Optical measuring method for ultra-thin layers e.g. polymer films

The invention relates to a method for the optical determination of chemical and physical Properties of ultra-thin layers, such as the chemical structure of molecules of the Arrangement of the molecules to each other and to a surface and for determining the thickness of the Molecular layer and the refractive index according to claim. 1

The invention further relates to a device for performing the method according to Claim. 13

To characterize thin films microscopic method for imaging acquisition are the topology of the sample and structure group specific methods for the study of Behavior of selected sample segments used. For the group-specific structure Investigations come spectroscopic and electrochemical methods are used. In particular, the investigation of very thin, mostly monomolecular films proves to be great Difficulty. Here, many studies focus on the characterization of Self- Assembly-layers.

In Langmuir, Vol. 14, 1998, for example on pages 808-815, 660-666 and 821-824, the Study the topology of SA-layers by atomic force microscopy (AFM) or described tunneling microscopy (STM). These methods allow the homogeneity of Layers investigate well. The chemical properties of such molecules and the connection Bonds between the molecules do not show up.

are also in Langmuir, Vol. 14, 1998, pages 17-30 and pages 113-123 by high-resolution transmission electron microscopy (TEM), the topological properties and restricted the chemical bonds investigated. Using these methods, the properties are the layer is usually detected without surface resolution. With the X-ray photoelectron Spectroscopy (XPS) can be the connection of the polymeric chains on the basis of electronic demonstrate state of the atoms. For XPS investigations into the sample must however High vacuum are transferred.

Using FTIR spectroscopy can be the individual structural groups of thin polymeric layers isolated characterize. The particular advantage of FTIR studies is that under in situ Conditions can be worked. To improve the detection limit is investigated smallest sample quantities like in reflection with grazing incidence. SA-layers may also be be characterized by FTIR measurements with polarized light. surface resolved Investigations of selected structural groups are possible by FTIR microscopy. The use is for chemical imaging in complex samples apart from the time factor especially limited by the superposition of the information in the IR spectrum. available for civilian applications until very recently, array detectors for imaging FTIR spectroscopy available. About the study of polymer layers with this technique are the proprietor of the Literature still not aware of any work. The previously published studies come from the medical field. In Nature Medicine, Vol. 3, 1997, pages 235-237 is z. B. the study of the interface between cell tissues and implants using imaging Infrared spectroscopy described.

The surface plasmon resonance is a very sensitive method for the characterization of dielectric properties of ultrathin layers and thickness determination in these Layers. Large distribution, the surface plasmon resonance in the biochemical Analysis found. The surface plasmon resonance is increasingly used for Characterization of polymer layers used. Trends in Polymers Science (TRIP), Vol. 2, 1994, Pages 313-323, the potential of the surface plasmon resonance is used to characterize very fine polymer films described.

Applications of surface-resolution surface plasmon resonance with the use of Array detectors are, for example, in Analytical Chemistry, Vol 70, 1998, pages 703-706. Vol. 69, 1997, pages 1449 to 1456 and pages 4939-4947 described.

In EP 0341927 A1 a sensor for surface plasmon resonance is used, the areally the sample (z. B. bound antibodies) scans. The screening is a achieved movable concave mirror. The sample is not the same structure sensitive to a Method examined by area and there is no array detection for surface plasmon Resonance used.

Compared to EP 0,341,927 A1, EP 0341298 A1, the adjustment of the angle with which the light on the surface plasmon resonance occurs to better resolved. This allows a better Signal are obtained.

In EP 0732583 A2 a method of surface-enhanced fluorescence is described metal clusters and their use in biosensors, as well as methods for preparing the Cluster. There is no investigation by surface plasmon resonance, no strukturguppenspezifische detection and no chemical mapping of the sample.

In US 4,877,747 observations of surface plasmon resonance are described, also with Metal clusters, as well as methods for the preparation of the cluster. There is no strukturguppenspezifische detection and no chemical mapping of the sample.

DE 24 56 452 A1 describes the investigation of surfaces by illumination with light, preferably visible light, wherein the surface by scanning (moving the sample) is examined. There is no FTIR spectroscopy, no polarization-modulated FTIR Spectroscopy to study the chemical structure, no detection of the thickness of the Sample. The method is not suitable for ultra-thin layers.

US 5,255,075 A describes the analysis of a sample with reflected light. There is no Surface resolution and any combination of two optical methods.

WO 92/03720 A1, DE 196 50 899 A1 and DE 43 15 211 A1 describe the application Surface plasmon resonance, but without a surface resolution. There is no application area-resolved methods or structurally sensitive methods.

