EP1395800A1

EP1395800A1 - Method for determining temperatures on semiconductor components

Info

Publication number: EP1395800A1
Application number: EP02740260A
Authority: EP
Inventors: Henning M. Hauenstein
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2001-04-21
Filing date: 2002-04-18
Publication date: 2004-03-10
Also published as: US6953281B2; DE10119599A1; US20030161380A1; WO2002086432A1

Abstract

The aim of the invention is to determine a temperature on a semiconductor component (1). To this end, an inquiry light wave (7) is irradiated onto a measuring point located on the semiconductor component, a response light wave (8, 8') radiated by the measuring point is detected, and the temperature of the measuring point is determined on the basis of a temperature-dependent property (R) of the response light wave (8, 8').

Description

Method for determining temperatures on semiconductor components

State of the art

The present invention relates to a method and a device for determining temperatures on semiconductor components. In the field of semiconductor technology, the performance of a component depends, among other things, on its permissible operating temperatures. A very common cause of failure is excessive temperatures during operation, which can severely damage or completely destroy the component. Both for the user who has to select suitable semiconductor components for a specific application or have to specify a manufacturer for the development of such an element, and for the manufacturer who specifies his product, the knowledge of the temperature of the component is therefore determined under certain conditions Operating conditions, of great interest.

It is state of the art to characterize the temperature of a semiconductor component using the so-called junction temperature _j , which can be determined, for example, by measuring the forward voltage of pn junctions of a component. (These are transitions between p-doped and n-doped regions of a semiconductor; they are, for example, part of rectifier and Zener diodes or are in Form of the intrinsic body diode of a field effect transistor before). This takes advantage of the fact that the voltage U _F us _uss , which must be applied to a pn junction in the direction of flow in order to let a specific current I flow, depends on the crystal temperature at the location of the pn junction.

The functional relationship U _flow (I, T _j ) can then be used to determine the temperature T _j by measuring the flow voltage U _F iuss for a given flow current I. A prerequisite for this, however, is knowledge of the function U _FI US _S d Tj), which is generally determined by a previous stationary calibration measurement by Uι _US s (I Tj).

A considerable disadvantage of this known method is, however, that the measuring current I has to be sent across the component in the flow direction. This means that this method cannot be used as long as a different operating state of the component prevents this flow current (e.g. during an avalanche breakdown or the like). In the case of complex integrated circuits, there can also be the problem that, in general, the permeability states of different semiconductor junctions in the component cannot be set completely independently of one another. It can therefore happen that there is interest in measuring the temperature of a specific p-n junction, which, however, only becomes transiently permeable under normal operating conditions of the component. In such a case, it is not possible to carry out a stationary calibration measurement at the p-n junction beforehand.

These peculiarities of the known method lead to it being used, for example, for examining the barrier breakthrough (Avalanche effect) of a diode is not usable. The avalanche state is characterized in that a voltage is so high in the reverse direction that the diode breaks down and a high current flows in the reverse direction (so-called Zener breakdown of a diode). The high fields and currents generally lead to a strong heating of the component, the hottest point being at the pn junction that breaks through. To determine the prevailing temperature with the known forward voltage method, one has to wait until the

Reverse current has almost completely decayed in order to then conduct a measuring current in the opposite direction through the p-n junction. This means that the known method can only be used with a certain time delay after the Zener breakthrough has subsided. However, the temperature at this point no longer corresponds to the temperature peak at the pn junction that occurs during the breakthrough, but mostly a significantly lower temperature, because between the end of the avalanche state and the start of the measurement, the heat is out of the range could already distribute the pn junction over a larger area of the component or even over the thermally coupled surroundings of the component. However, it is generally the transient temperature peaks that lead to damage to the component.

It is possible to obtain information about the temperature development in the semiconductor component by following the development of the flow current over time after a Zener breakthrough and by extrapolating this development to points in time before the measurement at to conclude temperatures that may have existed at the boundary layer at the time of the breakthrough. However, this process is fraught with considerable uncertainties. One reason for this is the shortness of the available measurement times and thus the limited accuracy of the temperature measurement, which is all the more extreme the higher the time resolution required. On the other hand, a fundamental problem is that only a mean value is measured by the flux current the temperature can be determined over the entire surface of the pn junction, but it is by no means certain that the avalanche current - and thus the temperature distribution in the avalanche state - is evenly distributed over the junction area.

