Method and device for measuring temperature radiation using a pyrometer wherein compensation lamps are used

Abstract: Method for measuring the radiation originating from one side of a wafer of semiconductor material using a pyrometer, wherein compensation radiation is projected onto that side to compensate for the reflectivity of the wafer of material and wherein the intensity of the compensation radiation is controlled subject to the amount of radiation measured by the pyrometer.

Description: When measuring the temperature of a wafer of semiconductor material, using a pyrometer with which the radiation generated according to the expression of Stefan Boltzmann is measured, the so-called emissivity is of great importance. The emissivity of an object has a value < 1 because of reflection occurring between the interior of the object and the outside environment, the so-called reflectivity. In the case of semiconductor wafers, the emissivity is found in practice to possibly vary between values of 0.4 and 0.9. This problem is adressed in US-A-4890245 wherein a method and apparatus is shown for detecting the temperature of a substrate, by measuring the intensity of infrared light from the substrate when it is irradiated by infrared light and also when it is not irradiated. The temperature is calculated from the transmissivity and emissivity of the substrate. It is a disadvantage of this known method and apparatus that the temperature of the substrate can only be measured when the radiation is interrupted. The present invention obviates the above problem; it provides a method for measuring the radiation originating from one side of a wafer of semiconductor material using a radiation thermometer or pyrometer, wherein the wafer is heated by heating means, characterized in that compensation radiation is projected onto the one side and/or the other side of the wafer to compensate for the reflectivity and/or the transparency of said wafer, and wherein the intensity of the compensation radiation is controlled subject to the amount of radiation measured by the pyrometer. Using the method according to the present invention a temperature measurement is therefore made of a wafer of semiconductor material which is independent of the emissivity of the object. US-A-3916690 disclosed an apparatus for measuring the temperature at the surface of an object by infrared radiation therefrom using a variably heated compensating radiator and a rotable chopper wheel. The heat supply to the compensating radiator is varied in accordance with a infrared-detector signal in such sense as to reduce the signal to zero whereby the temperature of the compensating radiator then equals the temperature of the object. NL-A-8701479 describes the continuous determination of an emission coefficient when radiation is measured which is reflected from a body, e.g. from moving metallic band. Further the present invention provides an apparatus for treating a wafer of semiconductor material, comprising: a treatment chamber wherein the wafer is treated; heating means disposed in said treatment chamber and for heating said wafer -one or more pyrometers or radiation thermometers for measuring radiation coming from siad wafer, characterized in that said pyrometer is disposed into a wall of the treatment chamber and in that one or more compensation lamps are provided for projecting compensation radiation onto the wafer of semiconductor material, wherein the intensity of the compensation lamps is controlled subject to the measurement value of the pyrometer. Further features, advantages and details will be elucidated in the light of a description of preferred embodiments thereof, with reference to the appended drawing, in which: Fig. 1 shows a schematic view of a preferred method according to the present invention. Fig. 2 shows a schematic view in perspective of a preferred embodiment of a device according to the present invention. Fig. 3 shows a section along line III-III of fig. 2. Fig. 4 shows a section along line IV-IV in fig. 2. Fig. 5 is a schematic side view of a second preferred embodiment of the present invention; and Fig. 6 shows a third preferred embodiment of the present invention. A pyrometer 1 is directed at a wafer of semiconductor material W to determine the amount of radiation originating from the wafer and the temperature thereof. The measurement output of the pyrometer 1 is connected to a control member 2 which in turn is connected to both a first compensation radiation source 3 and a second compensation radiation source 4. The first compensation radiation source 3 projects compensation radiation with a wavelength suitable for the pyrometer 1 (λ= 0.9-5.0µm) onto the region of the wafer W at which the pyrometer 1 is directed. It is demonstrated that for the value of the compensation radiation I c1 where I c1 = I eq is true, that is, the equilibrium radiation value I eq measured by the pyrometer, this I eq is the compensated radiation value for a wafer W with emissivity 1. From the expression of Stefan Boltzmann the temperature of the wafer W can now be derived from the measured I eq . A compensation radiation source must be precisely calibrated so that the amount of compensation radiation I c can be accurately controlled subject to the voltage to be supplied by the control member 2. The emissivity must be greater than 0.1-0.2 so that the formed control loop is sufficiently accurate and rapid. The radiation I c2 originating from the second compensation radiation source 4 compensates in a corresponding manner for the transparency or permeability of the wafer of semiconductor material W, when I c2 = I eq . A preferred embodiment of a device 11 (fig. 2, 3, 4) according to the present invention relates to a device for rapid heating (Rapid Thermal Processing (RTP)) of silicon wafers, for example for 30 seconds at a temperature of 300-1200°C, using infrared lamps, bulb filaments or graphite elements. A (circular) wafer of semiconductor material W is heated on the underside by infrared lamps 12, while on the upper side one or more pyrometers 13, 14 are received into a reflecting wall 15 together with associated compensation lamps 16 and 17 respectively. For details and advantages of the reflecting wall and the heating on the underside of the wafer W reference is made to the patent application EP-B-0 381 253 of same applicant published 08/08/90 Two compensation lamps 18 are further disposed on the underside, provided with a window 19 roughened on at least one side for projecting diffuse light onto the underside of the wafer W. Arranged between the compensation lamps 18 and the infrared lamps 12 is a water-cooled window 25 comprising cooling water to be supplied via openings 26 as well as two plates 20, 21 allowing passage of radiation. The water-cooled window 25 serves to absorb radiation from infrared lamps 12 in the wavelength region of the pyrometers 13, 14. It also ensures that the wafer of material W does not heat up unnecessarily on the underside and radiates less radiation to the underside. The plates 20, 21 are further cooled by the water. A window 22 is composed of quartz and is resistant to the forces occurring due to the vacuum which may be generated in the treatment chamber 24. The quartz window 22 can be further cooled with air by supply thereof through openings 27. A first pyrometer is preferably suitable for measurements in a temperature range of 500-1200°C (λ= 1.5-1.8µm) and a second pyrometer suitable for a temperature range of 200-800°C (λ = 3.0-3.3µm). The associated compensation lamps for the relevant wavelength are preferably embodied as halogen lamps of relatively low power (100-200 Watt). As preferred embodiment (not shown), a semi-reflecting mirror can be arranged between the compensation lamps and the wafer of semiconductor material, wherein the pyrometer also receives radiation via this semi-transparent mirror. This has the advantage that for each pyrometer only one opening needs to be arranged in the chamber. The semi-reflecting mirror is preferably a wafer of silicon material, optionally to be provided with a layer filtering the radiation according to wavelength. When the pyrometers display sensitivity to radiation coming from the infrared lamps, these lamps are preferably equipped with filters for filtering this radiation. The compensation radiation sources are preferably provided with a matt glass so that the intensity of the radiation is spread over a sufficiently large area. In a manner not shown, the radiation is preferably made diffuse using a facetted mirror or lens preferably composed of aluminium and silicon dioxide, which may or may not be provided with quartz. In a second preferred embodiment (fig.5) according to the present invention the temperature of a wafer of semiconductor material 31, which is heated by means of a holder 32 heated in a manner not shown here, is measured using an optic fibre 33 which is arranged through the holder 32 and connected in a manner not shown to a radiation meter the measurement value of which is compensated for the radiation coming from the holder 32 by means of a second optic fibre 34 which is arranged in a blind hole in the holder 32 and to which a radiation meter is likewise connected. In a third preferred embodiment (fig.6) according to the present invention a wafer of semiconductor material 36 is heated by a holder 37 heated in a manner not shown here and provided with a through-opening 38 and a blind hole 39. The radiation coming from these openings is guided via a lens 40 to detectors 41 and 42 of the schematically designated pyrometer 43. By means of radiation coming from the blind hole 39 compensation is made for the temperature radiation from the holder 37. In both the second and the third preferred embodiment the holder or chuck serves as compensation radiation. A radiation with a wavelength around 1.0 µm is preferably employed so that measurement can be made in a temperature use range of 0-1200°C. At the said wavelength there occurs no transparency of the silicon wafer in the said temperature range. The present invention is not limited to the above stated preferred embodiment for Rapid Thermal Processing; the method and device according to the invention are applicable in the semiconductor industry in installations for RTCVD, MBE, etc., or even in other applications, as may be apparent from the following claims.

