WO2006050950A1

WO2006050950A1 - Method and apparatus for removing impurities, and use of a cleaning agent

Info

Publication number: WO2006050950A1
Application number: PCT/EP2005/012055
Authority: WO
Inventors: Paul Leiderer; Johannes Graf; Mario Mosbacher; Boris Lukiyanchuk; Minghui Hong; Tow Chong Chong
Original assignee: Universität Konstanz; A*Star
Priority date: 2004-11-10
Filing date: 2005-11-10
Publication date: 2006-05-18
Also published as: DE102004054320A1

Abstract

In summary, the present invention comprises a method for removing impurities from a surface (14) of an object (12), comprising the steps of: providing a cleaning material (22); applying the cleaning material (22) as a solid to at least part of the surface (14) of the object (12) to be cleaned; introducing radiation (24), the radiant energy of the radiation (24) being at least partially absorbed by the object (12) and/or the cleaning material (22), in such a manner that the cleaning material (22) is heated and substantially sublimes into the gaseous state (S; L), and an apparatus for removing impurities from a surface of an object, as well as the use of a cleaning agent to remove impurities from a surface of an object.

Description

"Method and apparatus for removing impurities, and use of a cleaning agent"

Description

The present invention relates to a method for removing impurities from a surface of an object, to an apparatus for removing impurities from a surface of an object and the use of a cleaning agent for removing impurities from a surface of an object.

The cleaning of contaminated surfaces represents a serious problem in many fields of technology. In particular in nanotechnology, for example the production of semiconductor wafers for chip production, contaminated surfaces or foreign particles, such as for example dust particles, at a surface of the semiconductor wafer can greatly restrict the operation of an electronic component, such as for example a semiconductor chip, or even make it unsuitable. In view of the size of conventional and future nanostructures in particular in semiconductor fabrication, which are currently of the order of magnitude of less than approximately 100 nm and are being constantly reduced in size, it is necessary to remove even foreign particles of sizes or diameters of approximately 50 nm and below.

Numerous methods have been developed for cleaning semiconductor surfaces and/or for removing foreign particles from a semiconductor surface. By way of example, semiconductor manufacture has disclosed wet-chemical cleaning methods which can be used for foreign particles larger than approximately 100 nm. However, wet-chemical cleaning methods cannot be applied locally, i.e. for selected surface regions of an object in which, for example, impurities occur. Rather, wet-chemical methods can only be applied over the entire surface. Wet-chemical methods are also disadvantageous since the surface to be cleaned can very easily be damaged, and the disposal of the generally environmentally harmful chemicals or cleaning agents is generally expensive.

Furthermore foreign particles can be removed, for example, from the surface of a semiconductor structure by radiating in laser light, in which context a distinction is drawn between two conventional methods, namely Dry Laser Cleaning (DLC) and Steam Laser Cleaning (SLC). In the DLC method, the semiconductor structure is irradiated with laser radiation and the semiconductor structure is heated very quickly, in particular close to the surface. On account of the thermal expansion of the semiconductor structure, foreign particles are thrown off the surface. However, this method has the drawback that the surface to be cleaned is generally damaged, for example by optical near-field effects, or ablation of the surface occurs. Furthermore, this method can only remove foreign particles with a size or diameter of approximately 100 nm or more.

A further method for removing foreign particles is the SLC method, which is described, for example, in US Patent US 4,987,286. In the SLC method, the surface of the object to be cleaned, for example a semiconductor structure, is wetted with a liquid, such as for example a water-alcohol mixture, with the liquid penetrating in particular into spaces between the surface of the semiconductor structure and a foreign particle. Then, the object to be cleaned is irradiated with laser light and heated, with the liquid evaporating explosively and as a result throwing the foreign particles off the surface of the semiconductor structure. The SLC method can currently be used to remove foreign particles with a minimum size or diameter of approximately 60 nm. The SLC method likewise entails numerous drawbacks. By way of example, drops of liquid may condense at the surface to be cleaned, with the result that the laser light is focused and, on account of the associated increase in the energy density, the surface may be damaged. Furthermore, if a conventional SLC method is used, it is not always possible to establish whether all the foreign particles have been covered by or embedded in the liquid. Furthermore, when using liquids such as for example water, drying spots or watermarks may occur. In particular, liquid films with a thickness in the nanometer range are not easy in technical terms to prepare. In addition, wetting of the substrate is presupposed.