The object of the invention is now, by a method and an arrangement area-resolved information on layer thickness and connectivity, order and orientation of the Molecules constituting the ultra-thin film on a substrate to be obtained.

The object is achieved by a method having the features mentioned in claim. 1 Advantageous process variants are evident from the accompanying dependent claims.

The object is further achieved by a device having the features mentioned in claim 13 dissolved. Advantageous developments and refinements emerge from the subclaims.

According to the method for the optical determination of chemical and physical properties ultrathin layers the layer one on an optically transparent substrate with thin noble metal layer for the excitation of surface plasmons is simultaneously the optical molecular spectroscopy and surface plasmon resonance subjected. The Molecular spectroscopy and surface plasmon resonance can be resolved by area conducted sampling or by imaging the layer. The from the optical Molecular Spectroscopy spectra obtained are using special mathematical evaluated algorithms and from the binding of the molecules on the surface, which Orientation and functionalization determined. By means of surface plasmon resonance the thickness of the layer and / or the dielectric properties determined. The of the partial steps Values ​​obtained are superimposed, and from this, the chemical and physical properties in a particular area of ​​the layer surface dissolved shown.

is arrangement According to an optically transparent substrate, a prism for depositing the thin Noble metal layer provided with the ultra-thin layer. Based on the layer below is this provided an arrangement for measurement of surface plasmon resonance. Furthermore, based on the layer above or below this an arrangement for optical Spectroscopy provided. These two assemblies are associated with detectors with a Evaluation means for calculating the chemical and physical properties associated are, so that a specific region of the layer surface is represented dissolved.

Advantageously, the ultra-thin film with polarized infrared light and simultaneously with visible light by utilizing the surface plasmon resonance investigated. Here is a rapid change in the polarization direction appropriately.

This is accomplished by the use of a polarizer and an electro-optical polarization modulator achieved, the linearly polarized IR light changes very quickly in the direction of polarization. The IR Light is advantageously steered by deflecting the layer. The light reflected from the sample IR light is via a further deflecting mirror a sensitive infrared detector array supplied. The bundle of rays for excitation of the surface plasmon resonance is at the Boundary layer between optical substrate and metal layer is totally reflected. The reflected Radiation falls on a detector array for visible light. The combination of both Images can be derived the properties of the thin layer with very high resolution.

The advantage of the invention is that the from the concurrent use of a method optical molecule spectroscopy and a method of surface plasmon resonance to ultra-thin layers, they can be observed with an information gain, the Information gain in the statement about the order and orientation of mono- and Multi layers. The statement can be represented pictorially surface dissolved, resulting in can draw conclusions about the usefulness of ultrathin layers (eg. as a primer).

The invention will be explained in more detail by exemplary embodiments. In the drawings show:

<b>Fig.</b> 1 is a schematic representation of a first variant of a device according to the invention

<b>Fig.</b> 2 is a schematic representation of a second variant of a device according to the invention

<b>Fig.</b> 3 is a schematic representation of a third variant of a device according to the invention

<b>Fig.</b> 4 is a schematic representation of a fourth variant of an apparatus according to the invention

<b>Fig.</b> 5 is a schematic representation for illustrating the processing of the signals from the Detectors of the two sub-arrays

<b>Fig.</b> 6 is a schematic representation to illustrate the method according to the detection of the layer

<b>Fig.</b> 1 shows a first variant of a device according to the invention. The test sample is in the form of a layer <b>1</b> on a noble metal layer <b>7</b> applied. The noble metal layer<b>7</b> lies on a prism <b>8th</b> on, which serves as the optically transparent surface. is in the representation above the layer <b>1</b> an arrangement for optical spectroscopy shown. Below the layer<b>1</b> is an arrangement for surface plasmon resonance shown.

In the beam path direction is the arrangement for optical spectroscopy (above layer <b>1</b>) From a light source (not shown), a polarizer <b>3</b>, An electro-optic polarization modulator <b>4</b>, A first deflection mirror <b>5</b>(Layer <b>1</b>), A second deflecting mirror <b>5</b> and a detector <b>6</b>,

In the beam path towards the arrangement is to the surface plasmon resonance (below the layer <b>1</b>) From a light source (not shown) that a parallel beam <b>9</b> produced a prism <b>8th</b>, A thin layer of precious metal <b>7</b> and a detector <b>10</b>, Shown is also in strong simplified manner, an XY adjustment <b>12</b>With which the prism <b>8th</b> (With the precious metal layer <b>7</b> and the layer <b>1</b>) Adjusted against the two beam paths of the two sub-arrays can be.

