JP2000304709A - Method for measuring interface transition region - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate the measurement and evaluation of semiconductor element by applying an electron with a specific energy to the section of a substrate where two kinds of substances are laminated and measuring the amount of electrons with a specific energy loss that passes through a sample. SOLUTION: In a sample 1, a silicon oxide film 3 is formed on a silicon substrate and the section of the silicon substrate is cut out. A boundary transition region 4 exists at the boundary between a silicon crystal 2 and the silicon oxide film 3. For example, the width of the boundary transition region 4 is equal to or less than 1 nm and the thickness of the sample 1 is equal to or less than 100 nm. An electron beam, for example, with 200 keV is applied vertically to the surface of the sample 1. An electron beam 5 through a measurement region 6 is subjected to an energy loss that is specific to a material during the passage. Considering only the energy loss by plasmon induction in the silicon crystal 2, only an electron with 183.3 eV energy is detected by a detector 7. The electron intensity distribution of the energy is measured and an interface transition region width or the like is determined.

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 determining the thickness of an ultrathin film such as an ultrathin silicon oxide film formed on a silicon substrate, an interface transition region, and microroughness of an interface. Related to the measurement method.

[0002]

2. Description of the Related Art As semiconductor devices become more highly integrated or higher in density, semiconductor elements such as MOS transistors are reduced in size. In the miniaturization of the semiconductor element, a thin film of a material is required along with a reduction in pattern size.

As described above, when a semiconductor element is miniaturized and its design rule is reduced to about 100 nm, for example, MOS
The thickness of the gate oxide film of the transistor is extremely reduced to about 2 nm. Usually, the width of the transition region at the interface between the silicon substrate and the gate oxide film is as small as 1 nm or less. However, as the film becomes thinner, such a transition region width cannot be ignored in terms of the characteristics of the semiconductor element and needs to be controlled. For this,
Generally, a means for measuring the width of the transition region between the materials to be laminated becomes important. At the same time, the evaluation of the micro-roughness of the interface becomes important.

Further, means for measuring the thickness of a thin film material constituting a semiconductor element has also become important.
Thin films such as gate oxides are directly related to the properties of semiconductor devices, and their control is particularly important.

As a means for measuring the thickness of the ultra-thin oxide film and the micro roughness of the interface, there is, for example, an X-ray reflection method as described in JP-A-11-6804. As a means for measuring micro roughness or surface roughness, for example, the AFM (atomic force measurement) method is well known.

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

[0007]

The prior arts described above have the following problems, respectively.

For example, the interface or micro-roughness between the silicon substrate and the gate oxide film has changed greatly due to the heat treatment in the above-described manufacturing process, the cleaning of the silicon substrate surface, 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 the semiconductor device, the measurement and evaluation of the semiconductor element completed through the manufacturing process of the semiconductor device becomes important.

However, in the above-mentioned X-ray reflection method and AFM method, it is necessary to widen the measurement area of the sample, and it is necessary 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, the thickness of a sample to be formed needs to be about 100 nm in order to transmit an electron beam. In this case, the credibility of the measurement improves as the sample thickness decreases. For this reason, it is necessary to make the thickness of the sample to be a predetermined thickness and to be uniform. However, preparation of such a sample requires skill and a great deal of labor.

[0011] The above-mentioned problems become more apparent as the thickness of the thin film material forming the semiconductor element becomes thinner.

An object of the present invention is to solve the above-mentioned problems and to provide a measuring method for easily evaluating the thickness of an ultra-thin film used for manufacturing a semiconductor device, an interface transition region, an interface micro-roughness, and the like. It is in.

[0013]

For this purpose, in the measuring method of the present invention, a sample formed by cutting out a cross section of a substrate on which a first substance and a second substance are laminated is cut off with respect to the sample. Are irradiated with electrons having a predetermined energy, and the amount of electrons having a specific energy loss among the electrons transmitted through the sample is measured. Here, the specific energy loss is caused by plasmon excitation specific to the first substance or the second substance.

In addition, on the detector surface in the measuring method of the present invention, a large number of pixels each measuring the amount of electrons are arranged in a matrix. Then, the signal intensity distribution of the electrons of each pixel is taken for 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.