Consequently, it is an object of the present invention for foreign particles, in particular with sizes or diameters of less than approximately 50 nm, to be removed in a simple and effective way from a surface of an object, while the surface of the object as far as possible remains undamaged.

This object is achieved by a method for removing impurities according to Claim 1 , an apparatus for removing impurities according to Claim 12 and the use of a cleaning agent according to Claim 24. Preferred embodiments of the present invention form the subject matter of the dependent claims.

The present invention comprises a method for removing impurities from a surface or at or on a surface of an object, comprising the steps of:

- providing a cleaning material or material to be removed;

- applying the cleaning material as a solid or in the solid phase to at least part of the surface of the object to be cleaned;

- introducing and/or irradiating radiation or energy, with the radiant energy of the radiation or the energy being at least partially absorbed by the object and/or the cleaning material, in such a manner that the cleaning material is heated in particular within a short timescale and thereby substantially sublimes into the gaseous state.

In the present invention, the term Jntroducing" is used synonymous with the term ..irradiating". The transition stage for the cleaning material from the solid state to the gaseous state is substantially a sublimation process. In other words, during the step of introducing radiation or introducing energy, the pressure and temperature of the cleaning material or in its vicinity can be controlled in such a way that a phase transition of the cleaning material is only possible from the solid state to the gaseous state. Consequently, pressure and temperature of the cleaning material are controlled in such a way that with regard to a conventional pressure- temperature diagram a phase transition substantially crosses the sublimation curve, i.e. substantially only a sublimation process is possible.

In particular, in the context of the present invention, the term "substantially sublimes" is preferably to be understood as meaning that predominantly a phase transition from the solid phase to the gaseous phase takes place, i.e. the solid cleaning material predominantly changes from the solid state to the gaseous state without the cleaning material adopting the liquid state in the meantime. Furthermore, in the context of the present application, the term "substantially sublimes" is preferably to be understood as meaning that during the transition from the solid state to the gaseous state a transient liquid nonequilibrium state can be adopted. In other words, a phase transition from the solid phase to the gaseous phase takes place, and a brief liquid state can be assumed to be well removed from a thermal equilibrium.

Furthermore, the step of applying the cleaning agent to the object to be cleaned is preferably an adsorption or resublimation step. In other words, the pressure and temperature of the cleaning agent are controlled in such a manner that when the cleaning material is applied and substantially until the step of introducing the radiation, the triple point of the cleaning agent is substantially undershot. It is preferable for the temperature of the cleaning agent substantially to be kept below the temperature of the triple point until the radiation is introduced and the cleaning material substantially sublimes into the gaseous state. Similarly, it is preferable for the pressure of the cleaning agent or in the vicinity of the cleaning agent substantially to be kept below the pressure of the triple point until the radiation is introduced and the cleaning material substantially sublimes into the gaseous state.

During the transition of the cleaning material from the solid state to the gaseous state, the cleaning material is preferably substantially sublimed incompletely. In particular, it is preferable for cleaning material which adjoins the surface of the object to be cleaned to be sublimed. The cleaning material is applied to the surface of the object to be cleaned substantially in the form of a layer which at least partially covers the surface of the object to be cleaned. The thickness of the cleaning material or the layer of the cleaning material in a direction normal to the surface of the object to be cleaned is preferably between about 10 nm and about 400 nm, particularly preferably between about 50 nm and about 200 nm. During the step of introducing the radiation, cleaning material is substantially sublimed in a range preferably up to about 50 nm from the surface of the object to be cleaned, preferably up to about 10 nm from the surface of the object to be cleaned, particularly preferably up to about 1 nm from the surface of the object to be cleaned. It is also possible for preferably about 5% to about 50%, particularly preferably about 10% to about 20%, of the layer of cleaning material to be substantially sublimed from the surface of the object to be cleaned. Consequently, during the step of introducing the radiation, it is preferable at least briefly for a layer of gaseous cleaning material to be formed between the surface of the object to be cleaned and the remaining substantially solid cleaning material. As a result of the transfer of momentum from the gaseous cleaning material to the solid cleaning material or the contamination and/or as a result of the expansion of the gaseous cleaning material, the solid cleaning material and/or the contamination is accelerated in the direction away from the surface of the object to be cleaned and is thrown off the surface of the object to be cleaned. In the process, the solid cleaning material may preferably be substantially completely thrown off the surface, i.e. substantially the entire layer of remaining solid cleaning material is thrown off the surface. However, it is also possible for the layer of cleaning material to be broken up into at least two parts which are thrown off the surface of the object to be cleaned. In this case, it is advantageous for the foreign particles to be joined to the solid cleaning material, with the result that the foreign particles are also removed from the surface of the object to be cleaned.

