JPS6240702B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting the processing state during surface processing of a substrate by etching or the like in a photomask manufacturing process and accurately detecting the end point of the processing.

Photomasks used in the manufacture of semiconductors are usually made by applying a photoresist to a substrate such as glass that is vapor-deposited on the surface of a metal, and forming a photoresist film on this substrate. It is manufactured through a process of patterning the photoresist film by baking and then developing it with a prescribed developer, and a process of etching the metal thin film exposed by the development process. Among the above processes, especially the etching process Because highly accurate processing is required, it is necessary to accurately control the end point of the processing.

Therefore, various methods have been proposed for detecting the end point of this etching process with high accuracy.

For example, JP-A-56-158872 discloses that a light transmittance measurement area is provided outside the effective area on the photomask surface to detect the degree of progress of etching, and the light transmittance in this area is measured. The end point of the etching process is detected based on the
For each measurement, the difference between the two sample values before and after the amount of transmitted light is taken, the difference is averaged at about 10 consecutive points, and the end point of the etching process is determined by detecting when the average value approaches zero. ing.

By the way, as seen in the enlarged partial cross-sectional view of FIG. 1, the photomask 1 before etching treatment includes a glass substrate 1', an extremely thin metal oxide film 2, a vapor-deposited metal film 3, and the same metal oxide film as described above. 2', consists of a resist film part 4 from which unnecessary parts have been removed by development processing, and the amount of transmitted light of the photomask measured during etching processing depends on the type of metal deposited and the metal that is poorly soluble in the etching solution. Since it is influenced by the presence or absence of an oxide film, the material and thickness of the glass, etc., it changes variously as shown in the diagrams A to D in FIG. 2, depending on the elapsed time t of the etching process. Therefore, in the method disclosed in JP-A No. 56-158872, when the progress of etching temporarily stagnates as shown in diagram C, the end point of the etching process is reached at the time when the stagnation is reached. Therefore, there was a problem that the exact end point of the etching process could not be detected.

On the other hand, photomask 1 to be etched
Generally, the photomask is held by suction by a vacuum chuck in the spinner head, but with this method, the photomask may become distorted and lose its flatness, or the etching solution may get onto the back side of the photomask during low-speed rotation. Such inconveniences arise because there is a risk that the etching solution that has been mixed onto the back side of the photomask may get into the vacuum chuck of the spinner head. The method shown in FIGS. 3 and 4, that is, the glass substrate 1'
A fixed holding arm type spinner head is used that holds the spinner head fixedly at the four corners. This simple spinner head has, for example, four arms 5 arranged radially at equal angular intervals from the head part of the rotating shaft S, and a pair of positioning pins 7 are attached to a fixed part 6 at the tip of each arm 5. , 7 and support pin 8
are provided so that each corner of the substrate 1' is placed on each support pin 8, and is clamped and fixedly held by the positioning pins 7, 7, so that the substrate 1' can be rotated in a horizontal plane. It is composed of

Therefore, when performing an etching process while holding the photomask 1 in this simple spinner head, for example, as shown in FIGS. 3 and 4,
The light beams from the light emitting optical fibers 12 fixed to the tips of the U-shaped mounting arms 9 are transmitted to the light receiving optical fibers 1 through the photomask 1.
Since the arm 5 receives light and detects the amount of transmitted light, the arm 5 blocks the light beam for detecting the amount of transmitted light every 1/4 rotation. Therefore, the averaging process described above has the disadvantage that it becomes more difficult to accurately detect the end point of the etching process.

This invention was made to solve the above-mentioned disadvantages of the conventional method, and when a simple spinner head is used and during the progress of the etching process, there is a temporary stagnation as previously explained in FIG. In other words, even when the rate of change in transmittance temporarily becomes zero, and even when processing photomasks with any transmission characteristics,
It is an object of the present invention to provide a method that can accurately detect the end point of surface treatment such as etching treatment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 5 shows a schematic configuration of an example of an apparatus for implementing the method according to the present invention, in which an object to be processed, that is, a photomask 1, is placed at its four corners on support pins 8, as shown in FIG. , each corner is fixed by a pair of positioning pins 7, 7 so that it can be rotated in a horizontal plane. The light amount detection section is
An optical fiber 11 for receiving transmitted light provided close to the top of the photomask 1, an optical fiber 12 for projecting irradiated light provided close to the bottom of the photomask 1, an optical fiber 13 for receiving reflected light, and an optical fiber 11 , 13 and a holder (not shown) for holding the light emitting end of the optical fiber 12, and further the light receiving optical fiber 1.
1 and 13, respectively, and a light emitting element 16, such as a light emitting diode, to which the other end of the light projecting optical fiber 12 is connected. .