Advantages of the invention

The present invention provides a method and a device for determining temperatures on semiconductor components, which enable measurement at any time regardless of an operating state prevailing at a semiconductor junction. Another advantage of the invention is that it enables a spatially resolved temperature measurement, with which even uneven current intensity distributions at a semiconductor junction can be detected on the basis of the temperatures resulting therefrom. The measurement is time-resolved, with a resolution in the millisecond range and below.

These advantages are achieved by a method for determining a temperature on a semiconductor component with the following steps: Irradiation of an interrogation light wave onto a measuring point on the semiconductor component,

Detection of a response light wave emitted by the measuring point,

Detection of the temperature of the measuring point based on a temperature-dependent property of the response light wave.

The advantages are further achieved by a device for determining a temperature on a semiconductor component with a light source for irradiating an interrogation light wave onto a measuring point on the semiconductor component, a light-sensitive element for detecting a temperature-dependent property of the response light wave and a processing unit for converting one supplied by the light-sensitive element Detection value in a temperature.

A current value of the temperature-dependent property detected by the light-sensitive element is preferably converted into a temperature by comparing it with values of a reference curve which describes the property as a function of temperature.

Such a reference curve is expediently recorded in advance under static thermal conditions.

In order to identify the reference curve on the same component on which the measurements will be made later, To be able to record conditions, the device according to the invention is expediently equipped with an oven with which the temperature of the semiconductor component can be regulated in a stationary manner at a desired value.

Since temperature-dependent properties of the semiconductor component, such as linear and non-linear reflection coefficients. cients, refractive index, absorption coefficient, etc. can be locally variable in accordance with the functional structures formed on the semiconductor component, the reference curve is preferably recorded specifically for a single measurement point of the semiconductor component. A small surface or interface section of the semiconductor component which has a homogeneous structure is expediently chosen as the measurement point. At this

The measuring point of the same semiconductor component or of a structurally identical element is then also used to record the measurements of the heating of the semiconductor component induced by the operating current flow.

A plurality of such measuring points can be defined on a semiconductor component and reference curves can be recorded for those measuring points which belong to different p-n junctions or also to spatially separate areas of the same p-n junction.

The temperature distribution on the surface of an unpacked component or a component exposed from its packaging can thus be "mapped" to a certain extent. ' If only individual temperature measuring points are required, it may be sufficient to expose them in the packaging through a small hole with a cross section of a few mm ² .

A sufficiently intense monochromatic light source, in particular a laser beam, is preferably used as the interrogation light wave. Sufficiently intense means that the light must be intense enough to be able to evaluate the response signal. Too high an intensity would possibly heat up the component and falsify the measurement if the radiation were absorbed accordingly.

The response light wave can then be detected at the frequency of the interrogation light wave; with sufficient intensity of the interrogation light wave, the detection of harmonics at a multiple of the frequency of the interrogation light wave is also possible. If two monochromatic interrogation light waves are used, the response light wave can also be detected with the sum or difference of the frequencies of the two interrogation light waves. Such a procedure enables the intensity of the response light wave to be increased by tuning at least one interrogation light wave to a resonance of the material of the component.

The response light wave can be detected in the Fresnel reflection direction of the interrogation light wave, but it is also conceivable to evaluate a response light wave that is scattered in a non-directional manner in spatial directions other than the Fresnel reflection direction. A wavelength is preferably selected for the interrogation light wave at which the substrate material of the semiconductor component is transparent. In this way, it is avoided, on the one hand, that absorption of the interrogation light wave in the semiconductor component heats it and the measurement results are falsified, on the other hand, it is excluded that the charge light wave is induced by the immission of the interrogation light wave, which influences the switching behavior of the semiconductor component - could flow. Semiconductor materials generally have transparent regions in the near infrared at wavelengths above Iμm.