Furthermore, on account of the shear strength of the solid cleaning material, it is possible for foreign particles to be removed more easily and more effectively than is possible, for example, with a liquid cleaning agent.

With the process of the present invention, it is possible in particular for foreign particles of a size or diameter of less than or equal to approximately 50 nm to be substantially completely removed from the surface of the object. In this case, in particular it is not necessary to irradiate the entire surface of the object. Rather, the surface can be examined for impurities and then these impurities can be removed in a targeted way.

During the step of introducing radiation, it is preferable to introduce electromagnetic radiation, in particular laser radiation.

The process of the present invention can be used in particular to introduce laser radiation with a lower radiant power than, for example, in the conventional DLC process. This makes it possible to avoid damage to the surface of the object to be cleaned as a result of an excessively high radiant energy.

Furthermore, in particular there is no formation of droplets, as may occur, for example in the SLC method, with the result that undesired optical focussing of the radiation introduced is avoided, and consequently damage to the surface of the object to be cleaned can advantageously be prevented. Furthermore, the cleaning agent in the form of a solid is easier to control than, for example, a liquid film of a cleaning agent, with the result that it is possible to ensure in a simple manner that all foreign particles are covered by and/or embedded in the cleaning agent.

Furthermore, compared to the conventional DLC or SLC process, the difference between the refractive index of a foreign particle and the refractive index of the cleaning material is generally preferably lower than, for example, the difference between the refractive indices between air and a foreign particle to be removed (DLC process) or the difference in refractive index between a liquid which is used, such as a water-alcohol mixture, and the refractive index of the foreign particle to be removed (SLC process). Therefore, the optical field amplification at the foreign particles is advantageously reduced and damage to the surface of the object to be cleaned is avoided. This also reduces adhesion forces between a foreign particle and the surface of the object to be cleaned.

Furthermore, by using a solid cleaning material, it is advantageously possible to avoid drying spots at the surface of the object to be cleaned, as may occur when using liquids.

Also preferably, the radiant energy of the radiation introduced can substantially be absorbed by the object to be cleaned and/or substantially absorbed by the cleaning material. Consequently, the cleaning material may preferably either by heated indirectly, as a result of the object which is to be cleaned being heated by absorption of the radiant energy of the radiation introduced. However, it is also possible for the cleaning material preferably to be heated directly, by the radiant energy of the radiation introduced being substantially absorbed by the cleaning material. If the radiant energy is absorbed substantially directly by the cleaning material, it is advantageously possible to clean any desired object or a surface thereof and/or for foreign particles and/or impurities to be removed from a surface of any desired object.

However, it is preferably also possible for the pressure and temperature of the cleaning material to be controlled in such a manner that, as a result of introduction of the radiation, the cleaning material briefly passes through a liquid nonequilibrium state during the transition from the solid state to the gaseous state. The residence time in such a state is preferably in the range of a few nanoseconds or less, preferably less than approximately 100 ns, preferably between about 0.001 ns and about 100 ns, particularly preferably less than about 10 ns, preferably between about 0.01 ns and about 10 ns. In other words, the pressure and temperature are substantially not adjusted or controlled during the sublimation transition range. Rather, pressure-temperature pairs which in a conventional equilibrium phase diagram would be above the triple point briefly occur.

Also preferably, the cleaning material is moved substantially along the surface of the object and/or towards the surface of the object.

