WO2002095803A1

WO2002095803A1 - Method and device for thermally treating substrates

Info

Publication number: WO2002095803A1
Application number: PCT/EP2002/004791
Authority: WO
Inventors: Markus Hauf; Christoph Striebel
Original assignee: Mattson Thermal Products Gmbh
Priority date: 2001-05-23
Filing date: 2002-05-02
Publication date: 2002-11-28
Also published as: TWI283445B

Abstract

The invention relates to a simple and economical way to measure temperature based on pyrometers, enabling temperature to be measured in a precise manner even when said temperatures are low. Disclosed is a device and a method for thermal treatment of substrates, wherein the substrate is irradiated with at least first and second rays; predefined wavelengths of the first rays are absorbed between a first radiation source and the substrate; rays coming from the substrate are measured at the predefined wavelength with a radiation detector which is disposed on the same side as a second radiation source; the second rays emitted by the second radiation source are modulated and the second rays emitted by the second radiation source are determined.

Description

Method and device for the thermal treatment of substrates

The present invention relates to a method and an apparatus for the thermal treatment of substrates, in particular semiconductor wafers.

Computer chips and other electronic components are manufactured on round semiconductor wafers. This requires many different work steps and processes, such as B. structuring, lithography, ion implantation, etching or coating. Coating processes in particular require a defined temperature profile of the wafer in a given atmosphere for successful layer growth. However, a pure temperature treatment of the wafer in a vacuum often occurs as a post-treatment process for a previous treatment step, for example after implantation of ions to heal the damage caused as a result of the implantation in the crystal lattice of the wafer.

For the temperature treatment of wafers, rapid heating systems, also called RTP systems (Rapid Thermal Processing), are becoming increasingly important. They enable fast and well-defined thermal treatment of wafers under specified process conditions. RTP systems allow the wafer to be treated to be heated up to 1200 ° C and more within a few seconds. Heating rates of up to 500 ° C / s can be achieved. The decisive economic advantage of these systems compared to other thermal processing systems is their speed, which enables high throughput.

In order to be able to subject a substrate, such as a semiconductor wafer made of silicon, to temperature changes of up to a few hundred degrees per second, the wafer is subjected to a rapid heating system, as is known, for example, from DE-A-199 05 524, which was assigned to the applicant is heated with electromagnetic radiation. The well-known rapid heating system has ne process chamber made of quartz glass for receiving a substrate. Heating lamps are arranged above and below the process chamber, which generate electromagnetic radiation for the thermal treatment of the substrate. The heating lamps and the process chamber are surrounded by a further chamber (reflector chamber) which has reflecting inner walls in order to reflect electromagnetic radiation generated by the heating lamps.

The quartz glass in the process chamber is essentially transparent to the spectrum of electromagnetic radiation that is generated by the heating lamps. The process chamber has inflows and outflows for process gases, through which a suitable gas atmosphere can be generated within the process chamber during the thermal treatment of the substrate.

A pyrometer is provided as a temperature measuring device for measuring the wafer temperature. In order to distinguish between radiation emitted by the wafer and radiation reflected on the wafer and passing through the wafer, the radiation from the heating lamps is modulated. By means of this modulation, the radiation emitted by the substrate on the substrate can be distinguished from the reflected and transmitted radiation. Furthermore, the emissivity of the wafer can be determined on the basis of this distinction, which is necessary for determining the temperature of the wafer on the basis of the radiation emitted by it. Details of the modulation and the temperature determination method can be found in the aforementioned DE-A-199 05 524 or US-A-5, 154, 512.

However, the pyrometer-based temperature measurement has the problem that there is a strong radiation field in the process or reflector chamber, which makes it difficult to distinguish the radiation emitted by the wafer from the residual radiation. The temperature radiation emitted by the wafer and measured by the pyrometer can be superimposed by the residual radiation. This results in a very unfavorable signal (radiation emitted by the wafer) to the background (residual radiation) ratio. This problem increases in particular at low wafer temperatures, as the wafer decreases from _¬ emit radiation struck with decreasing temperature rapidly. Fertemperaturen at low Wa _¬ therefore also reduces the signal-to-background ratio. Below approximately 400 ° Celsius, the wafer emits very little radiation and, beyond this, it is more transparent to the heating radiation, so that the signal-background ratio deteriorates again. For temperatures below 400 ° Celsius, it is therefore usually no longer possible to determine the wafer temperature with a pyrometer using the conventional method.

