Mercury probe apparatus with improved safety

Abstract

To provide an apparatus for measuring electrical properties of a semiconductor wafer.SOLUTION: An apparatus comprises a wafer holder, a mercury probe for contacting the top surface of said wafer with a mercury column, wherein the mercury probe includes a capillary tube (21) for containing said mercury column, pneumatic control means (23) for applying a partial vacuum or pressure above said mercury column within said capillary tube (21), a probe arm (1) having said mercury probe affixed thereto, positioning means for controlling the position of said capillary tube (21) relative to the upper surface of said wafer, measurement means for causing an electrical current to flow through said wafer and for measuring electrical properties of said wafer, a first electrical contact electrically connected to said mercury column and to said measurement means, a second electrical contact electrically connected to said wafer holder and said measurement means, a clean mercury container (41), and a control unit in operating connection with the pneumatic control means (23), the positioning means and the measurement means.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a method and apparatus for measuring the electrical characteristics of a semiconductor wafer using a mercury column as one of the contacts, which improve safety and reduce the need for maintenance.

Background Art

[0002] The use of a mercury column as a non-invasive contact for measuring the electrical characteristics of a semiconductor wafer is well known in the art. However, mercury is highly toxic, posing both health risks and environmental pollution risks, and thus its handling is dangerous and requires specially trained personnel.

[0003] U.S. Patent No. 4,587,484 describes an apparatus for measuring the electrical characteristics of a semiconductor wafer through a mercury column. The wafer contacts the capillary from above, and mercury is drawn from the reservoir into the capillary by a vacuum. If the sealing between the wafer and the capillary is incomplete, a significant amount of mercury may leak out.

[0004] U.S. Patent No. 7,253,649 describes a similar configuration for measuring the electrical characteristics of a wafer, where the mercury column contacts the wafer from below. In this configuration, the amount of mercury that leaks out in case of a sealing defect is reduced, but the large amount of mercury required to reach the sample through a relatively long tube and held in the reservoir still poses a significant risk in case of a failure of the pneumatic system.

[0005] Japanese Laid-Open Publication No. 6044521 describes an apparatus for measuring the electrical characteristics of a semiconductor wafer via a mercury probe, in which mercury is bubbled and purified in a reservoir between measurements. Regular purification reduces the frequency of mercury cartridge replacement, but still, periodic replacement is necessary because contaminants cannot be completely removed from the mercury.

[0006] All of the devices described above are typically 1 to 2 cm 3 equipped with a relatively large mercury reservoir with a volume of, and this is in fluid communication with the capillary. Therefore, in the case of a seal failure or a malfunction of the pneumatic system, there is a risk of a large amount of mercury flowing out.

[0007] During measurement, the mercury is contaminated by the oxidation of mercury and by the fine particles and other contaminants collected from the surface of the wafer. As a result, it is necessary to periodically replace the mercury contained in the device, and this replacement is carried out by manually replacing the entire unit equipped with the mercury reservoir.

[0008] In the system described above, by reducing the amount of mercury held in the reservoir, the risk of a large amount of mercury flowing out can be reduced, but as a price, the required replacement interval of the mercury containment unit becomes shorter. The reason is that when the same amount of contamination is introduced into the mercury, the smaller the amount of the mercury, the faster the measurement accuracy decreases. Depending on the cleanliness around the device and the amount of measurements performed, the replacement of mercury in a device with a supply amount of 1 to 2 cm 3 may be required at a frequency of 2 to 3 weeks. Summary of the Invention Problems to be Solved by the Invention

[0009] From the above, an object of the present invention is to eliminate or at least improve the drawbacks of the prior art solutions. More specifically, an object of the present invention is to provide a mercury probe device with improved safety for measuring the electrical characteristics of a semiconductor wafer, which reduces the risk of mercury outflow without increasing the frequency of maintenance. A further object of the present invention is to provide a measuring device with improved safety, in which new mercury can be used for measurement without manual maintenance. Another further object of the present invention is to provide a measuring device with improved safety, in which the evaporation of mercury and the release of mercury vapor are substantially eliminated. Means for Solving the Problems

[0010] The above object has been achieved by developing the device according to claim 1. Exemplary embodiments of the device according to the present invention are presented in claims 2 to 9. The above object has been further achieved by developing the method according to claim 10. Preferred variants of the method are presented in claims 11 to 14.

