JP2001118832A - Method and instrument for measuring depth of etched groove, film thickness, and step - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and instrument by which the depth of the groove of an insulating material formed on a substrate can be measured accurately without being affected by an underlying wiring structure and a technology by which the height of a formed step or the thickness of a formed film can be measured. SOLUTION: A section to be measured is measured in such a way that measuring light having a wavelength in a region in which the light is not affected by wiring 3 and 3a-3f and polarized in the width wise directions of grooves 4a, 4c, 4c-4n, 5a, 5b, 5c-5n, 6a, 6b, 6c-6n,..., 32a, 32b, 32c-32n, 33a, 33b, and 33c-33n is projected upon the section at right angles and the section is measured based on the intensity of the reflected light from the section.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to measurement of an etching depth, a film thickness and a step of an insulating film on a wiring of a semiconductor substrate, and more particularly, to an etching depth for measuring a depth of a groove of an insulating film during etching in real time. The present invention relates to a measurement method, a method for measuring the thickness of an insulating film formed in a film forming step, and a method for measuring a step of an insulating film formed in an etching step.

[0002]

2. Description of the Related Art In a wiring process for a semiconductor substrate, as the miniaturization progresses, a conventional processing method of etching a metal film formed to form a wiring has an excessively large aspect ratio. Good shape cannot be obtained.

Therefore, a groove is formed in an insulator formed on a Si substrate in advance, and a metal layer for wiring including the inside of the groove is formed on the insulator.
This metal layer is uniformly polished to the surface of the insulator by CMP (Chemical Mechanical Polishing), thereby removing the wiring metal on the insulator and leaving the metal only in the grooves formed in the insulator. (Damascene process). In this case, since the electric resistance of the wiring metal is determined by the cross-sectional area of the wiring, it is necessary to control the depth of the groove of the insulator with high precision.

FIGS. 14A and 14B are schematic sectional views showing a process for forming a groove in an insulator.
14A shows the state before the groove is formed, and FIG. 14B shows the state after the groove is formed. That is, as shown in FIG. 14A, an insulating layer 54 made of an insulator is formed on a Si substrate 51 placed in an etching chamber (not shown) so as to surround the conductor wiring 52. . In this state, a mask 55 having a pattern of a groove to be etched is placed on the insulating layer 54 to perform etching. Thus, as shown in FIG. 14B, an etching groove 56 corresponding to the mask pattern is formed in the insulating layer 54 at a predetermined depth.

In these etching processes, the depth is measured and monitored during the process so that the etching groove 56 to be formed has a predetermined depth, and the end of the etching process is controlled.

As shown in FIG. 15A, the principle of measuring the depth of the etching groove 56 during the etching process is to irradiate the Si substrate 51 during the etching process to obtain two reflected lights R ₁ from the Si substrate 51. It is performed by detecting the R _2.

That is, the two reflected lights R ₁ and R ₂ are reflected light R ₁ from the bottom of the etching groove 56 during etching and reflected light R ₁ from the mask 55 on the surface of the Si substrate 51.
₂ , interference light is generated by an interference phenomenon between the _two reflected lights R ₁ and R ₂ and detected by the optical sensor 57. This interference light periodically changes in intensity as the etching groove 56 being processed becomes deeper. In addition, the amount of change in the depth when the interference light changes by a half cycle (or one cycle) between the poles is physically determined, and the ratio of the etching rate of the layer where the etching groove 56 is formed to the etching rate of the mask 55 is determined. In the case where the etching selectivity is infinite, it means that the irradiated single wavelength light is １ ／ deeper. Thus, the depth of the etching groove 56 can be measured.

As described above, the depth of the etching groove 56 during processing is measured, and as shown in FIG. 15 (b), the etching depth is compared with a calculated reference value to confirm, and the end point of the etching process is determined. Controlling. In this confirmation, since the cycle time of the intensity waveform of the interference light and the etching depth for each cycle time are known, the etching depth for each unit time can also be calculated. Can be.

The mask 55 is etched by selecting a material which is harder to be etched than the layer in which the etching groove 56 is formed in the mask 55 so that the etching does not progress. Depending on the material of the layer in which the groove 56 is formed, the mask 55 may be considerably etched. The etching speed of the mask 55 is the etching speed at that time.

