DE3242856A1 - METHOD FOR CLAMPING AND COOLING A SEMICONDUCTOR DEVICE DURING IT'S PROCESSING - Google Patents

Description

The invention relates to a device for clamping a semiconductor plate during its processing in a Vacuum chamber and relates more particularly to a hydraulically operated die clamping device, the effectively cools the platelet.

When processing semiconductor wafers, it is sometimes necessary to expose the wafers to high temperatures which e.g. for the diffusion of impurities "for the growth" of. epitaxial layers, for annealing metallic semiconductor contacts and the like. Are desirable. In many places in the course of the Machining, however, it is undesirable to expose the platelets to elevated temperatures, as this leads to uncontrolled diffusion of imperfections beyond prescribed limits and for the separation of imperfections at epitaxial interfaces comes.

Often, semiconductor plates are coated with a pattern of photoresist material before further processing, which, for example, determines a pattern for implanted imperfections during ion implantation. The photoresist materials commonly used have relatively low melting points. If the photoresist material is exceeded in processing the melting point, it degrades the quality of the design or destroyed it perfect So it is desirable _f Halbleiterplattchen only to subdue elevated temperatures when a particular process step makes this absolutely necessary and, if necessary, for cooling the To ensure platelets to prevent elevated temperatures from being reached at all.

In the manufacture of integrated circuits, a number of processes have been developed that make the application of high-energy Contain rays that are directed onto silicon wafers and for which purpose, for example, the ion implantation

tion that includes ion beam milling and reactive ion etching. In each case an ion beam is generated in a source and with different acceleration onto a target directed. Ion implantation has become a very common method for introducing impurities or impurities in semiconductor wafers that have become the bulk of semiconductor wafers by using the momentum of energetic ions as a means of embedding them in the crystal lattice of the semiconductor material are introduced.

To the extent that energetic ions on a semiconductor plate hit and migrate into the mass of the same, heat is generated by the atomic collisions. This warmth can become quite considerable as the energy level or the current level of the ion beam is increased.

One of the main goals in commercial semiconductor processing is seen as high throughput in platelets processed per unit of time. One of the ways to do this in an ion beam system is in using a beam of relatively high power. In doing so, however, large amounts of heat can be generated, which, as already mentioned, are undesirable.

As a result, most of the industrial equipment capable of generating high energy rays becomes platelets processed in batches in order to distribute the incident power over a large area and thereby the heating of the to reduce individual targets. A system for batch processing with mechanical movement of the platelets during implantation is disclosed in U.S. Patent 3,778,626. In general, batch processing systems are large around the batches and they are mostly only used for high-dose implants. Also, throughput is anything but optimal because of the time required to change the lots by hand.

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It has also been suggested to alternate heating To reduce scanning of targets.

Cooling by conductivity has also already been used, to alleviate the platelet heating problem. For this purpose, the platelets are e.g. in thermal contact with cooled metal plates brought. Another attempted solution consists in feeding a gas behind a plate * around a pipe between the back of the plate and the cooled support surface, see US Pat. No. 4,261,762. Also centrifugal forces have been used to press platelets against chilled surfaces.

According to US-PS h 282,924 platelets are pressed against pliable ₀ thermally conductive polymers, in order to promote the thermal contact. A clamping ring actuated by means of a cam presses a semiconductor plate against a convex curved plate, where a flexible, thermally conductive material adheres to the surface. The plate is cooled by freon circulating in a cavity in the housing.

In any case of cooling by conductivity, an effort is made to ensure an intimate contact between the plate and the to achieve a cooled surface. Since the wafer is machined under strong negative pressure, every gap closes between the platelet and the cooled surface offer the possibility of conduction cooling. In practice it is difficult to achieve this intimate contact because the semiconductor die Has irregularities in the surface.