Further, the signal intensities of a plurality of pixel lines are added to obtain a signal intensity distribution of electrons, and the micro-roughness of the interface transition region is measured together with the width of the interface transition region.

Further, in the measuring method of the present invention, in a sample having a film thickness distribution, the width of the interface transition region at each of the measurement points having different film thicknesses in the sample is determined by the measuring method. The minimum value of the data distribution of the width of the interface transition region with respect to the sample film thickness is regarded as the true width of the interface transition region, and the micro roughness of the interface transition region is determined from the maximum value of the data distribution. Alternatively, the incident angle between the electron irradiation surface of the sample and the electrons is changed, the width of the interface transition region is determined at each incident angle by the measurement method, and the incident angle of the determined width of the interface transition region is determined. Is defined 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 sample formed by cutting out a cross section of a substrate in which a first substance, a second substance, and a third substance are laminated in this order is prepared. Are irradiated with electrons having a predetermined energy, and the amount of electrons having a specific energy loss among the electrons transmitted through the sample is measured by a detector. Here, the specific energy loss is caused by plasmon excitation specific to the first substance, the second substance, or the third substance.

A large number of pixels for measuring the amount of electrons are respectively 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 a pixel line. The film thickness of the second substance is determined from the change in the signal intensity of the electrons corresponding to the interface transition region of the second substance and the change in the signal intensity of the electrons corresponding to the interface transition area between the second substance and the third substance. Is done. Here, 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.

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 method is used to measure the interface transition region, the micro roughness, the thickness of the ultra-thin film, etc. of the material to be laminated.

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

[0022]

Next, a first embodiment of the present invention will be described with reference to FIGS. In the first embodiment, the basic concept of the measurement method of the present invention will be described. Here, the interface transition region width and the interface micro-roughness between the silicon substrate and the silicon oxide film are evaluated.

FIG. 1 is a perspective view of a sample for explaining the measuring method, and FIG. 2 is a schematic diagram of an apparatus for explaining the measuring method. FIG. 3 is a schematic diagram of an image for explaining the measurement 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 obtained by forming a silicon oxide film as a second substance on a silicon substrate as a first substance and cutting out a cross section of the silicon substrate. Here, an 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 thickness of the sample 1 is 100 nm or less.

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

The electron beam 5 receives an energy loss peculiar to the material during transmission 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 electrons having the energy of 183.3 eV are 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, a description will be given based on a specific measuring device as shown in FIG. FIG. 2 is a cross-sectional view of an analytical electron microscope having a transmission electron microscope and a post-column electron energy loss spectrometer.

The electron beam exiting the electron gun 8 is accelerated by an acceleration tube 9 at a predetermined acceleration voltage. For example, it is accelerated to have an energy of 200 keV. Then, the incident lens 10
Then, the light is irradiated onto the sample 1 attached to the sample holder 11 through a diaphragm and the like. Here, the sample holder 11 is driven by the sample holder driving unit 12. The sample holder driving unit 12 controls the position or the angle 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 an energy filter 14. By this filtering, only electrons having a specific energy are taken out and imaged on the CCD 16 via the image lens 15. This imaging data is also stored together with the data for driving the sample holder.
The processing is performed by the PU 13.

The CCD image 17 shown in FIG.
6 is formed. Hereinafter, a case of imaging an electron that has suffered energy loss due to the above-described plasmon 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. Similarly, the silicon oxide image 3a is an electron image transmitted through the silicon oxide film 3. Then, an interface transition region image 4a is formed between these electron images. Such CCD images are subjected to various data processing to determine the interface transition region width and the like.

Next, a method of evaluating the interface transition region width and the micro roughness by such data processing will be described.

In order to evaluate the width of the interface transition region, data processing is performed along the pixel lines 18, 19 and 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 electrons that have passed through the silicon crystal, and the intensity 22 is for electrons that have passed through the silicon oxide film. And the area | region where such intensity | strength changes respond | corresponds to an actual interface transition area | region. As shown by the broken line in FIG. 4, the width of the interface transition region is a point a at which a tangent at an intermediate value between the intensities 21 and 22 intersects the lines of the intensities 21 and 22.
And b.

