JP3387446B2 - Measurement method of interface transition region - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron beam irradiation method for obtaining the film thickness of an ultrathin film such as an ultrathin silicon oxide film formed on a silicon substrate, the interface transition region, and the microroughness of the interface. Regarding the measurement method in.

[0002]

2. Description of the Related Art A semiconductor device such as a MOS transistor is reduced in size as a semiconductor device is highly integrated or has a higher density. In the miniaturization of this semiconductor element, a thin film of material is required as the pattern size is reduced.

When the semiconductor element is miniaturized as described above and the design rule thereof is about 100 nm, for example, MOS is used.
The thickness of the gate oxide film of the transistor is extremely thinned to about 2 nm. Normally, the transition region width at the interface between the silicon substrate and the gate oxide film is as small as 1 nm or less, but with the thinning, such a transition region width cannot be ignored in terms of the characteristics of the semiconductor element and its control is required. For this,
Generally, the means for measuring the width of the transition region between the laminated materials becomes important. At the same time, the evaluation of the above-mentioned microroughness of the interface becomes important.

Furthermore, a means for measuring the film thickness of a thin film material which constitutes a semiconductor element has become important.
The thin film such as the gate oxide film is directly related to the characteristics of the semiconductor device, and its control is particularly important.

As a means for measuring the film thickness of the ultra-thin oxide film and the interface microroughness, there is an X-ray reflection method as described in, for example, Japanese Patent Laid-Open No. 11-6804. AFM (atomic force measurement) method, for example, is well known as a means for measuring microroughness or surface roughness.

Further, as a means for measuring the thickness of the ultrathin oxide film or the width of the interface transition region, a well-known TEM is used.
There is a (transmission electron microscope) method.

[0007]

The conventional techniques described above have the following problems, respectively.

For example, the interface between the silicon substrate and the gate oxide film or the microroughness greatly changes due to the heat treatment in the above manufacturing process, the cleaning of the surface of the silicon substrate, and the like.
Similarly, the interface between the silicon substrate and the silicide layer also changes through the above manufacturing process. For this reason, in the analysis of a semiconductor device, it is important to measure and evaluate the semiconductor element completed through the manufacturing process of the semiconductor device.

However, in the above X-ray reflection method and AFM method, it is necessary to widen the measurement area of the sample, and it is essential to remove the thin film material other than the thin film material to be evaluated. For this,
It becomes difficult to prepare a measurement sample after manufacturing a semiconductor device.

In the case of the TEM method, it is necessary to make the thickness of the sample to be about 100 nm in order to transmit the electron beam. In this case, the thinner the sample film, the more reliable the measurement is. For this reason, it is necessary to make the film thickness of the sample uniform to a predetermined film thickness. However, the preparation of such a sample requires skill and much labor.

The above problems become more apparent as the thin film material forming the semiconductor element becomes thinner.

An object of the present invention is to solve the above problems and provide a measuring method for easily evaluating the film thickness, interface transition region, interface microroughness, etc. of an ultrathin film used for manufacturing a semiconductor device. Especially.

[0013]

Therefore, according to the measuring method of the present invention, the cross section of the substrate in which the first substance and the second substance are laminated is cut out, and Are irradiated with electrons having a predetermined energy, and the amount of electrons having a specific energy loss among the electrons passing through the sample is measured. Here, the specific energy loss is caused by plasmon excitation peculiar to the first substance or the second substance.

On the surface of the detector of the measuring method of the present invention, a large number of pixels, each of which measures the amount of electrons, are arranged in a matrix. Then, the signal intensity distribution of the electrons of each pixel is taken with respect to the pixel line, and the width of the interface transition region is determined from the change in the signal intensity of the electrons corresponding to the interface transition region.

Furthermore, the signal intensities of a plurality of pixel lines are added to obtain an electron signal intensity distribution, and the width of the interface transition region and the microroughness of the interface transition region are measured.

Further, in the measuring method of the present invention, in the sample having the film thickness distribution, the width of the interface transition region is determined by the measuring method at each measurement location in the sample where the film thickness is different, and the determination is performed. The minimum value of the data distribution of the width of the interface transition region with respect to the sample film thickness is set as the true width of the interface transition region, and the microroughness of the interface transition region is determined from the maximum value of the data distribution. Alternatively, the incident angle of the electron irradiation surface of the sample and the electron is changed, the width of the interface transition region at each incident angle is determined by the measurement method, the incident angle of the determined width of the interface transition region The minimum value of the data distribution for is taken as the true width of the interface transition region.

