JPH0562944A - End point detector of plasma etcher - Google Patents

Abstract

PURPOSE:To eliminate the effect of the drift with time of the whole plasma and to detect a desired emission spectrum. CONSTITUTION:When the intensity of a prescribed plasma spectrum is measured by a photodetector 31 in a spectroscope 30, the intensity of a plasma including all wavelengths is simultaneously detected by a photodetector 72 and the intensity of the prescribed plasma spectrum is corrected by the intensity of the plasma including all wavelengths in a control and arithmetic circuit 40.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a detector for detecting an end point of a plasma etcher in a plasma etching (dry etching) process of a semiconductor process.

[0002]

2. Description of the Related Art As shown in FIG. 3, a plasma etcher is a method in which a high-frequency voltage is applied to electrodes 10a and 10b sandwiching a semiconductor wafer 5 while flowing a reaction gas into a chamber 1 to turn the gas into a plasma on the wafer. Is an apparatus for efficiently etching a fine pattern.

The process in which the plasma etcher is most often used at present is the etching of the SiO ₂ film. The etching of the SiO ₂ film will be described. A desired pattern is baked on the SiO ₂ film formed on the Si substrate with a photoresist, and the developed wafer 5 is connected to the electrodes 10a and 10b.
Set in between. A large number of fine holes 12 are formed in the electrode 10a in order to easily turn the gas into plasma on the wafer 5. Then, when a high frequency voltage is applied to the electrodes 10a and 10b while flowing a mixed gas of CF ₄ and Ar into the chamber 1, the SiO ₂ in the portion where the resist has been removed causes the reaction of CF ₄ + SiO ₂ → SiF ₄ ↑ + CO ₂ ↑. It rises and is gradually etched.

The problem here is the control of the reaction time. When the time is insufficient, SiO as shown by the dotted line A in FIG.
_{If 2} is not completely removed and remains, and if the time is too long, the etching proceeds to the bottom of the resist as shown by the dotted line B, resulting in a so-called overetch state. All of these can be fatal defects in the quality of the product.

What has been considered there is a method of controlling the reaction time while monitoring the plasma emission intensity of the gas (CO ₂ here) generated by the reaction. CO
The spectral intensities of the _two gases change with the reaction time, as shown in Fig. 5 (A). That is, there is a region that gradually decreases from the start of etching as it progresses, there is a portion that sharply drops near the end of etching, and there is a region that gradually weakens to an over-etched state. Therefore, the optimum etching state can be obtained by controlling the reaction end time with reference to the time point at which the change in the spectrum intensity occurs abruptly.

This is achieved by providing a quartz glass window (viewport) 15 on the side wall of the chamber 1 shown in FIG. 3, and guiding the plasma light in the chamber to the spectroscope 30 through the condenser lens 20 from there. To be achieved. Condensing lens 2
0 is arranged so that the plasma light is focused on the entrance slit 32 of the spectroscope 30, and the spectroscope 30 measures the spectrum of the plasma light. In the case of the etching of SiO ₂ described above, the emission spectrum of CO ₂ gas (440.2 nm or 482.5 n
m) is used. The reaction time can be controlled by detecting the emission spectrum of this CO ₂ gas by the photodetector 31 and feeding it back to the high frequency power source or the like via the control circuit.

[0007]

However, in recent years, the miniaturization of semiconductors has progressed rapidly, and it has become difficult to detect the etching end point accurately by the conventional method. That is, the resist opening in FIG. 4, that is, the size of the etching pattern is reduced to the sub-micron order, and the ratio of the opening to the entire area of the wafer is close to 10% in the past and around 5% recently, and in the near future. Is expected to fall below 1%.

The decrease in the aperture ratio means that the amount of CO ₂ generated in the above-described example of etching SiO ₂ is decreased, and the ratio of the emission spectrum due to CO ₂ in the entire plasma light is decreased. It means to do.

