JPS6086833A - Method and apparatus for measuring depth of etching of semiconductor device - Google Patents

Abstract

PURPOSE:To measure the depth of etching easily by detecting light intensity in a section where the light intensity of diffraction beams from a section to be etched and diffraction beams from a section not etched is brought to the same extent. CONSTITUTION:An etching-depth measuring section consisting of a coherent light source 31, a sensing section 32 and a detecting treating section 34 is mounted to a dry etching device constituted by a vacuum chamber 35, an upper electrode 36, a lower electrode 39 and a high-frequency power supply 40. Coherent light projected from the light source 31 is reflected by a material to be etched 38, and detected by the sensing section 32 as a diffraction pattern. According to such constitution, there is a section, where the intensity of diffraction beams from a through-hole or a deep groove for isolating an element and the intensity of diffraction beams from patterns except said pattern are brought to the same extent, in the diffraction pattern, the treating section 34 detects the change of light intensity at the point, and the through-hole having a minute area and the depth of etching can be measured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method and apparatus for measuring the depth of etching in a dry etching process during semiconductor device manufacturing.

[Background of the Invention] In the process of manufacturing semiconductor devices, dry etching is one of the techniques for etching a wiring pattern or other element pattern using a resist as a mask.

At this time, it is necessary to monitor the end point of the etching.

Conventional etching will be explained with reference to FIG.

Conventionally, when etching the material 11 to be etched using the resist 10 as a mask, the material 11 to be etched was etched until the base 12 was exposed. Therefore, the end point of etching can be monitored by measuring things that change when the substrate 12 is exposed, specifically, the composition of the processing atmosphere, the reflectance of the surface, the speed of etching, etc. I was able to do that.

However, as semiconductor devices have progressed, it has become necessary to finish etching at a certain depth before the first layer is exposed.

For example, when etching a through hole to connect upper and lower wiring, two stages of etching are performed to create a slope at the edge of the groove, so the first stage of etching must end at a certain depth. There is.

Also, 1. As an element isolation technique indispensable for the '5 μm process, there is a method of isolating elements using U-shaped grooves, but in this case, it is necessary to etch the material to be etched without a base to a specific depth.

Here, a conventional example of monitoring the end point by detecting changes in the etching speed will be described with reference to FIGS. 1, 2, and 3. This technique measures etching speed by measuring depth.

FIG. 1 shows a conventional example including a processing chamber 5, an upper electrode 6, and a lower electrode 8.
This is an example applied to a dry etching device consisting of a high frequency power source 9, a coherent light source 1, and a half mirror.
2, a sensing section 3 that measures the scene, and a detection processing section 4.

In this apparatus, an original beam emitted from a coherent light source 1 reaches a target 7 to be etched.

The material to be etched 7 has the cross-sectional shape shown in FIG. 2, and the material to be etched 11 formed on the base 12 is etched using the resist 10 as a mask. An optical path difference 2·a is generated between the light reflected on the remaining surface 15 and the light reflected on the etched surface 16.

Here, δ is the depth of the eclipse and is a function of time that increases with time, so it is assumed to be δ(1). The time rate of change of δ shows different values depending on the etching speed (depending on the material to be etched). The coherent source reflected on the surface of the etched object 7 is a half mirror 2
It is reflected and reaches the sensing part 3.

Here, the areas of the remaining surface 15 and the etched surface 16 are respectively A
Assuming r and A1, the intensity I of the light reaching the sensing section 3 is expressed by the following equation (1). Here, it is assumed that the reflectances of the two surfaces are approximately equal.

roeIA tX p (i (1) t )+, /;
i txp(i (ωt+-7δ(f)))+2=Ar
+AL +2FCO5-j-δ(t) ftl where λ is the wavelength of the coherent source and ω is the angular velocity.

Therefore, when I is detected, the result is as shown in FIG.

When the etching ends, the base 12 is exposed and the speed of etching changes, so the waveform of I changes as shown in FIG. I can do it. Also,
By measuring the phase of the change in I, the depth can be measured from equation (1).

However, the area of the etched portion of the U-shaped groove b with the through hole (hole for wiring connection) is small.

