and detection method for end point of etching - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an etching apparatus by which the end point of an etching operation can be detected at a precise timing without especially limiting the specific substrate of a film to be etching and to provide a detecting method for the end point of the etching operation. SOLUTION: The concentration of titanium atoms which are contained in an etchant 3 inside an etching tank is detected by an atomic concentration detector from the start of an etching treatment (Step S2), a control device detects the end point of the etching treatment on the basis of the linear time differentiated value of the atomic concentration (Step S3, Step S4), a control signal is given to a robot arm, a case is pulled up from the etching tank (Step S5), and the case is immersed in a rinsing liquid in a cleaning tank (Step S6).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an etching method in which an object having a film formed on its surface is immersed in an etching solution in an etching bath to selectively etch a specific substance constituting the film. The present invention relates to an apparatus and an etching end point detection method.

[0002]

In a manufacturing process of a semiconductor device such as a MOSFET, for example, a salicide structure in which the surfaces of a source, a drain, and a gate electrode are made into a metal silicide is formed to reduce the parasitic resistance and reduce the MO.
There is a technique for improving the operation speed of the SFET. For example,
When titanium silicide, which is commonly used as a metal silicide, is formed, a gate sidewall oxide film or LOCO
Unreacted unnecessary titanium present on the surface of the S oxide film or the like must be removed by selective wet etching using a solution of ammonia and hydrogen peroxide as an etchant.

A problem in this case is when to end the etching. In other words, if the etching time is insufficient, unnecessary titanium remains on the MOSFET (under-etching), resulting in poor insulation between the gate and the source and drain. If the etching time is set excessively to prevent this, , M
In some cases, the etching reaches the layer (titanium silicide layer) necessary for the OSFET (overetching), and when an electrode is formed thereon, the contact resistance increases. Therefore, how to properly detect the end point of the etching determines the quality of the device characteristics and the reproducibility (yield) thereof.

A conventional technique for accurately detecting the end point of such etching is disclosed in, for example, Japanese Patent Laid-Open No.
There is one disclosed in JP-A-201807. This is achieved by irradiating an interface between the Si semiconductor substrate, which is immersed in an etching solution and being etched, and an oxide film (SiO ₂ ) with an infrared beam consisting of only a fundamental wave and a first harmonic component as probe light. The second harmonic component contained in the infrared beam reflected at the interface between the substrate and the oxide film is detected, and the end point of the etching is detected based on the change.

Assuming that this conventional technique is applied to the case where titanium is etched as described above, there are the following problems. First, it is difficult to select an appropriate probe light that transmits titanium and reflects at the interface with titanium silicide as the probe light that replaces the infrared beam.

Further, when the object to be etched has a fine pattern equal to or smaller than the diameter of the probe light, it is difficult to obtain information suitable for end point detection by the probe light. Furthermore, during the etching of titanium, a large amount of bubbles are generated in the etching solution,
Scattering of the probe light occurs and hinders the detection operation. From the above, the applicability is considered to be poor.

As described above, when the end point of etching is directly detected from the state of the surface of the material to be etched,
As described above, since there are many restrictions on the etching target and the detection operation, accurate detection may not be performed in some cases.

Further, as a prior art, Japanese Patent Laid-Open No. 6-26
No. 0479 is disclosed. this is,
The ion concentration in the etching solution is measured by the ion detecting means, and the end point of the etching is detected when the ion concentration is saturated.

However, actually, not all the members to be etched, such as metals, existing in the etching solution are ionized. Therefore, if the end point of the etching is detected based on the ion concentration, an error corresponding to the ratio of the non-ionized member to be etched is included. In addition, there is a problem that the amount of change in the concentration is small near the end point of the etching where the ion concentration is saturated, and it is difficult to detect the end point at an optimal timing.

[0010] The present invention is to solve the above-mentioned problems,
An object of the present invention is to provide an etching apparatus and an etching end point detecting method capable of detecting an etching end point at an accurate timing without particularly limiting a specific substance of a film to be etched.

[0011]

In order to achieve the above object, according to the etching apparatus of the first aspect or the method of detecting the end point of the etching according to the seventh aspect, the etching solution contains: The atomic concentration of the specific substance (for example, titanium) constituting the coating formed on the surface of the object gradually increases. The atomic concentration is detected by the atomic concentration detecting means, and the end point detecting means detects the end point of the etching based on the primary time differential value of the atomic concentration.

For example, when the specific substance of the film to be etched is substantially etched, the change in the atomic concentration of the specific substance dissolved in the etching solution is reduced, so that the first-order time differential value is also at a low level. Therefore, since the first-order time differential value of the atomic concentration of the specific substance is equal to or less than the predetermined level, the end point of the etching can be detected at an accurate timing without particularly limiting the type of the specific substance.