It is preferable for the cleaning material to be provided in the gaseous state. By way of example, the preferably gaseous cleaning material can be blown along the surface of the object to be cleaned or blown towards the surface of the object to be cleaned. The object to be cleaned is preferably cooled to a temperature lower than the freezing point of the gaseous cleaning material at a predetermined pressure of the gaseous cleaning material, with the result that the gaseous cleaning material is deposited as a solid on the surface of the object to be cleaned. It is particularly preferable for pressure and temperature of the system comprising cleaning agent and object to be cleaned to be selected in such a manner that the preferably gaseous cleaning agent, when it is being applied to the object to be cleaned, is close to the triple point of the cleaning agent. In other words, pressure and temperature of the preferably gaseous cleaning agent are controlled in such a way that the step of applying the cleaning agent to the object to be cleaned is substantially a resublimation step. In this case, it is preferable for the object to be cleaned to be controlled to a temperature less than or equal to the temperature of the cleaning agent at the triple point.

It is advantageously possible for a gaseous cleaning material, during the step of applying the cleaning material, to penetrate into openings in the foreign particle and/or to penetrate into openings between the foreign particle and the surface of the object to be cleaned and then to be substantially resublimed there. During the substantially explosive transition of the cleaning agent from the solid state to the gaseous state, momentum is transmitted from the cleaning agent to the foreign particles; the direction of the momentum transmitted, on account of the cleaning agent being arranged between the foreign particle and the surface of the object to be cleaned, is substantially a direction away from the surface of the object to be cleaned. In other words, the foreign particle is thrown off the surface of the object to be cleaned.

Also preferably, cleaning material is provided in the fluid, preferably liquid state. In this case, the cleaning material can be sprayed onto the surface of the object to be cleaned, in which case, after the liquid cleaning material has been applied, the cleaning material freezes to form a solid. It is preferable for the pressure and temperature of the cleaning agent to be controlled in such a manner that after the cleaning material has been applied and substantially up until the step of introducing the radiation, the triple point of the cleaning agent is substantially undershot. It is preferable for the temperature of the cleaning agent to be kept below the temperature of the triple point substantially until the radiation has been introduced and the cleaning material has substantially sublimed into the gaseous state. Similarly, it is preferable for the pressure of the cleaning agent to be kept below the pressure of the triple point substantially until the radiation has been introduced and the cleaning material has substantially sublimed into the gaseous state. Also preferably, the cleaning material can be provided in the form of solid particles. By way of example, it is possible for a multiplicity of small solid particles to be blown onto the surface of the object to be cleaned and irradiated with radiation on contact with the object to be cleaned.

The object to be cleaned is particularly preferably a metal, a dielectric or a semiconductor wafer, particularly preferably a silicon or germanium wafer with an optional oxide layer. Furthermore, the object to be cleaned may be a semiconductor wafer with existing metallic structures, such as for example interconnects and/or structures of other materials, such as for example low-k materials, i.e. materials with a low dielectric constant, in particularly with a dielectric constant of less than 3.

It is also particularly preferable for the cleaning material to be CO₂ and/or naphthalene and/or a noble gas. It is advantageous for the sublimation line in the conventional pressure-temperature diagram for CCMo be in regions which are technically easy to implement. In particular, the triple point of CO₂, which is at a temperature of T = 216.45K and a pressure of p = 520OhPa, can advantageously easily be undershot.

It is advantageous for the temperature of the object during the step of applying the cleaning material to be lower than the sublimation point of the cleaning material.

It is particularly preferable for laser radiation to be introduced during the radiation step.

The present invention also comprises an apparatus for removing impurities from a surface of an object, comprising:

- a provision apparatus for providing a cleaning material or material to be removed, and - a radiation source for radiation and/or an energy source,

the cleaning material being provided from the provision apparatus,

the cleaning material being applied to the surface of the object as a solid or in the solid phase, and

the cleaning material being heated by at least partial absorption of the radiant energy of the radiation by the object and/or by at least partial absorption of the radiant energy of the radiation by the cleaning material and/or by introduction of energy into the object and/or by introduction of energy into the cleaning material, in such a manner that it substantially sublimes into the gaseous state.

It is particularly preferable for the provision apparatus to be designed to provide the cleaning material in the gaseous state and/or in the fluid, preferably liquid state and/or in the form of solid particles.

The application process or deposition process of the cleaning material is particularly preferably a sublimation process.

