JP3326317B2 - Voltage measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage measuring device for measuring a voltage of an integrated circuit or the like by a method of detecting an electric field intensity using a probe provided with an electro-optic material having an electro-optic effect.

[0002]

2. Description of the Related Art LiTaO ₃ having an electro-optical effect has been conventionally used.
There is a voltage measuring device that measures a voltage of a predetermined portion of an integrated circuit or the like in a non-contact manner using a probe including an electro-optical material such as an electronic device. This device has an EO (Electro-
Optic) Connect the probe tip 702 to the DUT (sample) 7
When the probe is placed in the electric field of No. 03 and the probe 702 is irradiated with a light beam through the objective lens 701, the refractive index of the electro-optic material changes according to the electric field strength.
The polarization state of the reflected light beam changes, and the voltage of the sample is measured by detecting this with a photodetector (optical unit). As a product using this, for example, an EO-prober manufactured by Hamamatsu Photonics KK (EOP
-01).

[0003]

However, such a voltage measuring device has the following problems. When a high-frequency probe (RF probe) is brought into contact with a pad of an integrated circuit, the EO probe tip needs to be retreated far away so as not to hinder the operation, resulting in poor operability. After the above operation, before measuring the sample (IC to be measured) on the sample stage, the EO probe tip is positioned with high precision on the order of μm at the center of the sample chip and the center of the optical system for measurement. It was necessary to match, but the method and procedure for that were very complicated. After the above operation, when measuring the sample on the sample stage,
It is necessary to position the tip of the EO probe tip at the focal point of the objective lens and to position the sample such that there is a gap of several μm from the tip of the EO probe tip. However, the method and procedure for that are complicated.

An object of the present invention is to solve such a problem and to provide a voltage measuring apparatus which is simple in positioning procedure and excellent in operability.

[0005]

According to the present invention, there is provided a probe provided with an electro-optic material in which a refractive index of a crystal changes in accordance with an electric field intensity.
In a voltage measuring apparatus for measuring a voltage of an integrated circuit by using a method of measuring electric field intensity from a change in a polarization state of light transmitted through the electro-optic material by causing light to enter the electro-optic material, a sample on which the sample is mounted A stage, a first stage group capable of moving the sample stage, and the probe and an objective lens for measurement are integrally formed, and the probe is mounted on a quartz plate.
Micro balance method formed with a horseshoe-shaped void
The mechanism is attached to one disk and the other disk
Is a probe unit on which a dummy probe as a balancer is mounted, a revolver on which the probe unit and an objective lens for alignment are mounted, and which can move on the same axis by rotation, and a revolver Attached, a function of separating laser light incident from the outside and reflecting light reflected at the end face of the electro-optical material into orthogonal polarization components and converting it into an electric signal, and incident light for pattern observation from the outside a function of outputting a light came back feeding the probe unit or the objective lens for the alignment to the outside, above the probe unit
Probe unit by changing the angle of the light reflected at the end
Means to detect when the tip of the
An optical system unit, a second stage group that can move the optical system unit, and position information from the optical system unit, and can control at least the driving and stopping of the second stage group. It is characterized by having control means.

[0006]

According to the present invention, a probe having an electro-optical material and an objective lens for measurement are integrated. Thereby, the focus is always focused on the tip of the electro-optic material, and the positioning for determining the relative position between the probe and the objective lens is not required. The objective lens for contact detection and the objective lens for alignment are attached to the revolver, so that the objective lens can be easily exchanged only by rotating the revolver by raising it in the Z-axis direction without retracting the entire optical system. Can be. The sample stage and the optical system can be moved using an electric stage. Thus, the center of the sample chip can be easily adjusted to the center of the optical system. In addition, an optical system that detects a change in the angle of light reflected at the probe tip end is provided.
It was configured such that it was detected that the probe was in contact with the sample, and the probe was further moved upward to position a predetermined gap between the probe and the sample. Thereby, the positioning operation is simplified. The probe is a horse on a quartz plate.
A micro balance system formed with a hoof-shaped void
It is attached to one disk part of the mechanism and the other disk part
Attach a dummy probe as a balancer.
When contacting the sample, use a very weak force (about 0.1 g)
I tried to hit. This can cause damage to the contact surface due to contact
Can be prevented.

