DE102004050370B3 - Liner layer thickness measuring device for semiconductor wafer, has electron detector detecting electrons in analyzer region and emitting signals for several positions of analyzer, and unit receiving signals to determine layer thickness - Google Patents

Abstract

The device has an analyzer (34) arranged on a side of a semiconductor wafer (10) and including a material in a region. An electron detector (50) is arranged in a direction approximately lateral from the analyzer. The detector detects electrons emitted in the region and emits signals for several positions of the analyzer. A unit receives the emitted signals that are used for determining a layer thickness (26) of a liner layer.

Description

The The invention relates to a layer thickness measuring device for determining the layer thickness a liner layer. The invention also relates to methods for determination the layer thickness of one on one with the coating thickness gauge.

to Integrated circuit fabrication is commonly done on semiconductor wafers provided with different electrical properties layers applied and each lithographically structured. A lithographic Structuring step may consist of a photosensitive Apply Resist, this with a desired structure for the relevant Level to illuminate and develop, and then the thus resulting resist mask in the underlying layer in an etching step transferred to. The resist mask can also be used to create areas to define those targeted in a subsequent implantation step to be changed in their electrical properties.

The progressive miniaturization in semiconductor technology also the production of increasingly powerful electronic components. So can For example, dynamic random access memory (DRAM) is nowadays being manufactured which contain a plurality of memory cells. memory cells DRAM memory is usually used arranged in the form of a matrix on a semiconductor wafer. The memory cells usually consist of one storage capacitor and one each Selection transistor. In a read or write operation is the storage capacitor with an electrical charge, the corresponds to a respective data value via the selection transistor. or unloaded.

in the With the ever-decreasing structure resolutions, the manufacturing process has changed the memory cells established a structure in which the inner and outer capacitor electrode of the storage capacitor can be arranged in a deep trench. The inner capacitor electrode forms the storage node of the memory cell and becomes common by filling up the deep trench made with a conductive filler. at This known as a trench capacitor construction is by means of a so-called buried strap a connection of the inner capacitor electrode generated to the selection transistor. The selection transistor is for example as a planar transistor between the deep trenches of the memory cell array educated. But it is also known a structure in which the buried strap formed as a source or drain terminal of the selection transistor becomes. In these so-called vertical memory cells results a particularly space-saving design.

With the ever increasing integration densities of integrated circuits increase In general, the requirements for the dimensional stability of a on the semiconductor substrate to be formed structure to ensure the functionality of the circuit. This also relates to layer thicknesses of liner layers, as below explained becomes.

at the production of memory cells with trench capacitors often used so-called liner layers whose layer thicknesses while of the manufacturing process must be precisely controlled. So For example, on the side wall of the trench, which is a first Plate of the trench capacitor forms, a dielectric layer attached, which is also known as a dielectric. Then the ditch with a electrically conductive Material forming a second plate of the trench capacitor, filled, wherein the dielectric layer is the sidewall of the trench and the conductive material separates. This layer, which consequently contains the two plates of the Capacitor separates, for example, an oxide, a nitride or a sequence of oxide and nitride layers.

In subsequent process steps, for example, in the upper part of the trench along a side wall formed a collar, which sunk below is to form a recess. Inside the recess becomes the so-called buried strap formed, where previously the recess covered in a first step by another liner layer is to prevent the doping substances from the electrical conductive Buried strap laterally diffuse.

The layers described in the above two examples must have respect to their layer thickness be precisely controlled. For example, the former is Layer also for the value of the storage capacity responsible for the trench capacitor. The second liner layer is allowed For example, not too thin be.

Out US-A 6,002,740 a measuring device is known in which the transmission a perpendicular to a front side of a photomask incident X-ray to inspect the photomask.

In JP-A-09133521 shows a film thickness gauge in which X-rays an X-ray source over a Collimator penetrate a semiconductor wafer. The proportion of the transmitting X-ray is determined by means of an X-ray sensors determined.

In DE-A1-10242962 is a device for local determination of the layer thickness, in which samples are clamped in a sample holder so that they are exposed under irradiation of electron beams perpendicular to the beam axis, the samples being rotated perpendicular to and around the beam axis.

In Ch. Steinbach et al., "A Scanning Wire Beam Profile Monitor ", IEEE Transactions on Nuclear Science, Vol. NS-32, pages 1920-1922, will describe a detector that uses a thin metal wire moved through a particle beam to the profile of the particle beam to determine.

