JP3011504B2 - Evaluation device for semiconductor light emitting 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 semiconductor light emitting device evaluation apparatus for inspecting electrical characteristics and light emitting characteristics of semiconductor light emitting devices such as light emitting diodes (LEDs) and laser diodes.

[0002]

2. Description of the Related Art When manufacturing a semiconductor device using a semiconductor wafer, it is necessary to examine the characteristics of the wafer in advance and select the wafer. This is because, if the determination of whether or not the wafer is defective is not properly performed, the yield, the reliability, and the cost are increased. Similarly, even after a large number of elements are formed on a wafer, it is necessary to examine the characteristics of the individual elements and judge the quality of the individual elements, and accurately perform selection based on the characteristic values. In particular, in recent years, the application of LEDs has been rapidly expanding from single lamps to arrays and display panels, and a large number of LED pellets having more uniform characteristics have been demanded.

In a conventional epitaxial wafer for LED, after forming an element, the wafer is divided into pellets, and then electrical characteristics and luminous characteristics are examined by sampling inspection. In particular, luminance sorting of the pellets based on luminous efficiency is widely performed. I have.

[0004] However, this conventional method has a dilemma between shortening the time spent for work and improving the inspection accuracy. That is, when the time is reduced, the inspection accuracy is reduced by the number of the extracted samples, and the uniformity of the characteristics among the selected pellets cannot be obtained with good reproducibility.
In the case of the light emitting diode, the variation in the characteristics within the wafer surface is large for each lot, and the reproducibility is not sufficient.
Therefore, in-plane luminance unevenness of the completed display is caused. Conversely, when accuracy is considered, it takes a long time to increase the number of sampling samples.

[0005] Therefore, a method of sorting at the wafer stage before dividing into pellets is considered. This corresponds to an application of the die sorting method performed in the IC.

When this die sorting method is used for LEDs, since electrical separation of the LEDs is not performed at the wafer stage, the devices are separated by attaching the wafer to an adhesive sheet and half-dicing. Then, the respective elements are sequentially scanned and driven to emit light, and the luminous efficiency is measured based on the light detection level. For example, in FIG. 5, the input pulse current to the LED is a light emission output detection signal of the LED, and the lower the light emission efficiency of the LED, the larger the difference between the peak levels of the input pulse current wave and the light emission output wave. Therefore, the luminous efficiency can be determined based on the difference between the peak levels. The same applies to the case of DC driving.

[0007]

However, even if separation between elements is performed, scattering of light between adjacent pellets is unavoidable, and the light output level fluctuates due to the mutual interference, so that an accurate measured value can be obtained. There is no problem. As a result of actual trials, there were many discrepancies with the values measured by dividing into pellets, and the accuracy that could withstand practical use was not obtained.

The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to provide a wafer stage which is not affected by mutual interference due to light scattering between adjacent pellets. It is an object of the present invention to provide a semiconductor light emitting device evaluation device which enables the device evaluation of the above.

[0009]

According to a first aspect of the present invention, there is provided an apparatus for evaluating a semiconductor light emitting device, wherein a plurality of light emitting devices formed on a semiconductor wafer emit light in pulses, and an optical waveform from each of the light emitting devices. And an evaluation processing means for estimating and evaluating the luminous efficiency of each light emitting element from the lifetime of the minority carrier indicated by the decay time constant in the optical waveform.

According to a second aspect of the present invention, there is provided an apparatus for evaluating a semiconductor light emitting element, wherein the element scanning means switches the plurality of light emitting elements one by one as an object to be measured one by one, and an element to be measured. And light detecting means for detecting a light waveform from the light source.

According to a third aspect of the present invention, there is provided an apparatus for evaluating a semiconductor light emitting element, wherein the element driving means comprises: a probe needle connected to one of the plurality of light emitting elements; Pulse current supply means for supplying a pulse current via the one probe needle, and relatively moving the semiconductor wafer and the one probe needle so that the one probe needle is connected to a plurality of light emitting elements. And a device to switch the device to be measured by sequentially connecting the devices to the device to be measured.