[0010] Known materials related to these are (1) JP-A-60-86833 and (2) JP-A-61-290308.

In the method (1), during the etching process, a change in the light intensity of a portion where the light intensity of the diffracted light from the etched portion and the light intensity of the diffracted light from the non-etched portion is substantially the same is detected and the etching is performed. A technique for measuring depth is disclosed.

(2) means for irradiating the sample surface being etched with coherent light vertically to 65
A technique using a laser beam emitting a wavelength shorter than 3 nm is disclosed.

[0013]

However, when the method of forming the groove depth during the etching process is applied to the process of forming the groove in the insulating layer shown in FIG. 14, the layer forming the groove is an insulator. Therefore, at the bottom of the groove, all light is transmitted without being reflected. Therefore, as shown in FIG. 16, the light is affected by the fine structure of the wiring 52 formed on the underlying Si substrate 51, and causes complicated behavior such as diffraction and scattering in the insulating layer 54. In addition, the depth signal shown in FIG. 15B becomes complicated, and it becomes difficult to calculate the depth from the signal of the optical sensor. Reference numeral 55 denotes an insulating mask.

Further, in the structure shown in FIG. 14, only one layer of wiring is formed below the insulating layer. In general, however, four or five layers of wiring may be stacked, and the depth signal is The situation becomes more complicated, and in such a case, as a practical matter, it becomes impossible to calculate the depth from the signal of the optical sensor.

The present invention has been made based on these circumstances, and a method and apparatus for accurately measuring the depth of a groove of an insulator formed on a semiconductor substrate without being affected by a lower wiring structure. It is another object of the present invention to provide a technique for measuring a formed step and a film thickness.

[0016]

According to the first aspect of the present invention, a wiring made of a conductive material or a semiconductor material is formed inside a groove, and a dielectric surface formed on the wiring and a dielectric surface formed on the wiring. Light is irradiated to the etching groove or the step applied to the dielectric surface, and at least one of the depth of the etching groove, the depth of the step, and the film thickness of the formed dielectric is reflected by reflected light. In the method of measuring the depth of the etching groove, the step, and the film thickness, measuring the values of the two measured portions, the measurement is performed in a region where the wavelength of the light is not affected by the wiring at the time of measurement, and the wiring is formed. Using light polarized in the width direction of the groove, irradiating the light to the portion to be measured substantially perpendicularly, and measuring the value based on information on reflected light from the portion to be measured. Etch groove depth, step and It is a method of measuring the thickness.

According to the second aspect of the present invention,
The wavelength of the light is in a region that does not enter the inside of the groove in which the wiring is formed, and is a method of measuring the depth, step, and film thickness of an etching groove.

According to the third aspect of the present invention,
The method of measuring the depth, step and film thickness of an etching groove, wherein the wavelength of the light is larger than twice the value of the width of the groove in which the wiring is formed.

According to the means of the invention of claim 4,
A wiring made of a conductive material or a semiconductor material is formed inside the groove, and light is applied to a dielectric surface formed on the wiring and an etching groove or a step processed on the dielectric surface, and reflected light is applied. The depth of the etching groove, the depth of the step, or the film thickness of the formed dielectric is measured at least one value of a portion to be measured, and the measurement of the etching groove depth, the step, and the film thickness is performed. In the apparatus, the measurement uses light polarized in the width direction of the groove in which the wavelength of the light is not affected by the wiring at the time of measurement and the wiring is formed, and the light is transmitted to the measurement target portion. An apparatus for measuring an etching groove depth, a step, and a film thickness, which irradiates substantially vertically, and measures the value based on information of reflected light from the measured portion.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

First, the basics of the principle of measuring the depth of a groove or the like according to the present invention will be described.

FIG. 1 is a schematic sectional view of an object to be measured for measuring the depth of a groove or the like. SiO ₂ layer 2 is formed on a Si substrate 1, a groove 4a that Al wiring 3 formed thereon has a predetermined groove width _{W 1,} 4b, are formed separately by 4c ... 4n.

