Method for manufacturing a semiconductor device

Abstract

A method of manufacturing a semiconductor device, comprising: - determining a local target thickness (T) of a semiconductor wafer (1) and / or a layer formed on a semiconductor wafer (1) as a material (2) to be etched by calculating a local thickness (B1) based on a thickness of the material (2) to be etched at a position for endpoint determination (5a), and subtracting a predefined relative etching depth (15) from the local thickness (B1) to determine the local target thickness (T); and - Etching the material to be etched (2) while monitoring its thickness at the end-point determination position (5a) and terminating the etching process as soon as the determined thickness of the material to be etched (2) at the end-point determination position (5a) corresponds to the local target thickness (T) or less, wherein in the course of determining the local target thickness (T), the calculation of the local thickness (B1) is carried out based on thicknesses which are determined at a plurality of positions at the end-point determination position (5a) during the rotation of the semiconductor wafer (1).

Description

[0001] The present invention relates to methods for manufacturing a semiconductor device which etch a semiconductor wafer or a layer formed on a semiconductor wafer as a material to be etched. State of the art

[0002] Japanese patent application JP H07-130 812 A discloses a technique in which a spatial etch rate pattern on the surface of a semiconductor wafer is derived as a function of process conditions by using in situ ellipsometry in conjunction with statistical modeling techniques.

[0003] When a semiconductor wafer or a layer formed on a semiconductor wafer is etched as the material to be etched, it is desirable that a target thickness of the material to be etched after etching be identical to a post-process representative value of thicknesses of the material to be etched determined after etching. In some cases, a specific position on the material to be etched is set as an end-point determination position, and an end point for the etching process is determined by monitoring the thickness at the end-point determination position during etching. In this etching process, when the thickness of the material to be etched at the end-point determination position before etching is large, the etching depth increases until the target thickness is reached; when the thickness of the material to be etched is small, the etching depth decreases until the target thickness is reached.

[0004] In a process where the etching process is performed until the material to be etched reaches the target thickness at the endpoint determination position, thickness variations within the material to be etched are not taken into account. In particular, if the material to be etched at the endpoint determination position is thicker than other areas of the material to be etched, the etch depth becomes too large and a post-process representative value becomes smaller than the target thickness. Conversely, if the material to be etched at the endpoint determination position is thinner than other areas of the material to be etched, the etch depth becomes too small and the post-process representative value becomes larger than the target thickness.

[0005] The document DE 10 2010 015 944 A1 relates, among other things, to a monitoring device for monitoring the thinning of at least one semiconductor wafer in a wet etching device. The monitoring device has a light source configured to emit coherent light of a light waveband for which the semiconductor wafer is optically transparent. Furthermore, the monitoring device has a measuring head arranged in a non-contact manner with a surface of the semiconductor wafer to be etched, wherein the measuring head is configured to irradiate the semiconductor wafer with the coherent light of the light waveband and to receive radiation reflected by the semiconductor wafer. Furthermore, the monitoring device has a spectrometer and a beam splitter, via which the coherent light of the light waveband is directed onto the measuring head and the reflected radiation is directed onto the spectrometer.Furthermore, the monitoring device has an evaluation unit. This unit serves to determine the thickness of the semiconductor wafer from the radiation reflected by the semiconductor wafer during the thinning process.

[0006] JP 2013-069842 A describes a correction method related to wafer manufacturing, namely when the wafer deviates from a desired state during manufacturing. The thickness and shape of the wafer are monitored during a wet etching process. A dedicated wet etching device drops the etchant from a supply nozzle over the center of a wafer held on a turntable. The etchant is completely distributed over the wafer surface by rotating the turntable at a predetermined speed. The wafer thickness is measured using a thickness gauge. The amount of etchant is controlled based on the measurement results. If the thickness and shape of the wafer deviate from a desired state during the wet etching process, the wet etching process can be corrected immediately.Consequently, re-etching to correct insufficient etching and wafer scrap due to excessive etching can be avoided.

[0007] JP 2012-004294 A discloses a substrate processing apparatus and method that enable uniform etching even when there is an uneven in-plane thickness distribution. This known substrate processing apparatus comprises a mounting table for holding and rotating a workpiece; an etchant supply part for supplying an etchant to the workpiece held on the mounting table; a measuring part for measuring a thickness of the workpiece supplied with the etchant or a thickness of a film formed on the workpiece supplied with the etchant; and a control part for controlling the mounting table, the etchant supply part, and the measuring part. Based on a measurement result of the measuring part, the control part causes the etchant supply part to supply the etchant to a portion thicker than a predetermined range.

[0008] The present invention was developed to solve the described problem. An object of the present invention is to provide methods for manufacturing a semiconductor device capable of reducing an error between a target thickness of a material to be etched after etching and a post-process representative value, wherein the post-process representative value is a representative value for thicknesses of the material to be etched determined after etching.

