JPS635541A - Semiconductor wafer measuring device - Google Patents

Abstract

PURPOSE:To transmit the temperature of a sample placing stand to a sample to be measured without loss and to contrive to obtain highly accurate measured results by a method wherein the sample to be measured is fixed and supported on the surface of the temperature-controlled sample placing stand through a sheet-type metal plate having heat conductivity, electric conductivity and malleability. CONSTITUTION:A heat generating unit which sets the temperature of a sample placing stand 5a at a controlled temperature and a sheet-type metal plate 5b; which is provided between the sample placing stand 5a and a semiconductor wafer to be measured and has heat conductivity, electric conductivity and malleability; are provided. As the metal plate 5b comes to have compatibility with the semiconductor wafer and the roughness of the contact surface of the sample placing stand 5a and is closely adhered to them by the malleability which the sheet-type metal plate 5b has, the temperature of the sample placing stand 5a can be transmitted to the sample to be measured without loss and highly accurate measured results can be obtained. Moreover, by adding a metal plate which is thin like about 0.2 mm and consists of indium and so on, measured results with higher accuracy can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to semiconductor wafer measurement equipment, such as DLTS (Deep Level Transi...
The present invention relates to techniques effective for use in semiconductor wafer measuring devices for evaluating semiconductor materials and devices, including the ENTSpec troscopy method.

[Conventional technology]

It is conceivable to use liquefied nitrogen to measure the characteristics of low-temperature operating devices such as Josephson devices and to evaluate semiconductor materials and devices using the DLTS method. However, liquefied nitrogen has a constant temperature due to its vaporization.
A low temperature of about 6°C is formed. Therefore, it is extremely difficult to use this as a negative heat source and an electric heater or the like as a positive heat source to set the temperature of the sample mounting table to an intermediate temperature or to change it with a predetermined temperature gradient. This is because liquefied nitrogen always tries to form the above-mentioned low temperature through its vaporization. Furthermore, if an attempt is made to generate the above-mentioned intermediate temperature using a powerful electric heater, the consumption of liquefied nitrogen and the electric power of the electric heater will be enormous, making it extremely uneconomical and impractical. Therefore, the applicant of the present application has previously developed a low-temperature measurement device that can control the temperature with high precision (-Japan Micronics Co., Ltd., see product catalog 'FP-1500BJ).

[Problem that the invention seeks to solve]

The inventors of the present application attached a temperature sensor to the semiconductor wafer to be measured, which was fixed to the sample mounting table whose temperature is precisely controlled as described above, and measured the actual temperature. It was found that there was a relatively large difference between the temperature output from the temperature sensor and the temperature output from the temperature sensor. As a result of examining the above causes, the inventor of the present application found the following. In other words, even with a sample holder that is highly accurate (temperature-controlled) as described above, there are extremely fine irregularities on the surface of the sample holder and the bottom surface of the semiconductor wafer under test, so there is no contact between the two. There are many surfaces, which impede heat conduction.

As a result, even if the temperature of the sample mounting table is controlled accurately, the temperature is not directly transmitted to the semiconductor wafer, resulting in a relatively large temperature difference between the two. Therefore, using the temperature of the sample mounting table as a parameter,
This results in evaluating the characteristics of the semiconductor wafer, and it is not possible to evaluate the characteristics with high reliability.

An object of the present invention is to provide a semiconductor wafer measuring device that enables highly accurate semiconductor wafer characteristic evaluation.

The above and other objects and novel features of this invention include:
It will become clear from the description of this specification and the accompanying drawings.

[Means for solving problems]

A brief overview of typical inventions disclosed in this application is as follows.

That is, a heat generating device that sets the temperature of the sample mounting stage to a controlled temperature, and a sheet-like heat generating device that is provided between the sample mounting stage and the semiconductor wafer to be measured and that has thermal conductivity, electrical conductivity, and malleability. A metal plate is provided.

[For production]

According to the above-mentioned means, due to the malleability of the sheet-like metal, the metal plate adheres to the semiconductor wafer and the sample mounting table according to the unevenness of the contact surfaces thereof, so that the temperature of the sample mounting table is maintained without loss. It can be transmitted to semiconductor wafers.

〔Example〕

FIG. 1 shows a sectional view of a main part of a semiconductor wafer measuring device according to the present invention, and FIG. 2 shows a horizontal sectional view taken along line A--B. , in other words, Figure 1 is
This is a vertical sectional view taken along the line AB in FIG. 2.