FIGS. 2A and 2B show grooves 4a, 4b and 4c between Al wirings 3 which are conductors of the device shown in FIG.
... The polarization direction of the light irradiated perpendicularly to the 4n repetition pattern is changed to the groove width direction (0 °, 180 °) and the groove length direction (90
And 270 °) is a graph showing the spectral reflectance (light intensity) for each wavelength of the irradiation light when it is changed to 270 °. Note that FIG.
FIG. 2A shows a case where the groove width is 0.35 μm, and FIG.
FIG. 2C shows the case where the groove width is 0.30 μm, and FIG. 2C shows the case where the groove width is 0.15 μm.

As can be seen from these graphs, when the polarized light is irradiated in the groove length direction, the spectral reflectance changes due to the difference in the groove width, but when the polarized light is irradiated in the groove width direction, the spectral reflectance changes. Even if it does not change. Particularly in the wavelength region longer than twice the groove width, the three graphs almost coincide. This means that when the irradiation polarization is set to the groove width direction and the wavelength is longer than twice the groove width, the irradiation light is emitted to the grooves 4a, 4b, 4c.
It is considered that the light is reflected near the entrances of the grooves 4a, 4b, 4c,. In other words, this means that the reflected light is not affected by the structure of the layers formed below the entrances of the grooves 4a, 4b, 4c... 4n.

FIG. 3 shows a case where the object to be measured is a dielectric. That, Si SiO ₂ layer 2a on the substrate 1a is deposited, a groove 5a of the groove width _{W 2} on the SiO ₂ layer 2a, 5b,
A repeating pattern of 5c... 5n is formed. FIG.
FIG. 7 is a graph showing the spectral reflectance when the irradiation direction is changed to the groove width direction (0 °) and the groove length direction (90 °) when the groove width W ₂ is 0.2 μm. is there. As shown in this graph, in the case where the measured object is the grooves 5a, 5b, 5c,.
The influence of the reflectance by the polarization direction is very small, and even light having a wavelength longer than twice the groove width interferes with the grooves 5a, 5b,
5n indicate that it is possible to enter the inside of 5c... 5n.

[0026] Based on the above results, a side schematic view in FIGS. 5 (a) as an object to be measured, an arrow as shown cross-sectional view at A, a predetermined groove width W ₃ on the Si substrate 1b in (b) Groove 6a,
6b, 6c... 6n are formed by forming Al wirings 3a, and an SiO ₂ layer 2b is formed thereon. The object to be measured is placed on a table of an etching chamber (not shown), and when the etching is being performed, the polarization direction is the groove width direction via the insulating mask 7 from above and the groove width direction is 2 mm. The depth of the etching grooves 8a, 8b, 8c... 8n is measured by using light having a wavelength longer than twice as irradiation light.

In this case, the irradiation light is applied to the grooves 6a, 6b, 6c.
Light does not enter the inside of 6n, but is reflected near the frontage of the grooves 6a, 6b, 6c... 6n. In other words, optically the Al wiring 3
There is no structure below the surface of a. Therefore, the reflected light from the groove bottom for measuring the depth of the etching grooves 8a, 8b, 8c... 8n is not affected by the Al wiring 3a, and diffraction and scattering due to the light do not occur.
As the etching progresses, the etching grooves 8a, 8b, 8
.. 8n can be accurately measured for the etching grooves 8a, 8b, 8c... 8n.

As shown in FIG. 6 (a) as a schematic side view and FIG.
The etching grooves 8a, 8b, 8c... 8n of the _two layers 2b and Al
Since the groove 6a of the wiring 3a, 6b, the direction of 6c ... 6n be orthogonal, etched groove 8a formed on the SiO ₂ layer 2b, 8b, 8c ... 8n is hardly affected by polarization, polarization direction To grooves 6a, 6b, 6c of Al wiring 3a
.. 6n, the same operation as in FIG. 5 can be obtained. The same functional portions as those in FIG. 5 are denoted by the same reference numerals.

The depth of the groove during the above-mentioned etching process
The measurement principle itself uses commonly used ones.
I use it. As shown in FIG.
Irradiate the Si substrate 1c during the chucking process to
Reflected light R from₁, R ₂By detecting
Is going.

