Positioning stage for cryogenic chip probing.

Abstract

The invention concerns a wafer positioning stage with 4 degrees of freedom for use in a cryogenic environment and suited for cryogenic chip probing. 10 Special focus has been attended to realize high speed and considerable lifetime improvements with respect to current piezo based positioners. In the presented concept we introduce cryogenic compatible electromagnetic linear motors in close 15 distance to the contacting probes which enables high speed, no wear and precise displacements. All required 4 degrees of freedom, positioning in X, Y, rotation around Z and probing action Z displacement have been integrated in a stand-alone module. 20 Special attention has been put to keep the substrate table at the desired temperature under moving circumstances and minimizing the dissipation during cryogenic chip probing.

Description

The invention concerns a wafer positioning stage with 4 degrees of freedom for use in a cryogenic environment 5 and suited for chip probing. Special focus has been attended to realize high speed and high precision compared to state-of-the-art piezo based positioners or non-cryogenic compatible stages which are positioned far away of the probing location. 10 Also, special attention has been paid to minimizing dissipation during testing. Chips for quantum computing need to be tested under cryogenic environmental conditions. Testing involves accurate positioning of each chip in X,Y and Rz 15 position and a vertical Z motion for bringing probes to the points of interest for testing. For this a stage with four controlled degrees of freedom is needed. Present cryogenic stages are based on piezo based stick- 20 slip actuators. These actuators, due to their frietion contacts which introduce wear, are not suitable for infinite travel and therefor suffer from lifetime issues. Also, they typically have low translation speeds Alternative stages are based on electric motors which 25 are not cryogenic compatible and therefore placed at room temperature on a long distance from the actual points of interest, which compromises positioning performance like speed and precision and create thermal leakage to the probing environment. The above-mentioned disadvantages have been overcome in the presented concept where we introduce cryogenic compatible electromagnetic linear motors in close distance to the probing location to realize a 4 DoF positioning stage. Special attention has been put to keep the substrate table at the desired temperature under moving 5 circumstances and minimizing the dissipation during chip probing. The exact nature of this invention, as well as its objectives become clear in the accompanying drawings 10 wherein: Fig.1 Is the 3D view of the system indicating the various components to realize the requirements. 15 Fig.2 Is a cross section of the system at the substrate table location. Fig.3 Is a 3D view to indicate the thermal connections. 20 A rigid base plate (1) is mounted with compliant and low thermal conduction supports (2) on a cryostat frame (3). The magnetic stators of cryogenic compatible electromagnetic stages, stator X1 (4) and stator X2 (5) 25 are mounted on the base plate (1). A third stator Y (6) is on one side mounted on carriage X2 (7) in such a way that only a rotation about the Z axis and rotation about the X axis is possible while the other end is mounted on carriage X1 (8), in such a way that only translation in Y 30 direction and rotations about the X,Z and Y axes is possible. The stator Y (6) is foreseen with a carriage (9), which holds a parallel guiding mechanism (12), which enables possible Z displacement of a substrate table (13). The Z position of the substrate table (13) is determined 5 by its support by a roller (14), on a profiled cam (15), on carriage (10), which can be relatively positioned with respect to carriage (9), to adjust the Z displacement of the substrate table (13). Each carriage is equipped with electromagnetic coils to 10 create a drive force with respect to the stator. The position of each carriage with respect to the stator is determined by a cryogenic compatible interferometer system (16). The moving substrate table (13) has a flexible 15 connection to the statie low temperature spot (17), via C shaped thermal conductors (1 8). The moving carriages also have a flexible connection to the statie base plate (1), via C shaped thermal conductors. 20 The base plate (1) can be connected to a high-power cooling system. To thermally isolate the substrate table (13) from the carriages (9) and (1 0), the substrate table is supported by three leafspring-isolators (19) oriented in such a 25 way that the position of the substrate table (1) is fixed in six degrees of freedom to the vertical moving part (20) of the parallel guiding mechanism. A bridge (21) to mount test probes (22), is connected with high stiffness to the base plate (1) for optimized 30 position stability. A park position (23) is foreseen for loading and unloading of the substrate (24) To minimize thermal dissipation, due to forces in Z direction on the substrate table (13) during testing, the carriages (9) and (10) are connected to each other with a spring (25) which can, together with the profiled cam 5 (15), be tuned in such a way that it off-loads the forces on the carriages (9) and (10).

