JP2003294431A - Method and device for measurement of pattern film thickness in semiconductor manufacturing process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a device for easily measuring film thickness of a miniaturized repetitive thin film pattern by using X-ray fluorescence measurement. <P>SOLUTION: This method is for using X-ray fluorescence to measure film thickness of a pattern structure section. However, an excitation X-ray 1 used as a probe should be of its beam diameter larger than the pattern dimension of the measuring object so that its irradiation range includes a number of repetitive patterns. Also, the plane directional dimension of the pattern should be used when converting the detected X-ray dosage into the film thickness. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for measuring a pattern portion film thickness in a semiconductor manufacturing process.

[0002]

2. Description of the Related Art In order to form semiconductor elements and wirings in semiconductor manufacturing, steps are repeated in the following order. First, a thin film is formed on the entire surface of the wafer by a film forming process. Next, a resist film is applied on the entire surface of the wafer, and exposure is performed according to the pattern shape by a lithography process to remove only the exposed resist portion or only the unexposed resist portion. Next, the thin film other than the portion protected by the resist film that has not been removed, that is, the thin film portion whose surface is exposed is removed by etching or the like.
Finally, the resist film remaining as a protective film during etching is removed. As a result, the exposure pattern is transferred to the initially formed thin film. A part of the thin film left without being removed is used as a semiconductor element or wiring. Since the surface of the pattern manufactured in such a process is protected by the resist, the film thickness is not changed by etching. Therefore, when it is desired to know the film thickness of the pattern portion, the film thickness of the thin film before pattern formation may be measured. For that purpose, methods such as 4-terminal resistance measurement, eddy current measurement, optical interference measurement, ellipsometer measurement, and fluorescent X-ray measurement are used.

[0003]

Recently, a method of embedding a metal in a groove portion removed by etching and using it as a wiring is also adopted. In this case, a metal thin film is formed on the entire surface of the wafer after removing the resist, and the metal thin film other than the metal filling the groove is removed by an etch back process or a CMP process. CMP is a Chemical Mec
The abbreviation of "hanical Polishing", the CMP process is a process of polishing the surface chemically and mechanically and smoothing the surface to smooth the surface. In these steps, it is basically necessary to remove all metal in a portion higher than the surface of the thin film forming the groove and leave a metal wiring having the same thickness as the thin film, that is, the depth of the groove. However, in reality, the surface of the thin film itself that constitutes the groove is partly removed, and similarly the film thickness of the metal wiring becomes thinner than the original depth of the groove. Further, the metal wiring portion may be removed more than the thin film surface, and the wiring film thickness may be further reduced. As described above, a situation occurs in which the film thickness of the metal wiring is different from the film thickness of the thin film forming the groove immediately after the film formation.

When it is attempted to measure the film thickness of the wiring pattern formed by the above steps, the conventional method for measuring the film thickness of the thin film before pattern formation has the following problems. Not available. First, the film thickness of the wiring pattern is different from the film thickness of the thin film before pattern formation. Therefore, measurement after pattern formation is required. Since it is necessary to measure a wide range of thin films with no structure in the surface direction in 4-terminal resistance measurement and eddy current measurement, it cannot be used after pattern formation. Secondly, the optical interferometry and ellipsometer measurement cannot measure a metal thin film because only a thin film that transmits light can be measured. Third, in fluorescent X-ray measurement,
The film thickness of each wiring can be obtained by using an excited X-ray having a beam diameter smaller than that of each wiring pattern, but it is not realistic to make the beam diameter as small as the pattern size.

Similarly, when the upper layer is selectively grown in accordance with the pattern structure, there is no wide-area thin film having no structure in the surface direction during the process, and therefore the same problem occurs when measuring the film thickness. .

An object of the present invention is to propose a method and apparatus for simply measuring the film thickness of a repetitive thin film pattern which has been miniaturized using fluorescent X-ray measurement, in order to solve the above problems.

[0007]

In order to solve the above problems, in the present invention, the film thickness of the pattern structure portion is measured using fluorescent X-rays. However, the structure is such that a large number of repetitive thin film patterns are included in the measurement region without gaps. Also, when converting the detected fluorescent X-ray dose into film thickness,
The in-plane dimension of the thin film pattern is used.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method of utilizing fluorescent X-rays for film thickness measurement is well known, but the physical measurement target is the number of atoms in the sample. It is assumed that the thin film to be measured is uniform in the excitation region irradiated with the excitation X-ray, and the atomic number density in the film is assumed, and the detected fluorescence X-ray dose is converted into the film thickness. Considering such restrictions, in order to measure the film thickness of a thin film having a pattern structure, the beam diameter of excited X-rays must be equal to or smaller than the pattern size. Since the pattern size to be actually measured is as small as 1 micrometer or less, it is not realistic to prepare such an excitation X-ray in a small analytical measuring device.