[0009] The object underlying the invention is achieved in a method for producing a semiconductor device according to the invention with the features of claim 1, alternatively with the features of claim 3 and further alternatively with the features of claim 5. Advantageous further developments are the subject of the respective dependent claims.

[0010] In some examples, a method of manufacturing a semiconductor device includes setting a local target thickness of a semiconductor wafer and / or a layer formed on a semiconductor wafer as a material to be etched by calculating a local thickness based on a thickness at an endpoint determination position of the material to be etched, and subtracting a predefined relative etch depth from the local thickness to determine the local target thickness, and etching the material to be etched while monitoring its thickness at the endpoint determination position, and stopping the etching process once it is determined that the thickness of the material to be etched at the endpoint determination position is equal to or less than the target thickness.

[0011] According to a first aspect of the present invention, in the course of determining the local target thickness, the calculation of the local thickness is carried out based on thicknesses determined at a plurality of positions at the end point determination position during the rotation of the semiconductor wafer.

[0012] According to an alternative aspect of the present invention, in the course of determining the local target thickness, an average value of the thicknesses of the material to be etched at the end-point determination position and at a symmetrical position (5b) which is symmetrical to the end-point determination position with respect to a center point of the semiconductor wafer is calculated as the local thickness.

[0013] According to a further alternative aspect of the present invention, the relative etch depth is calculated during or before setting the local target thickness by calculating a pre-process representative value, which is a representative value for thicknesses of the material to be etched, based on thicknesses of the material to be etched at a plurality of positions and by subtracting a target thickness of the material to be etched after etching from the pre-process representative value.

[0014] Further details, advantages, and features of the present invention will become apparent from the following description of exemplary embodiments with reference to the drawings. It shows: Fig. 1 a position for determining the end point on a material to be etched; Fig. 2 a cross-sectional view of the material to be etched; Fig. 3 shows a position for end point determination and the like in Embodiment 2; Fig. 4 shows an example of an apparatus arrangement in Embodiment 2; Fig. 5 a cross-sectional view of the material to be etched; Fig. 6 is a view showing the operation of the apparatus during the etching process; Fig. 7 is a view showing the position for end point determination in the comparative example; Fig. 8 is a view for explaining an etching process in the comparative example; Fig. 9 is a cross-sectional view of the material to be etched in the comparative example; Fig. 10 an example table with measured values ​​for the thickness of an SI wafer before and after etching; Fig. 11 shows a position for end point determination and the like in Embodiment 3; Fig. 12 a rotation trajectory of an endpoint determination; and Fig. 13 the surfaces of the material to be etched before and after etching.

[0015] Manufacturing methods for a semiconductor device based on embodiments of the present invention will be described with reference to the figures. The same or corresponding components are denoted by the same reference numerals, and repetition of their explanations is omitted. Embodiment 1.

[0016] A method for manufacturing a semiconductor device according to Embodiment 1 uses a semiconductor wafer or a layer formed on a semiconductor wafer as the material to be etched and etches the material to be etched. The method for manufacturing a semiconductor device according to Embodiment 1 first performs a target setting step and then performs an etching step.

[0017] The target setting step is described below. In the target setting step, a local thickness is first calculated based on the thickness of the material to be etched at a position for endpoint determination. Fig. 1 shows a position for endpoint determination 5a on a material 2 to be etched, which is a semiconductor wafer 1 or a layer formed on a semiconductor wafer 1. In the case where the semiconductor wafer 1 is the material 2 to be etched, the semiconductor wafer 1 can be, for example, a Si wafer, and the Si wafer itself is the material 2 to be etched. Fig. 1 shows an example including nine measurement points 6 on the surface of the semiconductor wafer 1 for calculating a pre-process representative value and a post-process representative value, which will be described later. One of the nine measurement points coincides with the end-point determination position 5a. The measurement points 6 are arranged in a vertical line and a horizontal line, forming a cross shape as a whole. A local thickness, which represents the thickness of the material 2 to be etched at the end-point determination position 5a, is calculated using a well-known method.

[0018] According to a method for measuring the thickness of the material 2 to be etched, the material 2 to be etched is irradiated with light having a wavelength that allows the light to penetrate the material 2 to be etched, and the thickness of the material to be etched is measured based on the intensity of the interfering light reflected from the surface and bottom of the material 2 to be etched and the refractive index.In addition, a method is used in the case where light having a wavelength that allows the light to penetrate the material 2 to be etched cannot be used, by irradiating the material 2 to be etched with light that does not have the property of penetrating the material 2 to be etched, and the thickness of the material 2 to be etched that has been etched is measured from the intensity of the interfering light, which is the optical path difference between the path that the light travels when it is reflected from a region that is protected from etching by means of a resist or the like and the path that the light travels when it is reflected from an etched region.