According to the etching apparatus according to the second aspect or the etching end point detecting method according to the eighth aspect, by performing the etching, the concentration of the specific substance (for example, titanium) ionized in the etching solution gradually increases. As a result, the resistivity of the etching solution decreases. The resistivity is detected by the resistivity detecting means, and the end point detecting means obtains a primary time differential value of the resistivity, and detects an etching end point based on the primary time differential value. Therefore, the same effect as the first or seventh aspect can be obtained.

According to the etching apparatus of the third aspect or the method of detecting the end point of the etching of the ninth aspect, by performing the etching, the concentration of the specific substance (for example, titanium) contained in the etching solution is gradually increased. Then, the light absorbency of the etching solution gradually decreases. The light absorbance is detected by the light absorbance detecting means, and the end point detecting means obtains a primary time differential value of the light absorbance, and detects an etching end point based on the primary time differential value. Therefore, claim 1
Or, an effect similar to that of 7 is obtained.

According to the etching apparatus of the present invention, the atomic concentration of the specific substance (for example, titanium) contained in the etching solution is detected by the atomic concentration detecting means. The detecting means detects the end point of the etching based on the second-order differential value of the atomic concentration. Therefore, the end point of the etching can be detected more accurately.

According to the etching apparatus of the present invention, the resistivity of the etching solution is detected by the resistivity detecting means, and the endpoint detecting means detects the secondary time of the resistivity. The differential value is obtained, and the end point of the etching is detected based on the secondary time differential value. Therefore, the same effect as the fourth or tenth aspect can be obtained.

According to the etching apparatus of the present invention, the light absorption degree of the etching solution is detected by the light absorption degree detecting means.
The end point detecting means obtains a second time differential value of the light absorbance, and detects the end point of the etching based on the second time differential value. Therefore, the same effect as the fourth or tenth aspect can be obtained.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. FIG. 2 is a functional block diagram showing a configuration of the etching apparatus. The etching tank 1 is provided inside the overflow tank 2.
The inside of the etching tank 1 is filled with an etching solution 3 composed of ammonia and a hydrogen peroxide solution.

One end of a pipe 4 for discharging the etching solution 3 overflowing from the etching tank 1 is connected to the outer bottom of the overflow tank 2, and the other end of the pipe 4 is connected to an atomic concentration measuring device (atomic Concentration detecting means) 5
It is connected to the. A valve 6 for opening and closing is provided in the middle of the pipe 4. In addition, the atomic concentration measuring device 5 includes:
A pipe 7 (a valve 7a is provided in the middle) is connected so that the etching solution 3 in the etching tank 1 can be directly collected.

The atomic concentration measuring device 5 is, for example, an ICP (Indu
ctively Coupled Plasma) emission spectrometer. In the ICP emission spectrometer, a high frequency current is caused to flow into a stream of an inert gas such as argon by an induction coil to generate plasma, and an etching solution 3 as a sample is sucked and sprayed by a pneumatic nebulizer and introduced into the plasma. To emit light. Then, the atomic concentration of the specific substance contained in the etching solution 3 can be obtained by detecting, with a spectrometer (monochromator), the emission amount of a specific wavelength generated by the specific substance contained in the sample. It is. In this case, the atomic concentration may be either an absolute value or a relative value based on a certain detection time point.

The detection signal of the atomic concentration measuring device 5 is supplied to a control device (end point detecting means) 8 composed of, for example, a personal computer or the like. The control device 8 performs data processing on the given detection signal of the atomic concentration as described later, displays the result graphically on a display, or outputs a control signal to the robot arm 9 based on the result to drive the robot arm 9. It has become.

The atomic concentration measuring device 5 has two discharge pipes 11 and a pipe 10 for circulating the etchant 3.
And 12 are connected. The pipe 11 is a pipe 10
, And the pipe 12 is connected to the pipe 10 via the filter 13. Pipes 11 and 1
2 are provided with valves 11a and 12a, respectively.
You can choose to pass or not. In the middle of the pipe 10, a circulation pump 14 is provided,
The other end of the pipe 10 is introduced into the etching tank 1.

The robot arm 9 is provided for moving a case (not shown) in which a plurality of objects to be etched are set between the inside of the etching tank 1 and the cleaning tank 15. The cleaning tank 15 is provided inside the overflow tank 16 like the etching tank 1 and is filled with a cleaning liquid 17 such as ultrapure water. In the cleaning solution 17,
One end of the circulation pipe 18 is introduced, and the pipe 18
The other end is connected to the atomic concentration measuring device 19 via the valve 18a on the way.

The atomic concentration measuring device 19 is used for detecting the degree of contamination of the cleaning liquid 17 by cleaning the object after etching, and determining the replacement time of the cleaning liquid 17. is there. One end of a discharge pipe 20 is connected to the atomic concentration measuring device 19, and the other end of the pipe 20 is introduced into the cleaning tank 15 via a filter 21 and a circulation pump 22.