The present invention proposes, based on a new idea, fluorescent X-ray measurement for collectively measuring a region wider than individual pattern dimensions to be measured and determining the film thickness of the thin film pattern. The new idea is to remove the limitation that the object to be measured should be a uniform thin film in the measurement area, and to make a wide area where many patterns are repeated as the measurement area. The information obtained by the measurement is not the film thickness of each pattern, but the average film thickness of the patterns included in the measurement region. Therefore, it is not necessary to make the measurement region smaller than the size of the fine structure to be measured, and conversely, the greater the number of samples contained in the measurement region, the higher the accuracy of the average value, and therefore the wider the measurement region is desirable. Further, it is necessary to suppress the vibration so that the measurement position does not shift as the measurement area becomes smaller. However, in the present invention, such a requirement can be suppressed. Therefore, it is an excellent point of the present invention that it is easy to cope with further miniaturization of the pattern dimension to be measured.

The present invention will be described in detail below using mathematical expressions. First, the fluorescent X-ray dose detected by the fluorescent X-ray measurement is expressed as follows.

B = C · ∫∫∫ (a (x, y) · G1
(X, y, z)) ・ D (x, y, z) ・ (e (x, y)
-G2 (x, y, z)) dx-dy-dz (integration range:
(Entire measurement area × thickness) where B is the detected fluorescent X-ray dose, D (x, y, z)
Is the volume atom number density of the element to be measured in the film at the position (x, y, z), and (a (x, y) · G1 (x, y, z)) is the position (x, y, z). Excitation X-ray irradiation density of (e (x,
y) · G2 (x, y, z)) indicates the detection efficiency for the fluorescent X-ray emitted at the position (x, y, z). G1 (x,
y, z) indicates the transmittance when the excited X-ray enters the position (x, y, z). Therefore, G1 (x, y, 0)
= 1. Similarly, G2 (x, y, z) indicates the transmittance until the fluorescent X-ray emitted at the position (x, y, z) reaches the sample surface. Therefore, G2 (x, y,
0) = 1. C represents a constant determined by the energy of excited X-rays, the type of element to be measured, the fluorescent X-ray energy of the object to be detected, the measurement time, the unit system in the formula, and the like. x and y indicate coordinates on two axes orthogonal to each other along the sample surface, and z indicates a depth from the sample surface. "Thickness" in the integration range
Indicates the thickness of the target thin film pattern. Only a part where both a (x, y) and e (x, y) are positive values in the integration contributes to the fluorescence X-ray dose B. The contribution area is the measurement area.

When the pattern is repeated two-dimensionally along the sample surface, the above equation can be appropriately approximated to obtain the following equation. Here, S1 represents the area of the unit structure.

∫∫∫G1 (x, y, z) D (x, y,
z) ・ G2 (x, y, z) dx ・ dy ・ dz
(Integration range: Within unit structure) = S1 ・ B / (C ・ (∫∫
a (x, y) · e (x, y) dx · dy)) (integration range: entire measurement area) When the repeating structure along the sample surface exists in only one direction, the Define the repeat width as any suitable width. By doing so, the above basic formula can be used without changing the definitions of S1 in the above formula and "in the unit structure" of the integration range.

In the equation, (∫∫a (x, y) · e (x, y)
Since dx · dy) is determined by the characteristics and arrangement of the optical element, the value calibrated by some reference measurement can be used as a constant.

Next, the equation for calculating the film thickness is derived by rewriting the integral on the left side of the above equation. First, assuming that the attenuation of X-rays inside the sample is negligibly small, G1 (x, y, z) = G2 (x,
Let y, z) = 1. As a result, it can be rewritten as follows.

∫∫∫G1 (x, y, z) D (x, y,
z) ・ G2 (x, y, z) dx ・ dy ・ dz
(Integration range: Within unit structure) = ∫∫∫D (x, y, z)
dx · dy · dz (integration range: within unit structure) Here, when the thin film sample to be measured is viewed from above, the region containing the element to be measured and the other region in the xy plane are clearly separated, and Atomic number density D (x, y,
Consider the case where z) is D and 0. Hereinafter, the range including the element to be measured in the unit structure is referred to as a unit measurement target range, and the area in the xy plane is the unit measurement target area S
Set to 2. In addition, the film thickness in the unit measurement target range is T (x,
y). We further transform the equation using these definitions. Subsequently, the film thickness T (x, y) within the unit measurement target range
Is also considered as a constant value T.