[0019] Fig. 2 is a cross-sectional view of the material 2 to be etched. Fig. Figure 2 shows a surface 11 of the material 2 to be etched before etching and a surface 12 of the material 2 to be etched after etching. The thickness of the material 2 to be etched varies according to the accuracy of the previous step. In the Fig. 2, the thickness of the material 2 to be etched at the endpoint determination position 5a is relatively large. The thickness of the material 2 to be etched at the endpoint determination position 5a on the surface 11 represents a local thickness B1. A pre-process representative value B2 is a value that represents the thicknesses measured at a plurality of positions on the surface 11 before etching, e.g., an average value of the thicknesses of the material 2 to be etched at the nine measuring points 6 in Fig. 1 before etching. The pre-process representative value B2 may be any value representing the thicknesses of the material 2 to be etched, which is determined based on the thicknesses of the material 2 to be etched at a plurality of positions during or before the target setting step, and is not limited to an average value.

[0020] A relative etching depth 15 is calculated during or before the target setting step by subtracting a target thickness A1 of the material 2 to be etched after etching from the pre-process representative value B2. The target thickness A1 is an ideal thickness for the entire material 2 to be etched after etching. For example, a predefined etching depth can be used unchanged as the relative etching depth 15. A post-process representative value A2, which represents thicknesses measured at a plurality of positions on the surface 12 after etching, is optional but effective for evaluating a result. The post-process representative value A2 can, for example, be an average value for the thicknesses of the material 2 to be etched at the nine measuring points 6 in Fig. 1 after etching. The post-process representative value A2 may be any value representing the thicknesses of the material 2 to be etched, which is determined based on the thickness of the material 2 to be etched at a plurality of positions after the process is performed, and is not necessarily limited to an average value.

[0021] A local target thickness T is a thickness for determining an end point for the etching process at an end point determination position 5a, which is necessary to reduce an error between the target thickness A1 and the post-process representative value A2. In the target setting step, the local target thickness T is calculated by calculating the local thickness B1 and then subtracting the predefined etching depth 15 from the local thickness B1 using the aforementioned calculation method.

[0022] The etching step is then carried out. During the etching step, the material 2 to be etched is etched while the thickness of the material 2 to be etched at the endpoint determination position 5a is monitored. As soon as it is determined that the thickness of the material 2 to be etched at the endpoint determination position 5a corresponds to or less than the local target thickness T, the endpoint for the etching process is considered to have been reached and the etching process is terminated. By carrying out the etching step, the surface 11 of the material 2 to be etched is Fig. 2 etched to surface 12.

[0023] The more the uniformity of the etching improves, the more similar the shapes of surface 11 and surface 12 become. In particular, as in Fig. As shown in Figure 2, the difference t1 between the local thickness B1 and the pre-process representative value B2 becomes approximately identical to the difference t2 between the local target thickness T and the post-process representative value A2. The etching process ensures that the material 2 to be etched is etched by a thickness that is approximately identical to the relative etching depth 15 in all areas of the material 2 to be etched, and an error between the target thickness A1 and the post-process representative value A2 can be reduced.

[0024] If the etching process in the etching step is performed until the thickness of the material 2 to be etched at the end-point determination position 5a matches the target thickness A1, the post-process representative value A2 becomes smaller than the target thickness A1. Accordingly, an error between the target thickness A1 and the post-process representative value A2 cannot be reduced. However, in the method for manufacturing a semiconductor device according to Embodiment 1, an error between the target thickness A1 and the post-process representative value A2 can be reduced by setting the local target thickness T.

[0025] The method for manufacturing a semiconductor device according to Embodiment 1 can be modified in various ways within a range without losing the associated features. For example, the arrangement of the measurement points 6 and the end-point determination position 5a can be appropriately changed. Furthermore, the difference between the post-process representative value and the target thickness A1 can be determined by measuring the thicknesses of the material to be etched at a plurality of positions after the etching step and calculating a post-process representative value of the thicknesses of the material to be etched based on the measured thicknesses.In addition, at least one of the maximum value, minimum value, mean value, and standard deviation can be determined for the thicknesses of the material to be etched measured at a plurality of positions during or after the target setting step, and for thicknesses of the material to be etched at a plurality of positions after the etching step, or difference values ​​at a plurality of positions determined by subtraction. Furthermore, the thicknesses of the material to be etched can be weighted according to their distance from the center of the semiconductor wafer when calculating the pre-process representative value (B2).

[0026] The material to be etched may consist of or include Si, or consist of or include C, or consist of or include metal. The material to be etched may be, for example, Si, SiO2, SiON, SiN, C, SiC, SiOC, SiCN, Al, AlCu, Cu, Ti, Ni, Pt, GaN, or the like. When performing the etching step, a generally known etching method such as dry etching or wet etching is used. These modifications can be suitably applied to methods for manufacturing semiconductor devices according to other embodiments. Embodiment 2.