<b>Fig.</b> 2 shows a schematic representation of a second variant of an inventive Device. Compared to the<b>Fig.</b> 1 is in the beam path of the optical arrangement Spectroscopy (above layer <b>1</b>) A first lens <b>11</b> after the first deflection mirror <b>5</b> and a second lens <b>11</b> before the second deflecting mirror <b>5</b> provided. With the XY-adjustment<b>12</b> , the prism <b>8th</b> (With the precious metal layer <b>7</b> and the layer <b>1</b>) Relative to the focal point of the Lenses can be adjusted.

<b>Fig.</b> 3 shows a schematic representation of a third variant of an inventive Device. Opposite to<b>Fig.</b> 2 accounts for the two lenses <b>11</b> and the XY-adjustment <b>12</b>, At Location of a detector <b>6</b> is an array detector <b>6</b>'Are provided.

<b>Fig.</b> 4 shows a schematic representation of a fourth variant of an inventive Device. The layer<b>1</b> is considered by both methods from below. Compared to the representations in <b>Fig.</b> 1 to 3, the measurement with the polarized infrared light by Attenuated total reflection prism at the boundary layer <b>8th</b> - layer <b>1</b>, To stimulate the Surface plasmons are instead of continuous precious metal layer <b>7</b> metal clusters <b>7</b>' With Dimensions used in the nanometer range. The metal clusters<b>7</b>'Can simultaneously optical resonance amplification of the infrared spectra are used.

In <b>Fig.</b> 5 is shown schematically how the signal processing by the two detectors <b>6</b>.<b>10</b> takes place.

<b>Fig.</b> 6 serves to illustrate the method according to the detection of the layer <b>1</b>,

For the investigation of very thin layers is a rapid change in the polarization direction expedient. This is accomplished by the use of a polarizer<b>3</b> and an electro-optic polarization modulator <b>4</b> achieved, the linearly polarized infrared light very quickly Polarization direction changes. According to the<b>Fig.</b> 2 is the IR radiation <b>2</b> having a first lens <b>11</b> very finely on the layer <b>1</b> focused. The reflected radiation from the layer surface is from a second lens <b>11</b> collected and via a deflection mirror <b>5</b> the detector <b>6</b> supplied. At the same time, the layer <b>1</b> from the bottom to the surface-resolution surface plasmon Resonance, by a noble metal layer on the <b>7</b> reflected parallel beam <b>9</b>, that from a detector <b>10</b>, A CCD detector is intercepted, examined. The beam<b>9</b> becomes at the interface between the prism <b>8th</b> and precious metal layer <b>7</b> totally reflected. The space resolution the polarization-modulated IR radiation <b>2</b> is by scanning the layer <b>1</b> means an XY adjustment <b>12</b> reached.

In the <b>Fig.</b> 3, the area resolution of the polarization-modulated infrared radiation <b>2</b> through a Infrared array detector <b>6</b>'Made. For this purpose, the layer<b>1</b> with a parallel, polarization modulated radiation beam of IR radiation <b>2</b> a first deflecting mirror <b>5</b> illuminated. The reflected parallel beams is a further deflection mirror<b>5</b> the array detector <b>6</b>'Is supplied.

According to the <b>Fig.</b> 5 is of the IR-detector as a detector <b>6</b> recorded polarization modulated IR radiation <b>2</b> via a multiplexer <b>13</b> separated into two signals. Of the DC component of the signal is with an electronic filter <b>14</b> separated and a computer <b>16</b> supplied for further processing. The alternating component of the signal by the modulation of the Polarization direction through the polarizer <b>3</b> and the polarization modulator <b>4</b> arises is with a special amplifier <b>15</b> selectively amplified and also the computer <b>16</b> supplied. From the two spectra can the information of interest are read out. The DC can also be used as a reference, so that disturbances of the measurement process hidden will. The image signal of the CCD detector as the detector<b>10</b> directly to the computer <b>16</b> supplied.

The principle of data processing and image combining shows, as described above, <b>Fig.</b> . 5 The infrared spectra obtained for each pixel are a chemometric Evaluation algorithm supplied. This algorithm calculates prior modeling special chemical and physical properties of the layer <b>1</b> from the infrared spectra. These Properties are calculated individually for each pixel, and give a composed Overall picture of the distribution of certain characteristics in the investigated layer surface. In a following step is the image of Oberlächenplasmonen resonance added taken by the A special method of contrast and resolution of the depicted chemical and physical properties can be improved.