JPH0888258A - Method for evaluating electrical characteristics of semiconductor materials - Google Patents

Abstract

(57) [Summary] [Purpose] Directly measure the electrical characteristics of patterned micro-operation areas such as LSI and ULSI. According to a method of evaluating electrical characteristics of a semiconductor material of the present invention, a semiconductor material piece is mounted on a sample mounting table so that a probe having a fine probe is brought into contact with an operating region of a surface or a cross section of the semiconductor material piece so that current can be measured. Place on. On the other hand, a charged particle source such as an electron gun or an ion gun is arranged so that an electric current can be applied to the vicinity of the operation region, and the electron beam or the ion beam is focused and irradiated to the operation region or the vicinity thereof. Then, the probe is brought into contact with a portion corresponding to the operation region so that a part of the applied current flows to the probe of the probe, the probe is scanned to measure the current, and a change in the current in the operation region is detected. Since the change of the current thus detected depends on the electric resistance value of the operating region, the resistance value distribution of the operating region can be evaluated, and the impurity concentration is estimated by converting from the electric resistance value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating electric characteristics of semiconductor materials.

[0002]

2. Description of the Related Art Conventionally, in the manufacturing process of semiconductor devices such as LSI and ULSI, a semiconductor substrate patterned by a fine processing technique such as photoetching is used because a minute region of a surface layer of a semiconductor material is used as an operation region. Impurities are added by ion implantation or thermal diffusion from the surface to a very small and limited area of the material, and then heat treatment is performed again to diffuse and activate the added impurities electrically, thereby reducing the source and A semiconductor element with a drain formed is obtained. FIG. 6 shows an example of a semiconductor device manufactured in this manner. An operating region 2 such as p ⁺ and n ⁺ layers is formed on a semiconductor substrate (base) 1 and phosphorous silicate as a protective oxide film is further formed. It has a structure in which a glass film (PSG) 3 and an aluminum layer 4 as an electrode are formed.

Generally, in a semiconductor device such as an LSI or ULSI, the size of an operating region such as a source or a drain (corresponding to the operating region 2 such as a p ⁺ or n ⁺ layer in FIG. 6) is, for example, 16 MB. The size of the random access memory (DRAM) is 1 μm or less, and the size of the operating region becomes smaller as the degree of integration is improved.

On the other hand, in the manufacture and development of semiconductor devices such as LSI and ULSI, precise control of the electrical characteristics such as the size of the operating area, the electric resistance value, and the carrier concentration is indispensable, and the operating area becomes smaller. The precision of the control is required more and more, and in order to answer it, the evaluation and estimation of the electric characteristics of the semiconductor material are required to be accurate.

[0005]

By the way, in the operation region where the semiconductor material is doped with impurities as described above,
The specific resistance and carrier concentration change in the range of length, width, and depth of several tens nm to 1 μm. Since the operating characteristics of the finally manufactured semiconductor device differ depending on the magnitude or depth of the change in the specific resistance and the degree of change in the specific resistance in the depth direction, it is possible to control the change in the specific resistance. It is indispensable for designing and manufacturing semiconductor devices. That is, in the manufacturing process of a semiconductor device, it is indispensable to estimate the change in the specific resistance of the semiconductor material (semiconductor substrate) used in the operating region near the surface in the order of nm.

However, a means for directly measuring the change in the specific resistance of the operating region of a semiconductor device such as LSI or ULSI has not been known so far, and the conventional method for evaluating the electrical characteristics of semiconductor materials has been that of impurities. A method of estimating the manufacturing process such as injection and thermal diffusion by performing simulation on a computer has been used. Then, as a means to support the accuracy of this simulation, a direct method of measuring the resistivity in the depth direction of the operating region and an indirect method of estimating it by measuring the concentration distribution of the added impurities have been used. , In these cases,
In many cases, a sample in which impurities are diffused into a large-area sample that is not patterned like an actual semiconductor device is experimentally created and measured, and the impurity is introduced into a 1 μm region such as a semiconductor device such as LSI or ULSI. It was not possible to evaluate the three-dimensional impurity distribution including the lateral direction and the specific resistance distribution when added and diffused.

