JPS60192338A - Endpoint detecting method - Google Patents

Abstract

PURPOSE:To enable to detect an endpoint without fail by a method wherein the amount of fluctuations per prescribed time of the level of an electric signal is calculated, said amount of fluctuations is discriminated with the passage of time, and a judgement wherein the layer thickness has become zero is given when the fact that the above is in the first condition is detected in prescribed number of times. CONSTITUTION:A developing solution 52 is filled up in a developing vessel 51, and the lower layer 60 having the surface layer (the photoresist layer whereon a pattern is exposed) to be developed is fixed. A sideviewing lens barrel 20 is fixed in such a manner that the incident light sent from a prism 42 will be intersecting at right angle with the surface of the surface layer 61 using a fittings 36. The incident light coming from the prism 42 is reflected to the surface of the surface layer 61 and on the surface of the lower layer 60, and the intensity of the entire reflected light is changed. This reflected light reaches the tip of an optical fiber code 10, and it is conducted to an O/E converter 3 through the intermediary of an optical fiber code 12. The O/E converter 3 converts the incident optical signal, i.e., the change in intensity of the reflected light, into an analog electric signal using the photoelectric conversion element such as a photodiode and the like. Said analog electric signal is converted into a digital electric signal by an A/D converter 4, and it is inputted to a central processing unit (CPU)1.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is applicable to detecting the end point of etching when creating a circuit pattern by etching a semiconductor device, etc., or detecting the end point of development of a circuit pattern prior to etching. Regarding the method.

[Prior art]

Photolithography technology is used to create semiconductor devices such as integrated circuits.

This is deposited on the bottom layer of a plate-like material that will become a semiconductor substrate.
A layer made of other substances is formed by coating to create a multilayer structure, and a corrosion-resistant material such as photoresist is further applied to the surface layer, a circuit pattern is exposed, and this is developed to expose the photoresist layer to light. The exposed or unexposed portions are removed to form a circuit pattern. This is then immersed in a corrosive liquid (etching medium) to corrode the areas where the surface photoresist has been removed, exposing the underlying layer.Finally, the photoresist on the surface layer is removed to form a predetermined circuit pattern. It is something to create.

By the way, the progress of development when forming a circuit pattern with a corrosion-resistant material, that is, the progress of removal of the corrosion-resistant material, or the progress of corrosion of the surface layer during etching, that is, the corrosion has completed to the surface of the underlying layer. Detection of whether or not it has been carried out is important for quality control.

Conventionally, such an end point detection method is known, for example, in JP-A-55-104452, which converts reflected light of coherent light into an electrical signal and calculates the time derivative of this analog signal. However, since the signal changes near the end point are gradual, this determination is difficult.

In addition, it is difficult to distinguish between stationary noise in the signal processing system and the signal to be detected, and furthermore, if there is reflected light from, for example, bubbles in the corrosive liquid, it may be difficult to determine that the process has not finished yet. The determination of completion is uncertain, and if something goes wrong, a delay in completion may occur, resulting in so-called over-eating, which may lead to the production of defective products.

[Object of the invention] The present invention has been made in view of the above circumstances,
The object of the present invention is to propose a method for detecting an end point in etching and the development process that precedes it, which can reliably detect the end point, eliminates the influence of electrical noise, and prevents false detection.

[Structure of the invention]

The end point detection method according to the present invention is a method for detecting the end point of detecting when the layer thickness of IN of 2N having different refractive indexes has reached zero. projecting coherent light from the , detecting the reflected light of the coherent light and converting it into an electrical signal, adjusting the level of the electrical signal to fluctuate per predetermined time, and converting it into a first state within a predetermined range. , the second state increases over a predetermined range, or the third state decreases beyond a predetermined range over time, and when the first state is detected a predetermined number of times, the layer It is characterized in that it is determined that the thickness has become zero.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on drawings showing embodiments thereof.

FIG. 1 is a block diagram showing an apparatus for implementing the end point detection method according to the present invention.

The laser oscillator 2 emits a 1le-Ne laser beam, and the laser beam is transmitted to a side viewing barrel 20, which will be described later, via an optical fiber cord 10. The optical fiber cord 10 has a center of gravity structure in which the optical fiber cord 11 is surrounded by a large number of strands of the optical fiber cord 12 from the binding device 13 to the tip side, and the laser beam from the laser oscillator 2 is The light is transmitted to the side viewing barrel 20 via the fiber cord 11, and as described later, the reflected light from the side viewing barrel 20 is transmitted to the O/E (photoelectric) converter 4 via the optical fiber cord 12.
It is configured to be returned to A side-viewing lens barrel 20 whose legs 34 are fixed to a fixture 36 attached to the bottom surface of a developing tank 51 of an automatic developing device 50 is connected to the tip of the optical fiber cord 10.

