BRIEF DESCRIPTION OF THE DRAWINGS
The drawings schematically show the subject matter of the present invention which will be described with reference to the accompanying drawings, in which:
FIG. 1 is a schematic representation of the apparatus for height measurement of a structured substrate by means of the confocal principle according to the state of the art;
FIG. 2
a is a schematic representation of the apparatus according to the present invention for scanning the surface of a semiconductor substrate on a line-by-line basis, wherein the slot-shaped aperture is oriented in the Y direction;
FIG. 2
b is a schematic representation of the apparatus of the present invention for scanning the surface of a semiconductor substrate on a line-by-line basis, wherein the slot-shaped aperture is normal to the X direction;
FIG. 3
a is a schematic representation of the two-dimensional detector used for height measurement, for example a CCD chip or a CMOS chip, wherein the different wavelengths are detected at different locations x. The wavelength spectrum for different points in the X direction is plotted in the Y direction.
FIG. 3
b is a schematic representation of a height profile, wherein the height of the wafer at location x can be derived from the y position of the intensity maximum;
FIG. 4 is a schematic representation of the arrangement and relative movement of the semiconductor substrate, the white-light illumination and the illumination spot and the slot-shaped aperture, respectively;
FIG. 5
a is a schematic representation of three structures having different heights on a semiconductor substrate, wherein each height is simultaneously detected by using a white-light illumination spot and the slot-shaped aperture; and
FIG. 5
b is a schematic representation of a plan view of three structures having different heights on a semiconductor substrate.
DETAILED DESCRIPTION
Equivalent features and elements in different views of the drawings have been designated with the same reference numerals for clarity.
FIG. 1 shows a schematic representation of an apparatus for the height measurement of a structured substrate by means of the confocal principle according to the state of the art (source: SPIE's 46th Annual Meeting, San Diego, USA, 2-3 Aug. 2001, Paper by the Stil Firm). A point-shaped white-light source 3 is projected onto surface 5a of substrate 5. Projecting lens 7 has strong chromatic aberrations, i.e. the light of the source having different wavelengths, shown as 11.1, 11.2 and 11.3, is imaged onto different planes. If the light reflected from surface 5a of substrate 5 is imaged, via a beam splitter 9, onto a point-shaped aperture 30, having its distance held constant to beam splitter 9, light of only one wavelength 11.2 passes into spectrometer 15. The light from other wavelengths 11.1 and 11.3 is not focused on a point of surface 5a of structured substrate 5 and is therefore greatly attenuated and impinges on point-shaped aperture 13 as a light spot. When the chromatic aberrations of the projecting lens 7 are known, the current height of substrate 5 can be derived by a measurement in spectrometer 15. It must be noted, however, that only those wavelengths which fulfill optimum focus conditions (11.2) are imaged in the spectrometer with the greatest intensity. The current height of the substrate can therefore be determined from an intensity measurement of each wavelength.
Since the wavelength correlates with the height on the substrate, the structural height can be concluded from a wavelength measurement. To achieve this, the light is spectrally split up and imaged on a CCD row. Each dot on the row therefore corresponds to a certain height of the structure on the substrate.
FIG. 2
a is a schematic representation of the apparatus according to the present invention for measuring the height profile. The light of a white-light source 3 is parallelized with the aid of a lens system 17 in the illumination beam path 16 and projected onto surface 5a of a substrate 5 preferably in the form of a slot-shaped illumination spot via a beam splitter 9 and a focusing lens system 7. Lens system 7 has a strong chromatic aberration, so that light of different wavelengths is imaged onto different planes of substrate 5. A precise description of the focused planes will be given with reference to FIG. 5. Beam splitter 9 directs the light reflected from surface 5a of substrate 5 in detection beam path 18 with lens system 19 first onto slot-shaped aperture 21 and then onto detector 29 via lens system 25, wherein aperture 21 only passes light beams of wavelengths fulfilling the focus conditions of a line-shaped section of surface 5a (cf. FIGS. 5a, 5b). The light emitted by slot-shaped aperture 21 is directed via a grid 23 normal to the X direction, and detected by a two-dimensional detector 29, wherein different locations of the spectral components on the substrate 5 are obtained even though grid 23 is still a dispersive element. Since only light of one wavelength passes grid 23 in this case, there is no spectral dispersion. Slot-shaped aperture 21 is oriented in the Y direction in the present figure, is therefore directed out of the paper plane, so that only the aperture frame is visible in the present figure. 27.1 and 27.2 designate two light beams of different locations of equal height on a line section of surface Sa of structured substrate 5 or in two-dimensional detector 9. A line of a plurality of dots on planes of the same height and the same wavelength on the detector is therefore imaged.