[0007]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
FIG. 1 is a configuration diagram showing one embodiment of a voltage measuring device according to the present invention. In the figure, 1 is a base portion, 2 is a base portion 1
A first X stage mounted on the X stage and movable in the X-axis direction, 3 is a first Y stage mounted on the X stage 2 and movable in the Y-axis direction, and 4 is a Y stage A first Z stage 5 mounted on the Z stage and movable in the Z-axis direction is a θ stage mounted on the Z stage 4 and rotatable in a horizontal plane. Note that a portion including the stages 2, 3, 4, and 5 is referred to as a first stage group.

Each of the stages 2 to 5 is electrically controlled by a motor driver / controller 25, and each stage has a position detecting function, and sends the position information to the motor driver / controller 25. Reference numeral 6 denotes a sample table mounted on the Z stage 5, and 7 denotes a sample mounted on the sample table 6. Sample 7 is an IC wafer or packaged IC.
C and the like, and a drive signal is given from the RF probe 9. The RF probe 9 is moved by the manipulator and the IC
Move to touch the pad. In the figure, the manipulator is included in the RF probe 9. RF probe 9
Is mounted on the RF platen 8.

Reference numeral 11 denotes a second X stage movable in the X-axis direction, which is mounted on the bridge 10. The bridge 10 is a support frame for keeping the X stage 11 and the mechanism and optical system mounted thereon at an appropriate height with respect to the sample stage. Reference numeral 12 denotes a second Y stage mounted on the second X stage 11 and movable in the Y-axis direction. Reference numeral 13 denotes a second Y stage mounted on the second Y stage 12 and movable in the Z-axis direction. Z stage. Note that a portion including the X, Y, and Z stages is referred to as a second stage group. Stage 11, 1
The stages 2 and 13 have a position detecting mechanism, and the stages 2 and 3
Controlled by the motor driver / controller 25 in the same manner as in the steps 4 and 5, the position information is sent to the motor driver / controller 25.

Reference numeral 14 denotes an optical system unit, which is fixed to the second Z stage 13. FIG. 2 shows the optical system unit 1.
FIG. 4 is a diagram showing the details of FIG. Laser light input from the laser light source 15 is collimated by a collimating lens 201,
It is sent to an objective lens (not shown) at a slight angle by the wedge plate 206. The returned light is polarized beam splitter 2
At 13, the photodiodes are decomposed in the orthogonal direction.
At 214b, it is converted into an electric signal. Reference numerals 207 to 209 denote mirrors for synthesizing and decomposing illumination light for observing the pattern of the sample with the laser light, and capturing them with a camera.
07 is a dichroic mirror, 208 is a half mirror,
209 is a reflection mirror.

Reference numerals 204 and 205 denote wavelength plates for adjusting the polarization state to an arbitrary state. 202, 2
03 is a monitor for adjusting the polarization state of the input light.
02 is a polarizer, and 203 is a photodiode. 21
Reference numerals 1 and 212 are optical systems for detecting that the probe has contacted the sample, 211 is a beam splitter,
Reference numeral 2 denotes a four-division photodiode.

FIG. 3A shows a four-division photodiode 212.
(PDa, PDb, PDc, PDd) front view,
When the probe is not in contact with the sample, the spot is at the center of the quadrant, but when the probe is in contact with the sample, the spot moves in the horizontal direction. The movement of the spot is, for example,
Detection is performed by a circuit as shown in (b). This circuit detects the movement of the spot by converting the current flowing through the right and left photodiodes (two each) into a voltage and obtaining the difference.