Furthermore, it is preferable for the object to be a metal, a dielectric or a semiconductor wafer, particularly preferably a silicon or germanium wafer with an optional oxide layer. Furthermore, the object to be cleaned may be a semiconductor wafer with existing metallic structures, such as for example interconnects and/or structures of other materials, such as for example low-k materials. Also preferably, the cleaning material is CO₂ and/or naphthalene and/or a noble gas.

It is particularly preferable for the temperature of the object for deposition or application of the cleaning material to be less than the sublimation point of the cleaning material.

Furthermore, it is preferable for the radiation source to be a laser radiation source.

Furthermore, the present invention comprises the use of a cleaning material, in particular CO₂ and/or naphthalene and/or a noble gas to remove impurities and/or foreign particles, such as for example dust particles, from a surface of an object, the cleaning material being applied as a solid to at least part of the surface of the object and being heated by the introduction of radiation in such a manner that the cleaning material is substantially sublimed into the gaseous state.

It is also possible for the cleaning material to be heated by the introduction of energy. By way of example, the object to be cleaned may preferably be heated by electric current which flows through the object to be cleaned.

Furthermore, it is also possible for the cleaning agent to be heated directly, in which case energy can be transmitted into the cleaning material preferably on the basis of electric current or also preferably by particle radiation onto the cleaning material.

The transition of the cleaning material from the solid to a gaseous state is preferably a sublimation process.

The text which follows describes preferred variant embodiments of the method of the present invention on the basis of accompanying drawings, in which: Fig. 1 shows a diagrammatic sectional view of a preferred embodiment of the cleaning apparatus of the present invention during the step of applying cleaning materials;

Fig. 2 shows a conventional pressure-temperature diagram for CO2;

Fig. 3 shows a sectional view in accordance with Fig. 1 during the step of adjusting radiation.

Figure 1 shows a diagrammatic sectional view of a device 10 for removing impurities from a semiconductor substrate 12 or preferably from a surface 14 of the semiconductor substrate 12. The semiconductor substrate 12 may, for example, be a conventional silicon semiconductor wafer which is used or produced for the production of semiconductor chips, for example memory chips, in the computer industry. The semiconductor substrate 12 comprises the substantially planar surface 14, in which case it is also possible for the substantially planar surface 14 to have structures and/or topographies. Foreign particles 16 are arranged on the substantially planar surface 14 of the semiconductor substrate 12. The foreign particles 16 may, for example, be dust which has collected on the surface 14 during the manufacturing process, for example during grinding, of the semiconductor substrate 12 or the memory chip. Furthermore, Figure 1 shows a radiation source 18. The radiation source 18 may, for example, be a laser 18, for example an Nd:YAG laser or an excimer laser. Figure 1 also shows a provision device 20 for providing cleaning material 22. The provision device 20 may, for example, be a pressure vessel with an opening or valve or gas feed line or nozzle by which, for example, CO₂ gas 22 can be blown onto the semiconductor substrate 12 as preferred cleaning agent 22. In Figure 1 , the provision apparatus 20 is arranged substantially perpendicular to the surface 14 of the semiconductor substrate 12, so that the CO₂ gas 22 impinges on the surface 14 substantially perpendicular to a normal direction NR to the surface 14. However, it is also possible for the provision apparatus 22 to be arranged substantially parallel to the surface 14, i.e. substantially perpendicular to the normal direction NR to the surface 14. In this case, the CO₂ gas 22 at least partially moves substantially parallel to the surface 14 along the semiconductor substrate 12. Furthermore, the provision apparatus 20 may be arranged movably, making it possible for the cleaning material 22 to be applied to any desired regions of the surface 14. If, for example, a liquid cleaning material 22 is used, the provision apparatus 20 is of corresponding design.