To improve the signal-background ratio in pyrometer-based temperature measurement in RTP systems, it is proposed in DE-A-40 12 614 to produce the process chamber from an OH-containing quartz material. Such a quartz material has the property of absorbing infrared light in the wavelength range between 2.6 μm and 2.8 μm. The wafer located in the process chamber is thus heated by radiation, the spectrum of which has a gap between 2.6 μm and 2.8 μm. A viewing window is provided in the quartz chamber, which is transparent in the wavelength range mentioned and through which a pyrometer is aimed at the wafer. The pyrometer now measures infrared radiation from the wafer with a wavelength of 2.7 μm. Since the radiation from the heating lamps in the wavelength range of 2.7 μm cannot penetrate into the process chamber, the pyrometer only measures temperature radiation emitted by the wafer.

With this method, the temperature radiation of the wafer can thus be determined very well. However, to determine the temperature of the wafer, it is also necessary to know its reflectivity and transmissivity at the wavelength of 2.7 μm.

The method for determining the transmissivity and emissivity known from DE-A-199 05 524, which uses a characteristic modulation in order to emit reflected radiation that passes through the wafer measure, cannot be used here, since the relevant lamp radiation in the wavelength range of 2.7 μm is already absorbed on the process chamber wall.

According to the invention, the present invention is therefore based on the object of providing a pyrometer-based temperature measurement of substrates in a simple and inexpensive manner, which enables an exact temperature measurement even at low temperatures.

According to the invention, this object is achieved by a device for the thermal treatment of substrates, in particular semiconductor wafers, which has at least one first and at least one second radiation source, at least one transparent shield between the first radiation source and the substrate, which absorbs predetermined wavelengths of radiation, at least one on the On the side of the second radiation source, the radiation detector arranged on the substrate and measuring radiation with the predetermined wavelengths has a device for modulating the radiation emitted by the radiation source and a device for determining the radiation emitted by the second radiation source. The invention thus provides for filtering of certain wavelengths starting from the first radiation sources, which are in the measuring range of a radiation detector directed onto the wafer. In this way, the signal-to-background ratio of the substrate radiation to the residual radiation can be considerably improved. In addition, at least the unfiltered lamps located on the side of the radiation detector are modulated and the radiation emanating from them is determined, as a result of which the reflectivity of the wafer can be determined, which in turn makes a conclusion about the emissivity of the wafer in the range of the measurement wavelength of the pyrometer allowed. The temperature of the wafer can now be determined on the basis of the emissivity and the radiation emitted by the wafer.

According to a preferred embodiment of the invention are lung Strah ^¬ sources on opposite sides of the substrate arranged to to achieve a separation of the filtered and unfiltered radiation. In particular, the second radiation sources are arranged only on the side of the substrate to which the radiation detector is directed in order to measure on the pyrometer essentially only radiation emitted by the wafer and reflected on it.

According to a preferred embodiment of the invention, a device is provided for regulating the first radiation sources, which are regulated as a function of the pyrometer-based temperature determination of the wafer in order to subject the wafer to a specific temperature profile. Advantageously, a device for controlling the second radiation sources is also provided, so that they are operated constantly or possibly also certain setpoints are controlled. Thus, only the first, filtered radiation sources are used for the temperature control of the wafer. This prevents jumps in the intensity of the reflected lamp radiation, which is in the range of the measurement wavelength of the pyrometer, which facilitates the temperature determination.

The radiation sources are advantageously heating lamps. According to one embodiment of the invention, the transparent shield, which absorbs the predetermined wavelengths of the lamp radiation, is formed by the bulbs of the heating lamps. In this way, the desired filter function can be achieved in a simple and inexpensive manner. In particular, a simple replacement of the heating lamps in existing systems can be retrofitted.

In an alternative embodiment of the invention, the transparent shield is a process chamber wall which lies between the first radiation sources and the substrate and which absorbs the predetermined wavelength. The absorbing process chamber wall is arranged on the side of the substrate facing away from the pyrometer, so that it is ensured that no radiation with the predetermined wavelength falls on the side of the substrate facing away from the radiation detector. The transparent shield advantageously has at least one filter layer for absorbing the predetermined wavelengths, which according to one embodiment can be spatially separated from a further transparent material, such as a process chamber wall made of quartz glass. The transparent shield preferably has OH-enriched quartz glass, which preferably absorbs wavelengths between 2.6 μm and 2.8 μm. In order to prevent the transparent shield, which absorbs predetermined wavelengths, from overheating, a device for cooling the same is provided. The cooling device preferably has a cooling gas or a cooling liquid.

According to a preferred embodiment of the invention, the radiation detector is a pyrometer. The substrate is preferably a coated semiconductor wafer, in particular with a CO and / or Ti coating. In order to make a separate transmissivity for determining the emissivity superfluous, the wafer preferably has a low transmissivity. The transmissivity of the substrate is preferably below 0.15.

