JPH02221880A - Measurement for electrical characteristic of semiconductor device - Google Patents

Abstract

PURPOSE:To accurately measure electrical characteristics in a large current region even in a wafer state by supplying a current sufficient for making a contact resistance between a probe and an electrode small enough. CONSTITUTION:In a measuring method for electrical characteristics of a semiconductor device in the wafer state by using the wafer prober, the probe is brought to contact with a prescribed electrode on the semiconductor device in the first place. The current sufficient for making the contact resistance between the probe and the electrode small enough is supplied between the probe and the electrode. Next, the measurement for the electrical characteristics of the semiconductor device is performed by a tester connected to the wafer prober. Thus, a variance in measured values caused by the contact resistances is prevented efficiently, and the electrical characteristics in the large current region can be accurately measured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of measuring electrical characteristics in a wafer state of a semiconductor device mainly used for high power applications.

[Conventional technology]

In power semiconductor devices, the static characteristics in the small current range where normal operation occurs, which affects the dynamic characteristics such as breakdown, are thermal theory, and the static characteristics in the high current range near the maximum current specification that must be guaranteed as a product. The static properties of are also important electrical properties.

Conventionally, the static characteristics of a semiconductor device in a large current region have been measured at a fairly late stage of the assembly process, which is the latter stage of the product manufacturing process. For this reason, a defect in the static characteristics of a semiconductor device in a large current region (below a guaranteed value, etc.) can only be detected very late in the assembly process. Therefore, when a defect in static characteristics in a large current region is detected, the semiconductor device is already a semi-finished product and considerable added value has been added, so there is a loss of time and cost until the defect is detected. becomes big.

If defects in static characteristics in the large current region could be detected at the early stage of the manufacturing process, the loss of time and cost up to the point of defect detection could be minimized.

Furthermore, if the static characteristics in the large current region can be accurately measured in the wafer state, information such as the correlation between the physical position of the wafer and the static characteristics in the large current region can be obtained. It becomes possible to provide more accurate feedback to sea urchin flies for the purpose of improving static characteristics, resulting in improved product quality.

Therefore, various approaches have been taken to date to realize the measurement of static characteristics of power semiconductor devices in a wafer state in a large current region. For example, improving wafer testers to support large currents, improving the structure of probe needles, improving the connection method between probe needles and probe cards,
These included improving the method of extracting current from the probe needle, and creating a special wafer stage with almost no voltage drop even when a large current was passed through it. Almost all of these approaches have been found to be essential for measuring static characteristics in the high current range in the wafer state.

[Problem to be solved by the invention]

However, although the above-mentioned individual technologies are almost being established, the technology for measuring static characteristics in a large current region in a wafer state has not yet been completed. In particular, when the static characteristics of the same semiconductor device are measured multiple times, there is a problem of so-called measurement error, in which the measured values differ each time. In other words, if the standard deviation indicating the variation in measured values is σ, and the ratio of ±3σ to the average value of the measured values is calculated as the measurement error, this is ±10 to ±20% (acceptable speed ±
The problem was that it was large (5%).

The reason for this is thought to be as follows. It is possible to measure static characteristics of assembled power semiconductor devices by extracting electrical signals from external connection terminals that are firmly electrically connected to electrodes by soldering, ultrasonic wire bonding, etc. . On the other hand, with a power semiconductor device in a wafer state, it is not possible to perform the above-mentioned measurements, and a wafer prober is used to hold the power semiconductor device in a wafer stage on a wafer stage. The static characteristics must be measured using a wafer tester connected to a wafer prober by touching the tip of a probe needle. Therefore, the contact portions between the electrodes on the wafer surface and the probe needles and between the wafer back surface and the wafer stage are unstable, and the contact resistance of these contact portions increases, resulting in measurement errors. This tendency becomes more pronounced in the large current region. In particular, the contact resistance between the electrode on the wafer surface and the tip of the probe needle is
larger than that between the wafer surface and the wafer stage;
This is thought to be the main cause of measurement errors.

This invention was made in order to solve the above-mentioned problems, and provides a method for measuring the electrical characteristics of a semiconductor device that can accurately measure the electrical characteristics in a large current region even in a wafer state. The purpose is to

[Means to solve the problem]

The method for measuring the electrical characteristics of a semiconductor device according to the present invention is a method for measuring the electrical characteristics of a semiconductor device in a wafer state using a wafer prober, and includes the step of bringing a probe into contact with a predetermined electrode of the semiconductor device. , supplying a current sufficient to sufficiently reduce the contact resistance between the probe and the electrode between the probe and the electrode;
and measuring electrical characteristics of the semiconductor device using a tester connected to the wafer prober.

[Effect]

In this invention, after supplying a current sufficient to sufficiently reduce the contact resistance between the probe and the electrode of the semiconductor device that is in contact with the probe, the electrical characteristics of the semiconductor device are measured. , the measured value is 10-
There is no variation due to contact resistance between the tube and the electrode.

(Example) Hereinafter, a method for measuring static characteristics in a large current region of a power transistor in a wafer state, which is an example of the present invention, will be described. When using a wafer prober to measure the static characteristics of power transistors in the wafer state in the high current range, the above-mentioned improvements to the equipment, namely improvements to the wafer tester connected to the wafer prober to support large currents, and probes are required. Improvement of the needle structure, improvement of the connection method between the probe needle and probe card, improvement of the method of extracting current from the probe needle, and production of a special wafer stage with almost no voltage drop even when a large current is passed. It is assumed that such things have been done. Using these improved devices, we will calculate the current amplification factor h for a power transistor with a maximum specified current of 50A.
FE was measured. Note that a curve tracer is used as a wafer tester connected to a wafer prober for measuring the current amplification factor hFE.

