Patent Publication Number: US-2009239314-A1

Title: Methods of Manufacturing a Semiconductor Device

Description:
TECHNICAL FIELD 
     The present inventions generally relates to the manufacturing of semiconductor devices. 
     BACKGROUND 
     In semiconductor manufacturing, a photoresist pattern is produced by imaging a reticle pattern on a photoresist and developing the photoresist. Afterwards, etching is conducted to transfer the photoresist pattern to the underlying layer. These steps are repeated multiple times to produce a multi-layer semiconductor device. Also, a hard mask pattern may be used to structure an underlying layer. 
     There is a general desire to monitor and control etching and material deposition processes that occur during semiconductor manufacturing. For example, end point detection during etching is required to produce a desired critical dimension (CD). 
     SUMMARY OF THE INVENTION 
     One embodiment provides a method of manufacturing a semiconductor device. At least one structured layer is produced in a semiconductor substrate. During such producing of at least one structured layer, there is provided at least once a process which changes the volume of at least one layer of the semiconductor substrate or of at least one layer deposited on the semiconductor substrate. Such process could be an etching process or a deposition process. It is measured a change in volume of such at least one layer using fluorescence. For example, a signal indicative of the intensity of X-Ray fluorescence may be determined. 
     In another embodiment, there is also provided during the producing of at least one structured layer in a semiconductor substrate a process which changes the volume of at least one layer of the semiconductor substrate or of at least one layer deposited on the semiconductor substrate. In this embodiment, it is measured a change in volume of such at least one layer using reflection of electromagnetic waves. For example, X-Rays reflected by the substrate are measured and a signal is provided indicative of the intensity of the reflected X-rays. 
     In another embodiment, there is provided a method of manufacturing a semiconductor device in which there is provided a top first layer of a semiconductor substrate and a second layer of the semiconductor substrate beneath the first layer, the two layers having a different refractive index for X-Ray radiation. The first layer of the semiconductor substrate is etched. During etching, the substrate is irradiated with X-Rays. The X-Rays reflected by the substrate are measured and it is provided a signal indicative of the reflected X-rays. It is determined a change in the signal and an end point of the etching process is associated with the change in the signal. The change in signal is caused by a changed reflectivity when the material of the first layer is at least partly etched away and the X-Rays are then at least partly reflected by the second layer. 
     In another embodiment, there is provided a method of manufacturing a semiconductor device which comprises a process which etches a top first layer of a semiconductor substrate or produces such layer, wherein a second layer of the semiconductor substrate is located beneath the first layer. The materials of the first and second layers and the angle of incidence of the incident X-Rays are chosen such that total reflection of the incident X-Rays occurs or disappears when at least a part of the first layer has been processed. The occurrence or disappearance of total reflection corresponding to an increase or drop in the intensity of the reflected X-Rays, which corresponds to the end of the etching or layer producing process. The method may be used for end point detection. Accordingly, in this embodiment, the occurrence or disappearance of total reflection of X-Rays is an indication of the completion of a process step. 
     A further embodiment regards an apparatus for the manufacturing of semiconductor devices. The apparatus comprises means for changing the volume of at least one layer of a semiconductor wafer or of at least one layer deposited on the semiconductor wafer, an X-Ray radiation source, an X-Ray detection device detecting and measuring a signal indicative of the intensity of X-Rays reflected or emitted by fluorescence by the semiconductor wafer, and evaluating means for associating the signal with the course of the change in volume process. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings show different exemplary embodiments and are not to be interpreted to limit the scope of the invention. 