In an alternative embodiment of the invention, a second radiation detector is provided, which is preferably arranged in such a way that it enables a transmissivity measurement in order to be able to determine the emissivity of the substrate even more precisely. In one embodiment of the invention, the second radiation detector measures radiation outside the predetermined wavelengths in order to be able to measure non-absorbed and modulated radiation from the radiation sources. The second radiation detector preferably measures radiation below and above the predetermined wavelengths in order to be able to determine a transmissivity of the substrate in the range of the predetermined, absorbed wavelength via an interpolation, preferably a linear interpolation.

In an alternative embodiment of the invention, which is used in particular when the pistons of the heating lamps contain the filter function. ten, the second radiation detector is directed towards the side of the substrate facing away from the second radiation source and measures radiation with the predetermined wavelength. In this way, radiation emanating from the second heating lamps and passing through the wafer can be used directly for a transmissivity determination.

The object on which the invention is based is also achieved by a method for the thermal treatment of substrates, in particular semiconductor wafers, with the following method steps: irradiating the substrate with at least one first and at least one second radiation, absorbing predetermined wavelengths of the first radiation between a first radiation source and the substrate, measuring a radiation coming from the substrate at the predetermined wavelengths with a radiation detector which is arranged on the same side as a second radiation source, modulating the second radiation emanating from the second radiation source and determining the second radiation emanating from the second radiation source. This method enables the advantages already mentioned in relation to the device, namely the improvement of a signal-background ratio through the absorption of predetermined wavelengths of the first radiation, and the determination of the emissivity of the wafer through the modulation of the second radiation.

The present invention is explained in more detail below on the basis of preferred exemplary embodiments of the invention with reference to the drawings. The drawing shows:

Figure 1 is a schematic sectional view through a rapid heating system according to a first embodiment of the present invention.

Figure 2 is a schematic sectional view through a rapid heating system according to a second embodiment of the present invention.

3 is a graphical representation of the relationship between transmissivity and reflectivity for certain wafers; 4 shows a temperature measurement curve for a wafer coated with cobalt, which is being thermally treated; 5 shows a graphical representation for the determination of the measuring range for a transmissivity measurement according to an embodiment of the present invention.

The invention is explained in more detail below on the basis of preferred exemplary embodiments of the present invention.

1 shows in cross section a rapid heating system 1 for rapid heating of semiconductor wafers according to a first embodiment of the invention. A process chamber 2, which receives a semiconductor wafer 3, is formed by an upper transparent plate 4 and a lower transparent plate 5, preferably quartz plates. The wafer 3 to be processed is placed on a holding device 6 in the process chamber 2. Inlets and outflows for process gases, by means of which a gas atmosphere suitable for the process can be produced, are not shown.

Heaters, in the form of lamp banks 7 and 8, are mounted above and / or below the process chamber 2. The plates 4 and 5 lie between the wafer 3 and the lamp banks 7 and 8 and thus have the effect of a transparent shield to form a closed process chamber. The entire arrangement is enclosed by an outer furnace chamber 9, which also forms the side walls of the process chamber 2 and whose walls can be mirrored at least in sections. The lamp banks 7 and 8 each have a multiplicity of rod-shaped tungsten halogen lamps 10 and 1 arranged in parallel. Alternatively, other lamps such as point lamps can also be used. The wafer 3 is heated with the electromagnetic radiation emitted by the lamps. In the embodiment according to FIG. 1, the lamp bulbs of the heating lamps 10 of the upper lamp bank 7 have lamp bulbs which absorb predetermined wavelengths of the lamp radiation. In the currently preferred embodiment of the invention, the lamp bulbs are made of OH enriched quartz glass and they absorb wavelengths in the range between 2.6 μm and 2.8 μm. This ensures that radiation from the upper lamp bank has a gap in the range between 2.6 and 2.8 μm. The lamp bulbs of the lamps 11 of the lower lamp bank 8 are essentially transparent to the entire spectrum of the electromagnetic radiation from the lamps, so that the entire spectrum falls on the wafer 3 in the process chamber 2.

The radiation from the lamps 11 of the lower lamp bank is modulated by a modulation unit (not shown in more detail) with a characteristic parameter, as is known, for example, from the aforementioned DE-A-199 05 524, which is made the subject of the present invention, by repetitions to avoid.

