DE102007048295A1 - Apparatus and method for thickness measurement - Google Patents

Abstract

The invention relates to a measuring device (10) for optical, in particular interferometric, thickness measurement, in particular for use in wet grinding processes. According to the invention, it is provided that an exit region of a measuring light beam is designed to be liquid-tight.

Description

The The invention relates to a measuring device for measuring thickness, in particular for use in wet grinding processes, and a method for measuring thickness.

From the US 6,768,552 B2 For example, an apparatus and a method for measuring thickness using optical measuring principles, in particular interferometry, are known. In the known device, a measuring head is equipped with an optical system which allows a targeted loading of the object to be measured with a measuring light beam, in particular laser light, and transmits the signal response caused by reflection to an evaluation device. The measurement light beam passes through an air gap and a liquid film before it impinges on the measurement object. By interference of the light waves reflected by the measurement object with light waves which have been coupled into a reference system, a thickness of an optically transparent layer applied to the body or the thickness of an optically transparent body can be determined. Application of such a device and a process to be carried out therewith, for example in the production of semiconductors, in which the observance of tight tolerances for the thickness of wafers or layers applied thereto plays an essential role in the yield in the production process.

The The object of the invention is a device and a method to provide for thickness measurement, in a simple way in a production process can be integrated.

These The object is achieved by a device having the features of the claim 1 and solved by a method having the features of claim 12.

at the device according to the invention is provided that an exit region of a measuring light beam is liquid-tight is trained. This allows for at least partial Immersing the measuring device in a formed on the measuring object Liquid film, while the optical thickness measurement takes place through the liquid film. Thus, the number reduced by optical interfaces because of the measuring process no interface between air and liquid must be taken into account. In addition, by the partial immersion the measuring device in the liquid film optical aberrations avoided, which affects the accuracy of measurement could lead. In particular, effects remain Vibrations on the surface of the liquid film, as in particular when carrying out the measuring method can occur during a process step without negative influence on the measuring method, since no measurement through an air-water interface. movements in the liquid film play due to the immersion of the Measuring device in the liquid film no or only a negligible role for accuracy of the optical measuring method.

at the production of semiconductor devices become carrier substrates, in particular silicon wafers, in a manufacturing process by means of different process steps modified in their properties. Before the start, during or after such a manufacturing process can be provided in particular, a thickness of the carrier substrate to reduce. This can be done, for example, by removing material by grinding, in particular by wet grinding done. there must be the thickness of the carrier substrate in regular Intervals are checked to a compliance to ensure the desired target thickness. A Application of the method for other wet processes such as etching processes or coating processes is also conceivable.

For a robust thickness measurement is inventively the Liquid film between the measuring head and the measuring object constructed, through which determines the desired thickness can be. Particularly advantageous, the inventive Device for process control during a process step, in which a process fluid is used, take place, because to complete the measurement is not complete Removal of the process fluid is necessary. The at Manufacturing process used process fluid can either for the formation of the liquid film be used between the measuring device and the object to be measured or it will displaced by supplying a different liquid.

With the device according to the invention can either directly during the wet grinding process or during processing breaks between several consecutive wet grinding operations Thickness measurement can be made without this drying the substrate would be necessary. Thus allows the device of the invention a clear Acceleration of the thickness measurement during this production step. In addition, due to the possibility of frequent Thickness measurement an improved production result can be achieved.

In Embodiment of the invention is at least one liquid supply for forming a liquid film between the measuring device and the measurement object provided. By the provided liquid Dirt particles are emitted from the surface of the test object displaced, which affect the measurement accuracy could.

In Another embodiment of the invention is provided that an optical System for a thickness measurement by the between measuring device and Test object trained liquid film set up is. The design of the optical system is based on a thickness measurement through a fluid film between the measuring device and the object to be measured optimized.

In Another embodiment of the invention is provided that a measuring head at least partially housed in a housing and an optically transparent cover plate liquid-tight is arranged on the measuring head and / or on the housing. The measuring head can be designed as a separate entity that the necessary for performing the measurement method optical Contains components. The measuring head can with the help of the housing in the region of the exit of the measuring light beam liquid-tight against the fluid used for the measurement is sealed off become. The cover plate serves as a passage window for the measuring light beam and ensures the desired Isolation of the measuring head from the liquid. Preferably it is in the cover plate to a plane parallel plate Glass or plastic, at least partially so on the measuring head is present that a sealing effect is achieved.