Here, the interface transition region is a transition region between a silicon material and a silicon oxide film or a transition region between a silicon material and a silicide film.

Further, in the measuring method of the present invention, the cross section of a substrate in which the first substance, the second substance and the third substance are laminated in this order is cut out, Are irradiated with electrons having a predetermined energy, and the amount of electrons having a specific energy loss among the electrons passing through the sample is measured by a detector. Here, the specific energy loss is caused by plasmon excitation peculiar to the first substance, the second substance, or the third substance.

A large number of pixels for measuring the amount of electrons are arranged in a matrix on the surface of the detector, and the signal intensity distribution of the electrons of each pixel is taken with respect to the pixel line. The film thickness of the second substance is determined from the change in the signal intensity of the electron corresponding to the interface transition region of the second substance and the change in the signal intensity of the electron corresponding to the interface transition region of the second substance and the third substance. To be done. Here, the first substance is a silicon crystal, the second substance is a silicon oxide film, and the third substance is a silicon film or a silicide film.

In the present invention, the sample is irradiated with electrons having a predetermined incident energy, the electron intensity having a specific energy loss among the electrons transmitted through the sample is measured, and the data processing of the electron intensity is performed as described above. The interface transition region, microroughness, ultrathin film thickness, etc. of the material to be laminated by the method are measured.

Here, it is not always necessary to make the film thickness of the sample uniform, the sample preparation becomes very easy, and no special skill or labor is required in preparing the sample. Then, the method of the present invention is very effective for speeding up the analysis and evaluation of a semiconductor device that is miniaturized or densified, and facilitates realization of a high-performance semiconductor device.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Next, a first embodiment of the present invention will be described with reference to FIGS. The basic concept of the measuring method of the present invention will be described in the first embodiment. Here, the interface transition region width between the silicon substrate and the silicon oxide film and the interface microroughness are evaluated.

FIG. 1 is a perspective view of a sample for explaining the measuring method, and FIG. 2 is a schematic view of an apparatus for explaining the measuring method. 3 is an image schematic diagram for explaining the measuring method, and FIG. 4 is a signal distribution diagram for evaluating the interface transition region width.

As shown in FIG. 1, a sample 1 is a sample obtained by forming a silicon oxide film, which is a second substance, on a silicon substrate, which is a first substance, and cutting out a cross section of the silicon substrate. Here, the interface transition region 4 exists at the boundary between the silicon crystal 2 and the silicon oxide film 3. The width of the interface transition region 4 drawn on the line in FIG. 1 is 1 nm or less.
The sample 1 has a thickness of 100 nm or less.

The surface of the sample 1 is irradiated with the electron beam 5 from the vertical direction. The electron beam 5 has a constant energy and is set to, for example, 200 keV. The electron beam 5 transmitted through the measurement region 6 is measured by the detector 7 for the intensity of only electrons having a specific energy.

The electron beam 5 undergoes energy loss peculiar to the material while passing through the sample 1. Therefore, energy loss due to plasmon excitation in the silicon crystal 2 (16.7 eV)
Considering only the above, only the electron having the energy of 183.3 eV is measured by the detector 7. Then, the electron intensity distribution of this energy is measured to determine the interface transition region width and the like.

Next, description will be made on the basis of a specific measuring device as shown in FIG. FIG. 2 is a sectional view of an analytical electron microscope in which a transmission electron microscope is equipped with a post-column type electron energy loss spectroscopic analyzer.

The electron beam emitted from the electron gun 8 is accelerated by an accelerating tube 9 with a predetermined accelerating voltage. For example, the energy is accelerated to 200 keV. Then, the incident lens 10
Then, the sample 1 attached to the sample holder 11 is irradiated through the aperture and the like. Here, the sample holder 11 is driven by the sample holder drive unit 12. The sample holder driving unit 12 is configured to control the position or the angular relationship between the sample 1 and the incident electron beam with the CPU 13.

The electron beam that has passed through the sample 1 and has received a specific energy loss is processed by an electromagnetic lens and filtered by the energy filter 14. By this filtering, only the electrons having a specific energy are taken out and imaged on the CCD 16 through the image lens 15. This imaging data is also C along with the data for driving the sample holder.
It is processed by the PU 13.