[0007] For example, in the indirect method, by using a surface analyzer such as Auger electron spectroscopy or secondary ion mass spectrometry, the distribution of impurities can be measured in the depth direction with accuracy of nm order, but in the lateral direction. 0.1 μm is the limit, and the sensitivity is insufficient to evaluate a low concentration diffusion region of 0.001% to 0.0001%.

Furthermore, not all impurities existing in the operating region are involved in electrical conduction, and some may exist in a so-called electrically inactive state, so that a true specific resistance distribution can be obtained. There was also the problem that there was no guarantee that it would be possible to do so.

On the other hand, the two-probe method, the four-probe method, the spreading resistance method and the like are known as methods for directly measuring the specific resistance. All of these methods measure the specific resistance by measuring the current flowing through the semiconductor material or by measuring the voltage between two opposing terminals. It cannot be smaller than the diameter of the needle. At present, the limit is several tens of μm, and therefore the LS, which is an assembly of elements of 1 μm or less.
It has been impossible to evaluate the electrical characteristics of semiconductor devices such as I and ULSI.

On the other hand, since the scanning probe microscope developed in recent years can observe the surface morphology of the sample in atomic order and can also evaluate the electronic state of the sample, the surface of various materials including semiconductor materials can be evaluated. Is being used for morphological evaluation on the atomic order. The method of evaluating the material surface by this scanning probe microscope is to detect the tunnel current flowing from the sample by bringing the sharpened probe close to the sample, or to bring the probe into contact with the sample. This is a method of observing the surface morphology of the sample in atomic order by detecting the deflection of the probe with a highly sensitive photodetector, and the position resolution is extremely high.

However, the scanning probe microscope used to execute the former method is particularly called a scanning tunneling microscope, and the current measured by this one reflects the electronic state of the material surface immediately below the probe. Therefore, the electric resistance of the material itself cannot be measured.

The scanning probe microscope used for carrying out the latter method is particularly called an atomic force microscope, and in principle, it is similar to the spreading resistance method because the probe is brought into direct contact with the sample. However, since the probe is sharpened, the specific resistance can be evaluated with a resolution on the order of nm or less. However, in this case, unlike macroscopic methods such as the two-probe method and the four-probe method, the purpose is to measure the specific resistance of a specific portion of over 1 million patterned minute elements. As it is difficult to supply current to that part, in addition, since the surface of the semiconductor material is covered with an insulating film such as an oxide film, the element under the insulating film or between the insulating films should be evaluated directly. However, it has not been put to practical use until now in the evaluation of electric properties of semiconductor materials.

The present invention has been made in view of such conventional problems, and a local resistance of a minute operating region of a semiconductor material having an operating region of 1 μm or less like a semiconductor device such as LSI and ULSI. An object of the present invention is to disclose a method for evaluating electrical characteristics of a semiconductor material, which can be used for evaluating the electrical characteristics of the semiconductor material by easily and highly accurately detecting a change in value.

[0014]

According to the method for evaluating electric characteristics of a semiconductor material of the present invention, the semiconductor material is placed on a placing table which can be moved and adjusted, and charged particles are continuously applied to a predetermined portion of the semiconductor material. , And any part of the semiconductor material is brought into contact with the probe to scan, and part of the current supplied to the semiconductor material by the charged particles is measured by the probe, and at the same time the ground current from the base part of the semiconductor is measured. The current ratio between the current value measured by the probe and the ground current value at each contact portion of the probe is obtained.

