JP3043129B2 - Plasma etcher endpoint detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a detection apparatus 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 to apply a high-frequency voltage to electrodes 10a and 10b sandwiching a semiconductor wafer 5 while flowing a reaction gas into a chamber 1 to convert the gas into plasma on the wafer. Thus, the apparatus can efficiently etch a fine pattern.

[0003] The process in which the plasma etcher is most frequently used at present is the etching of a SiO ₂ film. The etching of the SiO ₂ film will be described. A desired pattern is baked with a photoresist on the SiO ₂ film formed on the Si substrate, and the developed wafer 5 is placed on the electrodes 10a and 10b.
Set in between. In the electrode 10a, a large number of fine holes 12 are formed in order to easily convert the gas on the wafer 5 into plasma. 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 from which the resist has been removed causes a reaction of CF ₄ + SiO ₂ → SiF ₄ ↑ + CO ₂を. It rises and is gradually etched.

The problem here is the control of the reaction time. If the time is insufficient, 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 below the resist as shown by the dotted line A, resulting in a so-called overetch state. All of these can be fatal defects in product quality.

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

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

[0007]

However, in recent years, the miniaturization of semiconductors has rapidly advanced, and it has become difficult to accurately detect the end point of etching by the conventional method. In other words, the opening of the resist in FIG. 4, that is, the size of the etching pattern is reduced to the order of sub-micron, and the ratio of the opening to the entire area of the wafer is also about 10% from the conventional one, and recently about 5%, and in the near future. Is expected to decrease to less than 1%.

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

The output of the spectroscope under such conditions is shown in FIG.
As shown in FIG. 5A, the etching end point is not clearly readable, and the signal has an extremely poor S / N ratio as shown in FIG. 5B. In this case, even if the external noise of the detection system is suppressed as much as possible to improve the S / N ratio, the last remaining problem is the temporal drift of the entire plasma light.

The drift of the entire plasma contains a lot of low frequency components, and the amplitude of the drift is close to the change in the spectral intensity of CO _2. Therefore, it is extremely difficult to remove the drift by electric means. It has become.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and has as its object to eliminate the influence of a temporal drift of plasma light as a whole when detecting a desired emission spectrum.

[0012]

In order to solve the above-mentioned problems, an apparatus for detecting an end point of a plasma etcher according to the present invention uses a condensing lens to convert plasma light generated in a chamber of a plasma etcher into an entrance slit of a spectroscope. In a plasma etcher endpoint detection device that focuses and separates a plasma emission spectrum of a gas generated by a chemical reaction due to etching and controls an etching end time while monitoring the intensity change, the light is guided by the condensing lens. A perforated mirror having an opening through which the central light of the plasma light passes with a light beam substantially filling the substantial opening of the spectroscope, and having an annular reflector around the opening to deflect the peripheral light of the plasma light. And a plane where the plasma light deflected by the annular reflecting portion of the perforated mirror is collected. A photoelectric conversion element disposed, and having a calculating means for correcting the spectral output spectral intensity of the spectrometer at 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 entire plasma light including all wavelengths is measured simultaneously, and the specific plasma light spectrum intensity is measured for the entire plasma light. 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]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be specifically described below with reference to FIGS. The same parts as those of the apparatus shown in FIG. 3 are denoted by the same reference numerals, and description thereof will be omitted.

A cylindrical member 50 shown in FIG. 2 is disposed between the spectroscope 30 and the chamber 1 of the plasma etcher shown in FIG. FIG. 2A shows this cylindrical member 5.
2 (B) is a side view of the internal configuration and light path of the cylindrical member 50, and FIG. 2 (C) is a view of the shape of a mirror mounted inside the cylindrical member 50. Each is shown.

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

A 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 on the photodetector 72. In this embodiment, the condenser lens 20 is a quartz plano-convex lens with a diameter of φ30 mm and f50 mm, and a sufficiently bright lens with an F number of about 1.66. 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 middle of the path. The configuration of the mirror 60 and other plasma light split by the beam splitter 70 will be described later in detail.

The plasma light having passed 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 etching ₂ , light of 440.2 nm or 482.5 nm is selected to detect a change in plasma light of CO ₂ , and 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 change in the intensity of the entire plasma light. Therefore, if the output of the photodetector 72 is used to normalize the change in the intensity of the plasma light of the gas, which is output from the photodetector 31 and is caused by a predetermined reaction, it is possible to obtain a signal from which the influence of the drift of the entire plasma light has been removed. Will be done.

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

The mirror 60 and the beam splitter 7
Numerals 0 are fixed inside the inner cylindrical member 55, and are disposed at an angle of approximately 45 ° with respect to the optical axis.
As shown in FIG. 2C, a hole 62 is formed in the mirror 60 around the optical axis. The size of the hole 62 may be a size that sufficiently satisfies the amount of light 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 opening of the spectroscope 30 (a light beam that sufficiently covers the grating of the spectroscope) can pass through. In the present embodiment, the F
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 quantity required by the spectroscope 30. Light that cannot pass through the hole 62 is reflected by the annular zone 63 of the hole 62 of the mirror 60, enters the beam splitter 70, and
Focused on 2.

