JP7581021B2 - Method for reducing power consumption of prober and prober - Google Patents

Description

The present invention relates to a prober that inspects the electrical characteristics of electronic devices (semiconductor chips) formed on a wafer, and in particular to a power consumption reduction method and prober that reduces power consumption while a probe needle is in contact with an electrode pad of a semiconductor chip while the wafer is held on a wafer chuck.

In the semiconductor manufacturing process, various processes are performed on a thin, plate-like wafer to manufacture multiple chips each having an electronic device. The electrical characteristics of each chip are inspected using a prober such as that disclosed in Patent Document 1, and then the chips are separated using a dicing device.

The prober is comprised of a wafer chuck (table), probes, a tester, etc. The inspection method using a prober involves placing the wafer to be inspected on the holding surface of the wafer chuck and holding it by suction. After this, the probe needles are brought into contact with the electrode pads of each chip (probing), and the signals output from the electrodes of the chip are measured by the tester to electrically inspect whether or not it is operating normally.

In tests that measure electrical characteristics by bringing probe needles into contact with a semiconductor wafer, the semiconductor wafer is always raised to a predetermined position to ensure optimal contact. The optimal amount of lift is achieved by controlling the motor current and torque of the servo motor that drives the wafer chuck.

The magnitude of the motor current must take into account not only the contact pressure of the multiple probe needles to the multiple electrode pads within a certain range, but also force components that affect the drive of the target axis other than the contact load (such as frictional forces when driving the stage and the weight of the stage itself). Therefore, conventionally, an overdrive is performed to further raise the wafer W within a range of several tens to several hundreds of μm after the wafer and probe needles come into contact, and then the wafer is stopped there.

JP 2018-117095 A

In the above conventional technology, the torque of the servo motor that maintains the height during contact (device test time) requires a torque greater than that required when moving the wafer chuck. As a result, the prober consumes a lot of power during the holding time. In addition, the load capacity, which is a function of the prober's performance, is determined by the torque during contact (load on the servo motor). However, in recent years, the number of electrode pads on the wafer has increased due to the miniaturization and miniaturization of electronic devices, and there is a demand to increase the load capacity.

The object of the present invention is to provide a method for reducing power consumption of a prober and a prober that solves the problems of the conventional technology described above, reduces power consumption, and increases the load capacity.

To achieve the above object, the present invention provides a method for reducing power consumption in a prober that holds a wafer on which electrode pads of semiconductor chips are formed on a wafer chuck, raises the wafer to a predetermined position using a servo motor, and brings a probe needle into contact with the electrode pad to inspect electrical characteristics. The wafer chuck is raised and stopped by the servo motor, and then lowered a predetermined amount to be held at the predetermined position and the inspection is performed.

In the above-mentioned method for reducing power consumption of a prober, it is preferable that the predetermined amount is between 1 μm and the maximum possible movement amount.

In the above-mentioned method for reducing power consumption of a prober, it is desirable that the predetermined amount is about 1 μm.

In the above-mentioned method for reducing power consumption of a prober, it is preferable that the predetermined position is a position where a contact pressure that ensures reliable electrical contact between the probe needle and the electrode pad can be obtained.

To achieve the above object, the present invention provides a prober that holds a wafer on which electrode pads of semiconductor chips are formed on a wafer chuck, raises the wafer to a predetermined position using a servo motor, and brings a probe needle into contact with the electrode pad to test electrical characteristics. The prober includes a vertical movement mechanism for the wafer chuck, which is made up of a ball screw and a guide, the servo motor that drives the vertical movement mechanism, and a control device that raises and stops the wafer chuck, and then lowers it a predetermined amount to hold it in the predetermined position.

In the above prober, it is desirable that the predetermined amount is between 1 μm and the maximum movable amount.

In the above prober, it is desirable that the predetermined amount is about 1 μm.

According to the present invention, the wafer chuck holding the wafer is raised by a servo motor, stopped, and then lowered a specified amount to hold it in a specified position, and the electrical characteristics are inspected by contacting the probe needles with the electrode pads formed on the wafer, thereby reducing the power consumption required to hold the wafer chuck during inspection.