In US-A-3,175,083 shows a detector assembly comprising an X-ray target which emits electrons under the irradiation of X-rays. The X-ray target is outside arranged the detector for detecting the electrons.

The Controlling layer thicknesses in the nanometer range will be at future Technology generations to an increasingly dominant challenge become. Known measuring methods for controlling layer thicknesses are, for example, the investigation with a scanning electron microscope and a transmission electron microscopy (TEM) analysis. The two Although procedures achieve the necessary Resolution, But each have significant disadvantages in the analysis of vertical ins Substrate of a semiconductor wafer introduced layers. Both procedures are for one thing for the structure formed on the semiconductor wafer destructive, since for this purpose with both methods only cross sections of a semiconductor wafer can be measured. Second, measurements according to the two First-mentioned process very time consuming.

It Therefore, an object of the invention is a coating thickness gauge and a Offer a method for determining the layer thickness of a liner layer, which overcome the above problems.

• – einen Substrathalter, der geeignet ist, einen Halbleiterwafer aufzunehmen, wobei der Halbleiterwafer auf einer Vorderseite eine strukturierte Oberfläche mit Vorsprüngen oder Gräben aufweist, die an ihren im wesentlichen vertikal zur Vorderseite angeordneten Seitenwänden mit der Linerschicht bedeckt sind;
• – eine Röntgenquelle, die geeignet ist, eine erste Seite des Halbleiterwafers aus einer ersten Richtung mit Röntgenstrahlung zu bestrahlen, wobei die erste Richtung im wesentlichen parallel zu Seitenwänden der Vorsprünge angeordnet ist;
• – ein Analysator, der auf der der ersten Seite abgewandten zweiten Seite des Halbleiterwafers angeordnet und in einer zweiten Richtung verschiebbar ist, wobei der Analysator in einem ersten Bereich ein Material umfasst, das geeignet ist, in Abhängigkeit der von der Röntgenquelle einfallenden Röntgenstrahlung Elektronen zu emittieren;
• – ein Mittel zum Verschieben des Analysators entlang der zweiten Richtung;
• – einen Elektronendetektor, der seitlich vom Analysator ungefähr in der zweiten Richtung angeordnet ist und geeignet ist, die im ersten Bereich emittierten Elektronen nachzuweisen und für mehrere Positionen des Analysators jeweils ein Signal auszugeben; und
• – ein Mittel zum Empfangen der mehreren Signale, das geeignet ist, aus den mehreren Signalen die Schichtdicke der Linerschicht zu bestimmen.

This object is achieved according to the invention by a layer thickness measuring device for determining the layer thickness of a liner layer, comprising:

• A substrate holder adapted to receive a semiconductor wafer, the semiconductor wafer having on a front surface a structured surface having projections or trenches covered with the liner layer at their side walls substantially vertical to the front side;
• An X-ray source adapted to irradiate a first side of the semiconductor wafer with X-radiation from a first direction, the first direction being substantially parallel to sidewalls of the projections;
• An analyzer arranged on the second side of the semiconductor wafer facing away from the first side and displaceable in a second direction, the analyzer comprising in a first region a material which is suitable for emitting electrons in dependence on the X-ray radiation incident from the X-ray source ;
• A means for displacing the analyzer along the second direction;
• An electron detector disposed laterally of the analyzer in approximately the second direction and adapted to detect the electrons emitted in the first region and to output a signal for each of several positions of the analyzer; and
• - A means for receiving the plurality of signals, which is adapted to determine from the plurality of signals, the layer thickness of the liner layer.

According to the invention the structure to be measured is irradiated with an x-ray beam. The Liner has according to the laws of the Lambert-Beer law a weakening of the X-ray result. After passing through the sample, the X-ray hits to an analyzer into which an X-ray sensitive material is admitted. The re X-rays sensitive Material emits electrons when exposed to X-rays. These are analyzed by means of an electron detector, whereby the Analyzer is scanned under the sample by means of a controller. Depending on homogeneity the coverage or thickness of the liner layer arise on this Way for every position of the analyzer has certain electron intensities, the close to the edge covering to let. This allows a nondestructive Measurement of the layer thickness of the liner layer.

