Test equipment

Abstract

The present invention provides a test device (100) for electrically testing an integrated circuit on a wafer (102). The test device (100) comprises: a vacuum chamber (124); a chuck (101) for holding the wafer (102); a probe card (103) for electrically contacting the integrated circuit; a moving device for moving the chuck (101) relative to the probe card (103); a first radiation shield (110) arranged inside the vacuum chamber (124) and encapsulating the chuck (101) and the probe card (103); and a cooling unit (126) thermally connected to the first radiation shield (110). An apparatus for moving a chuck (101) relative to a probe card (103) comprises a support column (107, 201, 202, 203) having a first end and a second end, the first end of the support column (107, 201) being attached to the chuck (101), and a first radiation shield (110) comprising a first fixed part (111) and a first movable part (112), the first fixed part (111) having a first opening (113) through which the support column (107, 201) is arranged, and the first movable part (112) being attached to the support column (107, 201, 202) and being arranged to cover the first opening (113).

Description

Technical Field

[0001] The invention relates to a testing device as described in the preamble of the accompanying independent claim. Background Art

[0002] Semiconductor device manufacturing is a common process for creating integrated circuits on wafers made of semiconductor materials using a multi-step sequence of photolithography and chemical processing steps. As part of the process, the integrated circuits created on the wafer are usually tested for functional defects by applying special test patterns to them. This testing is performed by using a test device called a wafer prober.

[0003] Examples of known wafer probers include a chuck for holding a wafer to be tested and a probe card for electrically contacting the integrated circuits on the wafer. The probe card is electrically connected to an electronic test unit, which performs electrical tests on the integrated circuits according to a test program. The test program defines the content of the test patterns and the sequence in which they are applied to the integrated circuits. The chuck and the probe card are arranged inside the chamber, which allows the integrated circuits to be tested in a controlled environment. For electrical testing, the probe card is held in place while the wafer mounted on the chuck is moved between test positions. In each test position, the contact elements of the probe card are arranged to electrically contact the contact pads of a group of integrated circuits, which are then electrically tested by the electronic test unit.

[0004] A problem associated with known wafer probers is that testing of integrated circuits is time-consuming and energy-consuming and is difficult or even impossible at very low temperatures, especially below 4 K. This is because the space in which the integrated circuits are tested is not well thermally shielded from its surroundings. Furthermore, in known wafer probers, there are heat-generating parts and components in the test space, which makes cooling thereof difficult. Summary of the invention

[0005] The main object of the present invention is to reduce or even eliminate the prior art problems presented above.

[0006] The object of the present invention is to provide a test device for electrically testing integrated circuits on a wafer. In more detail, the object of the present invention is to provide a test device capable of electrically testing integrated circuits on a wafer at extremely low temperatures and even at less than 4K. A further object of the present invention is to provide a test device capable of quickly and energy efficiently cooling the space where the test integrated circuit is located to the desired test temperature and using a minimum amount of energy to maintain the temperature. A further object of the present invention is to provide a test device in which the space where the test integrated circuit is located is well thermally shielded from its surroundings.

[0007] In order to achieve the above objects, the testing device according to the invention is characterized by what is presented in the characterizing part of the attached independent claim. Advantageous embodiments of the invention are described in the dependent claims.

[0008] A test device according to the present invention comprises: a vacuum chamber; a chuck for holding a wafer including an integrated circuit; a probe card for electrically contacting the integrated circuit on the wafer; a moving device for moving the chuck relative to the probe card; a first radiation shield, which is arranged inside the vacuum chamber and encapsulates the chuck and the probe card; and a cooling unit, which is thermally connected to the first radiation shield. In the test device according to the present invention, the device for moving the chuck relative to the probe card comprises a support column having a first end and a second end, the first end of the support column being attached to the chuck, and the first radiation shield comprises a first fixed part and a first movable part, the first fixed part having a first orifice through which the support column is arranged, and the first movable part being attached to the support column and arranged to cover the first orifice.

