JP3295591B2 - Electric waveform measuring probe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention is used for measuring semiconductor devices. In particular, the present invention relates to a probe of an apparatus for measuring an electric waveform with high time resolution and high spatial resolution while operating a high-speed semiconductor electronic circuit having a fine structure.

[0002]

2. Description of the Related Art In recent years, the frequency of signals handled in the field of electronics has reached 250 GHz, and the means for observing these high-speed electric waveforms cannot keep up with technological progress. is there. Furthermore, as the miniaturization of elements progresses, not only the time resolution but also the spatial resolution of the electric waveform measuring device cannot keep up with the current technological advances.

In order to observe high-speed phenomena such as a high-speed operation state of a minute element, a sampling oscilloscope has been conventionally known as a typical one. However, the speed that can be measured is limited by the width of the electric pulse for sampling and the time constant determined by the electric resistance and capacitance of the measurement system, and the time resolution is limited. In addition, since the signal to be measured is taken out of the measuring point by a cable or a waveguide, the signal to be measured is disturbed, and there is a problem in its reliability.

As a technique for solving such a problem, an EO sampling method utilizing an electro-optic effect of an optical crystal has been recently studied (Takeshi Kamiya, Ryo Takahashi,
"Electro-optic sampling using a semiconductor laser as a light source",
Applied Physics Vol. 61, No. 1, p. 30, 1992). In the field of lasers, optical pulses in the sub-picosecond range have become relatively easy to obtain, and the optical sampling method attempts to use these laser pulses for sampling electrical signals. According to this method, it is possible to directly measure the potential at the point to be measured in a non-contact manner at a higher speed than in the conventional electronic measurement without drawing a signal outside. This method can be said to replace the electrical pulse for sampling in the sampling oscilloscope with the optical pulse. However, it is difficult for the EO sampling method to measure the absolute value of a signal.
Furthermore, there is a practical problem in monitoring and controlling the position of the probe with high spatial resolution.

Another method for directly measuring the potential at a point to be measured with high spatial resolution is an electron beam tester (G. Plows "Electron-Beam Probing" Semiconductor an).
d Semimetals Vol.28 (Measurement of High-Speed Sig
nals in Solid State Devices) Chap. 6, p. 336, Edited
by RKWillardson and Albert C. Beer, Academic Pres
s, 1990). An electron beam tester is a powerful means for observing an electric signal inside an IC in an operation diagnosis and analysis technique of the IC. However, the time resolution is low and cannot be used for measuring ICs using high-speed transistors. In addition, there is an inconvenience that a high vacuum is required as a measurement environment.

As a technique for measuring an electric waveform with high time resolution and high spatial resolution, a scanning tunneling microscope (ST)
M) or those using a scanning atomic force microscope (SFM) are also known (Japanese Patent Application Laid-Open No. 7-35826). STM and SFM are devices for observing the surface shape of an object to be measured with high spatial resolution, and have been rapidly developed and spread recently. Since these devices can obtain a three-dimensional image at an ultra-high spatial resolution at the atomic level, they are very suitable for observing the surface shape of a semiconductor integrated circuit or the like. A photoconductive switch is incorporated in the probe of such a device, and is turned on and off by irradiating a light pulse. This makes it possible to measure an electrical waveform at an arbitrary point on the device under test with a spatial resolution of submicron by STM or SFM and a temporal resolution of subpicosecond by optical sampling.

[0007]

SUMMARY OF THE INVENTION STM or SFM
In an electric waveform measuring apparatus using a device, a sharp probe as a measuring probe and a current flowing between the terminal and the device to be measured are brought into a conductive state by light irradiation in order to sample a current between the terminal and the device to be measured. A photoconductive switch formed on a cantilever is used. In order to improve the performance of the device, it is important that the tip of the terminal is as sharp as possible and that the photoconductive switch is located as close to the terminal as possible. Also,
Photoconductive switches are required to have a structure in which unnecessary carriers are not excited by light.

An object of the present invention is to provide an electric waveform measurement probe capable of suppressing generation of unnecessary carriers in a photoconductive switch and performing highly reliable measurement.

[0009]

SUMMARY OF THE INVENTION An electric waveform measuring probe according to the present invention has a pointed terminal which is brought close to an object to be measured, and a light irradiator for sampling a current between the terminal and the object to be measured. In the electric waveform measurement probe including a photoconductive switch that is brought into a conductive state by the method and a terminal and a cantilever that supports the photoconductive switch, the light receiving portion of the photoconductive switch is different from the side on which the terminal of the cantilever is provided. A light reflecting film or a light absorbing film for preventing unnecessary carriers from being photo-excited is provided around the light receiving portion, which is formed on the opposite surface.