In Another embodiment of the invention is provided that the housing at least one liquid inlet and at least one Liquid outlet for providing the liquid film has. By a suitable arrangement of the liquid outlet It will cause soiling on the surface of the test object washed away from the measuring range of the measuring head so as to achieve a reliable thickness measurement. In addition, by the supply of liquid through the housing an undesirable adhesion of the housing on the test object prevents to after performing the measurement to allow a quick removal of the measuring head.

In Another embodiment of the invention is provided that the measuring head limited with the housing at least one cavity, the liquid is flowed through. This will ensures a simple and compact construction of the housing, the Cavity serves as a fluid guide between the Liquid inlet and the liquid outlet.

In Another embodiment of the invention is provided that the housing a wall portion having, with at least one recess is provided as a passage for one of the measuring head deflected measuring light beam and / or as liquid outlet for the liquid. An outer surface of the wall section is immediate during the measuring process arranged adjacent to the surface of the measurement object. The Recess in the wall section allows either an undisturbed Passage of the measuring light beam from the measuring head to the object is discharged, and / or serves as a liquid outlet between the housing and the test object and can communicate connected to the cavity and the liquid inlet be. If both the measuring light beam of the measuring head and the over the liquid inlet provided Liquid pass through the recess, so is the optical path between measuring head and measuring object constantly supplied with fresh, contamination-free liquid, whereby a high measuring accuracy is guaranteed.

In Further embodiment of the invention, the cavity is at least designed substantially annular, so that at least one partial flow around a section of the measuring head with Liquid can be ensured. By the annular Design of the cavity can be over the liquid inlet flowing liquid evenly be distributed in the housing. Starting from the cavity, the Liquid over one or more recesses in the direction of the DUT. this makes possible a substantially turbulence-free liquid stream, whereby the influence of the flowing liquid is reduced to the measurement result. Preferably, the volume of the cavity many times larger than that Volume of during the measurement period through the recess or recesses outflowing liquid, so that a flow calming of the liquid can take place in the cavity.

additional or alternatively it can be provided to the liquid set a predeterminable temperature so that the liquid flowed around portion of the measuring head also substantially the predetermined temperature is, thus a particularly good To ensure measurement precision.

In a further embodiment of the invention, the cavity is assigned at least one, in particular provided in the housing, venting device. Preferably, the venting device is arranged in the vertical direction above the measuring range determined by the measuring object. Thus, air bubbles that are introduced into the cavity with the inflowing liquid can escape upwards through the ventilation device, without leading to disturbances of the measuring process. The venting device can be designed as a bore extending at least substantially in the vertical direction, as a cavity provided with a pressure-relief valve, or as a filter membrane, preferably at the upper end of the cavity. In a vertical bore, a liquid column forms whose height is proportional to the fluid pressure in the cavity. Through the liquid column, air bubbles contained in the liquid can escape. In the case of a pressure relief valve, it is possible to increase the volume flow of the fluid in each case for a short time in such a way that the pressure relief valve opens and air accumulated in the cavity can escape. In a filter membrane, a gas-permeable and liquid-tight filter serves to separate the air bubbles contained in the liquid.

In Another embodiment of the invention is provided that the measuring head Sealing devices for sealing reception in the housing assigned. By provided on the measuring head and / or in the housing Sealing devices, for example, as ring seals with round or profiled cross section or be designed as flat gaskets can, is an uncontrolled outflow of liquid from the limited by the measuring head and the housing cavity avoided. Preferably, the sealing means are arranged so that a gap between a lens arrangement in the measuring head or an optically transparent protective window on the measuring head and the optical transparent cover plate can be kept liquid-free.

In Another embodiment of the invention is provided that the measuring light beam and the liquid outlet is substantially coaxially aligned with each other are. This ensures that dirt is on the surface of the object to be measured by the concentric to Measuring light beam exiting liquid flow washed away which ensures an undisturbed thickness measurement is.

