DE102005054552A1 - Test device and method for detecting cracks on semiconductor substrates have unit to locally heat different parts of the substrate and pyrometer to measure local temperature and detect differences - Google Patents

Abstract

A test device (1) for detecting cracks on semiconductor substrates comprises a holder (2) for at least one substrate (7), a test device and a unit to move the substrate with respect to the test device. The test unit comprises at least one heat source (4) to locally heat the substrate and at least one pyrometer with a detector (5) to measure the local temperature of the substrate. An independent claim is also included for a method for the above in which the temperature is measured at two different points and the temperature difference compared with a threshold value, a crack being indicated if this value is exceeded.

Description

The The invention relates to a device for testing semiconductor substrates, in particular semiconductor wafers, for cracks. It concerns further a method for inspecting semiconductor substrates.

One Semiconductor wafer, such as silicon, after its production with a variety of layers of electrically conductive or insulating Material provided, which structures by etching processes become. While In the manufacturing process, the wafer is repeatedly planarized.

By its small thickness makes a semiconductor wafer susceptible to damage such as cracks. Because such Cracks can lead to failure of a component, the semiconductor wafer must be checked for damage between the individual production steps. For cost reasons it is appropriate for this purpose one possible Use sensitive procedure to damage already while possible early in the morning Recognize manufacturing process and sort out the affected wafer to be able to.

From the US 6,906,794 B2 For example, a device for inspecting semiconductor wafers is known, which detects damage by means of an optical method. For this purpose, the device has a light source for irradiating the semiconductor wafer and an imaging unit with a camera for imaging the region to be inspected on the semiconductor wafer. The semiconductor wafer is movable relative to the light source to the camera and also arranged tiltably.

The However, semiconductor wafer inspection equipment does not allow automatic testing. Rather, it is operated by an operator and also the actual one exam and judgment of the captured images is done by the operator and is through the imaging process and image processing software only supported.

The Although inspection of semiconductor wafers is more accurate than one Inspection with sheer Eye, but very time-consuming and thus cost-intensive. In addition, damage how very fine cracks are difficult to detect with optical methods.

task The invention is therefore to provide a device with which a simple and fast, but at the same time very sensitive exam Semiconductor wafers on cracks possible is.

Furthermore It is another object of the present invention to provide a method for testing from semiconductor wafers to cracks.

According to the invention this Problem solved with the subject of the independent claims. advantageous Further developments of the invention are the subject of the dependent claims.

A inventive device for testing from semiconductor substrates to cracks comprises a holder for receiving one or more semiconductor substrates, a test unit and a motion unit for moving the semiconductor substrate and the test unit relative to one another, wherein the test unit at least a heat source for local warming of the semiconductor substrate and at least one pyrometer with a detector for local measurement of the temperature of the semiconductor substrate.

Under a crack becomes here and in the following a crack-shaped damage of the semiconductor substrate understood not only its surface, but the entire thickness of the semiconductor substrate or at least substantial parts thereof concerns and the mechanical and thermal conduction properties of Semiconductor substrate measurably influenced.

The Invention goes from consideration from that inspection of semiconductor substrates, in particular of semiconductor wafers, if possible automatically feasible and still have a close examination of the Semiconductor should allow. For this purpose, the property is exploited that one undamaged Semiconductor wafer heat relatively good conducts, while over one damage like a crack away the heat conduction almost comes to a halt.

advantageously, are provided as a detector one or even more thermopile. A thermopile is characterized by easy handling and a relatively low susceptibility for disturbances. A thermopile usually comprises a plurality of thermocouples connected in series, whose function is based on the Seebeck effect: then arises the boundary layers of two different metals, which together be connected, a thermoelectric voltage. This is temperature dependent and allowed through their measurement a conclusion to the temperature.

A thermopile measures the temperature of a body using the radiation emitted by him. Heat radiation is at a Connection of the thermopile, the for a better absorption capacity blackened is, absorbed, causing a warming to the other, before the radiation protected Connection leads and induces the thermoelectric voltage.

Thermopiles can enter through the back switching several thermocouples multiply the thermoelectric voltage and thus form a sensitive heat detector, which allows a non-contact and very fast temperature measurement.

The heat source is advantageously on the same side of the semiconductor substrate arranged like the detector. Thus, the re-radiated, and not the much weaker transmitted radiation analyzed.

