JP3300545B2 - Method for evaluating electrical properties of semiconductor materials - Google Patents

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 electrical characteristics of a semiconductor material.

[0002]

2. Description of the Related Art Conventionally, in a process of manufacturing a semiconductor device such as an LSI and an ULSI, a semiconductor substrate patterned by a fine processing technique such as photoetching is used in order to use a minute area of a surface layer of a semiconductor material as an operation area. Impurities are added to a very small, limited region of the material by ion implantation or thermal diffusion from the surface, and the heat treatment is performed again by heat treatment to electrically activate the diffused and added impurities. A semiconductor element on which a drain or the like is formed is obtained. FIG. 6 shows an example of a semiconductor device manufactured in this manner. An active region 2 such as a p ⁺ or n ⁺ layer is formed on a semiconductor substrate (base) 1, and a phosphorus 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.

In general, in semiconductor devices such as LSIs and ULSIs, the size of an operation region such as a source or a drain (corresponding to an operation region 2 such as a p ⁺ or n ⁺ layer in FIG. 6) is, for example, 16 MB. The random access memory (DRAM) has a size of 1 μm or less, and the size of the operation region becomes smaller as the degree of integration increases.

On the other hand, in the manufacture and development of semiconductor devices such as LSIs and ULSIs, precise control of electrical characteristics such as the size of an operating region, electric resistance, and carrier concentration is indispensable, and as the operating region becomes smaller. Increasingly, the precision of the control is required, and in order to meet the demand, the evaluation and estimation of the electrical characteristics of the semiconductor material are required to be accurate.

[0005]

By the way, in the operation region to which the impurity is added in the semiconductor material as described above,
The specific resistance and the 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 at which this specific resistance changes, and further, 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 in designing and manufacturing semiconductor devices. That is, in a semiconductor device manufacturing process, it is essential to estimate a change in specific resistance in an operating region near the surface on the order of nm for a semiconductor material (semiconductor substrate) to be used.

However, a means for directly measuring a change in the specific resistance of an operating region of a semiconductor device such as an LSI or ULSI has not been known so far. A method of estimating manufacturing processes such as injection and heat diffusion by performing simulation on a computer has been adopted. As a means to confirm the accuracy of the simulation, a direct method of measuring the resistivity in the depth direction of the operation region and an indirect method of estimating by measuring the concentration distribution of the added impurity 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 as in an actual semiconductor device is prepared on a trial basis and measured, and the impurity is diffused into a 1 μm region such as a semiconductor device such as an LSI or ULSI. It was not possible to evaluate the three-dimensional impurity distribution and resistivity distribution including the lateral direction when added and diffused.

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 an accuracy on the order of nanometers. Has a limit of 0.1 μm, and the sensitivity is insufficient to evaluate a diffusion region having a low concentration of 0.001% to 0.0001%.

Further, not all the impurities present in the operation region are involved in the electric conduction, and some of the impurities may exist in a so-called electrically inactive state. There was also a problem that there was no assurance.

On the other hand, as a method for directly measuring the specific resistance, a two-probe method, a four-probe method, a spread resistance method and the like are known. In each of these methods, the specific resistance is measured 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, and currently has a limit of several tens of μm, and therefore LS, which is an aggregate of elements of 1 μm or less,
It has not been possible to evaluate the electrical characteristics of semiconductor devices such as I and ULSI.

On the other hand, a scanning probe microscope developed recently can observe the surface morphology of a sample in the atomic order and also can evaluate the electronic state of the sample. Is used for morphological evaluation in the atomic order. The method of evaluating the material surface by this scanning probe microscope is a method in which a sharpened probe is brought close to the sample, and a tunnel current flowing from the sample is detected. This is a method of observing the surface morphology of a sample in the atomic order by detecting the deflection of a probe with a highly sensitive photodetector, and has extremely high positional resolution.

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

A scanning probe microscope used to execute the latter method is particularly called an atomic force microscope, and is in principle the same as the spread resistance method since 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 a macroscopic method such as a two-probe method or a four-probe method, the purpose is to measure the specific resistance of a specific portion of a microscopic element having more than one million patterns. 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, it is necessary to directly evaluate the element under the insulating film or between the insulating films. And it has not been put to practical use for evaluating the electrical characteristics of semiconductor materials.