The CCD image 17 shown in FIG. 3 is the CCD 1 described above.
It is what was imaged on 6. Hereinafter, the case of imaging an electron that has undergone energy loss due to the plasmon described above will be described as an example. Silicon crystal image 2a of CCD image 17
Is an electron image transmitted through the silicon crystal 2 described in FIG. Further, the silicon oxide image 3a is also an electron image that has been transmitted through the silicon oxide film 3. Then, the interface transition region image 4a is formed between these electronic images. Various data processing is performed on such a CCD image to determine the interface transition region width and the like.

Next, a method for evaluating the interface transition region width and microroughness by such data processing will be described.

In order to evaluate the width of the interface transition area, data processing is performed along the pixel lines 18, 19, 20 on the CCD shown in FIG. For example, pixel line 18
Is plotted on the horizontal axis and the image signal intensity is plotted on the vertical axis, a graph as shown in FIG. 4 is obtained. Here, the intensity 21 is for an electron that has passed through a silicon crystal, and the intensity 22 is for an electron that has passed through a silicon oxide film. Then, such a region where the intensity transitions corresponds to an actual interface transition region. The width of the interface transition region is, as shown by a broken line in FIG. 4, a point a where a tangent line at an intermediate value between the strength 21 and the strength 22 and a line of the strength 21 and the strength 22 intersect.
It is calculated from the length between b and b.

In order to evaluate the microroughness, the image signal intensities of a large number of pixel lines described in FIG. 3 are integrated. That is, the signal intensity distributions corresponding to the respective pixel lines in FIG. 4 are all overlaid. When the intensity data is accumulated and the points a and b are determined in the same manner as shown in FIG. 4, the length between the points a and b in this case is the microroughness and the interface transition region width. Will correspond to the sum of and. Therefore, the desired microroughness value is obtained by subtracting the value of the interface transition region width from the above added value.

However, as described above, skill and great effort are required to accurately prepare a measurement sample having a wall thickness of about 100 nm. Therefore, in the usual preparation of the measurement sample, the thickness of the sample varies as shown in FIG.

Next, as a second embodiment of the present invention,
A case where the present invention is applied to the measurement of a normal sample having a variation in wall thickness will be described with reference to FIGS. 5 to 7.
The basic measurement method is the same as that described in the first embodiment. Here, FIG. 5 is a perspective view of a sample for explaining the measurement method, and FIG. 6 shows a change in the transition region width depending on the film thickness of the measurement location inside the sample. In addition, FIG.
The method for improving the accuracy of the transition region width will be described, and the change in the transition region width depending on the angle between the sample surface and the electron beam is shown.

As shown in FIG. 5, the sample 23 has variations in wall thickness. Also in this case, the interface transition region 26 exists at the boundary between the silicon crystal 24 and the silicon oxide film 25. Then, the surface of such a sample 23 is irradiated with an electron beam, and the intensity distribution of the transmitted electron beam is measured as in the first embodiment. Here, as shown in FIG. 5, the above-described intensity distribution measurement is performed in each of the plurality of measurement regions 27, 27a, 27b ... And the transition region in each measurement region is obtained by the method described in the first embodiment. Width is required.

In this case, it is necessary to evaluate the film thickness of the measurement area. This film thickness evaluation is performed as follows. The film thickness t of the region through which the electron beam has passed is expressed by the following equation.
That is, t = A · ln (I1 / I0). Where A: constant, I1: total amount of electrons reaching the detector, I
0: Total amount of transmitted electrons without energy loss.
In this way, the relative comparison of the film thicknesses at the measurement points can be made.

In FIG. 6, the horizontal axis indicates the film thickness at the measurement point as a relative value by the above method, and the vertical axis indicates the transition region width value at each measurement point. The value of the transition region width obtained is
It increases apparently as the film thickness at the measurement point increases. Here, as shown in FIG. 6, when the film thickness at the measurement location becomes a certain value or less, the value of the transition region width becomes substantially constant. That is,
There is a transition region width value 28 shown in FIG. Further, as shown in FIG. 6, the value of the transition region width is almost constant even when the film thickness at the measurement location is a certain value or more. That is, FIG.
There is a transition area width value 29 shown in. The transition region width value 28 thus obtained becomes the true transition region width. The microroughness is the value obtained by subtracting the transition region width value 28 from the transition region width value 29. The reason for this is that as the film thickness at the measurement location becomes thicker, the microroughness corresponding component is added to the electron intensity distribution of the sample transmission as in the case described in the first embodiment.