Further features and advantages of the invention result from the following description of exemplary embodiments with reference to the attached figures. Show it:

1 shows a schematic view of a measuring device according to the invention;

Fig. 2 shows an example of the temporal development of the

Reflectivity of the surface of a semiconductor component and a development of the temperature determined therefrom;

3 shows a measuring method which is suitable for use with a pulsed laser as the light source;

4 shows the spatial course of the interrogation and response light wave in a case where the response light wave le the second harmonic of the interrogation light wave is detected; and

5 shows the spatial course of the interrogation and response light wave when the classically reflected or the transmitted interrogation light wave is detected as the response light wave.

1 shows a highly schematic device according to the invention for determining temperatures on a semiconductor component 1. In the device shown here, the semiconductor component 1 is on an arrangement of displacement tables 2, 3 in two directions (relative to the exposed surface of the component 1) the Fig. in the horizontal direction and perpendicular to the plane of the drawing) slidably arranged. The device 1 ^'is surrounded on a thermostatically controlled oven 4, which has an entrance and exit window 5, 6 for a query fiber 7 and an answer light wave. 8 A laser 9, for example a solid-state laser, in which rare earth ions are used as laser-active species, serves as the light source for generating the interrogation light wave. Depending on the type of ions used and their carrier crystals, such lasers can have wavelengths in the range of approx. 1.0-1.5 μm.

The interrogation light wave 7 generated by the laser 9 is directed to a measuring point on the surface of the semiconductor component 1; the response light wave 8 emanating from there passes through a filter 10 and is emitted by a light-sensitive - lo ¬

element 11, e.g. a PIN photodiode, a pyroelectric detector or the like collected. The filter 10 serves to shield the light-sensitive element 11 from ambient light. Depending on the expected intensity of the interrogation light wave, the filter 10 can be a simple colored glass filter or an interference filter. Under certain circumstances, which will be discussed in more detail later, the use of a grating monochromator may also be necessary.

A beam portion distributed by a beam splitter 12 from the interrogation light wave 7 is directed to a second light-sensitive element 13.

An evaluation and arithmetic unit 14 is connected to both light-sensitive elements 11, 13 in order to calculate the ratio of the intensities of the waves collected by the two light-sensitive elements and thus to determine the reflection coefficient R of the measuring point. A temperature sensor 15 is also connected to the evaluation and arithmetic unit 14 and is used to detect the temperature inside the furnace 4.

In a first phase of the method according to the invention, a reference curve is generated which indicates the dependence of the reflection coefficient of the surface of the semiconductor component 1 on its temperature. For this purpose, the furnace 4 with the semiconductor component 1 located therein is slowly heated up, and during the heating up the re- Inflection coefficient R of the surface is determined by forming the ratio of the intensity signals supplied by the light-sensitive elements 11, 13 and stored as a function of the temperature T prevailing in the furnace 4 at the time of the determination in a memory of the evaluation / arithmetic unit 14.

If the surface of the semiconductor component 1 is structured and has a reflection coefficient which differs from location to location, then such a reference curve is obtained for a plurality of measuring points at which temperature measurements are to be carried out later under operating conditions of the semiconductor component.

As a first example of using the reference curve to determine a temperature of the semiconductor component 1 and the operating conditions, the case is considered that these operating conditions are stationary. In this case, it is sufficient to irradiate the interrogation light wave 7 onto the semiconductor component 1 under exactly the same geometric conditions as when the reference curve was recorded and to collect the response light wave 8 reflected by its surface in order to compare its temperature-dependent intensity with the intensity captured by the light-sensitive element 13 , The comparison provides a reflection coefficient R, which can be clearly assigned to a temperature of the semiconductor component 1 on the basis of the reference curve. With this method, however, only slow temperature changes of the semiconductor component 1 can be detected. For the semiconductor developer and user, however, it is important to know the temperatures that can occur transiently in the course of a switching operation, that is to say when the component is in non-stationary operation. A principle of detecting such transient temperature profiles is illustrated with the aid of FIG. 2. For measuring a temperature

) running on the semiconductor component 1, a switching process that 0 leads to heating is repeated cyclically. 2 shows in a first partial diagram as curve R (t) the course of the reflectivity R as a function of time t over two switching cycles. In reality, the reflectivity cannot be measured with the accuracy of the curves shown, but 5 is very noisy, so that expediently with the aid of a lock-in amplifier, which can be part of the evaluation and computing unit 14, and which is related to the switching cycle of the component 1 coupled, an average course of the reflectivity R is determined in the course of a cycle, which is then converted into a time-dependent course of the temperature T (t) using the reference curve R (T).