To measure the wafer temperature, a pyrometer 13 is provided as a temperature measuring device, which is arranged on the side of the lower lamp bank and is directed toward the side of the wafer facing the lower lamp bank 8. The measuring range of the pyrometer 13 lies in a wavelength range which lies in the gap of the radiation from the upper lamp bank. For example, the pyrometer 13 measures radiation with wavelengths of 2.7 μm. Thus, the pyrometer 13 essentially only measures radiation that is emitted by the wafer 3 or radiation that emanates from the second unfiltered lamps 11 of the lower lamp bank 8 and is reflected on the wafer. Because the radiation from the second lamps 11 has a modulation, the radiation emitted by the wafer, which does not have this modulation, can be distinguished from the reflected lamp radiation. In addition to the wafer radiation, only radiation from the unfiltered lamps 11 of the lower lamp bank 8 falls into the measuring range of the pyrometer, so that there is an improved signal-to-background ratio compared to the known system, in which radiation from the upper lamp bank with wavelengths that are in fall into the measuring range of the pyrometer, enter it. In addition to the pyrometer 13, which is aimed at the wafer, a so-called lamp pyrometer is provided, which is directed at at least one of the unfiltered and modulated lamps 11 of the lower lamp bank 8 in order to determine its radiation intensity. The reflectivity of the wafer can be determined on the basis of the determined radiation intensity of the lamps 11 and the intensity of the radiation originating from the second lamps 11, measured on the pyrometer 13, which is reflected on the wafer 3 and can be distinguished from the wafer radiation on the basis of the modulation determine. The reflectivity in turn allows a conclusion to be drawn about the emissivity of the wafer, which is necessary for determining the temperature of the wafer, since the measured wafer radiation alone, without knowledge of the emissivity, does not allow any conclusion to be drawn about the temperature of the wafer.

Another factor in determining emissivity is transmissivity, i.e. the permeability of the wafer in the range of the measured wavelength. In the case of semiconductor wafers which have a very low transmissivity by nature, such as, for example, highly doped wafers with a metal layer, the transmissivity does not have to be determined separately, since this is negligible. If necessary, a constant can be used for the emissivity determination (emissivity = 1 - transmissivity - reflectivity), so that a sufficiently precise determination of the emissivity is possible solely by determining the reflectivity.

Alternatively, the transmissivity of the wafer can also be measured. For this purpose, a second pyrometer (not shown) can be provided, which is directed, for example, towards the side of the wafer facing away from the lower lamp bank and likewise measures radiation in the range of 2.7 μm. Since the upper lamp bank does not emit any radiation in this wavelength range due to the filter function of the lamp bulbs, only the radiation from the unfiltered lamps 11 of the lower lamp bank, which has passed through the wafer, falls into the pyrometer in addition to the actual wafer radiation. This in turn has a modulation that enables a differentiation to the wafer radiation. Because the radiation intensity the unfiltered lamps 11 of the lower lamp bank 8 is known, the transmissivity of the wafer can now be determined.

Of course, a small proportion of the radiation originating from the unfiltered lamps 11 of the lower lamp bank 8 can fall into the pyrometer through multiple reflection on the mirrored furnace chamber walls and the top of the wafer. However, this radiation is negligible and can be taken into account when the system is initially calibrated.

After knowledge of the reflectivity and the transmissivity, the emissivity of the wafer 3 can now be determined precisely. The temperature of the wafer can be determined very precisely on the basis of the radiation emitted by the wafer, which can be determined either by the pyrometer 13 or the upper pyrometer (not shown). This applies in particular also at low wafer temperatures at which the intrinsic radiation of the wafer 3 is low, specifically because of the improved signal-to-background ratio between the wafer radiation and the lamp radiation.

The heating devices can now be regulated on the basis of the known temperature. In the currently preferred embodiment of the invention, only the filtered lamps 10 of the upper lamp bank 7 and, if appropriate, filtered lamps of the lower lamp bank 8 are used for the control. The unfiltered lamps 11 of the lower lamp bank 8 are either operated constantly or are controlled to specific setting points. This prevents jumps in the intensity of the lamp radiation which is used for the reflectivity and, if appropriate, transmissivity measurement of the wafer. Thus, a known, essentially constant lamp radiation is always available for the reflectivity or transmissivity measurement, which enables an improved temperature determination for the wafer.

2 shows a rapid heating system according to an alternative embodiment of the invention. It consists of an outer chamber 20, the one Metal chamber or steel chamber with any geometric cross section can be. Both rectangular and round chambers are possible. The chamber inner wall is preferably partially or completely mirrored by means of a highly reflective layer. The chamber wall has a small opening 21 which allows radiation to be measured to emerge from the interior of the chamber. Through this opening, the radiation to be measured either falls directly into a radiation measuring device located behind it and not shown in the figure, preferably a pyrometer, or it is guided to the latter via a conductor arrangement such as optical fibers.