FIG. 1 is a side view of a prober 10 according to one embodiment of the present invention; 1 is a diagram illustrating the operation of a wafer chuck 20 according to one embodiment of the present invention; FIG. 1 is an explanatory diagram for measuring the holding torque of the wafer chuck 20. Table showing the measurement results of FIG. 3 according to one embodiment 1 is a graph showing the change in motor torque and speed over time when the wafer chuck 20 is raised and then lowered according to an embodiment of the present invention. Comparison table showing the measurement results of motor load factor, instantaneous torque, encoder information, and power consumption according to the conventional method and the embodiment A table showing the results of comparing the load capacity when the holding torque is set to 70% between the conventional example and the embodiment.

Figure 1 is a side view of a prober 10 used in a wafer test system that inspects the electrical characteristics of multiple semiconductor chips formed on a wafer W. The prober 10 includes a base 12, a Y stage 13, a Y movement unit 14, an X stage 15, an X movement unit 16, a Zθ stage 17, a wafer chuck 20, a card holder 25, a probe card 26, a wafer alignment camera (not shown), an upper and lower stage 30, a needle alignment camera 31, a temperature sensor (not shown), a cleaning plate 32, etc.

The wafer W is held on the upper surface of the wafer chuck 20 by various holding methods such as vacuum suction. The card holder 25 has a holding hole 25a that holds the outer periphery of the probe card 26, and the probe card 26 is held in the holding hole 25a. The probe card 26 has probe needles 35 arranged according to the arrangement of the electrode pads (not shown) of the semiconductor chip to be inspected.

The needle alignment camera 31 captures an image of the probe needle 35 of the probe card 26. The position of the probe needle 35 can be detected based on the image of the probe needle 35 captured by the needle alignment camera 31. The cleaning plate 32 polishes the tip of the probe needle 35 during cleaning in order to improve the contact resistance between the probe needle 35 and the wafer W during contact.

While holding the wafer W on the wafer chuck 20, the prober 10 moves the probe card 26 having the probe needles 35 relative to the wafer chuck 20, that is, raises the wafer chuck 20 in the Z-axis direction using a servo motor. As a result, the electrode pads on the wafer W come into electrical contact with the probe needles 35.

The tester supplies various test signals to the semiconductor chip through terminals connected to the probe needles 35, and receives and analyzes the signals output from the semiconductor chip to perform device tests to determine whether the semiconductor chip is operating normally.

The operation of bringing the electrode pads into contact with the probe needles 35 is performed by detecting the positions of the probe needles 35 and the wafer W, and then rotating the Zθ stage 17 so that the arrangement direction of the electrode pads of the semiconductor chip coincides with the arrangement direction of the probe needles 35. The control device then moves the Zθ stage 17 so that the electrode pads to be inspected are positioned under the probe needles 35, and then uses a servo motor (not shown) to raise the wafer chuck 20, bringing the electrode pads into contact with the probe needles 35.

When the electrode pad is brought into contact with the probe needle 35, the electrode pad is raised from a height position (contact start position) where the surface of the electrode pad comes into contact with the tip of the probe needle 35 to an even higher position (movement end position). The contact start position is detected by the needle alignment camera 31. Conventionally, the movement end position is set to a height position obtained by adding to the contact start position the amount of displacement of the tip of the probe needle 35 that results in an amount of deflection of the probe needle 35 that provides a contact pressure that ensures reliable electrical contact between the probe needle 35 and the electrode pad.

In reality, the number of probe needles 35 is, for example, several hundred, and the movement end position is set to a predetermined value so that reliable electrical contact is achieved between all of the probe needles 35 and the electrode pads. The amount of movement from this contact start position to the movement end position is the overdrive amount.

High throughput is required for semiconductor manufacturing equipment such as the prober 10, and in wafer test systems, testing throughput is improved by simultaneously testing multiple chips with a single contact between the probe and the electrode pad.