Claims: A method for measuring the radiation originating from one side of a wafer (W) of semiconductor material using a radiation thermometer or pyrometer (1,13,14,43), wherein the wafer is heated by heating means (12,32,37), characterized in that compensation radiation is projected onto the one side and/or the other side of the wafer to compensate for the reflectivity and/or the transparency of said wafer (W), and wherein the intensity of the compensation radiation is controlled subject to the amount of radiation measured by the pyrometer. An apparatus (11) for treating a wafer (W) of semiconductor material, comprising: a treatment chamber wherein the wafer (W) is treated; heating means disposed in said treatment chamber and for heating said wafer; and one or more pyrometers or radiation thermometers for measuring radiation coming from said wafer, characterized in that said pyrometer is disposed into a wall of the treatment chamber and in that one or more compensation lamps are provided for projecting compensation radiation onto the wafer of semiconductor material, wherein the intensity of the compensation lamps is controlled subject to the measurement value of the pyrometer. An apparatus according to claim 2, wherein the heating means comprise infrared lamps which are disposed on one side of the wafer of semiconductor material to be inserted and wherein the pyrometer and the compensation lamps are disposed on the other side of the wafer of semiconductor material. An apparatus according to claim 2 or 3, wherein a matt glass or facetted mirror or lens is arranged in front of the compensation lamp in order to provide a diffuse bundle of compensation light. An apparatus according to claims 2, 3 or 4, wherein a number of second compensation lamps are disposed on the side of the wafer remote from the pyrometer. An apparatus according to claims 5, wherein between the second compensation lamps and the infrared lamp a water-cooled window is arranged.

Inventors: MAEX KAREN IRMA JOZEF, VANDENABEELE PETER MICHEL NOEL, MAEX, KAREN IRMA JOZEF, VANDENABEELE, PETER MICHEL NOEL
Applicants: IMEC INTER UNI MICRO ELECTR, INTERUNIVERSITAIR MICROELEKTRONICA CENTRUM VZW
Application year: 1991
Main classification: G01J5
IPC codes: G01J5, H01L21