JPH08236592A - Measuring method of stepped part - Google Patents

Abstract

PURPOSE: To provide the measuring method of stepped part of which the measurement precision is not affected at all by the oscillation and the positional slippage of the levels of observation and measurement point. CONSTITUTION: The surface of a substrate 101 is coted with polyimide material or silicon material so as to form a transparent film in thickness not exceeding about 1μm forming a viscous transparent film 103 in even thickness. Thus, the irregularity of the substrate 101 directly corresponds to the thickness of the transparent film 103. That is, assuming an arbitrary point of the surface of the substrate 101 to be a point X, the value of (the value at the point X) + (the film pressure at the point X) may have a constant value, regardless of the position of the point X. Furthermore, assuming the observation points to be the points a and b, the difference Da-Db of the film thickness Da and Db will become the measurement value of the stepped part 102. After the measurement of this stepped part 102, the viscous transparent film 103 is released using a solvent to restore the substrate 101 to the state before the measurement of the stepped part 102 to finish the stepped part measurement step.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a step measuring method, and more particularly to a step measuring method used when measuring an etching step formed on a substrate of a semiconductor device.

[0002]

2. Description of the Related Art Generally, in a semiconductor device manufacturing process, a technique for forming minute etching steps of several hundred angstroms to several μm on the surface of a substrate formed of a single substance, such as a silicon substrate. Is an important technique used in element isolation and formation of a capacitance film in a semiconductor element. Usually, in a semiconductor manufacturing factory, the etching rate is routinely controlled by measuring the etching step in the semiconductor manufacturing process. Since this etching step is an extremely minute step, it is desired to measure the step accurately as a step measuring method.

As a conventional method for measuring the level difference of this kind,
Two step measuring methods are known, including a mechanical measuring method and an optical measuring method. Moreover, there are two measuring methods as the mechanical measuring method, and two measuring methods are also known as the optical measuring method. Hereinafter, FIG. 5, FIG. 6, FIG.
These conventional examples will be described with reference to FIGS. 8 and 9.

FIG. 5 shows a substrate 101 having a step 102,
FIG. 7 is a conceptual diagram showing a first measurement method of a mechanical measurement method including a fixing stage 116 and a measuring needle 117, and FIG.
Is the measuring needle 117 in the first mechanical measuring method.
FIG. 6 is a diagram showing the substrate 101, the tip of the measuring needle 117, and the movement path 118 of the tip when the above is moved. In FIG. 5, in the present measurement method, the substrate 10 that is an object to be measured.
1 is fixed on the fixing stage 116 with a vacuum chuck or the like so as not to slip, and a measuring needle 117 having a tip shape as shown in FIG. 6 is brought into contact with the surface of the substrate 101, It is moved while sliding along the moving line 118 shown in FIG. Then, the step 102 (Y1) (see FIG. 6) is measured by converting the movement path 119 of the measuring needle 117 as shown in FIG. 6 into an electric signal. In the first mechanical measurement method, when measuring the step 102 (Y1) shown in FIG.
In accordance with the size of the height Y1 of the substrate 101, the measuring needle 117 contacting the surface of the substrate 101 is prevented from bouncing at the stepped portion of the surface or scratching the surface of the substrate 101. In order to enable a slow and smooth surface scanning, the tip shape of the measuring needle 117 is formed in a specific spherical shape having a radius of curvature r, for example, as shown in FIG.

Next, FIG. 7 shows a substrate 1 having a step 102.
01, including a polishing stage 120 and a measuring needle 117,
It is a conceptual diagram which shows the 2nd measuring method of a mechanical measuring method.
In FIG. 7, in the present measurement method, the substrate 101, which is an object to be measured, is placed on the scanning polishing stage 120 whose surface is polished very smoothly, and is used in the first mechanical measurement method. The measuring needle 117 having the same tip shape as that of the measuring needle is installed so that its tip comes into contact with the surface of the substrate 101 so as to move only in the vertical direction with respect to the polishing stage 120. Then, the substrate 101 is moved along the movement line 121 by slowly sliding it on the polishing stage 120 at a constant speed. The vertical movement of the measuring needle 117 caused by the movement of the substrate 101 is converted into an electric signal, and the step 102 is measured in the same manner as in the case of the first mechanical measuring method.