According to one Another aspect of the invention is a method comprising the steps of: Forming a liquid film between the measuring head and the measured object, emitting a measuring light beam from the measuring head through the liquid film to the measurement object and evaluation the reflected from the measurement object portions of the measuring light beam for Thickness measurement provided. It is advantageous that through the Formation of the liquid film between the measuring head and the object to be measured a process control, for example during a wet grinding process or between successive ones wet-chemical processing steps for the test object can be done without complete drying of the DUT to bring about.

In Embodiment of the method is provided that during of the measuring liquid between the measuring head and the measurement object is supplied. By the constant Supply of fresh, contamination-free liquid constant measuring conditions are guaranteed at the measuring point. About that In addition, on the surface of the measurement object adhering impurities are eliminated, the negative impact could have on the accuracy of the measurement process. moreover can be due to the permanent supply of fresh liquid ensure a homogeneous liquid film, so that the optical conditions for the measuring head to Thickness measurement on the measurement object are clearly predictable.

In Another embodiment of the method is provided that the thickness of the liquid film at an interval of 0.5 mm to 5 mm, preferably from 1.5 mm to 3.5 mm. With Such a thickness of the liquid film may be non-contact Sampling of the test object can be ensured without a Guide the measuring head over the test object with complex and expensive high-precision mechanics to have to make. In addition, one represents Thickness of the liquid film at the specified interval only a slight impairment for the optical Scanning with the aid of the measuring light.

In Another embodiment of the invention is provided that as a liquid Water, especially deionized water, is used. Water, in particular deionized water, is used in various wet-chemical processes and when wet grinding anyway as a rinse solution for removing process residues and / or used as a coolant.

In Another embodiment of the invention is provided that for surveying the thickness of an interferometric method is used. It acts it is a highly accurate, yet robust, optical measuring method, with its help, the thickness reliably on layers Substrates or the thickness of the substrates can be determined.

In a further embodiment of the invention, it is provided that a confocal distance measuring method, in particular a chromatic confocal measuring method or a Z-scanning method, is used to measure the layer thickness of the measuring object. Such methods are described in the German patent application DE 10 2004 049 541 A1 described in more detail, which is hereby incorporated by reference into the subject of the disclosure.

In Another embodiment of the invention is provided that the measuring light beam a wavelength in an interval of 1100 nm to 1500 nm, preferably from 1200 nm to 1400 nm, in particular from 1300 nm. With light wavelengths in the specified Intervals can advantageously the thickness of silicon substrates be determined.

In Another embodiment of the invention is provided that the measuring process during or after a machining process performed on the target, especially a wet grinding process. This allows a very exact process control or regulation for the machining process, since the success Of the machining process are frequently checked can, without the measurement object being elaborately prepared, for example, must be dried.

Further Advantages and features emerge from the claims as well from the following description of an embodiment, which is reproduced with reference to the drawing. Showing:

1 FIG. 3 is an axial sectional view of a measuring device for measuring thickness, FIG.

2 : a top view of the housing, and

3 : a detail enlargement from the 1 ,

One in the 1 illustrated measuring device 10 includes a measuring head 12 , a housing 14 for partially receiving the measuring head 12 , a light guide 16 and a liquid conductor 18 ,

The measuring head 12 includes a cubic, one-sided beveled mirror housing 20 with a deflecting mirror screwed into the bevelled area 21 and one with the mirror housing 20 connected lens housing 22 , The lens housing 22 is essentially rotationally symmetrical and encloses a lens arrangement 23 for focusing the over the light guide 16 and the deflecting mirror 21 coupled measuring light beam.

The lens housing 22 has a first, substantially cylindrically shaped portion with an integrally formed, circumferential shoulder, on which a pressure ring 24 rests. The pressure ring 24 is provided with holes for mounting screws, which is a fixation of the measuring head 12 on the housing 14 enable.

Below the encircling shoulder faces the lens housing 22 a circumferential groove 25 on which, to receive a sealing ring 26 is provided, the sealing on the inner surface 27 one in the housing 14 introduced stepped bore 28 is applied. Below the circumferential groove 25 the lens housing tapers 22 and forms a second, cylindrical section. The second cylindrical section is followed by a third section, which serves as an adapter section 30 is referred to. The contour of the adapter section 30 is in the 3 shown in more detail.