[0017]     ∫∫∫D (x, y, z) dx ・ dy ・ dz (integration range: within unit structure)     = ∫∫∫Ddx ・ dy ・ dz                                     (Integration range: Unit measurement target range x thickness)     = D ・ ∫∫T (x, y) dx ・ dy (integration range: unit measurement target range)     = D ・ T ・ ∫∫dx ・ dy (integration range: unit measurement target range)     = D ・ T ・ S2 Therefore, the following two equations can be obtained.

T = (S1 / S2) .B / (C.D.)
(∫∫a (x, y) ・ e (x, y) dx ・ dy)) (Integration range: whole measurement area) ∫∫T (x, y) dx ・ dy (Integration range:
Unit measurement target range) = S1 ・ B / (C ・ D ・ (∫∫a
(X, y) · e (x, y) dx · dy)) (integration range:
Based on the former formula, the fluorescent X-ray dose B and the pattern area ratio (S1 /
It can be seen that T can be obtained based on S2).

For example, in the case of a wiring structure of a repeating pattern (see FIG. 2), if two dimensions of the wiring width W and the repeating pitch width P are known, (S1 / S2) = P / W, so the film thickness It is possible to obtain T. FIG. 2 is a cross-sectional view of the thin film, and shows a state in which a large number of wirings are arranged in a direction perpendicular to the paper surface.

For example, in the case of a plug structure having a repeating pattern (see FIGS. 3A and 3B), the area S of the unit structure is
If the two values of 1 and the wiring cross-sectional area S2 of the plug are known, the film thickness T can be obtained. FIG. 3A is a view of the sample seen from above, showing a repetitive structure of plugs in the xy plane and S1.
And the range corresponding to S2 are shown. The plug is a short wiring that connects a lower layer wiring and an upper layer wiring, which are parallel to the wafer surface, up and down. The wiring cross-sectional area of the plug refers to a cross-sectional area when the plug wiring is cut along a plane (xy plane) parallel to the wafer surface. FIG. 3B is a perspective view showing the plug structure in three dimensions.

When the pattern area ratio (S1 / S2) is calculated, the design value of the pattern portion may be used as it is. However, if a deviation from the design value is feared, the in-plane dimension of the pattern portion may be different. It is necessary to obtain it by measuring means. Therefore, in the fluorescent X-ray film thickness measuring device incorporating the above method,
Optical microscope, electron microscope, or SPM (Scanni)
By incorporating a surface length measuring function such as ng Probe Microscope), it is possible to perform length measurement in the surface direction and film thickness measurement in the depth direction at the same time in the same device. SP
M is STM (Scanning Tunneling)
Microscope), AFM (Atomic F)
orce Microscope), SNOAM (Sc
anning Near-Field Optical
Atomic-Force Microscope)
It is a general term for a microscope that traces the surface of a sample with a sharp-pointed needle, detects its electrical, physical, and optical characteristics, and measures the surface shape and characteristics of the sample with atomic and molecular sizes. .

Regarding the latter equation, F which indicates the surface shape
The following rewriting is performed using (x, y). Here, the relationship of F (x, y) -F0 = T (x, y) is used. When the surface shape F (x, y) is measured by SPM or the like, it does not have information on the inside of the sample, so the offset F0 must be taken into consideration with the film thickness T (x, y). .

[0023]     ∫ ∫ T (x, y) dx ・ dy     = ∫∫ (F (x, y) -F0) dx · dy     = ∫∫F (x, y) dx · dy−F0 · S2     = ∫∫F (x, y) dx · dy− (F (x, y) −T (x, y)) · S2                                           (Integration range: Unit measurement target range) Finally, the following equation can be obtained.

T (x, y) = F (x, y)-(1 / S
2) ・ ∫∫F (x, y) dx ・ dy (integration range: unit measurement target range) + (S1 / S2) ・ B / (C ・ D ・ (∫∫
a (x, y) · e (x, y) dx · dy)) (integration range: entire measurement area) Therefore, based on the fluorescence X-ray doses B, S1, S2 and the surface shape F (x, y). It can be seen that T (x, y) is required. T (x, y) is the surface shape F (x, y) to which the film thickness information is added, and represents the cross-sectional shape.