According to one preferred embodiment the means for moving the analyzer is a piezo controller.

According to this Course of action the analyzer is very precise at a fixed distance along the second direction parallel to the surface of the semiconductor wafer move. This can easily a variety of measurement points taken along the second direction, which is a precise survey allow the liner layer.

In a further preferred embodiment For example, the first section of the analyzer has an area that is approximately one nanometer is.

According to this procedure, preferably only X-rays within a small range in the analyzer with emission of Electrons detected in the electron detector. This allows accurate scanning of the X-ray penetrating the liner layer. Thus, the layer thickness of the liner layer can be determined with high accuracy.

According to one another preferred embodiment The analyzer includes a nano-tip, the first at its end Having region comprising electron-emitting material.

Nano-tips are used, for example, in atomic force microscopy (AFM = atomic force microscopy) used. The nano-tip is at its end in this embodiment first area provided with an electron-emitting material. This allows a simple and low-cost production of the analyzer the coating thickness gauge, in particular on the manufacturing technology of AFM technology resorted can be.

According to one another preferred embodiment The analyzer is formed as a plate that is in an interior area the first region with the electron-emitting material and in an outside area surrounding the interior, opposite X-rays includes inert material.

According to this embodiment For example, an inert material may be the carrier for the actual X-ray form sensitive first area. The arranged in the first region electron-emitting Material can be easily applied to this carrier. Thus is it is possible a cost-effective and simple analyzer in the coating thickness gauge, without expensive and difficult-to-manufacture elements of nano-technology instructed to be.

In a further preferred embodiment corresponds to the first side of the semiconductor wafer of the front of the semiconductor wafer.

According to this The procedure is provided with projections or trenches surface of the semiconductor wafer aligned in the direction of the X-ray source.

According to one another preferred embodiment The second side of the semiconductor wafer corresponds to the front side of the semiconductor wafer.

Usually have trenches for example, a trench capacitor of a DRAM memory device a depth of about ten Micrometer up. The thickness of the semiconductor wafer is at least about an order of magnitude higher. Because the x-rays after penetrating the liner layer still the complete semiconductor wafer to the back could go through interferes with noncoherent Radiation or reflections on sidewalls noticeable. By the reversal of the beam direction radiates through the x-ray radiation the semiconductor wafer from the back. This reduces the effect of the long ways, that of the X-rays must be covered in the substrate of the semiconductor wafer, so that overall a higher one Accuracy can be achieved.

• – Bereitstellen des Schichtdickenmessgeräts;
• – Bereitstellen des Halbleiterwafers, wobei der Halbleiterwafer auf der Vorderseite eine strukturierte Oberfläche aufweist;
• – Durchführen einer ersten Messung, wobei mit dem Mittel zum Empfangen die mehreren Signale als erste Messergebnisse abgespeichert werden;
• – Abscheiden einer Linerschicht auf der Vorderseite des Halbleiterwafers;
• – Durchführen einer zweiten Messung, wobei mit dem Mittel zum Empfangen die mehreren Signale als zweite Messergebnisse abgespeichert werden;
• – Subtraktion der ersten Messergebnisse von den zweiten Messergebnissen zur Bestimmung von dritten Messergebnissen; und
• – Bestimmen der Schichtdicke der Linerschicht aus den dritten Messergebnissen.

The object is also achieved by a method for determining the layer thickness of a liner layer of a semiconductor wafer with a layer thickness gauge, the following steps being carried out:

• - Providing the coating thickness gauge;
• Providing the semiconductor wafer, wherein the semiconductor wafer has a structured surface on the front side;
• - performing a first measurement, wherein the means for receiving the plurality of signals are stored as first measurement results;
• Depositing a liner layer on the front side of the semiconductor wafer;
• - Perform a second measurement, wherein the means for receiving the plurality of signals are stored as second measurement results;
• - subtracting the first measurement results from the second measurement results to determine third measurement results; and
• Determining the layer thickness of the liner layer from the third measurement results.

at the method according to the invention the semiconductor wafer is subjected to a first layer thickness measurement, being on the front with the textured surface still no Li nerschicht is applied. This is done after the first measurement Depositing the liner layer, and a second measurement is performed. By Difference can be influenced by a roughened back of the semiconductor wafer are eliminated, so that as a result only the change resulting from the sidewall coating.