A pipe 23 for discharging the overflowing cleaning liquid 17 from the cleaning tank 15, like the overflow tank 2, is provided at the outer bottom of the overflow tank 16.
Is connected, and the other end of the pipe 23 is connected to an atomic concentration measuring device 19. An opening / closing valve 24 is provided in the middle of the pipe 23.

FIG. 3 shows a MOSF to be etched.
It is sectional drawing which shows a part of structure of ET25 typically,
(A) shows the state before etching, and (b) shows the state after etching. A source region 28 and a drain region 2 are formed inside a well 27 diffused in a semiconductor substrate 26.
9 are also formed by diffusion. A gate electrode 31 made of polysilicon is formed on the surface of the well 27 between the source region 28 and the drain region 29 via a gate oxide film 30. Gate electrode 3
Sidewall oxide films (sidewalls) 32 are formed on both sides of 1.

The source region 28 and the drain region 29 and the gate electrode 31 of the MOSFET 25 having the above-mentioned basic configuration.
After removing the oxide film on the surface, a titanium film 34 is formed on the entire surface by a sputtering method or the like, and is subjected to a short-time heat treatment at 625 ° C. for 60 seconds in an argon gas atmosphere, for example.

Then, a titanium silicide film 33 is formed only on the source region 28, the drain region 29 and the surface of the gate electrode 31. FIG. 3A shows this state. Only the unreacted titanium film 34 existing as a film on the surface of the MOSFET 25 is selectively removed by etching, and the MOSF shown in FIG.
The state of the ET 25a is set. That is, the titanium constituting the titanium film 34 corresponds to the specific substance.

Next, the operation of the first embodiment will be described with reference to FIGS.
This will be described with reference to FIGS. FIG. 1 is a flowchart showing the control contents of the control device 8. Control device 8
When a keyboard (not shown) is operated and a command for starting etching is input, first, the processing shifts to a processing step S1 of "etching start", and the control device 8 drives the robot arm 9 to form a large number of MOSFETs 25. The case accommodating the processed wafer is immersed in the etching solution 3 in the etching bath 1 to start the etching process. Then, the processing shifts to the processing step S2 of “read atomic concentration”.

The etching solution 3 is supplied in an amount equal to or larger than the volume of the etching bath 1. When the circulating pump 14 is driven, the etching solution 3 overflowing the etching bath 1 is removed from the overflow bath 2 → pipe. 4
It circulates through the path of → atomic concentration measuring device 5 → pipe 11 → pipe 10 (circulation pump 14) → etching tank 1 →.

When the etching process is started, MOSF
The portion of the titanium film 34 formed on the surface of the ET 25 exposed to the etchant 3 is selectively etched,
Titanium atoms elute into the etching solution 3. In the processing step S2, the control device 8 A / D converts and reads the titanium atom concentration in the etching solution 3 detected by the atomic concentration measuring device 5 at an appropriate time interval. It moves to the processing step S3 of "calculation". In processing step S3, the control device 8 calculates a first-order time differential value of the titanium atom concentration read in step S2. Then, the process proceeds to the determination step S4 of “density saturation?”.

Here, FIG. 4 shows an example of a change in the concentration of titanium atoms in the etching solution 3 on the vertical axis, with the lapse of time from the start of the etching process as the horizontal axis. In the initial stage of the etching process, the concentration of titanium atoms increases substantially in proportion to time, but when the etching process proceeds to a certain extent, almost all portions to be selectively etched are etched, so that the increase in the concentration gradually becomes saturated. As shown.

FIG. 5 shows the value obtained as the first-order time differential value when the titanium atom concentration changes as shown in FIG. 4 on the vertical axis. That is, immediately after the start of the etching process, the first-order time derivative of the titanium atom concentration shows a positive value, and does not change while maintaining a substantially flat level as the titanium atom concentration increases in proportion to the time. When the increase in the titanium atom concentration shows a tendency to saturate, the first-order time differential value gradually decreases. When the titanium film 34 is substantially etched and the titanium atom concentration approaches a substantially saturated state, the first-order time difference is reduced. The derivative approaches zero.

In the judgment step S4, the control device 8
Determines whether or not the titanium atom concentration is saturated, that is, whether or not the end point of the etching has been reached, based on whether or not the first-order time differential value of the titanium atom concentration has approached zero to some extent according to the above principle. "NO" because the concentration is not saturated
If the determination is made, the process proceeds to steps S2 and S3, and the reading of the titanium atom concentration and the calculation of the primary time differential value are repeated.

Then, the titanium film 34 exposed to the etching solution 3 is etched to approach a state in which the titanium atom concentration is substantially saturated.
Determines that the first-order time derivative has become substantially zero (FIG. 4).
(At the time point indicated by the arrow in FIG. 5) and the processing step S5 of “end of etching”.