Next, the average film thickness T in the unit measurement target range is obtained using the above equation. The results are as follows, and the same result as the film thickness T when a sample having a constant film thickness is measured is obtained.

T = (S1 / S2) .B / (C.D.)
(∫∫a (x, y) · e (x, y) dx · dy)) (integration range: entire measurement area) S when determining the surface shape F (x, y), S1, and S2
Although the surface shape is measured by PM or the like, by incorporating the surface shape measuring function in the fluorescent X-ray film thickness measuring apparatus of the present invention, the sectional shape can be measured in one apparatus.

Up to this point, G1 (x, y, z) = G2
The calculation has been advanced assuming that (x, y, z) = 1, but if this assumption is not appropriate, the film thickness T or T (x, y) can be calculated by a simple equation as in the above calculation. It cannot be represented. In such a case, first, the film thickness T or T
G1 (x, y, z) and G2 (x, y, based on the specific structure of the thin film pattern, assuming (x, y) as appropriate.
z) is calculated. Next, the G1 (x, y,
z) and G2 (x, y, z) are used to determine the film thickness from the detected fluorescence X-ray dose. If the film thickness obtained here matches the initially assumed film thickness, it can be seen that the initially assumed film thickness was correct. If there is a deviation, the same thing is repeated using the corrected assumed film thickness. When the assumed film thickness and the analyzed film thickness match, the correct film thickness is obtained. Further, depending on the actual structure of the thin film pattern, it may be possible to calculate an equation for obtaining the film thickness T or T (x, y) in the same manner as above by incorporating a specific structure in the calculation. In that case, it is not necessary to repeat the calculation.

[0028]

EXAMPLES Examples will be described with reference to the drawings. In this embodiment, the measurement example of the sample having the wiring structure is shown, but the repeated wiring structure is not the only target sample. For example, a repeating pattern structure of the plug is also included in the scope of the present invention.

FIG. 1 is a diagram showing a measurement sample and a fluorescent X-ray measuring instrument. The TEG 5 is provided on the surface of the wafer 4,
Excited X-ray 1 is irradiated there. TEG (Test El
The “element group” is a measurement-dedicated area created according to the measurement conditions, and is used to monitor the manufacturing process of an actual device that cannot be directly measured. Excited X-ray 1
Only the portion irradiated by is the measurement region 15, and the fluorescent X-rays 14 emitted therefrom are measured using the fluorescent X-ray detector 3. Further, the excitation X-ray focusing mirror 2 is used to narrow the irradiation range of the excitation X-ray 1. The TEG used in this method is created at the same time as the pattern to be managed so that its pattern shape is the same as the pattern to be managed. It also limits the substructure created by previous processes so that the substructure does not affect the measurement. The beam diameter of the excitation X-ray and the TEG are adjusted according to the pattern size so that the irradiation range of the excitation X-ray includes many patterns.
Set the size of. A collimator may be used instead of the condenser mirror to prepare an excitation X-ray beam having a required beam diameter. In an actual device, TE in the wafer 4
It is necessary to specify the position of G5 and adjust the measurement area to that position, and an optical microscope or the like built in for that purpose is used.

FIG. 4 shows a wiring pattern after CMP. The surface of the wiring portion 8 left after the CMP is not horizontal but has a hollow shape. The wiring pitch 6 and the wiring width 7 of the wiring pattern are obtained by SEM measurement, and the film thickness of the wiring portion is obtained based on the value of the pattern area ratio (S1 / S2) obtained therefrom. In the film thickness measuring method according to the present invention, the average film thickness 9 as shown by the broken line is obtained.

FIG. 5 shows a wiring pattern after CMP similar to that of FIG. In this example, the wiring pitch 6 and the wiring width 7 of the wiring pattern are obtained by AFM measurement, and the film thickness 9 of the wiring portion is obtained based on the value of the pattern area ratio (S1 / S2) obtained therefrom. In the AFM measurement, the surface shape 10 of each wiring can also be measured. Therefore, according to the present invention, not only the flat average film thickness 9 shown by the broken line but also the average wiring cross-sectional shape 11 can be obtained. Therefore, the film thickness 12 in the vicinity of the side wall of the wiring, the film thickness 13 at the bottom of the cut-out shape of the wiring, and the like can be obtained. Wiring cross-sectional area and film structure 11 obtained from flat film thickness 9
The wiring cross-sectional areas obtained from are almost equal.

[0032]

The present invention is carried out in the form as described above, and has the following effects.