The output of the spectrometer under these conditions is shown in FIG.
As shown in FIG. 5A, the etching end point cannot be clearly read, and as shown in FIG. 5B, the signal has an extremely poor S / N ratio. In this case, even if the electrical external noise of the detection system is suppressed as much as possible and the S / N ratio is improved, the last remaining problem is the temporal drift of the entire plasma light.

Since the drift of the whole plasma contains many low frequency components and the amplitude thereof is close to the change in the spectral intensity of CO ₂ , it is extremely difficult to remove it by electric means. Has become.

The present invention has been made to solve the above-mentioned problems, and an object thereof is to eliminate the influence of the temporal drift of the entire plasma light when detecting a desired emission spectrum.

[0012]

In order to solve the above-mentioned problems, an end point detecting device for a plasma etcher according to the present invention uses a condensing lens to direct plasma light generated in a chamber of the plasma etcher to an entrance slit of a spectroscope. In the end point detection device of the plasma etcher, which is focused, the plasma emission spectrum of the gas generated by the chemical reaction due to the etching is spectrally taken out, and the etching end time is controlled while monitoring the change in the intensity of the gas. And an optical member that is arranged between the plasma light and the incident slit and divides the plasma light in a different direction, and a photoelectric conversion element arranged on a plane where the plasma light divided in the different direction is focused.
Arithmetic means for correcting the spectral output spectrum intensity of the spectroscope with the output of the photoelectric conversion element.

[0013]

When the specific plasma light spectrum intensity from the reaction product gas by etching is measured, the intensity of the whole plasma light including all wavelengths is measured at the same time, and the specific plasma light spectrum intensity of the whole plasma light is measured. By correcting with the intensity, the influence of the drift of the entire plasma light is removed from the specific plasma light spectrum intensity.

[0014]

Embodiments of the present invention will be specifically described below with reference to FIGS. 1 and 2. The same parts as those of the device shown in FIG. 3 are designated by the same reference numerals and the description thereof will be omitted.

The cylindrical member 50 shown in FIG. 2 is arranged between the chamber 1 of the plasma etcher shown in FIG. 1 and the spectroscope 30. FIG. 2A shows the cylindrical member 5
0 is a plan view, FIG. 2 (B) is a side view of the internal structure and light path of the cylindrical member 50, and FIG. 2 (C) is the shape of the mirror mounted inside the cylindrical member 50. Shown respectively.

The cylindrical member 50 comprises an inner cylindrical member 55 fixed to the spectroscope 30 with screws or the like, and the inner cylindrical member 5.
5, the outer cylindrical member 5 sliding in the direction of the arrow along the outer peripheral surface of
1 and.

The condenser lens 20 is fixed inside the outer cylindrical member 51, and focuses the plasma light from the plasma etcher on the entrance slit 32 of the spectroscope 30 and the photodetector 72. In this embodiment, the condensing lens 20 is a plano-convex quartz lens with a diameter of 30 mm and f50 mm, and a sufficiently bright lens with an F number of about 1.66 is used. As is apparent from the drawing, the plasma light is focused on the photodetector 72 by arranging the mirror 60 and the beam splitter 70 in the path on the way. The configuration of the mirror 60 and the other plasma light split by the beam splitter 70 will be described in detail later.

The plasma light passing through the entrance slit 32 of the spectroscope 30 is diffracted by a grating (not shown) and detected by the photodetector 31. SiO
_In the case of the etching of ₂ , the light of 440.2 nm or 482.5 nm is selected to detect the change of the CO ₂ plasma light, and the light of this wavelength is detected by the photodetector 31. The CO ₂ plasma light detected by the photodetector 31 is photoelectrically converted and input to the control / arithmetic circuit 40.