According to a fourth aspect of the present invention, there is provided an apparatus for evaluating a semiconductor light emitting device, wherein the device driving means corresponds to a plurality of probe needles connected to the plurality of light emitting devices, respectively, and a device to be measured. One pulse current generating means for supplying a pulse current via a probe needle, and a measuring element switching means for switching a measuring element by sequentially connecting this one pulse current generating means to a plurality of probe needles. It is characterized by having.

According to a fifth aspect of the present invention, there is provided an apparatus for evaluating a semiconductor light emitting device, wherein the light detecting means includes a photoelectric conversion means for outputting waveform information of the received light, and a light generated from any position on the semiconductor wafer. And light collecting means for concentrating the light on the light receiving portion of the photoelectric conversion means.

According to a sixth aspect of the present invention, in the apparatus for evaluating a semiconductor light emitting device according to the present invention, the condensing means comprises a converging mirror.

According to a seventh aspect of the present invention, there is provided the apparatus for evaluating a semiconductor light emitting device, wherein the condensing means comprises an optical fiber cable.

[0016]

According to the present invention, the luminous efficiency of the semiconductor light emitting device has a strong correlation with the lifetime of the injected minority carriers, and the lifetime of the minority carriers is not affected at all by the mutual interference of the adjacent pellets. Focusing on
This is the configuration described above including the measurement of the lifetime of the minority carrier.

According to the present invention, the minority carrier lifetime is obtained from the decay time constant of the emission waveform of the device under test, and the luminous efficiency of the device under test is estimated from this lifetime. Device evaluation can be performed at the wafer stage without being affected by mutual interference due to light scattering between the devices.

In addition, by sequentially switching a plurality of light emitting elements one by one as an object to be measured, it becomes possible to sequentially and automatically measure a large number of elements on a semiconductor wafer.

Further, by concentrating light generated from any position on the semiconductor wafer to the light receiving portion of the photoelectric conversion means, accurate measurement can be performed regardless of the positional relationship between the light receiving portion of the photoelectric conversion means and the element. It becomes possible. In particular, a plurality of probe needles are used, and a system for switching the element to be measured by switching the connection between the probe needles and the pulse current generating means, or a configuration in which the probe needles are moved without moving the semiconductor wafer. It is convenient in the case.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of the evaluation device according to the first embodiment of the present invention. In this figure, reference numeral 100 denotes a wafer on which a large number of LEDs 200 to be evaluated are formed, and the wafer 100 has been subjected to a half-die processing. Reference numeral 300 denotes the cut groove. The wafer 100 is electrically separated between the elements by the cut grooves 300.

Reference numeral 1 denotes a measurement stage, and a wafer 10
Numeral 0 is mounted on the measurement stage 1. Reference numeral 2 denotes an XY table, and the measurement stage 1
The wafer 100 is placed on the Y table 2, thereby being moved in the XY plane, so that the wafer 100 is also moved. Reference numeral 3 denotes an XY table driving device that drives the XY table 2.

Reference numeral 4 denotes a probe needle, the tip of which is in contact with the electrode of one LED 200 and is electrically connected to the LED 200. In this state, the probe needle 4
00, a pulse current is supplied.
The ED 200 is pulse-lit.
The probe needle 4 is used for the wafer 1 in the XY plane described above.
The movement of 00 causes the LEDs 200 to be sequentially connected to each other, whereby all the LEDs 200 are scanned. A pulse current generator 5 supplies a pulse current to the probe needle 4.

Reference numeral 6 is a photodetector, 7 is a waveform analyzer, 8 is a data processor, and 9 is a data output device. Photodetector 6
Is for receiving light from the LED 200 and performing photoelectric conversion, and the output signal is given to the waveform analyzer 7. FIG.
In the above, the pulse current given to the LED 200,
Is a light detection signal when the LED 200 is turned on by the pulse current. As shown in this figure, the detection signal has a waveform whose peak level is lower than that of the power supply pulse current and is dull. The waveform analyzer 7 calculates the peak value of the output signal waveform of the photodetector 6, approximates the decay waveform by an exponential function, and obtains the decay time constant by the least square method. This time constant indicates the lifetime of the minority carrier. Here, the exponential function is represented by the following equation.