The test unit can be stationary and the semiconductor substrate relative to the test unit be arranged movably. When a semiconductor wafer as a semiconductor substrate is provided, the wafer is advantageously around an axis rotated by its center perpendicular to its surface, to allow an inspection with the fixed test unit.

The Heat source for example, a light source, a heated gas or a sound source can be, has a distance d to the detector. Between the heat source and the detector is thus an area with an extension of of the order of magnitude d. If the semiconductor material in this area is undamaged, so it is relatively homogeneous Thermal conduction properties on. Thus, the wafer rotates about an axis through its center and the detector and the heat source are stationary arranged, so the detector measures a temporally largely constant Temperature.

paint over however heat source or detector a crack, so there is a crack inside of the area between heat source and detector, so change the heat conduction properties of Substrates abrupt, which is noticeable by a temperature jump power.

A another possibility the detection of a crack arises when the test unit another pyrometer with a detector at a distance d 'from the detector of first pyrometer is arranged comprises.

at a simultaneous measurement with both detectors can be a crack thereby recognize that the difference between them measured temperatures is greater as it is due to the different distance from the heat source alone would be expected. At a distance d 'of at most 10 mm leaves a very good resolution in the location of cracks.

advantageously, At least one detector is designed without an imaging optics. Such a detector has on the one hand a relatively high temperature sensitivity and allows the exam a semiconductor substrate even at a rather low heating. To the otherwise it can be arranged at a short distance from the semiconductor substrate be achieved and thereby achieved a particularly good spatial resolution.

The Semiconductor substrate typically has a thickness of at most 1 mm, its transmissivity in the wavelength range between 1 μm and 10 μm is at least 50%.

The inventive device has the advantage of being beneficial by exploiting the thermal conduction properties of the semiconductor substrate and by the use of thermopiles particularly sensitive and fast automatic inspection allowed. Also very fine cracks, which are not caused by an optical inspection or only with great effort can be recognized affect the heat conduction of the semiconductor substrate strong enough to with the inventive device to be detected. In addition, the non-contact measurement Influences of the local wafer temperature by the measurement itself as well as damage the wafer surface avoided.

To The present invention comprises a method for testing Semiconductor substrates from cracks following steps: First locally heats the semiconductor substrate at a point y. Subsequently or also at the same time, the local temperatures T (x) and T (x ') at two different points x and x 'from the Semiconductor substrate measured.

From the temperatures T (x) and T (x ') is the difference D = T (x) - T (x') is formed and compared with a predetermined threshold value T _S. If D exceeds this threshold value T _S , then this is a sign that there is a crack between the positions x and x '. This can be displayed or recorded by means of a signal.

to local warming the semiconductor substrate becomes a heat source, for example a light source, a heated one Gas or a sound source used. The measurement of the temperature takes place by a pyrometric method, advantageously by thermopile as detectors.

The Semiconductor substrate and the test unit, the the heat source and the thermopile are moved relative to each other, so that during the testing procedure the entire area of the semiconductor substrate, or at least that of cracks in particular vulnerable Edge area overlined becomes.

In particular, when the semiconductor substrate is a nearly circular semiconductor wafer, this is advantageously around an axis rotates through its center perpendicular to its surface at the angular velocity ω. In this way, the semiconductor wafer can be particularly easily inspected by the fixed test unit.

The Temperatures T (x) and T (x ') in places x and x 'can either at two consecutive times with a single detector be measured, which successively passes over the positions x and x '. At a time t is then the point x in a measuring window of the detector and at time t 'the Point x ', so that T (x) at time t and T (x ') measured at time t ' become.

she can but also measured at the same time with two different detectors of which the first at some point above the Point x is located while the other at the same time over is located at the point x '.

To calculate the difference D T _measurement (x) advantageously to the local signal background .DELTA.T (x) is corrected temperature T (x) = T _measure (x) instead of the measured temperature - .DELTA.T (x) is used.

The Temperature measurement is namely, because they are pyrometrically over The emitted radiation takes place, especially in the infrared Wavelength range relatively transparent Semiconductor substrates or those with locally different surface properties by factors like the emissivity of the surface material which form the signal background ΔT (x).

to Determining the local signal background .DELTA.T (x), there are various possibilities. Either it is determined by a measurement of the local temperature T (x) without preceding Warming of the Semiconductor substrate determined.

Or it is determined by _measuring the temperature T _measurement (x) at time t with a detector and the local signal background ΔT (x) at time t + Δt with another detector.

