Pattern projection apparatus and exposure method for manufacturing a semiconductor device

Abstract: An aligner includes a system for projecting a pattern on an original plate (R) onto a substrate (W), a stage (3) for moving the substrate in two dimensions to sequentially project the pattern on the substrate, first and second devices for determining a change in projection magnification of the system in accordance with the output of a sensor (15) for measuring at least one of temperature, humidity, and atmospheric pressure, and in accordance with the amount of illumination accumulated by detecting exposure light for exposing the substrate to the pattern, a device for sequentially detecting marks (M W ) in first and second shot zones on the substrate when an interferometer (14) measures the distance the stage is moved, a device for determining the ratio at which the substrate expands or contracts using the output of the detecting device, and a device (11) for adjusting the magnification of the system-for projecting the pattern, on the basis of an output from the ratio determining device and the first and second determining devices.

Description: The present invention relates to pattern projection apparatus for use in the process of manufacturing a semiconductor device, wherein an electronic circuitry pattern is projected onto a semiconductor substrate, and to an exposure method. In projection aligners, when alignment marks formed on semiconductor substrates or wafers are detected, the result of the detection is used to align wafers with masks or reticles on which electronic circuitry patterns are to be formed, and then an exposure operation is performed. There are two alignment methods. In a die-by-die method, alignment is carried out chip by chip formed on the wafer. In a global method, the positions of several chips on the wafer are determined, and the distance the entire wafer deviates from a desired position is computed on the basis of the distance each chip deviates. A wafer-mounting stage is moved to a position so that the distance each chip deviates decreases to a minimum, and then alignment is performed. The wafer-mounting stage can be moved to align the center of each chip. However, the magnification of a projection lens must be changed in order to align points within each chip. During this operation, conventionally, the chip magnification with which each chip is formed is calculated on the basis of the gaps between a plurality of alignment marks within each chip, which marks have already been exposed collectively. The accuracy with which the chip magnification is calculated depends upon the size of the chip formed. For example, when a 15 mm x 15 mm chip is formed on a 5-inch wafer, the gap between alignment marks is only 15 mm, whereas the size of the wafer is 125 mm. When one method is utilized to determine the positions of the alignment marks, the accuracy with which magnification (wafer magnification in this case) is calculated can be expected to increase approximately eight-fold because the marks of the entire wafer are measured. Chip magnification varies primarily during the process of manufacturing semiconductors. In general, manufacturing semiconductors includes a plurality of processes, in each of which wafers are subjected to various treatments, such as heating. The wafers may deform because of heat treatment and the like. When they deform, that is, expand or contract, chip magnification fluctuates. This fluctuation must be precisely calculated before alignment can be performed with accuracy, or otherwise exposure accuracy may deteriorate. US-A-4666273 discloses projection apparatus in accordance with the preamble of the claims, in which light energy supplied to the optical means is measured and atmospheric pressure and the magnification of the system is adjusted to compensate. EP-A-0116940 discloses a step-and-repeat projection device with fine adjustment of the pattern reduction ratio compensate for dimensional changes. US-A-4765741 discloses a laser interferometer correcting device for correcting the measurements determined by the laser interferometer to compensate for environmental temperature changes. According to one aspect the present invention provides a pattern projection apparatus comprising: an illumination system for illuminating an original plate with exposure light; a projection optical system for projecting a pattern on to a substrate, the pattern being formed on the original plate illuminated with the exposure light from said illumination system; a stage for moving the substrate in two dimensions so as to sequentially project the pattern formed on the original plate on to shot zones on the substrate; a laser interferometer for measuring the change in position when said stage is moved; an environment measuring device for measuring atmospheric pressure; a first magnification determining device for determining a change in the projection magnification of said projection optical system in accordance with an output of said environment measuring device; a second magnification determining device for determining a change in the projection magnification of said projection optical system in accordance with the amount of illumination accumulated by detecting the exposure light; and a magnification adjusting