That is, I (t) = exp (−t / τ) · I ₀ , where I ₀ is a peak value, t is a decay time, τ
Is the decay time constant. This τ is obtained by approximation.

The data processor 8 obtains the luminous efficiency of the element based on the lifetime data from the waveform analyzer 7, compares the luminous efficiency with a standard value, and compares the luminous efficiency with the target LED 200.
Has a function of determining whether or not the product is a non-defective product, and determining a rank of the product. In detail, the process as shown in the flowchart of FIG. . The details will be described later. The evaluation result in the data processing device 8 is transmitted to the data output device 9
Is printed out.

The data processor 8 has a function of generating a measurement instruction signal each time one LED 200 starts measurement. Reference numeral 10 denotes a synchronous control device.
0 corresponds to the target LED 200 in response to the measurement instruction signal.
Of the target LED 2 with respect to the probe needle 4
It controls the timing of supplying a pulse current to 00 and taking in measurement data. That is, upon receiving the measurement instruction signal, the synchronization control device 10 firstly performs XY
A drive timing signal for the table drive device 3 is generated. As a result, the XY table driving device 3 becomes XY
When the table 2 is driven, the target LED 200 is
Is positioned with respect to When the synchronization control device 10 knows the completion of the positioning based on the time and the response from the drive device 3, it generates a pulse supply timing signal to the pulse current generator 5 and a data capture timing signal to the waveform analysis device 7. The pulse current generator 5 outputs a pulse current to the probe needle 4 in response to the pulse supply timing signal. The waveform analyzer 7 captures the output signal of the photodetector 6 as analysis data in response to the data capture timing signal. Such synchronization control is performed every time the measurement instruction signal is received from the data processing device 8, the LEDs 200 on the wafer 100 are sequentially scanned one by one, and the measurement of each LED 200 is sequentially and reliably performed.

Hereinafter, the data processing apparatus 1 will be described with reference to FIG.
The function of 0 will be described. First, initialization is performed in step ST1. In this initial setting, the type, diameter, measurement mode, and the like of the wafer are set. The type of the wafer is a type of an element formed on the wafer, for example, an ID based on a type such as a red LED of a luminescent color, a green LED,
It indicates an ID or the like set for each element material, and is referred to when selecting a standard value to be compared with measured data in an evaluation process described later. The aperture is the diameter of a wafer, and is referred to instruct the XY table driving device 3 via the synchronous control device 10 with a drive stroke when positioning one element of the XY table 2. The measurement mode indicates, for example, a mode for measuring all the elements or a mode for partially measuring the element, and in the case of a partial measurement, specifies a pitch indicating how many elements are to be measured. Also works as a thing.

After this initial setting, in step ST2, the setting of the wafer 1 on the measurement stage 1 is instructed to a wafer transfer device (not shown). As a result, one wafer 1 is taken out from the wafer supply cassette, set on the measurement stage 1, and preparation for measurement is completed by alignment of the wafer 100 (positioning in the X, Y, and Z directions). Will send a work completion notification. Upon receiving this work completion notification, measurement of each LED 200 is started.

First, in step ST3, the above-mentioned measurement instruction signal is given to the synchronization control device 10. Then, one LED 200 is positioned with respect to the probe needle 4 and driven to emit light, and the optical data is taken into the waveform analyzer 7 via the photodetector 6.

Next, in step ST4, an analysis instruction signal is given to the waveform analyzer 7 via the synchronization controller 10. At this time, the waveform analyzer 7 obtains the minority carrier lifetime from the above-described waveform peak value and decay time constant of the acquired data.

Then, in step ST5, the luminous efficiency indicated by the lifetime data from the waveform analyzer 7 is obtained from a calibration curve. This calibration curve shows the correlation between the lifetime of the minority carrier and the luminous efficiency, and is obtained by acquiring data by actual measurement in advance and presetting it. A simple way of presetting is to take the form of a table, and the intermediate value is calculated by interpolation.