Heating devices in the form of an upper lamp bank 27 and a lower lamp bank 28 are provided in or on the chamber ceiling and in or on the chamber floor. The lamp banks 27, 28 preferably have lamps 29 and 30, respectively, which can also shine in visible light. In particular, the lamp banks each have a plurality of tungsten-halogen lamps 29 and 30 as heating lamps. In contrast to the first exemplary embodiment, all the lamp bulbs of the lamps 29, 30 are made of a material which is essentially transparent to the entire radiation spectrum of the lamps. These can be rod-shaped lamps or arbitrarily arranged point-shaped lamps. It is also possible to equip the lower lamp bank 28 with rod-shaped lamps and the upper lamp bank 27 with point-shaped lamps or vice versa. Both types of lamps are also possible within a lamp bank 27, 28. If both lamp banks 27, 28 consist of rod-shaped lamps, arrangements are possible in which the flashlights of the upper lamp bank 27 are arranged parallel to the flashlights of the lower lamp bank 28 or arrangements in which the flashlights of the upper lamp bank 27 are opposite the flashlights of the lower Lamp bank are crossed, preferably at right angles.

Between the lamp banks 27 and 28 is a substrate 33 to be treated, such as. B. a disk-shaped semiconductor wafer, preferably made of silicon. The wafer 33 can be uncoated, coated and / or implanted his. Coated wafers are advantageously used. Wafers with a Co or Ti layer or a combination thereof are preferred since their transmission coefficient (transmissivity) is less than 0.15 at temperatures of 350 ° C. The disk-shaped wafer 33 is arranged with its upper side 35 and with its lower side 36 parallel to the lamp banks 27 and 28.

A plate-shaped transparent shield 38 is arranged between the upper lamp bank 27 and the upper side 35 of the wafer 33. In the same way, a transparent shield 39 is provided between the underside 36 of the substrate 33 and the lower lamp bank 28. The shields 38 and 39 span the entire chamber 20, so that the inner volume of the chamber 20 is divided into three. In particular, the shields 38 and 39 form a process chamber 42 inside the chamber 20, in which the substrate 33 is located. In the inner process chamber 42, a process atmosphere which is conducive to the desired process can be formed with partly aggressive gases and under high or low pressures without impairing or closing the lamps 29, 30 of the lamp banks 27 and 28 or the mirrored inner wall of the chamber 20 contaminate. Corresponding gas inflows and outflows are provided for this, but these are not shown in FIG. 2.

The upper shield 38 is designed to absorb predetermined wavelengths or wavelength ranges from the spectrum of the heating radiation emitted by the upper lamp bank 27, so that the upper side of the substrate 33 is heated by a heating radiation which has a wavelength spectrum with at least one gap. Such an absorption effect can be achieved by appropriate filters in the form of one or more coatings of the shield 38 or one or more filter foils which are applied to a transparent base material, ie a transparent base plate. Quartz glass is preferably used for the transparent base material. If filter foils are used, these foils do not necessarily have to be attached to the transparent base plate or be in direct contact with it. Rather, the filter foils can be spatially separated from the transparent base plate and be closer to the upper lamp bank 27 than to the transparent base plate. Such a spatially separated arrangement of filter foils and transparent base plate is also referred to below as shield 38.

Such coatings and foils make it possible to remove predetermined wavelength ranges from the spectrum of the heating radiation. This can be one or more wavelength intervals and / or discrete individual wavelengths.

In the preferred embodiment of the invention shown in FIG. 2, the plate-shaped transparent shield 38 is made of quartz glass enriched with OH. This quartz glass has the property of absorbing infrared light in the wavelength range between 2.6 μm and 2.8 μm, which creates a gap in the wavelength spectrum of the heating radiation in this interval. Difficulties that can arise with the coating of quartz plates and the holding of filter foils are avoided by using an OH-enriched quartz plate.

Since the shield 38 is heated by the absorption of part of the heating radiation, cooling of the latter may be necessary, since a warm shield 38 itself emits thermal radiation, which can impair the desired temperature profile of the substrate 33.

To cool the shields 38 and, if appropriate, the shield 39, a cooling gas can be provided which flows outside the process chamber 42 via the shields. However, it is also possible to let the cooling gas flow through corresponding cooling lines, which are located inside the shields 38, 39. In such a case, the use of a coolant such as an oil is also possible. If the shielding 38, for example from a transparent base plate with one or more spatially separated filter foils, so the cooling medium can flow between the foils and the transparent base plate.

While parts with predetermined wavelengths are removed from the shielding 38 from the heating radiation generated by the lamp bank 27, the lower shielding 39 is transparent for these wavelengths. It is preferably a plate made of ordinary quartz glass.

During operation of the system, the heating radiation is primarily emitted by the upper lamp bank 27, with which the wafer 33 is heated to a predetermined temperature. This radiant heat consists of a spectrum of different wavelengths. 2 shows qualitatively two beams for two different wavelengths of this heating radiation, namely beam 44, which represents a light beam with a wavelength of 2.7 μm and beam 45, which represents a light beam with a wavelength of 2.3 μm.