[0015]

In the method for evaluating the electrical characteristics of the semiconductor material of the present invention, the semiconductor material is mounted on the sample mounting table so that the probe having a fine probe is brought into contact with the operating region of the surface or the cross section of the semiconductor material piece to measure the current. Place it. On the other hand, a charged particle source such as an electron gun or an ion gun is arranged so that an electric current can be given near the operation region, and charged particles such as an electron beam or an ion beam are focused and irradiated to the operation region or its vicinity. To do. Then, the probe is brought into contact with a portion corresponding to the operation region to scan so that a part of the applied current flows to the probe of the probe, and the current is measured. As this probe, a scanning probe microscope or the like having a mechanism capable of reducing the contact area to several tens of nm or less and having a mechanism for keeping the contact pressure between the probe and the sample constant is suitable, but the probe is a predetermined part including the operating region. Is configured to be able to scan, and a change in current in the operation region is detected.

Since the change in the current thus detected depends on the electric resistance value of the operating region, the resistance value distribution of the operating region can be evaluated, and the impurity concentration can be estimated by converting from the electric resistance value.

The charged particles used as the current source may be an electron beam or an ion beam. Further, both of them have a function as a scanning microscope, so that the measurement site of the semiconductor material can be easily selected and the probe of the scanning probe microscope can be easily aligned with the measurement site.

Further, when the ion beam is used, the depth of penetration of ions into the substrate of the semiconductor material can be set to several nanometers or less. Therefore, in the shallow operating region, more precise measurement can be performed, and in the operating region. A three-dimensional evaluation is also possible by adopting a method of measuring the current at each depth while etching. On the other hand, when the electron beam is used, the penetration depth becomes deep, but the electron beam diameter can be narrowed down to about 1 nm, so that the resistance distribution on the plane can be precisely measured. Further, if both are used in combination, it is possible to perform measurement with higher accuracy.

In addition to the charged beam such as the electron beam or the ion beam as the charged particle source, another probe may be brought into contact with a predetermined portion of the semiconductor material and an electric current may be sent through the probe. .

[0020]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 shows an apparatus for evaluating electrical characteristics of a semiconductor material used in an embodiment of the present invention, in which a piezo actuator and a stepping motor 6 are used for three-dimensional directions X, Y (directions perpendicular to the plane of FIG. 1) and Z. Scanning probe microscope system 10 having an optical detection system 9 for detecting irregularities on the sample surface, which has a sample mounting table 7 capable of fine and coarse movements and a conductive probe 8, and an electric charge at a specific portion of the sample. Electron beam irradiation system 11 for giving an electric charge, an ion beam irradiation system 12 for giving an electric charge to a specific portion of a sample, and a control system (CPU) composed of a microcomputer for collectively controlling each of these components. 13, an input device 14 for inputting an operation command to this device, and a display device 15 for performing a monitoring operation.

The sample mounting table 7 can hold the sample 16 in either a horizontal or vertical direction, and the stepping motor 6 coarsely moves the sample 16 in the X, Y and Z directions up to the μm order. A step scan controller 17 is provided for aligning the probe 8 so that the probe 8 comes into contact with a specific portion. Further, the piezo actuator 5 allows the angstrom in the X and Y directions (1.0 × 10
^-10 m) An XY scanning system 18 for precision scanning and a Z-axis controller 19 for controlling the Z direction in conjunction with the optical detection system 9 are provided, and the scanning probe microscope system 10 is used to The shape can be observed and positioned on the order, and the contact pressure of the probe can be adjusted.

Further, the scanning probe microscope system 10 is equipped with a current detecting device 20 for detecting an electric current by bringing the tip of the probe 8 into contact with the sample 16, and at the same time, the sample mounting table 7 has a bottom surface of the sample 16 or an arbitrary portion. A ground current detection device 21 for measuring a current flowing from a specific portion, for example, a semiconductor base portion to the ground, of the current supplied to the sample 16 by grounding is also provided.