In each of the first and second conventional mechanical measuring methods, in order to reduce the influence of external vibration on the measurement accuracy, the entire measuring device is mounted on the seismic isolation table in any case. The measure to put it is adopted. However, in these first and second mechanical measuring methods, since the measuring needle 117 is physically in contact with the surface of the substrate 101, there is a possibility that scratches may be formed on the surface of the substrate 101. . This not only damages the semiconductor substrate to be measured, but also causes a reduction in the yield in fine processing in the manufacturing process of the semiconductor device.
In addition, there is a possibility that particles (dust) will be generated due to the scratches, and when particles are further generated from the metal film, the particles are mediated by the measuring needle 117, and thereafter. If it adheres to the semiconductor substrate such as silicon to be measured, it may cause heavy metal contamination that adversely affects the electrical characteristics of the semiconductor device depending on the subsequent processing steps.

Further, in the above mechanical measuring method,
In principle, there is a problem that the tip aspect of the measuring needle 117 limits the aspect ratio of the measurable groove. For example, in FIG. 6, when the value of the radius of curvature r of the tip of the measuring needle 117 is set to a value sufficiently smaller than the numerical values of X1 and Y1, the depth is Y1 and the width is X1.
When measuring the step 102 (Y1) corresponding to the groove 1 of 1, the aspect ratio Y
For a step 102 (Y1) corresponding to a groove where 1 / X1 is approximately 0.5 tan (θ / 2) or more, it is theoretically impossible to measure the step (generally, the value of θ is 90 degrees or more). is there). That is, when the value of the depth Y1 of the groove and the value of the width of the groove have the same value, it is impossible to measure the step corresponding to the groove.

As a conventional step difference measuring method for improving the problems in such a mechanical step difference measuring method, there is the following optical step difference measuring method. This optical measuring method also has two measuring methods as described above.
These conventional examples will be described with reference to FIGS. 6, 7, 8 and 9.

FIG. 8 shows a substrate 101 having a step 102,
It is a conceptual diagram which shows the 1st optical measuring method containing the laser source 122, the intensity sensor 123, the reflecting plate 124, the half mirror 125, and the polishing stage 126. In FIG. 8, in the present measuring method, first, a laser beam having a wavelength λ and a beam narrowed down to be narrower than the width X1 of the step 102 is output from the laser source 122 onto the substrate 101, which is an object to be measured. And irradiate. The emitted laser light is decomposed into the measurement light 127 and the reference light 128 by the half mirror 125. The measurement light 127 is reflected on the surface of the substrate 101, the reference light 128 is reflected by the reflection plate 124, and both reflected lights are combined and input to the intensity sensor 123. In the intensity sensor 123, a change in the intensity of the combined light that changes in response to a change in the phase difference ξ between the measurement light 127 and the reference light 128 is observed. The phase difference ξ from the reference light 128 is replaced and detected. In such an observation system,
The substrate 101 is moved on the polishing stage 126 along the moving line 1
By parallel translation along 29, an optical path difference is generated in the reflected light from the surface of the substrate 101 with respect to the incidence of the measurement light 127 corresponding to the height Y1 of the step 102, and this optical path difference causes an input to the intensity sensor 123. A change occurs in the intensity of the combined light that is generated. The change in the light intensity observed in the intensity sensor 123 corresponds to the phase difference ξ between the measurement light 127 and the reference light 128 as described above, and this phase difference ξ causes the step 102 on the surface of the substrate 101 to be different. It is simply calculated. Even in the first optical measuring method, the entire measuring device is placed on the seismic isolation table in order to reduce the influence of external vibration. However,
Also in this first optical measurement method, since the optical path is almost entirely present in the air, the refractive index changes slightly due to changes in temperature, pressure, etc. There is a problem in that the optical path difference fluctuates and the step measurement accuracy decreases.