That is, the two reflected lights R ₁ and R ₂ are used as the etching grooves 9a, 9b, 9c.
reflected light from the n bottom _{R 1} and Si mask on the surface of the substrate 1c 7
is formed by the reflected light R ₂ from a, 2 two reflected light R
₁ , an optical sensor 1 that generates interference light due to the interference phenomenon of R ₂
0 is detected. This interference light is applied to the etching groove 9 during processing.
As the depths a, 9b, 9c,. Moreover, the amount of change in the depth when the interference light changes by a half cycle (or one cycle) between the poles is physically determined, and the etching rate and the mask of the layer in which the etching grooves 9a, 9b, 9c. When the etching selectivity, which is the ratio of the etching rates of 7a, is infinite, it means that the irradiated single wavelength light is 深 く deeper. Thereby, the depths of the etching grooves 9a, 9b, 9c... 9n can be measured.

As described above, the etching grooves 9a being processed are
The depths of 9b, 9c... 9n were measured, and as shown in FIG. 7B, the etching depth was compared with a calculated reference value and confirmed.
It controls the end point of the etching process. In this confirmation, since the cycle time of the intensity waveform of the interference light and the etching depth for each cycle time are known, the etching depth for each unit time can also be calculated. Can be.

In the etching of the mask 7a, a material which is less likely to be etched than the layer in which the etching grooves 9a, 9b, 9c... 9n are formed in the mask 7a is selected.
Although the etching is prevented from proceeding, the mask 7a may be considerably etched depending on the material of the layer in which the etching grooves 9a, 9b, 9c... 9n are formed during the etching. The etching rate of the mask 7a is the etching rate at that time.

Next, the measuring apparatus of the present invention will be described. FIG. 8 is a schematic diagram of a measuring device showing an embodiment of the present invention.

The structure of the measuring apparatus is roughly divided into a depth calculating section 23 connected to a measuring head 22 fixed to an upper portion of a chamber 21 of an etching apparatus (not shown).

An Si substrate 1d on which a groove is formed by etching is set in the chamber 21. An observation window 24 made of quartz glass is provided above the chamber 21, and a measuring head 22 is connected to an upper surface of the observation window 24.

As shown in FIG. 9, the measuring head 22 can change the irradiation position of the measuring probe light on the object to be measured by the provided automatic XY stage 25.

The measuring head 22 moves according to the traveling direction of light.
Tungsten lamp 26, optical fiber 27, lens 2
8, polarizer 29, interference filter 30, and photodetector 31
It is composed of The ultraviolet light output from the tungsten lamp 26 passes through an optical fiber 27, is further collimated into parallel light by a lens 28, is changed to linearly polarized light by a polarizer 29, and is vertically passed through an observation window 24 as a Si substrate which is an object to be measured. Irradiate 1d surface. The reflected light from the Si substrate 1d travels in the same optical path as the irradiation light in the opposite direction, and enters the photodetector 31 through the optical fiber 27.

In the interference filter 30, only light of a specific wavelength is transmitted, and the transmitted reflected light is input to the photodetector 31. The photodetector 31 is configured to output an electric signal corresponding to the intensity of the received reflected light.

According to these configurations, first, before the etching by the etching apparatus is started, the probe light for measuring the depth of the depth measuring apparatus is applied to the portion (cell) of the Si substrate 1d where the groove (not shown) is formed. The XY stage 25 is moved to the measurement position so as to irradiate and enter the photodetector 31. Next, when the etching starts, the signal of the photodetector 31 is input to the depth calculator 23. The depth calculator 23 detects an extreme point of the depth signal that becomes a periodic signal.

In the depth calculation, as described in the background art, when the signal changes by a half cycle (or one cycle), the depth is determined assuming that the depth has changed by the depth calculation reference value. As the depth calculation reference value, an output value from a depth calculation reference value correction unit (not shown) is used.

The reference value for calculating the depth by detecting a pole at the depth calculator 23 is calculated by calculating the average of the reference values obtained while the depth signal changes from the pole to the pole. Used.