By irradiating excitation X-rays so that a large number of repetitive patterns are included in the irradiation range and measuring the fluorescent X-ray dose from the irradiation range, the average film thickness of the pattern thin film is determined based on the pattern area ratio. You can ask. Further, the cross-sectional shape of the pattern thin film can be obtained based on the pattern surface shape.

By incorporating a surface length measuring function such as an optical microscope, an electron microscope, or SPM into the fluorescent X-ray film thickness measuring device, the length measurement in the surface direction and the film thickness measurement in the depth direction can be summarized in the same device. Can be done by Further, by incorporating a surface shape measuring function such as SPM, it is possible to measure the sectional shape of the pattern portion in the same device.

Since the measurement area can be widened, it is not necessary to focus the beam to the extent of the pattern size, and it is not necessary to suppress the vibration to a low level. Therefore, it is easy to cope with further miniaturization in future semiconductor processing. .

With respect to the wiring of the semiconductor integrated circuit, the film thickness of the wiring portion can be obtained based on the wiring width and pitch.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention together with a TEG.

FIG. 2 is a cross-sectional view of a patterned thin film showing a wiring structure of a repeating pattern.

FIG. 3A is a view of a repeating pattern of a plug structure seen from above the thin film. FIG. 3B is a perspective view three-dimensionally showing a repeating pattern of the plug structure.

FIG. 4 is a diagram showing an example in which a wiring pattern is measured in combination with an SEM.

FIG. 5 is a diagram showing an example of performing measurement of a wiring pattern in combination with AFM.

[Explanation of symbols]

1 Excited X-ray 2 Condensing mirror for excitation X-ray 3 Fluorescent X-ray detector 4 wafers 5 TEG 6 wiring pitch 7 wiring width 8 wiring 9 Film thickness (measurement result) 10 Surface shape 11 Membrane structure (measurement results) 12 Film thickness near wiring sidewall 13 Film thickness at the bottom of the cut-out shape of the wiring 14 X-ray fluorescence 15 measurement area

Continued front page    F term (reference) 2F067 AA27 BB01 BB17 CC17 HH04                       JJ03 KK01                 2G001 AA01 BA04 CA01 KA11 LA11                       MA05 RA04 SA02                 4M106 AA01 BA04 CA48 DH03 DH25                       DH34

Claims (8)

[Claims] 1. A structure in which a large number of repetitive thin film patterns are included in a measurement region without gaps, the measurement region is irradiated with excitation X-rays, and fluorescent X-rays emitted therefrom are detected, and the detected amount thereof is detected. And a thin film pattern film thickness measuring method for obtaining the film thickness of the thin film pattern based on the in-plane dimension of the thin film pattern. 2. The thin film pattern film thickness measuring method according to claim 1, wherein the thin film pattern film thickness is obtained based on the in-plane size of the thin film pattern measured by a measuring method having a function of measuring the in-plane size. 3. The thin film pattern film thickness measuring method according to claim 2, wherein the thin film pattern cross-sectional shape is obtained based on surface shape information measured by a measuring method having a surface shape measuring function. 4. The thin film pattern film thickness measuring method according to claim 1, wherein the thin film pattern is a semiconductor integrated circuit wiring, and the in-plane dimension is a wiring width and a pitch of the semiconductor integrated circuit wiring. 5. An excitation X-ray source for irradiating the measurement region with excitation X-rays, wherein the measurement region includes a large number of repeating thin film patterns without gaps, and the excitation X-rays are applied to the measurement region. An optical circuit for guiding, an X-ray detector for detecting fluorescent X-rays emitted from the measurement region, an optical circuit for guiding the fluorescent X-rays emitted from the measurement region to the X-ray detector, and the detection. A thin film pattern film thickness measuring device comprising: an analyzing means for obtaining a film thickness of the thin film pattern based on a fluorescent X-ray dose and an in-plane dimension of the thin film pattern. 6. The thin film pattern film thickness measuring device according to claim 5, wherein the thin film pattern film thickness measuring apparatus has a built-in in-plane dimension length measuring function, and obtains the thin film pattern film thickness based on the in-plane dimension of the thin film pattern measured by the function. 7. The thin film pattern film thickness measuring apparatus according to claim 6, which has a surface shape measuring function and obtains a thin film pattern cross-sectional shape based on surface shape information measured by the function. 8. The thin film pattern film thickness measuring device according to claim 5, wherein the thin film pattern is a semiconductor integrated circuit wiring, and the in-plane dimension is a wiring width and a pitch of the semiconductor integrated circuit wiring.