[0011] Hereinafter, preferred embodiments of the device according to the present invention and its operation will be described in detail with reference to the following attached drawings.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0013] The same reference numerals in different figures denote the same components.

[0014] FIG. 1 is a cross-sectional side view of a probe arm 1 of an apparatus according to the present invention, with a probe head disposed at a measurement position. The probe head includes a base 20 fixed to the probe arm 1, a capillary 21 preferably made of a dielectric material, most preferably glass, a first electrical contact 24 at least partially disposed within the capillary 21 and preferably formed of a metal wire, and pneumatic control means 23, e.g., a fluid connection for selectively generating a partial vacuum or ambient pressure within the capillary 21 to draw up, hold, and release mercury within the capillary 21. During measurement - as shown in FIG. 1 - a mercury column M is disposed within the capillary 21 such that the lower surface of the mercury column M contacts the upper surface of a sample, i.e., a wafer W. The first electrical contact 24 contacts, preferably penetrates into, the mercury column M. In order for the device to operate properly, a mercury column M sufficiently high in the capillary must be drawn up so that an electrical contact occurs between the first electrical contact 24 and the mercury column M. As shown in the figure, during measurement, only the mercury present within the capillary 21 is moved by the fluid pressure supplied through the fluid connection 23, and thus, if the sealing of the contact between the capillary 21 and the wafer W is not sufficiently good, only this very small amount of mercury may leak out. According to a particularly preferred exemplary embodiment, the inner diameter of the capillary 21 is 1.7 mm, the height of the mercury column is about 10 - 15 mm, and thus the mass of mercury within the probe head is less than 0.5 grams.

[0015] The wafer W is disposed on a wafer holder 3, preferably formed by a chuck. The wafer holder 3 may have vacuum grooves for holding a bowed wafer flat against the surface of the wafer holder 3. At least a part or preferably the whole of the wafer holder 3 or its upper surface is preferably made of a conductive material, in which case, when the wafer W is disposed on the wafer holder 3, an electrical connection is established between the lower surface of the wafer W and the upper surface of the wafer holder 3.

[0016] In the exemplary embodiment shown in FIG. 1, the capillary 21 is fixed to the probe head 2 by a metal sleeve 22 that also provides electrical shielding against external electrical noise.

[0017] The apparatus includes positioning means for changing the relative position between the probe head 2 and the wafer holder 3. The positioning means (not shown) must have three degrees of freedom with respect to the relative movement of the probe head with respect to the wafer holder 3. Thus, the positioning means may include at least one vertical positioning means and at least two of one or two horizontal positioning means and one or two rotational positioning means having a vertical axis. In this way, the vertical distance between the probe head 2 and the wafer holder 3 can be changed, and the probe head can be positioned at at least one position above an arbitrary portion of the surface of the wafer holder 3 and not above the wafer holder 3. This can be achieved in any manner known to those skilled in the art, such as using an XYZ stage for linear movement of the wafer holder or the probe head, or using two separate XYZ positioning means for moving each of them. Instead of or in addition to horizontal translational movement, the wafer holder 3 and / or the probe arm 1 may be rotated about two different vertical axes.

[0018] According to the exemplary embodiment shown in FIG. 1, the probe arm 1 includes a gas flow path 11 and a gas tube 12 for blowing an inert gas onto the measurement site to remove particles from the surface of the wafer W so as to reduce mercury contamination and as a result extend the life of each mercury filled.