The present invention is particularly suitable for use in an electric waveform measuring probe having a structure in which a cantilever is formed of a photoconductive material and a part thereof is formed as a photoconductive switch. The structure in which the cantilever is formed of a photoconductive material makes it easy to form a photoconductive switch on the probe, and at the same time can easily manufacture a large number of probes. It can be supplied stably. However, in such a structure, since the structure of the probe itself is a photoconductive material, if there is any positional change in the optical system or the probe itself, the light irradiation point fluctuates and an unnecessary carrier is changed. May be photoexcited and affect measurement accuracy. A similar effect can occur when the spot size of the light beam is larger than the light receiving portion of the photoconductive switch. According to the present invention, the possibility of photoexcitation of such unnecessary carriers can be reduced.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a view for explaining an embodiment of the present invention, and shows the structure and use of an electric waveform measuring probe (hereinafter simply referred to as "probe"). This probe 1
It is attached to the probe holder 2 of an electric waveform measuring device using M or SFM, and is used for measuring the electric waveform of the DUT 3 such as a high-speed semiconductor electronic circuit. Tip 1
Has a sharp terminal 11 to be brought close to the DUT 3;
A current between the terminal 11 and the device under test 3 A photoconductive switch 12 which is brought into a conductive state by light irradiation to sample a current between the device under test and the terminal 11 and the photoconductive switch 12 is supported. And a cantilever 13 to be used. The signal from the terminal 11 is transmitted to the photoconductive switch 12.
14 for taking out to the electric waveform measuring device via the
Is provided.

The measurement using the probe 1 is performed by irradiating the photoconductive switch 12 with a light pulse while the terminal 11 is in contact with the object 3 to be measured or is arranged at a minute distance such as an atomic distance. Will be That is, the current generated between the terminal 11 and the DUT 3 by the light pulse irradiation is sampled. Thereby, the potential of each point of the DUT 3 can be obtained, and the operating state of the DUT 3 or the electric field distribution can be obtained.

As the light pulse to be irradiated, a short pulse laser beam is used. By setting the repetition frequency of this light pulse to a frequency slightly shifted from the frequency of the electric signal of the device under test 3, and measuring the current flowing at this time,
Perform sampling. At this time, the electric signal of the device under test 3 is measured by an oscilloscope or other well-known measuring device as a signal having a difference frequency between the repetition frequency of the light pulse and the frequency of the electric signal, that is, a beat component.
Further, the repetition frequency of the light pulse may be synchronized with the frequency of the electric signal of the device under test 3 to change the optical path length of the light pulse to be irradiated. Further, even if the repetition frequency of the light pulse is synchronized with the frequency of the electric signal of the device under test 3 and the phase of the electric signal is changed, the same effect as changing the optical path length of the light pulse can be obtained.

It is necessary to arrange the terminal 11 perpendicularly to the surface of the device under test 3. Control for this purpose uses a function as STM or SFM. In other words, feedback control is performed so that the average current is constant using the STM function, or the spot position of the light beam reflected by the cantilever 13 is detected using the SFM function and the position is fixed. Feedback control is performed so that By scanning the terminal 11 in the in-plane direction of the DUT 3 while holding the position in the direction perpendicular to the surface of the DUT 3, the surface shape of the DUT 3 is changed in the same manner as a normal STM or SFM. It can be observed with a submicron spatial resolution.

To manufacture such a probe, the terminal 11
, The photoconductive switch 12 and the cantilever 13 are preferably formed of the same material. That is, a substrate different from any of the cantilever 13, the terminal 11, and the photoconductive switch 12 is used as a substrate, and a convex portion or a concave portion is formed on a part of the substrate. And a structure including a photoconductive switch, wherein at least a portion of the substrate is removed such that the structure operates as a cantilever.
Therefore, the photoconductive switch 12 is not specially formed, and when the electrode 14 for extracting a signal is formed, a region of a gap between the electrode 14 and the terminal 11 is formed with the photoconductive switch 12. Become. Photoconductive switch 12
Is formed on the surface of the cantilever 13 opposite to the side on which the terminal 11 is provided. Around the receiver,
A light reflecting film or a light absorbing film for preventing unnecessary carriers from being photo-excited is provided.

The use of a photoconductive material for the probe structure itself facilitates the formation of the photoconductive switch 12 on the probe. It is preferable that a semiconductor material is used for the substrate, and the projections or depressions are formed by anisotropic etching. In particular, a Si substrate is used as a substrate, and (11)
1) The structure formed by the surface may be a projection or a depression. By using such a structure, a sharp terminal can be formed. Further, by applying the semiconductor process technology by anisotropic etching of the semiconductor, a large number of probes can be easily manufactured at the same time, and a low-cost and highly reliable probe can be stably supplied.