This procedure is suitable for use in conjunction with a continuous light source for the interrogation period.

3 illustrates a measurement method that is suitable for use with a pulsed laser as the light source. 3, three curves are shown superimposed on one another. provides. A first curve 20 indicates the reflectivity 'R of the surface of the semiconductor component 1 as a function of the time t. The curve repeats itself in each operating cycle of the semiconductor component with the duration ti. A second curve 21 indicates the time-dependent intensity of the pulsed laser, its period tχ + ε differs from the period t _{x of} the operating cycle by a very small, non-vanishing value ε. This difference ε is shown exaggerated in the figure in order to make it clear how the position of the laser pulses of curve 21 changes over time t

Moves with respect to the operating cycle of the component 1. With each laser pulse, the curve 20 is scanned - in different cycles - with a different phase position, and a sample value for the reflection coefficient is obtained, which corresponds to an alternate phase position of the cyclic curve 20. The sequence of the scans obtained in this way results in a curve 22, the course of which on an elongated time scale corresponds to the course of the reflectivity curve 20 in each individual cycle. By choosing the value ε on the order of the laser pulse duration, the

Aspect ratio can be set; a temporal resolution of the reflectivity measurement corresponding to the laser pulse duration _t can be achieved.

In the previous description, it was assumed that the response light wave, which is collected and evaluated to determine the temperature, originates from the interrogation light wave by reflection on the surface of the semiconductor device. elements according to the classic laws of Fresnel optics. This does not necessarily have to be the case. For example, it is conceivable not to collect the reflected beam as the response light wave, but rather light that is diffusely reflected on the surface of the component 1.

It may also prove expedient to use nonlinear optical phenomena on the surface or also on another interface of the semiconductor component instead of linearly reflected light in the conventional manner. The easiest way to do this is to double the frequency on the surface. Optical frequency doubling or general mixing of sum and difference frequencies are non-linear optical processes that can occur in non-inversion-symmetrical media. In the usual semiconductor materials, the inversion symmetry is broken only at interfaces. Therefore, sum and difference frequency mixing can only occur at interfaces. But it is precisely the interfaces, e.g. see between differently doped zones of the semiconductor component or between the semiconductor substrate and a metallization whose temperatures are important to know in order to be able to optimize the load capacity of semiconductor components, or also to optimize models which allow temperature distributions in a semiconductor component to be mathematically simulated under operating conditions.

An advantageous variant of the beam guidance on the semiconductor component 1 when using the second harmonic 0

as the answer light wave 8 is shown in FIG. 4. Here the interrogation light wave 7 hits two. opposite equal angles to the surface normal to a measuring point on the surface of the semiconductor component 1. Due to the non-linear interaction of the light arriving from two different directions with ^' the half ^' iter surface, frequency-doubled light is produced which is partially emitted in the direction of the surface normal. This response light wave is practically free of background with the frequency of the interrogation light wave. Although the intensity of the frequency-doubled response light wave is many orders of magnitude lower than that of the interrogation light wave, the response light wave can therefore be separated from the background, if necessary using additional filters or a monochromator, and detected as a photosensitive element 11 with the aid of a photomultiplier.

According to another further development, a polarizer can be provided in the beam path of the interrogation light wave - regardless of whether it is a light wave at the frequency of the interrogation light wave or a harmonic thereof - in order to detect the intensity of the response light wave in a polarization-dependent manner. When the laser 9 supplies polarized light, so ^'of this polarizer can be, in particular or- oriented, orthogonal to the polarization direction of the laser to detect only a depolarized component in the reflected from the component 1 light in response light wave and so much of the intensity of the reflected light to suppress. If a umpole In the previous description, it has been assumed that the response light wave 8 is emitted on the surface of the semiconductor component 1 into the half space from which the interrogation light wave 7 strikes the surface. As ^J FIG. 5 shows, however, there is also the possibility of '11 the trans- mittierte of the semiconductor device 1 portion of the interrogating light shaft 7 by means of a photosensitive element' absorb light response shaft 8 and so the likewise temperature-dependent absorption coefficient of the

IC to detect semiconductor material 1. While a wavelength of the interrogation light wave 7 in a region of complete transparency of the semiconductor substrate will preferably be selected for reflection measurements, a wavelength at the edge of the transparency is recommended for transmission measurements.