Here, comparing the slopes of both curves near the time point indicated by the arrows in FIGS. 4 and 5, the slope of the curve indicating the first-order time differential value is larger due to the characteristics of the etching process. . That is, in the vicinity where the titanium atom concentration becomes substantially saturated, the first-order time differential value changes more greatly than the titanium atom concentration. Therefore, for example, if a threshold value is set near “0” with respect to the first-order time differential value and the end point of the etching is detected, an appropriate time point as the end point can be more reliably detected.

In processing step S5, the control device 8
Gives a control signal to the robot arm 9 and
The etching process is terminated by pulling the case in which 25 is set from the etching tank 1. Thereafter, the process proceeds to the processing step S6 of the “cleaning process”, in which the case pulled up from the etching bath 1 by the robot arm 9 is immersed in the cleaning liquid 17 in the cleaning bath 15 and the filter 2 is removed.
Cleaning is performed for a predetermined time by the cleaning liquid 17 circulated while removing impurities through the cleaning liquid 17.

When the cleaning step is completed, the case is pulled up from the cleaning liquid 17 and the processing is completed. at this point,
The MO in the state shown in FIG.
The SFET 25 becomes the MOSFET 25a from which the unnecessary titanium film 34 has been removed as shown in FIG.

As described above, according to this embodiment, the concentration of titanium atoms contained in the etching solution 3 in the etching bath 1 is detected by the atomic concentration detector 5 from the start of the etching process, and the control device 8 The end point of the etching is detected based on the primary time derivative of the atomic concentration, and when the end point is detected, the case is pulled up from the etching solution 3 in the etching bath 1 to terminate the etching process and shift to the cleaning process. did.

Therefore, it is possible to directly detect the concentration of titanium atoms and to detect the appropriate time as the end point of etching more reliably than before by using the first-order time differential value. In addition, the material (specific substance) constituting the film is not particularly limited, and any material that can be subjected to ordinary wet etching can be used.

In addition, as in the present embodiment, the object to be etched is the MOSFET 25 in which the gate electrode 31 and the like are formed in an extremely fine pattern, and the timing for determining the end point of the etching is severe. Is particularly effective.

FIGS. 6 and 7 show a second embodiment of the present invention. Only parts different from the first embodiment will be described. The configuration of the second embodiment is the same as that of the first embodiment, and the processing in the control device 8 is different. In the flowchart of the control device 8 shown in FIG. 5, step S3 of the first embodiment is the same as the processing step S2 of "secondary time differential value calculation".
3a.

In the processing step S3a, the control device 8 calculates and obtains a second time differential value of the titanium atom concentration. Then, in the next step of determining "concentration saturation?", It is determined whether or not the titanium atom concentration is saturated based on the secondary time differential value.

FIG. 7 shows the value obtained as the secondary time derivative when the titanium atom concentration changes as shown in FIG. 4 on the vertical axis. That is, for a while after the start of the etching process, as shown in FIG. 5, the first-order time differential value of the titanium atom concentration maintains a flat positive value, and during that time, the second-order time differential value becomes zero. . Then, when the concentration of titanium atoms shows a tendency to saturate and the first-order time differential value starts to decrease, the second-order time differential value decreases and shows a negative value. The flat minimum value (negative value) is maintained while the primary time differential value decreases linearly.

When the rate of decrease of the first-order time differential value decreases, the second-order time differential value increases. When the titanium film 34 is etched and the titanium atom concentration approaches a substantially saturated state, the second-order time differential value increases. The derivative approaches zero.

In the judgment step S4a, the control device 8
According to the above principle, it is determined whether or not the titanium atom concentration is saturated depending on whether the second-order time differential value of the titanium atom concentration has reached a minimum value after showing the minimum value, that is, whether or not the etching end point has been reached. Judge. If the density is not saturated and the determination is “NO”, steps S2 and S
3a, the reading of the titanium atom concentration and the calculation of the secondary time differential value are repeated.

Then, the titanium film 34 is etched, and the titanium atom concentration approaches a substantially saturated state.
In 4a, when the control device 8 determines that the second-order differential value of the titanium atom concentration has become substantially zero (at the time indicated by the arrows in FIGS. 4 and 7), the process shifts to the processing step S5 of "end of etching". Subsequent processing is the same as in the first embodiment.

Here, when comparing the slopes of the two curves near the time point indicated by the arrows in FIGS. 5 and 7, the slope of the curve indicating the secondary time differential value is larger than the slope of the curve indicating the primary time differential value. Since it is large, if the end point of the etching is detected based on the secondary time differential value in which the change in the value near “0” becomes larger, the appropriate time as the end point can be more reliably detected.

As described above, according to the second embodiment, the concentration of titanium atoms contained in the etching solution 3 in the etching bath 1 is detected by the atomic concentration detector 5, and the control device 8 determines the concentration of the titanium atoms. The end point of the etching is detected based on the next time differential value. Therefore, an appropriate time point as the end point of the etching can be detected more reliably.