The accuracy of the transition region width obtained by the method of the present invention also depends on the angle between the sample surface and the electron beam. In the angle dependence of the transition region width, the angle between the incident direction of the electron beam and the transition region surface is important. In FIG. 7, on the horizontal axis,
The angle between the incident direction of the electron beam and the transition region surface is taken as the tilt angle of the sample. Then, the vertical axis shows the transition region width obtained by this inclination angle. As can be seen from FIG. 7, the transition region width value 30 has a minimum value at a certain inclination angle. The tilt angle in this case is such that the incident direction of the electron beam is horizontal to the transition region surface. Such a minimum value is the true transition region width to be obtained.

Next, a case where the present invention is applied to the film thickness measurement of a thin film will be described as a third embodiment with reference to FIGS. 8 and 9. Here, FIG. 8 is a perspective view of a sample for explaining the measuring method, and FIG. 9 corresponds to the one described in FIG. 4 and shows an image signal intensity distribution of transmitted electrons having energy loss in plasmon excitation. is there.

As shown in FIG. 8, the sample 31 is formed by cutting out the gate electrode portion of the MOS transistor. Here, a polysilicon 34 which is a gate electrode is formed on the silicon crystal 32 through a silicon oxide film 33 which is a gate oxide film. The polysilicon 34 contains a large amount of phosphorus impurities. In FIG. 8, the film thickness of the silicon oxide film 33 is about 2 nm. The thickness of the sample 31 is 100 nm or less.

The electron beam 35 is irradiated from the direction perpendicular to the surface of the sample 31 as described above. Then, the image signal intensity distribution on the pixel line on the CCD can be obtained in the same manner as described in the first embodiment with reference to FIG. here,
The intensity 36 is that of electrons that have passed through the silicon crystal 32, and the intensity 37 is that of electrons that have passed through the silicon oxide film 33. The intensity 38 is that of electrons that have passed through the polysilicon 34. The film thickness of the silicon oxide film 33 is
As shown in FIG. 9, the pixel line position of the intermediate value between the intensities 36 and 37 is c, the pixel line position of the intermediate value between the intensities 37 and 38 is d, and the length between the points c and d is Required from the beginning.

In the above-described embodiments, the case where the measurement is performed in the interface region between the silicon substrate and the silicon oxide film and the case where the gate electrode portion of the MOS transistor is used has been described. The present invention is not limited to such a case. The present invention can be similarly applied to the measurement of the interface region between the diffusion layer of the source / drain region of the MOS transistor and the silicide layer thereabove. Similarly, the present invention can be applied to measurement of the interface region between polysilicon and a silicide layer in a gate electrode having a polycide structure.

Alternatively, the thin film measuring method of the present invention is
The same can be applied to the measurement of the film thickness of the capacitive insulating film of the capacitor in the memory cell portion of the RAM as described in the third embodiment.

Further, in the embodiment of the present invention, the case where the energy loss of electrons is due to plasmon excitation has been described. The present invention is not limited to such energy loss. In addition, focusing on the energy loss specific to the specific material, the electron intensity distribution having the energy loss may be obtained in the same manner as described in the embodiment.

[0046]

As described above, in the present invention, the sample is irradiated with electrons having a predetermined incident energy.
Then, among the electrons that have passed through the sample, the electron intensity having a specific energy loss is measured. This electron intensity data processing is performed to measure the interface transition region, microroughness, film thickness of the ultra-thin film, etc. of the laminated material.

Therefore, in the present invention, in the analysis of the semiconductor device, the measurement and evaluation of the semiconductor element completed through the manufacturing process of the semiconductor device becomes easy.

Further, in the method of the present invention, it is not always necessary to make the sample film thickness uniform, the sample preparation becomes very easy, and no special skill or labor is required in preparing the sample.

As described above, the measuring method of the present invention is very effective in speeding up the analysis and evaluation of a semiconductor device that is miniaturized or densified, and promotes realization of a high-performance semiconductor device. Become.

[Brief description of drawings]

FIG. 1 is a perspective view of a sample for explaining a measuring method according to a first embodiment of the present invention.

FIG. 2 is a schematic view of an apparatus for explaining the measuring method according to the first embodiment of the present invention.