Further preferred embodiments are in the subclaims specified.

The The invention will now be described with reference to the accompanying drawings. In show the drawing:

1 schematically a cross-sectional view of a layer thickness gauge according to the invention in a first embodiment;

2 schematically a cross-sectional view a coating thickness gauge in a second embodiment;

3 schematically in a cross-sectional view of a film thickness gauge in a third embodiment;

4 schematically in a cross-sectional view of a film thickness gauge in a fourth embodiment;

5A and 5B schematically gray level representations of the measurement results in the determination of the layer thickness of the liner layer for a uniform sidewall coverage and an uneven sidewall coverage; and

6A and 6B schematically a cross-sectional view of another possible embodiment of the layer thickness gauge according to the invention, wherein in each case schematically different stages of the method for determining the layer thickness are shown.

The Invention will be exemplified below for a film thickness gauge and a Method for determining the layer thickness of a on a vertical to the surface a semiconductor wafer applied to the liner layer thickness measuring device in the Production of trench-shaped Structures on a semiconductor wafer explained. In these trench-like structures, which themselves are not the subject of the invention, it may, for example, to Trench capacitors in DRAM production act.

The Invention leaves but also for use other objects for which the layer thickness gauge is used Layer thickness of one on a vertical to the surface of a semiconductor wafer applied liner layer with high accuracy and non-destructive should be determined. Exemplary here are integrated circuits for logic modules or generally other thin film technology products, such as e.g. TFT displays cited.

In 1 is a schematic cross section through a coating thickness gauge 5 with a semiconductor wafer 10 shown. The semiconductor wafer 10 is on a substrate holder 18 stored. The semiconductor wafer 10 is at least partially on the front 12 with a regular pattern of protrusions 14 provided, for example, by a circuit pattern of a random access memory device (DRAM). The semiconductor wafer 10 is on the front 12 with a liner layer 16 Mistake. In the liner layer 16 it may be, for example, an oxide or nitride or a combination of oxide and nitride layers. The liner layer 16 is formed for example by conformal deposition and has a layer thickness 26 on.

As explained at the beginning are for example in DRAM production trenches with a depth of about 10 microns with trench widths of about 100 nanometers often with a liner layer in the range of a few nanometers lined.

Above the textured front 12 is an x-ray source 20 appropriate. The X-ray source 20 irradiated the front 12 of the semiconductor wafer 10 from a first direction 22 with x-rays. The first direction 22 is substantially parallel to the side walls of the projections 14 selected. The front 12 thus defines a first page 30 of the semiconductor wafer 10 which is irradiated with X-rays.

Because the steepness of the side walls of the projections 14 Usually is controlled so, for example, in an etching process that the side walls are arranged vertically, the X-ray source 20 usually perpendicular to the first page 30 of the semiconductor wafer 10 aligned. The first direction 22 is thus substantially perpendicular to the front 12 of the semiconductor wafer 10 ,

On the front side facing away from the back of the semiconductor wafer 10 is an analyzer 34 arranged. The analyzer 34 is along a second direction 24 slidably, the terwafers at normal incidence of X-rays along the first direction substantially parallel to the surface of the semicon 10 is arranged. The back of the semiconductor wafer 10 thus defines a second page 32 about which the analyzer 34 is displaceable substantially at a constant distance. This is a means to move the analyzer 34 provided, for example, a piezo-control 42 includes.

The analyzer 34 includes in a first area 38 a material that under the action of the X-ray source 20 incident X-rays emit electrons. The material of the first area 38 may be plastic, for example.

As in 1 shown is the material in the first area 38 of the analyzer 34 Part of a plate 36 that is slightly opposite the second direction 24 is inclined. The inclination of the plate 36 is chosen so that the from the x-ray source 20 emitted X-radiation on the first area 38 meets without the plate 36 to go through. For example, there is an inclination of 45 degrees, as in 1 shown, sufficient.

The plate 36 is in the outside of the first area 38 defined interior area formed by an outdoor area, which forms a second area 40 Are defined. Preferably, the material is selected to be inert in the outer region as compared to X-rays. As inert material are all materials in question, which emit significantly fewer electrons when irradiated with X-rays compared to the first area. This construction ensures that essentially only the first area 38 attached material emits electrons.