FIGS. 8 to 11 show a third embodiment of the present invention. The same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. Hereinafter, only different parts will be described. FIG. 8 is a functional block diagram showing the electrical configuration of the etching apparatus. The atomic concentration measuring device 5 is removed from the configuration of the first embodiment shown in FIG. 2, and a resistivity measuring device (resistivity detecting means) is used instead. 35 are provided.

The resistivity measuring device 35 obtains a resistance value by, for example, arranging two electrodes having a predetermined interval in the etching solution 3 and measuring a current value flowing when a predetermined voltage is applied between the electrodes. In this configuration, the resistivity of the etching solution 3 is determined by considering the distance between the electrodes and the electrode area. In this case, the resistivity may be either an absolute value or a relative value based on a certain detection time point. Other configurations are the same as in the first embodiment. The object to be etched is the same MOSFET 25 as in the first embodiment.

Next, the operation of the third embodiment will be described with reference to FIGS. FIG. 9 is a flowchart showing the control contents of the control device 8. Instead of step S2 in the flowchart of the first embodiment shown in FIG. 1, a processing step S7 of “reading resistivity” is arranged. Further, instead of steps S3 and S4, a processing step S8 of “primary time differential value calculation” and a determination step S9 of “resistivity saturation?” Are arranged. Others are the same as the first embodiment.

The etching process is started, and step S1 is performed.
When the case in which the MOSFET 25 is set is immersed in the etching solution 3, the control device 8 determines the resistivity of the etching solution 3 output from the resistivity measuring device 35 in the processing step S7 at an appropriate time interval. When the data is read after the D conversion, the process proceeds to step S8. In the processing step S8, the control device 8 calculates a primary time differential value of the etching liquid 3 read in the step S7.
Then, control proceeds to a decision step S9.

Here, FIG. 10 shows an example of a change in the resistivity of the etching solution 3 on the vertical axis, with the lapse of time from the start of the etching process on the horizontal axis. As time elapses, the concentration of titanium atoms in the etching solution 3 increases and metal ions increase, so that the electrical conductivity of the etching solution 3 increases, and the reciprocal, resistivity, gradually decreases.

FIG. 11 shows the value obtained as the first-order time differential value when the resistivity changes as shown in FIG. 10 on the vertical axis. That is, since the resistivity decreases almost linearly immediately after the start of the etching process,
The first-order time differential value is a substantially flat negative value. Then, as the increase in the concentration of titanium atoms shows a tendency to saturate, the rate of decrease in the resistivity of the etching solution 3 also decreases, and the first-order time differential value gradually increases and approaches zero.

In the judgment step S9, the control device 8
Determines whether or not the resistivity is saturated, that is, whether or not the end of the etching has been reached, based on whether or not the first-order time differential value of the resistivity of the etching solution 3 approaches zero to some extent according to the above principle. . "NO" because the concentration is not saturated
If it is determined, the process proceeds to steps S7 and S8, and the reading of the resistivity and the calculation of the primary time differential value are repeated.

Then, the titanium film 34 is etched, and the concentration of titanium atoms approaches a substantially saturated state, and accordingly, the resistivity of the etching solution 3 approaches zero. When it is determined that the next-time differential value has become substantially zero (at the time indicated by the arrows in FIGS. 10 and 11), the processing step S of "end of etching"
Move to 5. Subsequent processing is the same as in the first embodiment.

As described above, according to the third embodiment, from the start of the etching process, the etching solution 3
Is detected by the resistivity measuring device 35, and the control device 8
Detects the end point of etching based on the primary time derivative of the resistivity. Therefore, the same effect as that of the first embodiment can be obtained.

FIGS. 12 and 13 show a fourth embodiment of the present invention. Only parts different from the third embodiment will be described. The configuration of the fourth embodiment is the same as that of the third embodiment, and the processing in the control device 8 is different. In the flowchart of the control device 8 shown in FIG. 12, step S8 of the third embodiment is replaced by processing step S8a of “secondary time differential value calculation”.

In the processing step S8a, the control device 8 calculates and obtains a secondary time differential value of the resistivity of the etching solution 3. Then, in the next step "S9a" for determining "resistivity saturated?", It is determined whether or not the resistivity of the etching solution 3 is saturated based on the secondary time differential value.

FIG. 13 shows that the resistivity of the etching solution 3 is shown in FIG.
When the value changes as shown by 0, the value obtained as the secondary time differential value is shown on the vertical axis. That is,
For a while after the start of the etching process, the secondary time derivative of the resistivity of the etching solution 3 maintains a flat negative value in the primary time derivative shown in FIG. The value will be zero. When the decrease in the resistivity of the etching solution 3 gradually shows a tendency to saturate and the primary time differential value starts to increase, the secondary time differential value also increases, and the primary time differential value increases linearly. While
The secondary time derivative maintains a flat maximum.