FIG. 2 is a vertical cross-sectional view showing the configuration of the side viewing barrel 20, FIG. 3 is a vertical cross-sectional view showing the configuration of the main body 2OA, and FIG. 4 is an external view showing the connecting portion 20B with the optical fiber cord 1o. It is.

The main body 208 consists of a lens barrel 31 and fixing legs 34.

The lens barrel 31 is formed into a rectangular cylinder shape with a square bottom in cross section, and has a substantially square opening 3 whose base is at the bottom of the lens barrel 31.
5 is provided on one side, and this opening 35 has a 1l
A glass plate 33 coated so as not to reflect e-Ne laser light (0.633 μm) is fitted in a watertight manner.

A circular hole is formed from the upper end surface of the lens barrel 31 to the upper edge of the opening 35, and a female thread is carved on the inner peripheral surface of the hole. An O-ring 32 made of synthetic resin is fitted inside. A right-angled prism 42 is attached to the bottom of the lens barrel 31 so that its front axis is perpendicular to the surface of the glass plate 33. That is, as shown in FIG. 5, the prism 42 is mounted on the bottom of a cylindrical prism holder 40, which has an inner diameter slightly larger than the outer diameter of the sleeve 24, which will be described later, and has a male thread carved on its outer circumferential surface. The prism holder 40 is held by a protruding support plate 43, 43, and is screwed into the lens barrel 31. The prism holder 4o is screwed into the lens barrel 31 up to the tip of the female screw. As a result, one surface of the prism 42 substantially faces the glass plate 33.

Furthermore, a leg 34 is attached to the bottom of the lens barrel 31. This leg 34 is a screw whose length direction and axial direction are aligned with the length direction of the lens barrel 31, and is screwed into a female thread carved in a fixture 36 installed on the bottom surface of the developer tank 51 as described above. As a result, it is fixed to the developer tank 51.

Connection part 20B with optical fiber cord 10, Holter 21
, a presser ring 22, a stop ring 23, etc.

The holder 21 is made of stainless steel, the outer diameter of the upper part is the same as the outer length of the cross section of the lens barrel 31, and the lower part is formed with a slightly smaller diameter than the upper part and is engraved on the lens barrel 31. It is a cylinder with a male thread carved into it so that it can be screwed into a female thread.
A stainless steel sleeve 24 of an appropriate length is loosely fitted around the optical fiber cord 10 with its lower end surface matching the distal end surface of the optical fiber cord 10 described above. A stop ring 23 made of stainless steel is fixed to a position near the lower end of the portion of the sleeve 24 that protrudes downward from the lower end of the holder 21 with a set screw 23'. It is slightly shorter than the axial dimension of the prism holder 40 described above.

A stainless steel presser ring 22 is loosely fitted between the stop ring 23 of the sleeve 24 and the holder 21 and has a male thread that engages with a female thread that is formed on the lens barrel 31.

Therefore, first screw the prism holder 40 to which the prism 42 is fixed into the inner bottom of the lens barrel 31, and then screw the sleeve 2 until the lower end of the stop ring 23 comes into contact with the two surfaces of the prism holder 40.
4. Insert the lower end into the lens barrel 31. and the prescribed tool (
(not shown) is inserted into the upper opening of the lens barrel 31, the retaining ring 22 is rotated, and the stop ring 23 is screwed downward until it abuts the upper part of the stop ring 23, so that the stop ring 23 is sandwiched between it and the prism holder 40. shall be. As a result, the optical fiber cord 10 is fixed to the lens barrel 31 with its tip separated from the upper surface of the prism 42 by a very small distance and with its optical axis aligned. After that, when the lower small diameter part of the holder 21 is screwed into the female thread cut in the lens barrel 31, the O-ring 32 provided at the upper end of the lens barrel 31 creates a liquid-tight state between the lens barrel 31 and the holder 21. Become.

By assembling the side viewing barrel 20 in this way, the laser beam transmitted from the optical fiber cord IO is transmitted through the prism 4.
2, its traveling direction is changed by 90 degrees, and the light is transmitted through the glass plate 33 and projected to the outside, and the light that passes through the glass plate 33 from the outside and enters the prism 42 has its traveling direction changed by 90 degrees. and enters the optical fiber cord 10.