Returning to FIG. 1, reference numeral 16 denotes a signal processing device for displaying the outputs of the photodiodes 214a and 214b by performing processing such as differential amplification. Reference numeral 17 denotes an illumination light source, and reference numeral 18 denotes a monitor camera. An image processing device 19 converts a signal from the camera 18 so that the signal can be displayed on the monitor 20 or processed by the computer 26. A marker is printed on the center of the monitor 20 so that the center of the optical system is adjusted to match the marker position.

A revolver 21 is attached to the optical system unit 14. Reference numeral 22 denotes an objective lens, and reference numeral 23 denotes a probe unit including a probe tip made of an electro-optic material or the like, a probe tip holding mechanism, and a contact position detecting mechanism. The first objective lens 22 and the probe unit 23 have an integral structure.
The upper end is attached to the revolver 21. A second objective lens 24 is attached to the revolver 21, and by rotating the revolver 21, the probe unit 23 and the objective lens 24 can be moved on the same axis.

The probe unit 23 has, for example, an EO probe tip bonded to a quartz plate and fixed by a hollow ceramic tube as shown in FIG. 4, and a mechanism for fixing the EO probe tip to the objective lens 22. is there. Such a probe unit 23 is connected to the objective lens 22 by a configuration as shown in FIG. In FIG. 5, 5
Reference numeral 02 denotes a grooved ring that engages with the lower end of the objective lens 22, and the upper end of the cylinder 503 (to which the probe unit 23 is attached) is screwed to the ring 502 with a screw 504.

The relative distance between the objective lens 22 and the EO probe tip is adjusted so that the laser beam is focused at the tip of the probe. As shown in FIG. 6, for example, the EO probe tip is attached to one disk portion of a microbalance-type mechanism formed by a horseshoe-shaped gap portion 604, 605 in a quartz plate 601. The other disk has a dummy probe tip 6 as a balancer.
03 is attached. For this structure, Ri per very weak force when the tip of the probe hits another object (about 0.1 g), damage to the contact surface by contacting
Can be prevented.

The second objective lens 24 includes the RF probe 9
Is used for positioning for bringing the sample into contact with the sample 7, and has a lower magnification than the objective lens 22.

The motor driver / controller 25 is controlled by a computer 26 or an operation panel 27,
Drives or controls a motor (not shown) of each stage. Reference numeral 28 denotes a contact position detection circuit which processes the output of the four-division photodiode 212 by a circuit as shown in FIG. 3B to detect that the tip of the probe unit 23 has come into contact with the sample 7, and outputs the output. When a certain specified value is exceeded, the motor driver / controller 25 and the computer 26 are notified by an interrupt or status.

The procedure for measuring a sample in such a configuration will be described below. FIG. 7 as an example of a sample
The following describes an example of measuring an IC wafer as shown in FIG. Note that there are multiple IC chips on the wafer,
There is a pad for wiring.

(1) The first X stage 2 and the first Y stage 3 are driven to move the sample stage 6 to a position where the sample 7 is placed. (2) Place the sample 7 and move the first X stage 2 and Y stage 3 to the initial position. This (1) and
In the operation (2), the second X stage 11, the second Y stage 12, and the third Z stage 13 have been retracted to the upper limit positions.

(3) The revolver 21 is rotated to bring the objective lens 24 above the sample 7. (4) The second Z stage 13 is moved while looking at the monitor 20, and the objective lens 24 is lowered to a position where the sample 7 can be observed. (5) Perform alignment (adjustment in the θ direction). The sample stage 6 is moved to determine a scribe line to be used for alignment. As shown in FIG. 8A, the sample table 6 is moved so that the left end of the scribe line comes to the marker point on the monitor 20.
And press a predetermined key. Next, as shown in FIG. 8B, the scribe line is moved in the X direction and in the Y direction such that the right end of the scribe line is located at the same position (FIG. 8B).
(c)) Move the sample stage 6 and press a predetermined key. The computer 26 calculates the amount of θ rotation from the position information taken from the monitor driver / controller 25 when a predetermined key is pressed, and rotates the θ stage 5.