This completes the measurement of one LED 200. In step ST6, it is determined whether or not all the elements have been measured.
After the above-described positioning of the LED 200 with respect to the probe needle 4 is performed, the process returns to step ST3. That is,
Steps ST3 to ST7 are repeated until all the elements have been measured.

When the measurement of all the elements is completed, in step ST8, an instruction is given to a wafer transfer device (not shown) to return the target wafer 100 to the measured wafer storage cassette.

Thereafter, in step ST9, it is determined whether or not the measurement has been completed for all wafers. If not, the process returns to step ST1. That is, steps ST1 to ST9 are performed until the measurement for all wafers is completed.
Is repeated.

When the measurement has been completed for all the wafers, the processing results are printed out by the data output device 9 in step ST10. At this time, C
It may be monitored at RT.

According to the present embodiment, the LED 200 to be measured is
The minority carrier lifetime is determined from the decay time constant of the emission waveform of
Since the luminous efficiency of 200 is estimated, high-precision evaluation of device characteristics at the wafer stage can be performed without being affected by mutual interference due to light scattering between adjacent pellets, and throughput is reduced. improves.

Further, by sequentially switching the plurality of LEDs 200 one by one as an object to be measured, a large number of LEDs 200 on the semiconductor wafer 100 can be sequentially and automatically measured, thereby improving the throughput. Thereby, the LED on the wafer 100
All 200 inspections can be realized, and defective wafers and defective elements can be prevented from flowing to the next step, which can contribute to improvement of wafer quality control. Therefore, it is possible to map the luminous efficiency in the wafer, and to improve the reliability of die sort, greatly improve the accuracy of luminance sorting, and significantly reduce in-plane luminance unevenness that occurs in the manufacturing process of arrays and display panels. And the production yield can be improved.

FIG. 3 shows the configuration of the evaluation device according to the second embodiment of the present invention. In this figure, here,
A plurality of probe needles 4 are provided to multi-probe the LED 200. That is, each probe needle 4 is provided opposite a plurality of LEDs 200, and all the probe needles 4 are simultaneously connected to the corresponding LEDs 200. A switch 11 is interposed between the pulse current generator 5 and the plurality of probe needles 4 so that the pulse current generator 5 is selectively connected to one probe needle 4 by the switch 11. Has become. The switching control is performed by the synchronous control device 1
Performed by 0. According to the command from the data processing device 10, the synchronization control device 10 performs one L while measuring one group of LEDs 200 corresponding to the number of the probe needles 4.
Each time the measurement of the ED 200 is started, one pulse current generator 5 is sequentially switched and connected to the plurality of probe needles 4 to switch the LED to be measured. When the measurement of the LEDs 200 connected to all the probe needles 4 is completed, the synchronous control device 10 drives the XY table 2 to position and connect the next group of LEDs 200 to the probe needles 4, and 11, L of this group
The ED 200 is sequentially switched as the element to be measured.

Condensing mirrors 12 and 13 are provided between the measuring stage 1 and the photodetector 6, and the light generated from the LED 200 is first reflected by the condensing mirror 12 and To the light receiving portion of the photodetector 6 by the condenser mirror 13.

The other structure is the same as that shown in FIG.

According to this embodiment, the number of times of mechanical positioning of the wafer 100 can be reduced by the number of the probe needles 4 and the speed of measurement can be increased. Here, assuming that the number of probe needles 4 is N, the number of times of mechanical positioning is reduced to 1 / N times as compared with that shown in FIG. The time is also approximately 1 / N. Therefore, the throughput is greatly improved.

In this embodiment, since the light is received from a wide area of the wafer 100, the light receiving state of the photodetector 6 may be a concern. Is also guided to the light receiving section of the photodetector 6, so that the problem is solved.

Further, the light-collecting efficiency of the light-collecting mirror is constant (ideally, "1") for any of the probed LEDs 200, and the light-collecting efficiency of any of the probe needles 4 is large. It is preferable that the shadow is not shadowed on the LED 200, but the carrier lifetime is not particularly affected since it is not affected at all if a waveform is obtained.