The optical fiber 11 for receiving transmitted light and the optical fiber 12 for projecting irradiated light have their respective ends forming the same angle θ to the right and left sides of the drawing with respect to the normal to the surface of the substrate 1', and are substantially coaxial. It is located in
The end of the light-receiving optical fiber 11 is held in the holder so as to be out of the direction of injection of the processing liquid and the position of injection collision of the processing liquid onto the substrate 1'. The optical fiber 13 for receiving reflected light is held in the holder so that its end portion is symmetrical to the end portion of the optical fiber 12 for projecting light with respect to the normal line.

The photoelectric conversion elements 14 and 15, which respectively convert the light received through the light-receiving optical fibers 11 and 13 into electrical signals proportional to the amount of light, increase their output voltage in proportion to the amount of received light. is configured to do so. The output voltage from the photoelectric conversion element 14 for transmitted light is amplified by an amplifier 17, and this amplified detection signal _V1 is sent to a central processing unit (hereinafter abbreviated as CPU) 22 via an A/D converter 18. It is also input to one terminal of the comparator 19. The other terminal of the comparator 19 is connected to the CPU 22 via the D/A converter 20.
The output from the comparator is inputted as a threshold value V _2i (i=1, 2, 3...) via the D/A converter 20, and when the detection signal V ₁ exceeds this threshold value V _2i 19 outputs a discrimination signal E _p . This discrimination signal E _p is transmitted to the latch circuit 21
is held for a predetermined time, the CPU sends it as an END signal.
22, and when this END signal is input a predetermined number of times, the CPU 22 sets a new threshold value V _2i in the comparator 19, and by repeating the comparison operation, finally the detection signal V 2i is input within a predetermined time. ₁ no longer exceeds the threshold.

The irradiation light from this light projection optical fiber 12 is
As described above, since the arm 5 interrupts the rotation of the spinner head every 1/4 rotation, that is, every fixed period of time, the detection signal V ₁ corresponding to the amount of transmitted light has a relatively large rectangular shape as shown in FIG. Fluctuations in a pulse-like manner. As the etching process for the photomask 1 progresses over time t, the amount of transmitted light gradually increases, and correspondingly, the clock pulse-shaped detection signal _V1 changes its signal level as shown in FIG. In addition, in Figure 6, V ₀
is the detection signal value when the irradiation light from the light projecting optical fiber 12 is blocked by the arm 5, and V′ ₁ is the detection signal value corresponding to the specific amount of transmitted light of the photomask 1 before etching processing. be. Furthermore, although the pulse interval of this clock pulse-like detection signal V ₁ is not constant, as is clear from FIG.
This is because it is output at intervals corresponding to the removed portion.

Figure 8 shows this clock pulse-like detection signal.
This figure shows in more detail the change in the signal level of V ₁ as time t passes from the start of the etching process, and the rectangular pulse-like signal shown in FIG. , are shown with their pulse intervals constant. Here, the END signal output from the latch circuit 21 is
Every time three values are input to 2, the CPU 22 adds the deviation value E to the previous threshold value to calculate a new threshold value, and repeatedly sets this threshold value to the comparator 19 to perform the etching process. In the case of detecting the end point, it can be seen that the detection signal V ₁ no longer exceeds the threshold set for the 10th time even after the predetermined time T _E has elapsed.

On the other hand, similarly to the output voltage of the photoelectric conversion element 14 for reflected light, the amplifier 23 and the A/D converter 2
4. A comparator 25, a D/A converter 26, and a latch circuit 27 are provided, and the detection signal ν ₁ in this case is processed almost in the same way as the detection signal V ₁ . .

Similar to FIG. 8, FIG. 9 omits the rectangular pulse-like signals in FIG. 6, and makes the pulse intervals constant, and shows changes in the signal level of the clock pulse-like detection signal _ν1 with respect to the amount of reflected light. This detection signal ν ₁ corresponds to the amount of reflected light specific to the metal oxide film 2, for example, until the metal oxide film 2 on the lower surface of the metal thin film 3 in FIG. 7 starts to be removed by etching. The signal value ν' is approximately equal to ₁ , rapidly decreases when the metal oxide film 2 is removed, and finally reaches an almost constant detection signal value corresponding to the amount of reflected light on the upper surface of the substrate 1'. It can be seen that the etching process has been completed.