[0009] The test apparatus according to the present invention can be used to perform electrical testing on integrated circuits on a wafer. The test apparatus can be referred to as a wafer prober. The wafer to be tested is mounted on a chuck that is moved between test positions using a moving device. In each test position, a probe card makes electrical contact with one or more integrated circuits, which can then be electrically tested.

[0010] The chuck is used to hold the wafer during testing of the integrated circuit. The chuck can be, for example, a mechanical chuck including a plurality of heat conducting pins for holding the wafer on a substrate of the chuck. Alternatively, the chuck can be, for example, an electrostatic chuck including a metal substrate coated with a layer of dielectric material. By providing a voltage difference between the metal substrate and the wafer, electrostatic forces hold the wafer on the chuck. In order to maintain the flatness of the wafer and promote the rapid transfer of heat from the wafer, the chuck is preferably made of a heat conducting material such as copper or gold. The chuck can be made of gold-plated copper. These materials provide good thermal properties and performance.

[0011] The chuck moves relative to the probe card with the moving device. The movement is transmitted to the chuck to which the first end of the support column is attached through the support column. The chuck is preferably flat and arranged substantially vertically relative to the longitudinal axis of the support column. The second end of the support column extends out from the first radiation shield. The moving device includes one or more actuators, which are attached to the support column for moving the support column and therefore the chuck attached to the first end of the support column. The one or more actuators are attached to the support column in a manner that they are outside the first radiation shield so that they do not heat the interior of the first radiation shield. Preferably, the one or more actuators are attached to the second end of the support column and are configured to move the support column in different directions.

[0012] The support column may be a single piece or a multi-piece. The support column may include a first column part and a second column part arranged successively in the longitudinal direction of the support column. The first end of the first column part may be attached to the chuck, and the second end of the first column part may be attached to the first movable part. The first end of the second column part may be attached to the first movable part, and the second end of the second column part may be attached to one or more actuators or to the second movable part of the second radiation shield. In the case where the second end of the second column part is attached to the second movable part, the support column may include a third column part, the first end of the third column part may be attached to the second movable part and the second end of the third column part may be attached to one or more actuators. The support column may be a pipe fitting, and it may be arranged to pass through the first movable part. The support column may include a plurality of pipe fittings, which may be partially nested with each other, or arranged successively in the longitudinal direction of the support column. The first movable part may be attached between two consecutive pipe fittings. The support column may be made of metal (such as stainless steel) or other materials with good mechanical properties and low thermal conductivity.

[0013] The probe card is used to electrically contact the integrated circuits on the wafer. The probe card may include a printed circuit board (PCB) and one or more contact elements that may be arranged to make electrical contact with the contact pads of the integrated circuits. The test equipment may include a camera for optically locating the contact elements on the probe card and the contact pads on the wafer. By using this information, the contact pads of the integrated circuit to be tested may be aligned with the contact elements of the probe card.

[0014] The probe card can be thermally and mechanically attached to a probe card holder, which is mechanically attached to a first fixed part of the first radiation shield using a thermal isolation support (e.g., a thin-walled stainless steel tube). Depending on the shape and form of the contact element, the probe card can be, for example, a needle-type, vertical pin-type, or MEMS (micro-electromechanical system) type probe card. The contact elements of the probe card can be made of, for example, tungsten or a tungsten / rhenium alloy. The contact pads of the integrated circuit can be made of, for example, aluminum, copper, a copper alloy, or many types of solders (such as lead-tin and tin-silver). Typically, the probe card is customized for each type of wafer so that each integrated circuit on the wafer can be electrically tested.

[0015] The chuck and the probe card are arranged inside a first radiation shield comprising two shielding parts. The first shielding part (i.e., the first fixed part) has a first aperture through which a support post is arranged so that a first end of the support post extends to the interior of the first radiation shield. The first aperture is preferably sized in such a way that the support post does not touch the first fixed part in any position of the chuck. Preferably, the shape of the first aperture is circular. The second shielding part (i.e., the first movable part) is attached to the support post and is arranged to cover the first aperture in any position of the chuck. The first aperture can be closed with the first movable part.