device for adjusting the projection magnification of said projection optical system on the basis of the outputs of said first and second magnification determining devices; characterised by: said environment measuring device being adapted to measure environment temperature; said laser interferometer being adapted to measure the change of position of said stage when said stage is moved; a mark detecting device for sequentially detecting marks corresponding to a first shot zone and a second shot zone on the substrate, said mark detecting device including an imaging optical system for detecting the marks in the first and second shot zones without using said projection optical system; an expansion or contraction ratio determining device for determining an expansion or contraction ratio for the substrate from the output of said mark detecting device; the magnification adjusting device being adapted to adjust the projection magnification in accordance with the outputs of said expansion or contraction ratio determining device, and said first and second magnification detecting devices; and a laser interferometer correcting device for correcting the measurements determined by said laser interferometer in accordance with the output of said environment measuring device. According to a second aspect the present invention provides an exposure method for use in manufacturing a semiconductor device comprising the steps of: illuminating an original plate with exposure light; sequentially projecting a pattern onto shot zones on a substrate by using a stage which moves the substrate in two dimensions, the pattern being formed on the original plate illuminated with the exposure light; measuring the change in position of the stage using a laser interferometer; measuring atmospheric pressure; determining a change in projection magnification of said projection optical system and generating a first detected magnification value based thereon, the determination being performed using the measurement of atmospheric pressure; determining a change in projection magnification of the projection optical system and generating a second detected magnification value based thereon, the determination being performed in accordance with an amount of illumination accumulated by detecting the exposure light; adjusting the projection magnification of the projection optical system on the basis of the first and second detected magnification values; characterised by the steps of: sequentially detecting marks in a first shot zone and marks in a second shot zone on the substrate using an imaging optical system and not said projection optical system; determining the ratio at which the substrate expands or contracts, the ratio determination being performed using an output of said mark detecting device; adjusting the projection magnification of the projection optical system on the basis of the first and second detected magnification values and the expansion or contraction ratio; measuring environmental temperature; and correcting the measurements determined by said laser interferometer in accordance with the measured temperature. The imaging magnification of the projection optical system changes when the exposure operation is repeatedly performed. Consequently, the number of exposure operations is accumulated and the accumulated value is calculated to correct the imaging magnification. By appropriately performing the above two types of correction, the accuracy with which magnification is calculated using such measurements improves markedly when compared to a conventional aligner. Embodiments of the present invention will now be described with reference to the accompanying drawings, in which: Fig. 1 is a schematic view for illustrative purposes only showing an aligner; Fig. 2 is a schematic view of aligning marks formed on a wafer; Fig. 3 is a view showing the relative positions of the aligning marks on a wafer; Fig. 4 is a schematic view of a wafer divided into several zones; and Fig. 5 is a schematic view showing an embodiment of an aligner in accordance with this invention. Fig. 1 is a schematic view showing the main components of a projection aligner for illustrative purposes only. A light beam is emitted from an illumination source 2 used for exposure purposes. It projects an electronic circuitry pattern onto a wafer W mounted on a wafer stage 3 capable of moving two-dimensionally, which pattern is formed on a reticle R mounted on a reticle stage 12 capable of moving two-dimensionally. This projection is performed with the aid of a projection lens 1. The reticle stage 12 and the wafer stage 3 have laser interferometers 13 and 14, respectively, along two axes X and Y. The laser interferometers 13 and 14 measure the positions of the stages with high accuracy. Numeral 15 denotes an environment sensor which, at any time, monitors at least one of the following: the ambient temperature, humidity, and atmospheric pressure, and transmits monitored values to an interferometer correction device 17. Temperature sensors 16 measure the temperatures of the reticle R and the wafer W mounted on the stages 3 and 12, respectively. The interferometer correction device 17 corrects the value of the laser wavelength which is used as a measurement reference value and is stored in this device 