Note that the condensing mirrors 12 and 13 correspond to the wafer 1
It would be best if it could cover the entire 00 surface, but this is not necessary. It is sufficient that the light collecting mirrors 12 and 13 cover the existing positions of all the LEDs 200 to which the probe needles 4 are connected.

FIG. 4 shows the configuration of the evaluation device according to the third embodiment of the present invention. In the apparatus shown in this figure, the light collecting means is constituted by an optical fiber cable. Reference numeral 14 denotes the fiber condenser. The fiber concentrator 14 includes a plurality of optical fiber cables 15, and the optical fiber cables 15 are used in a state where the optical fiber cables 15 are opposed to a plurality of LEDs 200. That is, one end of each optical fiber cable 15 is connected to the LE to which the probe needle 4 is connected.
The other end is arranged near the light receiving section of the photodetector 6. Thereby, the LED 20
Light from the optical detector 6 through the optical fiber cable 15
To the light-receiving part of.

The other structure is the same as that of the second embodiment shown in FIG.

According to this embodiment, the same operation and effect as those of the device described in the second embodiment can be obtained.

Further, according to the present embodiment, the probe needle 4
There is no error factor that the light is shadowed on the photodetector 6, and the apparatus can be made more compact.

Here, the results of a specific test performed with the system configuration of the first embodiment shown in FIG. 1 will be described. The sample element at that time was an LED of green emission color formed on a GaP wafer, and one cassette (25) of 2 ″ φ GaP wafers on which the LEDs were formed was prepared.
About 2000 LEs per wafer at 1mm pitch
D was measured according to the procedure shown in FIG.

FIG. 6 shows a correlation diagram between lifetime and luminous efficiency for data processing at that time.

As a result, in the conventional method, two wafers
The measurement was completed for all of the 2,000 × 25 LEDs in the measurement time when the limit was 0. Therefore, according to the above embodiment, the measurement on the wafer can be performed more finely than the conventional method by two digits or more, and the measurement time is as fast as several seconds per point. Obviously, according to the second and third embodiments, the speed is further increased. For example, 100
Using up to 200 multiprobes can reduce the measurement time by 20% or more.

As described above, according to the apparatus of the present invention, highly accurate measurement results and evaluation results can be obtained in such a short time. FIG. 7 shows a histogram of the obtained lifetime. This lifetime can be replaced by the luminous efficiency.
And the results obtained by measuring the 20 samples according to the conventional method, all of which were consistent within a ± 5% deviation range. The figure of ± 5% is so small that it is not clear which error is in which measurement method.

As described above, when the pulse current generator 5 used in the concrete implementation has a life time of about 50 to 400 nsec,
The rise, fall, duration, and number of repetitions of the pulse are not limited and can be appropriately selected depending on the measurement object. Similarly, the photodetector 6 only needs to have a response speed such that a lifetime can be seen. In general, a photocell, a PIN photodiode, an APD, and a streak camera may be appropriately selected.

In the above-described embodiment, the attenuation waveform is approximated by an exponential function, and the time constant is obtained by the least square method.
Conveniently may be carried out an approximation to determine the time from 0.9I ₀ as shown in FIG. 5 until attenuated to 0.2i _0.

Although the measurement wafer has been described as having a pattern of electrode-patterned and electrically separated elements by a half die, a wafer before dicing or a non-electrode wafer may be measured. In this case, an average value of a region wider than one element can be obtained due to the spread of the conduction current path, and the tendency of the entire wafer can be determined with fewer measurement points. As a result, quality monitor management of the wafer can be performed earlier during the wafer process.

[0056]

As described above, according to the present invention, the lifetime of the minority carrier is determined from the decay time constant of the emission waveform of the device under test, and the luminous efficiency of the device under test is estimated from this lifetime. Because
Element evaluation at the wafer stage can be performed without being affected by mutual interference due to light scattering between adjacent pellets, and the throughput is improved.

Further, by sequentially switching a plurality of light emitting elements one by one as an object to be measured, it becomes possible to sequentially and automatically measure a large number of elements on a semiconductor wafer. This also improves the throughput.