[0016] The first radiation shield acts as a thermal shield, thereby reducing the heat transfer. In other words, the first radiation shield is a thermal radiation shield. The first radiation shield defines a substantially enclosed space into which the chuck and the probe card are placed. Preferably, the only path that photons can enter the space enclosed by the first radiation shield is the gap between the first fixed part connected to the first aperture and the first movable part. The number of photons leaking through the gap can be reduced by geometry and by adjusting the emissivity of the surface.

[0017] The first fixed part may be mechanically attached to the vacuum chamber or to another radiation shield enclosing the first radiation shield together with a thermally isolating support (e.g., a thin-walled stainless steel tube). The first fixed part may include a cylindrical sidewall, an upper end wall attached to the upper edge of the sidewall around its periphery, and a lower end wall provided with a first orifice and attached to the lower edge of the sidewall around its periphery. The first movable part may include a circular plate positioned below the lower end wall of the first fixed part to cover the first orifice. The lower end wall of the first fixed part may be provided with a first lip around the first orifice, and the circular plate of the first movable part may be provided with a second lip arranged at its outer edge and facing the first lip. The first lip and the second lip together with the lower end wall and the circular plate form a labyrinth seal that provides a tortuous path for photons and thus limits the amount of thermal radiation entering the first radiation shield. The first fixed part and the first movable part of the first radiation shield may be made of aluminum, for example.

[0018] The cooling unit is thermally connected to the first radiation shield. In this text, the expression "thermally connected" means that two components are connected so that heat can be conducted therebetween. The cooling unit is used to cool the interior of the first radiation shield to a desired test temperature and to maintain the test temperature during testing of the integrated circuit. The test temperature inside the first radiation shield may, for example, be in the range of 1-4K. Heat is transferred from the first radiation shield via one or more thermal couplings connected between the cooling unit and the first radiation shield. The thermal coupling may be, for example, a cable or a rod made of copper or aluminum. Preferably, the cooling unit is thermally connected to both the first fixed part and the first movable part. The cooling unit may include one or more temperature stages, each of the one or more temperature stages being configured to provide a specific temperature to the part to which the cooling unit is thermally connected. The cooling unit may be a closed-loop circulating cooler based on helium.

[0019] A vacuum chamber allows testing of integrated circuits in a controlled environment. Various equipment may be used to control conditions such as pressure and temperature inside the vacuum chamber. Testing equipment may include, for example, a vacuum pump attached to the vacuum chamber for controlling the pressure and a cooling unit attached to the vacuum chamber for controlling the temperature inside the vacuum chamber. The vacuum chamber may be made of, for example, stainless steel or aluminum. When testing integrated circuits, the pressure inside the vacuum chamber is typically less than 10E-4 mbar.

[0020] The test equipment includes an electronic test unit for electrically testing the integrated circuits on the wafer. The electronic test unit is electrically connected to a probe card. The probe card provides an electrical path between the electronic test unit and the integrated circuits on the wafer, thereby allowing the integrated circuits to be tested and verified. The electronic test unit tests the integrated circuits according to a test program that defines the content of the test patterns and the sequence in which they are applied to the integrated circuits. The electronic test unit may include a processor and a memory including a computer program code, the memory and the computer program code being configured to cause the electronic test unit to electrically test the integrated circuits using the processor.

[0021] An advantage of the test device according to the invention is that it is capable of electrically testing integrated circuits on a wafer at extremely low temperatures, and even at temperatures below 4 K. Another advantage of the test device according to the invention is that the space in which the test integrated circuits are located, i.e. the interior of the first radiation shield, can be quickly and energy efficiently cooled to the desired test temperature and the temperature can be maintained using a minimum amount of energy. Another advantage of the test device according to the invention is that the space in which the test integrated circuits are located is well thermally shielded from its surroundings.

[0022] According to an embodiment of the invention, the first movable part has a second aperture through which the support column is arranged. The first movable part is attached to the support column so that there is no gap or a minimal gap between the support column and the first movable part. Preferably, in this embodiment, the support column is a one-piece pipe. The shape of the second aperture is preferably circular.