17 so that the laser wavelength used for calculating measurements can be corrected to an appropriate value. This correction is based on measurements input from the environment monitoring sensor 15 and the temperature sensors 16. The interferometer correction device 17 uses the temperature of the stages to calculate the expansion or contraction of the stages, and corrects the value of the laser wavelength by considering the expansion or contraction of the stages. Numeral 18 denotes a device for correcting atmospheric pressure magnification of the projection lens 1 (hereinafter referred to as the pressure magnification correcting device). The projection lens 1 is used for reducing the pattern on the reticle R and projecting it onto the wafer W . The pressure magnification correcting device 18 receives data on the atmospheric pressure from the interferometer correction device 17, calculates the fluctuation in magnification caused by fluctuations in the atmospheric pressure, and then outputs data on the fluctuation in magnification to a magnification adjusting device 11. Numeral 19 denotes an illuminance sensor which transmits detected illuminance to an accumulating illuminance meter 20 every time an exposure operation is performed. A light beam is emitted from an illumination source 4 used for alignment purposes, passes through a beam splitter 5 and the projection lens 1, thus illuminating wafer marks M w on the wafer W . The wafer marks are grate-like marks as shown in Fig. 2. The light beam is reflected from the wafer W and then reaches the beam splitter 5 through the projection lens 1. The light beam is then reflected from the beam splitter 5, passes through an imaging optical system 6, and then reaches an imaging device 7, such as a charge coupled device (CCD) camera. An image of the wafer marks M w is formed on the imaging surface of the imaging device 7. An analog output from the imaging device 7 is converted by a position measuring device 8 into a two-dimensional digital signal. A template of the wafer marks M w has already been stored in the position measuring device 8. The pattern of the wafer marks M w imaged by device 7 is matched with the pattern of the wafer marks M w from the stored template by computations performed by the position measuring device 8. This computation determines the positions of the wafer marks M w relative to the imaging device 7 to the highest degree of accuracy. The position of the reticle R relative to the imaging device 7 is calculated by calculating means (not shown) and stored in the position measuring device 8, which computes the deviation from the relative positions of the reticle R and the wafer W . Numeral 10 denotes a computing unit which receives data on the above-mentioned deviation, computed by the position measuring device 8, to calculate the expansion or contraction of the wafer W . The magnification adjusting device 11 adjusts the imaging magnification of the projection lens 1. This adjustment is based on inputs from the computing unit 10, the pressure magnification correcting device 18 and the accumulating illuminance meter 20. In operation, the interferometer correction device 17, at any time, corrects the value of the laser wavelength by considering not only fluctuations in the laser wavelength caused by changes in the physical properties of the atmosphere, but also the expansion or contraction of the wafer caused by changes in the temperature of the stage. This correction is based on measurements made by the environment sensor 15 and temperature sensors 16. Such an operation corrects magnification errors of the stage. At the same time, atmospheric pressure measured by the environment sensor 15 is output to the pressure magnification correcting device 18. This device 18, at any time, transmits to the magnification adjusting device 11 the amount the projection magnification is changed due to fluctuations in atmospheric pressure. The accumulating illuminance meter 20 accumulates the amount of illuminance every time an exposure operation is performed and outputs an accumulated value to the magnification adjusting device 11. In this way, the magnification adjusting device 11 calculates a correction coefficient K , which takes into account changes in atmospheric pressure and in projection magnification caused by the energy absorption of the projection lens 1 attendant to the exposure operation. It is assumed that the wafer W has already been mounted on the stage 3 by mounting means (not shown) and has been aligned substantially with the reticle R . It is also assumed that chips, such as those shown in Fig. 3, are formed on the wafer W . The stage 3 first moves so that wafer marks ML on a chip indicated by L in Fig. 3 enter the visual field of the imaging device 7. The method described previously is used to measure the distance Dlx that the wafer marks ML deviate along the X axis. Then, the stage 3 moves so that wafer marks MR on a chip indicated by R in Fig. 3 enter the visual field of the imaging device 7. The laser interferometer 14 measures the distance H that the stage 3 moves in this operation. The distance Drx that the wafer marks MR deviate along the X axis is measured. The computing unit 10 calculates, from Dlx , Drx and H , the ratio Mx at which the wafer expands or