Claims

1 The invention concerns a device with the characteristic that: A base plate is equipped with a electromagnetically driven substrate table and with High stiffness is associated with test probes, which together in a vacuum environment at very low temperature be kept; This substrate table relative to test probes can be in four degrees of freedom (X,Y,Z,Rz) aligned, making the testing on the substrate table products present at this low temperatures can occur; The substrate table, via a thermally insulating support is mounted on a positioning device with 4 controlled degrees of freedom (X,Y,Z.Rz) and with flexible thermal conductors, made in a C shape, is connected to a cold spot in such a way that the substrate table at the desired temperature be held; The substrate table can be equipped with a test wafer or another substrate, that by means of of one or more clamps against the substrate table can be pressed whereby the wafer to be tested or substrate via thermal conduction at the desired temperature can be maintained; A backlash-free parallel guide, executed with flexible elements, connected on one side with the thermal insulating support and connected to a roller, supported by a, translation table provided with a ridge profile, which in can move in the Y direction and where the other end of the parallel conductor is connected to another 5 translation table that can move in the Y direction; That the above-mentioned ridge profile a further to determine transmission ratio realizes between a displacement in the Y direction of the ridge profile at relative to the idler roller, causing the idler roller to form a Z 10 undergoes translation; D The substrate table can move in the Y direction create if both translation tables are in the Y direction move, but the position relative to each other remains the same; 15 The substrate table can move in the Z direction make as the position of both translation tables at changes relative to each other, causing the the aforementioned roller follows the ridge profile causing the roller to shift in the Z direction 20 is being forced; B two translation tables moving in the Y direction, backlash-free linear guide parts that only allows displacement in the Y direction and where each translation table of electromagnetic coils is 25 provide that can withstand a reaction force in the Y direction apply to the ones provided with magnets direct guidance (Y) and where the position of the translation table with respect to linear guidance in The Y direction is determined by means of a position sensor 30 measured; This straight guide (Y) on one side is connected to a translation table in a backlash-free manner X direction and in such a way that it only a can make angular displacement about the Z-axis and about the X-axis and on the other side with a translation table in X direction is connected without play in such a way that this e and angular displacement about the X, Y, and Z axes possible enables, as well as a translation in the Y direction makes whereby the linear guide (Y) both a translation in the X direction as well as a rotation around Z as can make; Every translation table in the X direction, free of backlash is connected via a direct line and in such a way that it only allows movement in the X direction and where every translation table of the electromagnetic coils are provided which a be able to exert a reaction force in the X direction on the magnetically equipped linear conductors (X) and where the position of the translation table relative to of the straight guidance in the X direction by means of a position sensor is measured; All translation tables with the electric coils as well as the linear conduction Y, via flexible thermal C-shaped conductors are connected to the base frame that is connected to a second one cold spot, with higher cooling capacity; That there is a magnetic under the substrate table shielding is located which ensures that the by the magnets and electromagnetic coils generated field strength at the location of the substrate table is reduced; 2 An establishment in accordance with the preceding conclusion, where between both translation tables in the Y direction, a spring element is placed that the by the roller and associated profile induced force in the Y direction in the desired situation, for example during contact with the test probes, compensates, whereby the dissipated power in the electromagnetic coils of the Translation tables in the Y direction are reduced.

3. An establishment according to one or more of the previous conclusions regarding the position of the translation tables in relation to their direct guidance by means of a stiff in the direction of movement frictional contact, where the frictional force in the direction of movement can be controlled by a separate actuator be affected after switching off the power by the magnetic coils, in the translational direction, on its place is held so that no heat more is dissipated to the translation tables in to hold position.

4. An establishment within the meaning of claim 3, where the Friction force in the direction of motion not active is influenced, but is always present.

5. An establishment within the meaning of claim 2, where the substrate table due to the spring present between the Translation tables in the Y direction, a force equilibrium forms with the test probes, whereby between the test probes and the substrate table a frictional force in X,Y and Rz directions are realized, whereby the substrate table relative to the test probes in X,Y and Rz is held in place, whereby the magnetic coils of the translation tables not no longer need to be ratified and therefore there are no Heat is dissipated during testing.

6. An establishment within the meaning of claim 2, where the substrate table due to the spring present between the Translation tables in the Y direction, a force equilibrium forms with the test probes and with at least two on placed at a mutual distance (in the XY plane) stops in Z direction, connected to the same frame as the test probes, whereby between the stops and the substrate table a friction force 5 is realized in the X, Y, and Rz directions, whereby the substrate table relative to the test probes in X,Y and Rz are held in place, whereby the magnetic coils of the translation tables not no longer need to be ratified and therefore there are no 10 heat is dissipated during testing.

7. An establishment within the meaning of claim 2, where the substrate table due to the spring present between the Translation tables in the Y direction, a force equilibrium forms with the test probes and with at least two on 15 placed at a mutual distance (in the XY plane) positioning pins, connected to the same frame as the contact probes , where the positioning pins during testing the X,Y,Rz position between the test secure probes and the substrate table in a form-fitting manner, 20 whereby the magnetic coils of the translation tables no longer need to be reinforced and therefore no heat is dissipated during testing.

8. An establishment according to one or more of the 25 preceding conclusions, where the connection between the base frame and the external environment (cryostat) is executed by a low-stiffness spring element so that high-frequency vibrations from the cryostat be reduced, affecting the stability of the 30 positioning improves.

9. An establishment according to one or more of the previous conclusions, regarding the substrate table can be driven to a parking position where the clamps by movement over a ridge profile can be opened automatically and whereby the substrate free from the by a separate Z actuator substrate table can be lifted, creating space 5 is formed to transport this substrate further.

10. An establishment according to one or more of the previous conclusions, but without magnetic shielding 10 I2 L1 £ / 1 TZ

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