(6) The sample stage 6 is positioned so that the center of the chip to be measured is located at the optical center of the optical system unit 14, the objective lens 22, and the probe unit 23. The second X
The stage 11 and the second Y stage 12 are set at the center position of the movable range. The sample stage 6 is moved so that the center of the chip to be measured comes to the marker on the monitor 20. The following is performed in order to perform the measurement with high accuracy. As shown in FIG. 9, the sample table 6 is moved so that the square corner of the chip comes to the marker of the monitor 20, and a predetermined key is pressed. The same operation was performed for three rectangular points. The center position is determined by the computer 26, and the sample stage 6 is moved to the determined position.

(7) A software limit of the movable range of the second X stage 11 and the second Y stage 12 is specified. As shown in FIG. 10, the second X stage 11 and the second Y stage 12 are moved so that the positions of the pads of the chip and the like are located at the positions of the markers on the monitor 20, and a predetermined key is pressed to specify. The computer 26 stores this position, and applies a limit by software at the time of measurement. This is to prevent the probe unit 23 from hitting the RF probe 9.

(8) The RF probe 9 is brought into contact with the chip pad while watching the monitor 20. (9) Move the second Z stage 13 to retract to the upper limit. (10) The revolver 21 is rotated to switch from the objective lens 24 to the objective lens 22. (11) The second Z stage 13 is lowered while watching the monitor 20 until the pattern of the sample 7 can be seen. (12) Turn on the laser light source 15 and input the laser light to the optical system unit 14.

(13) The second X stage 11 and the second Y stage 1 are arranged such that a spot comes on a pattern to be observed.
Move 2 That is, the output of the image processing device 19 is processed by the computer 26, displayed on the computer, and the amount of movement is calculated by instructing with the cursor to drive the second X stage 11 and the second Y stage 12. (14) Lower the second Z stage 13 until the electro-optic material at the tip of the probe unit 23 contacts the sample 7. The output of the photodiode 212 for detecting the contact position in the optical system unit 14 is processed by the contact position detection circuit 28,
It instructs the motor driver / controller 25 directly or indirectly via the computer 26 to operate to stop the second Z stage 13 from lowering.

(15) The second Z stage 13 is moved upward so as to open a predetermined gap (for example, several μm). (16) Driving the sample 7 from the RF probe 9 (signal source and R
The signal line to the F probe 9 is not shown in the figure), and the output of the photodiode 214 in the optical system unit 14 is processed by the signal processing device 16. As described above, the electric field (eventually, pattern voltage) waveform on a certain pattern of the sample can be measured.

The configuration of the present invention is not limited to the embodiment. For example, in the above embodiment, the stage is driven by a motor, but may be manually operated. In addition, the probe is configured to move together with the optical system unit in addition to the objective lens, but the optical system unit does not necessarily have to move together, so that the probe unit and the objective lens move integrally. It should just be.

[0028]

As described above, according to the present invention, since the sample stage is mounted on all stages in the X, Y, Z, and θ directions, alignment is easy. Further, since the probe unit 23 made of an electro-optical material and the objective lens 22 are integrally formed and attached to the revolver 21 together with the contact detection and alignment objective lenses, the entire optical system is raised in the Z direction without being retracted, and the revolver 21 is not moved. The objective lens can be easily converted simply by rotating the lens, and operations such as positioning are easy. Further, since the revolver 21 is used and the stage is used, the operation of aligning the center of the chip with the center of the optical system is easy.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of a voltage measuring device according to the present invention.

FIG. 2 is a diagram showing a configuration of an optical system unit.

FIG. 3 is a diagram showing a configuration of a four-division photodiode and a detection circuit.