[0023] According to an embodiment of the present invention, the testing device includes a second radiation shield arranged inside the vacuum chamber and encapsulating the first radiation shield, the second radiation shield including a second fixed part and a second movable part, the second fixed part having a third orifice through which a support column is arranged, and the second movable part is attached to the support column and arranged to cover the third orifice.

[0024] The second radiation shield comprises two shielding parts. The first shielding part (i.e., the second fixed part) has a third aperture through which the support column is arranged so that the second end of the support column extends out of the second radiation shield. The third aperture is preferably sized so that the support column does not touch the second fixed part in any position of the chuck. Preferably, the shape of the third aperture is circular. The second shielding part (i.e., the second movable part) is attached to the support column and is arranged to cover the third aperture in any position of the chuck. The third aperture can be closed with the second movable part.

[0025] The second radiation shield acts as a thermal shield, thereby reducing heat transfer. In other words, the second radiation shield is a thermal radiation shield. The second radiation shield defines a substantially enclosed space into which the first radiation shield is placed. Preferably, the only path that photons can enter the space enclosed by the second radiation shield is a gap between the second fixed part connected to the third aperture and the second movable part. The number of photons leaking through the gap can be reduced by geometry and by adjusting the emissivity of the surface.

[0026] The second fixed part may be mechanically attached to the vacuum chamber or to another radiation shield enclosing the second radiation shield together with a thermally isolating support (e.g., a thin-walled stainless steel tube). The second fixed part may include a cylindrical sidewall, an upper end wall attached to the upper edge of the sidewall around its periphery, and a lower end wall provided with a third orifice and attached to the lower edge of the sidewall around its periphery. The second movable part may include a circular plate positioned above the lower end wall of the second fixed part to cover the third orifice. The lower end wall of the second fixed part may be provided with a first lip around the third orifice, and the circular plate of the second movable part may be provided with a second lip arranged at its outer edge and facing the first lip. The first lip and the second lip together with the lower end wall and the circular plate form a labyrinth seal that provides a tortuous path for photons and thus limits the amount of thermal radiation entering the second radiation shield. The second fixed part and the second movable part of the second radiation shield may be made of aluminum, for example.

[0027] An advantage of the second radiation shield is that it further improves the thermal shielding of the test rig, whereby the desired test temperature inside the first radiation shield can be achieved and maintained with a minimum amount of energy compared to a test rig having only one radiation shield.

[0028] According to an embodiment of the invention, the second movable part has a fourth aperture through which the support column is arranged. The second movable part is attached to the support column so that there is no gap or a minimal gap between the support column and the second movable part. Preferably, in this embodiment, the support column is a one-piece pipe. The shape of the fourth aperture is preferably circular.

[0029] According to an embodiment of the present invention, the cooling unit has a first temperature level thermally connected to the first radiation shield and a second temperature level thermally connected to the second radiation shield. The temperature levels of the cooling unit are configured to provide different temperatures to the radiation shield. The temperature achievable with the first temperature level is lower than the temperature achievable with the second temperature level. The temperature provided by the first temperature level may, for example, be in the range of 3-5K or about 4K, and the temperature provided by the second temperature level may, for example, be in the range of 45-55K or about 50K. Heat is transferred from the first radiation shield by one or more thermal couplings connected between the first temperature level and the first radiation shield. Heat is transferred from the second radiation shield by one or more thermal couplings connected between the second temperature level and the second radiation shield. The thermal coupling may be, for example, a cable or a rod made of copper or aluminum. Preferably, the first temperature level is thermally connected to both the first fixed part and the first movable part, and the second temperature level is thermally connected to both the second fixed part and the second movable part.

[0030] An advantage of a cooling unit with two temperature levels is that the space where the test integrated circuit is located (ie, the interior of the first radiation shield) can be cooled to the desired test temperature more quickly and more energy efficiently.

