CN112097626A - A method for measuring the thickness of metal thin films based on resistance method - Google Patents

Abstract

The present invention provides a method for measuring the thickness of a metal thin film based on a resistance method. The measuring method includes a method for obtaining a resistance value data curve of the metal thin film of a workpiece to be measured; the resistance value data curve reflects the resistance value of the metal thin film and the thickness of the metal thin film. The resistance-thickness standard curve of the corresponding relationship; when measuring the thickness of the metal film, according to the resistance value of the metal film to be measured, the metal film thickness corresponding to the resistance value is obtained from the resistance-thickness standard curve; the present invention is simple to operate and can measure It has a wide range of thickness, and this method belongs to non-contact measurement, which will not cause damage to the sample to be tested, and belongs to non-destructive testing technology.

Description

A method for measuring the thickness of metal thin films based on resistance method

technical field

The invention relates to the field of semiconductor manufacturing, in particular to a method for measuring the thickness of a metal thin film based on a resistance method.

Background technique

In recent years, with the advancement of technology, various semiconductor devices such as optoelectronic devices, laser devices, microelectronic devices, integrated circuits, etc. are developing towards the direction of miniaturization, and the thickness of the metal electrodes of their basic materials is getting thinner and thinner. Materials with a thickness of less than 1 μm are usually referred to as thin-film materials. The thickness of metal thin films will largely affect its physical properties such as mechanics, optics, electricity, and magnetism, thereby affecting the performance of semiconductor devices. Low-cost and accurate measurement of metal film thickness is of great practical importance.

At present, the measurement methods of metal film thickness mainly include mechanical measurement method, optical measurement method and electrical measurement method.

The early mechanical measurement method is the mechanical probe method, also known as the profile method, and the typical representative equipment is a step meter. This method uses a tiny high-precision mechanical stylus (usually only a few microns) to contact the surface of the film to be tested, and moves on the surface of the object to sense the change of the surface profile. The height difference is the film thickness. The method has the advantages of good stability and large measurement range. However, this method is based on the mechanical movement of the probe, and its accuracy is limited by the size of the probe used; in addition, the most serious is that the probe moves on the sample surface, which will scratch the surface of the film, which is a destructive detection.

In order to avoid contact, scanning probe microscopy was developed, which is to use scanning probe microscopy to measure related parameters of thin films. AFM is the most representative scanning probe microscope. The probe of atomic force microscopy is placed on a microcantilever. On the above, the deformation of the microcantilever under the interaction force between the probe and the film atoms is measured by the principle of optical lever, so as to measure the topography of the film surface. It has the advantages of high resolution and non-destructive measurement. However, because this method uses the optical lever principle to measure the deformation of the micro-cantilever, it is easily affected by factors such as photoelectric noise and vibration; and the equipment is relatively expensive and the test cost is high.

The measurement principle of the optical measurement method is to use the optical polarization and interference characteristics. Among them, the ellipsometry method is widely used, and its typical representative equipment is an ellipsometer. When the polarized light is incident on the film from the air, the polarization component of the reflected light will change with the thickness of the film, the angle of incidence, etc. The thickness of the film can be inverted and deduced by detecting and analyzing the changes in the polarization state of the incident light and the reflected light. The method has the characteristics of non-destructive, non-contact, high precision and high sensitivity. However, there is a film thickness period in ellipsometry, and only within this period can the exact film thickness value be measured by using ellipsometry. If the measurement range exceeds this period, the thickness of the film will have multiple uncertain values, so The film thickness measured by ellipsometry generally ranges from 1nm to 1μm, and the film thickness of about 10nm is the best; in addition, this method is an indirect measurement method, which relies on the fitting of the dispersion model to obtain the film thickness, but the dispersion The modeling process is complex and tedious, which will bring a lot of uncertainty to the measurement results.

Compared with other methods, the electrical measurement method has relatively poor accuracy, but it has the advantages of simplicity, rapidity and low cost. The electrical measurement methods mainly include resistance method, capacitance method and quartz crystal method. Among them, the resistance method is a relatively simple electrical measurement method. It usually uses an electric bridge to measure the current and voltage at both ends of the sample, and then deduces the film resistance value. However, the contact pressure between the probe and the film is large during the measurement, and the film is easily scratched. Lower pressure creates higher contact resistance, both of which can lead to inaccurate measurement data.

SUMMARY OF THE INVENTION

The invention provides a method for measuring the thickness of a metal thin film based on a resistance method, which is simple to operate and can measure a wide range of thicknesses, and the method belongs to non-contact measurement, which will not cause damage to the sample to be measured, and belongs to non-destructive testing technology.

The present invention adopts the following technical solutions.