Next, using the microcomputer system 30 surrounded by a dashed line in FIG.
This will be explained based on the flowcharts shown in FIGS. 0 and 11.

First of all, the deviation values E and e (these are values that serve as a guideline for detecting the degree of progress of the surface treatment state) are determined in advance through experiments.
Each corresponds to the amount of transmitted light and the amount of reflected light. ) and the detection time T _E are set in the internal memory of the CPU 22 using an input device (not shown). Next, the unique transmitted light amount and unique reflected light amount of the photomask 1 before processing are measured, and each corresponding detected value is set. V ₁ and ν' ₁ are set in the internal memory of the CPU 22. <Step> In this case, the unique amount of transmitted light and the unique amount of reflected light are calculated using the light emitting optical fiber 12 shown in FIG.
The amount of transmitted light I _T and the amount of reflected light I _R with respect to the amount of irradiated light I from the metal thin film 3, and I _L in the figure represents the amount of absorbed and diffusely reflected light in the metal thin film 3. And P indicates a detection location.

Next, the CPU 22 reads the deviation values E, e set in its internal memory and the detected signal values V' ₁ ,
ν′ ₁ and the threshold value V ₂₁ =V′ ₁ +E, ν ₂₁ =ν′ ₁
-e are respectively calculated, and the threshold value V ₂₁ is input to the comparator 19 via the D/A converter 20, and the threshold value ν ₂₁ is input to the comparator 25 via the D/A converter 26. <Step> Next, although not shown, an etching liquid is injected onto the photomask 1 from an injection nozzle, and at the same time, the photomask 1 is rotated at a constant speed together with the spinner head to start the etching process.
<Step> Next, the CPU 22 sets, for example, "3" as an initial value for counting the END signal that is latched by the latch circuits 21 and 27 and output after a predetermined time has elapsed.
is set in the built-in register based on the control program. <Step> After that, when the output value V ₁ corresponding to the amount of transmitted light exceeds the threshold value V ₂₁ =V' ₁ +E, the END signal is output from the latch circuit 21 in response to the determination signal from the comparator 19. Check repeatedly for the presence of . <Step> When one END signal is input, in the next step, "1" is subtracted from the initial value "3" set in the register in the CPU 22, and then the latch circuit 21 receives the input from the CPU 22. The END signal is reset by the command. <Step> Next, check whether the contents of the register to which the initial value "3" was set has become "0". <Step> If not, return to step again and check for the presence or absence of the END signal. Check.

In this way, the detection signal corresponding to the amount of transmitted light is
When V ₁ exceeds the set threshold value V ₂₁ =V' ₁ +E three times, the result is YES in step 11, and the process moves to step (FIG. 11), where the CPU 22 sets the new threshold value V ₂₂ =V ₂₁ +E. is set in the comparator 19 via the D/A converter 20. After that, for example, "3" is set as the initial value for counting the END signal by the CPU.
22 register is set <step>, and then the timer is activated. <Step> This is because the processing state is detected by the change in the detection signal _V1 corresponding to the amount of light transmitted through the photomask 1 from now on only during the detection time T _E as shown in FIG.

Next, the CPU 22 controls the latch circuit 21.
Check the presence or absence of the END signal <Step>,
If the END signal is output, the same processing as that from the previous step is executed from step to step. As a result of the check in the step, if the contents set in the register become '0', the timer is reset and the process returns to the step again.At this time, a new threshold value is set as V ₂₃ =V ₂₂ +E.
is calculated by the CPU 22, and this threshold value is calculated by the D/A
It is input to the comparator 19 via the converter 20.

Also, the check results in the step
If the END signal is not latched in the latch circuit 21, it is checked in the next step whether or not a time has elapsed, and if the time has not exceeded, the process returns to the step again to check the presence or absence of the END signal.

In this way, the threshold value is sequentially updated by the deviation value E until the amount of light transmitted through the photomask 1 hardly changes, in other words, until the END signal latched to the latch circuit 21 is no longer output, the threshold value is sequentially updated by the deviation value E. Repeat each process. As shown in FIG. 8, for example, when the 10th threshold value is set, the detection signal V ₁ will not exceed the 10th threshold value within the preset time T _E. , so we move from step to step.