The probe needles 35 are provided in correspondence with the electrode pads of each chip. In recent years, the number of chips that are simultaneously tested has tended to increase. For example, when testing 50 or more chips simultaneously, where each chip has 50 electrode pads, the probe card 26 will be provided with 50 x 50 = 2,500 probes.

When the probe needles 35 are brought into contact with the electrode pads, the wafer chuck 20 is raised by the overdrive amount from the contact start position between the electrode pad and the probe needles 35 to a predetermined position and then stops. The probe needles 35 bend due to the rise by the overdrive amount and come into contact with the electrode pads with a predetermined contact pressure. For example, if the desired contact pressure of one probe needle 35 is 5 g, then in the case of 2,500 probes, the probe card 26 will receive an upward pressure of 12.5 kg in total at the center.

The probe card 26 is made of a multi-layer epoxy resin with a wiring pattern, and when a large pressure is applied to the center, it bends and deforms upward. The deformation of the probe card 26 effectively reduces the amount of overdrive, lowering the contact pressure. Therefore, the amount of overdrive had to be set taking into account the reduction in contact pressure caused by the deformation of the probe card 26.

2 is a diagram showing the operation of the wafer chuck 20 according to one embodiment. Conventionally, the wafer chuck 20 is driven to rise by a servo motor to a predetermined position, and then stops. In contrast to the conventional method, in this embodiment, the wafer chuck 20 is controlled to rise in the Z-axis direction by the servo motor, stop, and then lower a predetermined amount to a predetermined position and hold it there.
Here, the predetermined amount is preferably at least 1 μm based on the experimental results described later, and must be at most within a range in which reliable electrical contact is achieved between the probe needle 35 and the electrode pad. Hereinafter, the maximum predetermined amount in which reliable electrical contact is achieved between the probe needle 35 and the electrode pad is referred to as the maximum movable amount.
The maximum possible movement amount can be obtained by evaluating each probe card 26 and determining the maximum downward movement amount that maintains reliable electrical contact between all of the probe needles 35 and the electrode pads.
An example of the predetermined amount is 1 to several μm.

The predetermined position is a position where a contact pressure is obtained that ensures reliable electrical contact between the probe needle 35 and the electrode pad. The wafer chuck 20 is raised and lowered as follows, by driving a vertical movement mechanism consisting of a ball screw and a guide (not shown) with a servo motor.

(1) The wafer chuck 20 is at a predetermined Z-axis height before the probe needles 35 and the wafer W come into contact. (2) The control device drives the servo motor to raise the wafer chuck 20 in the Z-axis direction, bringing the probe needles 35 into contact with the wafer W and raising the wafer chuck 20 to a predetermined position. (3) The control device then controls the wafer chuck 20 to be lowered in the Z-axis direction by 1 μm to the maximum movable amount, preferably 1 to several μm, and more preferably about 1 μm, and maintains that position.

The device test is performed while the control device holds the position of the wafer chuck 20. This allows the servo motor to reduce the holding torque during the device test, thereby reducing the power consumption of the prober 10. Furthermore, being able to reduce the torque during the device test also reduces the load on the servo motor. Therefore, this embodiment makes it possible to increase the load capacity that is limited by the load rate of the servo motor.

The effect of not raising and stopping the wafer chuck 20, but raising it, stopping it, and then lowering it a predetermined amount of 1 μm to the maximum movable amount, preferably 1 to several μm, and more preferably about 1 μm, can be considered as follows: When the wafer chuck 20 is raised, a torque is required to counter the "load due to friction between the ball screw and guide" + the "gravity load of the vertically moving parts." When it is lowered, it becomes the "load due to friction between the ball screw and guide" - the "gravity load of the vertically moving parts."

Therefore, the torque required by the servo motor is lower for descending than for ascending. A servo motor (usually an AC servo motor) is used. An AC servo motor performs position retention control (servo lock) after positioning is complete, so if positioning is performed with a low-torque operation, the retention torque when stopped will be low. This control is effective not only for up-down mechanisms, but also when there is a difference in torque depending on the direction of motor rotation (CW/CCW).

