JPH0362545A - Instrument for measuring mobility of carrier - Google Patents

Abstract

PURPOSE:To effectively measure the mobility of a carrier by providing the second probe which is electrically insulated from the first probe at a position separated from the first probe by a fixed distance and using one of the probes as a probe for injection and the other as a probe for detecting injected carriers. CONSTITUTION:When a potential difference is given in advance to an electrode of a power source 14 fitted to a sample 3, injected electrons move along an electric field and, when they reach a point just below a probe 1, the electric potential is instantaneously changed and a pulse-like change is caused in the tunnel current between the probe 1 and sample 3. When the pulse is detected by means of a detection circuit 11 and the time lag between the detected pulse and the voltage pulse first applied across a probe 2 is measured with a timer 12, the flying time tau of the injected electrons can be found. When the interval (d) between the probes 1 and 2 is measured in advance by means of a scanning tunnel microscope STM, the average speed of the injected electrons can be found from v=d/tau (where, v = speed). Therefore, the mobility of electrons is measured at a very small area on the surface of the sample.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention is equipped with two probes, and measures the shape of a sample surface, and also measures carriers in a specific micro region on the sample surface. The present invention relates to an evaluation device for measuring mobility.

(Prior art) Carrier mobility on the semiconductor surface is an important parameter that influences the characteristics of semiconductor devices, but as devices become smaller, local carrier mobility in minute regions on the surface There is a growing need to seek In particular, the carrier mobility in the direction along steps, grain boundaries, Peter interfaces, etc., or in the direction perpendicular to them, is a practically important quantity. In order to measure such local carrier mobility, (i) estimate the surface shape and find the target location (step, etc.), (5) inject electrons into the target location. (m) It is required to detect electrons at some distance. Among these, (ii), (ui)
For example, consider electron injection and detection.

A high spatial resolution of l- or less is required.

Pair excitation of electrons and holes by light, which is often used as an electron injection method, is not useful as a local method because it is difficult to make the light beam diameter submicron. Festivals are also difficult. On the other hand, when using an electron beam, it is possible to observe the surface shape by using an SEM;
By focusing and irradiating the SEM's electron beam onto the specific location found by the method, the requirements of (and) are also satisfied. However, the energy of the SEM electron beam is so high that not only are electrons injected deep below the surface, but atoms are excited and desorbed near the surface.

This causes various problems such as surface heating.
At present, it is difficult to say that electron injection using SEM is suitable for measuring mobility.

(Problem to be solved by the invention) In this way, the conventional technology simultaneously achieves surface topography imaging, which is necessary to measure local mobility, and injection of low-energy electrons into a specific micro region. The present invention has been made to overcome this technical difficulty, and has developed a device that images the semiconductor surface and locally injects and detects electrons at the target location. This is what we provide.

[Structure of the Invention] (Means for Solving Problem m1) In order to achieve the above objects, the present invention utilizes scanning tunneling microscopy (STM) technology.

That is, in STM, a second probe that is electrically insulated from the STM probe is provided at a certain distance from the STM probe, and by moving the probe or the sample, both probes are connected to the sample surface. The gist is to scan along the

In the above configuration, the STM probe is used for STM surface sensing and is aligned to a target location to act as an electron detector. On the other hand, the second probe acts as an electron emitter and locally injects electrons.

But surface m%? It is also possible to use a scanning electron microscope (SEM), that is, to combine SEM and STM.

(Function) By providing two probes, the surface of a sample such as a semiconductor substrate can be observed first with the first probe, and then the surface of a sample such as a semiconductor substrate can be observed using the first and second probes. The movement of carriers in a microscopic area on the target sample surface is detected and the mobility is measured.

(Example) Examples of the present invention will be described below in Figures 1 (a), (b), and 2.
This will be explained using the drawings and FIG.

FIG. 1(a) shows the probe section of the present invention. The probe section is composed of two probes 1.2 that are electrically insulated from each other. The probe is made of tungsten, but is not particularly limited to this material. Any metal that is difficult to oxidize, such as platinum and platinum alloys (platinum-rhodium, platinum-iridium), can be used. The insulating substrate 15 that supports these probes may be made of any material, such as plastic or ceramic, as long as it is a highly insulating material. FIG. 1(b) shows a mechanism for moving a probe according to the present invention and a mechanism for moving a sample facing the probe.

The probe is brought close to the sample surface 3 by a normal probe approach mechanism 4 of the STM. Since the lengths of probes 1 and 2 are not exactly equal, when one of them approaches surface 3 first and the distance from surface 3 becomes about 1 nm, probe 1 (temporarily, probe l
A tunnel current flows between the surface 3 and the surface 3, which enables operation as an STM. The following measurements are performed as follows.