In order to evaluate the micro roughness, the image signal intensities at a large number of pixel lines described with reference to FIG. 3 are integrated. That is, the signal intensity distributions corresponding to the respective pixel lines in FIG. 4 are all superimposed. When such intensity data accumulation processing is performed 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 determined by the micro roughness and the interface transition region width. Will correspond to the sum of. Therefore, by subtracting the value of the interface transition region width from the added value, the required micro roughness value is obtained.

However, to accurately prepare a measurement sample having a thickness of about 100 nm requires skill and great effort as described above. For this reason, in the preparation of a normal measurement sample, the thickness of the sample varies as shown in FIG.

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

As shown in FIG. 5, the sample 23 has a thickness variation. 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 electron beam is irradiated on the surface of the sample 23, 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 a plurality of measurement areas 27, 27a, 27b,..., And the transition area is determined in each measurement area by the method described in the first embodiment. Width is required.

In this case, it is necessary to evaluate the thickness of the measurement area. This film thickness evaluation is performed as follows. The film thickness t in the region where the electron beam has transmitted 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, a relative comparison of the film thickness at the measurement location can be made.

In FIG. 6, the horizontal axis indicates the film thickness at the measurement point as a relative value according to the above method, and the vertical axis indicates the value of the transition region width at each measurement point. The value of the obtained transition area width is
As the film thickness at the measurement point increases, the apparent value increases. Here, as shown in FIG. 6, when the film thickness at the measurement location becomes equal to or less than a certain value, the value of the transition region width becomes substantially constant. That is,
There is a transition region width value 28 shown in FIG. In addition, as shown in FIG. 6, even when the film thickness at the measurement location becomes a certain value or more, the value of the transition region width becomes substantially constant. That is, FIG.
The transition region width value 29 shown in FIG. The transition region width value 28 obtained in this manner becomes a true transition region width. Further, the micro roughness is obtained by subtracting the transition region width value 28 from the transition region width value 29. The reason for this is that when the film thickness at the measurement location increases, the micro-roughness-corresponding component is added to the electron intensity distribution of the sample transmission, as 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, the horizontal axis is
The angle between the incident direction of the electron beam and the transition region surface is taken as the tilt angle of the sample. The vertical axis represents the transition region width obtained at this inclination angle. As can be seen from FIG. 7, the transition region width value 30 takes a minimum value at a certain inclination angle. The inclination angle in this case is such that the incident direction of the electron beam becomes 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 measurement of the thickness of a thin film will be described as a third embodiment with reference to FIGS. 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 by plasmon excitation. is there.

As shown in FIG. 8, the sample 31 is formed by cutting out the gate electrode of a MOS transistor. Here, polysilicon 34 as a gate electrode is formed on silicon crystal 32 via silicon oxide film 33 as a gate oxide film. This polysilicon 34 contains a large amount of phosphorus impurities. In FIG. 8, the 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 on the surface of the sample 31 from a vertical direction. Then, the image signal intensity distribution on the pixel line on the CCD is obtained in the same manner as described in FIG. 4 in the first embodiment. here,
The intensity 36 is for electrons that have passed through the silicon crystal 32, and the intensity 37 is for electrons that have passed through the silicon oxide film 33. And the intensity 38 is that of electrons passing through the polysilicon 34. The thickness of the silicon oxide film 33 is
As shown in FIG. 9, the position on the pixel line having an intermediate value between the intensities 36 and 37 is represented by c, and the position on the pixel line having an intermediate value between the intensities 37 and 38 is represented by d. It is required from that.

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

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

In the embodiment of the present invention, the case where the energy loss of electrons is caused by plasmon excitation has been described. The present invention is not limited to such energy losses. In addition, by paying attention to the energy loss specific to a 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, a sample is irradiated with electrons having a predetermined incident energy.
Then, the electron intensity having a specific energy loss among the electrons transmitted through the sample is measured. The data processing of the electron intensity is performed to measure an interface transition region, a micro roughness, a thickness of an extremely thin film, and the like of the laminated materials.

