JPH07174800A - Surface measuring instrument - Google Patents

Abstract

PURPOSE:To prevent generation of leak current due to the contact of an electrode and accurately measure charge distribution by using an electrode where the air gap on a semiconductor surface can be varied and by measuring C-V (capacityvoltage) while applying voltage by changing the gap. CONSTITUTION:Silicon oxide film 2 is formed on silicon 1 and an electrode 3 is brought closer to the oxide film 2 by a variable mechanism 4 for measuring C-V characteristics. A rough-move mechanism by a micrometer and a fine-move mechanism by a piezoelectric actuator are provided at the movable mechanism 4 and capacity is measured and then the distance from the oxide film 2 is obtained. The electric field in the most of oxide film 2 exists M on the outermost surface of the interface with the silicon 1 and is nearly uniformly distributed in the film 2. Therefore, by changing gap and performing C-V measurement at three points, each electric charge can be measured. Also, when electric charge is properly distributed, C-V measurement is performed for many times by changing gap. Then, when data are analyzed by a CPU, the electric charge distribution in the film 2 can be estimated without any destruction.

Description

Detailed Description of the Invention

[0001]

The present invention relates to semiconductor surface measurement,
In particular, the present invention relates to a measuring method and apparatus suitable for measuring the interface state density of the interface between a semiconductor and an insulator, and the charge and its distribution in an insulating film.

[0002]

2. Description of the Related Art A typical method for measuring a semiconductor surface is a method for obtaining a capacitance-voltage (CV) characteristic.
The CV measurement includes a high frequency (1 MHz) method, a low frequency method, a quasi-static method and the like. Usually, as shown in FIG. 2, an insulator 2 is formed on a semiconductor substrate 1, and an electrode 3 made of metal or polycrystalline silicon is formed on the insulator 2 by vapor deposition or chemical vapor deposition (CVD). Then, CV characteristics were obtained as a so-called metal-oxide-semiconductor MOS structure. Further, as a simple method, as shown in FIG. 3, MO or a mercury or indium-gallium alloy is put on the insulator.
It had an S configuration.

The surface photovoltage is measured by Japanese
Applied Physics, 23 (1984) 14th
51 to 1461 (Japanese Journal of Applie
d Physics, 23 (1984) PP1451-1461). This is shown in FIG. That is, a transparent insulator 6 such as Mylar is placed between the transparent electrode 3 ″ and the semiconductor, and the light 8 is emitted.

[0004]

CV of the above-mentioned prior art
In the measurement method, when the electrode contacts the insulator, it was difficult to obtain information near the surface of the insulator, that is, the charge distribution. Remove the insulating film little by little by chemical etching, etc.
The information near the surface was obtained by repeating the -V measurement. On the contrary, in the shape as shown in FIG. 4, a thin spacer cannot be obtained, and the thickness is at most several tens of μm. If the thickness of the silicon oxide film does not become 2 μm or less as described later, an accurate surface can be obtained. It cannot be measured.

When the insulating film on the surface of the semiconductor is very thin, a leak current flows when the electrode is attached, and the CV characteristic cannot be measured accurately.

An object of the present invention is to solve these problems.

[0007]

The above problems can be solved by providing an electrode having a variable air gap with the semiconductor surface. That is, the measurement is performed in the form of an insulator and an air condenser connected in series. Instead of air, an inert gas such as dry nitrogen or vacuum may be used.

Depending on the doping amount of the semiconductor, it is usually M
In the OS structure, CV measurement is performed when the SiO ₂ film thickness is 1 μm or less. This is because the capacitance hardly changes with voltage when the thickness is 2 μm or more. Therefore, the relative permittivity (SiO ₂
3.9), it is desirable that the air gap be 0.5 μm or less.

The gist of the present invention is to provide a surface measuring device for applying a voltage between an object to be measured and an electrode, wherein a plurality of distances between the object to be measured and the electrode are set for one object to be measured. In the surface measuring device, the surface measuring device is provided with means for holding at different distances and applying the voltage at each distance.

[0010]

In the air gap electrode, the distance from the semiconductor surface can be obtained by measuring the capacitance. Many S
The electric field in iO ₂ is large at the interface with the semiconductor (Si) and the outermost surface, and is small in the film and distributed almost uniformly. Therefore, assuming that there is a delta function electric charge at the interface and the outermost surface, and assuming a uniform distribution in the film, it is possible to obtain each electric charge by changing the gap of the air gap electrode and performing CV measurement at three points. it can. Even when the charge is appropriately distributed, a large number of CV measurements can be performed by changing the gap, and the charge distribution in the film can be determined (estimated) nondestructively by data analysis by a computer.