Table 1 (Table 1A to Table 1D) and Table 2 (Table 2A to Table 2D) show that in two power transistors a and b in different wafer states, the tip of the probe needle is connected to the power transistor. After contacting the predetermined electrodes a and b,
1.2.3,5,7゜10.15,20,30.40.
These are the measurement results of the power amplification factor hFE when N-flow Ic of 50 (A) is applied using two different methods (1) and (2). Note that this measurement was performed three times for each power transistor a and b, and the first
Table A to Table 1C are the results of three measurements for power transistor a1, and Tables 2A to 2C are for power transistor b.

Method 1 is a conventional method, and 1(A)
The current amplification factor hFE is measured by increasing the collector current IC in steps up to ~50 (A).

On the other hand, method (2) is a method according to an embodiment of the present invention, in which a collector current I of 60 A is first applied for a short period of time, and then 50 A (
The current amplification factor hFE is measured by decreasing the collector current IC stepwise from A) to 1(A). In addition, in Tables 1D and 2D, σ is the standard deviation of the three measurement results (Tables 1A to 1C, Tables 2A to 2C), and ±3σ (%) is the standard deviation of 3σ. The ratio of the three measurement results to the average value (hereinafter referred to as error rate 1) is shown.

As is clear from Tables 1 and 2, there are large variations in the measurement results of the method, and along with this, the error rate (±3σ (%
)) is also large. Especially when the collector current I is 15 to 50 (
The error rate in section A) is a value that cannot be ignored.

On the other hand, the measurement results of method ① have small variations, and the maximum error rate (±3σ (%)) is 3.45%, which is within the allowable range (15
%). 1, -°\, (Hereinafter, blank space) Table 1A Table 2A Table 18 Table 28 Table 1C Table 2C Table 1D Table 2D Figures 1 and 2 are from Table 1 and 2, respectively. It is a figure which graphed the measurement result of a table. In the same figure, 11° and 12 are respectively method 1. The average value of three measurements is shown. Regarding 11, the width of the maximum and minimum values of the measurement results is also displayed, but j! 2 is not shown because its width is small. As shown in these figures, the average of the measurement results of method I [1 is the average of method H 1i! From f72, collector current ■. It is slightly lower in the 5-50A section.

As mentioned above, method 1. The cause of the difference in measurement results between I can be inferred as follows. As previously mentioned,
Contact resistance (for example, surface oxidation of the aluminum electrode can be considered) exists between the electrodes on the wafer surface of the power transistors a and b and the probe needle. Due to the presence of this contact resistance, the current amplification factor hFE, which is the measurement result of method (2), is a lower value than the actual value, and the variation from measurement to measurement becomes large.

On the other hand, in method (2), a collector current r of 60 A is initially passed. It is thought that the collector current IC of 60 A has the effect of reducing the contact resistance between the electrode on the wafer surface and the probe needle to the extent that it does not affect the measurement results.

One of the reasons for this is presumed to be that passing a large current of about 60 A causes dielectric breakdown of the surface oxide film of the aluminum electrode, which is considered to be one of the contact resistances.

In other words, as in method (2), the measurement results obtained after passing a current of a predetermined level (in this example, 60A> or higher) may be the electrical characteristics of the semiconductor device in the high current region in the wafer state. It can be said that this is an accurate value with good reproducibility.

In other words, as in Method ■, 1!
If you measure the static characteristics in the high current region after passing a current between the electrode on the wafer surface and the probe needle, it is possible to accurately measure the static characteristics in the high current region even for semiconductor devices in the wafer state. be able to.

As a result, defective products can be detected at an early stage (at the sea urchin fly stage), and losses in time and cost can be minimized. In addition, it is possible to provide more accurate feedback to the sea urchin flies to improve static characteristics in the high current region, further improving product quality.

In this example (method ①), after 6 OA of collector current I was allowed to flow, it was gradually lowered from 50 to 1 (A), and first, the collector current ① was 60 A. After flowing, the measurement may be carried out stepwise from 1 to 50 (A) as in the method.The essential requirement is to check the contact resistance between the electrode on the wafer surface and the probe needle IAl before the actual measurement. It is sufficient to flow a current that sufficiently reduces the current between the electrode and the probe needle. It is also possible to incorporate the measurement method according to the present invention into a test program of a wafer tester.

(Effects of the Invention) As explained above, according to the present invention, after supplying sufficient current between the probe and the electrode to sufficiently reduce the contact resistance between the probe and the electrode of the semiconductor device that is in contact with the probe, Because it measures the electrical characteristics of semiconductor devices, it effectively prevents variations in measured values due to contact resistance, and enables accurate measurement of electrical characteristics in large current regions even in wafer state. effective.

[Brief explanation of the drawing]

FIGS. 1 and 2 are graphs showing the effects of the method for measuring the electrical characteristics of a semiconductor device, which is an embodiment of the present invention. In the figure, 11 is the measurement result by the conventional measurement method, 1
2 shows the measurement results according to the measurement method of one embodiment of the present invention. In each figure, the same reference numerals do not indicate the same or corresponding parts. Agent Masuo Oiwa Figure 1 Figure 2

Claims (1)

[Claims] (1) A method for measuring the electrical characteristics of a semiconductor device in a wafer state using a wafer prober, the method comprising: bringing a probe into contact with a predetermined electrode of the semiconductor device; and measuring the contact resistance between the probe and the electrode. An electrical method for a semiconductor device comprising: supplying a current sufficient to reduce the current sufficiently between the probe and the electrode; and measuring electrical characteristics of the semiconductor device with a tester connected to the wafer prober. How to measure physical characteristics.