When the gradient of the rise of the first-order time differential value decreases, the second-order time differential value decreases, and the titanium film 34 is etched, so that the decrease in the resistivity of the etching solution 3 is substantially saturated. As it approaches, its second-order time derivative approaches zero.

Here, comparing the slopes of the two curves near the time point indicated by the arrows in FIGS. 11 and 13, the slope of the curve indicating the secondary time derivative is smaller than the slope of the curve indicating the primary time derivative. Since it is large, if the end point of the etching is detected based on the secondary time differential value, the appropriate time as the end point can be more reliably detected.

As described above, according to the fourth embodiment, the resistivity of the etching solution 3 in the etching bath 1 is measured by the resistivity detector 3.
5, the control device 8 detects the end point of the etching based on the secondary time derivative of the resistivity. Therefore, an appropriate time as the end point of the etching can be more reliably detected, and the same effect as that of the second embodiment can be obtained.

FIGS. 14 to 17 show a fifth embodiment of the present invention. The same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. Only different parts will be described below. FIG. 14 is a functional block diagram showing an electrical configuration of the etching apparatus. The atomic concentration measuring device 5 is removed from the configuration of the first embodiment shown in FIG. 2, and a light absorption measuring device (light absorption detecting device) is used instead. Means 36 are provided.

The light absorption measuring device 36 is, for example, a measuring device using an absorptiometric method, and the light projected by a light projecting element (such as a discharge tube using deuterium or hydrogen) is applied to the etching solution 3. In this configuration, the light is transmitted and received by a light receiving element (a vacuum photoelectric tube, a photomultiplier tube, a photodiode, or the like) to detect light absorbance (absorbance). In this case, the light absorption may be either an absolute value or a relative value based on a certain detection time point. Other configurations are the same as those of the first embodiment, and the object to be etched is the same MOSF as that of the first embodiment.
ET25.

Next, the operation of the fifth embodiment will be described with reference to FIGS. FIG. 15 shows the control device 8
5 is a flowchart showing the control contents of FIG. Instead of step S2 in the flowchart of the first embodiment shown in FIG.
A processing step S10 of “reading of light absorption” is arranged. Further, instead of steps S3 and S4, a processing step S11 of “calculation of a first-order time differential value” and a determination step S12 of “light absorption degree saturated?” Are arranged. Others are the same as the first embodiment.

The etching process is started, and step S1
When the case in which the MOSFET 25 is set is immersed in the etching solution 3, the control device 8 sets the light absorption of the etching solution 3 output from the light absorption measuring device 36 in the processing step S7 at appropriate time intervals. A / D
After the conversion and reading, the process proceeds to processing step S11. In processing step S11, control device 8 executes step S1.
A first-order time differential value of the light absorbance read at 0 is calculated. Then, control goes to a decision step S12.

Here, FIG. 16 shows an example of a change in the light absorbency of the etching solution 3 on the vertical axis, with the lapse of time from the start of the etching process on the horizontal axis.
As the concentration of titanium atoms in the etching liquid 3 increases with the passage of time, light emitted from the light projecting element is absorbed by the etching liquid 3, and the light absorption is substantially equal to the concentration of titanium atoms. It rises in proportion.

FIG. 17 shows the value obtained as the first-order time differential value when the light absorbance changes as shown in FIG. 16 on the vertical axis. In this case, the curve of the light absorbance draws a rise curve substantially similar to the titanium atom concentration in the first embodiment (as an example), and the curve of the primary time differential value is also substantially the same as that of FIG. Become. That is, since the light absorbance increases substantially linearly immediately after the start of the etching process, the first-order time differential value becomes a substantially flat value. Then, as the increase in the concentration of titanium atoms shows a tendency to saturate, the increase in the light absorbance of the etching solution 3 also becomes saturated, and accordingly, the first-order time differential value gradually decreases and approaches zero.

In the judgment step S12, the control device 8
Is to determine whether the light absorbance is saturated according to whether the first-order time derivative of the light absorbance of the etching solution 3 approaches zero to some extent, in other words, whether the end time of the etching has been reached. to decide. If the concentration is not saturated and "N
If it is determined to be "O", the process proceeds to steps S10 and S11, and the reading of the light absorption and the calculation of the primary time differential value are repeated.

Then, the titanium film 34 is etched and the titanium atom concentration approaches the state of being substantially saturated, and accordingly, the optical absorption of the etching solution 3 approaches zero. When it is determined that the first-order time differential value of the degree has become substantially zero (at the time indicated by the arrows in FIGS. 16 and 17), the process proceeds to the processing step S5 of “etching completed”. Subsequent processing is the same as in the first embodiment.

As described above, according to the fifth embodiment, from the start of the etching process, the etching solution 3
Is detected by the light absorbance measuring device 36, and the control device 8 detects the end point of the etching based on the primary time derivative of the light absorbance. Therefore, the same effect as that of the first embodiment can be obtained.