Next, a case where the present invention is applied to film thickness measurement and step measurement will be described. Both the film thickness measurement and the step measurement are not performed during the processing, but are each performed after the processing is completed, that is, after a predetermined film thickness or a step is formed. In addition, each of the measurement lights uses polychromatic light.

FIG. 10A is a schematic explanatory view of the principle of measuring the film thickness, and FIG. 11A is a schematic explanatory view of the principle of measuring the level difference.
In each case, the measured object was Al on the Si substrates 1e and 1f.
The wirings 3e, 3f are grooves 32a, 32b, 32c ... 32n,
33n, 33a, 33b, 33c... 33n. Furthermore, SiO ₂ layers 2e and 2f are formed thereon, and the formed SiO ₂ layers 2e and 2f are targets.

That is, polychromatic light is irradiated onto the SiO ₂ layers 2e and 2f formed on the Si substrates 1e and 1f, and each reflected light is detected and separated. FIG. 10
A theoretical waveform is obtained by curve fitting that minimizes the difference between the spectral signal shown in FIG. 11B and the spectrum signal shown in FIG. 11B, and the actual waveform is obtained from the film thickness or the step value used for calculating the theoretical waveform. Can be obtained.

That is, a spectrum signal waveform f (film thickness (step) d ₀ , wavelength λ) detected by a spectroscope (not shown)
And the theoretical waveform f (d
₀ ^′ , λ), and a theoretical waveform curve that minimizes the difference between the two curves is selected.

Each case will be further described. FIGS. 12 (a) and 12 (b) are schematic diagrams in the case of film thickness measurement, FIG. 12 (a) is a side sectional view, and FIG. FIG.

[0047] That is, formed on the lower portion of the SiO ₂ layer 2e for measuring, grooves 32a, 32 b, 32c ... polarized in the groove width direction of the Al wiring 3e are separated by 32n, and 2 times the groove width _{W 4} Using longer multi-wavelength light for irradiation light,
When irradiated from above the SiO ₂ layer 2e, the irradiated light does not enter the grooves 32a, 32b, 32c... 32n between the Al wirings 3e but is reflected near the frontage of the grooves 32a, 32b, 32c. FIG. 10 when measuring the film thickness
The theoretical waveform shown in (b) may have a structure in which the portion below the Al wiring 3e is ignored.

FIGS. 13 (a) and 13 (b) are schematic diagrams in the case of step measurement, and FIG. 13 (a) is a side sectional view of FIG.
FIG. 3B shows a cross-sectional view taken along arrow A.

[0049] That is, polarized formed in the lower portion of the step of measuring, grooves 33a, 33b, the groove width direction of the Al wiring 3f which are separated by 33c ... 33n, and groove width _{W 5}
When the multi-wavelength light longer than twice the wavelength is used as the irradiation light and the irradiation is performed from above the step, the irradiation light is applied to the groove 33 between the Al wirings 3f.
a, 33b, 33c... 33n, without entering
33a, 33b, 33c... 33n are reflected near the frontage, so that the theoretical waveform shown in FIG. 11 (b) when measuring a step may have a structure in which the portion below the Al wiring 3f is ignored.

Although the basic configuration shown in FIG. 8 does not change in any case as the measuring apparatus, the measuring head shown in FIG. 9 uses polychromatic light as the irradiation light, so that the interference filter is not used. And a photodetector uses a spectroscope.

In each of the embodiments described above, the case where the Al wiring is used as the base wiring has been described, but it goes without saying that the same can be applied to the case where the Cu wiring or the Au wiring is used.

As described above, in the prior art, if there is an underlying wiring pattern, the reflected light behaves in a complicated manner, so that high-precision measurement is impossible. Since it is not affected by the underlying wiring, highly accurate measurement is possible.

[0053]

According to the present invention, it is possible to accurately measure the depth, the film thickness, and the step of the groove of the insulator formed on the semiconductor substrate without being affected by the lower wiring structure.

When the measuring means according to the present invention is used in an etching apparatus, the end of the etching process can be accurately detected.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of an object to be measured.

FIGS. 2A to 2C are graphs of spectral reflectance (light intensity) for each wavelength of irradiation light with a changed groove width.