Light with a wavelength of 2.7 μm is absorbed by the shield 38, which consists of an OH-enriched quartz plate, ie the beam 44 cannot penetrate the shield 38 and is swallowed by it. The wavelength of the beam 45, on the other hand, is outside the absorption area of the shield 38 and penetrates it unhindered. According to the drawing, it also penetrates the lower shield 38 and is reflected on the mirrored inner wall of the outer chamber 20, penetrates the shield 38 again and strikes the wafer 33. Since the wafer 33 itself is highly reflective, only a part of the Beam 45 absorbed and the rest reflected. Incidentally, this is one of the reasons why the radiant heat must be so intense. As can be seen in the drawing, multiple repetitions of the reflections are possible, in which part of the beam is always absorbed by the wafer. Finally, the beam 45 falls on the opening 21 in the chamber 20 and reaches the radiation detector. The lamps 30 of the lower lamp bank 28 are controlled so that they radiate weaker than the lamps 29 of the upper lamp bank 27. Furthermore, the radiation from the lamps 30 is weakly modulated. The radiation spectrum of the lamp bank 28 is advantageously the same radiation spectrum as that of the lamp bank 27. The shield 39 allows the modulated radiation of the lamp bank 28 to pass through unhindered. A beam 49 with a wavelength of 2.7 μm and a beam 48 for a wavelength of 2.3 μm are also shown here. Both rays pass through the shield 39 unhindered, are largely reflected by the substrate 33 and strike the opening 21 in the outer chamber 20.

Radiation is also emitted from the warm wafer 33. In FIG. 2, the wafer radiation is shown in dashed lines, with beam 51 symbolizing a beam with a wavelength of 2.7 μm and beam 52 symbolizing a beam with a wavelength of 2.3 μm.

The corresponding signal background conditions for a measurement of the pyrometer at 2.3 μm and at 2.7 μm are indicated in FIG. 2. As expected, the signal-background ratio for radiation of the wavelength 2.7 μm is enormously improved compared to the signal-background ratio for radiation of the wavelength 2.3 μm, since in the latter a considerable portion results from the heating radiation from the upper lamp bank and the radiation emitted by the wafer this wavelength is covered.

A pyrometer is used to determine the temperature of the wafer, which measures radiation with a wavelength of 2.7 μm. At this wavelength, a good signal-to-background ratio of wafer radiation and the reflected radiation at the wafer results because exclu ^¬ Lich radiation from the lower bank of lamps 28 with this wavelength falls on the pyrometer. Due to the modulation of the lamp radiation of unte ^¬ ren bank of lamps, the wafer radiation can in the above-described manner can be easily separated from the reflected radiation at the wafer. The radiation intensity of the lamps of the lower lamp bank is, as described above wrote, by means of a pyrometer or in some other way, such as _¬ example, a measurement of the electrical power consumed by the lamps, determined. Thus, the reflectivity of the wafer and its emissivity can be determined again in the manner described above. The temperature of the wafer can now be determined on the basis of the emissivity and the wafer radiation.

The use of the invention has proven to be particularly advantageous in the production and processing of wafers which are provided with a Co or Ti layer. Since CoSi _{2 is} a good electrical conductor, silicon wafers are coated with Co and heated to produce electrical contacts from CoSi ₂ . The formation of CoSi ₂ takes place in the temperature range between 400 ° C and 500 ° C, ie for the defined temperature control of the wafer it is necessary to control its temperature below 400 ° C.

With the described invention, the specific properties of cobalt are exploited. These include high surface reflectivity. As can be seen in FIG. 3, a wafer coated with cobalt has a transmissivity which is so low and essentially constant that a separate determination is not necessary. 3 shows the transmissivity of a wafer over the reflectivity. In addition, the lines of constant emissivity are drawn into the diagram as dashed lines. These decrease from left to right, since transmission, reflectivity and emissivity add up to 1 at any time. The diagram shows the transmission numbers for different reflectivities for different wafers: First, for an uncoated silicon wafer, a coated wafer and a cobalt-coated wafer. The transmission numbers of the uncoated wafer are predominantly greater than 0.15, while those of the coated and cobalt-coated wafers are consistently less than 0.15. The wafers coated with cobalt are thus particularly suitable for the above-mentioned temperature control according to the invention, since a separate determination of the reflectivity is not necessary. FIG. 4 shows the temperature profile of a wafer coated with cobalt in arbitrary time units, which was thermally treated in a rapid heating system according to FIG. 2. The temperature rises to 450 ° C in order to remain at this value for a certain time and then to decrease again. The temperature profile was monitored once using temperature sensors that were in direct contact with the wafer (curve A) and once using a pyrometer (curve B), using the above method. The remarkable coincidence of the temperature curve detected by the pyrometer with the temperature curve measured by the temperature sensors is remarkable. Both curves are almost congruent, even for temperatures below 300 ° C. At the beginning, the pyrometer shows slight fluctuations, but when the heating process starts, these disappear and the pyrometer curve corresponds to the temperature sensor case. A brief peak in the pyrometer curve during the cooling process is due to a lamp test.