In order to solve the problem of the first optical measuring method, in Japanese Patent Laid-Open No. 3-255902, a second optical measuring method is used as a step measuring method in comparison with the first optical measuring method. A method has been proposed. FIG.
Substrate 101 having step 102, laser source 122, intensity sensor 123, reflector 124, half mirror 125, polishing stage 126, athermal glass 130 and 1
No. 3, including No. 31 according to Japanese Patent Application Laid-Open No. 3-255902
It is a conceptual diagram which shows the optical measuring method of. The measuring method itself by this step difference measuring method is similar to the case of the above-mentioned first optical measuring method, but in this proposal, as shown in FIG. Athermal glasses 130 and 131 made of a transparent solid substance are characteristically inserted in the optical paths of the measurement light 127 and the reference light 128, respectively. In this second optical measurement method, the measurement light 127 and the reference light 1
The influence of air fluctuations on the measurement accuracy is eliminated by preventing a state in which air having a different temperature directly intervenes in the optical path of 28.
Since the medium through which 7 and the reference light 128 pass is a solid substance, it is not affected by pressure fluctuations and temperature fluctuations, and the temperature of the solid substance is constant, or as shown in FIG. In addition, as a solid substance, the athermal glass (Athermal glass whose optical path length hardly changes due to temperature changes)
It is said that the use of Glass) can minimize the occurrence of measurement error. However, no new proposal has been made regarding measures against external vibration.

[0011]

Any of the above-described conventional step measuring methods includes the case of the first and second mechanical measuring methods and the case of the first and second optical measuring methods. Also in the step measuring method, the distance from the observation point to the observation point on the surface of the substrate is measured with a measuring needle in the mechanical measuring method and with a laser beam in the optical measuring method, and the substrate is measured. The step is measured by detecting the change in the distance measurement value due to the step on the surface of the. However, in these step difference measuring methods, as a method for measuring an extremely small step difference on the substrate of the semiconductor device, accuracy deterioration due to external vibration and relative height between the observation point and the measurement point during scanning are considered. The only countermeasures against the decrease in accuracy due to deviations are to install seismic removal equipment for vibrations and to correct the displacement of heights such as smoothing. However, there is a drawback that the step measurement accuracy is insufficient in terms of etch rate control in the semiconductor manufacturing process.

The object of the present invention is to solve the above-mentioned drawbacks,
Compared to the conventional step measurement method, it is less affected by external vibrations and displacement between the observation point and the height of the measurement point,
Another object of the present invention is to provide a step difference measuring method capable of measuring a step difference more accurately without being affected by atmospheric temperature fluctuations and pressure fluctuations.

[0013]

The step measuring method of the present invention is a step measuring method for optically measuring a minute step existing on the surface of a substrate formed of a single substance or a film-like measurement sample. A first step of applying a transparent viscous substance to the surface of the substrate or the measurement sample to form a transparent film having a flat surface on the surface of the substrate or the measurement sample, and the substrate or the measurement sample The film thicknesses D1 and D2 (D1> D2) of the transparent film corresponding to the unevenness of the step existing on the surface of the substrate are optically measured, and the step difference is obtained from the difference (D1-D2) between the film thicknesses D1 and D2. A second step, and, following the second step, a third step of peeling the transparent film from the surface of the substrate or the measurement sample with a predetermined solvent;
It is characterized by having at least.

As the transparent viscous substance for forming the transparent film, a polyimide material or a silica material may be used, or after the BPSG film is grown, the B
The PSG film may be heated and reflowed to form a transparent film.

[0015]

Next, the present invention will be described with reference to the drawings.