In FIG. 1, there is a first .
It is joined to the upper surface of the second thermal conductor 6.7. Although not particularly limited, these heat conductors 6.7 have a fan-shaped cross-section formed by dividing a circle into four equal parts, as shown in FIG. Of these four sectors, two sectors 6 connected to the center and symmetrically arranged at the center are used as second heat conductors. In other words, the hollow space at the center is used as a storage area for the electric heater 12. Therefore, the positive temperature created by the electric heater 12 is
The heat is transmitted to the sample mounting table 5a through the second heat conductor 6. The lower half of this second thermal conductor 6 has been cut off.

Further, the remaining two sector shapes are used as first heat conductors, and are spatially separated from the second heat conductor except for the upper joint portion 6a. The first thermal conductor 7 has a fan-shaped cross section in its upper half as shown in FIG. are combined. The upper surface of this joint portion 6a is joined to the sample mounting table 5.

The lower half of the first heat conductor 7 is formed into a ring shape (doughnut shape) with a hollow space. The protruding lower half of the storage section that stores the electric heater 12 passes through this hollow section in a space-separated manner. By doing this,
Since a relatively large storage chamber can be formed, an electric heater 12 with relatively large power can be used.

The lower portion of the first heat conductor 7 is hollow in the shape of a ring. By forming the tank into a ring shape in this manner, a tank having a relatively large capacity can be formed.

Although this hollow portion 8 is not particularly limited as a refrigerant,
It is used as a second tank into which liquefied nitrogen is injected. A first tank 11 having a similar configuration is provided below the second tank 8. The center of the first tank 11 is hollow as described above, and the storage section passes through it in a space-separated manner.

Liquefied nitrogen is injected into the first tank 11 through the supply pipe 13. Valve B1 controls the supply of the liquefied nitrogen.

The first tank 11 and the second tank 8 are connected by a metal tube 9 having thermal conductivity.

As a result, when liquefied nitrogen exceeds the volume of the first tank 11, the liquefied nitrogen is injected into the second tank 8 through the metal pipe 9. Moreover, in this second tank 8,
An exhaust pipe 10 is provided for exhausting vaporized nitrogen gas. This exhaust pipe 10 passes through the second tank 8 and is led out to the outside. The reason for this is that the outside temperature is
This prevents transmission through 0. Valve B2
is for controlling the exhaust gas.

Although not particularly limited, in this embodiment, the second tank 8 is provided with a metal pipe for returning a certain amount or more of liquefied nitrogen to the first tank 11 (not shown).

The first tank 11 is attached to the second tank 8 in such a manner that it is suspended by the three pipes.

An opening is provided at the top of the box 3. The thermal conductor 6
, 7 are mounted below the opening of the box body 3 by means of a heat insulating member 4. The first vacuum chamber 1 is constituted by the heat conductors 6 and 7 and the box body 3. This first vacuum chamber 1 is evacuated by connecting an exhaust port 13a provided at the bottom of the box 3 to a vacuum source (not shown). That is, the first vacuum chamber 1 includes the electric heater 12
It is used as a heat insulating means for the heat of vaporization of liquefied nitrogen and the heat conductors 6 and 7.

Further, the sample mounting table 5a and the like are provided with a lid 14 that covers the upper part thereof, and constitutes the second vacuum chamber 2. This 1i1
There is an observation window 1 on the top surface corresponding to the sample mounting table 5a of No. 4.
4a is provided. This second vacuum chamber 2 is also evacuated by a vacuum source (vacuum pump) in the same manner as described above, thereby making it evacuated (not shown). The reason why the sample holder is evacuated in this way is that dew condensation occurs due to water vapor in the air due to low temperatures. Although not particularly limited, a manipulator equipped with a probe arm may be provided around the upper part of the box 3 in order to facilitate measurement of elements formed on a semiconductor wafer. That is, a probe arm 15 penetrates from the side wall of the lid 14 and extends into the vacuum chamber 2, and the position of the tip of the probe 18 is finely adjusted by a positioning mechanism 19 provided at its tip. One end of the bellows 16 is on the '114 side,
The other ends are closely fixed to the probe arms 15, respectively.

Thereby, the degree of vacuum in the vacuum chamber 2 is maintained while making the flow arm 15 movable as described above.