FIGS. 18 and 19 show a sixth embodiment of the present invention. Only parts different from the fifth embodiment will be described. The configuration of the sixth embodiment is the same as that of the fifth embodiment, and the processing in the control device 8 is different. In the flowchart of the control device 8 shown in FIG. 18, step S11 of the fifth embodiment is replaced by processing step S11a of “secondary time differential value calculation”.

In the processing step S11a, the control device 8 calculates and obtains a second time differential value of the light absorbance of the etching solution 3. Then, in the next step of determining “light absorption degree saturated?”, Whether or not the light absorption degree of the etching liquid 3 is saturated is determined based on the secondary time differential value.

FIG. 19 shows the value obtained as the secondary time derivative when the light absorbance changes as shown in FIG. 16 on the vertical axis. That is, the mode of the change is the same as that of the second-order derivative of the titanium atom concentration in the second embodiment, and for a while after the start of the etching process, as shown in FIG. Since the differential value maintains a flat positive value, the second-order time differential value becomes zero during that time. Then, when the light absorbance shows a tendency to saturate and its first-order time derivative starts to decrease, the second-order time derivative decreases and shows a negative value.
With the change of the next time differential value, the flat minimum value (negative value) is maintained, and then it starts to increase. When the titanium film 34 approaches the state where the light absorbance is almost saturated by etching, the second
The next-time derivative approaches zero.

In the judgment step S12a, the control device 8 determines whether the light absorbance is saturated, that is, determines whether the light absorbance is saturated, based on whether the second-order time differential value of the light absorbance reaches a minimum value after showing the minimum value. It is determined whether or not the end point has been reached. If it is determined that the density is not saturated and the determination is "NO", the process proceeds to steps S10 and S11a, and the reading of the light absorbance and the calculation of the secondary time differential value are repeated.

Then, the titanium film 34 is etched, and the light absorbance approaches a substantially saturated state.
If it is determined in 2a that the secondary time differential value has become substantially zero (at the time indicated by the arrows in FIGS. 16 and 19), the processing shifts to the processing step S5 of "etching end". Subsequent processing is the same as in the first embodiment.

As described above, according to the sixth embodiment, the light absorbance of the etching solution 3 in the etching tank 1 is detected by the light absorbance measuring device 36, and the control device 8 detects
The end point of the etching is detected based on the next time differential value. Therefore, the same effects as in the second embodiment can be obtained.

The present invention is not limited to the embodiment described above and shown in the drawings, and the following modifications or extensions are possible. The atomic concentration detecting means in the first and second embodiments may use ICP mass spectrometry or atomic absorption spectrometry. In the third and fourth embodiments, the end point of the etching may be detected by detecting the electric conductivity which is the reciprocal of the resistivity and is equivalent to the substantial resistivity. The object to be etched is not limited to the MOSFET 25, and may be any object that is usually subjected to wet etching. Further, the specific material constituting the coating is not limited to titanium. Various detections may be performed on the etching liquid 3 directly collected from the etching tank 1.

[Brief description of the drawings]

FIG. 1 is a flowchart showing control contents of a control device according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of an etching apparatus.

FIGS. 3A and 3B are diagrams schematically showing a cross section of a MOSFET as an etching target, wherein FIG. 3A shows a state before etching, and FIG.
Indicates the state after etching.

FIG. 4 is a diagram illustrating an example of a change in titanium atom concentration with time from the start of an etching process.

FIG. 5 is a diagram showing a first-order time differential value of a change in titanium atom concentration with time from the start of an etching process.

FIG. 6 is a view corresponding to FIG. 1, showing a second embodiment of the present invention.

FIG. 7 is a diagram showing a second-order time differential value of a change in the concentration of titanium atoms over time from the start of the etching process.

FIG. 8 is a view corresponding to FIG. 2 showing a third embodiment of the present invention.

FIG. 9 is a diagram corresponding to FIG. 1;

FIG. 10 is a diagram showing an example of a change in resistivity of an etching solution with time from the start of an etching process.

FIG. 11 is a diagram showing a first-order time differential value of a change in resistivity of an etching solution with time from the start of an etching process.

FIG. 12 is a view corresponding to FIG. 1, showing a fourth embodiment of the present invention;

FIG. 13 is a view showing a second-order differential value of a change in resistivity of an etching solution with the passage of time from the start of an etching process.

FIG. 14 is a view corresponding to FIG. 2, showing a fifth embodiment of the present invention;

FIG. 15 is a diagram corresponding to FIG. 1;

FIG. 16 is a diagram showing an example of a change in light absorbance of an etching solution with the passage of time from the start of an etching process.

FIG. 17 is a diagram showing a first-order time differential value of a change in light absorbance of an etching solution with time from the start of an etching process.

FIG. 18 is a view corresponding to FIG. 1, showing a sixth embodiment of the present invention.

FIG. 19 is a diagram showing a second-order time differential value of a change in optical absorbance of an etching solution with time from the start of an etching process.