A method for measuring the thickness of a metal thin film based on a resistance method, the measuring method includes a method for obtaining a resistance value data curve of a metal thin film of a workpiece to be measured; Resistance-thickness standard curve; when measuring the thickness of the metal film, according to the resistance value of the metal film to be measured, the thickness of the metal film corresponding to the resistance value is obtained from the resistance-thickness standard curve.

The metal film is arranged on the substrate of the workpiece; the method for obtaining the resistance value data curve of the metal film of the workpiece to be measured includes the following steps;

Step 1. Clean the substrate and dry it;

Step 2, adding a first mask on the substrate to grow electrodes for measurement on the substrate by a mask process;

Step 3, removing the mask, preparing standard thin films with the same surface area and different thicknesses on the substrate; connecting the thin films with the electrodes;

Step 4: Measure the thickness of the standard film and the corresponding resistance value;

Step 5: Fitting the obtained data to obtain a resistance-thickness standard curve reflecting the relationship between the film resistance and the film thickness.

When measuring the thickness of the metal film on the workpiece, first use the methods described in steps 1 to 2 to generate electrodes on the workpiece to be measured, and then prepare the metal film to be measured connected to the electrode on the workpiece substrate; then measure the resistance of the metal film , according to the measured sheet resistance, find out the thickness of the metal film from the resistance-thickness standard curve.

In the first step, the substrate is a glass sheet or a polished silicon wafer with a flat surface. When the substrate is a silicon wafer, the surface of the silicon wafer is plated with an insulating layer, and the composition of the insulating layer is silicon oxide, silicon nitride, oxide A combination of one or more of aluminum.

In the second step, the electrodes used for measurement include a cathode and an anode, and the material components of the electrodes are one or a combination of silver, copper, gold, and aluminum.

The standard film with the same surface area but different thickness in the step 3, the preparation process includes three methods;

In the first method, before the thin film is grown, a second mask is applied to the thin film growth area, and the thin film is grown by a mask process;

In the second method, after the film is grown, if the measurement accuracy needs to be improved, laser scribing is used on the sample;

In the third method, after the film is grown, if the measurement accuracy is not high, a diamond knife is used for scribing the sample.

In step 4, measure the thickness of the standard thin film with a step meter, ellipsometer or atomic force microscope; measure the resistance of the standard thin film with an electric bridge.

The growth process of the electrode, the standard film and the film to be measured includes magnetron sputtering, thermal evaporation, electron beam evaporation and atomic layer deposition;

When measuring the thickness of the metal film on the workpiece, if the surface area of the metal film to be measured is the same as the standard film, it can be directly brought into the resistance-thickness standard curve for calculation; if the surface area of the metal film to be measured is different from the standard film, pass The following formula converts the resistance of the film to be measured into the equivalent standard film resistance, and then brings it into the resistance-thickness standard curve;

公式一；The conversion formula is

formula one;

Among them, R1 is the equivalent standard film resistance, R2 is the film resistance to be measured, l1 is the standard film length, a1 is the standard film width, l2 is the standard film length, and a2 is the standard film width.

The growth process of the film to be measured is the same as that of the standard film.

Compared with the traditional resistance measurement method, the present invention has the following beneficial effects:

1. In the process of measuring the thickness of the metal film to be measured, only the resistance of the sample needs to be measured. There are many types of resistance measuring equipment, and the price is low, the test cost is low, and the operation is simple and easy to popularize.

2. Since the present invention does not use the probe to directly contact the surface of the film, it belongs to non-contact measurement and will not cause damage to the sample to be tested, which is a non-destructive testing technology.

3. In terms of the surface size of the sample to be measured, if the measurement accuracy is high, laser scribing is used to greatly increase the accuracy of the sample size; if the measurement accuracy is not high, the diamond knife is used for scribing, and the operation is very simple. Greatly shorten the measurement time.

4. The thickness range that can be measured by the present invention is very wide, from a few nanometers to several hundreds of nanometers, and the measurement error can be controlled within 10%.

Description of drawings

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments:

Accompanying drawing 1 is the schematic diagram of the first mask;

Accompanying drawing 2 is the schematic diagram of the second mask;

Figure 3 is a schematic diagram of a resistance-thickness standard curve.

Detailed ways

As shown in the figure, a method for measuring the thickness of a metal thin film based on a resistance method, the measuring method includes a method of obtaining the resistance value data curve of the metal thin film of the workpiece to be measured; the resistance value data curve reflects the resistance value of the metal thin film and the metal thin film. The resistance-thickness standard curve of the film thickness correspondence; when measuring the metal film thickness, according to the resistance value of the metal film to be measured, the metal film thickness corresponding to the resistance value is obtained from the resistance-thickness standard curve.