[0027] A method for manufacturing a semiconductor device according to Embodiment 2 has many similarities with that of Embodiment 1, so the differences from Embodiment 1 will be mainly described. Fig. 3 shows the end-point determination position 5a and the like in Embodiment 2. A center point 5c is a central position on the semiconductor wafer. A plurality of measurement points 6 are arranged on a straight line passing through the center point 5c. Some of the plurality of measurement points 6 coincide with the end-point determination position 5a, the center point 5c, and a symmetrical position 5b. The symmetrical position 5b is symmetrical to the end-point determination position 5a with respect to the center point 5c of the semiconductor wafer. In other words, the symmetrical position 5b and the end-point determination position 5a are point-symmetrical to the center point 5c of the semiconductor wafer. In the target setting step in Embodiment 2, the thickness of the material to be etched at the end-point determination position 5a and the symmetrical position 5b are measured, and an average value of the thicknesses is calculated as a local thickness.A predefined relative etching depth is then subtracted from the local thickness to calculate a local target thickness.

[0028] Fig. 4 shows an example of an apparatus arrangement in Embodiment 2. The semiconductor wafer 1 is mounted on a wafer table 8, which is in a rotation initial position. A thickness measurement sensor 5 is arranged above the wafer table 8 and configured to be moved by a scanning mechanism 7. A double-sided arrow 7a indicates a range within which the scanning mechanism 7 allows measurement to be performed by the thickness measurement sensor 5. A nozzle scan arm 9, which includes an etchant discharge nozzle 3, is shown adjacent to the wafer table 8.The thickness measuring sensor 5, the scanning device 7, the nozzle scanning arm 9, and the wafer table 8 are controlled by a control unit 10a to measure thicknesses of the material 2 to be etched, wherein the thickness measuring sensor 5 is used alone or in combination with the scanning device 7 or the wafer table 8, and to perform an etching process using the nozzle scanning arm 9 and the wafer table 8.

[0029] The measurement of the thickness of the material to be etched 2 in Fig. 3 is carried out as follows: the control unit 10a controls the scanning device 7 to position the thickness measurement sensor 5 at a measurement position and instructs a thickness measurement control unit 10b to perform a measurement; and the thickness measurement control unit 10b measures a thickness of the material 2 to be etched based on the intensity of the interfering light and the refractive index and returns a thickness value to the control unit 10a. This process is performed for each individual measurement point 6, the end-point determination position 5a, and the symmetrical position 5b. In the target setting step, the control unit 10a calculates, for a local thickness, an average value of the thicknesses at the end-point determination position 5a and the symmetrical position 5b obtained in the thickness measurement described above.

[0030] In addition, the control unit 10a calculates a pre-process representative value, which represents a representative value for thicknesses at a plurality of measurement points 6 determined by the thickness measurement described above. The pre-process representative value is, for example, an average value of the thicknesses of the material 2 to be etched at a plurality of measurement points 6. Of course, it is not a problem that the end-point determination position 5a and the symmetrical position 5b coincide with some of the plurality of measurement points 6.

[0031] Fig. 5 is a cross-sectional view of the material 2 to be etched. On the surface 11, the thickness of the material 2 to be etched at the endpoint determination position 5a is smaller than the thickness of the material 2 to be etched at the symmetrical position 5b. The local thickness B1 is an average value of the thicknesses of the material 2 to be etched at the endpoint determination position 5a and the symmetrical position 5b. The pre-process representative value B2 is smaller than the local thickness B1.

[0032] The relative etching depth 15 is calculated during or before the target setting step by subtracting a target thickness A1 of the material to be etched after etching from a pre-process representative value B2. The calculation process is carried out by the control unit 10a. The target thickness A1 is often a value predefined in a recipe or the like, but of course, a function can also be used to automatically select a recipe from a plurality of recipes in which different target thicknesses A1 are specified according to the range of the pre-process representative value B2. In the target setting step, as in Fig. 5, the local target thickness T is calculated by subtracting the relative etching depth 15 from the local thickness B1.

[0033] In the etching step, a single-wafer wet etching process is performed on the material 2 to be etched. Fig. 6 is a view showing the operation of the apparatus during the etching step. While the thickness of the material 2 to be etched at the end-point determination position 5a is monitored by the thickness measurement sensor 5 in the etching step, an etchant is supplied to the material 2 to be etched by the nozzle 3 of the nozzle scanning arm 9, while the semiconductor wafer 1 is rotated by the wafer table 8. While the material 2 to be etched is wet-etched with the supply of the etchant, the nozzle 3 is reciprocated in a rotary motion by a scanning motion 9a of the nozzle scanning arm 9. Thereafter, an average value of thicknesses whose positions are closest to the rotation start position and to a 180° position is calculated among the thicknesses of the material 2 to be etched at the end point determination position 5a, which are continuously supplied and continuously calculated by the thickness measurement control unit 10b.Once it is determined that the mean value is equal to or less than the local target thickness T, the control unit 10 detects an end point for the etching process and terminates the etching. Afterward, the wafer table 8 returns to its initial rotation position.