The electron beam irradiation system 11 and the ion beam irradiation system 12 have the accuracy of converging the beam diameter in the order of nm. You can get an enlarged image of The electron beam irradiation system 11 and the ion beam irradiation system 12 are arranged in a direction of 0 to 180 ° with respect to the direction of the probe 8 of the scanning probe microscope system 10, and observe and confirm the position of the operation area on the surface of the sample 16. Further, the ion beam irradiation system 12 is arranged so that the surface of the sample 16 can be etched. In this case, in order to facilitate the observation of the surface of the sample 16, and in consideration of the good convergence of the electron beam and the ion beam and the ease of alignment, the electron beam irradiation system 11 uses the probe 8 as the electron beam. The angle of the ion beam irradiation system 12 is set to 30 to 90 ° with respect to the
It is preferable to set so that

The control system 13 is a sample table 7
Control of the stepping motor 6, XY drive of the piezo actuator 5, an optical detection system 9 for detecting shake of the probe 8 according to the unevenness of the sample 16, and a piezo actuator for moving the sample 16 up and down according to the size of the shake. 5, the Z-axis servo, the measurement of the amount of current flowing through the probe 8 and the sample mounting table 7, the scanning of the electron beam emitted from the electron beam irradiation system 11 and the ion beam irradiation system 12, and the scanning of the ion beam respectively are controlled. Various control calculation processes for collectively measuring the two-dimensional or three-dimensional resistivity distribution or capacitance distribution of the operating region on the cross section or the surface of the sample 16 are executed.

Next, an electric characteristic evaluation method executed by the above-mentioned electric characteristic evaluation apparatus for semiconductor materials will be described. As shown in FIG. 2 in an enlarged manner, the sample 16 of the semiconductor material is placed and positioned on the sample placing table 7. The sample 16 has a structure in which the resistance change region 16B of the operation region shown by hatching is formed on the base 16A, and the electrode 16C is formed on the surface. Then, in order to measure the electrical characteristics in the depth direction of the operation region of the sample 16, the positional relationship is set so that the probe 8 is brought into contact with the cleaved cross section of the semiconductor element for scanning.

The probe 8 of the scanning probe microscope system is supported by a conductive cantilever 23. The current flowing through the probe 8 and the cantilever 23 is detected by the current detecting device 20, and at the same time the voltage detecting device 24 detects the voltage. Is detected, and the current flowing from the semiconductor base 16A to the ground 25 is also detected by the current detecting device 21.

The charged beam 22 is emitted from the electron beam irradiation system 11 or the ion beam irradiation system 12 in the above-described arrangement, and the charged beam 22 is irradiated so as to be converged on the surface of the sample 16 in the vicinity of the operation region. Thereby, through the wiring on the surface of the sample 16 or the electrode 16C,
Alternatively, the operating region 1 is directly operated without passing through the wiring or the electrode 16C.
A charge is supplied to the sample containing 6B.

This charge temporarily accumulates on the surface of the sample 16 and a local potential difference is generated. This potential difference is large due to the current density of the charged particles and the specific resistance of the heterogeneous region such as the operating region 16B of the semiconductor sample 16. But different. Therefore, the electric charge supplied to the surface of the sample 16 by the irradiation of the charged beam flows as a current according to the potential gradient formed by the above potential difference, and is transferred to the outside from the base 16A of the sample 16 and the probe 8 of the scanning probe microscope system 10. Although flowing out, these currents can be measured by the current detecting devices 20 and 21, and the specific resistance of the operating region 16B can be obtained from the current ratio. In addition, the scanning probe microscope system 1
By using the probe 8 of 0 as a terminal of the voltage detection device 24, the potential of the operation region 16B can also be measured.

Next, by scanning the scanning probe microscope system 10 with the piezo actuator 5 of the sample mounting table 7, it is possible to measure the distribution of the specific resistance and the potential distribution in the two-dimensional XY direction. Here, the surface of the sample 16 can be measured by changing the mounting position of the sample 16. When measuring the surface of the sample 16,
The surface of the sample 16 is etched by the ion beam irradiation system 12 to remove the electrode 16C and the oxide film, the operation region 16B is exposed, and the specific resistance distribution in that region is measured.