[0019] The measurement is performed at the position of the probe head shown in FIG. 1, that is, the position where the capillary 21 and the mercury column M contact the surface of the wafer W. The apparatus according to the present invention further includes electrical measurement means (not shown) having two terminals. The electrical measurement means is suitable for supplying a voltage or a current between its terminals. The first terminal of the electrical measurement means is connected to the electrical terminal 25 of the probe head. The electrical terminal 25 is electrically connected to the first electrical contact means 24, the first electrical contact means 24 is electrically connected to the mercury column M, and the mercury column M contacts the upper surface of the wafer W. The second terminal of the electrical measurement means is electrically connected to the wafer holder 3 and, through the wafer holder 3, to the lower surface of the wafer W. The electrical measurement means can measure the current-voltage characteristic, that is, the resistance, of the wafer by generating one of a DC voltage and a DC current between its terminals and measuring the other of the DC voltage and the DC current, or the electrical measurement means can measure the capacitance-voltage characteristic of the wafer W by generating one of an AC voltage and an AC current between its terminals and measuring the other of the AC voltage and the AC current.

[0020] After the measurement is completed, a partial vacuum that is at least about 5 to 15 Hgmm lower than the ambient pressure is created through the fluid connection portion 23, and as a result, the mercury column M rises from the surface of the wafer W. There is a very slight deviation between the lower surface of the capillary 21 and the upper surface of the wafer W, which allows air to enter the space below the mercury column M and escape therefrom, but is small enough to prevent mercury leakage when the mercury column M is not held by the pressure difference between the space above the mercury column M and the surroundings. A gap is formed.

[0021] The device according to the present invention is operatively connected to a pneumatic control means 23, a positioning means, and a measuring means, and further includes a control unit (not shown) for controlling the partial vacuum supplied by the pneumatic control means, for controlling the position of the mercury probe via the positioning means, and for controlling the voltage supplied by the measuring means. According to a preferred embodiment, the control unit is suitable for receiving and processing the measurement results of the measuring means and, in particular during the mercury replacement operation, for controlling at least the operation of the pneumatic control means based on the measurement results.

[0022] Figure 2 shows the probe arm 1 and the probe head of the device according to the present invention at the stages before and after measurement when the mercury column M is held from above by a partial vacuum. The probe head having the probe arm 1 can be raised (or the wafer can be lowered), and then the relative horizontal movement and / or rotational movement of the probe head and the wafer can be performed by the positioning means to select different measurement sites. On the new measurement site, the probe head is lowered onto the surface of the wafer W, the capillary 21 is brought into contact with the upper surface of the wafer W, the partial vacuum holding the mercury is released, the space above the mercury column M is pressurized, and thereby the mercury column M is lowered to contact the upper surface of the wafer W.

[0023] Figure 3 shows the apparatus according to the invention during the mercury replacement operation. When the trigger conditions are met, the apparatus according to the invention performs the mercury replacement operation, i.e., the apparatus updates the mercury held in the capillary. This is done by releasing the partial vacuum holding the mercury column M and allowing the mercury to fall into the container, and then pulling up a new mercury column. The release of the used mercury and the pulling up of the new mercury column can be performed using the same container with the same effect as the prior art solution, but the result is merely a dilution of the contamination. However, in the particularly preferred exemplary embodiment shown in Figure 3, two different containers are provided, namely, a clean mercury container 41 for storing clean mercury and a contaminated mercury container 42 for storing used mercury. Figure 3 shows the first stage of the mercury replacement operation, i.e., when the used mercury (not shown) is released into the contaminated mercury container 42. The contaminated mercury container 42 is preferably disposed within the clean mercury container 41 such that the bottom of the contaminated mercury container 42 rests on the surface of the clean mercury, with the result that the static pressure at the bottom of the clean mercury container 41 remains the same regardless of how many mercury replacement operations are performed, thereby ensuring that it is easy to pull up the new mercury column by the same amount each time.