FIG. 4 is a configuration example of a probe unit.

FIG. 5 is a diagram showing a connection state between an objective lens and a probe unit.

FIG. 6 is a configuration diagram of an EO probe tip.

FIG. 7 is an explanatory view when an IC wafer is used as a sample;

FIG. 8 is a diagram showing a procedure for determining a scribe line.

FIG. 9 is a diagram for explaining positioning of a sample stage.

FIG. 10 is a diagram for explaining an operation of designating a software limit;

FIG. 11 is a main part configuration diagram showing an example of a conventional voltage measuring device.

[Description of Signs] 1 Base 2 First X stage 3 First Y stage 4 First Z stage 5 First θ stage 6 Sample table 7 Sample 8 RF platen 9 RF probe 10 Bridge 11 Second X stage 12 second Y stage 13 second Z stage 14 optical system stage 15 laser light source 16 signal processing device 17 observation light source 18 camera 19 image processing device 20 monitor 21 revolver 22 first objective lens 24 second objective lens 23 Probe unit 25 Motor driver / controller 26 Computer 27 Operation panel 28 Contact position detection circuit PDa, PDb, PDc, PDd Photodiode

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Nao Sugiyama 2-9-132 Nakamachi, Musashino-shi, Tokyo Yokogawa Electric Corporation (72) Inventor Masashi Oikawa 2-9-132 Nakamachi, Musashino-shi, Tokyo Inside Kawa Electric Co., Ltd. (72) Inventor Tsutomu Yamazaki 2-9-132 Nakamachi, Musashino-shi, Tokyo Yokogawa Electric Co., Ltd. (72) Inventor Kiyoaki Koyama 2-9-132 Nakamachi, Musashino-shi, Tokyo Yokogawa Electric Inside (72) Inventor Mitsuhiro Suzuki 2-93-2 Nakamachi, Musashino-shi, Tokyo Inside Yokogawa Electric Corporation (72) Inventor Nasunori Hayashi 2-9-132 Nakamachi, Musashino-shi, Tokyo Yokogawa Electric Corporation Examiner Osamu Komaki (56) References JP-A-7-174826 (JP, A) JP-A-4-29344 (JP, A) JP-A-7-72159 (JP, A) JP-A-6-224269 ( JP, JP-A-6-207914 (JP, A) JP-A-3-4102 (JP, A) JP-A-5-72299 (JP, A) International publication 89/1603 (WO, A1) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01R 31/00-31/44

Claims (1)

(57) [Claims] 1. A probe provided with an electro-optic material whose refractive index of a crystal changes according to an electric field intensity is placed in an electric field, light is incident on the electro-optic material, and the polarization state of the light transmitted through the electro-optic material is changed. In a voltage measuring apparatus for measuring a voltage of an integrated circuit by using a method of measuring an electric field intensity from a change, a sample stage on which a sample is mounted, a first stage group capable of moving the sample stage, and the probe And the objective lens for measurement have an integral structure, the probe is attached to one disk of a microbalance-type mechanism formed by providing a horseshoe-shaped gap in the quartz plate, and the other disk A probe unit to which a dummy probe as a balancer is attached, and this probe unit and an objective lens for alignment are attached, and both move on the same axis by rotation. A revolver that can be attached, and a function of attaching the revolver, separating laser light incident from the outside and reflecting light at the end face of the electro-optical material into orthogonal polarization components, and converting it into an electric signal, and a function for pattern observation. A function of outputting light that is incident from the outside and returns to the probe unit or the alignment objective lens, and a change in the angle of the laser light reflected at the tip of the probe unit. An optical system unit having means for detecting that the tip of the optical system unit has contacted the surface of the integrated circuit; a second stage group capable of moving the optical system unit; and receiving position information from the optical system unit; A voltage measuring device provided with control means capable of controlling driving and stopping of the second stage group. Apparatus.