Below, an embodiment based on the results of the experiment will be described. Figure 3 is an explanatory diagram for measuring the holding torque when the wafer chuck 20 is raised to a predetermined position. The wafer chuck 20 has a load cell 41, which is a load converter, placed on it, and is raised as shown by the arrow, and is restricted to a predetermined position by a fixed guide 40. The experiment was performed so that the output of the load cell 41 was 520 kgf at a position of 18,000 μm when the wafer chuck 20 was raised and stopped as in the conventional case, and when it was raised and then lowered instead of being raised and stopped.

Figure 4 is a table showing the experimental results of Figure 3. Figure 5 is a graph showing the time changes in motor torque and speed when the wafer chuck 20 is raised and then lowered. When the wafer chuck 20 is raised and stopped at the 18,000 μm position as in the conventional method, the holding torque is 70%. When the wafer chuck 20 is raised to 18,001 μm and then lowered to the 18,000 μm position as in the embodiment, the holding torque is 61%, that is, the holding torque can be reduced by only 9%.

Figure 6 is a table comparing the motor load factor, instantaneous torque, encoder information, and power consumption measurements when the wafer chuck 20 is raised and stopped in a conventional manner and in this embodiment. As a result, when the wafer chuck 20 is raised and stopped in the conventional manner, the motor load factor and instantaneous torque were 67%, and the power consumption was 26 W.

When ascending and descending in this embodiment, the motor load rate and instantaneous torque were 63%, and the power consumption was 24 W. As a result, it can be seen that ascending and descending the wafer chuck 20 can achieve significant power savings during long-term wafer testing. The encoder information indicates a value corresponding to the stop position as reference information, and the difference corresponds to 1 μm.

Figure 7 shows the results of comparing the load capacity when the holding torque is set to 70%. The holding torque is set to 70%, and the load capacity is measured by the load cell 41. In the conventional control, the load capacity is 520 kgf because the load is simply raised and stopped. In contrast, when the load is controlled to rise and then fall as in the embodiment, the load capacity can be increased to 605 kgf even with a holding torque of 70%.

10... prober 12... base 13... Y stage 14... Y moving part 15... X stage 16... X moving part 17... Zθ stage 20... wafer chuck 25... card holder 25a... holding hole 26... probe card 30... upper and lower stages 31... needle alignment camera 32... cleaning plate 35... probe needle 40... fixed guide 41... load cell W... wafer

Claims (7)

A method for reducing power consumption of a prober which holds a wafer on which electrode pads of semiconductor chips are formed on a wafer chuck, raises the wafer to a predetermined position by a servo motor, and brings probe needles into contact with the electrode pads to inspect electrical characteristics, comprising the steps of:
and after the wafer chuck is raised and stopped by the servo motor, the wafer chuck is lowered by a predetermined amount and held at the predetermined position, and the inspection is performed .
The method for reducing power consumption of a prober is characterized in that the predetermined amount is 1 to several μm . The method for reducing power consumption of a prober according to claim 1, characterized in that the predetermined amount is between 1 μm and the maximum movable amount. The method for reducing power consumption of a prober according to claim 1 or 2, characterized in that the predetermined amount is about 1 μm. The method for reducing power consumption of a prober according to any one of claims 1 to 3, characterized in that the predetermined position is a position where a contact pressure that ensures reliable electrical contact between the probe needle and the electrode pad is obtained. A prober for testing electrical characteristics of a wafer having electrode pads of semiconductor chips on a wafer chuck, lifting the wafer to a predetermined position by a servo motor and bringing probe needles into contact with the electrode pads, comprising:
a lifting mechanism for the wafer chuck, the lifting mechanism being composed of a ball screw and a guide;
The servo motor that drives the up-down mechanism;
a control device that raises and stops the wafer chuck, and then lowers the wafer chuck by a predetermined amount and holds the wafer chuck at the predetermined position;
Equipped with
The prober is characterized in that the predetermined amount is 1 to several μm . The prober according to claim 5, characterized in that the predetermined amount is between 1 μm and the maximum movable amount. 7. The prober according to claim 5, wherein the predetermined amount is about 1 [mu]m.