[0024] The clean mercury container 41 and the contaminated mercury container 42 are preferably covered by a cover plate 43 fixed on the clean mercury container 41 to limit the leakage of mercury vapor during the mercury exchange operation. A lid 5 is preferably arranged at the top part of the cover plate 43. The said lid is open during the mercury exchange operation, and otherwise the lid 5 is closed above the cover plate 43 to completely prevent the leakage of mercury vapor. The lid 5 is preferably biased towards the closed position so that it remains closed unless an operation to intentionally open it is performed. The clean mercury container 41, the contaminated mercury container 42, the cover plate 43, and the lid 5 together form a mercury storage unit, which safely stores mercury and enables the device to exchange the contained mercury used for measurement with completely clean mercury to be filled at any time. The cover plate 43 is provided above the contaminated mercury container 42 with a first through hole, i.e., a dropping hole 431, for directly dropping the used mercury from the capillary 21 into the contaminated mercury container 42.

[0025] Preferably, the first stage of the mercury exchange operation is performed by bringing the capillary into contact with the cover plate 43 such that the hole of the capillary is located above the through hole 431 of the cover plate 43. According to a further preferred embodiment, the cover plate 43 has a funnel-shaped recess 433 that promotes the safe dropping of the used mercury by providing an inclined surface around the upper periphery of the dropping hole 431 to guide any mercury droplets (which may be caused by the scattering of the dropped mercury) into the contaminated mercury container 42.

[0026] The cover plate 43 preferably further includes a first pressure relief hole 432 that is separate from the dropping hole 431 and is preferably smaller than the dropping hole 431. As a result, when the used mercury is dropped into the contaminated mercury container 42, a certain amount of air can escape from there. Moreover, the gas flow between the inside and outside of the mercury storage unit is restricted so that the leakage of mercury vapor is limited. The pressure relief hole 432 assists in the dropping because when the mercury moves downward from the capillary 21, the pressure inside the contaminated mercury container 42 will increase, and as a result, the movement of the mercury will slow down or even part of the mercury may be prevented from coming out of the capillary 21.

[0027] The cover plate optionally protrudes upward from the upper surface of the cover plate 43 and further includes a first rim 434 that surrounds the upper ends of both the dropping hole 431 and the first pressure relief hole 432 to prevent any leaked mercury droplets from rolling on the surface of the cover plate 43.

[0028] Figure 4 shows a preferred embodiment of the present invention during the second stage of the preferred variant of the mercury exchange operation, i.e., during the pulling up of the new mercury column from the clean mercury container 41. In this figure, the capillary 21 is disposed above the second through-hole, i.e., the drawing-in hole 435, of the cover plate 43. The cover plate preferably has a drawing-in pipe 436 reaching the bottom of the clean mercury container, whereby even when the level of mercury is low, clean mercury can be drawn in through the drawing-in pipe and further through the drawing-in hole 435. Preferably, a sealing element 437 is disposed around the upper end of the drawing-in hole 435 to assist the fluid sealing between the capillary 21 and the drawing-in hole 435 so that the partial vacuum provided in the capillary 21 does not draw in air from the side. The sealing element 437 is preferably formed of an elastic material. The cover plate 43 preferably further includes a second pressure relief hole 438 to allow ambient fluid, such as air, to enter the clean mercury reservoir when mercury is sucked up from the clean mercury reservoir. Thereby, the pulling up of mercury is promoted by providing a constant pressure equal to the ambient pressure, i.e., an overpressure with respect to the partial vacuum in the capillary 21. This overpressure may be provided by other means, such as by a pressurized gas cartridge fluidly connected to the clean mercury reservoir, or by a spring-biased or weighted cover that applies pressure to the mercury. These means may also be employed in combination. That is, the second pressure relief hole 438 provides a pressure equal to the ambient pressure, and at this time, pressure is applied to the clean mercury by the weight of the contaminated mercury container 42 and the contaminated mercury therein. Further, the contaminated mercury container may be spring-biased to apply a greater pressure to the underlying clean mercury. The second pressure relief hole 438 is preferably smaller than the drawing-in hole 435 so that the leakage of mercury vapor from the mercury-containing unit is limited.