The metal film is arranged on the substrate of the workpiece; the method for obtaining the resistance value data curve of the metal film of the workpiece to be measured includes the following steps;

Step 1. Clean the substrate and dry it;

Step 2, adding a first mask on the substrate to grow electrodes for measurement on the substrate by a mask process;

Step 3, removing the mask, preparing standard thin films with the same surface area and different thicknesses on the substrate; connecting the thin films with the electrodes;

Step 4: Measure the thickness of the standard film and the corresponding resistance value;

Step 5: Fitting the obtained data to obtain a resistance-thickness standard curve reflecting the relationship between the film resistance and the film thickness.

When measuring the thickness of the metal film on the workpiece, first use the methods described in steps 1 to 2 to generate electrodes on the workpiece to be measured, and then prepare the metal film to be measured connected to the electrode on the workpiece substrate; then measure the resistance of the metal film , according to the measured sheet resistance, find out the thickness of the metal film from the resistance-thickness standard curve.

In the first step, the substrate is a glass sheet or a polished silicon wafer with a flat surface. When the substrate is a silicon wafer, the surface of the silicon wafer is plated with an insulating layer, and the composition of the insulating layer is silicon oxide, silicon nitride, oxide A combination of one or more of aluminum.

In the second step, the electrodes used for measurement include a cathode and an anode, and the material components of the electrodes are one or a combination of silver, copper, gold, and aluminum.

The standard film with the same surface area but different thickness in the step 3, the preparation process includes three methods;

In the first method, before the thin film is grown, a second mask is applied to the thin film growth area, and the thin film is grown by a mask process;

In the second method, after the film is grown, if the measurement accuracy needs to be improved, laser scribing is used on the sample;

In the third method, after the film is grown, if the measurement accuracy is not high, a diamond knife is used for scribing the sample.

In step 4, measure the thickness of the standard thin film with a step meter, ellipsometer or atomic force microscope; measure the resistance of the standard thin film with an electric bridge.

The growth process of the electrode, the standard film and the film to be measured includes magnetron sputtering, thermal evaporation, electron beam evaporation and atomic layer deposition;

When measuring the thickness of the metal film on the workpiece, if the surface area of the metal film to be measured is the same as the standard film, it can be directly brought into the resistance-thickness standard curve for calculation; if the surface area of the metal film to be measured is different from the standard film, pass The following formula converts the resistance of the film to be measured into the equivalent standard film resistance, and then brings it into the resistance-thickness standard curve;

公式一；The conversion formula is

formula one;

Among them, R1 is the equivalent standard film resistance, R2 is the film resistance to be measured, l1 is the standard film length, a1 is the standard film width, l2 is the standard film length, and a2 is the standard film width.

The growth process of the film to be measured is the same as that of the standard film.

Example 1:

The steps in this example are as follows:

1) Select a glass sheet with a flat surface as the substrate, ultrasonically clean it with acetone and alcohol for 5 minutes, dry it with a nitrogen gun, and then dry it;

2) Place the first mask on the glass substrate, and use magnetron sputtering equipment to grow silver electrodes with a thickness of 1.5 microns;

3) Remove the first mask and use thermal evaporation equipment to grow copper films of different thicknesses;

4) Scribing the copper film with a laser to obtain a regular rectangular surface;

5) Use the step meter to measure the thickness of the film, and use the bridge to measure the resistance value of the film;

6) Fitting the obtained data to obtain a standard curve of the relationship between copper film resistance and film thickness, see attached figure;

7) Repeat steps 2) and 4) to prepare the copper thin film electrode to be tested;

8) Use the bridge method to measure the resistance of the copper film to be measured, and bring in the resistance-thickness standard curve of the copper film to obtain the theoretical value of the thickness of the copper film to be measured. As a comparison, use an ellipsometer to directly measure the thickness of the copper film to be measured. The results are shown in the attached table.

Example 2:

The steps in this example are as follows:

1) Select polished silicon as the substrate, clean it with standard RCA liquid, dry it with a nitrogen gun, and use PECVD equipment to deposit a 150nm-thick silicon nitride film on the substrate as an insulating layer;

2) Place the first mask on the substrate, and use magnetron sputtering equipment to grow silver electrodes with a thickness of 1.2 microns;

3) Replace the second mask, and use atomic layer deposition equipment to grow aluminum films of different thicknesses;

4) Use the step meter to measure the thickness of the film, and use the bridge to measure the resistance value of the film;

5) Fit the obtained data to obtain the standard curve of the relationship between the aluminum film resistance and the film thickness;

6) Repeat step 2) to prepare the aluminum film electrode to be tested, and scribe the aluminum film with a laser to obtain a regular rectangular surface;

7) Use the bridge method to measure the resistance of the aluminum film to be tested, and bring it into the standard curve of resistance-thickness of the aluminum film to obtain the theoretical value of the thickness of the aluminum film to be tested. As a comparison, use an ellipsometer to directly measure the thickness of the aluminum film to be tested. The results are shown in the attached table.