FIG. 1 is a conceptual diagram including a measurement sample substrate showing a procedure of a step measuring method according to the first and second embodiments of the present invention. First, referring to the evaluation sample of FIG. 1,
The step measuring method of this embodiment will be described. FIG. 1 (a)
In the above, the substrate 101 as an evaluation sample is formed by dry-etching a silicon substrate on which a patterned photoresist is placed to a thickness of about 500 Å and then peeling off the photoresist. Next, as shown in FIG. 1B, the substrate 101 is placed on a horizontal table 104, and a polyimide material or a silica material is used as a transparent viscous substance that functions as a viscous transparent film 103 after solidification. Is applied on the substrate 101.
In the step of applying the viscous substance, the liquid transparent viscous substance is slowly added to the substrate 10 so that air bubbles do not enter.
Drop on 1. At that time, it is necessary to form the viscous transparent film 103 on the unetched horizontal surface of the substrate 101 so that the viscous transparent film 103 has a uniform thickness. In this embodiment, since the viscous substance for forming the viscous transparent film 103 is a liquid, its surface becomes flat as shown in FIG. 1 (b) due to the surface tension. Further, since it is a liquid, it also enters the groove of the minute step portion, so that the unevenness of the substrate 101 directly corresponds to the thickness of the transparent film 103. That is, when an arbitrary point on the surface of the substrate 101 is set as the X point, the value of (height at the X point) + (membrane pressure at the X point) becomes a constant value regardless of the position of the X point. . When the viscous substance is a liquid, if the solvent escapes and solidifies, the refractive index of the viscous transparent film 103 to be formed fluctuates, so that it takes a long time to solidify. The material is selected and applied on the surface of the substrate 101 so that a transparent film having a thickness of about 1 μm or less is formed. Hereinafter, with reference to FIG. 1C, a process of optically measuring a step in this embodiment will be described.

In FIG. 1C, the step measurement is performed immediately after applying the viscous substance to the surface of the substrate 101 as described above.
It is performed on a flat table without inclination at a place where the coating process is performed so that the viscous substance does not flow. FIG.
As shown in (c), when the measurement points are points a and b, the film thickness measuring device 105 moving in parallel with the surface of the substrate 101 along the moving line 106 is used to measure each point. The film thickness is measured. The difference D between the film thicknesses Da and Db measured at the points a and b
a−Db is obtained as the measured value of the step 102. After the measurement of the step 102, as shown in FIG. 1D, the viscous transparent film 103 is peeled off using a solvent, and the substrate 1 is removed.
01 is returned to the state before the step measurement and the step measurement step is completed.

Next, a step measuring method according to a second embodiment of the present invention will be described with reference to FIGS. 1 and 2.
FIG. 1 is a conceptual diagram including a measurement sample substrate showing a procedure of a step measuring method according to the second embodiment, as in the case of the first embodiment. Hereinafter, the step measuring method of this embodiment will be described with reference to the evaluation sample of FIG. FIG.
In (a), the substrate 101 as an evaluation sample is
The silicon substrate on which the patterned photoresist is placed is dry-etched to about 1 μm, and then the photoresist is peeled off. Next, FIG.
As shown in (a), BPS is used as a transparent viscous substance.
Using G, the BPSG film 107 is formed on the substrate 10 by the CVD method.
2 is grown on the surface of No. 1 and further heated and reflowed as shown in FIG. 2B to flatten the surface of the BPSG film 107 grown on the surface of the substrate 101.
The process of forming the viscous transparent film 103 will be described.