In practice, however, there are also wafers whose transmittance is above 0.15. In FIG. 3, the uncoated calibration wafer would be such a case. Since the sum of transmittance, emissivity and reflectivity is always equal to 1, you can help yourself by carrying out a parallel transmission measurement for the wafer in addition to the above method, which is used together with the measured reflectivity to determine the emissivity and the wafer temperature.

For this purpose, as in the first exemplary embodiment, a further pyrometer is necessary, which is directed onto the wafer 33 through a corresponding opening in the chamber 20 above the upper lamp bank 27.

5, the transmission C of the OH-enriched upper quartz plate 4 is shown as line C. The transmission as it is clearly seen is the micron ^¬ ser quartz plate for wavelengths from 2.7 to 2.8 .mu.m equal to zero, that is, the plate is opaque to these wavelengths. In this wave length range ^¬ but is the wavelength for which the lower radiation ι y

tion detector measures the wafer reflectivity for emissivity determination. Strictly speaking, in order to link emissivity and transmittance to determine the temperature, the transmittance of the wafer would have to be determined at precisely this wavelength. However, this is not possible due to the opacity of the upper quartz plate 38 for light of this wavelength.

For this reason, the transmission of light of other wavelengths is measured and the transmission sought is extrapolated from this data. For this purpose, a filter is connected upstream of the upper pyrometer, which has a wavelength-dependent course of the transmission, as shown by curve D in FIG. 5. In the area of the optical opacity of the quartz plate 4, this filter has its greatest transparency. The transparency of the filter decreases towards smaller and larger light wavelengths.

In this way, two regions with wavelengths are cut out of the wavelength spectrum to the left and right of the absorption region of the quartz plate 38, which can reach the pyrometer above the lamp bank 27 despite the OH-enriched quartz plate 38 and filter. It is practical to choose the course of the transmission curve for the filter in such a way that the areas bordered by the filter curve and the quartz curve on the flanks of the absorption region for the quartz are approximately the same size.

If one is dealing with a wafer whose transmission number changes only weakly or approximately linearly with the wavelength, such as line E shown in FIG. 5 for the transmissivity of an example wafer, the transmission through the wafer can be seen measure for a wavelength from the area to the left of the absorption area of the quartz and the transmission through the wafer for a wavelength from the area to the right of the absorption area of the quartz. Since the transmission of the wafer changes only weakly or approximately linearly with the wavelength, the transmission for the desired wavelength can be determined from the absorption range of the quartz by averaging or approximation. By linking this transmission measurement with the one described above NEN measurement of the reflectivity of the wafer can now exactly determine the emissivity, even for wafers whose transmittance is greater than 0.15. This enables reliable temperature control in areas below 400 ° C up to approximately 300 ° C.

For the above transmission measurement, it is necessary that the lamps of the lower lamp bank are modulated in such a way that the radiation from the lamps of the respective upper and lower lamp banks can be distinguished. If such a distinction is provided by appropriate modulation, it is also possible to use a radiation detector, such as a pyrometer, for example, which is arranged below the lower lamp bank 28 for the transmission measurement. This can then be measured in the above manner from the radiation emanating from the upper lamp bank, which in turn is modulated and thus differs from the wafer radiation and the radiation from the lower lamp bank. The radiation falling on the pyrometer as a result of multiple reflection can either be taken into account in a calibration of the system, or it is neglected in determining the transmissivity.

However, the first example for the transmissivity measurement is preferred because, as in the first exemplary embodiment, the upper lamp bank is used for the temperature control of the wafers, while the lower lamp bank is kept constant or is controlled to specific setting points. This results in an essentially constant or changing intensity of the lamp radiation for the reflection and transmission measurement. In the case of the lamps used for temperature control, however, the intensity of the lamp radiation can change rapidly, causing jumps that can impair the reflection and transmission measurement.

Although the invention has been described on the basis of preferred exemplary embodiments, it is not restricted to the specific exemplary embodiments. In ^¬ play, the radiation intensity of the lamps can be used for the determination Instead of a lamp pyrometer, a suitable other measuring device, such as a device that calculates the intensity on the basis of the electrical power consumed by the lamps, is used. In addition, individual features of the above-described embodiments can be exchanged or combined with one another in any compatible manner.