Changes in the intensity of interference light as shown in FIG. 3 cannot be detected. That is, the depth of a through hole or U-shaped groove cannot be measured.

Moreover, especially regarding deep grooves for element isolation, the grooves are small and the depth cannot be measured even after processing using a scanning electron microscope or an optical microscope. This is because in a scanning electron microscope, the emitted secondary electrons are absorbed into deep grooves, and in an optical microscope, a sufficient amount of energy cannot be captured. Therefore, at present, there is no other way than to measure by breaking the etched object in the depth direction of the groove, that is, there is no non-contact, non-destructive measurement method.

[Purpose of the invention]

An object of the present invention is to eliminate the drawbacks of the above-mentioned prior art and to provide a semiconductor device in which the etching depth can be measured even when the etching area is small in the etching process during semiconductor manufacturing. The present invention provides a method and apparatus for measuring depth.

[Summary of the Invention] That is, the present invention focuses on the fact that the size of through holes or deep grooves for element isolation in the semiconductor device manufacturing process is smaller than other patterns formed on the substrate.

Therefore, when coherent light is incident, the reflected light is diffracted, and there are parts of the diffraction pattern where the intensity of the diffracted light from the through hole or deep groove is about the same as the intensity of the diffracted light from other patterns. . 2 on this point
The interference of two wavefronts is used to measure the depth when the etched area is small.

[Embodiments of the invention]

The present invention will be specifically described below based on embodiments shown in the drawings.

First, the principle of the present invention will be explained.

First of all, if we consider a multi-slit diffraction image in which the number of slits is N1 and the width is self, it becomes a curve 24 in FIG. 4, which follows the following equation.

Here, d is the width of the slit, t is the distance between the slit centers, λ is the wavelength of the light, b is the distance from the slit to the diffraction image plane, and X is the position on the image plane, which is the 90th order diffracted light, that is, the reflected light. This is based on the position of the light.

From this equation, it can be seen that the envelope 25 is the intensity distribution of the diffraction image of a single slit having a width d, and that the envelope 25 goes to 0 when the following equation holds true.

tarbθ=x/b=mλ/+! +31 Also,
When N is large enough to be 8 o'clock, a sharp peak appears due to interference, and the position of the peak follows the following equation.

% Formula % (41 In formulas (3) and (4), m is an integer, and θ is an angle indicating the direction.

Therefore, the diffraction patterns of slits with different widths are shown in Figure 5.
Shapes such as curve 62 and curve 66 are obtained. At this time,
The area between the X-axis and each curve is the amount of light of each light. In FIG. 5, as can be seen from equation (2), the slit forming the curve 66 has a smaller width and a smaller amount of light. However, at the position of color 64, the amounts of light of the two light beams become approximately the same. or,
In the region 65, the amount of light flux formed by the curve 63t is larger.

When the area ratio of the etched portion to the whole is about 10% or more, the etching depth can be measured by detecting a zero-dimensional light intensity change.

However, when the area of the etched part becomes smaller, not only the amount of light proportional to the area is reflected, but also the amount of light reflected in the 90th order direction becomes extremely small due to diffraction spreading to the surroundings, fx, I, As a result, the change in the light intensity of the interference light with the light reflected from the non-etched portion having a large area becomes small.

Therefore, when the above area ratio is reduced to about 10% or less, it becomes difficult to detect a change in the light intensity of the 0th order light, and in other than the 0th dimension, the reflected light from the etched part and the non-etched part become difficult to detect. It becomes possible to measure the etching depth by detecting a change in light intensity of an order in which the intensity of the reflected light becomes approximately the same.

Hereinafter, specific embodiments of the present invention will be described based on FIGS. 6 to 13.

This embodiment includes a vacuum chamber S5, an upper electrode 36, and a lower electrode 39.
This is an example in which the present invention is applied to a dry etching apparatus comprising a high frequency power source 40 and a coherent light source 3.
1, a sensing section 32, and a detection processing section 34.

The upper electrode 36 has a planar shape as shown in FIG.
An elongated hole 41 with a width of about three strokes is provided, and the electrode can be rotated within a range of 180 degrees around the center line of the electrode.

Further, a semicircular window 33 is provided at the top of the vacuum chamber.