Complicated devices are required overall for the known solutions, and it is not always the desired extent achieved in terms of cooling. In particular, mechanical clamping devices are relatively extensive and do not require only difficult but also time-consuming maintenance «Furthermore, mechanical tolerances and wear can lead to uneven

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or reduced clamping pressure for the platelets, which in turn increases the thermal conductivity between the platelets and the cooled surface is reduced.

The object of the invention is to provide a device for clamping and To create cooling of a semiconductor wafer in a vacuum chamber. In particular, effective cooling should be made possible during machining will. Specifically, by hydraulically clamping a semiconductor chip to a flexible, thermally conductive cushion rapid transfer of thermal energy is ensured.

In order to achieve the object on which the invention is based, a device for clamping a semiconductor wafer is provided created in a vacuum chamber having a housing, a press plate coupled to the housing for engagement with the wafer and a pressure plate which is movable with respect to the pressure plate. The pressure plate is between a retracted position, in which the pressure plate and the pressure plate delimit a Aufnähmeschlitz for the plate, and a platelet clamping position in which the pressure plate presses the plate firmly against the pressure plate. Further the device includes a fluid-containing member which is connected between the housing and the pressure plate and contains a fluid which, in response to a predetermined pressurization, actuates the member and causing the pressure plate to move into the position for clamping the wafer. The device also includes a device which applies the predetermined pressure to the fluid when the movement of the pressure plate in the platelet clamping position is desired, as well as a device that the pressure plate after lifting the predetermined Pressurizing the fluid in the withdrawn Position resets.

According to the invention, the device described above can also be a device for cooling the pressure plate

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"actuating fluids and a compliant thermally conductive Have cushion, which is arranged between the pressure plate and the plate. Thermal energy is from the platelet through the thermally conductive pad and the pressure plate transferred to the fluid.

The invention is described below with further advantageous details on the basis of an exemplary embodiment shown schematically explained in more detail. In the drawings shows!

1 shows a simplified diagram of a device according to the invention;

FIG. 2 shows a cross section through a device for clamping and cooling a semiconductor die according to FIG an embodiment of the invention ι

3 is an exploded perspective view of FIG Device for clamping and cooling a semiconductor die according to FIG. 2.

The device shown schematically in Fig. 1 for clamping a semiconductor wafer in a vacuum chamber and for cooling the wafer during its further processing includes a plate arrangement 6 in which a semiconductor wafer 8 in a receiving slot 10 for the wafer between a press plate 12, which is provided with a housing \ k is coupled, and a resilient, thermally conductive pad 16 is added. A pressure plate which can be moved with respect to the pressure plate 12 by means of a bellows 20 is connected to the housing I ^. The bellows 20 contains a fluid 22 which, depending on a predetermined pressurization for clamping, causes the expansion of the bellows 20 and a movement of the pressure plate 18 from the retracted position shown in FIG. In the platelet clamping position, the semiconductor wafer 8 and the thermally conductive pad 16 are pressed firmly against the pressure plate 12 by the pressure plate 18. The press

Plate 12 has an opening 24 that the front side of the semiconductor chip 8 exposed for an ion beam 26. The semiconductor wafer 8 is through along its peripheral edge the circumference of the opening 24 is held. Between the housing 14 and a return plate connected to the pressure plate 18 29 a return spring 28 is connected, which causes the retraction of the pressure plate 18 into the retracted position, when the predetermined clamping pressure is released.