Therefore, according to the present invention, in the analysis of the semiconductor device, the measurement and evaluation of the semiconductor element completed through the semiconductor device manufacturing process are facilitated.

Further, in the method of the present invention, it is not always necessary to prepare a uniform film thickness of the sample, the preparation of the sample 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 for speeding up the analysis and evaluation of a miniaturized or high-density semiconductor device, and promotes the realization of a high-performance semiconductor device. Become.

[Brief description of the drawings]

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

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

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

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

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

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

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

[Description of Signs] 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 Electrons Line 6, 27, 27a, 27b Measurement area 7 Detector 8 Electron gun 9 Accelerator tube 10 Incident lens 11 Sample holder 12 Sample holder driving unit 13 CPU 14 Energy filter 15 Image lens 16 CCD 17 CCD image 18, 19, 20 Pixel line 34 polysilicon

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2F067 AA26 AA27 AA46 BB17 CC15 DD07 HH06 KK06 LL02 LL19 RR21 2G001 AA03 BA11 CA03 EA05 FA18 GA13 HA13 KA11 KA20 LA11 RA01 4M106 BA02 CA24 CA48 DH03 DH02 5C033 RR02

Claims (12)

[Claims] 1. A sample formed by cutting out a cross section of a substrate on which a first substance and a second substance are laminated is irradiated with electrons having a predetermined energy to the cross section, and transmitted through the sample. A method of measuring an interface transition region, wherein an amount of electrons having a specific energy loss is measured among electrons that are emitted. 2. The method according to claim 1, wherein the specific energy loss is the first energy loss.
2. The method for measuring an interface transition region according to claim 1, wherein the measurement is caused by plasmon excitation specific to the substance or the second substance. 3. A detector surface on which the amount of electrons is measured,
3. The method according to claim 1, wherein a number of pixels for measuring the amount of electrons are arranged in a matrix. 4. A signal intensity distribution of electrons of each pixel is taken for a pixel on one straight line (hereinafter referred to as a pixel line) among the pixels, and the signal of the electrons corresponding to the interface transition region is obtained. 4. The method according to claim 3, wherein a width of the interface transition region is measured from a change in intensity. 5. The method according to claim 1, wherein the signal intensities of a plurality of pixel lines are added to obtain a signal intensity distribution of electrons, and the micro-roughness of the interface transition region is measured together with the width of the interface transition region. Item 5. The method for measuring an interface transition region according to Item 4. 6. In a sample having a film thickness distribution, the width of the interface transition region is determined by the measuring method according to claim 4 at each of measurement points having different film thicknesses in the sample, and the determined value is obtained. The minimum value of the data distribution of the width of the interface transition region with respect to the sample film thickness is taken as the true width of the interface transition region, and the micro roughness of the interface transition region is determined from the maximum value of the data distribution. Transition region measurement method. 7. The angle of incidence between the electron irradiation surface of the sample and the electrons is changed, and the width of the interface transition region is determined by the measurement method according to claim 4 at each of the angles of incidence, and the determined interface is determined. A method of measuring an interface transition region, wherein a minimum value of a data distribution of the width of the transition region with respect to the incident angle is set as a true width of the interface transition region. 8. The semiconductor device according to claim 1, 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. 3. The method for measuring an interface transition region according to item 1. 9. A sample formed by cutting out a cross section of a substrate in which a first substance, a second substance, and a third substance are laminated in this order, and having an electron having a predetermined energy in the cross section. Wherein the amount of electrons having a specific energy loss among the electrons transmitted through the sample is measured by a detector. 10. The method according to claim 9, wherein the predetermined energy loss is caused by plasmon excitation specific to the first substance, the second substance, or the third substance. 11. A large number of pixels each measuring an amount of electrons are arranged in a matrix on the surface of the detector.
The signal intensity distribution of the electrons of each pixel is taken with respect to the pixel line, the signal intensity change of the electrons corresponding to the interface transition region between the first substance and the second substance, and the second substance and the third substance 11. The method according to claim 9, wherein the film thickness of the second substance is determined from a change in the signal intensity of electrons corresponding to the interface transition region. 12. The method according to claim 9, 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. The method for measuring an interface transition region according to claim 10.