In the preferred variant embodiment of the present invention, the semiconductor substrate 12 is cooled to a temperature T below the freezing point of the CO₂ gas 22 at a predetermined pressure p. It is advantageously possible to work, for example, in a nitrogen or argon atmosphere, which prevents water from water vapour which is present in the working atmosphere, from accumulating on the object 12 to be cleaned. In this case, it is advantageously possible to work substantially at atmospheric pressure. In other words, the object 12 to be cleaned is in a gas atmosphere which substantially comprises, for example, argon gas and/or nitrogen gas and/or for example another noble gas, in which case the gas atmosphere is held substantially at ambient pressure, i.e. at approximately 1013hPa. The CO₂ gas 22 is in this case deposited on the semiconductor substrate 12 in the form of a solid. In this case, pressure p and temperature T of the CO₂ gas 22 are preferably selected in such a way that the triple point TP for the solid CO₂ 22 is undershot. In the conventional phase diagram for CO₂ gas 22 shown in Figure 2, this substantially involves pressure-temperature pairs which are in the hatched region. In particular, it is the case for these pressure-temperature pairs, at temperature T, psκ(T)< p <pτp, where PSK corresponds to a pressure along the sublimation curve SK and PTP corresponds to the pressure at the triple point TP. It is also the case for these pressure-temperature pairs that at a given pressure p the relationship T < Tsκ(p) ≤ Tγp applies, where TSK corresponds to the temperature along the sublimation curve SK and TTP corresponds to the temperature at the triple point TP. Figure 2 also illustrates a melting curve SchK and a boiling curve SdK for CO₂22.

Figure 3 shows a sectional view in accordance with Figure 1 , in which CO2 22 has been applied or deposited as a solid on the surface 14 of the semiconductor substrate 12. The deposition or application process is preferably a resublimation process RS. The thickness of the deposited solid CO₂ 22 layer can be monitored in situ, in which case it is typical to produce thicknesses from approximately 10 nm to approximately 400 nm. The thickness of CO₂ 22 deposited can be monitored, for example, on the basis of interferometric methods. In particular, the thickness of CO₂ 22 deposited can be monitored both during the deposition process and after the deposition has ended.

By means of the laser radiation source 18, electromagnetic laser radiation 24 is radiated onto the solid CO₂ 22. The CO₂ 22 is predominantly substantially sublimed, i.e. the solid CO₂ 22 substantially sublimes in regions which are irradiated with the laser irradiation 24. In boundary regions which the laser radiation 24 does not touch and/or which adjoin irradiated regions, it is in particular possible to briefly adopt a liquid phase state well away from the thermal equilibrium. In the preferred embodiment of the present invention, the laser radiation source 18 is an Nd:YAG laser which introduces electromagnetic laser radiation 24 with a wavelength of 532 nm and an energy density from approximately 50 mJ/cm² up to approximately 300 mJ/cm². The solid CO₂ 22 is substantially transparent to laser radiation 24 of this wavelength, so that the laser radiation 24 is substantially absorbed by the semiconductor substrate. The laser radiation source 18 is preferably arranged movably, so that the laser radiation 24 introduced substantially strikes regions of the surface 14 of the semiconductor substrate 12 or of the solid CO₂ 22 at which foreign particles 16, such as for example dust particles, are present. Therefore, on the basis of the preferred variant embodiment of the present invention, it is advantageously possible for impurities such as for example foreign particles 16 to be deliberately locally removed. Therefore, cleaning of the entire surface 14 of the semiconductor substrate 12 is not necessary, with the result that the throughput can be considerably increased and the preferred variant embodiment of the present invention can be used effectively and at low cost.

The laser radiation 24 is substantially absorbed by the semiconductor substrate 12 and therefore heats the semiconductor substrate 12. It is preferable for the energy density of the laser radiation 24 introduced to be lower than what is known as the melting threshold of the semiconductor substrate 12, i.e. the energy density which has to be supplied for the semiconductor substrate 12 to just start to melt. In this preferred embodiment, the melting threshold of the silicon semiconductor substrate is approximately 310 mJ/cm². It is advantageous for the laser radiation 24 substantially not to be focused by the solid CO₂ 22, with the result that incipient melting at the semiconductor substrate 12 and therefore damage to the surface 14 with an introduced energy density below the melting threshold of the semiconductor substrate 12 is avoided. On account of the heat generated in the semiconductor substrate 12, the solid CO₂ 22 is "explosively" converted into the gaseous phase, in which case, on account of the pressure selected, a sublimation process S (cf. Figure 2) from solid CO₂ 22 into the gaseous state takes place. On account of transfer of momentum of the subliming CO₂ 22, the foreign particles 16 are thrown off the surface 14 of the semiconductor substrate 12.