Accurate measurement cannot be performed if there is a leak in the insulating film when the C-V characteristic is obtained by the quasi-static method, but since there is always a gap in this method, tunnel current and discharge may occur. Unless it happens, CV measurements can be made even with very thin insulators.

Normal AC surface photovoltage measurement cannot be performed unless the semiconductor surface is inverted. Therefore, only N-type Si could be evaluated in the Si wafer. On the other hand, when this gap electrode is used, the P-type Si surface can be inverted by applying a DC bias to the transparent electrode, and it becomes possible to evaluate even an N-type semiconductor.

[0013]

EXAMPLES The present invention will be described below with reference to examples.

(Embodiment 1) As shown in FIG. 1, a silicon oxide film 2 having a thickness of 100 nm is formed on silicon 1, this wafer is placed on a sample table, and an electrode 3 is oxidized by a movable mechanism 4. Distance of about 100 nm from the film surface and about 15
It was possible to measure the CV characteristics by approaching the distance of 0 nm. In this case, the electrode moving mechanism 4 is a combination of a coarse adjustment unit using a micrometer and a fine adjustment unit using a piezoelectric actuator.

In the conventional mercury probe shown in FIG. 3, the mercury probe shown in FIG.
Assuming the positive charge distribution shown in the lower part of the configuration in (a), the charge Q induced on the semiconductor surface is

[0016]

[Equation 1]

[0017] Here, e is the electronic charge, t ₀ is the thickness of the insulating film, and ρ (χ) is the charge distribution in the insulating film.
The equation (1) becomes the following equation if the charge in the film is constant at q ₀ .

[0018]

[Equation 2]

On the other hand, in the case of the air gap electrode described above, the result is as shown in FIG.

[0020]

[Equation 3]

[0021] Here, ε is the relative permittivity of the insulator. Here, if t ₁ is changed to t ₂ , unknowns Q _i , q ₀ , Q
You can ask for ₃ . Such a positive charge distribution is S
This is very well applicable when plasma is irradiated with Si with iO ₂ . That is, in many cases, the positive charge distribution obtained by step-etching SiO ₂ is exactly as shown in FIG.

Even if the positive charge distribution shown in FIG.
It is possible to estimate the amount of induced charges from various CV characteristics by changing t ₁ and estimate the charge distribution by computer processing or the like.

(Embodiment 2) An important point in carrying out the present invention is to keep the air gap electrode parallel to the semiconductor of the sample. As shown in FIG. 6, the sub-electrodes 10 and 10 'are provided on both sides of the main electrode 3, and the movable mechanism 4'for adjusting the inclination of the sample table 9 by field-backing the balance of the respective capacities. It was possible to maintain the parallelism by moving it to correct the parallelism. Actually, the sub-electrodes are four sub-electrodes 10, 10 ', 10 ", 1 as shown in FIG.
0 '''was used, and two movable mechanisms were also used. Parallelism can be corrected if there are three or more sub-electrodes.

In addition to this, parallelism detection by optical application, such as detecting parallelism using a split light beam used in a compact disc player, is also conceivable.

(Embodiment 3) In the above embodiment, a vapor deposition film of gold was used as an electrode. The surface of the vapor-deposited film may have a rough surface and may not be a flat electrode. Therefore, when a mirror-polished Si wafer heavily doped with arsenic (As) was processed into an electrode, good measurement results could be obtained.

(Embodiment 4) A silicon wafer is usually 20 Å
A degree of natural oxide film is formed on the surface. Even if an electrode is attached to this and an attempt is made to measure the C-V characteristic, the leakage current is large and it is practically impossible to measure. When an air gap electrode is used in the configuration shown in FIG. 1, it is about 500Å (50n
It was possible to obtain C-V characteristics in m). That is, it can be said that the effects of surface treatment of Si can be evaluated using the present invention. For N-type Si of 100 ^- cm, the air gap is 0.
C-V measurement was possible at 5 μm or less, and good C-V characteristics were obtained at 0.1 μm or less.

(Embodiment 5) As shown in FIG. 8, by applying a bias voltage to the transparent electrode 3 ''', the surface potential of the semiconductor (Si) 1 can be controlled.
It was confirmed that it is possible to measure the surface light induced voltage by irradiating the light 8 with an arbitrary surface potential. This has the effect of facilitating the surface charge, interface state, and lifetime of bulk Si to be separately determined.