[0029] The cover plate optionally protrudes upward from the upper surface of the cover plate 43 and further includes a second rim 439 surrounding the upper ends of both the draw-in hole 431 and the second pressure relief hole 438 to prevent any leaked mercury droplets from rolling on the surface of the cover plate 43.

[0030] FIG. 5 shows another further preferred embodiment, in which the apparatus comprises a stop station 6 having a flat upper surface and being resistant to mercury, i.e., not chemically reacting with mercury, not forming an amalgam or alloy with mercury, and not being penetrable by mercury, i.e., not porous. Such a material is, for example, silicon dioxide, in which case the stop station 6 can be formed by one thermally oxidized Si wafer. The probe head in the stop position is shown in the figure, where the capillary 21 contacts the upper surface of the stop station in a manner that seals the fluid, and the mercury column M is lowered onto the surface of the stop station, i.e., the partial vacuum holding it is released. This is the standby position of the apparatus according to the invention, where the mercury column M is sealed from the ambient air, thus preventing its oxidation and extending its life. At the same time, mercury evaporation is also prevented in the standby position, thus improving safety.

[0031] Stop station 6 preferably comprises a self-aligning mechanism 61 that supports the flat surface of stop station 6. The self-aligning mechanism 61 facilitates the establishment of sealing contact between stop station 6 and capillary 21 by finely adjusting the inclination of stop station 6 when it comes into contact with capillary 21. For example, the self-aligning mechanism 61 may be formed by a block of elastic material that is compressed by the pressure exerted by capillary 21 to ensure the abutment of the upper surface of the stop station on the lower surface of capillary 21. FIG. 5 shows an exemplary embodiment in which stop station 6 is positioned at the top of lid 5. This is merely a convenient arrangement because this positioning means is accessible from the top of the mercury container from the start and stop station 6 does not occupy another space within the device. Alternatively, the stop station may be located at any other location within the device where the probe head is accessible..

[0032] According to the preferred exemplary embodiment shown in FIG. 5, lid 5 is provided with a spring 51 that biases lid 5 towards its closed position, whereby in the non-energized state and even when the mercury-containing unit is removed from the device according to the present invention, lid 5 is maintained firmly closed, preventing the evaporation and accidental outflow of the mercury contained therein. Lid 5 preferably also comprises an actuator 52 for opening and closing lid 5 during operation. Actuator 52 operates on, for example, hydraulic, electromechanical, or pneumatic principles and is preferably pneumatic.

[0033] A vertical guide sleeve 422 is preferably provided in the central portion of the contaminated mercury container 42. By inserting the guide rod 430 of the cover plate 43 into the guide sleeve 422, the movement of the contaminated mercury container 42 may be restricted so that it can only move in the vertical direction. Further, a compression spring 424 may be disposed around the guide sleeve 422 and the guide rod 430 so as to push down the contaminated mercury container 42 when the mercury-containing unit is assembled. The guide sleeve 422 may comprise a suitable abutment surface, such as a flange or shoulder 423, for the spring 424 to seat on.

[0034] FIG. 6 shows an exploded view of a particularly preferred embodiment of the mercury containment unit of the apparatus according to the present invention. In this case, the clean mercury container 41 is a receptacle that is open at its upper side and closed at its sides and bottom, and the contaminated mercury container 42 is formed as a bucket having a closed bottom, a closed side wall, and an open top. Further, the contaminated mercury container 42 and the clean mercury reservoir are sized such that the contaminated mercury container 42 fits within the clean mercury container 41. According to the preferred exemplary embodiment shown in the figure, the contaminated mercury container 42 is provided with a handle 421 that can be lifted and gripped with either a hand or tweezers, and thus the contaminated mercury container 42 can be more easily removed from and inserted into the clean mercury container 41.