contracts along the X axis. This calculation is based on the following equation: Mx = (Drx - Dlx + H)/H The stage 3 then moves so that wafer marks MU on a chip indicated by U in Fig. 3 enter the visual field of the imaging device 7. The laser interferometer 14 measures the distance V that the stage 3 moves in this operation. The distance Duy that the wafer marks MU deviate along the Y axis is measured in the same manner as described above. The stage 3 then moves distance V only so that wafer marks MD on a chip indicated by D in Fig. 3 enter the visual field of the imaging device 7. The distance Ddy that the wafer marks MD deviate along the Y axis is measured. The computing unit 10 calculates, from Duy , Ddy and V , the ratio My at which the wafer expands or contracts along the Y axis. This calculation is based on the following equation: My = (Duy - Ddy + V)/V The thus-calculated expansion or contraction ratios of the wafer, Mx and My , are output to the magnification adjusting device 11. This device 11 drives, on the basis of the above ratios Mx and My , a part 1-a of the projection lens 1 on the Z axis, that is, the optical axis direction of the projection lens 1 so that the projection magnification M of the projection lens 1 becomes M ' as expressed by the following equation: M' = M x K x 2 /(Mx + My) where K is the correction coefficient determined previously to correct changes in magnification caused by the exposure operation and also by fluctuations in atmospheric pressure. In this way, the magnification with which the pattern on the reticle R is projected is adjusted so that the expansion or contraction ratios of the wafer can be corrected. It is thus possible to cancel out errors which occur when the reticle R is aligned with the wafer W. Under such conditions, the exposure operation and stage movement are repeatedly performed for all chips on the wafer by either a die-by-die alignment method, by which alignment is carried out chip by chip, or the so-called global alignment method, by which alignment is carried out on the basis of the amount of deviation between the wafer and several chips on the wafer. A driving source 9 moves the stage 3 in either the X or Y direction to correct the positional deviation in either the X or Y direction in the same manner used when correcting the positional deviation in either the X or Y direction determined by the position measuring device 8. In the above-described arrangement four sets of wafer marks on four chips on a single wafer are measured to determine the expansion or contraction ratio of the entire wafer. However, with an increase in the diameter of wafers, the expansion or contraction ratios of the wafer vary according to the positions of chips on the wafer. In such a case, as shown in Fig. 4, a wafer is divided into several blocks so that the expansion or contraction ratios of the wafer for each block can be determined. The magnification of the projection lens 1 may be adjusted for each block. When the expansion or contraction ratios of the wafer and the correction coefficient for each block are expressed, respectively, as follows: Mxi, Myi and Ki, in which i = 1, 2, 3 and 4, the projection magnification for each block is adjusted to satisfy the following equation: M'i = M ( Ki 2/( Mxi + Myi)) where i = 1, 2, 3 and 4. Fig. 5 shows an embodiment of this invention. Components which are the same or similar to components shown in Fig. 1 are denoted by the same reference numerals. In this embodiment, the marks Mw are measured without the aid of the projection lens 1. This feature makes the embodiment different from the arrangement described above in which the marks Mw are measured with the aid of the projection lens 1. In this embodiment, the imaging device 7 forms the marks Mw on the wafer W into an image with the aid of the imaging optical system 6. The imaging optical system 6 is disposed near the projection lens 1 and outside the optical path of the light travelling from the wafer W through the lens 1 at a predetermined position relative to the lens 1. The reticle R is fixed in a predetermined position relative to the projection lens 1. The structure and operation of the device other than that described above are the same as in the arrangement shown in Fig. 1, and the explanations thereof are not repeated. In the embodiments described above, although the lens of the projection optical system is moved to adjust projection magnification, pressure between appropriate lenses in the projection optical system may be changed to adjust the projection magnification. As has been described, this invention makes it possible to correct alignment errors between the reticle and wafer caused by the expansion or contraction of the wafer, so that the reticle is aligned with the wafer with high accuracy. The individual components represented by the blocks shown in Figs. 1 and 5 are well-known in the semiconductor manufacturing art and their specific construction and operation is not critical. Moreover, the steps recited in the specification for carrying out the present invention can be easily programmed into well-known central processing units by persons of ordinary skill in the art and since such programming per se is not part of the invention, no further description thereof is deemed necessary.

