EP1587649B1 - Device for the high-precision machining of the surface of an object, especially for polishing and lapping semiconductor substrates - Google Patents

Abstract

A device for high-precision machining of the surface of an object, such as for polishing and lapping semiconductor substrates, in which the object is held on an accommodation surface for its machining. The accommodation surface can be deformed by means of a actuators connected to the surface in a positive-lock and/or non-positive-lock manner. The actuators are provided between a base plate and an accommodation plate that are mechanically biased relative to one another. The accommodation plate is configured, on its inside, with concentric grooves forming rigid rings in the axial direction. The individual rings are connected by solid substance joints. Piezo-stacks configured as actuator-sensor elements, as well as springs, are disposed between the faces of the rings and the base plates and are offset relative to one another by 120°.

Description

mit k = Konstante, v(t) = Geschwindigkeit, p = lokaler Druck und t = Bearbeitungszeit. Hieraus wird ersichtlich, dass eine Beeinflussung der lokalen Abtrennhöhe Δh nur über eine lokale Änderung des Druckes p möglich ist, während die Geschwindigkeiten verfahrensbedingt durch die Bewegung (Drehzahlverhältnisse) vorgegeben sind und keine lokale Einflussnahme gestatten.The invention relates to a device for high-precision machining of the surface of an object, in particular for polishing and lapping semiconductor substrates, according to the preamble of claim 1. Such a device is made US 6,325,696 B known. Typical applications are the processing of wafers, mask blanks as well as lenses, mirrors and other optical components.
Of particular importance in the high-precision machining of surfaces is, in addition to the relative speed between the surface to be processed and the polishing or lapping agent carrier, the processing pressure acting on the surface. According to the PRESTON hypothesis, the local separation height Δh for ablation processes (eg lapping, polishing, CMP) results according to the relationship $$\mathrm{\Delta }H=k\cdot p\int v\left(t\right)dt.$$

with k = constant, v (t) = speed, p = local pressure and t = processing time. It can be seen that influencing the local separation height .DELTA.h is only possible via a local change in the pressure p, while the speeds are predetermined by the movement (speed ratios) due to the method and do not allow any local influence.

It is well known that tools for processing objects, such as substrates, are deformed to effect defined shapes and / or machining conditions. A distinction is made between active and passive shape adaptation.

The DE 693 22 491 T2 discloses a passive shape adaptation by elastic body with convex and concave areas. The polish carrier can deform macroscopically depending on the workpiece surface, so that microscopically the convex portions of the workpiece are selectively polished.
In the DE 43 02 067 C2 the shape adaptation is achieved by a soft polishing pad.

In both cases, it is a purely passive method, without targeted influencing the surface shape of the object to be processed.

The U.S. Patents 5,635,083 and 6083089 describe active pneumatic conformations by pressure on the backside of the wafer. The wafer is not at the so-called. Chuck, but this is guided laterally by a retaining ring. The disadvantage is that only a certain invariant basic geometry can be scaled as a function of the pressure.

In the US 6,210,260 B 1, a chuck is described, which has under the tool surface a pressure chamber which serves by means of air for sucking the wafer or for pressing the wafer to the Poliemittelträger (polishing pad). Depending on the pressure applied, the chuck surface can be deformed either convexly or concavely with a certain invariant basic geometry globally, convective-concave deformations or targeted influencing of local areas, for example the edge, are not possible.

The use of piezoelectric elements to deform a surface on CMP tools is described in US Pat US 5,888,120 and EP 0 904 895 described.
The use of piezoelectric actuators per se is also known from US Pat. Nos. 4,934,803 and 4,923,302 in connection with a mirror adjustment. In the patent US 5,094,536 describes an actively deformable wafer chuck for lithography. Locally, the surface can be deformed by actuators, the necessary bias is generated by a vacuum chamber. The measurement of the geometry takes place via an image processing device.
Here, the workpiece to be machined and not the workpiece carrier is deformed directly, which leads to unwanted local unevenness, especially in thin-walled workpieces.

In US 5,888,120 and EP 0 904 395 A2 For the measurement of the film thickness, a device based on a laser interferometer is described. The bottom of the wafer is optically scanned through a window in the polishing tool. The The uniformity of the wafer is determined by measuring the removal rate in defined areas. As a result, control signals are generated for the actuators that adjust the required geometry of the wafer. However, the described device only allows the local film thickness measurement in the region of the window, and an influence of the window itself on the process can hardly be avoided.

The invention is based on the object to process the surface of objects with a universally applicable device and with the least possible effort and in a relatively short time even with process fluctuations, material inhomogeneities, etc. with high reproducible accuracy.
The object is solved by the features of claim 1.