[0034] The etching process turns the surface 11 into Fig. 5 up to the surface 12. After the etching process, the thickness of the material 2 to be etched is measured by means of the thickness measuring sensor 5 by controlling the scanning device 7. The thickness of the material 2 to be etched is measured in the area indicated by the double-sided arrow in Fig. 4 to measure the thickness of the material 2 to be etched at all measuring points 6 in Fig. 3. The post-process representative value A2 is calculated based on the measured thicknesses. Fig. Figure 5 shows a situation in which the post-process representative value A2 approximately matches the target thickness A1. By determining the post-process representative value A2, it is possible to determine the difference between the post-process representative value A2 and the target thickness A1 and to determine at least one of the maximum value, minimum value, mean value, and standard deviation as values ​​for the thicknesses measured at a plurality of positions on the wafer before and after etching, or to determine difference values ​​at a plurality of positions by subtraction. These values ​​can be used in etching quality control.

[0035] To facilitate understanding of the significance of the method for manufacturing a semiconductor device according to Embodiment 2, a comparative example will be described below. In explaining the comparative example, the differences from Embodiment 2 will be primarily described. Fig. Figure 7 is a view showing the endpoint determination position 5a in a comparative example. It is important that the endpoint determination position 5a is located at a position that represents the thickness of the material to be etched. Fig. Figure 8 is a view for explaining the etching step in a comparative example. While monitoring the thickness of the material 2 to be etched at the end-point determination position 5a using the thickness measurement sensor 5, the material 2 to be etched is etched by rotating the semiconductor wafer 1 and applying the etchant from the nozzle 3 onto the material 2 to be etched. In the comparative example, the material 2 to be etched is etched using a single-wafer wet etching process.

[0036] In a reaction-limited system, etching conditions that produce favorable uniformity can be easily determined, even if the nozzle 3 is located at a fixed position directly above the center of the semiconductor wafer 1. However, in a supply-limited system, favorable etching uniformity cannot be achieved if the etchant 4 discharged from the nozzle 3 is not evenly applied to the material 2 to be etched by the scanning movement 9a of the arm. To improve etching uniformity in a supply-limited system, it is necessary to optimize the etching rate and etchant amount, the number of revolutions of the semiconductor wafer, and the scanning movement 9a of the nozzle 3.In order to stabilize the etching uniformity, fluctuations in the etching rate caused by deterioration of the etchant 4 must be reduced by appropriate measures, for example by refreshing the components of the etchant.

[0037] Since the semiconductor wafer 1 in the comparative example is rotated while the end-point determination position 5a is at a fixed location, the end point is determined on a circle located at a distance from the rotation center of the semiconductor wafer 1. It is important that the end-point determination position 5a represents a position on the circle that represents the thicknesses of the material 2 to be etched. The uniformity of the thickness distribution within the regions of the material 2 to be etched and the etching uniformity must also be maintained at a good level.

[0038] Fig. 9 is a cross-sectional view of the material 2 to be etched in a comparative example. In the comparative example, the etching process is performed until the thickness of the material 2 to be etched reaches the target thickness A1 at the end point determination position 5a.

[0039] In particular, the etching process is performed to the etching depth 14. If the thickness of the material 2 to be etched at the endpoint determination position 5a on the surface 11 deviates from the pre-process representative value B2, an error between the target thickness A1 and the post-process representative value A2 cannot be reduced accordingly. Fig. 9 shows a situation where excessive etching is performed to make the post-process representative value A2 smaller than the target thickness A1 because the thickness of the material 2 to be etched at the end-point determination position 5a before etching is larger than the pre-process representative value B2. In the case of the comparative example, if there is too large a gap between the thickness of the material 2 to be etched at the end-point determination position 5a before etching and the pre-process representative value B2, an error between the target thickness A1 and the post-process representative value A2 cannot be reduced.

[0040] The methods for manufacturing a semiconductor device according to Embodiments 1 and 2 are not intended to realize the target thickness A1 at the end-point determination position 5a, but to set the local target thickness T, which represents a thickness to be realized at the end-point determination position 5a, in order to reduce an error between the target thickness A1 and the post-process representative value A2. In Embodiments 2, the local target thickness T is calculated by subtracting the relative etching depth 15 from the local thickness B1, which represents an average value of thicknesses of the material 2 to be etched at the end-point determination position 5a and at the symmetrical position 5b. In the case where the thickness of the material 2 to be etched, as shown in the cross-sectional view in Fig. 5, an error between the target thickness A1 and the post-process representative value A2 can be reduced more than in the case where a local thickness is defined only on the basis of the thicknesses at the end point determination position 5a.