Claims: A pattern projection apparatus comprising: an illumination system (2) for illuminating an original plate (R) with exposure light; a projection optical system (1) for projecting a pattern on to a substrate (W), the pattern being formed on the original plate (R) illuminated with the exposure light from said illumination system (2); a stage (3) for moving the substrate (W) in two dimensions so as to sequentially project the pattern formed on the original plate (R) on to shot zones on the substrate (W); a laser interferometer (14) for measuring the change in position when said stage (3) is moved; an environment measuring device (15) for measuring atmospheric pressure; a first magnification determining device (18) for determining a change in the projection magnification of said projection optical system (1) in accordance with an output of said environment measuring device (15); a second magnification determining device (19,20) for determining a change in the projection magnification of said projection optical system (1) in accordance with the amount of illumination accumulated by detecting the exposure light; and a magnification adjusting device (11) for adjusting the projection magnification of said projection optical system (1) on the basis of the outputs of said first and second magnification determining devices (17,19,20); characterised by: said environment measuring device (15) being adapted to measure environment temperature; said laser interferometer (14) being adapted to measure the change of position of said stage (3) when said stage (3) is moved; a mark detecting device (6,7) for sequentially detecting marks (Mw) corresponding to a first shot zone and a second shot zone on the substrate (W), said mark detecting device (6,7) including an imaging optical system for detecting the marks (Mw) in the first and second shot zones without using said projection optical system (1); an expansion or contraction ratio determining device (10) for determining an expansion or contraction ratio for the substrate from the output of said mark detecting device (6,7); the magnification adjusting device (11) being adapted to adjust the projection magnification in accordance with the outputs of said expansion or contraction ratio determining device (10), and said first and second magnification detecting devices (18,19,20); and a laser interferometer correcting device (17) for correcting the measurements determined by said laser interferometer (14) in accordance with the output of said environment measuring device (15). A pattern projection apparatus according to claim 1, including temperature sensing means (16) for sensing the temperature of said stage (3), wherein said laser interferometer correcting device (17) is also responsive to the measured temperature of said stage (3). An exposure method for use in manufacturing a semiconductor device comprising the steps of: illuminating an original plate (R) with exposure light; sequentially projecting a pattern onto shot zones on a substrate (W) by using a stage (3) which moves the substrate (W) in two dimensions, the pattern being formed on the original plate (R) illuminated with the exposure light; measuring the change in position of the stage (3) using a laser interferometer (14); measuring atmospheric pressure; determining a change in projection magnification of said projection optical system (1) and generating a first detected magnification value based thereon, the determination being performed using the measurement of atmospheric pressure; determining a change in projection magnification of the projection optical system (1) and generating a second detected magnification value based thereon, the determination being performed in accordance with an amount of illumination accumulated by detecting the exposure light; adjusting the projection magnification of the projection optical system (1) on the basis of the first and second detected magnification values; characterised by the steps of: sequentially detecting marks in a first shot zone and marks in a second shot zone on the substrate (W) using an imaging optical system (6,7) and not said projection optical system (1); determining the ratio at which the substrate (W) expands or contracts, the ratio determination being performed using an output of said mark detecting device (6,7); adjusting the projection magnification of the projection optical system (1) on the basis of the first and second detected magnification values and the expansion or contraction ratio; measuring environmental temperature; and correcting the measurements determined by said laser interferometer (14) in accordance with the measured temperature. An exposure method according to claim 3 including the steps of measuring the temperature of said stage (3), and correcting the measurements determined by said laser interferometer (14) in accordance with the measured temperature of said stage (3). A method of manufacturing a semiconductor device comprising the exposure method of claim 3 and including forming a semiconductor device from the substrate.

Inventors: SATO MAKOTO, SATO, MAKOTO, Sato, Makoto, c/o Canon Kabushiki Kaisha
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1992
Main classification: G03F7
IPC codes: G03F7, G03F9, H01L21