The adapter section 30 is according to the 3 on an end face 32 with a circumferential, circular groove 34 provided as a contact surface for a designed as O-ring sealing ring 36 serves. The sealing ring 36 lies on a circular disk-shaped cover made of glass 38 on. The cover plate 38 is in turn in a smaller diameter running second bore portion of the stepped bore 28 recorded and ensured in cooperation with the sealing ring 36 and the sealing surface 34 that the lens assembly 23 unaffected by environmental influences.

The depth of the groove 34 , the depth of the second hole for the cover plate 38 , the thickness of the cover plate 38 and the cord diameter of the sealing ring 36 are matched in terms of their dimensions such that the sealing effect between cover plate 38 and sealing ring 36 ensuring deformation of the sealing ring 36 is guaranteed. The face 32 of the circulating Bund 40 meets the first step in the stepped bore 28 on when the bolts of the pressure ring 24 be tightened, and thus limits the deformation of the sealing ring 36 ,

As from the representation of 1 can be seen, the housing has 14 one perpendicular to the central longitudinal axis of the housing 14 introduced inlet bore 44 in which a detachable hose coupling 42 screwed, the rapid, tool-free coupling and uncoupling of the liquid conductor 18 to or from the housing 14 allows. About the liquid conductor 18 can through the inlet hole 44 in one between the in the housing 14 provided stepped bore 28 and the Linsenge housing 22 formed cavity 46 a liquid, in particular water, flow. The liquid flows around the lens housing 22 to the top sealing gasket 26 and flows through several, in the 2 more detailed channels 64 in the lower section of the stepped bore 28 that there as an outlet nozzle 48 is formed.

Again 2 can be taken, are the channels 64 in the case 14 formed as extending in the radial direction of grooves, starting from the stepped bore 28 be fed with liquid. The channels 64 allow the fluid to flow past the in-bore 28 received cover plate 38 so that the liquid is in an at least nearly laminar flow through the exit nozzle 48 in the space between housing 14 and measuring object 54 can flow in and thus favors an exact thickness measurement.

Preferably, the liquid forms in the manner of a radial source flow, that is, starting from the outlet nozzle 48 evenly flowing out in the radial direction, the liquid film desired for the measurement 55 ,

The optical axis of the measuring head 12 and the bore axis 50 the outlet nozzle 48 are arranged concentrically to each other, so that the downflowing liquid, which as a source flow in the radial direction in the gap 52 between the case 14 and the measurement object 54 flows in, the liquid film 55 between housing 14 and measuring object 54 forms. Dirt particles are released by the liquid from the surface of the test object 54 from the impact area of the emitted by the measuring head and partly into the measuring head 12 back reflected measuring light beam displaced. Thus, a reliable and trouble-free measurement of the thickness of the measurement object 54 guaranteed.

In the case 14 is in one of the inlet hole 44 opposite wall section a ventilation device 56 intended. This includes a vertically extending vent hole 58 , one with the vent hole 58 and the cavity 46 communicating transverse bore 60 and one in the cross hole 60 arranged sealing plug 62 , The task of the ventilation device 56 consists of air bubbles that are conveyed with the inflowing liquid into the cavity and that are located in the upper area of the cavity 46 accumulate, dissipate. This is done by the cross hole 60 and the vent hole 58 allows. The in the cavity 46 In contrast, inflowing liquid may be due to the hydrostatic pressure of the in the vent hole 58 do not escape the liquid column present.

This ensures with little effort that when filling the cavity 46 with liquid the air to be displaced or air bubbles, which with the liquid through the inlet bore 44 in the cavity 46 enter, can be removed from the cavity. Due to the large volume of the cavity 46 and the prevailing, low flow rate, which ensures a calming of the liquid flow, the air bubbles in the upper region of the cavity 46 Thus, air bubbles are prevented from flowing downwards in the direction of the outlet nozzle 48 be entrained, where they could lead due to their optical power in the liquid to an undesirable impairment of the thickness measurement.