The tip of the probe arm 15 is roughly aligned by a stage mechanism (micro head stage) 17. Such a configuration is explained in detail in the low temperature prober of the applicant's earlier application (Japanese Patent Application No. 57-151299). In addition, the probe arm 1
A manipulator 20 for adjusting the tip position of the probe needle 18 is provided at the tip of the probe needle 5 . Note that instead of connecting the measuring element with such a probe, wiring may be directly provided to the measuring element. The probe needle 18 is connected to an external terminal of the vacuum chamber 2 by a lead wire 19.

In this embodiment, in order to efficiently transmit the controlled temperature of the sample mounting table 5a to the measurement sample (not shown) (semiconductor wafer), the surface of the temperature-controlled sample mounting table 5a has thermal conductivity and electrical conductivity. A sheet-like metal plate 5b having elasticity and malleability is provided. This metal plate 5b is made of an indium plate as thin as about 0.2 ++n, although it is not particularly limited. This metal plate 5b also functions as an electrode for electrical connection to the substrate side of a sample (semiconductor wafer) placed on its surface. Therefore, metal t
H5b is connected to the external measurement terminal of the vacuum chamber 2 via a lead wire 19.

The operating mode of temperature control of the low-temperature sample mounting table according to this embodiment will be described next.

In forming the desired low temperature, the above 1. The second vacuum chambers 1 and 2 are evacuated. After that, valve B1 is opened and liquefied nitrogen is supplied.

At this time, valve B2 for removing vaporized gas is also opened. The liquefied nitrogen that exceeds the capacity of the first tank 11 due to the injection of the liquefied nitrogen is injected into the second tank 8 through the metal pipe 9. When liquefied nitrogen is injected into the second tank 8 in this way, its vaporization flows into the second tank 8.
carried out by.

Therefore, since the above-mentioned low temperature of about -196° C. is formed in this second tank 8, the above-mentioned temperature is transmitted to the sample mounting table 5a through the thermal conductor 7 as the lowest temperature.

When the temperature is gradually increased from this state with a constant temperature gradient, the amount of vaporized gas exhausted by valve B2,
Reduce the amount of liquefied nitrogen supplied by valve B1. As a result, the atmospheric pressure in the second tank 8 increases, and the amount of liquefied nitrogen in the second tank 8 decreases. At the same time, the electric heater 12 is activated to gradually increase the temperature.

When the liquefied nitrogen in the second tank 8 runs out, the liquefied nitrogen is vaporized from the metal tube 9 to the first tank 11.

When the liquefied nitrogen is vaporized in the metal pipe 9 to the first tank 11, the -196
A low temperature of .degree. C. is generated and is transmitted to the heat conductor 7 through the second tank 8 and, together with it, the metal tube 9.

Since both the second tank 8 and the metal tube 9 are formed to have appropriate thermal resistance, the temperature of -196° C. formed by the vaporization is attenuated and transmitted to the heat conductor 7. Therefore, the temperature of the sample mounting table 5a is an intermediate temperature or a temperature that is the sum of the negative temperature formed through the thermal conductor 7 and the positive temperature formed by the electric heater 12 and formed through the thermal conductor 6. It is assumed to have a slope. In order to perform such temperature control, a temperature sensor is attached to the sample mounting table 5a.

In addition to the metal pipe 9, the heat conduction path for transmitting the low temperature generated in the first tank 11 to the second tank 8 is made of a heat conductive metal or the like, and includes an exhaust pipe 1o and the aforementioned liquefaction pipe (not shown). This is also done through these by forming a nitrogen return pipe.

Further, the sample mounting table 5a is provided with a clip or the like (not shown) for fixing a measurement sample such as a semiconductor wafer, etc., although not particularly limited, and the measurement sample is fixed to the surface of the sample mounting table 5a together with the metal plate 5b. It is fixedly supported so as to press against it. As a result, both surfaces of the metal plate 5b made of ingenium conform to the irregularities on the lower surface of the semiconductor wafer and the upper surface of the sample mounting table 5a due to its malleability.
Due to its high degree of adhesion, it adheres closely to both. Thereby, the temperature of the sample mounting table 5a is transmitted to the measurement sample (semiconductor wafer) without heat loss because the indium plate 5b also has good thermal conductivity. Thereby, evaluation of the DLTS method and the like can be performed with high accuracy using the temperature obtained from the temperature sensor of the sample measuring table 5a as a parameter.