[0035] The contaminated mercury container 42 is formed and sized such that the draw-in tube 436 of the cover plate 43 reaches the bottom of the clean mercury container 41. This can be achieved, for example, by making the horizontal dimension of the contaminated mercury container 42 smaller than the horizontal dimension of the clean mercury container 41 by an amount necessary to fit the draw-in tube 436, or by omitting the corner portions of the contaminated mercury container 42. Alternatively, this can also be achieved by providing the contaminated mercury container 42 with a through-hole that extends vertically through the contaminated mercury container 42, as shown in the figure.

[0036] FIG. 6 also shows an exemplary configuration of the first rim 434 and the second rim 439. In this embodiment, the first rim 434 surrounds the drop hole 431 and the first pressure relief hole 432, and the second rim 439 surrounds the draw-in hole 435 and the second pressure relief hole 438. The first rim 434 and the second rim 439 may have a common portion, or alternatively, may be formed as a single rim that surrounds all of the drop hole 431, the draw-in hole 435, the first pressure relief hole 432, and the second pressure relief hole 438.

[0037] FIG. 7 is a detailed view of an exemplary embodiment of the contaminated mercury container 42, with hidden lines shown as dashed lines so that details of the guide sleeve 422 having a shoulder 423 can be seen better.

[0038] The measuring method according to the present invention includes a step of bringing a capillary 21 containing a mercury column M into contact with the upper surface of a wafer W disposed on a wafer holder 3, a step of lowering the mercury column M so that an electrical contact is formed between the mercury column M and the upper surface of the wafer W, a step of passing an electric current between the mercury column M and the wafer holder 3 through the wafer W, and a step of measuring the electrical response of the wafer W. The method according to the present invention further includes a step of checking whether a trigger condition is satisfied, and a step of replacing the mercury column M from the clean mercury container 41 when the trigger condition is satisfied.

[0039] The trigger condition can be one or more of a manual trigger by a user, a trigger from a manufacturing control system, and a counter that counts the number of measurements performed that has reached a predetermined threshold. The threshold can be preset according to the cleanliness of the environment. For example, in an ISO 5-class industrial cleanroom compliant with the standard ISO 14644-1, the threshold can be set as high as 50,000, which means that up to 50,000 measurements can be performed with the same mercury column. However, in a research and development environment where the environment is not very clean, the threshold may be less than 5,000, which means that only thousands of measurements can be performed with the same mercury column. The amount and type of contamination on the wafer itself are also factors to be considered. For example, SiC wafers usually have more particulate contamination on their surfaces and tend to contaminate the mercury column with fewer measurement cycles.

[0040] The mercury available for exchanging the mercury column held in the capillary is preferably held in a sealed container that can be opened and closed by an actuator. Accordingly, the replacement of the mercury column includes opening the lid 5 that hermetically seals the clean mercury container 41, dropping the mercury column M, pulling up a new mercury column M from the clean mercury container 41, and closing the lid 5.

[0041] The replacement of the mercury column M can be performed by dropping the mercury column M into a larger container containing a larger amount of mercury and pulling up a new mercury column from the same container. As a result, contaminants are diluted within a larger mercury storage capacity, and the reproducibility of the measurement gradually decreases because the contamination level of the new mercury column gradually increases from the beginning.

[0042] In the method according to the present invention, the replacement of the mercury column M is performed by dropping the used mercury column into the contaminated mercury container 42 and then pulling up a new mercury column from the clean mercury container 41 different from the used mercury container. In this way, the starting composition of the mercury column M is always the same when the mercury column M is replaced. As a result, the reproducibility of the measurement is ensured until the mercury in the clean mercury container 41 runs out.