SUMMARY OF THE INVENTION The present invention has been made in view of such a conventional problem, and is directed to a semiconductor device having an operation region of 1 μm or less, such as a semiconductor device such as an LSI or ULSI, having a local resistance of a minute operation region. An object of the present invention is to disclose a method for evaluating the electrical characteristics of a semiconductor material that can easily and accurately detect a change in a value and can be used for evaluating the electrical characteristics of the semiconductor material.

[0014]

According to the method for evaluating the electrical properties of a semiconductor material according to the present invention, a semiconductor material is placed on a mounting table which can be moved and adjusted, and charged particles are continuously applied to a predetermined portion of the semiconductor material. And scans by contacting an arbitrary part of the semiconductor material with a probe, measuring a part of the current supplied to the semiconductor material by the charged particles with the probe, and simultaneously measuring the earth current from the base part of the semiconductor. The current ratio between the current value measured by the probe and the ground current value at each contact portion of the probe is measured.

[0015]

In the method for evaluating the electrical characteristics of a semiconductor material according to the present invention, a semiconductor material is placed on a sample mounting table so that a probe having a small probe is brought into contact with an operating area of a surface or a section of a semiconductor material piece so that current can be measured. Place. On the other hand, a charged particle source such as an electron gun or an ion gun is arranged so as to be able to apply a current near the operation region, and the charged particles such as an electron beam or an ion beam are focused on the operation region or in the vicinity thereof. I do. Then, the probe is brought into contact with a portion corresponding to the operation region and scanned 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 keeping the contact area between the probe and the sample constant, which can reduce the contact area to several tens of nm or less, is suitable. And a change in current in the operation area is detected.

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

The charged particles used as the current source may be an electron beam or an ion beam. In addition, by having a function as a scanning microscope, it is possible to easily select a measurement site of the semiconductor material and align a probe of the scanning probe microscope with the measurement site.

When an ion beam is used, the depth of penetration of ions of the semiconductor material into the substrate can be reduced to several nm or less, so that a more accurate measurement can be performed in a shallow operating region, and the operating region can be reduced. A three-dimensional evaluation is also possible by using a method of measuring current at each depth while etching. On the other hand, when an electron beam is used, the penetration depth becomes deeper, but the electron beam diameter can be reduced to about 1 nm, so that the planar resistance distribution can be measured accurately. If both are used in combination, more accurate measurement can be performed.

In addition to a charged beam such as an electron beam or an ion beam as described above as a charged particle source, another probe can be brought into contact with a predetermined portion of a semiconductor material to supply a current through the probe. .

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows an apparatus for evaluating the electrical characteristics of a semiconductor material used in one embodiment of the present invention. The piezoelectric actuator and a stepping motor 6 use a three-dimensional direction of X, Y (perpendicular to the plane of FIG. 1) and Z. A scanning probe microscope system 10 having a sample mounting table 7 capable of fine movement and coarse movement and an electrically conductive probe 8 and an optical detection system 9 for detecting irregularities on the surface of the sample; An electron beam irradiation system 11 for applying a charge, an ion beam irradiation system 12 for also applying a charge to a specific portion of a sample, and a control system (CPU) constituted by a microcomputer for controlling these components in a comprehensive manner 13, an input device 14 for inputting an operation command to the 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 performs coarse movement of the sample 16 in the X, Y, and Z directions to the order of μm. A step scan controller 17 is provided for positioning the probe 8 so as to be in contact with a specific portion, and the piezo actuator 5 further controls the angstrom (1.0 × 10 Å) in the X and Y directions.
^-10 m) An XY scan system 18 for precise scanning on the order and a Z-axis controller 19 for controlling the Z direction in conjunction with the optical detection system 9 are provided. It is possible to perform shape observation and positioning on an order and to adjust contact pressure of a probe.