Further, since a normal Si wafer is subjected to an ammonium hydroxide (NH ₄ OH and H ₂ O ₂ ) treatment, its surface is made P-type. Therefore, the lifetime measurement of N-type Si can be easily performed in FIG. 4 of the related art, but it is also difficult for P-type Si. On the other hand, in FIG. 8, by applying a positive voltage to the transparent electrode on the Si surface, the surface can be made N-type and the lifetime measurement can be performed.

(Embodiment 6) In the Si wafer of LSI, it was difficult to observe the substrate Si from the front side because it was usually hindered by the wiring and the gate electrode. On the other hand, as shown in FIG. 9, by making a hole on the back side of the Si wafer and setting the thickness of Si to about 20 μm, the AC surface photoinduced voltage is observed to evaluate Si with a resolution of about 1 μm. Became possible.

Example 7 In Example 4, the measurement was performed in the atmosphere. However, stable (good reproducibility) measurement may be difficult due to atmospheric humidity. It was confirmed that flowing dry nitrogen in the measurement system significantly ameliorated this problem. It was also confirmed that more stable measurement can be performed by placing the entire measurement system in a vacuum.

(Embodiment 8) In FIG. 1, the gap electrode can be oscillated at several 100 KHz by applying an AC voltage to the laminated piezoelectric actuator which is one of the movable mechanisms. As a result, the potential of the sample surface could be measured.

(Embodiment 9) In all the embodiments so far, the gap is air, nitrogen or vacuum, but it is also possible to fill the gap with a liquid. When silicon foil (C ₂ H ₆ OSi) ₄ is used, CV measurement is possible even with a gap of about 4 μm.

This is because the relative permittivity of silicone oil is 2.4.
This is because. If a liquid having a higher relative dielectric constant is used, the gap can be increased, but it is often ineffective because it must be washed and dried later.

Although Si is used as a semiconductor in the above embodiments, the present invention is also effective for compound semiconductors of III-V group or II-VI group such as GaAs.

According to the embodiment of the present invention, it is possible to obtain the charge distribution in the insulating film on the semiconductor surface without step etching. Further, it is possible to measure the surface of a semiconductor having a leaky insulating film or an extremely thin insulating film on its surface, that is, obtain the interface state and surface charge.

Further, according to the embodiment of the present invention, a scanning photon microscope, that is, an SPM (Surface) using the surface photoinduced voltage is used.
Photon Microscope, (Tadasuke Munekata, Applied Physics, 53rd
Vol. 3, No. 3 (1984) PP176), it is possible to easily obtain much information, that is, the interface state and lifetime, by applying a DC bias to the attracting electrode.
In addition, in the acceptance inspection of the Si wafer, both N type and P type can be evaluated, and the application range is widened. Further, also in the defect analysis of the LSI and the like, information on the Si and Si surfaces can be obtained with a resolution of about 1 μm in the structure in which Si of several tens μm to several μm left by etching Si from the back side is left.

[0037]

According to the present invention, the charge distribution in the object to be measured can be estimated efficiently.

[0038]

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is a diagram showing a conventional semiconductor surface measuring method.

FIG. 3 is a diagram showing a conventional semiconductor surface measuring method.

FIG. 4 is a diagram showing a conventional semiconductor surface measuring method.

FIG. 5 is a diagram showing an effect of one embodiment of the present invention, showing charge distributions in the conventional method (a) and the present invention (b).

FIG. 6 is a diagram showing an embodiment of the present invention.

FIG. 7 is a diagram showing an embodiment of the present invention.

FIG. 8 is a diagram showing an embodiment of the present invention.

FIG. 9 is a diagram showing an embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Semiconductor substrate, 2 ... Insulating film, 3 ... Electrode, 4 ... Movable mechanism, 5 ... Electrode connection rod, 6 ... Transparent spacer, 7 ... Glass plate, 8 ... Ray, 9 ... Sample stand, 10 ... Sub (auxiliary) Electrode, 1
1 ... Device / wiring layer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ryo Haruta 1-280, Higashi Koikekubo, Kokubunji, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. (72) Inventor, Tadasuke Mitsukata 1-280, Higashi Koikeku, Kokubunji, Tokyo Hitachi, Ltd. Central Research Laboratory (72) Inventor Shigeyuki Hosoki 1-280, Higashi Koikekubo, Kokubunji City, Tokyo Inside Central Research Laboratory, Hitachi, Ltd.

Claims (1)

[Claims] 1. A surface measuring apparatus for applying a voltage between an object to be measured and an electrode, wherein a distance between the object to be measured and the electrode is set to a plurality of different distances with respect to one object to be measured. A surface measuring device comprising means for holding and applying the voltage at each distance.