During the first detector is the sum of the effect of local heating, ie the actual Temperature increase, on the one hand and from surface effects on the other hand, the second detector measures when in a sufficient distance from the heat source is arranged, only the surface effects.

For the correction of the measured temperature T _measurement (x), a kind of mapping of the surface properties is thus carried out, from which the locally different signal background ΔT (x) results.

The signal background can thus be measured with the same device as the signal itself; even a simultaneous measurement of the signal background is possible. This results in the advantage of the method a significant time savings and a relatively low expenditure on equipment. Even complex software such as an image processing program can be dispensed with. Only simply provided options for storing the measurement data of temperature T _measurement (x) and signal background .DELTA.T (x) and for calculating the corrected signal T (x) and the difference D and for the comparison of D with the threshold T _S are necessary.

embodiments The invention will be described below with reference to the accompanying drawings explained in more detail.

1 a schematic side view of a device according to the invention for testing semiconductor wafers;

2a - 2d a plan view of the device at different times t ₁ to t ₄ ;

3 the local temperature T (x) at the position x on the semiconductor substrate at the same times t ₁ to t ₄ ;

4 an alternative embodiment of the device according to the invention;

5 a further alternative embodiment of the device according to the invention, which allows a possibility for correcting the measured temperature values on a local signal background.

Same Parts are provided in all figures with the same reference numerals.

1 shows a device 1 for testing a semiconductor wafer 6 cracks and similar damage. The device 1 has a holder 2 on top of the semiconductor wafer 6 stops during the testing process. In addition, the device includes 1 a test unit with a heat source 4 and a detector 5 as well as a movement unit 3 for moving the semiconductor wafer and the test unit relative to each other.

The heat source 4 serves for local heating of the semiconductor wafer 6 , The local temperature T of the semiconductor wafer 6 is using a pyrometer, which is the detector 5 includes, measured.

In the embodiment according to 1 lies the semiconductor wafer 6 on the bracket 2 up and will with the help of the movement unit 3 rotated about an axis through its center perpendicular to its surface. The test unit with the heat source 4 and the detector 5 is fixedly installed so that the semiconductor wafer 6 rotates under the test unit.

Particularly vulnerable to damage such as cracks is the edge area 7 of the semiconductor wafer 6 , Therefore, especially this border area 7 be checked for cracks, which is why the test unit with the heat source 4 and the detector 5 preferably over the edge area 7 is installed. But it can also be arranged to be movable, so that it is flexible for the inspection of the entire semiconductor wafer 6 can be used.

The 2a to 2d show in a plan view of the device 1 with the semiconductor wafer 6 the inspection process. The semiconductor wafer 6 according to 2a rotates about an axis through its center M at an angular velocity ω counterclockwise. The test unit with the heat source 4 and the detector 5 is stationary, with the heat source 4 and the detector 5 have a distance d to each other.

The semiconductor wafer to be tested 6 has a crack 8th whose detection is described below.

At a first time t ₁ is the crack 8th even before the heat source 4 and the detector 5 the test unit. Through the heat source 4 , which may be a light source, a heated gas or a sound source, for example, becomes the semiconductor wafer 6 locally heated. A short time later, the area heated at time t ₁ reaches the semiconductor wafer 6 the detector 5 , The detector 5 has, for example, a thermopile, which generates a voltage signal from the local temperature and in this way allows a measurement of the local temperature T.

2 B shows the constellation of test unit and crack 8th to each other at a second time t ₂ . By the rotation of the semiconductor wafer 6 with the angular velocity ω, the crack has 8th now moved on and is located between the heat source 4 and the detector 5 , At this time t ₂ , the detector registers 5 a further reading of the local temperature T. This second measured value T (t _2), as shown in 3 shown deviate from the previously recorded measured value T (t ₁ ).

At time t ₃ , the crack has 8th as in 2c shown further moved and is located just before the detector 5 , The crack 8th represents a kind of barrier to the process of heat conduction. The heat source 4 Heat introduced into the semiconductor substrate may propagate significantly worse over the crack than through the undamaged semiconductor substrate. Therefore, that is from the detector 5 at time t ₃ measured temperature T (t ₃₎ is typically relatively low.

Has the crack 8th however as in 2d shown below the detector 5 moved so that it is between the heat source 4 and the detector 5 no longer forms a barrier, the heat conduction can take place unhindered again. The at time t ₄ , the constellation in 2d is shown, measured temperature T (t ₄ ) is therefore comparatively high.