Next, depth measurement when etching the pattern shown in FIG. 8 on the object to be etched 58 will be described. This figure shows a case where the area of the etched portion is 1% of the total area.

As a coherent light source, H with a wavelength of 0.6528 μm is used.
A-ML laser is used.

FIG. 11 is a diffraction image at the surface 66 in FIG. 6, and bright patterns are generated on the lattice points as indicated by white circles in FIG. FIG. 12 shows the intensity pattern on the X-axis of FIG. 11 at this time. The distance between the peaks is 56° from equation (4).
It is. In addition, the diffraction images of area 19 (portion to be diffracted in the non-etched part) and area (etched part) 18 in FIG. 8 are curves 26 and 27 in FIG. 12, respectively. (A non-etched portion and a non-diffracted portion) 20 is added to the reflected light. -Also, since area 19 is ten times larger than area 18, the integral value of song @26 is ten times that of curve 27.

In FIG. 12, peak 29o and peak 30 have approximately the same intensity. In other words, the amount of light incident from the area (etched part) 18 and the area (portion to be diffracted by the non-etched part)
Since the amount of light incident from the point 19 becomes approximately the same, it is sufficient to set the positions of the electrode 36 and the sensing section 32 so as to capture the light reaching this point. When the intensity change of the interference light is measured while etching the object 38, the depth of the etching is calculated from the phase as shown in FIG.

Actually, the light reflected by the object to be etched 38 is expressed by the following formula due to the difference in refractive index between the resist 21 and the processing atmosphere 37, the reflected light from the surface 57, and the etching of the resist 21. The amount of light changes depending on the amount of light.

zxlγt asp(we-(n-1)αvtt)+7
r gap (wt+vlt) +γz asp(TR1-α11tsu1 friend=γtl +
, 1. R+γ,2 +2γ,y,C0t((1-(s-1)α)uz4)+
2γyγICO'(('-α)vzQ+21,11C6
1(nαvtQ (51) where tl, γr1γI are the rates of light reflected back from the surfaces 23, 22, and 57, respectively, W is the original velocity, L is the refractive index of the resist with respect to the processing atmosphere, and α is , the etching selection ratio between the resist 21 and the object to be etched 56, 11t is the etching speed of the object to be etched, and t is the time.

Therefore, it is possible to correct the formula (5), but γ, 2γr〉
Since γI(6), correction using the following equation is sufficient.

Wγ−+γr2+2γ−γrCoI((1−(w−1)
α)vg') +7+i.e., (nl
) is detected shallower by αvgt. When n21 or α×1, it can be ignored.

In addition, in this example, when etching a fine pattern on a complex pattern, it is difficult to predict a pattern in which changes in light intensity can be detected due to non-calculations, so the pattern is etched in advance and the light intensity is It is necessary to search for a pattern with large changes and set a sensing section at that position.

In such a case, the pattern is a combination of diffracted lights from patterns having various widths d. Only the following five cases are problematic here, but changes in light intensity can be detected for each reason.

First, consider a case where there are many etched portions.

In this case, from Equation (4), although the number of peaks in the diffraction pattern created by the etched portion is reduced, there is a point where the light intensity is about the same, which poses a problem. Consider the case where there are patterns having the same width dt, and the number of patterns is several times larger than the number of etched parts. At this time, since the number of peaks in the diffraction patterns created by these patterns is a fraction of the number according to equation (4), there are peaks that do not include the diffracted light from these patterns.

Thirdly, if there is a pattern with a width d comparable to that of the etched portions, and the number of patterns is equal to or less than the number of etched portions,
Since the area ratio itself is not large, it is possible to detect changes in light intensity.

Fourthly, when the area of the etched portion is large, the area ratio is approximately the same, so the conventional interference method can be applied.

Fifth, since there are strains with different widths d of the pattern other than the etched portion, the position of the 0 point according to equation (3) is different.
There may be cases in which the synthesized diffraction pattern does not have a zero point. In this case as well, the envelope of the 6-width diffraction pattern -
Therefore, the peak light amount that appears at the position past the 0 point can be calculated using the formula (2
) As can be seen, the intensity of the diffracted light from the etched part is a few percent of the zero-order light intensity, so the intensity of the diffracted light from the etched area is
There is a peak that is about -niO times larger, and it is possible to detect changes in light intensity.