Therefore, inspection of all elements on the wafer can be realized, and defective wafers and defective elements can be prevented from flowing to the next step, which can contribute to improvement of wafer quality control. Therefore, it is possible to map the luminous efficiency in the wafer, and to increase the reliability of die sort,
The accuracy of the luminance ranking can be greatly improved, and in-plane luminance unevenness defects occurring in the manufacturing process of an array, a display panel, or the like can be significantly reduced, and the manufacturing yield can be improved.

Further, by concentrating light generated from any position on the semiconductor wafer to the light receiving portion of the photoelectric conversion means, accurate measurement can be performed regardless of the positional relationship between the light receiving portion of the photoelectric conversion means and the element. It becomes possible. In particular, a plurality of probe needles are used, and a system for switching the element to be measured by switching the connection between the probe needles and the pulse current generating means, or a configuration in which the probe needles are moved without moving the semiconductor wafer. It is convenient in the case.

As a whole, the present invention can be expected to greatly improve productivity by its industrial use, and has extremely high practical value.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a semiconductor light emitting device evaluation apparatus according to a first embodiment of the present invention.

FIG. 2 is a flowchart showing processing contents of the data processing device shown in FIG. 1;

FIG. 3 is a block diagram showing a configuration of a semiconductor light emitting device evaluation apparatus according to a second embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration of a semiconductor light emitting device evaluation apparatus according to a third embodiment of the present invention.

FIG. 5 is a waveform diagram showing a pulse current supplied to a measurement target element and a detection signal of light emitted from the measurement target element.

FIG. 6 is a correlation diagram between the lifetime of a minority carrier and the luminous efficiency.

FIG. 7 is a histogram when the decay time constant τ is measured for a large number of LEDs by the device of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Measurement stage 2 XY table 3 XY table driving device 4 Probe needle 5 Pulse current generator 6 Photodetector 7 Waveform analyzer 8 Data processor 9 Data output device 10 Synchronous control device 11 Switching device 12, 13 Condensing mirror 14 Optical fiber concentrator 100 Wafer 200 LED power supply pulse current LED emission detection signal

Claims (7)

(57) [Claims] An element scanning means for pulsating a plurality of light emitting elements formed on a semiconductor wafer and detecting an optical waveform from each of the plurality of light emitting elements, and a minority carrier of a minority carrier indicated by an attenuation time constant in the optical waveform. An evaluation processing means for estimating and evaluating the luminous efficiency of each of the plurality of light emitting elements from a lifetime; 2. An element scanning means comprising: element driving means for sequentially switching a plurality of light emitting elements one by one as an object to be measured; and light detecting means for detecting a light waveform from the element to be measured. Item 2. An evaluation device for a semiconductor light emitting device according to item 1. 3. An element driving means, comprising: one probe needle connected to one of the plurality of light emitting elements; and a pulse current supplied to the element to be measured via the one probe needle. Pulse current supply means, and a target element switch for switching the target element by relatively moving the semiconductor wafer and the one probe needle and sequentially connecting the one probe needle to a plurality of light emitting elements. 3. The apparatus for evaluating a semiconductor light emitting device according to claim 2, further comprising means. 4. An element driving means comprising: a plurality of probe needles respectively connected to a plurality of light emitting elements; and a pulse current supplied to the measurement target element via a probe needle corresponding to the measurement target element. 3. A device according to claim 2, further comprising: two pulse current generating means; and a measuring element switching means for switching the measuring element by sequentially switching and connecting the one pulse current generating means to the plurality of probe needles.
An apparatus for evaluating a semiconductor light-emitting device according to claim 1. 5. A light detecting means, comprising: a photoelectric conversion means for outputting waveform information of a received light; and a light condensing means for concentrating light generated from any position on the semiconductor wafer to a light receiving portion of the photoelectric conversion means. 5. The apparatus for evaluating a semiconductor light emitting device according to claim 4, further comprising: means. 6. The apparatus for evaluating a semiconductor light emitting device according to claim 5, wherein the light collecting means comprises a light collecting mirror. 7. An apparatus for evaluating a semiconductor light emitting device according to claim 5, wherein said light condensing means comprises an optical fiber cable.