On the other hand, since the light incident on the photodetector 72 includes light of all wavelengths, the output of the photodetector 72 corresponds to the intensity change of the entire plasma light. Therefore, if the intensity change of the plasma light of the gas generated by the predetermined reaction, which is output from the photodetector 31, is normalized by the output of the photodetector 72, a signal in which the influence of the drift of the entire plasma light is removed is obtained. Will be

That is, the signal photoelectrically converted by the photodetector 72 is input to the control / arithmetic circuit 40, and the output from the photodetector 31 is corrected by dividing it by the output from the photodetector 72. As a result, in the temporal change of the spectrum intensity signal, the drift as shown in FIG. 5 (B) disappears, and the inflection point as shown in FIG. 5 (A) can be clearly recognized. As a result, it becomes possible to control the reaction time of the plasma etching based on the signal from the control / control circuit 40 in which the influence of the drift of the entire plasma light is removed.

The mirror 60 and the beam splitter 7
0 is fixed inside the inner cylindrical member 55, and is arranged at an angle of about 45 ° with respect to the optical axis.
As shown in FIG. 2C, a hole 62 is formed in the mirror 60 with the optical axis as the center. The size of the hole 62 may be a size sufficient to satisfy the light amount required by the spectroscope 30. That is, the size of the hole 62 may be any size as long as a light beam that fills the substantial aperture of the spectroscope 30 (a light beam that sufficiently covers the grating of the spectroscope) can pass through. In this embodiment, F of the condenser lens 20 is
In contrast to 1.66, the hole 62 is set to F3.5, and the plasma light passing through the hole 62 sufficiently satisfies the light amount required by the spectroscope 30. Further, the light that cannot pass through the hole 62 is reflected by the ring zone region 63 of the hole 62 of the mirror 60, enters the beam splitter 70, and is detected by the photodetector 7.
Focus on 2.

In this embodiment, behind the condenser lens 20,
Since the mirror 60 having a hole corresponding to the F number of the spectroscope is arranged, there is no loss of light quantity to the spectroscope, and there is no decrease in S / N ratio due to the decrease in light quantity. Further, since the perforated mirror is used, it is not necessary to consider the influence of the difference due to the thickness of the glass. Of course, in the present invention, instead of the perforated mirror, a half mirror or the like having no hole may be used to guide the plasma light to the photodetector 72 and the entrance slit 32 of the spectroscope.

Further, since the plasma light containing light of all wavelengths is not detected by utilizing the 0th order light in the spectroscope 30, the constitution of the spectroscope becomes extremely simple. Next, the light split by the beam splitter 70 and focused at a position different from that of the photodetector 72 will be described in detail.

The distance between the electrodes 10a and 10b of the plasma etcher shown in FIG. 1 is generally about 5 mm. Therefore, the light emitting surface of the plasma seen from the viewport 15 is like a horizontally long strip with a width of 5 mm.
When this is projected onto the entrance slit 32 (width of about 0.5 mm) by the condenser lens 20, the magnification of the condenser lens is 2 to 3 times, and the width of the light is 2.5 mm to 1.7 mm, which is extremely thin. It becomes a thing. Therefore, it is necessary to carefully control the attitude of the spectroscope 30 in order to firmly project the band of light on the slit.

[0025] Typically First, fit the wavelength of Ar to relatively strong spectral selective wavelengths in the spectrometer 30 is generated, after determining the spectroscope posture so that its output is maximum, the selected wavelength CO ₂ After re-adjusting to the spectrum, monitoring is started.

The control of the etching end point is slightly different depending on whether the focus of the condenser lens is set on the front side of the wafer or the center of the wafer.
Focusing of the condenser lens is required at the start of the monitor. Normally, for this focusing, the distance from the viewport to the tip of the condenser lens is measured by relying on the design value to determine the amount of extension of the condenser lens.

Therefore, the work of controlling the attitude of the spectroscope or focusing the focusing lens is troublesome and difficult to perform accurately. In this embodiment, the posture of the spectroscope and the focusing of the condenser lens can be easily adjusted. That is, a viewfinder is provided on the cylindrical member 50, and by looking through the viewfinder, the attitude of the spectroscope and the focusing of the condenser lens can be easily performed. The configuration will be described below.