The housing 14 contains fluid channels 30, 32 through which the fluid 22 in the bellows 2 0 is connected to a fluid system 34, which represents a closed circuit, the task of which is to cool the fluid 22 and to actuate the bellows 2 0. With the fluid channels 30, 32 are through corresponding fluid connections a pump 36 and a heat exchanger 38 coupled in series. The pump 36, which acts as a gear or centrifugal pump can be designed, allows the fluid 22 through the bellows 2 0 and the heat exchanger 38 with a flow rate of approx. Circulate 3.785 l / min (1 gallon / min). The heat exchanger 38 can be of such a type that the fluid 22 by a Cylinder 40 runs, which contains a cooled probe 42, which in turn contains a material, which by means of a cooling unit 44 is cooled. These and other suitable heat exchangers are known. One with the fluid system 3 ^ coupled Air-over-fluid reservoir 46 causes the fluid pressure to increase and the actuation of the bellows 2 0 when increased air pressure is supplied to its inlet. The fluid 22 should have a have a deep freezing point and can be easily pumped through the fluid system 3 ^ and the bellows 20. Besides, that should Fluid 22 must be compatible with the materials of the device, e.g. O-rings and have a high dielectric constant, since the pressure plate 18 is often part of an electrical circuit for measuring the dose. One of the preferred Fluid is methanol.

The plate assembly 6 is shown in detail in Figs. The bellows 2 0 is attached to the rear of the circular pressure plate 18 and to the housing 14 by means of corresponding retaining screws 50> 52. O-rings 5 ^ p 56 provide a vacuum seal between the fluid 22 and the external negative pressure environment. The bellows 20 can be any desired, sufficiently flexible bellows of appropriate dimensions, which can withstand the pressure difference between the vacuum environment and the fluid 22. A preferred material for the bellows is stainless steel. Connecting pins 58 are coupled to the rear of the pressure plate 18 and extend through holes in the housing 14 and are connected to the return plate 29 on the rear of the housing 14 on the return plate 29 is supported. The fluid channels 32 and 30, not shown here, establish a fluid connection between the bellows 20 and the fluid system 34 through the housing. The plate arrangement 6 is mounted rotatably about an axis 64. The fluid channels 30, 32 are connected to rotatable fluid connections on the axis 64. A plurality of retaining pins 66 protrudes from the housing 14 to the front. The pressure plate 18 is disk-shaped overall and has a convexly curved front side which creates an intimate thermal connection with the plate. A recess 68 for receiving the fluid 22 can be provided on the rear side of the pressure plate 18.

The thermally conductive pad 16, like a pad holder 70, belongs to a pad arrangement 69 shown in FIG 76 with an outer ring When the elements 72 and 76 are connected to one another, the inner ring 74 and outer ring 78 form concentric rings "between which the pad 16 is gripped. The cushion holder 70 has holes 80 at the locations corresponding to the retaining pins 66 of the housing 14.

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It has been shown to have superior heat transfer properties can be obtained when the pad 16 is made of a thermally conductive rubber, i.e. one with a thermally conductive one Fabric impregnated rubber. A pad 16 with a thickness in the range of 0.76 has proven to be suitable to 1.8 mm (0.03 to 0.07 inches), preferably 1.587 mm (1/16 inch) and a durometer hardness between 40 and 60. The durometer number indicates the hardness of the rubber, with high numbers indicating greater hardness. Known thermally conductive Cushions are thinner and harder. The substance that gives rubber its thermal conductivity must be a substance that does not reacts with or otherwise adversely affects the die. Preferred rubber additives for use in the case of silicon wafers, they are beryllium and aluminum.

The press plate 12 is also part of a press plate assembly 81 as well as a shield 82 which is attached to the front of the press plate 12 on spacers 84 and a plurality of spring loaded bumpers 86 which are attached to the shield 82 and extend through holes in the press plate 12 extend. The press plate 12 has a rearwardly projecting lip 88 along its lower edge and on both side edges. The opening 2k, which has a slightly smaller diameter than the semiconductor wafer to be processed, is provided in the press plate 12. The shield 82 is designed so that it does not block any part of the opening 2k. The task of the shield 82 is to absorb ion beam energy which would otherwise be absorbed by the press plate 12 and which would cause additional heating of the semiconductor plate 8. The press plate 12 and the shield 82 are each provided with aligned holes which correspond to the positions of the retaining pins 66 on the housing 14-.