FIG. 3 is an image schematic diagram for explaining the measuring method according to the first embodiment of the present invention.

FIG. 4 is a signal distribution diagram for explaining the measuring method according to the first embodiment of the present invention.

FIG. 5 is a perspective view of a sample for explaining a measuring method according to a second embodiment of the present invention.

FIG. 6 is a graph for explaining the measuring method according to the second embodiment of the present invention.

FIG. 7 is a graph for explaining the measuring method according to the second embodiment of the present invention.

FIG. 8 is a perspective view of a sample for explaining a measuring method according to a third embodiment of the present invention.

FIG. 9 is a signal distribution diagram for explaining the measuring method according to the third embodiment of the present invention.

[Explanation of symbols]

1,23,31 sample 2,24,32 Silicon crystal 2a Silicon crystal image 3a Silicon oxide film image 4a Interface transition region image 3,25,33 Silicon oxide film 4,26 Interface transition region 5,35 electron beam 6,27,27a, 27b Measurement area 7 detector 8 electron gun 9 Accelerator 10 incident lens 11 Sample holder 12 Sample holder drive 13 CPU 14 Energy filter 15 image lens 16 CCD 17 CCD image 18, 19, 20 pixel lines 34 Polysilicon

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01N 23/04 G01B 15/02 H01J 37/252 H01L 21/66

Claims (10)

(57) [Claims] 1. A sample prepared by cutting out a cross section of a substrate on which a first substance and a second substance are stacked is irradiated with electrons having a predetermined energy, and the sample is transmitted through the sample. The method for measuring an interface transition region is characterized in that the electron amount of electrons having energy loss caused by plasmon excitation peculiar to the first substance or the second substance among the electrons to be measured is measured. 2. The detector surface on which the electron amount is measured,
The interface transition region measuring method according to claim 1, wherein a large number of pixels for measuring the amount of electrons are arranged in a matrix. 3. An electron signal intensity distribution of each pixel is taken for pixels on one straight line of the pixels (hereinafter referred to as a pixel line), and the electron signal intensity corresponding to the interface transition region. The method for measuring an interface transition region according to claim 2, wherein the width of the interface transition region is measured from a change in intensity. 4. The signal intensity distribution of electrons is obtained by adding the signal intensities of a plurality of pixel lines, and the microroughness of the interface transition region is measured together with the width of the interface transition region. Item 3. A method for measuring an interface transition region according to Item 3. 5. In a sample having a film thickness distribution, the width of the interface transition region is determined by the measuring method according to claim 3 at each measurement location in the sample where the film thickness is different, and the determination is performed. The minimum value of the data distribution of the width of the interface transition region with respect to the sample film thickness is the true width of the interface transition region, and the microroughness of the interface transition region is determined from the maximum value of the data distribution. Measuring method of transition region. 6. The incident angle between the electron-irradiated surface of the sample and the electron is changed, and the width of the interface transition region is determined by the measuring method according to claim 3 at each incident angle, and the determined interface is determined. A method for measuring an interface transition region, wherein the minimum value of the data distribution of the width of the transition region with respect to the incident angle is the true width of the interface transition region. 7. The one of claims 1 to 6, wherein the interface transition region is a transition region between a silicon material and a silicon oxide film or a transition region between a silicon material and a silicide film. The method for measuring the interface transition region according to. 8. An electron having a predetermined energy in a cross section of a sample prepared by cutting out cross sections of a substrate in which a first substance, a second substance and a third substance are laminated in this order. Of electrons passing through the sample, which have energy loss caused by plasmon excitation peculiar to the first substance, the second substance, or the third substance, of the electrons transmitted through the sample are measured by the detector. A method for measuring the transition region of an interface. 9. A large number of pixels for measuring the amount of electrons are arranged in a matrix on the surface of the detector, and a signal intensity distribution of electrons of each pixel is taken with respect to a pixel line. The film thickness of the second substance is determined from the change in the signal intensity of the electron corresponding to the interface transition region of the second substance and the change in the signal intensity of the electron corresponding to the interface transition region of the second substance and the third substance. The method for measuring an interface transition region according to claim 8, wherein: 10. The method according to claim 8, wherein the first material is a silicon crystal, the second material is a silicon oxide film, and the third material is a silicon film or a silicide film. 9. The method for measuring the interface transition region according to item 9.