[0043] The method according to the present invention preferably further includes returning the probe head to the standby position. In this case, the capillary 21 is lowered onto the flat surface of the stop station 6, and the mercury column M descends and contacts the flat surface. This restricts the exposure of mercury to oxygen, and as a result, the oxidation of mercury is reduced. The return to the standby position is not necessary between each measurement of the same wafer, but is advantageous when the measurement is not expected to take a longer time. For example, the standby mode may be activated when the power of the device is turned off or when it enters the sleep mode, or after the measurement of a certain set of wafers, or in some cases, at the end of the measurement of one wafer.

[0044] According to a further variant of the method according to the invention, the raising of the mercury column M is carried out while supplying an AC voltage to the first terminal of the electrical measuring means connected to the first electrical contact 24 and measuring the capacitance of the first electrical contact 24. The first electrical contact has clearly different capacitance values in a first state not in contact with mercury and a second state in contact with mercury. This difference is increased in a preferred embodiment, since the clean mercury container 41 is made of an electrically insulating material and is placed in a metal holder connected to the ground potential or more preferably to the second terminal of the electrical measuring means. In this way, in the second state, the first electrical contact 24 is in contact with the mercury column M which continuously fills the draw-in tube 436 and reaches the bottom of the clean mercury container 41, and the clean mercury container 41 serves as an insulator in between, forming a capacitor with the metal holder. Preferably, the draw-in is continued until at least a sharp increase in the measured capacitance is detected, indicating that the mercury column M has contacted the bottom of the first electrical contact 24. More preferably, the draw-in is continued for a predetermined time after the detection of the increase such that a mercury column of sufficient height remains in the capillary 21 after the capillary 21 has been lifted. When the capillary 21 is lifted, the surrounding medium enters between the sealing element 437 and the capillary 21, as a result of which the ambient pressure no longer supports the mercury in the draw-in tube 436, and as a result, the mercury column M is separated at a location close to the bottom of the capillary 21. This separation occurs at a random location within a certain range. Accordingly, the predetermined time is preferably such that the additional height by which the mercury is drawn up during this time is of the same order as this range, so that this additional height ensures that the mercury column M remaining in the capillary 21 is sufficient regardless of the location of the separation within this range.

[0045] The partial vacuum applied within the capillary 21 has a draw-in vacuum value for pulling up mercury from the clean mercury container and a holding vacuum value for holding the mercury column M. The holding vacuum degree for holding a mercury column M with a height of 5 to 15 mm is minus 5 to 15 Hgmm with respect to the ambient pressure. Pulling up mercury from the clean mercury container 41 requires a larger pressure difference, which must be able to lift and hold not only the mercury within the capillary 21 but also the mercury column within the draw-in tube 436. Thus, the draw-in vacuum degree is stronger than the holding vacuum degree. For example, the draw-in vacuum degree can be about 50 to 70 Hgmm. Therefore, when a sufficient mercury height is reached, that is, when the draw-in is considered to be completed, the capillary 21 is lifted from the sealing element 437, and - preferably simultaneously - the partial vacuum applied within the capillary 21 is set to the holding vacuum value.

[0046] Generally, within the framework of this specification, expressions such as "upward", "downward", "top", "bottom", "vertical direction", "horizontal direction", and other similar expressions regarding the orientation, direction, and relative position or movement of various components should be understood as the orientation, direction, and relative position shown in the figures, which also corresponds to the actual intended configuration of the relevant components in an apparatus properly installed according to the present invention.

Claims

1. An apparatus for measuring electrical characteristics of a semiconductor wafer (W), comprising: A wafer holder (3); a mercury probe for contacting the top surface of the wafer (W) with a mercury column (M), the mercury probe including a capillary tube (21) for containing the mercury column (M); a pneumatic control means (23) for applying a partial vacuum or pressure above the mercury column (M) in the capillary tube (21); a probe arm (1) on which the mercury probe is attached; a positioning means for controlling the position of the capillary tube (21) relative to the top surface of the wafer (W); a measuring means for applying a current to the wafer and for measuring an electrical characteristic of the wafer; a first electrical contact (24) electrically connected to said mercury column (M) and said measuring means; a second electrical contact electrically connected to the wafer holder (3) and to the measuring means; A clean mercury container (41); a control unit in operative connection with said pneumatic control means (23), said positioning means, and said measuring means; Equipped with the mercury probe having at least one measurement location and a first mercury exchange location; The capillary tube (21) is separated from the clean mercury container (41) at the at least one measurement location; The capillary tube (21) is in fluid communication with the clean mercury container (41) at the first mercury exchange position. An apparatus comprising:

2. 2. Apparatus according to claim 1, characterized in that the clean mercury container (41) comprises a lid (5) for closing and hermetically sealing the clean mercury container (41).

3. 2. The apparatus of claim 1, further comprising a contaminated mercury container (42), the probe head having a second mercury exchange position, the probe head being in fluid communication with the contaminated mercury container (42) at the second mercury exchange position.

4. 4. The apparatus according to claim 3, characterized in that the clean mercury container (41) and the contaminated mercury container (42) are arranged in a single housing, the walls of which separate the mercury they contain.

5. 5. The apparatus according to claim 4, characterized in that the contaminated mercury container (42) is formed as a bucket that is placed in the clean mercury container (41), and the bottom of the contaminated mercury container (42) is adapted to rest on an upper surface of the mercury contained in the clean mercury container (41).

6. 6. The device according to claim 5, characterized in that the contaminated mercury container (42) is pressed down via a spring (424) by a cover plate (43) fixed on the clean mercury container (41).

7. 2. The apparatus according to claim 1, characterized in that the apparatus comprises a stop station (6) with a flat, smooth surface of a mercury-resistant material, and the probe head has a stop position on which the capillary tube (21) rests with a bottom abutment surface of the capillary tube (21) forming a sealing abutment with an upper surface of the stop station (6).

8. 8. Apparatus according to claim 7, characterized in that the stopping station (6) is formed by a silicon wafer having a thermally oxidized upper surface.

9. 8. The apparatus according to claim 7, characterized in that the stopping station comprises a self-aligning mechanism (61) for adjusting the alignment of the surface of the stopping station (6) to the alignment of the underside of the capillary tube (21) placed on the stopping station.

10. A method for measuring electrical properties of a semiconductor wafer (W) disposed on a wafer holder (3), comprising: bringing a capillary tube (21) containing a column of mercury (M) into contact with the upper surface of the wafer (W); lowering the mercury column (M) so that electrical contact is made between the mercury column (M) and the top surface of the wafer (W); applying a voltage between the mercury column (M) and the wafer holder (3) which is electrically connected to the wafer (W); performing an electrical measurement to determine at least one electrical parameter of the wafer (W); Including, checking whether a trigger condition is satisfied; When the trigger condition is satisfied, the mercury column (M) is replaced from a clean mercury container (41). The method of claim 1, further comprising:

11. 11. The method according to claim 10, wherein replacing the mercury column comprises opening a lid (5) hermetically sealing the clean mercury container (41), dropping the mercury column (M), pulling up new mercury column from the clean mercury container (41) and closing the lid (5).

12. 11. The method of claim 10, wherein replacing the mercury column comprises dropping the mercury column into a contaminated mercury container (42) and drawing new mercury column (M) from a clean mercury container (41) separate from the contaminated mercury container (42).

13. 11. The method according to claim 10, further comprising lowering the capillary tube (21) onto a flat surface of a stopping station (6) and lowering the mercury column (M) to contact the flat surface.

14. 11. The method of claim 10, wherein the trigger condition is one of: a manual trigger by a user; a trigger from a manufacturing control system; or a number of electrical measurements performed since a previous mercury exchange operation reaches a predetermined threshold.

15. 11. A method according to claim 10, characterized in that electrical measurements are carried out during the exchange of the mercury column (M) in order to control the height of the mercury column (M) drawn up to the capillary tube (21).

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