The liquid column in the vent hole 58 also allows a pressure relief for the inflowing fluid, allowing the flow rate of the fluid through the outlet nozzle 48 lies within a predefinable interval. With increasing influx of fluid into the cavity 46 The increase in pressure in the cavity leads to an outflow of excess liquid through the vent hole 58 ,

The measurement object 54 is a wafer made of silicon, as it is used for the production of semiconductors. This wafer is separated as a disc from a single crystal by sawing and then reduced in thickness in a wet grinding process step, wherein the measuring device 10 is used to determine the thickness of the wafer during or after the wet grinding processing step and, if necessary, to bring about a continuation or termination of the wet grinding process.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - US 6768552 B2 [0002]
• DE 102004049541 A1 [0025]

Claims (19)

Measuring device ( 10 ) for optical, in particular interferometric, thickness measurement, in particular for use in wet grinding processes, characterized in that an exit region of a measuring light beam is formed liquid-tight. Measuring device according to claim 1, characterized in that at least one liquid feed ( 44 . 46 . 64 ) for forming a liquid film ( 55 ) between the measuring device ( 10 ) and a measurement object ( 54 ) is provided. Measuring device according to claim 2, characterized in that an optical system ( 16 . 23 . 38 ) for a thickness measurement by the between measuring device ( 10 ) and measuring object ( 54 ) formed liquid film ( 55 ) is set up. Measuring device according to one of the preceding claims, characterized in that a measuring head ( 12 ) at least partially in a housing ( 14 ) and an optically transparent cover plate ( 38 ) liquid-tight on the measuring head ( 12 ) and / or on the housing ( 14 ) is arranged. Measuring device according to claim 4, characterized in that the housing ( 14 ) at least one liquid inlet ( 44 ) and at least one liquid outlet ( 46 ) for providing the liquid film ( 55 ) having. Measuring device according to one of claims 4 or 5, characterized in that the measuring head ( 12 ) with the housing ( 14 ) at least one cavity ( 46 ) limited, the liquid is flowed through. Measuring device according to one of claims 4 to 6, characterized in that the housing ( 14 ) has a wall portion which is provided with at least one recess ( 48 ), which serves as a passage for one of the measuring head ( 12 ) can be emitted measuring light beam and / or as liquid outlet for the liquid. Measuring device according to claim 7, characterized in that the cavity ( 46 ) is designed at least substantially annular, so that an at least partially flow around a portion of the measuring head ( 12 ) can be ensured with liquid. Measuring device according to claim 6, 7 or 8, characterized in that the cavity ( 46 ) at least one, in particular in the housing ( 14 ) provided, ventilation device ( 56 ) assigned. Measuring device according to one of claims 4 to 9, characterized in that the measuring head ( 12 ) Sealing devices ( 26 . 36 ) for sealing reception in the housing ( 14 ) assigned. Measuring device according to claim 7, characterized in that the measuring light beam and in the housing ( 14 ) provided liquid outlet ( 48 ) are aligned at least substantially coaxially with each other. Method for measuring thickness with an optical measuring device ( 10 ), in particular according to one of claims 1 to 11, with the steps: forming a liquid film ( 55 ) between the measuring head ( 12 ) and the measurement object ( 54 ), Emitting a measuring light beam from the measuring head ( 12 ) through the liquid film ( 55 ) to the measurement object ( 54 ), Evaluating the portions of the measuring light beam reflected by the object to be measured. A method according to claim 12, characterized in that during the measuring process liquid between the measuring device ( 10 ) and the measurement object ( 54 ) is supplied. Method according to claim 12 or 13, characterized in that the thickness of the liquid film ( 55 ) is set at an interval of 0.5 mm to 5 mm, preferably 1.5 mm to 3.5 mm. Method according to one of claims 12 to 14, characterized in that water, in particular deionized Water, used as a liquid. Method according to one of claims 12 to 15, characterized in that for measuring the layer thickness of the test object ( 54 ) an interferometric method is used. Method according to one of claims 12 to 15, characterized in that for measuring the layer thickness of the test object ( 54 ) a confocal distance measuring method, in particular a chromatic confocal measuring method or a Z-scanning method is used. Method according to claim 16 or 17, characterized that the measuring light beam is one wavelength in one interval from 1100 nm to 1500 nm, preferably from 1200 nm to 1400 nm, in particular of 1300 nm. Method according to one of claims 12 to 18, characterized in that the measuring operation during or after a on the measuring object ( 54 ) processing, in particular a wet grinding process.