The measured at the times t _i temperatures T are as in 3 evaluated evaluated. Of the measured at two consecutive times t _i and t _{i + 1} temperatures T, the difference D is formed. If, between these times t _i and t _{i + 1,} the heat conduction properties of the semiconductor substrate between the heat source 4 and the detector 5 have not changed significantly, the temperature difference D is relatively low.

However, has a crack between the times t _i and t _{i + 1} 8th into the area between the detector 5 and the heat source 4 pushed or in particular he has under the detector 5 moved through and thus leave this area again, the heat conduction properties of the semiconductor substrate have changed significantly in this area. This is reflected in a relatively large temperature jump D such as in 3 at D = T (t ₄ ) -T (t ₃ ).

For detecting cracks, a threshold value T _{S is} set. The threshold value T _S is based on empirical values or on experiments with semiconductor wafers whose damage and heat conduction properties are precisely known. If the temperature difference D exceeds the threshold value T _S , then there has been a crack between the affected times 8th under the detector 5 moved through.

The difference D is not only a difference between temperature measurements at different times, but by the movement of the semiconductor wafer 6 at the same time a difference from temperatures at different points on the semiconductor wafer relative to the test unit 6 , It can therefore be written as D = T (x) - T (x ').

As an alternative to the temperature measurement at different times, the temperature T of the semiconductor wafer 6 also at the same time as in 4 can be measured with two detectors.

Another detector 9 is at a small distance d 'from the detector 5 arranged so that a point x on the semiconductor wafer first under the detector 5 and then under the other detector 9 moved through. However, the temperature measurement takes place simultaneously, while the detector 5 measures the temperature of the semiconductor wafer at point x, measures the other detector 9 the temperature at a point x 'at a distance from d' to x. The distance d 'should be at most 10 mm.

To evaluate the measured data, the difference D = T (x) - T (x ') is again formed. If it is above the predetermined threshold T _S, there is a split between the two detectors 5 and 9 ,

With the described method can be cracks in the semiconductor substrate detect very accurately. The procedure has the advantage that it is different than optical inspection methods also very fine cracks or oblique Cracks can be detected by the no or for a visual inspection too little light would penetrate. Because the heat conduction properties of the semiconductor substrate by cracks and similar damages relatively strongly influenced be the described method is very sensitive.

The local temperature T of the semiconductor wafer 6 is measured as described with one or more thermopiles. This measuring method is a pyrometric measuring method and is based on the fact that the heat radiation registered by the detector is independent of the temperature of the semiconductor wafer 6 depends. The temperature measurement thus takes place via the emitted infrared radiation and is thus contactless.

This has several advantages. On the one hand, the measurement can be carried out very quickly within milliseconds or microseconds, on the other hand there is neither a temperature influencing of the measurement object nor a mechanical damage of the sensitive wafer surface. Passing the semiconductor wafer 6 Under the test unit is thus easily possible.

However, the radiation emitted by the semiconductor wafer is influenced not only by the local temperature T but also by surface properties of the semiconductor wafer. In the case of semiconductor substrates which have a relatively high transmissivity in the infrared wavelength range, this can be done by the detector 5 also registered signal through the material, which is located on the detector 5 remote side of the semiconductor wafer 6 is affected.

For a particularly accurate inspection of a semiconductor wafer 6 Therefore, the measured local temperature T (x) can be corrected by the location-dependent signal background .DELTA.T (x). There are various possibilities for determining the signal background ΔT.

A first possibility is a pyrometric measurement of the temperature T (x) without prior heating of the semiconductor wafer 6 , In this way, when the heat source is switched off, a kind of mapping of the local signal background ΔT (x) can be carried out. However, this requires a separate process step and therefore a certain amount of time.

However, the measurement of the local signal background ΔT (x) can also take place at the same time as the actual test. 5 shows a plan view of a semiconductor wafer 6 with a test unit next to a heat source 4 and a detector 5 also another detector 9 for determining the signal background .DELTA.T. While the heat source 4 and the detector 5 have a distance from each other d, the further detector is located 9 at a distance d 'from the detector 5 arranged and behind this, leaving the detector 5 between the heat source 4 and the other detector 9 lies. So has the other detector 9 a greater distance from the heat source 4 as the detector 5 ,

The distance d 'is chosen such that the local temperature T at the position of the further detector 9 not or only slightly by the heat source 4 is affected. This corresponds to the other detector 9 recorded temperature signal the signal background .DELTA.T, which is used for correction by the detector 5 measured temperature value T is used.