The pad arrangement 69, like the press plate arrangement 81, is attached to the housing I ^ so that the retaining pins 66 through the holes 8 0 in the upholstery holder 7 0 and through the

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Holes in the press plate 12 and in the shield 82 extend. By means of screwed onto the retaining pins 66 The cushion arrangement 69 is knurled head or clamping screws and the press plate assembly 81 attached to the housing 14 » When the cushion assembly 69 and the pressure plate assembly 81 are attached in the aforesaid manner, they are spring loaded standing bumper 86 on the front surface of the thermally conductive pad l6.

During use, the pressure plate 18 is initially in its retracted position, in which its rear side rests against the housing 14-. The pad 16 is adapted to the convexly curved front side of the pressure plate 18. Thus, between the press plate 12 and the pad 16, the receiving slot 10 for the semiconductor wafer is determined, which is also limited by the spring loaded bumpers 86, which guide the semiconductor wafer 8 and hold it in a position immediately behind the opening Zk »The semiconductor wafer 8 will introduced into the receiving slot 10 under gravity after the plate assembly 6 has been rotated into a platelet receiving position, as described in its entirety in US Pat. No. k 282 92 * f.

When the semiconductor wafer has been brought into position and the plate assembly 6 has been moved back into an upright position, the pressure plate 18 is brought into its chip clamping position, as shown in FIG. 2, by increasing the air pressure acting on the accumulator kS. This causes a pressure increase in the fluid system Jk and in the bellows 20 and the bellows 20 is expanded. The pressure plate 18 stretches the pad 16 slightly and clamps the semiconductor wafer 8 firmly against the pressure plate 12. Since the opening Zk is smaller than the diameter of the semiconductor wafer 8, it is clamped along its peripheral edge. It will be appreciated that press plates with different sized openings are used for different sized semiconductor dies to ensure that most of the semiconductor surface area is covered

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the ion beam 26 is exposed. In the plate clamp position the thermally conductive pad 16 is in intimate contact both with the semiconductor wafer 8 and with the pressure plate 18. This gives the semiconductor wafer 8 thermal energy transmitted by the ion beam 26 has a path of high thermal conductivity that passes through the cushion 16 and the pressure plate 18 leads to the fluid 22 contained in the bellows 2 0. Because the fluid 22 is continuously cooled and circulated through the bellows 20, as already mentioned, the thermal energy is dissipated from the plate assembly.

The bellows 20 not only provides linear movement of the pressure plate 18, but can because of the inherent flexibility of the bellows 2 0 slight angular movements of the Allow pressure plate 18 to compensate for tolerances in the rest of the plate arrangement and a uniform, to achieve clamping pressure acting on the semiconductor die. As already mentioned, a more even clamping pressure leads to better cooling of the semiconductor chip.

After the processing of the semiconductor plate 8 by means of Ion beam, the air pressure applied to the accumulator 46 is reduced, which reduces the fluid pressure in the bellows 2 0. Then the return spring 28 has sufficient force to reduce the To overcome fluid pressure and the compression of the bellows 2 0 as well as a movement of the pressure plate 18 in its retracted To effect position. The semiconductor wafer 8 is removed from the receiving slot 10 by rotating the plate assembly 6 is removed to a die ejection position as described generally in U.S. Patent 4,282,924. So that is the die machining cycle completed. No die ejector is required.

As mentioned earlier, it is in commercial semiconductor manufacturing of the utmost importance to maintain high throughput. The throughput is promoted when the standstill

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times of the machine for maintenance or other reasons can be reduced to a minimum. The plate assembly 6 shown in FIGS. 1 to 3 and described above has a structure that facilitates maintenance. The most frequently performed maintenance work consists of 1 ») replacing the thermally conductive pad 16 and 2.) replacing the press plate 12 for adaptation to semiconductor wafers of different sizes. Either one or both of these tasks can be carried out after the clamping screw 92 and the pressure plate assembly 81 and _s if necessary, the cushion assembly was dissolved 69 of retaining pins do 66th The new units are then attached and the clamping screws 92 tightened again.