The developing tank 51 is filled with a photoresist developer 52, and a lower layer 60 having a surface layer (a photoresist layer exposed with a circuit pattern) 61 to be developed with the developer 52 is held in an appropriate manner (not shown). Developing layer 5 by means
The base of 1 and its surface are fixed vertically. As mentioned above, the prism 42 is placed on the surface of this table N6.
The side-viewing lens barrel 20 is fixed by a fixture 36 attached to the bottom surface of the developing layer 51 so that the projected light beams from the side viewing lens barrel 20 are orthogonal to each other.

Therefore, the projected light from the prism 42 is reflected by the surface of the table 1at61 and the surface of the lower layer 62, and at this time, the two reflected lights, which are out of phase, interfere with each other due to the difference in optical path length, which is twice the thickness of the surface layer. As a result, the light intensity of the reflected light as a whole changes.

This reflected light enters the prism 42 via the glass plate 35, and its traveling direction is changed by 90°, and the optical fiber cord 10
to the tip of the O/
It is transmitted to the E converter 3.

The 07E conversion unit 3 converts the incident optical signal, that is, the intensity change of the two series of repulsed lights, into an analog electrical signal using a photoelectric conversion element such as a first diode, and this analog electrical signal is The signal is converted into a digital electrical signal by an A/D (analog/digital) converter 4 and inputted to 0 yen.

The CPU constitutes a microcomputer system together with the operating section 7, ROM 8, RAM 9, etc., and performs arithmetic processing of input signals.The results are displayed on the display device 5, and the above-mentioned automatic It is given to the developing device 500 control device as appropriate. Furthermore, ROM B is CPII
The RAM 9 stores data necessary for arithmetic processing, intermediate results of arithmetic operations, and the like.

Next, the operation of the apparatus configured as described above for carrying out the method of the present invention will be explained with reference to the flowchart of FIG.

First, the original signal to be processed by the CPII I in FIG. 7, that is, the intensity change of the reflected light from the surfaces of the surface layer 61 and the lower layer 60, is shown in the upper row, and the result of processing this signal by the CPU I is shown in the lower row. The processing contents of CPt11 will be explained.

First, a signal S instructs the developing device 50 to start development.
When the signal S is given, this signal S is also given to the CPU 1. As a result, the CPU 1 starts processing the original signal after the predetermined time T1 has elapsed, but this is to avoid unnecessary processing immediately after the start of development, which would result in false detection or the like.

CP[I 1 then starts sampling the original signal, for example by performing digitized sampling of the original signal for lOm seconds by means of the A/D converter 4. The data of reflected light intensity at each time point sampled in this way is processed, and FIG. 8 shows the data processing,
That is, this is a flowchart of H, L, and E determination.

The reflected light intensity data Di sampled at 10 msec intervals are sequentially stored in the RAM 9, but the number of pieces of data after sampling starts is n (if the electrical noise level of the device is high, n may be set to a relatively large number). When the noise level is low, n is set to be relatively small), the actual processing starts.

When the data Di (i>n) is read, the average value Di of the remaining n-2 pieces excluding the maximum and minimum values among the past n pieces of data Di-n''Dn including the data Di is calculated. Then, the average value Di-+ calculated at the time when the previous data Di-1 was read, that is, the maximum value among the data D1-n-1 to Dn-1. and the remaining n-2 average values Di excluding the minimum value
Let −+ be data representing the past. And both data D
By comparing i and DL+, the input signal value (
In order to eliminate the influence of the electrical noise of the device, let us take a value that is slightly larger than the average value of this electrical noise as 8■ Di −Di−t l
In the first state with <1 8V there is no substantial change in signal level, in the second state with Di -Di-t >AV the signal level is increasing and with Di -Di-+ <-ΔV In the third state, the signal level is decreasing, and the comparison results are determined as "E,""H," and "L." If there is no change in the signal value, that is, the reflected light intensity is constant.
In the case of "E", there are cases where the signal is near the maximum or minimum peak i, and there are cases where development has been completed, but this "E"
In this case, a termination determination is made.

FIG. 10 is a flowchart of termination determination.

The end determination is basically made based on "E", that is, whether the first state has been continuously detected a predetermined number of times N or more. However, as shown in FIG. 9, for example, after the "E" state has continued for a certain amount of time when the end state has actually been reached, some reason may occur before the "E" state is not detected until the predetermined number of times N when the end judgment is made. If a noise that is determined to be "H" or "L" is input, the result of the EHL determination is determined to be "H" or "r-", and the end determination is interrupted. In order to avoid such erroneous determinations, the CPU performs noise elimination as described above based on the past signal cycle.