In this embodiment, behind the condenser lens 20,
Since the mirror 60 provided with a hole corresponding to the F-number of the spectroscope is arranged, there is no loss of light quantity to the spectrometer, and no decrease in the S / N ratio due to a decrease in light quantity. Further, since a perforated mirror is used, it is not necessary to consider the effect of the difference in yield due to the thickness of the glass.

Further, since the detection of plasma light including light of all wavelengths is not performed by using the zero-order light in the spectroscope 30, the configuration of the spectroscope is extremely simplified. Next, 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 interval between the electrodes 10a and 10b of the plasma etcher shown in FIG. 1 is generally only about 5 mm. Therefore, the light emitting surface of the plasma viewed from the view port 15 is like a horizontally long band having a width of 5 mm.
When this is projected on the entrance slit 32 (width about 0.5 mm) by the condenser lens 20, the magnification of the condenser lens is 2-3 times, and the width of the light is extremely thin, 2.5 mm to 1.7 mm. It will be something. For this reason, in order to project the band of light firmly on the slit, the attitude of the spectroscope 30 must be carefully controlled.

[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 retuning to the spectrum, monitoring is started.

The control of the etching end point is slightly different depending on whether the focusing lens is focused on the front side of the wafer or on the center of the wafer.
At the start of monitoring, the focusing lens needs to be focused. Usually, this focusing measures the distance from the view port to the tip of the condenser lens depending on the design value, and determines the extension amount of the condenser lens.

For this reason, the operation of controlling the attitude of the spectroscope or the operation of focusing the condenser lens is troublesome and difficult to perform accurately. In this embodiment, the configuration is such that the attitude of the spectroscope and the focusing of the condenser lens can be easily performed. That is, a view finder is provided on the cylindrical member 50, and by looking at the view finder, the control of the attitude of the spectroscope and the focusing of the condenser lens are easily performed. Hereinafter, the configuration will be described.

A notch 5 is formed on the outer peripheral surface of the outer cylindrical member 51.
2, and a frame 56 for holding a focus mat 57 to be described later is located in the notch 52. The outer cylindrical member 51 is slidable in the direction of the arrow by a driving 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 direction of the arrow.

The outer peripheral surface of the inner cylindrical member 55 is provided with a frame 5 so as to be located within the cutout 52 of the outer cylindrical member 51.
6 is fixed, and a focus mat 57 is held in the frame 56. The focus mat 57 has a center line 57a on which a position and a direction conjugate with the entrance slit 32 can be determined. In the present embodiment, the longitudinal scribe line 57a corresponds to the longitudinal direction of the entrance slit 32 and the longitudinal direction of the plasma light band. The frame 56 and the focus mat 57 constitute a viewfinder.

Therefore, if the position of the spectroscope 30 is adjusted and fixed while looking through the viewfinder so that the band of the plasma light overlaps the score line in the longitudinal direction, the plasma light can be correctly and easily projected on 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 in that a control signal is obtained in which the influence of the drift of the entire plasma light is eliminated. For this reason, 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 deleted and the photodetector 72 is arranged at the position of the focus mat 57. Further, the present invention is not limited to the above embodiment.
For example, various modifications are possible for 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 being 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 there is no need to add any optical components in the optical path of the spectroscope, there is no adverse effect on the spectral accuracy due to the difference in yield and flare.

[Brief description of the 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 (A) to 2 (C), (A) is a plan view of a condenser lens portion shown in FIG. 1, (B) is a side view of an internal configuration and a light path, and (C) is It is a figure showing the shape of the mirror attached inside it.

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

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

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

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Chamber, 20 ... Condensing lens, 30 ... Spectroscope, 3
1, 72: photodetector, 32: entrance slit, 60: mirror, 70: beam splitter.

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 21/3065 A61B 3/00

Claims (3)

(57) [Claims] A plasma light generated in a chamber of a plasma etcher is focused by a condenser lens on an entrance slit of a spectroscope, a plasma emission spectrum of a gas generated by a chemical reaction by etching is spectrally extracted, and its intensity change is performed. An end point detection apparatus for a plasma etcher that controls an etching end time while monitoring the following. An opening for passing central light of the plasma light guided by the condenser lens with a light beam that substantially fills the aperture of the spectroscope. A perforated mirror having an annular reflector for deflecting peripheral light of the plasma light around the opening; and a plane on which the plasma light deflected by the annular reflector of the perforated mirror is collected. The disposed photoelectric conversion element, and the spectral output spectrum intensity of the spectroscope is corrected by the output of the photoelectric conversion element. An end point detection apparatus for a plasma etcher, comprising: 2. The method according to claim 1, wherein a part of the plasma light deflected by the annular reflecting portion of the perforated mirror is converged on a finder focus mat, and the attitude control of the spectroscope and the focusing of the condenser lens are performed. The apparatus for detecting an end point of a plasma etcher according to claim 1. 3. An inner cylindrical member integrally incorporating and fixing the finder focus mat is slidably provided with an outer cylindrical member integrally incorporating the condenser lens, and the outer cylindrical member is fixed to the inner cylindrical member. 3. The end point detecting apparatus for a plasma etcher according to claim 2, wherein the focus is adjusted by sliding with respect to the plasma etcher.