The die cooling performance of the apparatus shown in Figures 1-3 and described above was measured in an ion implantation system using a thermocouple adhered to the face of the die. 180 KeV As ions were implanted into a semiconductor wafer with a diameter of 100 mm. The fluid in the clamping arrangement for the semiconductor wafer was kept at a temperature of -25 ⁰ C, and it was applied, a fluid pressure of 3 x 5 ^a 't (50 psi) to overcome the force of the return spring and to clamp the semiconductor wafer. In At an input level of ion beam strength of 1.0 W / cm, the semiconductor wafer reached an equilibrium temperature of + 28 ° C; at an input power of 2.0 W / cm, the semiconductor wafer reached an equilibrium temperature of + 69 ° C Output temperature of -25 ° C. approx. 50 ° C./W / cm. Since the maximum temperature of semiconductor wafers coated with photoresist material is approx. 135 ° C., the device according to the invention can be operated in a wide range of input power values.

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Thus, according to the invention, there is a clamping device a semiconductor wafer in a vacuum chamber and for cooling the semiconductor wafer when ion beam energy is applied created. The hydraulically operated pressure plate enables even semiconductor die clamping pressure. The cooled fluid circulating through the bellows makes thermal energy effective from the pressure plate and dissipated from the semiconductor plate. The construction of the device facilitates maintenance.

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Claims (6)