First, the substrate 101 is formed in a CVD growth chamber using a gas of tetraethoxysilane as a raw material, and the BPSG film 107 is evenly covered with good coverage.
01 surface. At that time, the viscous transparent film 1 is applied to the unetched horizontal surface of the substrate 101.
It is necessary to heat and reflow the substrate 101 for about 30 minutes in a nitrogen gas atmosphere of 900 to 1000 ° C. after the BPSG growth so that 03 has a uniform thickness. By this heat reflow, the surface of the BPSG film 107 on the substrate 101 shown in FIG. 2A is flattened, and as shown in FIG. 2B, the surface is flattened and the viscous transparent film 103 is flattened. Is formed. Since this step is performed by using the CVD method as described above, B
When the PSG film 107 is formed, the BPSG also penetrates into the inside of the groove of the minute step portion on the upper surface of the substrate 101 with good coverage. Therefore, in the state where the viscous transparent film 103 is formed on the substrate 101 by the heat reflow, the unevenness on the surface of the substrate 101 has the flattened viscous transparent film 103.
It corresponds to the thickness of. In this step, the viscous transparent film 103 is grown to a thickness of about 1 μm or less.

Also in this embodiment, after forming the viscous transparent film 103, as shown in FIG. 1C, when the measurement points are points a and b, the substrate 10 is moved along the moving line 106.
The film thickness measuring device 105 moving in parallel to the surface of No. 1 measures the film thickness at each point, and the film thickness difference Da
-Db is obtained as the measured value of the step 102. After the measurement of the step 102, as shown in FIG. 1D, the viscous transparent film 103 is peeled off using a solvent, and the substrate 10 is removed.
1 is returned to the state before the step measurement and the step measurement step is completed.

In the present invention, as a material example of the viscous transparent film formed on the substrate 101, a polyimide material, a silica material, or a BPSG film having a flat surface by heat reflow is used.

As described above, in the step measuring method according to the present invention, after the transparent thin viscous transparent film 103 is formed flat on the surface of the substrate 101 in the measurement optical path for measuring the step,
The method is characterized in that a step corresponding to a change in the film thickness is obtained by optically measuring the film thickness of the viscous transparent film 103. Next, referring to FIGS. 3 and 4, in the first and second embodiments described above, the substrate 10
A method for optically measuring the film thickness of the transparent film above 1 will be described. Note that in FIGS. 3 and 4, the substrate 101
The upper transparent film is shown as transparent film 108.

In FIG. 3, the wavelength λ emitted from the laser source 109 and output through the spectral filter 110.
The laser light 113 is vertically incident on the point A of the transparent film 108 of the substrate 101 through the half mirror 111. In response to the incidence of this laser light, as shown in FIGS. 4A and 4B, at point A, part of the laser light is reflected to become reflected light 114, and part of the laser light becomes , Enters the inside of the transparent film 108 from the point A as transmitted light, is reflected at the point B on the boundary surface between the substrate 101 and the transparent film 108, and becomes the reflected light 115, and both reflected lights are combined on the surface of the transparent film 108. . This combined light is an interference wave of the reflected light 114 and the reflected light 115, and the refractive index of the transparent film 108 is n.
Then, when the film thickness D of the transparent film 108 satisfies the following equation, the intensity of the combined light becomes the maximum value.

2D = mλ / n (m = 1, 2, 3, ...). Therefore, in FIG. 3, using the spectral filter 110,
By changing the wavelength of the laser light, it is possible to obtain the wavelength λ _{1 of the} laser light that maximizes the intensity of the combined light such that 2D = λ ₁ / n that satisfies the above conditional expression. Based on the wavelength λ ₁ of the laser light and the value of the refractive index n of the transparent film 108 at this time, the film thickness of the transparent film 108 is obtained by setting D = λ ₁ / 2n.

That is, as seen in the conventional examples of FIGS. 8 and 9, the half mirror 124 and the surface of the substrate 101 are conventionally used to optically measure the step on the surface of the substrate 101. Step observation point and intensity sensor 124
The spatial propagation path of the laser light existing between the light receiving point and the light receiving point is incorporated into the optical path length on the step measurement, and the step is obtained by measuring the fluctuation of the optical path, in contrast to the present invention. In the optical step measuring method by measuring the film thickness of the transparent film 108 on the substrate 101, the spatial propagation path existing between the half mirror 111, the step observation point on the surface of the substrate 101 and the light receiving point of the intensity sensor 112. In principle, the fluctuation of the optical path length or the like has no influence on the film thickness measurement accuracy. Therefore, there is no influence on the step measurement accuracy due to the external vibration, the observation point at the time of measurement, and the displacement of the height of the measurement point.