On the other hand _, since the detection signal ν ₁ corresponding to the amount of reflected light changes as shown in FIG. A threshold value ν ₂₁ =ν′ ₁ −e with a constant deviation e is set for the threshold value ν 21 =ν′ 1 −e, and when the detection signal ν ₁ for the amount of reflected light falls below this threshold value ν ₂₁ , the comparison circuit 25 #E to the latch circuit 27 in response to the discrimination signal from
The TR signal is latched, and this #E・TR signal
The step is executed only after it is input to the CPU 22.
This will change to YES. Therefore, this point is set as the end point (the end point of the process), and the etching process is stopped at the next step. In this case, as in the case of the amount of transmitted light,
It can be used as an end point by counting the #E/TR signal a predetermined number of times with the CPU 22,
Furthermore, there is an advantage that detection errors are reduced.

Furthermore, in the above-mentioned embodiments, the deviation value E for calculating the threshold value was explained as being constant; however, the deviation value E does not necessarily have to be constant;
For example, the threshold value may be set by sequentially decreasing the deviation value E each time the threshold value setting is repeated.

Further, in the above-mentioned embodiments, the surface treatment involved in etching a metal thin film of a photomask has been described, but the method of the present invention can also be applied, for example, to detecting the end point in the development process of a photomask.

As explained above, the present invention detects whether the detection signal level corresponding to the amount of transmitted light of a plate-like object to be processed exceeds a predetermined threshold within a predetermined time in a processing step, and controls the progress of the processing. Accordingly, new threshold values are sequentially set, and the ratio comparison with the changing detection signal level is repeated, and the detection signal level does not exceed the newly set threshold within a predetermined time, and The end point of the surface treatment is defined as the point in time when the detection signal level corresponding to the amount of reflected light from the plate-shaped object to be treated exceeds a predetermined threshold within a predetermined time.
Even if a temporary stagnation of the surface treatment as described above occurs during the surface treatment process and the rate of change in transmittance becomes zero, it is possible to completely prevent the erroneous operation of regarding this point as the end point of the surface treatment. The end point of surface treatment can be detected very accurately. In addition, regardless of the transmitted light amount characteristics of the plate-like object to be processed, it is possible to use a simple spinner head as a holding means for the plate-like object to be processed, and the rotating arm of the head intermittently emits the irradiation light beam. Even in the case of interruption, the end point of surface treatment can be accurately detected.

[Brief explanation of the drawing]

FIG. 1 is an enlarged partial cross-sectional view showing, for example, the state of a photomask before etching processing, and FIG. 2 is a characteristic curve showing the change characteristics of the amount of transmitted light for various plate-shaped objects to be processed as the processing time t elapses. figure,
Figure 3 is a plan view of a simple spinner head;
FIG. 4 is a side sectional view of the IV-IV cross section taken in the direction of the arrow, FIG.
The figure is a waveform characteristic diagram of the amplified detection signal output by the photoelectric conversion element of the device shown in Figure 5 depending on the amount of transmitted light, and Figure 7 is the state of transmission and reflection on the metal thin film surface of the irradiation light irradiated to the photomask. 8 is a line diagram showing changes in the detection signal value corresponding to changes in the amount of transmitted light over time from the start of photomask etching processing to the end, and FIG. 9 is a diagram showing the amount of reflected light. A diagram showing a state of change in the detection signal value corresponding to a change in the first
0 and 11 are flowcharts showing one embodiment of the present invention. 1... Photomask, 14, 15... Photoelectric conversion element V _2i (i=1, 2,...)... Threshold (with respect to the detected value of transmitted light amount) ν _2i (i=1, 2,...)...
Threshold value (with respect to the detected value of the amount of reflected light), T _E ...predetermined time, E... Deviation (with respect to the detected value of the amount of transmitted light), e... Deviation (with respect to the detected value of the amount of reflected light).

Claims (1)

[Scope of Claims] 1. The surface treatment is carried out by irradiating a light beam onto a predetermined part of the plate-like object to be surface-treated and detecting the amount of transmitted light and reflected light of the plate-like object to be treated corresponding to the irradiated light beam. In the surface treatment method, a new threshold value is repeatedly set while the detection signal level of the amount of transmitted light exceeds a predetermined threshold within a predetermined time, and the detection signal level of the amount of transmitted light is The surface treatment is terminated when the level does not exceed a predetermined threshold within a predetermined time and the detection signal level of the amount of reflected light falls below the predetermined threshold. , surface treatment method. 2. The surface treatment method according to claim 1, wherein the surface treatment of the plate-shaped object to be treated is an etching treatment. 3. The surface treatment method according to claim 1, wherein the surface treatment of the plate-like object to be treated is a development treatment.