The first area 38 emitted electrons are emitted by an electron detector 50 detected along the second direction 24 is arranged. Electron detectors are all known detectors which make it possible to convert incident electrons into an electrical signal. Examples are photomultipliers or semiconductor detectors, but other detectors known to those skilled in the art are not excluded.

It should be emphasized at this point that the electron detector 50 need not have any precise spatial resolution capabilities for the incident electrons. The spatial resolution and thus the ability to change the layer thickness 26 the liner layer 16 It is determined by the interplay of the size of the first area 38 and moving the analyzer 34 achieved. The first area 38 For example, it may have an extension of about five nanometers, but smaller areas such as one nanometer are also possible.

The electron detector 50 is with a means for receiving the signals of the electron detector 52 connected, which may be, for example, a microprocessor circuit by means of an analog-to-digital converter with the electron detector 50 connected is. The means for receiving the signals registered for each position of the analyzer 34 along the second direction 24 a signal. The analyzer 34 thus, gradually scans the semiconductor wafer 10 penetrating X-ray radiation.

When the analyzer 34 located in a position through a line through the liner layer 16 is described by the electron detector 50 emitted signal proportional to the attenuation of the X-ray radiation through the semiconductor wafer 10 and thus through the liner layer 16 , Due to the different signal strengths can be from any position of the analyzer 34 on the uniformity of the covering of the side walls of the projections 14 and thus on the layer thickness 26 the liner layer 16 be closed back.

In 2 In a further embodiment, this is a cross-sectional view of the layer thickness measuring device according to the invention 5 shown. The coating thickness gauge 5 according to the embodiment of the 2 differs from that according to the 1 only by the positioning of the semiconductor wafer 10 , The X-ray source 20 , the analyzer 34 as well as the electron detector 50 have remained unchanged in their arrangement. In the following, only the differences from the execution according to 1 described.

As in 2 the semiconductor wafer is shown 10 aligned so that its front 12 in the direction of the analyzer 34 shows. The X-rays emitted by the X-ray source 20 is emitted, radiating through the semiconductor wafer 10 from the back. Since usually the semiconductor wafer 10 much thicker than the protrusions 14 are high, it is possible that in the substrate of the semiconductor wafer 10 scattered X-rays in the first area 38 of the analyzer 34 to meet.

Due to the reversal of the positioning of the semiconductor wafer 10 in the embodiment according to 2 is the way from the liner layer 16 to the analyzer 34 reduced. This reduces interference by non-coherent radiation in the substrate of the semiconductor wafer 10 and influences, for example, by reflections on the side walls of the projections 14 can arise. The use of a very small area of the first area 38 moreover reduces interfering influences by adjacent structures of the semiconductor wafer 10 ,

Another embodiment of the coating thickness gauge 5 is in 3 shown. Again, only the differences are compared to 1 explained, so that also to the above remarks in connection with the discussion of 1 is referenced.

The layer thickness measuring device according to 3 differs from the embodiments shown so far by a different structure of the analyzer 34 , As in 3 is shown for the analyzer 34 no plate used, but a so-called nano-tip 44 , Nano-tips 44 are known for example from the RFM technique and are used for atomic force microscopy. The nano-tip 44 For example, it can be constructed from a tube only a few nanometers thick, at the top, the semiconductor wafer 10 facing end, the first area 38 is arranged with the electron-emitting material. It is of course also conceivable that the entire nano-tip 44 the electron-emitting region 38 represents. In 3 is the semiconductor wafer 10 turn so shown that its front 12 the X-ray source 20 is facing.

In 4 is a fourth embodiment of the Coating thickness gauge 5 shown. The layer thickness measuring device according to 4 in turn uses the nano-tip 44 as an analyzer 34 , The semiconductor wafer 10 becomes from its back with X-rays from the X-ray source 20 irradiated. Thus, the structure is similar to that in the layer thickness measuring device 5 according to 2 , Furthermore, a piezo-control is schematically shown 42 shown that also with the means 52 connected to receive the signals. Thus, in a simple way, the signals of the electron detector 50 and the position of the nano-tip 44 be correlated.

As already explained above, the correlation of these two measured values results in an intensity image from which the coverage and layer thickness are calculated 26 the liner layer 16 can be concluded.

This is with reference to the 5A and the 5B explained again.