[Explanation of symbols]

1 is an etching tank, 3 is an etching solution, 5 is an atomic concentration measuring device (atomic concentration detecting means), 8 is a control device (end point detecting means), 25 is a MOSFET (object), 34 is a titanium film (coating), 35 Is a resistivity measuring instrument (resistivity detecting means), 3
Reference numeral 6 denotes a light absorption measurement device (light absorption detection means).

Claims (12)

[Claims] An object having a film formed on its surface is immersed in an etching solution in an etching bath to selectively etch a specific substance constituting the film. An atomic concentration detecting means for detecting an atomic concentration of the specific substance contained in the above, and obtaining a first time differential value of the atomic concentration detected by the atomic concentration detecting means, and performing the etching based on the first time differential value. And an end point detecting means for detecting an end point of the etching apparatus. 2. A method for selectively etching a specific substance constituting a film by immersing an object having a film formed on a surface thereof in an etching solution in an etching bath, A resistivity detecting means for detecting a resistivity; an end point detecting means for obtaining a first time differential value of the resistivity detected by the resistivity detecting means, and detecting an end point of the etching based on the first time differential value. And an etching device. 3. A method of selectively etching a specific substance constituting a film by immersing an object having a film formed on a surface thereof in an etching solution in an etching bath, A light absorbance detecting means for detecting light absorbency, a first time differential value of the light absorbance detected by the light absorbance detect means is obtained, and an end point of the etching is determined based on the first time differential value. An etching apparatus comprising: an end point detecting means for detecting. 4. A method of selectively etching a specific substance constituting a film by immersing an object having a film formed on a surface thereof in an etching solution in an etching bath, wherein An atomic concentration detecting means for detecting an atomic concentration of the specific substance contained in the target; and obtaining a second time differential value of the atomic concentration detected by the atomic concentration detecting means, and performing the etching based on the second time differential value. And an end point detecting means for detecting an end point of the etching apparatus. 5. A method for selectively etching a specific substance constituting a film by immersing an object having a film formed on a surface thereof in an etching solution in an etching bath, A resistivity detecting means for detecting a resistivity; an end point detecting means for obtaining a secondary time differential value of the resistivity detected by the resistivity detecting means and detecting an etching end point based on the secondary time differential value. And an etching device. 6. A method of selectively etching a specific substance constituting a film by immersing an object having a film formed on a surface thereof in an etching solution in an etching bath, wherein A light absorbance detecting means for detecting the light absorbency; obtaining a second time differential value of the light absorbance detected by the light absorbance detect means, and determining an end point of the etching based on the second time differential value. An etching apparatus comprising: an end point detecting means for detecting. 7. A method for selectively etching a specific substance constituting a film by immersing an object having a film formed on a surface thereof in an etching solution in an etching bath, comprising: The atomic concentration of the specific substance contained in the etching solution is detected by an atomic concentration detecting means, and a primary time differential value of the atomic concentration is obtained by an end point detecting means, and the etching is performed based on the primary time differential value. Detecting an end point of the etching. 8. A method for selectively etching a specific substance constituting a film by immersing an object having a film formed on a surface thereof in an etching solution in an etching tank, wherein the method comprises the steps of: Detecting the resistivity of the etchant by resistivity detection means, obtaining a primary time differential value of the resistivity by end point detection means, and detecting an end point of the etching based on the primary time differential value. Characteristic etching end point detection method. 9. A method for selectively etching a specific substance constituting a film by immersing an object having a film formed on a surface thereof in an etching solution in an etching tank, comprising: The light absorbance of the etching solution is detected by a light absorbance detecting means, and a first time differential value of the light absorbance is obtained by an end point detecting means, and an end point of the etching is detected based on the first time differential value. A method for detecting an end point of etching. 10. An object having a film formed on its surface is immersed in an etching solution in an etching bath,
In the method of selectively etching a specific substance constituting the coating, the atomic concentration of the specific substance contained in the etching solution is detected by an atomic concentration detecting means from the start of the etching, and the atomic concentration is detected by an end point detecting means. A method for detecting an end point of etching, wherein a second time derivative of the concentration is obtained, and the end point of the etching is detected based on the second time derivative. 11. An object having a film formed on its surface is immersed in an etching solution in an etching tank,
In the method for selectively etching a specific substance constituting the coating, the resistivity of the etchant is detected by a resistivity detecting means from the start of etching, and a secondary time differential value of the resistivity is detected by an end point detecting means. And detecting the end point of the etching based on the secondary time differential value. 12. An object having a film formed on its surface is immersed in an etching solution in an etching tank,
In the method for selectively etching a specific substance constituting the coating, light absorption of the etchant is detected by light absorption detection means from the start of etching, and secondary light absorption is detected by end point detection means. A method for detecting an end point of etching, wherein a time differential value is obtained and an end point of the etching is detected based on the secondary time differential value.