An example of calculating the specific resistance will be described with reference to FIG. 3 in which the current path is approximately replaced by an equivalent circuit. In this equivalent circuit, E is the local potential of the surface of the sample 16 generated by the supply of charged particles, I is the current amount of the charged particles, ib is the current flowing through the base 16A of the sample 16, and is is the scanning probe microscope 10. The current flowing through the probe 8 and ri are resistance values related to current diffusion at the irradiation point of the charged beam and correspond to contact resistance. rb is the specific resistance of the base 16A of the sample 16, and rd is the operating region 16B.
Has a different value depending on the contact portion of the probe 8. rs is the contact resistance of the probe 8, and rp is the resistance of the probe 8 and the cantilever 23 of the scanning probe microscope system 10.

The relational expression of is / ib = rb / (rd + rs + rp) (1) holds among these voltages, currents and resistances.

Here, rs is a spreading resistance and is represented by rs = p / 2πa. Here, p is the specific resistance of the portion of the operating region 16B in contact with the probe, and a is the radius of curvature of the portion of the tip of the probe in contact with the sample surface. Since the radius of curvature a is as small as 10 nm or less, rs >> r
d and rp, and the equation (1) can be approximated as follows.

Is / ib = rb / rs rb is uniformly determined by the sample 16. Further, the contact radius a at rs can be always maintained at a constant value by keeping the contact pressure of the probe 8 of the scanning probe microscope constant by the Z-axis control of the piezo actuator 5. Therefore, the current ratio is / ib changes only by the change in the specific resistance p of the operating region 16B of the sample 16, and the specific resistance distribution of the operating region 16B can be obtained by measuring the current ratio.

An electron beam is used as the charged beam 22,
Either an ion beam can be used, but in the case of an electron beam, the penetration depth into the semiconductor sample 16 becomes deep,
Since the depth is 100 to 1000 times deeper than that of the ion beam, the penetration depth of the electron beam may vary depending on the measurement site.
There is a possibility of passing B. On the other hand, in the case of the ion beam, the penetration depth is shallow, but there is a drawback that the irradiation site cannot be narrowed down as compared with the electron beam. Therefore, it is preferable to properly use the measurement target. That is, an ion beam can be used in a shallow operation region, and an electron beam can be used in a deep and narrow operation region.

<< Specific Example >> Next, the measurement results of the specific resistance of the p-type doped layer formed on the Si substrate, performed by the apparatus shown in FIG. 1, will be shown. The measured operating region is one in which boron B is added by ion implantation to an n-type Si wafer, heat treatment is activated to form an operating region having a depth of 300 nm and a width of about 1 μm, and an Al electrode is attached thereon. is there. It is estimated that the Si substrate has a specific resistance of about 200 Ω · cm and the operating region has a specific resistance of several Ω · cm. The distribution of the resistivity of the cross section in this region was measured as follows.

First, the sample was fractured by cleavage so that the cross section of the operation region appeared, and the sample was placed on the sample mounting table so that the fracture surface faced the probe of the scanning probe microscope. At this time, the sample is placed so that the fracture surface slightly projects from the tip of the sample mounting table so that the probe of the scanning probe microscope system can contact the fracture surface.

Next, the sample chamber (the part surrounded by the alternate long and short dash line in FIG. 1) is evacuated to a vacuum, and then an ion beam is generated to sputter-etch the fractured surface to remove the oxide layer on the surface and to make contact. Reduced resistance. In this case, the ion beam has an energy of 10 KeV and a diameter of 1 μm.
Ar ⁺ ions narrowed down to mφ were used.

Subsequently, an electron beam is generated and the sample is moved by a stepping motor while observing with an electron microscope, and the alignment is performed so that the probe of the scanning probe microscope system comes close to the measurement site. Observe the surface shape of the measurement site with and confirm that there are no extreme irregularities that hinder the current measurement.After that, fix the electron beam irradiation position to a point slightly distant from the measurement site and use the piezo actuator. While keeping the contact pressure of the probe of the scanning probe microscope system constant by controlling the Z-axis, the current measurement was performed in the XY directions.