For the above reasons, even when etching a single minute pattern on a complex pattern, it can be considered that there is always a diffraction pattern in which changes in light intensity can be detected.

Furthermore, it goes without saying that when etching the same type of object to be etched, there is no need to change the position of the sensing section.

In the embodiment described above, since a beam of coherent light with a diameter of about 1 to 3 mm is irradiated, the pattern of the etched object needs to be arranged regularly in the range irradiated with the beam. There is. Therefore, the material to be etched must be a memory wiring pattern, a deep trench for element isolation, a through hole, or other pattern.

However, it has the advantage that what is irradiated is a beam and the device is simple.

Furthermore, even if the beam irradiation position moves within a regular pattern during measurement, there is no problem with the measurement, and even if the distance between the lens and the etched object changes slightly, the measurement will not be affected. has the advantage of not causing any problems.

Next, a second embodiment will be described using FIGS. 14 to 17.

The second example is a case where there is a diffraction pattern in which only the light from the etched part is strong, that is, the number of repetitions per unit length (spatial frequency) of the etched part is different from that of other patterns. The effect is large when the spatial frequency is smaller than .

Consider the diffraction pattern of the pattern shown in FIG. FIG. 16 is a sectional view of FIG. 15.

In this case, the spatial frequency of the non-etched portion 67 is different from that of the etched portion 68.
This is because the wave number is twice as large as the opening wave number.

The intensity distribution of the diffraction pattern is as shown in FIG. 17 based on equation (2). In Fig. 17, the first curve 7o is the etched portion 67.
], and the curve 84 is the envelope. A curve 69 is a diffraction image formed by the non-etched portion 68, and a curve 8
3 is the envelope. The two curves are combined to form a curve 71
is formed.

In this case, it means that the light reaches only the ij1 etched areas such as the peak 72.

Therefore, for example, if the beam 720 yuan is made to interfere with the attenuated light of the beam 73, a large rate of change in intensity can be obtained.

In this embodiment, the main body of the dry etching apparatus, coherent light source, sensing section, and detection processing section are the same as those of the first embodiment. Attenuator 44 with ND filter, half mirror
43 is installed.

The light from the etched portion is reflected by the half mirror 43 and reaches the optical axis 58, and the light from other patterns is attenuated 644.
The light passes through the mirror 42 and the half mirror 46 and reaches onto the optical axis 5B, where they interfere with each other. The following detection is based on the first example.

In the third embodiment shown in FIG. 18, light from other than the etched portion, that is, reference light, is applied to the second embodiment.
This uses coherent light before it reaches the etching target 59. The reference source passes through the half mirror 45 and the attenuator 46 and reaches the 9 sensing section. The other configuration and operation are similar to the second embodiment.

In addition to having the functions of the second embodiment, this embodiment has the effect that there is no need for correction because there is no change in the reference light conditions due to the resist.

A fourth embodiment will be explained using FIG. 19.

The fourth embodiment is also generally similar in configuration to the first embodiment, but has a special feature: Ln71 for the optical fiber 47t- is included in the detection section. The use of the optical fiber 47 has the effect of protecting the sensing section 60 and the detection processing section 61 from high frequency noise.

A fifth embodiment will be described using FIG. 20 and FIG. 21.

The fifth embodiment also has a general configuration similar to the first embodiment, including a lens 48 and a nozzle mirror 49 provided on the upper electrode 52.
, a television camera 50, and a signal processing device 51.

The lens 48 has a diameter of several brocades, and its focus is on the object 53 to be processed.
It is located at the top. Alternatively, the focus may be slightly removed and the focal length may be slightly longer so that the beam diameter of the coherent light is approximately 0.5 to 1 u on the object 53 to be processed, or 54 in FIG. 55 is processed into a flat surface with a diameter of about 3 to 4 dragons.

During etching, the light that reaches the object to be processed 53 is reflected and diffracted,
The light reaches the lens 48 and is made into a group of parallel lights by the lens 48. The light beams pass through the half mirror 49 and reach the television camera 50, where a plurality of diffraction patterns are captured.