The materials of the cantilever 13, the terminal 11, and the photoconductive switch 12 include an IV group semiconductor such as Si, a III-V semiconductor such as GaAs, and a ZnSe or the like.
II-VI based semiconductors and the like can be used. When a Si substrate is used as the substrate, III-V based semiconductors or II-VI based semiconductors can be used.
It is preferable to use a VI semiconductor. In particular, in order to speed up the response of the photoconductive switch 12, GaAs must be 3
It is preferable to grow at a temperature of 00 ° C. or less. Ion implantation into GaAs grown at a normal temperature to introduce lattice defects and impurities also makes the photoconductive switch 1
2 can be speeded up.

The surface of the tip of the terminal 11 is preferably coated with a chemically stable metal. As such a metal, gold Au, platinum Pt or iridium Ir is preferably used.

The electrode 14 may be provided on either the same side as the terminal 11 or on the opposite side. When the light pulse is provided on the same surface as the terminal 11, the light pulse enters from the opposite side to the surface on which the electrode 14 is provided. However, if the thickness of the cantilever 13 is sufficiently small, there is a problem. It will not be.
When a metal coating is provided on the surface of the tip of the terminal, it is convenient to manufacture the same metal from the same metal. When the electrode 14 is provided on the surface opposite to the terminal 11, the photoexcited carrier flows so as to penetrate the cantilever 13, and the region operates as the photoconductive switch 12. Generally, the response speed of the photoconductive switch increases as the gap between the metal electrodes becomes smaller. However, it is difficult to form a gap of 1 micron or less with uniformity by a patterning method. On the other hand, when the electrode 14 and the terminal 11 are formed on the surface on the opposite side of the cantilever 13, it is relatively easy to form the film thickness of the cantilever 13 to 1 micron or less with uniformity, and it is relatively easy to form the photoconductive layer. The response speed of the switch can be increased, and the time resolution of the electric waveform measuring device using the switch can be increased.

[0020]

Next, specific embodiments of the present invention will be described.

2 and 3 are views showing the structure of the first embodiment of the present invention. FIG. 2 is a perspective view of the probe seen from the terminal side.
FIG. 3 is an enlarged plan view showing the back side of the terminal. In FIG. 3, the pyramid-shaped terminals are viewed from the back side, and are represented by hatching. In this embodiment, the body of the terminal 21, the photoconductive switch (hidden by the terminal 21 in FIG. 2) and the cantilever 23 are formed on the substrate 26 by the same material. A Pt coating 25 is provided on the tip surface of the terminal 21. An electrode 24 is provided on one surface of the cantilever 23, in this example, on the surface of the terminal 21 side, for extracting a signal from the terminal 21 to the electric waveform measuring device via the photoconductive switch. The light receiving portion 22 of the photoconductive switch is formed on the surface of the cantilever 23 opposite to the side on which the terminal 21 is provided, and around this light receiving portion 22 is to prevent unnecessary carriers from being optically excited. And a coating 27 as a light reflecting film or a light absorbing film. In FIG. 3, the coating 27 is indicated by hatching.

FIG. 4 is a sectional view showing the method of manufacturing the probe in each step. Here, the main body of the terminal 21, the photoconductive switch, and the cantilever 2 are made of GaAs by using a projection formed on the Si substrate by anisotropic etching as a template.
The method for forming 3 will be described as an example.

In this method, first, a square SiO ₂ mask 32 having sides in the <110> direction of this substrate 31 is provided on a Si (100) substrate 31 (FIG. 4A), and IPA is used as a surfactant. Perform anisotropic etching with a 15% KOH solution to which (isopropyl alcohol) is added (FIG. 4).
(B)). As a result, the etching stops at the (111) plane, and a pyramid-shaped projection, that is, a projection 33 is formed.
The projection 33 serves as a main body of the terminal 21. When the anisotropic etching is completed, the mask 32 is removed, a GaAs layer 34 is grown at 300 ° C. by molecular beam epitaxy (MBE) (FIG. 4C), and a Pt coating 25 is formed on the tip surface of the projection 33. At the same time, the electrode 24 is patterned (FIG. 4D). Here, the region between the electrode 24 and the Pt coating 25 becomes a photoconductive switch. Thereafter, the substrate 31 in the cantilever portion is wrapped (mechanically polished) to reduce the thickness to 1.
The thickness is reduced to 0 μm, and Si in the cantilever portion is completely removed with a KOH solution (FIG. 4E). Thus, the substrate 26 shown in FIG. 2 is formed. Finally, a coating 27 is formed on the back surface of the GaAs layer 34 (FIG. 4F).

As the thickness of the GaAs layer 34, the inventor of the present invention trially produced 0.5 μm and 1 μm, and obtained good results. However, any thickness may be used as long as desired characteristics can be obtained. By lowering the growth temperature of GaAs, the terminal 21, the photoconductive switch, and the cantilever 23 become polycrystalline. In this case, the carrier mobility decreases, but the mechanical strength of GaAs increases.