         FIG. 1  schematically shows an embodiment of an apparatus for manufacturing of semiconductor devices, the apparatus measuring a change in volume of at least one layer of a semiconductor substrate using X-ray fluorescence or X-ray reflection; 
         FIG. 2A  schematically an embodiment in which a change in volume of a semiconductor layer is measured using X-ray fluorescence, wherein a first signal is measured; 
         FIG. 2B  schematically an embodiment in which a change in volume of a semiconductor layer is measured using X-ray fluorescence, wherein a second signal is measured; 
         FIG. 3  a graph showing process control parameters in dependence on the difference of fluorescence intensities as measured in accordance with  FIGS. 2   a ,  2   b;    
         FIG. 4A  schematically a further embodiment of an apparatus for the manufacturing of semiconductor devices, the apparatus having a tunable angle of incidence; 
         FIG. 4B  an embodiment similar to  FIG. 4A , wherein X-rays are incident parallel to elongated structures on the top layer of a semiconductor device; 
         FIG. 5A  an example application of a change in volume process, wherein a pattern is etched into a substrate; 
         FIG. 5B  another example application for a change in volume process, wherein a structure is widened; 
         FIG. 5C  another example of a change in volume process, wherein a structure is thinned; 
         FIG. 5D  another example of a change in volume process, wherein a structure is etched into a top layer without breaking through the top layer; 
         FIG. 5E  another example application of a change in volume process, wherein a structure is etched into a top layer with a break through the top layer; 
         FIG. 5F  a top view of etched lines and spaces; 
         FIG. 5G  a top view of etched holes; 
         FIG. 6A  schematically the refraction of X-rays at the passage from vacuum to matter, including an indication of the critical angle of total reflection; 
         FIG. 6B  a graph showing the reflected intensity of X-rays in dependence of the incidence angle for two materials having a different refractive index; 
         FIG. 7  an embodiment of an in-situ process in which the etching of lines and spaces is monitored using X-ray reflection; 
         FIG. 8  an embodiment of an in-situ process in which a line etch is monitored using X-ray reflection; 
         FIG. 9  a graph showing the reflected intensity in dependence on the incident angle in a simulation of the reflectivity data of  FIG. 7 ; 
         FIG. 10  a graph showing reflected intensity in dependence of the thickness of a deposition layer; 
         FIG. 11  a flow chart indicating the steps of an embodiment of a method of manufacturing a semiconductor device; 
         FIG. 12  a flow chart indicating the steps of a further embodiment of a method of manufacturing a semiconductor device; 
         FIG. 13  a flow chart indicating the steps of a further embodiment of a method of manufacturing a semiconductor device; and 
         FIG. 14  a flow chart indicating the steps of a further embodiment of a method of manufacturing a semiconductor device. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
       FIG. 1  shows an embodiment of an apparatus which comprises an etch chamber  1  used in the process of manufacturing a semiconductor device. The etch chamber  1  comprises a chuck (not shown) supporting a semiconductor wafer  2 . As is well-known to those skilled in the art, the etch chamber also includes an upper electrode and a lower electrode (not shown). Inside the etch chamber  1  and between the electrodes, a gas plasma is provided. It is pointed out that etch chamber  1  is an example of an etch chamber only. Other etch chambers using other etching processes than plasma etching such as, e.g., ion beam etching or electron-induced reactive etching may be implemented as well. 
     The apparatus further comprises an X-ray radiation source  3  and an X-ray detection device  4 . In one embodiment, the X-ray radiation source  3  provides at least one incident X-ray beam of a specified spot size. In one embodiment, the X-ray radiation source  3  is adapted to scan at least a top layer of the wafer  2  with the incidence beam. In the embodiment of  FIG. 1 , there is schematically depicted an area  21  which represents a spot size. Incident light from the X-ray source  3  is either reflected in the area  21  of wafer  2  or an X-ray fluorescence signal is produced in the area  21 . The two different mechanisms of either X-ray reflection or X-ray fluorescence will be explained in more detail below. 
     It is pointed out that in other embodiments the X-ray radiation source  3  may not be scanning the wafer  2  but, e.g., illuminating the complete wafer  2 . Also, embodiments exist in which a sample volume that is representative of the wafer is irradiated only, without irradiating other areas. 
     The X-ray detection device  4  detects the signal that is reflected or emitted by fluorescence by area  21  of the semiconductor wafer when irradiated with X-rays by the X-ray radiation source  3 . The detection device  4  includes evaluating means for associating the signal with a change in volume that is applied to at least one layer of the semiconductor wafer during a process. The evaluating means may also be provided in a separate unit. 
     The X-ray radiation source  3  and the X-ray detection device  4  are located either inside or outside the etch chamber  1 . In one embodiment, they are located inside the etch chamber  1 . 
     It is pointed out that there may be several detection devices and several X-ray sources located at different angles and with different wavelengths. There may also be provided a control system (not shown) that gives feedback to the process during etch or deposition. The system may be used in-situ or ex-situ and may give feedback for etch of the actual or next wafer. 
     The apparatus shown in  FIG. 1  is suitable to carry out a plurality of methods which regard the measurement of a change in volume in at least one layer of the semiconductor wafer  2  by means of processes involving X-ray fluorescence or X-ray reflection. Also, a combination of X-ray fluorescence and X-ray reflection may be carried out.  FIGS. 11 to 14  depict general embodiments of such methods. 
     According to  FIG. 11 , in a first step  111  a semiconductor substrate is provided. In step  112  there is produced at least one structured layer in the semiconductor substrate. According to step  113 , during such producing of at least one structured layer, there is provided a process which changes the volume of at least one layer of the semiconductor substrate or of at least one layer deposited on the semiconductor substrate. A deposited structure could be, e.g., a photoresist. According to step  114  there is measured a change in volume of the at least one layer using fluorescence. 