The object to be processed in its surface, such as a semiconductor substrate, is adhered to a sandwich-like structure of two mechanically strained plates by adhesion, adhesion, suction, or the like. Between the mutually braced plates, one of which serves as a receiving surface for said support of the object, per se known actuator sensor elements are arranged, which, depending on the design, positively and / or non-positively connected to the receiving surface and these locally and / or can deform globally.
According to the invention, a pressure distribution in the working surface which is decisive for the machining process is determined before the beginning of the machining process when the object is held in the working position. For this purpose, the device with the recorded object to be processed with defined force against a specially trained, very flat counter surface or on the machine directly against a polishing plate, polish carrier, pad or similar. pressed.
This results in the processing surface a characteristic local compressive stress distribution whose size and distribution of the surface geometry (of the object and the counter surface) depends.

Another possibility is to distribute the pressure even during the machining process without its interruption (eg by stopping and / or lifting) determine. For this purpose, the already in working position, already acted upon by the normal contact pressure device is briefly loaded or relieved with an additional normal force acting on the working surface force.
By doing so, the local compressive stress distribution in the processing surface changes, and the amount of change (pressure increase or decrease) in turn depends on the surface geometry of the object and the mating surface. Both the pressure distribution generated by the force application before the machining process and the change in the pressure distribution in the machining surface brought about by an additional force during the machining process are detected as forces by the actuator sensor elements belonging to the respective surface region and an evaluation unit for the determination of the abovementioned Pressure distribution supplied.
From the calculated pressure distribution, manipulated variables for local deformation of the receiving surface of the sandwich-like structure are then generated for the actuator-sensor elements for the purpose of a defined surface processing of the object with site-specific influence. These local deformations serve as presetting values or controlled variables for the generation of defined spatially acting machining forces (pressings) on the surface of the object. Thus, the surface treatment directly with a preset and specifically adapted to the intended processing task and the given processing conditions pressure distribution. The presetting of the local deformations of the receiving surface can be done once prior to or during the machining process, for example in a continuous control process. In this way, it is not only possible to work towards a special shaping or to a very high degree of precision in their realization, but also directly occurring process fluctuations, such as material inhomogeneities, temperature changes, etc., can be taken into account, in particular without the additional checks and tests that were previously required must be performed, which interrupt the processing process to a considerable extent, delay, complicate and increase in effort. As a result, errors and inaccuracies resulting from dimensional variations or (for example, thermal) deformations of the processing object, the Capture surface, the lapping or polishing medium carrier and the machine-side guide (eg., Angular deviations) detected that allow an individual correction or adjustment for each workpiece to be machined.
Of particular importance for the achievable accuracy of the process is that no additional elements for the measurement are required by the determination of the pressure distribution according to the invention. So z. For example, when using known pressure measuring films for determining the pressure distribution (Tekscan Inc. / USA, Fuji / Japan, Pressure Profile Systems / USA) alone from their geometric errors (eg thickness variations) changed pressure distribution, as they do not occur in the actual processing. Thus, the integration of such measuring systems in conventional chucks is not possible or very expensive. Furthermore, these systems are relatively sensitive, so that the use is possible only under laboratory conditions and not under production conditions.
Of great advantage is also the ability to perform not only before the start, but also during the machining process, possibly even without interruption control measurements of the pressure distribution and compensate for any identified process fluctuations by appropriate control of the actuator-sensor elements.
The simple procedure with a force application results in considerable time savings over sometimes very complex measurements of the surface geometry, in which the above-mentioned sources of error are only partially taken into account.

The invention will be explained below with reference to exemplary embodiments illustrated in the drawing.

Figur 1:

Vorrichtung nach dem bekannten Stand der Technik zum Läppen bzw. Polieren der Oberfläche eines Halbleitersubstrates

Figur 2:

sandwichartige Anordnung zur Aufnahme des Bearbeitungsobjektes, bestehend aus zwei Platten mit dazwischenliegenden und in Ausgleichsmaterial eingebetteten diskreten Aktuator-Sensor-Elementen

Figur 3:

sandwichartige Anordnung zur Aufnahme des Bearbeitungsobjektes, bestehend aus zwei Platten und dazwischenliegender Piezokeramik mit segmentierten Metallisierungsschichten

Figur 4:

Stelleinrichtung in zwei Ansichten für konzentrische Verformungen der Aufnahmefläche für das Bearbeitungsobjekt

Show it:

FIG. 1:

A device according to the known state of the art for lapping or polishing the surface of a semiconductor substrate

FIG. 2:

sandwich-type arrangement for receiving the processing object, consisting of two plates with intermediate discrete actuator-sensor elements embedded in the compensation material

FIG. 3:

sandwich-type arrangement for receiving the processing object, consisting of two plates and interposed piezoceramics with segmented metallization layers

FIG. 4:

Actuator in two views for concentric deformations of the receiving surface for the object to be processed

The current state of the art for lapping the surface 1 of a semiconductor substrate 2 exemplifies FIG. 1 The semiconductor substrate 2 is attached to the underside of a receptacle 3 by adhesion, adhesion or suction. The surface 1 of the substrate 2 to be processed is placed on a lapping or polishing medium carrier 4 (also referred to as a pad), which is fastened on a lapping or polishing disk 5 which rotates horizontally. The lapping or polishing wheel 5 is rotated by a drive shaft 6 (symbolized by a rotary arrow 7 ). Via a further drive shaft 8 and the receptacle 3 is rotated (indicated by a rotary arrow 9), so that the semiconductor substrate 2, which is pressed with a defined force F (see arrow 10) on the lapping or polishing medium carrier 4 , on this rotated at a relative speed to the same. In addition, the semiconductor substrate 2 can be oscillated radially over the lapping or polishing medium carrier 4 (see arrow 11).
For the machining process, a lapping or polishing suspension 12 (slurry) is applied to the lapping or polishing medium carrier 4 via a corresponding metering device 13 .
For chemical-mechanical planarization, such a lapping or polishing suspension 12 is used, which contains active chemical components in addition to abrasive components. Important for the result of the machining process is the exact matching / agreement of the action times of mechanical and chemical components of the lapping or polishing suspension 12 .

FIG. 2 shows a sandwich-like arrangement for receiving the processing object, which consists of a concentric base plate 14 and a concentric receiving plate 15 . The base plate 14 is fixed to a shaft 16 . This can be connected to a drive shaft (not shown for reasons of clarity) stand. The receiving plate 15 with its receiving surface 17 serves to hold the (in FIG. 2 also not shown) processing object. Between the base plate 14 and the receiving plate 15 piezo stack 18 are arranged as discrete actuator sensor elements, which are embedded in compensating material 19 . For the processing operation of, for example, by gluing, adhesion, suction on the receiving plate 15 attached to the processing object, the pressure distribution over the receiving surface 17 is determined.
For this purpose, the machining object is acted upon by a force, for example, by placing it on the polishing plate / polish carrier / pad or the like. This results in the receiving surface 17, a characteristic local compressive stress distribution acting on the receiving plate 15 as forces on the piezoelectric stack 18 , which are non-positively and / or positively arranged between the base plate 14 and the support plate 15 . By means of their sensor function, the piezoelectric stacks 18 detect the force acting on them as a measure of the pressure distribution acting in the receiving surface 17 . For this purpose, the piezo stack 18 are electrically connected to an evaluation and control stage (not shown).
The transmission of energy and information to a frame-fixed analysis or control system can be done either via conventional rotary transformer (slip rings) or wirelessly.
From the pressure distribution in the receiving surface 17 (and thus on the surface of the processing object) as described, 18 manipulated variables are then determined in the said evaluation and control stage for the individual piezo stacks with which the receiving plate 15 is deformed defined in its receiving surface 17 in a location-specific manner (Actuator function of the piezo elements). Thus, the surface treatment sets directly with a preset and specially adapted to the intended machining task and the given processing conditions pressure distribution, which despite manufacturing tolerances, process fluctuations, material inhomogeneities, etc., a high reproducible accuracy can be achieved in the machining process.
The compensating material 19, in which the piezo stack 18 are embedded, has a lower rigidity than the piezo stack 18 and is used for flexible compensation between same. At the same time, the compensation material 19 for the piezo stack 18 is electrically insulating.

In FIG. 3 is one with FIG. 2 comparable sandwich-like structure of the concentric base plate 14 and the concentric receiving plate 15 shown, with the difference that here as actuator sensor elements not discrete piezostack, but a segmented piezoceramic 20 is provided, the segments queried individually in their sensor function and separately in their actuator function can be controlled. For isolation is located between the base plate 14 and the receiving plate 15 to the piezoceramic 20 around an insulation layer 21st
The mode of operation for adjusting the receiving surface 17 from the previously determined pressure distribution is basically the same as in the exemplary embodiment FIG. 2 described.