The scanning probe microscope system 10 is provided with a current detecting device 20 for detecting a 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 is connected to the bottom of the sample 16 or an arbitrary portion. And a ground current detecting 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.

The electron beam irradiating system 11 and the ion beam irradiating system 12 have the accuracy that the beam diameter converges on the order of nm, and the sample 16 and the probe 8 of the scanning probe microscope 10 are operated by operating the beam with the deflecting electrode. And an enlarged image can be obtained. 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 to observe and confirm the operation area of the surface of the sample 16. And 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 surface observation of the sample 16 and in consideration of the good convergence of the electron beam and the ion beam and the ease of the alignment, the electron beam is irradiated with the probe 8 in the electron beam irradiation system 11. Is set to be in the range of 30 to 90 ° with respect to the direction of the ion beam irradiation system 12 is set to 60 to 90 °
It is preferable to set so that

The control system 13 includes the sample table 7
Of the stepping motor 6, the XY drive of the piezo actuator 5, the optical detection system 9 for detecting the shake of the probe 8 according to the unevenness of the sample 16, and the piezo actuator for moving the sample 16 up and down according to the magnitude of the shake 5 controls the scanning of the electron beam and the ion beam emitted from the electron beam irradiation system 11 and the ion beam irradiation system 12, and measures the amount of current flowing through the probe 8 and the sample mounting table 7. In general, various control arithmetic processes for measuring a two-dimensional or three-dimensional specific resistance distribution or a capacitance distribution of an operation region on a cross section or a surface of the sample 16 are executed.

Next, a description will be given of an electrical characteristic evaluation method performed by the above-described semiconductor material electrical characteristic evaluation apparatus. As shown in an enlarged manner in FIG. 2, a sample 16 of a semiconductor material is mounted on the sample mounting table 7 and positioned. The sample 16 has a structure in which a variable resistance region 16B of the operation region indicated by hatching is formed on a base 16A, and an electrode 16C is formed on the surface. Then, in order to measure the electrical characteristics of the operating region of the sample 16 in the depth direction, the positional relationship is set such that the probe 8 is brought into contact with the cross section obtained by cleaving the semiconductor element to perform scanning.

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

In this state, the charged beam 22 is emitted from the electron beam irradiation system 11 or the ion beam irradiation system 12 and is irradiated so as to converge to a position near the operation area on the surface of the sample 16. Thereby, through the wiring or the electrode 16C on the surface of the sample 16,
Alternatively, the operating area 1 is directly passed without passing through the wiring or the electrode 16C.
Charge is supplied to the sample containing 6B.

This electric 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 an inhomogeneous region such as the operating region 16B of the semiconductor sample 16. Are different. Then, the charge supplied to the surface of the sample 16 by the irradiation of the charged beam flows as an electric current in accordance with the potential gradient formed by the above-mentioned potential difference, and is externally transmitted from the base 16A of the sample 16 and the probe 8 of the scanning probe microscope system 10. Although the current flows, these currents are measured by the current detection devices 20 and 21, and the specific resistance of the operation region 16B can be obtained from the current ratio. Scanning probe microscope system 1
By using the zero probe 8 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, the distribution of the specific resistance and the potential distribution in two-dimensional XY can be measured. 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 operating region 16B is exposed, and the distribution of the specific resistance in the 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 with an equivalent circuit. In this equivalent circuit, E is the local potential of the surface of the sample 16 generated by the supply of the 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 current of the scanning probe microscope 10. The current ri flowing through the probe 8 is a resistance value relating to current diffusion at the irradiation point of the charged beam and corresponds to a contact resistance. rb is the specific resistance of the base 16A of the sample 16, and rd is the operating area 16B.
Has a different value depending on the contacting portion of the probe 8 with the specific resistance of 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.

A relational expression of is / ib = rb / (rd + rs + rp) (1) is established among these voltage, current and resistance.

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 where the probe is in contact, and a is the radius of curvature of the portion of the tip of the probe that is in contact with the sample surface. Since the radius of curvature a is as extremely small as 10 nm or less, rs >> r
d, rp, and equation (1) can be approximated as follows.