5A shows a first intensity profile 54 How to obtain it when the layer thickness of the liner 16 homogeneous over the sidewalls of the projections 14 is applied.

In 5B On the other hand, a measurement result is shown in which the liner layer 16 For example, has gaps or has a very inhomogeneous surface.

During the first intensity course 54 to 5A is substantially rectangular, and thus follows the layer thickness of the liner, is the second intensity profile 56 to 5B to the surface of the liner layer applied along the sidewall of the protrusion 16 rounded down. By evaluating these grayscale images can thus easily on the quality of a deposition process to form the liner layer 16 be closed back.

Interference in the determination of the layer thickness 26 the liner layer 16 For example, it may also result from the back side of the semiconductor wafer 10 has a roughened surface. However, by means of the method according to the invention, its contribution can be eliminated in a simple manner, as described below in connection with FIG 6A and the 6B is explained.

In 6A is in turn a coating thickness gauge, for example, in one embodiment according to 1 shown. On the substrate holder 18 is the semiconductor wafer 10 filed, wherein the semiconductor wafer 10 on its back, the second side 32 facing, a roughened surface 58 having. The roughened surface 58 results in different intensities when moving the analyzer 34 along the second direction 24 without any inhomogeneities of the liner layer 16 must be present.

In order to eliminate these disturbing influences, in a first step of the method according to the invention, the layer thickness measuring device 5 provided as in 6A will be shown.

Subsequently, the semiconductor wafer 10 provided, wherein the semiconductor wafer 10 on the front side 12 has a textured surface. During this process step, however, the semiconductor wafer does not yet have a liner layer 16 on.

In the following, a first measurement is carried out in a further step, wherein the means 52 to receive the signals stores them as the first measurement results.

The semiconductor wafer 16 is below with the liner layer 16 on the front of the semiconductor wafer 10 provided, for example, by conformal deposition.

In the next step, a second measurement is performed, the mean 52 for receiving the multiple signals stores them as second measurement results.

Subsequently, in a further step, a third measurement result is determined by subtracting the first measurement results from the second measurement results. The layer thickness 26 the liner layer 16 is determined below from the third measurement results.

In summary, therefore, a pre- and a final measurement is performed, whereby by subtraction the influence of the roughened surface 58 the back of the semiconductor wafer 10 is eliminated. By the difference formation is only the change due to the coating of the side walls of the projections 14 with the liner layer 16 considered. This allows a very precise measurement of the sidewall coating.

5

Coating Thickness Gauge

10

Semiconductor wafer

12

front

14

projections

16

liner layer

18

substrate holder

20

X-ray source

22

first direction

24

second direction

26

layer thickness

30

first page

32

second page

34

analyzer

36

plate

38

first Area

40

second Area

42

piezo control

44

Nano-tip

50

electron detector

52

medium for evaluation

54

first Grayscale image

56

second Grayscale image

58

back

Claims (1)

Coating thickness gauge for determining the layer thickness of a liner layer, comprising: - a substrate holder ( 18 ), which is suitable for a semiconductor wafer ( 10 ), wherein the semiconductor wafer ( 10 ) on a front side ( 12 ) a structured surface with protrusions ( 14 ) or trenches which are at their substantially vertical to the front ( 12 ) arranged side walls with the liner layer ( 16 ) are covered; An X-ray source ( 20 ), which is suitable for a first page ( 30 ) of the semiconductor wafer ( 10 ) from a first direction ( 22 ) with X-rays, the first direction ( 22 ) substantially parallel to side walls of the projections ( 14 ) is arranged; An analyzer ( 34 ), which is on the first page ( 30 ) facing away from the second side ( 34 ) of the semiconductor wafer ( 10 ) and in a second direction ( 24 ) is displaceable, the analyzer ( 34 ) in a first area ( 38 ) comprises a material which is suitable as a function of the X-ray source ( 20 ) incident X-rays emit electrons; A means for moving the analyzer ( 34 ) along the second direction ( 24 ); and - an electron detector ( 50 ), the side of the analyzer ( 34 ) approximately in the second direction ( 24 ) is arranged and suitable in the first area ( 38 ) and for several positions of the analyzer ( 34 ) each output a signal; and - a means for receiving ( 52 ) of the plurality of signals that is suitable, from the plurality of signals the layer thickness ( 26 ) of the liner layer ( 16 ).