A special adjusting device for concentric deformations of the receiving surface, to which the processing object is attached, is in FIG. 4 shown in two views. There is a sandwich-like structure of the concentric base plate 14 (again as a counter-plate for the actuator-sensor elements) and a concentric receiving plate 22. This has, in contrast to the receiving plate 15 in the FIG. 2 and 3 23 on its inner side concentric grooves by the local weakening of the cross section of the receiving plate 22 concentric solid joints arise 27 through which the receiving plate 22 is radially deformable to a nearly any concave, convex or concave / convex surface profile in the adjustment range of said actuator-sensor elements , Between the concentric grooves 23 , very stiff rings 24 are formed on the inner surface of the receiving plate 22 in the axial direction, against which piezostacks 25 supported against the base plate 14 act as actuator-sensor elements. The base plate 14 and the receiving plate 15 are biased by springs 26 . The piezo-stacks 25 and the springs 26 each form staggered three-staggered arrangements with lines which are pronounced in the axial angle of 120 ° (see upper illustration in FIG FIG. 4 ). Each of these lines is formed by in each case three piezostacks 25 or springs 26 acting on the rings 24 . In addition, a further piezo stack 25 can be located in the center of this arrangement. With this arrangement, a statically determined system is given. The invention is However, neither on the described constructive shape still limited to the number of piezoelectric stack 25 shown on the circumference and the number of grooves 23, rings 24 and springs 26 .
The base plate 14 must be designed and dimensioned such that the forces introduced with the support of the piezo stack 25 can only cause minimal deformations. The greatest possible rigidity of the rings 24 is desirable, because in this way a small waviness of the deformed receiving plate 22 is achieved even in the case of a small number of piezo stacks 25 in the circumferential direction of the receiving plate 22 .
The determination of the pressure distribution on the outer surface of the receiving plate 22 (and thus on the surface of the attached processing object) and the local surface deformation of the receiving plate 22 determined therefrom by the piezo stack 25 is in principle again as in the exemplary embodiment FIG. 2 described.

List of used reference numbers

1 -

surface to be processed

2 -

Semiconductor substrate

3 -

admission

4 -

Lapping or polishing agent carrier

5 -

Lapping or polishing wheel

6, 8 -

drive shaft

7, 9 -

rotation arrow

10, 11 -

arrow

12 -

Lapping or polishing suspension

13 -

metering

14 -

baseplate

15, 22 -

mounting plate

16 -

shaft

17 -

receiving surface

18, 25 -

piezo stack

19 -

compensating material

20 -

piezoceramic

21 -

insulation layer

23 -

grooves

24 -

rings

26 -

feathers

27 -

Solid joint

Claims (8)

1. Device for the high-precision machining of the surface of an object (2), in particular for polishing and lapping of semiconductor substrates, in which the object (2) being machined is held on a receiving surface (17), which is deformable by a number of actuators (18, 20, 25) connected to the latter in a positive and/or non-positive manner, and the actuators are between two opposing mechanically prestressed plates, the base plate and the receiving plate, with the object (2) being held in a sandwich-like construction of two opposing mechanically prestressed plates (14, 15 or 14, 22), of which one forms the said receiving surface (17) and between which the said actuator-sensor elements (18, 20, 25) are arranged, and the actuator-sensor elements (18, 20, 25) are in contact with an evaluation and control unit, through which the local compressive stresses arising from each loading of the object (2) held in the receiving surface (17) are recorded from the forces acting on the actuator-sensor elements (18, 20, 25), from which a relevant pressure distribution for the surface of the object (2) to be machined is calculated and from this in turn for each actuator-sensor element (18, 20, 25) an effective control variable with respect to the intended machining of the surface of the object (2) for the local deformation of the receiving surface (17) is obtained as a presetting or control variable for the local machining pressure on the surface, characterised in that
   the receiving plate (22) is formed on its inner side with concentric grooves (23) developed in the axial direction with stiff rings (24), with the individual rings (24) being connected by solid joints (27) and that between the end surfaces of the rings (24) and the base plate (14) and displaced by 120° with respect to one another are piezo stacks (25) formed of actuator-sensor elements (18, 20, 25), and springs (26).
2. Device in accordance with Claim 1, characterised in that
   the said piezo stacks (18, 25) are the actuator-sensor elements.
3. Device in accordance with Claim 1, characterised in that
   a said arrangement of segmented piezo ceramic (20) is the actuator-sensor elements.
4. Device in accordance with Claim 1, characterised in that
   the plate (22) with the receiving surface (17) has structure elements to create defined deformations, for example concentric grooves (23) for a deformation with a concave, convex or concave/convex surface profile.
5. Device in accordance with Claims 1 and 4, characterised in that
   the plates (14, 22) of the sandwich-like construction are prestressed on opposing sides by springs (26).
6. Device in accordance with Claims 1 and 4, characterised in that
   the actuator-sensor elements (18, 20, 25) in a star-shaped arrangement on the inner side of the plate (22) engage with the receiving surface (17) for the object (2).
7. Device in accordance with Claim 1, characterised in that
   the plates (14, 22) are prestressed on opposing sides by a star-shaped arrangement of springs (26).
8. Device in accordance with Claims 6 and 7, characterised in that
   the star-shaped arrangement of the actuator-sensor elements (18, 20, 25) and of the springs (26) are displaced in an axial angle with respect to one another.

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