First, the apparatus is operated as an STM, and a voltage of about several volts is applied to microscopically observe the shape of the surface of a sample, for example, a silicon semiconductor substrate. At this time, the tunneling current is measured by a current detector 6 through one of the electrodes 5 attached to the sample. A piezoelectric element 7 is used to move the probe, and its movement is controlled by the STM control and scanning system, similar to normal STM. By using a large piezoelectric element, it is possible to observe a region of several −× several p with a resolution of inn or less, and it is not difficult to find steps or grain boundaries. A moving mechanism 8 is also provided on the sample in order to detect areas larger than -2.

When the target object 9 is found on the sample surface, the sample moving mechanism 8 and the piezoelectric element 7 position the probe l at an arbitrary location near the object 9. Next, a negative voltage pulse is applied from the pulse generator IO to the other probe 2 to inject electrons into the sample surface 3.

The width of the voltage pulse is several n5 ec, and the height of the pulse is a negative voltage of several volts to several tens of volts, and the specific values vary depending on the case. When a negative voltage is applied to the tip 2, electrons are injected into the sample 3 by tunneling or field emission (if the voltage is high), but if the tip 2 has sufficient sharpness, the area where the electrons are injected will expand. is on the order of several nm, and local injection of electrons is realized.

Specifically, the spread of the injection region is approximately equal to the in-plane resolution when probe 2 is used for STM.0 It is very difficult to achieve an in-plane resolution of about 1 nm with a polished probe used in normal STM. It is not difficult and therefore quite possible to realize an implantation area of several nm.

When a potential difference is applied to the electrode 5 attached to the sample by the power source 14, the injected electrons move along the electric field, and when they reach just below the probe 1, the potential there instantaneously changes and the probe A pulse-like change is caused in the tunnel current between the needle 1 and the sample 3.

This current pulse is detected by the detection circuit 11, and the time difference between this detection pulse and the voltage pulse initially applied to the probe 2 is measured using the timer 12.

The flight (travel) time τ of the injected electrons is measured. If the distance d between the probes 1 and 2 is measured in advance with an SEM, the average velocity of the injected electrons can be found from υ = d/τ (dividing υ by the electric field E applied to sample 3 mobility). In this way, the electron mobility in a minute area on the sample surface is measured.

Next, a specific numerical example is shown. As for the probes 1 and 2, probes with an interval of several p can be manufactured using microfabrication technology. The distance between probes 1.2 is 10. shall be. IV on silicon substrate 3
When an electric field of /as is applied, the time difference τ between the detection pulse and the voltage pulse initially applied to the probe 2 is determined by the timer 12.
was measured to be approximately 0.7 μsec.

Therefore, the electron mobility at this time is approximately 1430d/
It becomes vsec. The time resolution of the timer 12 is 1
n5ec or less is also possible, so the timer can sufficiently measure τ. As mentioned above, the voltage pulse applied to the probe 2 can be several n5 ec, which is much smaller than that. Regarding the detection of current pulses, the time constant of the detection system is a problem, but the shunt resistor 13 is set to 1Ω.
Then, the stray capacitance is several pF, and the time constant is several n5.
ec, so it does not have a large effect on the measurement of τ. When the injection current is 500 nA, the voltage pulse generated by the shunt resistor 13 is 0.5 ■V, and the high-speed preamplifier 11
is sufficient to activate the timer 12 via .

For the probes 1 and 2 of the embodiment of the present invention, a conductive material for the probe, such as tungsten, is selectively grown to form a needle-like body, and then a resist mask is etched by reactive ion etching using a selective resist mask. The tip of the tungsten needle was taper-etched using the regression of the tungsten needle to sharpen the probe. However, the selective growth of tungsten is
For example, it is also possible to selectively irradiate a spot with an electron beam or the like in a tungsten hexafluoride gas atmosphere. In this case, there is no need for a thick resist mask for selective growth, and furthermore, since the tip has already been sharpened, it is also possible to eliminate the need for Taber etching.

Further, by applying a positive voltage pulse to the probe 2, holes can be injected into the sample. In this case, the Hall mobility will be determined.

〔Effect of the invention〕

As described above, the mobility measurement device of the present invention can measure the surface shape of a sample and measure the electron mobility in a predetermined minute region of the surface.

[Brief explanation of drawings]

FIG. 1(a) shows the probe section of the mobility 81q determining device of the present invention, and FIG. 1(b) shows the moving mechanism of the probe section of FIG. 1(a) and the probe section facing the probe section. FIG. 2 is a schematic diagram of the operation of the probe when detecting the sample surface according to the present invention, and FIG. 3 is a schematic diagram of the operation of the probe when measuring the mobility of the present invention. 1.2... Probe 3... Sample (silicon substrate) 4... Probe approach mechanism 5...
Sample electrode 6... Current detector 7... Piezoelectric element 8... Sample moving mechanism 9... Measurement object 10... Pulse generator 11... Detection circuit 12... Timer 13... Shunt resistor 14...Power supply 15...Insulating board (8733)

Claims (1)

[Claims] The first probe is provided with a second probe that is electrically insulated from the first probe, and the first probe is provided at a certain distance from the first probe. An injection probe,
A carrier mobility measuring device characterized in that the other end is a detection probe that detects injected carriers (electrons or holes).