The attached tables of Examples 1 and 2 are as follows

In the above embodiment, the electrode material is preferably silver.

The rectangular pattern in the first mask is the electrode shape after growth.

The elongated strip pattern in the second mask is each standard thin film after growth, and each standard thin film has the same surface area but different thicknesses.

The rectangular patterns in the first mask can also be replaced with pairs of rectangles or pairs of circles corresponding to the long and narrow strip patterns in the second mask.

The workpieces used in steps 1, 2, and 3 are samples, which are used for measurement to obtain a resistance-thickness standard curve.

Claims (9)

1. a metal film thickness measurement method based on resistance method, is characterized in that: described measurement method comprises the method that obtains the resistance value data curve of workpiece metal film to be measured; Described resistance value data curve is to reflect the resistance value of metal film and The resistance-thickness standard curve corresponding to the thickness of the metal film; when measuring the thickness of the metal film, according to the resistance value of the metal film to be measured, the thickness of the metal film corresponding to the resistance value is obtained from the resistance-thickness standard curve. 2 . The method for measuring the thickness of a metal film based on a resistance method according to claim 1 , wherein the metal film is arranged on the substrate of the workpiece; the resistance value data curve of the obtained metal film of the workpiece to be measured is obtained. 3 . The method includes the following steps; Step 1. Clean the substrate and dry it; Step 2, adding a first mask on the substrate to grow electrodes for measurement on the substrate by a mask process; Step 3, removing the mask, preparing standard thin films with the same surface area and different thicknesses on the substrate; connecting the thin films with the electrodes; Step 4: Measure the thickness of the standard film and the corresponding resistance value; Step 5: Fitting the obtained data to obtain a resistance-thickness standard curve reflecting the relationship between the film resistance and the film thickness. 3. a kind of metal film thickness measurement method based on resistance method according to claim 2, is characterized in that: when measuring the metal film thickness on the workpiece, first with the method described in step 1 to step 2, on the workpiece to be measured Generate electrodes, and then prepare a metal thin film connected to the electrode on the workpiece substrate; then measure the resistance of the metal thin film, and find out the thickness of the metal thin film from the resistance-thickness standard curve according to the measured thin film resistance. 4. The method for measuring the thickness of a metal thin film based on a resistance method according to claim 3, wherein in the step 1, the substrate is a glass sheet or a polished silicon wafer with a flat surface, and when the substrate is a silicon wafer At the time, the surface of the silicon wafer is coated with an insulating layer, and the composition of the insulating layer is one or a combination of silicon oxide, silicon nitride, and aluminum oxide. 5. a kind of metal thin film thickness measurement method based on resistance method according to claim 3, is characterized in that: in described step 2, the electrode used for measurement comprises cathode and anode, and the material composition of its electrode is silver, copper, A combination of one or more of gold and aluminum. 6. a kind of metal thin film thickness measurement method based on resistance method according to claim 3, is characterized in that: the standard thin film of same surface area but different thickness in described step 3, its preparation process comprises three kinds of methods; In the first method, before the thin film is grown, a second mask is applied to the thin film growth area, and the thin film is grown by a mask process; In the second method, after the film is grown, if the measurement accuracy needs to be improved, laser scribing is used on the sample; In the third method, after the film is grown, if the measurement accuracy is not high, a diamond knife is used for scribing the sample. 7. a kind of metal thin film thickness measuring method based on resistance method according to claim 3, is characterized in that: in step 4, measure the thickness of standard thin film with step meter or ellipsometer or atomic force microscope; measure with electric bridge Resistance of standard thin films. 8 . The method for measuring the thickness of a metal thin film based on a resistance method according to claim 3 , wherein the growth process of the electrode, the standard thin film and the thin film to be measured comprises magnetron sputtering, thermal evaporation, and electron beam evaporation. 9 . and atomic layer deposition; When measuring the thickness of the metal film on the workpiece, if the surface area of the metal film to be measured is the same as the standard film, it can be directly brought into the resistance-thickness standard curve for calculation; if the surface area of the metal film to be measured is different from the standard film, pass The following formula converts the resistance of the film to be measured into the equivalent standard film resistance, and then brings it into the resistance-thickness standard curve; The conversion formula is

formula one; Wherein R ₁ is the equivalent standard film resistance, R ₂ is the film resistance to be measured, l ₁ is the standard film length, a ₁ is the standard film width, l ₂ is the standard film length, and a ₂ is the standard film width. 9 . The method for measuring the thickness of a metal thin film based on a resistance method according to claim 8 , wherein the growth process of the thin film to be measured is consistent with that of the standard thin film. 10 .

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