[0031] According to an embodiment of the present invention, the cooling unit has a third temperature stage thermally connected to the chuck and the probe card. Preferably, the third temperature stage is thermally connected to the probe card via a probe card holder. The temperature achievable with the third temperature stage is lower than the temperature achievable with the first temperature stage. The temperature provided by the third temperature stage may, for example, be in the range of 0.8-1.2K or about 1K. Heat is transferred away from the chuck via one or more thermal couplings connected between the third temperature stage and the chuck. Heat is transferred away from the probe card via one or more thermal couplings connected between the third temperature stage and the probe card. The thermal coupling may be, for example, a cable or rod made of copper or aluminum.

[0032] When the chuck is cooled by the cooling unit, heat from the wafer mounted on the chuck can be transferred to the chuck by conduction. Correspondingly, when the probe card is cooled by the cooling unit, heat from the wafer can be transferred to the probe card when the probe card is in electrical contact with the integrated circuit. The heat is transferred by conduction through the contact pads of the integrated circuit and the contact elements of the probe card. Therefore, the cooling unit can efficiently cool the wafer through the chuck and the probe card.

[0033] An advantage of using the third temperature stage of the cooling unit to cool the chuck and the probe card is that the space where the test integrated circuit is located (ie, the interior of the first radiation shield) can be cooled to a desired test temperature more quickly and more energy efficiently.

[0034] According to an embodiment of the present invention, the test apparatus includes a third radiation shield disposed inside the first radiation shield and enclosing the chuck and the probe card, the third radiation shield being thermally connected to a third temperature stage of the cooling unit.

[0035] According to an embodiment of the present invention, the fixed part of the radiation shield comprises a first lip around the aperture, and the movable part of the radiation shield comprises a second lip arranged at its outer edge, the first lip and the second lip being arranged to face each other. The first lip and / or the second lip may be provided with a seal made of an opaque material such as a metal-coated plastic. An advantage of the first lip and the second lip is that a labyrinth seal is formed between the fixed part and the movable part of the radiation shield. This provides a tortuous path for the photons and thus limits the amount of thermal radiation entering the radiation shield.

[0036] According to an embodiment of the present invention, the radiation shield includes a seal attached to a fixed part or a movable part for shielding a gap between the fixed part and the movable part. The seal may be attached to the fixed part so that the seal surrounds an aperture in the fixed part. The fixed part may include a lip around the aperture, the seal being attached to the lip. The seal may be attached to an outer edge of the movable part. The movable part may include a lip at its outer edge, the seal being attached to the lip.

[0037] According to an embodiment of the invention, the radiation shield comprises a solid ring attached to the fixed part together with a flexible element for closing the gap between the fixed part and the movable part.The flexible element surrounds an aperture in the fixed part.

[0038] Radiative heat transfer (emission / absorption) can be reduced by making the surfaces of one or more radiation shields and the inner surfaces of the vacuum chamber reflective. The heat reflective surface can be, for example, a polished metal. By making the surface locally absorbent, the proportion of the heat reflective surface can be maximized and only the non-idealities in the geometry can be compensated.

[0039] According to an embodiment of the present invention, at least one of the surfaces of the fixed part and the movable part facing each other is made heat absorbing. The heat absorbing surface ensures that photons cannot penetrate from the higher temperature side to the lower temperature side through the gap between the fixed part connected to the aperture and the movable part. The heat absorbing surface can be, for example, black anodized or painted black.

[0040] According to an embodiment of the present invention, a device for moving a chuck relative to a probe card includes a first actuator attached to a second end of a support column for moving the support column in three perpendicular directions. The movement is transmitted to the chuck to which the first end of the support column is attached through the support column. By using the first actuator, the chuck can be moved horizontally and vertically. The first actuator can be arranged outside the vacuum chamber, or inside the vacuum chamber but outside one or more radiation shields. The first actuator can be, for example, an electric motor that operates a screw that transfers rotational movement into linear movement. The advantage of having the first actuator outside one or more radiation shields is that the heat generated by the first actuator does not heat the space where the test integrated circuit is located, that is, the inside of the first radiation shield.