Claims

claims

1. Device for the thermal treatment of substrates, in particular semiconductor wafers, with at least one first and at least one second radiation source, at least one transparent shield between the first radiation source and the substrate, which absorbs predetermined wavelengths of radiation, at least one arranged on the side of the second radiation source , radiation detector directed onto the substrate, which measures radiation with the predetermined wavelengths, a device for modulating at least the radiation emanating from the second radiation source, and a device for determining the radiation emanating from the second radiation source.

2. Device according to claim 1, characterized in that the first and second radiation sources are arranged on opposite sides of the substrate.

3. Device according to claim 1 or 2, characterized by a device for regulating the first radiation sources.

4. Device according to one of the preceding claims, characterized by a device for controlling the second radiation sources.

5. Device according to one of the preceding claims, characterized in that the radiation sources are heating lamps.

6. The device according to claim 5, characterized in that the transparent shield is formed by the bulbs of the heating lamps.

Device according to one of claims 1 to 5, characterized in that the transparent shield is a process chamber wall lying between the first radiation sources and the substrate.

8. Device according to one of the preceding claims, characterized in that the transparent shield has at least one filter layer for absorption of the predetermined wavelengths.

9. The device according to claim 8, characterized in that the filter layer is spatially separated from a further transparent material.

10. Device according to one of the preceding claims, characterized in that the transparent shield has OH-enriched quartz glass.

11. Device according to one of the preceding claims, characterized in that the transparent shield absorbs wavelengths between 2.6 μm and 2.8 μm.

12. Device according to one of the preceding claims, characterized by a device for cooling the transparent shield.

13. The apparatus according to claim 12, characterized in that the cooling device comprises a cooling gas or a cooling liquid.

14. Device according to one of the preceding claims, characterized in that the radiation detector is a pyrometer.

15. Device according to one of the preceding claims, characterized in that the substrate is a coated semiconductor wafer.

16. The apparatus according to claim 15, characterized in that the coating has a CO and / or Ti coating.

17. Device according to one of the preceding claims, characterized in that the substrate has a transmissivity of less than 0.15.

18. Device according to one of the preceding claims, characterized by a second radiation detector directed onto the substrate.

19. The apparatus according to claim 18, characterized in that the second radiation detector radiation outside the predetermined

Measures wavelengths.

20. The apparatus according to claim 19, characterized in that the second radiation detector measures radiation below and above the predetermined wavelengths.

21. The apparatus according to claim 18, characterized in that the second radiation detector is directed towards the side of the substrate facing away from the second radiation sources and measures radiation with the predetermined wavelengths.

22. Process for the thermal treatment of substrates, in particular semiconductor wafers, with the following process steps:

Irradiating the substrate with at least a first and at least a second radiation, absorbing predetermined wavelengths of the first radiation between a first radiation source and the substrate,

Measuring a radiation coming from the substrate at the predetermined wavelengths with a radiation detector which is arranged on the same side as a second radiation source,

Modulating the second radiation emanating from the second radiation source, Determining the second radiation emanating from the second radiation source.

23. The method according to claim 22, characterized in that the first and second radiation are directed from opposite sides onto the substrate.

24. The device according to claim 22 or 23, characterized in that the first radiation source is regulated.

25. The method according to any one of claims 22 to 24, characterized in that the second radiation is controlled.

26. The method according to any one of claims 22 to 25, characterized in that the radiation is generated by heating lamps.

27. The method according to claim 26, characterized in that the predetermined wavelengths of the first radiation are absorbed by the pistons of the first heating lamps.

28. The method according to any one of claims 22 to 27, characterized in that the predetermined wavelengths of the first radiation is absorbed by a process chamber wall lying between the first radiation source and the substrate.

29. The method according to any one of claims 22 to 28, characterized in that wavelengths of the first radiation between 2.6 microns and 2.8 microns are absorbed.

30. The method according to any one of claims 22 to 29, characterized in ^¬ net that the predetermined wavelengths absorbing member is cooled. 20

31. The method according to claim 30, characterized in that the element is cooled with a cooling gas or a cooling liquid.

32. The method according to any one of claims 22 to 31, characterized in that the radiation coming from the substrate is measured with a pyrometer.

33. The method according to any one of claims 22 to 32, characterized in that a radiation coming from the substrate is measured with a further radiation detector.

34. The method according to claim 33, characterized in that the further radiation detector measures radiation outside the predetermined wavelengths.

35. The method according to claim 33 or 34, characterized in that the further radiation detector measures radiation below and above the predetermined wavelengths.

36. The method according to claim 33, characterized in that the further radiation detector is directed onto the side of the substrate facing away from the second radiation source and measures radiation with the predetermined wavelength.