As described above, in the first and second embodiments, the flat viscous transparent film 103 is formed on the surface of the substrate 101, and the film thickness of the viscous transparent film 103 is measured to measure the surface of the substrate 101. By using the method of measuring the level difference, it is possible to suppress deterioration of measurement accuracy due to external vibrations and displacement of the observation point and the height of the measurement point at the time of measurement, as well as air temperature fluctuations and pressure fluctuations. It is also possible to avoid the effect of.

[0027]

As described above, according to the present invention, a transparent film having a flat surface is closely formed on the surface of a substrate to be measured, and the step of the substrate is measured by measuring the film thickness of the transparent film. By substituting the method to measure the thickness optically,
It is possible to suppress the decrease in measurement accuracy caused by the vibration from the outside and the displacement of the height when moving the measurement point on the board, and also prevent the effects of temperature fluctuations and pressure fluctuations of the air. The effect is that you can.

Further, by applying the present invention to the above effects, even in a work site where daily general vibrations are present, under an environment of the anti-vibration equipment of a commonly used film thickness meter, There is an effect that it becomes possible to perform work such as monitoring the Si etching depth of the semiconductor substrate.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a substrate showing a measurement procedure according to a first embodiment of the present invention.

FIG. 2 is a conceptual diagram of a substrate showing a procedure for forming a substrate transparent film according to a second embodiment of the present invention.

FIG. 3 is a system configuration diagram showing an optical film thickness measuring method according to the present invention.

FIG. 4 is a conceptual diagram of a substrate showing the principle of film thickness measurement according to the present invention.

FIG. 5 is a conceptual diagram of a substrate showing a conventional method of measuring a step.

FIG. 6 is a diagram showing a relationship between a measuring needle and a step in the step measuring method of the conventional example.

FIG. 7 is a conceptual diagram of a substrate showing another conventional step measuring method.

FIG. 8 is a system configuration diagram showing an optical step difference measuring method according to a conventional example.

FIG. 9 is a system configuration diagram showing an optical step difference measuring method according to another conventional example.

[Explanation of symbols]

 101 substrate 102 step 103 viscous transparent film 104 horizontal stand 105 film thickness measuring device 106, 118, 119, 121, 129 moving line 107 BPSG film 108 transparent film 109, 122 laser source 110 spectral filter 111, 125 half mirror 112, 123 intensity Sensor 113 Laser light 114, 115 Reflected light 116 Fixing stage 117 Measuring needle 120, 126 Polishing stage 124 Reflector 127 Measuring light 128 Reference light 130, 131 Athermal stage

Claims (4)

[Claims] 1. A step measuring method for optically measuring a minute step existing on the surface of a substrate formed of a single substance or a film-shaped measuring sample, comprising: The first step of applying a viscous substance to form a transparent film having a flat surface on the surface of the substrate or the measurement sample, and the step corresponding to the unevenness of the step existing on the surface of the substrate or the measurement sample Thickness of transparent film D1 and D2
(D1> D2) is optically measured, and the step is obtained from the difference (D1-D2) between the film thicknesses D1 and D2.
And a third step of peeling the transparent film from the surface of the substrate or the measurement sample with a predetermined solvent, following the second step. 2. The step measuring method according to claim 1, wherein a polyimide material is used as the transparent viscous substance forming the transparent film. 3. The step measuring method according to claim 1, wherein a silica material is used as the transparent viscous substance forming the transparent film. 4. The transparent film is formed by growing a BPSG film as a transparent viscous substance forming the transparent film and then heating and reflowing the BPSG film by heating. Step measurement method.