At this time, the electron beam has an acceleration voltage of 5K.
It was converged to about 10 nmφ with V and current amount of 20 nA. The probe of the scanning probe microscope system was a cone of n-type Si crystal having a diameter of 10 μmφ, a height of 20 μm, and a radius of curvature of the tip of the cone of 10 nm or less.

The results measured under the above conditions are shown in FIGS.
It was as shown in In each case, the vertical axis shows the ratio is / ib between the amount of current flowing through the probe of the scanning probe microscope system and the amount of current flowing through the substrate base, and is plotted against the measurement position. FIG. 4 shows the current ratio distribution in the depth direction near the center of the cross section of the operation region of the semiconductor sample.
The specific current drops sharply around 300 nm (0.3 μm), and it can be seen that the resistance value has drastically increased. Confirm that the depth of the operating region is 300 nm. I was able to. Similarly, FIG. 5 shows a change in the current ratio in the horizontal direction, and the region where the current often flows is about 1 μm.
Therefore, it was confirmed that the width of the operation region was about 1 μm.

As described above, according to this embodiment, it is possible to measure the three-dimensional change in the specific resistance of a minute area of a semiconductor material such as a patterned LSI or ULSI, which has been difficult in the past, with an accuracy of nm order. (1) It is possible to measure the distribution of the specific resistance in a patterned minute region, and from the result, estimate the carrier concentration related to the electrical characteristics, design the semiconductor device such as IC, LSI, ULSI,
It can be used very effectively for process development, manufacturing, product management, and (2) without using pretreatment such as chemical etching or polishing, the ion beam irradiation system can be used to measure the surface of the sample to be measured. Etching,
After that, the distribution of the specific resistance at that portion can be measured, and the time and effort for evaluating the electrical characteristics of the semiconductor material can be greatly reduced.

[0042]

As described above, according to the present invention, it is possible to measure a three-dimensional change in the specific resistance of a minute region of a semiconductor material such as a patterned LSI or ULSI, which has been difficult in the past, with an accuracy of nm order. Therefore, it can be used very effectively for the evaluation of the manufacturing process of semiconductor materials.

[Brief description of drawings]

FIG. 1 is a functional block diagram of a semiconductor material electrical characteristic evaluation apparatus used in an embodiment of the present invention.

FIG. 2 is an enlarged view showing a usage state of the device.

FIG. 3 is an equivalent circuit diagram for electrical characteristic evaluation by the above device.

FIG. 4 is a graph showing a specific current characteristic in a cross-sectional direction of a semiconductor sample measured by the above apparatus.

FIG. 5 is a graph showing specific current characteristics in the surface direction of a semiconductor sample measured by the above device.

FIG. 6 is a structural cross-sectional view of a general semiconductor material.

[Explanation of symbols]

 5 Sample Placement Table 6 Stepping Motor 7 Piezo Element Positioning Device 8 Probe 9 Optical Detection System 10 Scanning Probe Microscope System 11 Electron Beam Irradiation System 12 Ion Beam Irradiation System 13 Controller 14 Input Device 15 Display Device 16 Sample 16A Base 16B Operating Area 16C Electrode 17 Step scan controller 18 XY scan system 19 Z-axis controller 20 Current detection device 21 Current detection device 23 Cantilever 24 Voltage detection device

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Miyuki Takenaka 1 Komukai Toshiba-cho, Kouki-ku, Kawasaki-shi, Kanagawa Toshiba Research & Development Center

Claims (1)

[Claims] 1. A semiconductor material is mounted on a mounting table that can be moved and adjusted, and charged particles are continuously supplied to a predetermined portion of the semiconductor material, and an arbitrary portion of the semiconductor material is probed. Contacting and scanning, a part of the current supplied to the semiconductor material by the charged particles is measured by the probe, and at the same time, an earth current from the base portion of the semiconductor is measured, and each contact portion of the probe is measured. The method for evaluating the electrical characteristics of a semiconductor material is characterized by obtaining a current ratio between a current value measured by the probe in the above and the ground current value.