Specifically, the process proceeds to step (2) in which the counter C2 is incremented by +1 each time it is determined that the state is other than "E". When the state of "E" is detected, the process proceeds to step (3), where the counter C1 is incremented by +1 and the wheat counter C2 (D value VC2) is read and stored.

Next, if the value VC2 of the counter C2 is not zero, that is, if the result of the previous HLE judgment was "°H" or "L", the value VC2 is memorized and then the counter C2 is reset (VO2=0) L, if we add the average value V02 excluding the minimum value from the past values of counter C2, this VO2 is the seventh
As shown in the figure with ■, it corresponds to the average half period of the past signal. Then, in step ■, the value VC1 of the counter C1
If it is larger than the predetermined value N, it is determined that the process has ended, but while it is small, the process returns to the HLE judgment.

In this way, when the state changes from "H" or "I2" to "E", the past average half cycle of the signal V C2 is first estimated, and from then on, while the "E" state continues, The number of times it is determined as "'E"' is counted, and when this reaches a predetermined number of times N[, an end determination is made.

On the other hand, until the state of “'E” continues for N times or more, “I]
If the state is "°" or "L'", proceed from step ① to step ②, and take the value VC of counter C1 and the safety factor of the average half period of the signal VC2 set in advance. A predetermined ratio, for example, a value vc2 of about 80% or 70%
' is compared, and if V C+<vc2 ', that is, if the state becomes "'H" or "L" within a time shorter than a predetermined ratio VC2' of the average half cycle VC2 of the past signal, For example, developing? Assuming that the noise is caused by air bubbles in If the state is "L", it is determined that the process has not ended, and the counter C1 is reset (VCI = 0).

On the other hand, if the end is determined in step (2), after a predetermined time period of 1 to 2 has elapsed, an end signal is output to the automatic developing device 50, and the developing solution is discharged, etc. progress is stopped.

〔effect〕

As detailed above, according to the end point detection method according to the present invention,
In detecting level fluctuations in the detected signal, a moving average value is used to determine a first state in which the level fluctuation is substantially zero, a second state in which it is substantially increasing, or a second state in which it is substantially decreasing. Since the detection and judgment of the end point can be carried out accurately, the end point can be accurately detected and judged, and since the influence of steady electrical noise from the judgment device etc. is eliminated, the end point can be judged accurately and without delay. It becomes possible.

Furthermore, in the embodiment, when determining the end, the average cycle of past signals is determined in advance, and the actual end determination is made only when a signal indicating the end is detected for a predetermined percentage of the average cycle or more. Therefore, reliable end point detection is possible.

In the above embodiment, the detection of the end point of development during pattern formation for etching was explained, but it is also possible to detect the end point of the gradual decrease process of the surface layer, which has a different refractive index from the lower layer, as well as the etching corrosion assumption. It is widely applicable.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an apparatus used to implement the present invention;
Fig. 2 is a longitudinal sectional view of the side viewing barrel, Fig. 3 is a longitudinal sectional view of its main body, Fig. 4 is an external view of its connecting sleeve, and Fig. 5 is a longitudinal sectional view of the side viewing barrel.
The figure is an external view of the prism holder, and Figure 6.8.9 is the CPU.
FIG. 7.10 is a flow chart showing the processing contents, and FIG. 7.10 is a graph showing the waveform of the signal. 1...CPU 2...Laser oscillator 3...O/
E converter 10, 11, 12... optical fiber code
20...Side viewing barrel 60...Lower layer 61...Surface layer patent Applicant Dainichi Nippon Electric Cable Co., Ltd. Agent Patent attorney Noboru Kono 6

Claims (1)

[Scope of Claims] 1. In an end point detection method for detecting when the thickness of a layer in which IN of two layers with different refractive indexes gradually decreases reaches zero, the surface side of the layer where the layer thickness gradually decreases. projecting coherent light from the base, detecting the reflected light of the coherent light and converting it into an electrical signal, determining the amount of variation in the level of the electrical signal per predetermined time, and converting this into a first state within a predetermined range. , a second state in which the increase exceeds a predetermined range, or a third state in which the decrease exceeds a predetermined range over time, and when the first state is detected a predetermined number of times, the An end point detection method characterized by determining that the layer thickness has become zero.