As an alternative to the variant embodiment of the present invention described above, the wavelength of the laser radiation 24 can be selected in such a manner that the laser radiation 24 is absorbed by the cleaning material 22 i.e. the radiant energy of the laser radiation 24 directly heats the cleaning material and converts it into the gaseous phase. By way of example, if CO₂ 22 is used as cleaning agent, it is possible to use a CO₂ laser which generates laser radiation with a wavelength of 10.6 μm. Laser radiation of this wavelength is substantially absorbed by the solid CO₂ 22 and therefore heats the solid CO₂ substantially directly. Therefore, it is advantageously possible for foreign particles 16 to be removed from any desired object as the surface to be cleaned. In this case, it is in particular also possible to prevent the surface 14 of the semiconductor substrate 12 from being damaged as a result of the laser radiation, since the laser radiation 24 has already been attenuated as a result of the absorption in the cleaning material 22. In addition, semiconductor materials have a lower absorption coefficient for infrared laser radiation than for the visible region, with the result that the probability of substrate damage by the laser is additionally reduced.

In a further preferred variant embodiment of the present invention, during the transition of the solid cleaning agent 22, i.e. for example the solid CO₂ 22, into the gaseous state, the liquid nonequilibrium state is briefly also adopted. This is indicated by way of example by dashed line L in Figure 2. The liquid state far from the thermal equilibrium is in this case adopted briefly, i.e. for a short period of time amounting to a few nanoseconds or less preferably between approximately 1 ns and approximately 100 ns, particularly preferably between approximately 5 ns and approximately 10 ns. On account of the brevity of the residence time in the liquid phase and the fact that this state is not a thermal equilibrium state, it is possible in this context to speak of "substantial sublimation". In this context, it should be noted that the dashed line L is substantially intended to indicate a transition from the solid phase to the gaseous phase, since a phase diagram by definition only applies in the equilibrium state. During this transition, sufficient momentum is transmitted to the foreign particles 16, such as for example dust particles, so that the foreign particles 16 are thrown off the surface 14 of the semiconductor substrate 12.

Furthermore, the preferred embodiment of the present invention, as illustrated by way of example in Figures 1 and 3, comprises a blowing device or suction device 26. By means of the blowing device 26, foreign particles 16 or fragments of the solid CO₂ 22 or combinations of foreign particles 16 with solid CO₂ 22, which have been thrown off the surface 14 of the semiconductor substrate 12 to be cleaned on account of the preferred process of the invention described above by way of example, can be blown or sucked off the surface 14 of the semiconductor substrate 12 to be cleaned and/or the semiconductor substrate 12 which is to be cleaned. Contamination of the surface 14 of the semiconductor substrate 12 to be cleaned as a result of foreign particles 16 which have already been removed is in this way substantially avoided. It is preferable for the preferred components of the apparatus 10 described above to be arranged in a housing or chamber 28 in which the pressure and temperature can be controlled or set and/or a suitable atmosphere, such as for example a nitrogen and/or argon atmosphere, can be produced.

The present invention is not restricted to the variant exemplary embodiments described above. Rather, the present invention also encompasses further modifications to these embodiments. By way of example, the laser radiation source 18 may be arranged substantially perpendicular to the surface 14 of the semiconductor substrate with the blowing or suction device 26 preferably being arranged substantially at an angle of approximately 45° with respect to the normal direction NR to the surface 14. Also preferably, the laser radiation source 18 may be arranged at an angle other than approximately 45° with respect to the normal direction NR to the surface 14. Furthermore, the laser radiation source 18 may also be a laser other than an Nd:YAG laser.

List of designations

10 Device for removing impurities

12 Semiconductor substrate

14 Surface

16 Foreign particles

18 Laser radiation source

20 Provision apparatus

22 Cleaning material

24 Laser radiation

26 Blowing or suction device

28 Chamber or housing

NR Normal direction

S line for a substantial sublimation process

L Line for a substantial sublimation process

RS Line for a resublimation process

SK Sublimation curve

SchK Melting curve

SdK Boiling curve

TP Triple point

PTP Pressure at the triple point

T_Tp Temperature at the triple point

Claims

1. Method for removing impurities from a surface (14) of an object (12), comprising the steps of:

providing a cleaning material (22);

applying the cleaning material (22) as a solid to at least part of the surface (14) of the object (12) to be cleaned;

introducing radiation (24), the radiant energy of the radiation (24) being at least partially absorbed by the object (12) and/or the cleaning material (22), in such a manner that the cleaning material (22) is heated and substantially sublimes into the gaseous state (S; L).