[0041] According to an embodiment of the present invention, a device for moving a chuck relative to a probe card includes a second actuator attached to a second end of a support column for rotating the support column about its longitudinal axis. The movement is transmitted to the chuck to which the first end of the support column is attached via the support column. The second actuator may be arranged outside the vacuum chamber, or inside the vacuum chamber but outside one or more radiation shields. The second actuator may be, for example, an electric motor operating a screw that transfers the rotational movement into a linear movement and transfers the linear movement back to the rotational movement of the support column. The advantage of having the second actuator outside one or more radiation shields is that the heat generated by the second actuator does not heat the space where the test integrated circuit is located, i.e., the interior of the first radiation shield.

[0042] According to an embodiment of the present invention, the support column includes one or more pipe fittings. A plurality of pipe fittings may be partially nested in each other, or may be arranged successively and continuously in the longitudinal direction of the support column. One or more movable parts may be attached between two continuous pipe fittings. The support column may be arranged as a pipe fitting passing through one or more movable parts. In this case, preferably, the support column is provided with a thermal radiation shielding member inside the pipe fitting to block the thermal radiation inside the pipe fitting. The support column may be a single-piece or multi-piece pipe fitting. Preferably, the pipe fitting has a round cross-section. The support column may be made of metal (such as stainless steel) or other materials with good mechanical properties and low thermal conductivity. The advantage of a support column made of one or more pipe fittings is that the heat transferred through the support column is minimal.

[0043] According to an embodiment of the present invention, the pipe is made of sheet metal. The advantage of sheet metal is that it can be easily formed into pipes.

[0044] According to an embodiment of the invention, the wall thickness of the tube is in the range of 0.05 mm to 0.3 mm. The advantage of having the wall thickness of the tube in this range is that it ensures that the heat transferred through the support column is minimal and the support column is stiff enough to maintain its shape.

[0045] According to an embodiment of the present invention, the cooling unit is a dry cryostat using a closed-loop helium cycle. When a dry cryostat is used, the vacuum chamber is kept at room temperature (not in a liquid nitrogen or liquid helium bath), and all low-temperature components are located inside the vacuum chamber. The dry cryostat may include multiple temperature levels, for example, a 50K level, a 4K level, and a 1K level. The advantage of a dry cryostat is that the space where the test integrated circuit is located (i.e., the inside of the first radiation shield) can be cooled to a temperature below 4K without immersing the entire system in a liquid helium bath.

[0046] The exemplary embodiments of the invention presented herein are not to be construed as limiting the applicability of the appended claims. The verb "comprise" is used herein as an open-ended limitation and does not exclude the presence of undescribed features. Unless expressly stated otherwise, the features described in the dependent claims can be freely combined with each other. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 showing a cross-sectional view of a test device according to a first embodiment of the invention,

[0048] Figure 2 shows a cross-sectional view of a test device according to a second embodiment of the present invention, and

[0049] Figure 3A-3E An exemplary structure of a radiation shield is shown. DETAILED DESCRIPTION

[0050] In different embodiments, the same or similar components are provided with the same reference numerals.

[0051] Figure 1 A cross-sectional view of a test device according to a first embodiment of the present invention is shown. The test device 100 includes a chuck 101 for holding a wafer 102 including an integrated circuit, and a probe card 103 attached to a probe card holder 104 for electrically contacting the integrated circuit on the wafer 102. The probe card 103 includes a contact element 105 that can be arranged to electrically contact the contact pad of the integrated circuit. Electrical testing of the integrated circuit is accomplished using an electronic test unit 106 electrically connected to the probe card 103. The probe card 103 provides an electrical path between the electronic test unit 106 and the integrated circuit on the wafer 102.

[0052] The chuck 101 can be moved relative to the probe card 103 using a moving device including a support column 107 having a first end and a second end. The first end of the support column 107 is attached to the chuck 101 so that the chuck 101 is perpendicular to the longitudinal axis of the support column 107. The moving device also includes a first actuator 108 for moving the support column 107 in three perpendicular directions, and a second actuator 109 for rotating the support column 107 around its longitudinal axis. The first actuator 108 and the second actuator 109 are attached to the second end of the support column 107 so that the movement is transmitted to the chuck 101 through the support column 107.