Claims flJ Device for clamping a semiconductor wafer during further processing in a vacuum chamber, characterized by - A housing, a press plate connected to the housing for engagement with the semiconductor die, - A pressure plate that is opposite the pressure plate between a retracted position in which the press plate and the pressure plate form a semiconductor wafer receptacle limit, and a semiconductor clamping position is movable in which the pressure plate firmly against the semiconductor wafer the press plate presses, - a fluid-containing member, which is connected between the housing and the pressure plate and contains a fluid » which, depending on a predetermined pressurization, the actuation of the member and the movement of the Pressure plate from the retracted to the semiconductor die clamping position causes - a device that allows the predetermined pressure on the Applies fluid when movement of the pressure plate to the die clamping position is desired, and - A device which returns the pressure plate to the retracted position after the predetermined pressure on the fluid has been released. 2. Device according to claim 1, characterized in that the fluid containing member has a bellows which upon application of the predetermined pressure and causes the pressure plate to be moved in the direction of the pressure plate. 3. Device according to claim 2, characterized in that between the pressure plate and a resilient, thermally conductive pad is disposed on the die to conduct heat causes between said elements when the pressure plate is in the die clamping pitch is located. 4. Apparatus according to claim 31 characterized in that the press plate with the front side of the semiconductor plate along the peripheral edge the same is in engagement, and that the pressure plate, the thermally conductive pad in the semiconductor die clamping position presses against the back of the semiconductor chip. 5. Apparatus according to claim 2, characterized in that the means for applying the predetermined pressure is a fluid channel through the housing to the bellows, which is suitable for connection to a pressure source. 6. Device according to claim 5 » characterized in that the device for resetting the pressure plate has a return spring, between the housing and the pressure plate is switched. 7. Apparatus according to claim 6, characterized in that the fluid comprises methanol. 8. Device for plaguing a semiconductor die in a vacuum chamber and for cooling the semiconductor die during its processing, marked by - a housing, - A press plate connected to the housing for engagement with the semiconductor die, - A pressure plate that is opposite the pressure plate between a retracted position in which the pressure plate and the pressure plate delimit a die receiving slot, and is movable to a die clamping position is, in which the pressure plate presses the semiconductor die firmly against the pressure plate, - A resilient, thermally conductive pad, which is arranged between the pressure plate and the semiconductor wafer is that it causes heat conduction between these elements when the pressure plate is in the die clamping position is located - A bellows connected between the housing and the pressure plate, which contains a fluid which, when a certain Pressurization actuation of the bellows and movement causes the pressure plate from the retracted position to the semiconductor die clamping position and with the pressure plate is in thermal contact, - A device that applies the predetermined pressure to the fluid when the movement of the pressure plate in the Die clamping position is desired, - A device for cooling the fluid and - A device for resetting the pressure plate in the retracted position when the predetermined one is canceled Pressure on the fluid, whereby thermal energy can be transferred from the semiconductor wafer through the cushion and the pressure plate to the fluid. 9. Apparatus according to claim 8, characterized in that the press plate with the front side of the semiconductor wafer along the peripheral edge the same is in engagement, and that the pressure plate, the thermally conductive pad in the semiconductor die clamping position presses against the back of the semiconductor die, 10. Apparatus according to claim 9. characterized in that the means for cooling the fluid comprises a pump and a heat exchanger which are connected to the bellows in a closed circuit, wherein the pump the fluid through the closed Circulate circuit including the bellows and the heat exchanger dissipates heat energy from the fluid. 11. The device according to claim 10, characterized in that the heat exchanger has a fluid chamber in which a cooled probe is arranged. 12. Apparatus according to claim 10, characterized in that the means for applying the predetermined pressure is an air-over-fluid reservoir which is connected to the bellows. 13 device according to claim 12, characterized in that the fluid comprises methanol. 14. Apparatus according to claim 9, characterized in that the thermally conductive pad is at least 0.76 mm (0.03 inches) thick. 15 device according to claim 14, characterized in that the thermally conductive Pad having a thermally conductive material containing rubber. 1.6. Device according to claim 15 » characterized in that the thermally conductive Pad has rubber, which contains beryllium. 17 · Device according to claim 9s characterized in that, through the Press plate extends an opening which has slightly smaller dimensions than the semiconductor wafer, and that the pressure plate has a convexly curved front face that longitudinally extends the die in the die clamping position of the peripheral edge presses against the circumference of the opening, and that the pressure plate on its rear side immediately behind the Semiconductor die is connected to the bellows. 18. Device according to claim I7, characterized in that bumpers are provided which fix the semiconductor wafer in the receiving slot in its position in relation to the opening » 19. Apparatus for cooling a semiconductor wafer during ion implantation in an ion implantation chamber, marked by - a housing, - A press plate which is connected to the housing for Engagement with the semiconductor die along the peripheral edge thereof, - A pressure plate that is opposite the pressure plate between a retracted position in which the pressure plate and the pressure plate delimit a semiconductor wafer receiving slot, and a semiconductor wafer clamping position movable is where the pressure plate is the semiconductor die presses firmly against the press plate, - A cushion arrangement with a resilient thermally conductive cushion, which is between the pressure plate and the semiconductor plate is arranged so that it causes heat conduction between these elements when the pressure plate is in the die-clamping position, and with a pad holder that holds the thermally conductive pad lengthways holds its circumference and is connected to the housing, - eittioBalg, which is between the housing and the pressure plate is switched and contains a fluid which, when a predetermined pressure is applied, the expansion of the bellows and causing the pressure plate to move from the retracted position to the die clamping position, the fluid being in thermal contact with the pressure plate, - A device for applying the predetermined pressure to the fluid when the movement of the pressure plate in the Die clamping position is desired, - A device for cooling the fluid and - A device for resetting the pressure plate in the retracted position when the predetermined one is canceled Pressure on the fluid, whereby thermal energy can be transferred from the semiconductor die through the cushion and the pressure plate to the fluid. 20. Apparatus according to claim 19, characterized in that the press plate and the cushion assembly to the housing by a plurality of Pins are connected which extend through the pad assembly and the press plate, as well as through a plurality of Fasteners connected to the pins, by removing the fasteners from the pins the press plate and pad assembly is readily available is removable from the device.