15 limit range, so that even slight temperature-dependent changes in the absorption coefficient lead to a measurable change in intensity of the transmitted response light wave 8 '. By using the beam splitter 12 and detecting the divided beam in the photosensitive element 13, absolute coefficients can be determined in the evaluation or arithmetic unit 14, also in the example according to FIG. 5, both the absolute reflection and transmission coefficients, from the ratio of Signals from the detectors or light-sensitive elements 11 'and 13. If reflection and transmission are measured simultaneously, this is the case with certain ones

Sample geometries possible and requires a further detector element, that is, a total of d-rei detector elements 11, 11 ', 13, the absorption coefficient of the semiconductor material 1 and

Claims

claims

1. A method for determining a temperature on a semiconductor component (1), comprising the steps:

Irradiation of an interrogation light wave (7) onto a measuring point on the semiconductor component,

Detecting a response light wave (8, 8 ^) emitted by the measuring point, - Detecting the temperature of the measuring point on the basis of a temperature-dependent property (R) of the response light wave (8, 8).

2. The method according to claim 1, characterized in that the temperature is detected by comparing a current value (R (t)) of the temperature-dependent property with values of a reference curve (R (T)).

3. The method according to claim 2, characterized in that the reference curve (R (T)) is recorded in advance under static thermal conditions.

4. ^' Method according to claim 2 or 3, characterized in that the reference curve (R (T)) is recorded specifically for a single measuring point of the semiconductor component (1).

5. The method according to any one of the preceding claims, characterized in that the query light wave (7) is monochromatic and the response light wave (8, 8 ^λ ) is detected at the frequency of the query light wave (7).

6. The method according to any one of claims 1 to 4, characterized in that the query light wave (7) is monochromatic and the response light wave (8) is detected at a multiple of the frequency of the query light wave (7).

7. The method according to any one of claims 1 to 4, characterized in that two monochromatic interrogation light waves (7) are used, and the response light wave (8) is detected at the sum or difference of the frequencies of the two interrogation light waves (7).

8. The method according to any one of the preceding claims, characterized in that the temperature-dependent property is the intensity or the polarization of the response light wave (8).

9. The method according to any one of the preceding claims, characterized in that the response light wave (8) is detected in the Fresnel reflection direction of the interrogation light wave.

10. The method according to any one of claims 1 to 8, characterized in that the response light wave (8) through undirected scattering on the surface of the semiconductor component (1) is obtained.

11. The method according to any one of the preceding claims, data carried in that one wavelength is selected for the interrogating light shaft (7), wherein the substrate material of the semiconductor component (1) transpa rent ^¬ is.

12. Device for determining a temperature on a semiconductor component, with a light source (9) for irradiating an interrogation light wave (7) onto a measurement point on the semiconductor component (1), a light-sensitive element (11) for detecting a temperature-dependent property of the measurement point emitted response light wave (8), characterized by a processing unit (14) for converting a detection value supplied by the light-sensitive element (11) into a temperature.

13. The apparatus according to claim 12, characterized in that the processing unit (14) has a memory for at least one reference curve (R (T)) of the temperature-dependent property as a function of temperature.

14. Device according to one of claims 12 to 13, characterized by an oven (4) for regulating the temperature of the semiconductor component (1).

15. The device according to one of claims 12 to 14, characterized by at least one actuator (2, 3) for displacing the semiconductor component (1) relative to the light source (9) and the light-sensitive element (11).

16. The device according to one of claims 12 to 15, characterized in that the light source (9) is a laser.

17. Device according to one of claims 12 to 16, characterized in that the light-sensitive element (11) is a photomultiplier.

18. Device according to one of claims 12 to 17, characterized in that a polarizer is arranged between the semiconductor component (1) and the light-sensitive element (11).