The effects obtained from the above examples are as follows. That is, (11) By fixing and supporting the measurement sample (semiconductor wafer) on the surface of a temperature-controlled sample table via a sheet-like metal plate having thermal conductivity, electrical conductivity, and malleability, the above-mentioned sheet Due to the malleability of the shaped metal, the metal plate conforms to the irregularities of the contact surfaces of the semiconductor wafer and the sample mounting table and comes into close contact with it, so that the temperature of the sample mounting table can be transmitted to the measurement sample without loss. The effect is that highly accurate measurement results can be obtained.

(2) The simple configuration of adding a thin metal plate of indium or the like with a thickness of approximately 0.2 m provides the effect that the above-mentioned highly accurate measurement results can be obtained.

(3) Although liquefied nitrogen is used as a negative heat source to control the temperature of the sample mounting table, a first tank and a second tank are provided, and a liquefied nitrogen supply pipe that also serves as a heat resistance means is provided between them. By connecting the two, a multi-stage negative heat source can be constructed.

This provides the effect that the electric heater that generates a positive temperature can generate a desired intermediate temperature with a smaller amount of electric power.

(4) By being able to control the temperature or temperature gradient with high precision, the reliability of evaluation of semiconductor materials and devices, including the DLTS method, can be improved. For example, if a semiconductor crystal is kept at a low temperature and excited by light irradiation, injection, or other methods, most of the traps will be filled with carriers. When the temperature is raised from this temperature at a rate of about 1° C. per second or less, the trapped carriers dissociate and flow due to the electric field. This is called a thermally stimulated current, and it can be used to evaluate the depth and concentration of traps in a semiconductor crystal. In such an evaluation, reliability can only be obtained if the temperature gradient of the sample mounting table can be controlled with high precision and kept constant. In this way, in the evaluation of semiconductor materials and devices, reliability increases as temperature control becomes more precise.

Although the invention made by the present inventor has been specifically explained above based on Examples, it goes without saying that this invention is not limited to the above Examples and can be modified in various ways without departing from the gist thereof. Nor. For example, the metal plate 5b may be made of anything other than indium as long as it has electrical conductivity, thermal conductivity, and malleability. For example, it can be replaced with gold. Further, the two thermal conductors 6 and 7 as means for controlling the temperature may be directly attached to the lower surface of the sample mounting table 5, respectively. Also, if the number of tanks is 3 or more,
Substantially more multiple stages of negative temperatures may be formed by liquefied nitrogen. Alternatively, the heat conductor may be divided into smaller pieces to equalize the temperature transmitted to the sample mounting table.

Furthermore, liquefied freon or the like may be used as the refrigerant.

This invention is a low-temperature sample used for evaluating semiconductor materials and devices! ! It can be widely used as a two-place stand.

〔Effect of the invention〕

A brief explanation of the effects obtained by typical inventions disclosed in this application is as follows. That is, by fixing and supporting the measurement sample on the surface of a temperature-controlled sample mounting table via a sheet-shaped metal plate that has thermal conductivity, electrical conductivity, and malleability, the spreadability of the sheet-shaped metal is improved. Due to its ductility, the metal plate adapts to the irregularities of the contact surfaces of the semiconductor wafer and the sample mounting table and comes into close contact with the metal plate, so that the temperature of the sample mounting table can be transmitted to the measurement sample without loss. As a result, highly accurate measurement results can be obtained.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of the present invention, and FIG. 2 is a horizontal cross-sectional view taken along the line AB in FIG. 1.

Claims (1)

[Claims] 1. A sample mounting stage, a heat generating device for setting the sample mounting stage at a controlled temperature, and a thermal conductive heat generating device provided between the sample mounting stage and the semiconductor wafer to be measured. A semiconductor wafer measuring device characterized by comprising a sheet-like metal having electrical conductivity and malleability. 2. The above-mentioned heat generating device includes a first tank with thermal conductivity provided with a supply pipe of a refrigerant that forms an ultra-low temperature by vaporization, and a thermally conductive metal installed on the top of the first tank. A second tank with thermal conductivity connected through a pipe, an exhaust pipe provided with a valve that selectively exhausts vaporized gas in the second tank, and a part of the second tank. a first thermal conductor that is coupled to conduct heat to the sample mounting stage; an electric heater; and a first thermal conductor that conducts heat generated by the electric heater to the sample mounting stage; Claim 1, characterized in that the second heat conductor has a second heat conductor whose surface is largely separated from one another, and a vacuum chamber that accommodates the heat source and the heat conductor.
Semiconductor wafer measuring device as described in . 3. The semiconductor wafer measuring device according to claim 1 or 2, wherein the sheet-like metal plate is a metal containing indium as a main component.