[0053] The chuck 101 and the probe card 103 are arranged inside a first radiation shield 110 including a first fixed part 111 and a first movable part 112. The first fixed part 111 has a first aperture 113 through which the support column 107 is arranged so that the first end of the support column 107 extends to the inside of the first radiation shield 110. The first movable part 112 has a second aperture 114 through which the support column 107 is arranged. The first movable part 112 is positioned below the lower side wall of the first fixed part 111 and is attached to the support column 107 so that it covers the first aperture 113. The lower end wall of the first fixed part 111 is provided with a lip 115 surrounding the first aperture 113, and the first movable part 112 is provided with a lip 116 arranged at its outer edge and facing the lip 115.

[0054] The first radiation shield 110 is arranged inside a second radiation shield 117 comprising a second fixed part 118 and a second movable part 119. The first fixed part 111 of the first radiation shield 110 is mechanically attached to the second fixed part 118 of the second radiation shield 117 but thermally isolated therefrom. The second fixed part 118 has a third aperture 120 through which the support column 107 is arranged so that the second end of the support column 107 extends out of the second radiation shield 117. The second movable part 119 has a fourth aperture 121 through which the support column 107 is arranged. The second movable part 119 is positioned above the lower side wall of the second fixed part 118 and is attached to the support column 107 so that it covers the third aperture 120. The lower end wall of the second fixed part 118 is provided with a lip 122 surrounding the third aperture 120, and the second movable part 119 is provided with a lip 123 arranged at its outer edge and facing the lip 122.

[0055] The second radiation shield 117 is arranged inside the vacuum chamber 124. The second fixing part 118 of the second radiation shield 117 is attached to the vacuum chamber 124. The vacuum chamber 124 allows testing of integrated circuits in a controlled environment. The pressure inside the vacuum chamber 124 is controlled with a vacuum pump 125.

[0056] The test apparatus includes a cooling unit 126 for cooling the wafer 102 to a desired test temperature and for maintaining the test temperature during testing of the integrated circuit. The cooling unit 126 includes three temperature stages 127, 128, and 129, each of which is configured to provide a specific temperature to a part to which the cooling unit is thermally connected. The first temperature stage 127 is thermally connected to the first radiation shield 110, and the second temperature stage 128 is thermally connected to the second radiation shield 117. The temperature achievable with the first temperature stage 127 is lower than the temperature achievable with the second temperature stage 128. Heat is transferred from the first radiation shield 110 through a thermal coupling 130 connected between the first temperature stage 127 and the first radiation shield 110. Heat is transferred from the second radiation shield 117 through a thermal coupling 131 connected between the second temperature stage 128 and the second radiation shield 117. The third temperature stage 129 is thermally connected to the chuck 101 and the probe card 103. The temperature achievable with the third temperature stage 129 is lower than the temperature achievable with the first temperature stage 127. Heat is transferred away from the chuck 101 and the probe card 103 through the thermal coupling 132 connected between the third temperature stage 129 and the chuck 101 and the probe card holder 104 .

[0057] Figure 2 A cross-sectional view showing a testing device according to a second embodiment of the present invention. Figure 2 Test equipment and Figure 1 The test apparatus of is different in that the support column 107 includes three column parts 201, 202 and 203, and the first movable part 112 and the second movable part 119 do not have an orifice. The first end of the column part 201 is attached to the chuck 101, and the second end of the column part 201 is attached to the first movable part 112. The first end of the column part 202 is attached to the first movable part 112, and the second end of the column part 202 is attached to the second movable part 119. The first end of the column part 203 is attached to the second movable part 119, and the second end of the column part 203 is attached to the actuators 108 and 109.