[0041] Fig. Figure 10 shows an example table with measured values ​​of thicknesses of an SI wafer before and after etching. "Before" represents a measurement before etching, and "after" represents a measurement after etching. Based on the measurement results at 49 points on the wafer surface, it can be observed that there are some fluctuations in the thicknesses of the wafer before and after etching. Accordingly, a local thickness is preferably determined based on measured values ​​measured at a plurality of positions, as in Embodiment 2. Embodiment 3.

[0042] A method for manufacturing a semiconductor device according to Embodiment 3 has many similarities with that of Embodiment 2, so the differences from Embodiment 2 will be mainly described. Fig. 11 shows the end point determination position 5a and the like in Embodiment 3. In Embodiment 3, the measurement of thicknesses at the end point determination position 5a, the symmetrical position 5b, and the measurement points 6 described in Embodiment 2 is performed four times at a rotation angle 16a of, for example, 45°. The thicknesses include thicknesses at the end point determination position 5a, the symmetrical position 5b, and the measurement points 6 obtained in four measurements, and the measurement points 6 include a plurality of measurement points 6a arranged in a straight line, a plurality of measurement points 6b arranged in a straight line, a plurality of measurement points 6c arranged in a straight line, and a plurality of measurement points 6d arranged in a straight line.Of course, it is not a problem that the endpoint determination position 5a, the center point 5c, and the symmetrical position 5b coincide with some of the majority of the measurement points 6. This applies to the measurement points 6b, 6c, and 6d.

[0043] In the target setting step in Embodiment 3, a local thickness of the semiconductor wafer 1 is calculated using a predefined rotation angle 16a of 45°, and a relative etching depth is subtracted from the local thickness. In Embodiment 3, thicknesses at a plurality of measurement points 6a arranged in a straight line are measured using the method shown in Fig. 4 in a state where the wafer table 8 on which a semiconductor wafer 1 is mounted is in the rotation start position, and an average value of the thicknesses of the material to be etched 2 at the end-point determination position 5a and the symmetrical position 5b, each of which coincides with one of the measurement points 6a, is calculated as a local thickness. Furthermore, after the semiconductor wafer 1 is rotated by a rotation angle of 45°, thicknesses at the plurality of measurement points 6b arranged in a straight line are measured, and an average value of the thicknesses of the material to be etched 2 at the end-point determination position 5a and the symmetrical position 5b, each of which coincides with one of the measurement points 6b, is calculated as a local thickness.

[0044] Furthermore, after the semiconductor wafer 1 is rotated by a rotation angle of 45°, thicknesses are measured at the plurality of measurement points 6c arranged in a straight line, and an average value of the thicknesses of the material to be etched 2 at the end-point determination position 5a and the symmetrical position 5b, each of which coincides with one of the measurement points 6c, is calculated as a local thickness. Finally, after the semiconductor wafer 1 is rotated by a rotation angle of 45°, thicknesses are measured at the plurality of measurement points 6d arranged in a straight line, and an average value of the thicknesses of the material to be etched 2 at the end-point determination position 5a and the symmetrical position 5b, each of which coincides with one of the measurement points 6d, is calculated as a local thickness.

[0045] In this way, four local thicknesses at different positions are calculated. Next, the relative etching depth of each of the four local thicknesses is subtracted, and an average of the values ​​obtained by the subtraction is calculated as the local target thickness T. In other words, four local target thicknesses are determined, and then an average of these values ​​is calculated as the local target thickness T for use in the etching step. The local target thickness determined by averaging a plurality of local target thicknesses is hereinafter referred to as the average local target thickness. The four thicknesses determined at the end-point determination positions 5a and the four thicknesses determined at the symmetrical positions 5b are thicknesses located at positions that are the same distance from the center point 5c, and the average local target thickness has a value that reflects the thicknesses at eight positions arranged in a circular pattern.

[0046] The relative etching depth 15 is calculated by calculating representative values ​​of thicknesses at the measuring points 6a, 6b, 6c, and 6d during or before the target setting step, and then calculating an average of these four representative values ​​as a pre-process representative value, and by subtracting a target thickness of the material to be etched after etching from the pre-process representative value.

[0047] While the etching process is being performed with the rotation of the semiconductor wafer 1 in the etching step, the thicknesses of an object to be etched are continuously measured at the end-point determination position 5a. Then, an average value of thicknesses whose positions are closest to the rotation start position and whose positions are 45°, 90°, 135°, 180°, 225°, 270°, and 315° below the thickness of the material 2 to be etched is continuously calculated. Once the average value is determined to be equal to or less than the average local target thickness, an end point for the etching process is detected, and the etching process is terminated. The method for manufacturing a semiconductor device according to Embodiment 3 can reduce an error between the target thickness A1 and the post-process representative value A2 in the case where the distribution of the thicknesses of an object to be etched has a waviness. Embodiment 4.