These patterns are subjected to signal processing during etching, and patterns in which the light intensity changes are extracted and detected.

In other words, changes in light intensity can be detected without having to search for patterns in which light intensity changes.

As described above, the embodiments Fi shown in FIGS. 6, 14, 18, 19, and 20 are effective only when the etching pattern of the object to be etched is arranged regularly. This is a great method. However, the present invention can also be used to measure etched patterns of minute areas that are irregularly arranged within an irregular pattern.

Let us consider the case where the portion to be etched is etched in a pattern having a planar shape and a cross-sectional shape as shown in FIGS. 26 and 24.

Consider the case where the region 75 in FIG. 23 is irradiated with light.

As in the above example, according to equation (2), the light reflected from the etched portion 74 forms a pattern within the envelope curve 6!1 in FIG. 5, and the other patterns form within the curve 62. Create a pattern within the envelope.

Therefore, in the vicinity of one point 64, the intensities of the two lights become equal.

The device configuration of this example is shown in the 22nd prisoner. The apparatus of this embodiment is similar to the embodiment shown in FIG.
A coherent light source 76 is set on the object to be etched 81 to have a beam diameter ranging from several μm to about 100 μm in diameter, and the beam diameter can be varied by changing the position of the lens 82. That is, the lens 82 is set at a position where it focuses on a point that is several steps away from the object 81 to be processed. Although the beam diameter of the beam emitted from the coherent light source 76 is several degrees, it is converted into a parallel beam of about 0.5 mm by the lens system 77 and enters the lens 82 . By doing this, even if the distance between the lens 82 and the etched object 81 changes somewhat,
The beam diameter on the object to be etched 81 hardly changes.

At this time, the reflected and diffracted tail light is parallelized by the lens 82, reflected by the half mirror 7B, and received by the television camera 79. The received signal is processed by the signal processing system 80)
The original intensity changes are extracted and detected.

In this embodiment, if an etched portion exists, the depth can be measured even if coherent light is irradiated to the area where b is present.

In addition, since the pattern does not need to be regular in this example, it can be used to measure the etching depth when etching through holes in semiconductor devices other than memories, deep grooves for element isolation, and element patterns. can.

〔Effect of the invention〕

According to the present invention, when measuring the depth of etching by interferometry in the etching process during the manufacturing of semiconductor devices, even if the area of the etched part is minute, Since the intensity of the emitted light and the original emitted from the non-etched area can be made to be the same, it is possible to measure the depth of through-holes and deep grooves for element isolation, where the area of the etched area is minute, using interferometry. Become.

In particular, deep grooves for device isolation could not be measured using conventional scanning electron microscopes or other optical microscopes, and could only be measured by destroying them, but now they can be measured using non-elutriation in-process methods. It's now possible.

[Brief explanation of drawings]