1

contraption

2

bracket

3

moving unit

4

heat source

5

detector

6

Semiconductor wafer

7

border area

8th

Crack

9

Another detector

M

Focus

ω

angular velocity

d

distance

d '

distance

Claims (26)

Contraption ( 1 ) for testing semiconductor substrates for cracks ( 8th ), which has a holder ( 2 ) to the one or more semiconductor substrates, a test unit and a motion unit ( 3 ) for moving the semiconductor substrate and the test unit relative to one another, characterized in that the test unit has at least one heat source ( 4 ) for local heating of the semiconductor substrate and at least one pyrometer with a detector ( 5 ) for locally measuring the temperature of the semiconductor substrate. Apparatus according to claim 1, characterized in that as a detector ( 5 ) a thermopile is provided. Device according to claim 1 or 2, characterized in that the heat source ( 4 ) on the same side of the semiconductor substrate as the detector ( 5 ) is arranged. Device according to one of claims 1 to 3, characterized that the test unit stationary and the semiconductor substrate relative to the test unit is movably arranged. Device according to one of claims 1 to 4, characterized in that the heat source ( 4 ) and the detector ( 5 ) have a distance d from each other. Device according to one of claims 1 to 5, characterized in that it comprises a further pyrometer with a detector ( 9 ) disposed at a distance d 'from the first pyrometer. Device according to claim 6, characterized in that that the distance d 'at most 10 mm. Device according to one of claims 1 to 7, characterized in that at least one detector ( 5 ) is designed without imaging optics. Device according to one of claims 1 to 8, characterized in that as a heat source ( 4 ) A light source is provided. Device according to one of claims 1 to 8, characterized in that as a heat source ( 4 ) is provided a heated gas. Device according to one of claims 1 to 8, characterized in that as a heat source ( 4 ) A sound source is provided. Device according to one of claims 1 to 11, characterized in that as a semiconductor substrate, a semiconductor wafer ( 6 ) is provided. Apparatus according to claim 12, characterized in that the semiconductor wafer ( 6 ) is arranged rotatable about an axis through its center M perpendicular to its surface. Device according to one of claims 1 to 13, characterized in that the semiconductor substrate has a thickness of at most 1 mm. Device according to one of claims 1 to 14, characterized that the semiconductor substrate in the wavelength range between 1 .mu.m and 10 .mu.m, a transmissivity of at least 50%. A method of inspecting semiconductor substrates for cracks, comprising the steps of: locally heating the semiconductor substrate at a point y by a heat source ( 4 ); - Pyrometric measurement of the local temperatures T (x) and T (x ') of the semiconductor substrate at two different points x and x' on the semiconductor substrate; - calculation of the difference D = T (x) - T (x '); Comparing D with a predetermined threshold T _S ; Output a signal that has a crack ( 8th ) between the points x and x 'if D> T _S. The method of claim 16, wherein the temperature T is measured with one or more thermopiles. Method according to Claim 16 or 17, in which the temperatures T (x) and T (x ') coincide with two detectors ( 5 . 9 ), whereby a detector ( 5 ) the temperature T (x) at the point x and the further detector ( 9 ) measures the temperature T (x ') at point x'. Method according to one of Claims 16 to 18, in which the semiconductor substrate is moved relative to the stationarily arranged test unit such that the point x at a time t and the point x 'on the semiconductor substrate in a measuring window of the detector (z) at the time t'. 5 ) and T (x) at time t and T (x ') at time t' are measured. A method according to any one of claims 16 to 19, wherein the Semiconductor substrate about an axis through its center M perpendicular to its surface rotated at an angular velocity ω. Method according to one of Claims 16 to 20, in which the temperature T _corrected by the local signal background ΔT (x) is corrected to calculate the difference D instead of the measured temperature T (x) (x) = T (x) -ΔT (x) is used. Method according to Claim 21, in which the local signal background ΔT (x) is determined by a measurement of the local temperature T (x) without preceding Er heating of the semiconductor substrate is determined. The method of claim 21, wherein the local signal background ΔT (x) thereby it is determined that the temperature T (x) at time t with a detector and the local signal background .DELTA.T (x) at the time t + Δt is measured with another detector. Method according to one of claims 16 to 23, in which as a heat source ( 4 ) a light source is used. Method according to one of claims 16 to 23, in which as a heat source ( 4 ) a heated gas is used. Method according to one of claims 16 to 23, in which as a heat source ( 4 ) Sound waves are used.