[0048] A method for manufacturing a semiconductor device according to Embodiment 4 has many similarities with Embodiments 2 and 3, so the differences from Embodiments 2 and 3 will be mainly described. Fig. 12 shows a rotation trajectory for end-point determination 5d, on which thicknesses at the end-point determination position 5a are acquired by means of continuous rotation 16b and the like. In the target setting step, a local thickness is measured while the semiconductor wafer 1 is rotated. More specifically, while the semiconductor wafer 1 is rotated by, for example, one revolution, the thickness of the material 2 to be etched at the end-point determination position 5a is measured at a plurality of measurement points, and a local thickness representing the thicknesses on the rotation trajectory for end-point determination 5d can be obtained by an average calculation or a mode value determination or the like. It should be noted that after the calculation of the local target thickness T, the etching step can be performed immediately without stopping the rotation.

[0049] The relative etching depth, which is used to calculate the local target thickness T, is naturally calculated during or before the target setting step. The relative etching depth is calculated, for example, by calculating the pre-process representative value B2, which is a representative value for thicknesses of the material to be etched based on the thicknesses of the material 2 to be etched at a plurality of positions on a straight line passing through the center point 5c, and by subtracting the target thickness A1 from the pre-process representative value B2.

[0050] Fig.13 shows the surface 11 of the material 2 to be etched before etching and the surface 12 of the material 2 to be etched after etching. The greater the waviness of the thicknesses of the surface 11, the greater the variation in the local thicknesses at the thickness measurement positions used in the calculation of the local thickness. Since the semiconductor wafer 1 is rotated, the thickness of the material 2 to be etched is monitored during the etching step on the rotation trajectory for endpoint determination 5d. Accordingly, the local thickness calculated before etching is preferably determined by a measurement on the rotation trajectory for endpoint determination 5d. Since the local thickness is calculated in Embodiment 4 in connection with a rotation of the semiconductor wafer 1, the local thickness, which can assume different values ​​depending on the rotation angle of the semiconductor wafer 1, can be smoothed.Thus, an error between the target thickness A1 and the post-process representative value A2 can be reduced.

[0051] In the target adjustment step and the etching step, while the semiconductor wafer 1 is rotated, the thickness of the material 2 to be etched can be measured at a plurality of measuring points, and a derived mean or modal value can be calculated as the local thickness. By using the same method for both the measurement of the layer thicknesses in the target adjustment step and the measurement of the layer thicknesses in the etching step, an etching process is enabled that accurately reflects the relative etch depth 15 and enables a reduction in the error between the target thickness A1 and the post-process representative value A2.

[0052] In all the embodiments described above, the method for calculating the pre-process representative value B2 is not limited to a specific method. The pre-process representative value B2 can be calculated, for example, by averaging the thicknesses measured at a plurality of positions located at regular intervals on the surface of the wafer, or by averaging measured values ​​whose density changes with the distance from the wafer center, or by measuring values ​​weighted depending on their distance from the wafer center.

[0053] In embodiments 2 to 4, the etching process is performed during rotation of the semiconductor wafer 1. However, instead of stopping the etching process once an average value of thicknesses of the material 2 to be etched, which is continuously calculated, coincides with the local target thickness T or less only once, a determination based on a thickness obtained by smoothing fluctuations of the material 2 to be etched using a moving average allows for the reduction of outliers in the thickness due to disturbance and the influence of waviness, and the reduction of an error between a target thickness A1 and the post-process representative value A2. It should be noted that the technical features of the embodiments described above can be used in suitable combinations.

[0054] According to the embodiments described herein, a target thickness of a material to be etched after etching is not used as a local target thickness. Instead, a local thickness is calculated based on a thickness of the material to be etched at a position for endpoint determination, and a predefined relative etch depth is subtracted from the local thickness, thereby determining a local target thickness. Accordingly, the deviation of a post-process representative value from the target thickness can be reduced by setting the relative etch depth to an appropriate value. It should be noted that a method for setting an appropriate value for the relative etch depth is disclosed in the present application. List of reference symbols 1 semiconductor wafer 2 material to be corroded 3 nozzles 4 Etchant 5 Thickness measuring sensor 5a Position for endpoint determination 5b symmetrical position 5c Center 5d rotation trajectory for endpoint determination 6 measuring points 6a Measuring points 6b Measuring points 6c Measuring points 6d measuring points 7 scanning device 7a double-sided arrow 8 wafer table 9 Nozzle scanning arm 9a Scanning movement 10a Control unit 10b Control unit for thickness measurement 11 Surface 12 Surface 14 Etching depth 15 relative etching depth 16a Angle of rotation 16b Rotation A1 Target thickness A2 Post-process representative value B1 Local thickness B2 Pre-process representative value T Local target thickness t1 Difference between local thickness B1 and pre-process representative value B2 t2 Difference between local target thickness T and post-process representative value A2