The response of the photoconductive switch can be sped up by growing the GaAs layer 34 at a normal crystal growth temperature and implanting ions to introduce lattice defects and impurities. In that case, the main body of the terminal 21, the photoconductive switch, and the cantilever 23 are formed in a single crystal, and the terminal 21 is formed by a pyramid composed of a (111) plane of GaAs.

FIGS. 5 and 6 show the structure of the second embodiment of the present invention. FIG. 5 is a perspective view of the probe viewed from the back side of the terminal, and FIG. 6 is an enlarged view of the back side of the terminal. FIG. 4 is a plan view similar to FIG. 3. In the first embodiment, the electrodes are provided on the same surface as the terminals, but in the second embodiment, the electrodes and the terminals are provided on the opposite surface. That is, the main body of the terminal 41, the photoconductive switch (only the light receiving portion 42 is shown) and the cantilever 43 are formed of the same material, and a signal from the terminal 41 is taken out to the electric waveform measuring device via the photoconductive switch. Therefore, an electrode 44 (shown by hatching in FIG. 6) is provided on the surface opposite to the terminal 41. The light receiving portion 42 of the photoconductive switch is formed on the surface of the cantilever 23 opposite to the side on which the terminal 21 is provided, and around the light receiving portion 22, in order to prevent unnecessary carriers from being optically excited. Is provided as a light reflection film or a light absorption film (shown by hatching).

In order to manufacture a probe having this structure, an electrode is formed after removing Si in the cantilever portion, instead of forming an electrode simultaneously with the formation of the Pt coating in the method shown in FIG. Moreover, it can also be manufactured by another method. Such a method will be described with reference to FIG.

FIG. 7 is a sectional view showing a method of manufacturing the probe according to the second embodiment. This method differs from the method shown in FIG. 4 in that a concave portion formed in a Si substrate is used as a mold. That is, SiO ₂ is deposited on the Si (100) substrate 51.
A mask 52 is provided, and a square hole having sides in the <110> direction is formed (FIG. 7A). Subsequently, 30% K containing IPA (isopropyl alcohol) as a surfactant is added.
Perform anisotropic etching with OH solution. Thus, (1)
The etching stops at the 11) plane, and an inverted pyramid-shaped concave portion 53 is formed (FIG. 7B). Next, the mask 52 is
And 3 by molecular beam epitaxy (MBE).
A GaAs layer 54 is grown at 00 ° C. (FIG. 7C), and patterning of the electrode 44 and formation of the coating 47 are performed (FIG. 7D). Thereafter, a pedestal 57 is attached to the surface of the GaAs layer 54 with an adhesive (FIG. 7E),
Lapping to a thickness of 0 μm,
Is completely removed (FIG. 7 (f)). Finally, a Pt coating 45 is formed on the tip surface of the terminal 41 (FIG. 7G).

[0029]

As described above, according to the present invention,
Especially when the probe structure itself is formed of a photoconductive material,
Unnecessary carriers can be prevented from being optically excited. Further, even with other probe structures, generation of unnecessary carriers due to the photoconductive switch can be suppressed, and there is an effect that highly reliable measurement can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an embodiment of the present invention.

FIG. 2 is a perspective view showing a probe according to the first embodiment of the present invention.

FIG. 3 is a partially enlarged plan view of a tip end side of the probe of the first embodiment.

FIG. 4 is a diagram showing a method for manufacturing the probe of the first embodiment.

FIG. 5 is a perspective view showing a probe according to a second embodiment of the present invention.

FIG. 6 is a partially enlarged plan view of the back side of the terminal of the probe according to the second embodiment.

FIG. 7 is a diagram showing a method for manufacturing a probe according to a second embodiment.

[Description of Signs] 1 probe 2 probe holder 3 DUT 11, 21, 41 terminal 12 photoconductive switch 13, 23 cantilever 14, 24, 44 electrode 22, 42 light receiving unit 25, 45 Pt coating 26, 31 51, substrate 27, 47 coating 32, 52 mask 33 convex portion 53 concave portion 34, 54 GaAs layer 57 pedestal

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G01R 31/28-31/3193 G01R 1/06-1/073 G01R 19/00 G01N 13/12 G01N 13 / 16 G01N 37/00

Claims (1)

(57) [Claims] 1. A sharp-pointed terminal which is brought close to an object to be measured, a photoconductive switch which becomes conductive by light irradiation to sample a current between the terminal and the object to be measured, An electric waveform measurement probe including a cantilever supporting the photoconductive switch, wherein a light receiving portion of the photoconductive switch is formed on a surface of the cantilever opposite to a side on which the terminal is provided; An electric waveform measurement probe, wherein a light reflection film or a light absorption film for preventing unnecessary carriers from being excited by light is provided around a light receiving portion.