Fig. 1 is a vertical cross-sectional view of the conventional example, Fig. 2 is a longitudinal cross-sectional view of the object to be etched, Fig. 3 is a graph showing intensity changes of interference light, and Fig. 4 is a graph showing a multi-slit diffraction pattern. , FIG. 5 is a graph showing the diffraction patterns of two single slits with different widths, FIG. 6 is a longitudinal cross-sectional view of the example, and FIG. 7 is a plan view of the electrode.
Fig. 8 is a plan view showing an example of the etching pattern, Fig. 9 is a vertical sectional view of Fig. 8, Fig. 10 is a plan view showing the area where the pattern is formed, and Fig. 11 is a diffraction pattern on a screen. Figure 12 is a graph for explaining the diffraction pattern in Figure 8, Figure ε is a graph showing changes in the intensity of interference light, Figure 14 is a longitudinal cross-sectional view of the example, and Figure 15 is an eclipse. A graph showing an example of the engraving pattern, FIG. 16 is a vertical cross-sectional view of FIG. 15, FIG. 17 is a graph for explaining the diffraction pattern of FIG. 15, FIG. 18 is a vertical cross-sectional view of an example, and FIG. 20 is a longitudinal sectional view of the embodiment, FIG. 21 is a diagram showing the shape of the lens, FIG. 22 is a longitudinal sectional view of the embodiment, and FIG. 25 is a longitudinal sectional view of the embodiment. A diagram showing an example, FIG. 24 is a longitudinal sectional view of FIG. 23. 31... Coherent light source 32... Sensing part 1
Figure 3 Figure ζ (Time z Figure 4 The big mouth of the mouth) Figure 5Iii2] θ Placement of statues Figure 6 $BWJ 9 Figure q !t Figure 0000000 o Oo o Oo O o 0 00-←To÷-→Toyuχ 0000000 o o o o Oo . Time #I product 1.'i'i, t θ 13th TljU (ginban) Plexus I4th 15rB [Figure 16 #Body 212 θ 楕 /F31;4 1 /'? fl 65 6/ Figure 21 4 $22 Figure 23 Figure 5 24th Proceedings Amendment (Spontaneous) Case Indication 1988 Special ii'l Application No. 194312 Name of the invention Relationship between the method for measuring the etching depth of a semiconductor device and the person and time who corrects the device Name of patent applicant (5101 Co., Ltd.!1) Manufacturing company representative person 1 ,++ rrI〒l■Chiyo, Tokyo "1-ku Marunouchi-chome-5-1 Danritsu Co., Ltd. f+Internal phone number 11;・
212-1111L major representative) Subject of amendment Contents of amendment in the detailed description of the invention column 1 of the specification Page 5, lines 7 and 8 [Iocl〆I
rl XP (L(t)t) 〆yllXp (i Cω
t+7a(t)))l''J as [IocVT;'-p(L
ωt)+i'i;1txp<i<ωt+7δ(t))]
Correct it with J. 2. Correct “I=” on page 7, line 17 of the specification to [1”-J. 3. Correct “color 64” on page 9, line 2 of the specification to “dot 64.” 4. , page 12 of the specification, lines 7 to 13, “Ioc
(rl g3:p(wt-CrL-1>αvlt)+r
rexp<wt+vlt)+r, exp<wt-αva
t>l"=rt"+r,'+r,"+2
rtrr cos(< 1-(W-1)α), "zQ+
2r, f, cllll! ((+-α)vat) 12r, r
las (nαvat) (5)j to 2r*rpc
m ((d0+ ('-2)vat) ) (Corrected as 51J. 5. Specification, page 12, line 14 [tAs "re"
# Correct J to [y, gr,, y, J - 6 #4 Correct "W" in the 15th line of page 12 of the specification to "ω". l In the specification, page 12, line 18, "υL" is corrected to "rdo is the initial film thickness of the resist, and V- is". 8. Specification, page 13, line 2 [I″r, +r,”+2rarrco! ((1(n-1
) α) Sheet t) (7) J as “Ioc r, * + r, *
+2r4rraa (T(vat −(do−αν#
t) (ru'-1))) (7) Correct it as J. 2. In the third line of page 15 of the specification, "(roux 1) shallow by αvat" is corrected to "(guo-1) shallow by (do-αvat)".

Claims (1)

[Claims] t. Of the diffraction patterns obtained by irradiating the semiconductor device with light while etching the etched pattern of the semiconductor device and reflecting it from the semiconductor device, diffraction from the etched portion A method for measuring the etching depth of a semiconductor device, characterized in that the etching depth is measured by detecting a change in light intensity in a portion where the light intensity of the light and the diffracted light from the non-etched portion are approximately the same. 2. The etching of the semiconductor device according to claim 1, wherein the portion where the light intensity is the same is a portion where diffracted light other than the 0th order of the diffracted light is obtained. Depth measurement method. (v) Irradiation means for irradiating light onto a pattern consisting of an etched portion and a non-etched portion of a semiconductor device, and a beam of light emitted from the etched portion and the non-etched portion of the non-zero-order diffraction pattern. An etching device for a semiconductor device comprising an interference means for making the intensity of light beams emitted from a coherent light source or a coherent light source the same and causing interference, and a sensing means for sensing a change in light intensity obtained by the interference means. Depth measuring device. 4. The etching depth measuring device for a semiconductor device according to claim 3, wherein the irradiation means includes a variable means for varying the magnitude of the luminous flux of the light.