FIG. 3 is a schematic cross-sectional view of a measured object of a dielectric.

FIG. 4 is a graph of spectral reflectance (light intensity) for each wavelength of a dielectric body to be measured.

FIG. 5 (a) is a schematic explanatory view of depth measurement according to the present invention, and (b)
Sectional drawing in A section.

6A is a schematic explanatory view of depth measurement according to a modification of the present invention, and FIG.

FIG. 7A is a diagram illustrating the principle of measuring depth, and FIG. 7B is a graph illustrating the principle of measuring depth.

FIG. 8 is a schematic diagram of a configuration of a measuring apparatus according to the present invention.

FIG. 9 is a configuration diagram of a measuring head of the present invention.

FIG. 10 (a) is a schematic explanatory view of film thickness measurement of the present invention,
(B) Explanatory drawing of curve fitting.

FIG. 11A is a schematic explanatory view of step measurement according to the present invention;
(B) Explanatory drawing of curve fitting.

FIG. 12 (a) is a schematic explanatory view of the film thickness measurement of the present invention,
(B) Sectional view in A section.

FIG. 13 (a) is a schematic explanatory view of step measurement according to the present invention,
(B) Sectional view in A section.

14A and 14B are schematic explanatory views of a groove forming process, in which FIG. 14A shows a state before forming a groove and FIG.

15A is a diagram illustrating the principle of measuring depth, and FIG. 15B is a graph illustrating the principle of measuring depth.

FIG. 16 is an explanatory diagram of a problem in the related art.

[Explanation of symbols]

1, 1a-1f... Si substrate, ₂ , 2a-2f.
Layer, 3, 3a-3f ... Al wiring, 4a, 4b, 4c-4
n, 5a, 5b, 5c to 5n, 6a, 6b, 6c to 6
n,... 32a, 32b, 32c to 32n, 33a, 33
b, 33c to 33n: groove, 7: mask, 8a, 8b, 8
c to 8n, 9a, 9b, 9c to 9n: etching groove, 1
1: optical sensor, 22: measuring head

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2F065 AA25 AA30 BB18 CC17 EE00 FF44 FF49 FF51 FF61 GG02 GG21 GG24 HH03 HH09 HH13 JJ01 JJ02 JJ09 LL02 LL04 LL22 LL33 LL67 PP03 PP11 Q4842M04A06 DJ01 CB09 EB03

Claims (4)

[Claims] A wiring made of a conductive material or a semiconductor material is formed inside a groove, and light is applied to a dielectric surface formed on the wiring and an etching groove or a step applied to the dielectric surface. Irradiating, measuring the value of one measured part at least one of the depth of the etching groove or the depth of the step or the film thickness of the formed dielectric by reflected light, etching groove depth, In the method of measuring the step and the film thickness, the measurement is performed using light polarized in a width direction of the groove in which the wavelength of the light is not affected by the wiring at the time of the measurement, and the wiring is formed. Irradiating the measured portion substantially perpendicularly, the etching groove depth characterized by measuring the value based on the information of the reflected light from the measured portion,
Method for measuring steps and film thickness. 2. The etching light source according to claim 1, wherein the wavelength of the light is in a region that does not enter the inside of the groove in which the wiring is formed. Measuring method. 3. The etching groove depth and step according to claim 1, wherein the wavelength of the light is larger than twice the width of the groove in which the wiring is formed. And measuring method of film thickness. 4. A wiring made of a conductive material or a semiconductor material is formed inside the groove, and light is applied to a dielectric surface formed on the wiring and an etching groove or a step formed on the dielectric surface. Measuring the value of one measured part by at least one of the depth of the etching groove or the depth of the step or the film thickness of the formed dielectric by reflected light, etching groove depth, step And in the film thickness measurement device, the measurement is performed in a region where the wavelength of the light is not affected by the wiring at the time of the measurement, and using light polarized in the width direction of the groove in which the wiring is formed. Irradiating the measured portion almost perpendicularly, the etching groove depth characterized by measuring the value based on information of the reflected light from the measured portion,
Measurement device for steps and film thickness.