Claims

[1] A method of manufacturing a semiconductor device, comprising: - determining a local target thickness (T) of a semiconductor wafer (1) and / or a layer formed on a semiconductor wafer (1) as a material (2) to be etched by calculating a local thickness (B1) based on a thickness of the material (2) to be etched at a position for endpoint determination (5a), and subtracting a predefined relative etching depth (15) from the local thickness (B1) to determine the local target thickness (T); and - Etching the material to be etched (2) while monitoring its thickness at the end-point determination position (5a) and terminating the etching process as soon as the determined thickness of the material to be etched (2) at the end-point determination position (5a) corresponds to the local target thickness (T) or less, wherein in the course of determining the local target thickness (T), the calculation of the local thickness (B1) is carried out based on thicknesses which are determined at a plurality of positions at the end-point determination position (5a) during the rotation of the semiconductor wafer (1). [2] Method according to claim 1, wherein during the etching process the semiconductor wafer (1) is set into rotation during etching. [3] A method of manufacturing a semiconductor device, comprising: - determining a local target thickness (T) of a semiconductor wafer (1) and / or a layer formed on a semiconductor wafer (1) as a material (2) to be etched by calculating a local thickness (B1) based on a thickness of the material (2) to be etched at a position for endpoint determination (5a), and subtracting a predefined relative etching depth (15) from the local thickness (B1) to determine the local target thickness (T); and - Etching the material (2) to be etched while monitoring its thickness at the end-point determination position (5a), and terminating the etching process as soon as the determined thickness of the material (2) to be etched at the end-point determination position (5a) corresponds to the local target thickness (T) or less, wherein, in the course of determining the local target thickness (T), an average value of the thicknesses of the material (2) to be etched at the end-point determination position (5a) and at a symmetrical position (5b) which is symmetrical to the end-point determination position (5a) with respect to a center point (5c) of the semiconductor wafer (1) is calculated as the local thickness (B1). [4] The method according to claim 3, wherein, in setting the local target thickness (T), a calculation of the local thickness (B1) and a subtraction of the relative etching depth (15) from the local thickness (B1) are performed each time the semiconductor wafer (1) is rotated by a predefined rotation angle, and an average value of the plurality of values ​​determined by subtraction is calculated as the local target thickness (T). [5] A method of manufacturing a semiconductor device, comprising: - determining a local target thickness (T) of a semiconductor wafer (1) and / or a layer formed on a semiconductor wafer (1) as a material (2) to be etched by calculating a local thickness (B1) based on a thickness of the material (2) to be etched at a position for endpoint determination (5a), and subtracting a predefined relative etching depth (15) from the local thickness (B1) to determine the local target thickness (T); and - Etching the material (2) to be etched while monitoring its thickness at the end-point determination position (5a), and ending the etching process as soon as the determined thickness of the material (2) to be etched at the end-point determination position (5a) corresponds to the local target thickness (T) or less, wherein the relative etching depth (15) is calculated during or before the determination of the local target thickness (T) by calculating a pre-process representative value (B2) that is a representative value for thicknesses of the material (2) to be etched based on thicknesses of the material (2) to be etched at a plurality of positions, and by subtracting a target thickness (A1) of the material (2) to be etched after etching from the pre-process representative value (B2). [6] The method according to claim 5, wherein the plurality of positions lie on a straight line passing through the center (5c) of the semiconductor wafer (1). [7] The method according to claim 5 or 6, wherein the plurality of positions includes the end point determination position (5a) and a symmetrical position (5b) which is symmetrical to the end point determination position (5a) with respect to a center point (5c) of the semiconductor wafer (1). [8] The method according to claim 4, wherein the relative etching depth (15) is calculated by calculating a representative value of thicknesses of the material to be etched (2) based on thicknesses at a plurality of positions located on a straight line passing through the center point (5c) of the semiconductor wafer (1) each time the semiconductor wafer (1) is rotated by the rotation angle, and by calculating an average value from the plurality of the determined representative values ​​in the form of a pre-process representative value (B2), and subtracting a target thickness (A1) of the material to be etched (2) after etching from the pre-process representative value (B2). [9] Method according to one of the preceding claims, wherein the thicknesses of the material to be etched (2) are measured at a plurality of positions after etching, a post-process representative value (A2) for the thicknesses of the material to be etched (2) is calculated on the basis of the measured thicknesses, and a difference between the post-process representative value (A2) and a target thickness (A1) of the material to be etched (2) is determined. [10] Method according to one of claims 5 to 8, wherein at least one of the maximum value, minimum value, mean value and standard deviation is determined for the thicknesses of the material to be etched (2) measured at a plurality of positions during or before the determination of the local target thickness (T), and the thicknesses of the material to be etched (2) measured at a plurality of positions after the etching, or difference values ​​therebetween at a plurality of positions. [11] Method according to one of claims 5 to 8, wherein the thicknesses of the material (2) to be etched are weighted in the calculation of the pre-process representative value (B2) according to their distance from the center (5c) of the semiconductor wafer (1).

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