[0058] Figure 3A-3E An exemplary structure of a radiation shield is shown. More specifically, Figure 3A-3E A close up view showing the closed gap between the first fixed part 111 and the first movable part 112 of the radiation shield. Figure 3A In FIG. 1 , a seal 301 is shown, which is attached to the first fixed part 111 such that the seal 301 surrounds the first aperture 113. The seal 301 is pressed against the first movable part 112 such that the gap between the first fixed part 111 and the first movable part 112 is closed. Figure 3B Radiation shielding and Figure 3AThe radiation shield of is different in that the first movable part 112 includes a lip 116 arranged at its outer edge to reduce the number of photons leaking through the gap. Figure 3C Radiation shielding and Figure 3A The radiation shield of is different in that the first fixing part 111 comprises a lip 115 to which the seal 301 is attached. Figure 3D Radiation shielding and Figure 3C The radiation shield of is different in that the first movable part 112 includes a lip 116 arranged at its outer edge to reduce the number of photons leaking through the gap. Figure 3E , a structure is shown in which the gap between the first fixed part 111 and the first movable part 112 is closed by a solid ring 302 attached to the first fixed part 111 together with a flexible element 303. The flexible element 303 surrounds the first aperture 113.

[0059] Only advantageous exemplary embodiments of the invention are described in the drawings. It is clear to the person skilled in the art that the invention is not limited to the examples presented above, but that the invention may vary within the limits of the claims presented below. Some possible embodiments of the invention are described in the dependent claims, and they are not to be regarded as limiting the scope of protection of the invention in this way.

Claims

1. A test device, include: - Vacuum chamber, - a chuck for holding a wafer comprising an integrated circuit, - a probe card for electrically contacting the integrated circuits on the wafer, - a moving device for moving the chuck relative to the probe card, - a first radiation shield arranged inside the vacuum chamber and enclosing the chuck and the probe card, and - a cooling unit thermally connected to the first radiation shield, Features: - means for moving the chuck relative to the probe card comprising a support post having a first end and a second end, the first end of the support post being attached to the chuck, and - said first radiation shield comprises a first fixed part having a first aperture through which said support column is arranged, and a first movable part attached to said support column and arranged to cover said first aperture.

2. The test device according to claim 1, Features: The first movable part has a second aperture through which the support post is arranged.

3. The test device according to claim 1 or 2, Features: The testing device comprises a second radiation shield arranged inside the vacuum chamber and enclosing the first radiation shield, the second radiation shield comprising a second fixed part and a second movable part, the second fixed part having a third aperture through which the support column is arranged, the second movable part being attached to the support column and arranged to cover the third aperture.

4. The test device as claimed in claim 3, Features: The second movable part has a fourth aperture through which the support column is arranged.

5. The test device as claimed in claim 3, Features: The cooling unit has a first temperature level thermally connected to the first radiation shield and a second temperature level thermally connected to the second radiation shield.

6. The test device as claimed in claim 5, Features: The cooling unit has a third temperature stage thermally connected to the chuck and the probe card.

7. The test device as claimed in claim 1, Features: The first fixed part of the first radiation shield comprises a first lip surrounding the first aperture, and the first movable part of the first radiation shield comprises a second lip arranged at an outer edge thereof, the first lip and the second lip being arranged facing each other.

8. The test device as claimed in claim 1, Features: The first radiation shield includes a seal attached to the first fixed part or the first movable part for shielding a gap between the first fixed part and the first movable part.

9. The test device according to claim 1, Features: The first radiation shield comprises a solid ring attached to the first fixed part together with a flexible element for closing a gap between the first fixed part and the first movable part.

10. The test device according to claim 1, Features: At least one of the surfaces of the first fixed part and the first movable part facing each other is made to absorb heat.

11. The test device according to claim 1, Features: The means for moving the chuck relative to the probe card includes a first actuator attached to the second end of the support post for moving the support post in three perpendicular directions.

12. The test device according to claim 11, Features: The means for moving the chuck relative to the probe card includes a second actuator attached to the second end of the support post for rotating the support post about its longitudinal axis.

13. The test device according to claim 1, Features: The support column includes one or more tubes.

14. The test device as claimed in claim 13, Features: The tube is made of sheet metal.

15. A test device as claimed in claim 13 or 14, Features: The wall thickness of the tube is in the range of 0.05 mm to 0.3 mm.

16. The test device according to claim 1, Features: The cooling unit is a dry cryostat using a closed loop helium gas cycle.

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