Is / ib = rb / rs rb is determined uniformly by the sample 16. Further, the contact radius a in rs can always be kept 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 a change in the specific resistance p of the operation region 16B of the sample 16, and the specific resistance distribution of the operation region 16B can be obtained by measuring the current ratio.

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

<< Specific Example >> Next, the results of measurement 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 described. The measured operating region is obtained by adding boron B to an n-type Si wafer by ion implantation, performing heat treatment and activating it, forming an operating region having a depth of 300 nm and a width of about 1 μm, and attaching an Al electrode thereon. is there. The specific resistance of the Si substrate is about 200 Ω · cm, and the specific resistance in the operating region is estimated to be several Ω · cm. The distribution of the resistivity of the cross section of this region was measured as follows.

First, the sample was broken by cleavage so that the cross section of the operating region appeared, and the sample was placed on the sample mounting table so that the broken surface was directed to the probe of the scanning probe microscope. At this time, the sample is mounted so that the fracture surface slightly protrudes 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 (a portion surrounded by a dashed line in FIG. 1) is evacuated to vacuum, and then an ion beam is generated. 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, the sample is moved by a stepping motor while observing with an electron microscope, and the position is adjusted so that the probe of the scanning probe microscope system is located near the measurement site. Observe the surface shape of the measurement site with, confirm that there are no extreme irregularities that may interfere with the current measurement, and then fix the irradiation position of the electron beam at a point slightly distant from the measurement site. The current in the XY direction was measured while keeping the contact pressure of the probe of the scanning probe microscope system constant by the Z-axis control.

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

The results measured under the above conditions are shown in FIGS.
It was as shown in In all cases, 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 is plotted on the vertical axis with respect to the measurement position. FIG. 4 shows the distribution of the current ratio in the depth direction near the center of the cross section of the operation region of the semiconductor sample.
It can be seen that the specific current drops sharply at about 300 nm (0.3 μm), and it can be seen from this that the resistance value sharply increases, and that the operating region depth is 300 nm. Was completed. Similarly, FIG. 5 shows a change in the current ratio in the horizontal direction.
Therefore, it was confirmed that the width of the operation region was about 1 μm.

As described above, according to this embodiment, the 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, is measured with an accuracy on the order of nm. (1) The distribution of specific resistance in a minute patterned area can be measured, and from the results, the carrier concentration related to electrical characteristics can be estimated, and the design of semiconductor devices such as IC, LSI, and ULSI can be performed.
It can be used very effectively for process development, manufacturing, and product management. (2) The surface of a sample to be measured using an ion beam irradiation system can be used without performing pretreatment such as chemical etching or polishing. Etching,
Thereafter, the distribution of the specific resistance at that portion can be measured, and the number and time required for evaluating the electrical characteristics of the semiconductor material can be greatly reduced.

[0042]

As described above, according to the present invention, the 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, can be measured with an accuracy on the order of nm. It can be used very effectively for evaluation of a manufacturing process of a semiconductor material.

[Brief description of the drawings]

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

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

FIG. 3 is an equivalent circuit diagram of evaluation of electric characteristics by the above-described device.

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

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

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

[Explanation of symbols]

 Reference Signs List 5 sample mounting 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 detector 21 Current detector 23 Cantilever 24 Voltage detector

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Miyuki Takenaka 1 Komukai Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture Toshiba R & D Center (56) References JP-A-51-53477 (JP, A) JP-A-60-165733 (JP, A) JP-A-4-100252 (JP, A) JP-A-4-280648 (JP, A) JP-A-5-67654 (JP, A) JP-A-2-253552 (JP) , A) JP-A-62-168326 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/66 G01N 37/00

Claims (1)

(57) [Claims] 1. A semiconductor material is placed on a mounting table that can be moved and adjusted, a charged particle is continuously supplied to a predetermined portion of the semiconductor material, and an arbitrary portion of the semiconductor material is probed by a probe. Scanning by contacting, measuring a part of a current supplied to the semiconductor material by the charged particles by the probe, and simultaneously measuring a ground current from a base portion of the semiconductor; Determining a current ratio between a current value measured by said probe and said earth current value in (1).