A notch 5 is formed on the outer peripheral surface of the outer cylindrical member 51.
2 is formed, and a frame 56 that holds a focus mat 57, which will be described later, is located in the cutout portion 52. The outer cylindrical member 51 is slidable in the arrow direction by a drive mechanism (not shown) using the frame 56 as a guide. Thus, the focus can be adjusted by sliding the outer cylindrical member 51 in the arrow direction.

On the outer peripheral surface of the inner cylindrical member 55, the frame 5 is positioned so as to be located in the notch 52 of the outer cylindrical member 51.
6 is fixed, and the focus mat 57 is held in the frame 56. On this focus mat 57, a center line 57a is marked which can identify the position and direction conjugate with the entrance slit 32. In this embodiment, the scoring lines 57a in the longitudinal direction correspond to the longitudinal direction of the entrance slit 32 and the longitudinal direction of the band of plasma light. The frame 56 and the focus mat 57 form a viewfinder.

Therefore, while looking through the viewfinder, if the attitude of the spectroscope 30 is adjusted and fixed so that the band of the plasma light is firmly overlapped with the scoring line in the longitudinal direction, the plasma light is correctly and easily projected onto the entrance slit 32. can do. In addition, focusing can be easily and accurately performed while looking through the viewfinder.

The present invention is characterized by obtaining a control signal in which the influence of the drift of the entire plasma light is removed. Therefore, it is not always necessary to provide a viewfinder, and the configuration shown in FIG. 2 may be such that the beam splitter 70 is removed and the photodetector 72 is arranged at the position of the focus mat 57. Furthermore, the present invention is not limited to the above embodiment.
For example, various modifications can be made to the positional relationship between the mirror 60, the photodetector 72, and the like.

[0032]

According to the present invention, the end point detection of the plasma etcher can be prevented from becoming inaccurate due to the drift of the entire plasma light, and accurate etching can be performed even on a wafer having a low aperture ratio. Further, since it is not necessary to add any optical component in the optical path of the spectroscope, there is no adverse effect on the spectral accuracy due to the difference of the light and the flare.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an overall configuration of a plasma etcher and an endpoint detection device according to the present invention.

2 includes (A) to (C), (A) is a plan view of the condenser lens portion shown in FIG. 1, (B) is a side view of the internal configuration and a light path, and (C) is It is a figure which shows the shape of the mirror attached in the inside.

FIG. 3 is a schematic diagram showing an overall configuration of a conventional plasma etcher and endpoint detection device.

FIG. 4 is a diagram showing a state of etching SiO ₂ .

FIG. 5 is a graph including (A) and (B) showing the relationship between the spectral intensity of CO ₂ and time in the plasma etching process.

[Explanation of symbols]

1 ... Chamber, 20 ... Condensing lens, 30 ... Spectroscope, 3
1, 72 ... Photodetector, 32 ... Incident slit, 60 ... Mirror, 70 ... Beam splitter

Claims (3)

[Claims] 1. A plasma light generated in a chamber of a plasma etcher is focused by a condenser lens on an entrance slit of a spectroscope, and a plasma emission spectrum of a gas generated by a chemical reaction due to etching is spectrally extracted and its intensity change. In an end point detection device of a plasma etcher for controlling the etching end time while monitoring, an optical member that is arranged between the condenser lens and an entrance slit and divides the plasma light into the entrance slit and a direction different from the entrance slit. And a photoelectric conversion element arranged on a plane where the plasma light divided in the different directions is focused, and an arithmetic means for correcting the spectral output spectrum intensity of the spectroscope with the output of the photoelectric conversion element. End point detection device for plasma etcher. 2. The optical member for splitting the plasma light comprises:
The end point detection device of the plasma etcher according to claim 1, wherein the end point detection device is a mirror having a hole. 3. The end point detection device for the plasma etcher according to claim 1, wherein a part of the plasma light divided in the different directions is focused on the focus mat for the viewfinder. ..