2. Method according to Claim 1 , in which the cleaning material (22) is moved substantially along the surface (14) of the object (12) and/or towards the surface (14) of the object (12).

3. Method according to one of the preceding claims, in which the cleaning material (22) is provided in the gaseous state.

4. Method according to one of the preceding claims, in which the cleaning material (22) is provided in the liquid and/or fluid state.

5. Method according to one of the preceding claims, in which the cleaning material (22) is provided in the form of solid particles.

6. Method according to one of the preceding claims, in which the deposition process is a resublimation process.

7. Method according to one of the preceding claims, in which the object (12) is a metal and/or a dielectric and/or a semiconductor wafer.

8. Method according to Claim 7, in which the semiconductor wafer is a silicon or germanium wafer with an optional oxide layer, in particular with existing metallic structures and/or structures of other materials.

9. Method according to one of the preceding claims, in which the cleaning material (22) is CO₂ and/or naphthalene and/or a noble gas.

10. Method according to one of the preceding claims, in which the temperature of the object (12) is lower than the sublimation point of the cleaning material (22).

11. Method according to one of the preceding claims, in which the radiation step involves introducing laser radiation.

12. Apparatus (10) for removing impurities (16) from a surface (14) of an object (12), comprising:

a provision apparatus (20) for providing a cleaning material (22), and

a radiation source (18) for radiation (24),

the cleaning material (22) being provided from the provision apparatus (20),

the cleaning material (22) being applied as a solid to the surface (14) of the object (12), and

the cleaning material (22) being heated by at least partial absorption of the radiant energy of the radiation (24) by the object (14) and/or by at least partial absorption of the radiant energy of the radiation (24) by the cleaning material (22), in such a manner that it substantially sublimes into the gaseous state (S; L).

13. Apparatus (10) according to Claim 12, in which the cleaning material (22) is moved substantially along the surface (14) of the object (12) and/or towards the surface (14) of the object (12).

14. Apparatus (10) according to Claim 12 or 13, in which the provision apparatus (20) is designed to provide the cleaning material (22) in the gaseous state.

15. Apparatus (10) according to one of Claims 12 to 14, in which the provision apparatus (20) is designed to provide the cleaning material (22) in the liquid and/or fluid state.

16. Apparatus (10) according to one of Claims 12 to 15, in which the provision apparatus (20) is designed to provide the cleaning material (22) in the form of solid particles.

17. Apparatus (10) according to one of Claims 12 to 16, in which the deposition process is a resublimation process.

18. Apparatus (10) according to one of Claims 12 to 17, in which the object (12) is a metal and/or a dielectric and/or a semiconductor wafer.

19. Apparatus (10) according to Claim 18, in which the semiconductor wafer is a silicon or germanium wafer with an optional oxide layer, in particular with existing metallic structures and/or structures of other materials.

20. Apparatus (10) according to one of Claims 12 to 19, in which the cleaning material (22) is CO₂ and/or naphthalene and/or a noble gas.

21. Apparatus (10) according to one of Claims 12 to 20, in which the temperature of the object (12) is lower than the sublimation point of the cleaning material (22).

22. Apparatus (10) according to one of Claims 12 to 21 , in which the cleaning material (22) at normal pressure is moved substantially along the surface (14) of the object (12) and/or towards the surface (14) of the object (12).

23. Apparatus (10) according to one of Claims 12 to 22, in which the radiation source (18) is a laser radiation source.

24. Use of a cleaning material (22), in particular of CO₂, naphthalene or a noble gas, to remove impurities (16) from a surface (14) of an object

(12), the cleaning material (22) being applied as a solid to at least part of the surface (14) of the object (12) and being heated by the introduction of radiation (24), in such a manner that the cleaning material (22) is substantially sublimed into the gaseous state (S; L).