FIG. 2
b is another schematic representation of the apparatus according to the present invention for measuring the height profile. 11.1 and 11.2 in FIG. 2b designate light beams of different wavelengths or colors of different locations in different planes on surface 5a of substrate 5, which fulfill the focus conditions. FIG. 2b is rotated by 90° in the X direction with respect to FIG. 2a in order to illustrate the correlation between the wavelength or color and a location illuminated by the white-light spot on structured substrate 5.
The light emitted by white-light source 3 is parallelized with a lens system 17 in illumination beam path 16 and projected onto surface 5a of a structured substrate 5 preferably in the form of a slot-shaped illumination spot via a beam splitter 9 and a focusing lens system 7. Lens system 7 has strong chromatic aberration, so that light of different wavelengths is imaged onto different planes of substrate 5. A precise description of the focused planes will be given with reference to FIGS. 5a and 5b. Beam splitter 9 first directs the light reflected from surface 5a of substrate 5 in detection beam path 18 with lens system 19 onto slot-shaped aperture 21 and grid 23, and then onto detector 29 via lens system 25, wherein aperture 21 only passes light beams of wavelengths which fulfill the focus conditions of a line-shaped section of surface 5a (cf. FIGS. 5a and 5b). The light emitted by slot-shaped aperture 21 is spectrally dispersed over a grid 23 arranged in the X direction and detected with a two-dimensional detector 29, wherein different locations of the spectral components on the structured substrate are obtained. A schematic representation of the detector is shown in FIG. 3a.
In contrast to the prior art, as shown in FIG. 1, wherein only one wavelength reaches spectrometer 15 due to the use of a point-shaped white-light source 3 and a point-shaped aperture 13, the use of a spot-shaped light source, the slot-shaped aperture and the one-dimensional grid result in a plurality of wavelengths impinging on the two-dimensional detector simultaneously. This is how a shorter recording time is needed for the same surface area.
FIG. 3
a is a schematic representation of two-dimensional detector 29 used in FIG. 2b for measuring, such as a CCD chip, in which the different wavelengths are split up in the Y direction and are registered at different locations. In the Y direction the wavelength spectrum blue, green and red is plotted for different points on the substrate surface in the X direction. The light impinges on the CCD chip on a line-by-line basis.
FIG. 3
b shows how the Y position of the intensity maximum can be used as an indication of the height of the structured substrate at location X. This representation of the substrate profile is obtained by rotating the representation in FIG. 3a by 90° counter clockwise. There are two height maxima shown on the height profile, caused by the reflection of light of a blue wavelength, and an absolute height minimum on the surface caused by the reflection of light of the red wavelength. Light of a green wavelength indicates structures of mean height.
FIG. 4 is a schematic representation of the inventive arrangement and relative movement 33 of substrate 5, white-light illumination or illumination spot 31 and slot-shaped aperture 21. In an advantageous embodiment of the present invention, an illumination spot 31 having a diameter greater than the length of the slot-shaped aperture in the illumination beam path impinges on substrate 5. Substrate 5 rests on an XY scanning stage which, by means of raster-scan movements 33, ensures that the entire substrate 5 is illuminated successively and therefore the entire height profile of substrate 5 is detected. In a preferred embodiment, illumination spot 31 further has the shape of a line corresponding to the slot-shaped aperture.
FIG. 5
a is a schematic representation of three structures having different heights, wherein the respective heights are detected on a line through the use of a white-light illumination spot providing a plurality of wavelengths 27.3, 27.4 and 27.5. Wavelengths 27.3, 27.4 and 27.5 are imaged on planes 28.3, 28.4 and 28.5 due to chromatic aberrations and fulfill the focus conditions of each structural height of 5.1, 5.2 and 5.3, and are recorded in correspondence to FIG. 3a.
FIG. 5
b is another schematic representation of structures on a substrate 5 scanned by means of a scanning movement 21.1 relative to slot-shaped aperture 21. Each of the 3 structures 5.1, 5.2 and 5.3 with different heights are covered by the aperture, so that their measurements can be taken simultaneously.
The arrangements and methods shown are in particular for the so-called macro inspection of wafers, they are, however, not limited in this respect.
Patent Application
20080031509