     Such fluorescence in one embodiment is X-ray fluorescence. In other embodiments, instead of X-rays, electromagnetic waves of other wavelengths may be used for exciting fluorescence such us UV light. 
     X-ray fluorescence (XRF) occurs when materials are exposed to high energetic radiation such as X-ray radiation or Gamma-ray radiation. Following ionization, electrons in higher orbitals fall into the lower orbital to fill the hole left behind. In falling, energy is released in the form of a photon. This so-called fluorescence radiation is characteristic for the atoms present. Further, the fluorescence intensity is directly related to the amount of each material in a given sample. 
     In the embodiment of  FIG. 11 , fluorescence is used in controlling the volume of a probed material. A change in volume is measured and used for process monitoring. It is pointed out that with a known density a change in volume is equivalent to a mass change. Accordingly, volume change and mass change are equivalent. 
       FIGS. 2A ,  2 B and  3  show a possible example of a method using X-ray fluorescence. According to  FIG. 2A , there is provided a sample volume  22  comprising two layers, a top layer  221  and an underlying layer  222 . The top layer  221  comprises a material A and the other layer  222  comprises a material B. In  FIG. 2   a , a first measurement is carried out previous to the process that leads to a change in volume of layer  221  such as an etching process. The intensity of a first fluorescence signal is measured. This intensity depends on the volume A 1  of the layer  221  before the change in volume. After the change in volume, a measurement post to the process is carried out, see  FIG. 2B . Such post measurement yields a second value for the intensity of the fluorescence which is dependent on the changed volume A 2 . In the example of  FIGS. 2A ,  2 B, the volume of the first layer  221  has decreased such that the intensity of the fluorescence signal has decreased as well. 
     Alternatively, measurements are made at other or additional times between start and end of a process that leads to a change in volume. Also, measurements may be taken essentially continuously to allow endpoint detection. 
     According to  FIG. 3 , the relative measurements can be extended to obtain absolute values by using a calibration between intensity differences (pre/post measurement according to  FIGS. 2A ,  2 B) and the parameter of interest such as volume and mass. Using such calibration, the measured intensity can be evaluated in terms of a process control parameter. 
     The sensitivity of this method will be dependent on the ratio between the depth up to which a volume change is introduced into the sample and the depth from which fluorescence radiation can be collected and evaluated (in the following referred to as information depth). The lower this ratio, the higher the sensitivity. 
     The information depth may be customized by using grazing incidence primary X-ray radiation.  FIG. 4A  shows parts of an apparatus used in the process of manufacturing a semiconductor device which is largely similar to the apparatus of  FIG. 1 . With apparatus of  FIG. 4A , the penetration depth of the incidence beam and thus the information depth of the fluorescence radiation can be tuned by the angle of incidence α. The angle of incidence a may be tuned between the angle of total reflection and an angle of normal incidence dependent on the material properties. 
     More particularly, in  FIG. 4A  there is provided a sample volume  22  which is part of a semiconductor wafer such as semiconductor wafer  2  of  FIG. 1 . The sample volume  22  includes a first layer  221  of material A and a second layer  222  of material B which is beneath the first layer  221 . There is further provided an X-ray source  3  and a detector system  4 . 
     X-rays from source  3  are radiated on the sample  22 . The signal detected by detector system  4  is formed by fluorescence signals from material A of layer  221  and material B of layer  222 . However, the collected fluorescence signal comes mainly from the upper layer  221  of etched structures, particularly, before the etching of the top layer  221  has been completed. The penetration depth of the primary X-rays of source  3  may be tuned by varying the angle of incidence α. 
     As more and more material A is etched away during etching, the fluorescence signal of layer  221  is reduced, until a minimum is reached. Further, eventually, an additional fluorescence signal from material B of layer  222  becomes stronger in the course of the etching process. By determining the minimum of the fluorescence signal from material A and/or determining the fluorescence signal of material B, the course of the etching process can be followed. This can be used, for example, for endpoint detection of the etching process. 
     Similar remarks apply in case a layer of material is deposited. With increased deposition, the fluorescence signal of the deposited material increases. 
     According to the described method, direct measurement of volume or mass change is possible. The volume change can be obtained locally as the fluorescence signal can be restricted to a sample volume which is defined by the spot size of the XRF times the information depth of the fluorescence radiation. As the X-ray radiation is local, the fluorescence signal is also local and this way a spatial resolution of the signal is naturally provided for. 
       FIGS. 5A to 5E  show sample applications of processes which change the volume of a substrate or the top layer of the substrate. In  FIGS. 5A to 5E , the top drawing shows the substrate before the process and the bottom drawing shows the substrate after the process. 
     According to  FIG. 5A , a pattern  52  is etched into a flat surface  51  of the substrate. According to  FIG. 5B , a structure  53  is widened to a structure  54 . According to  FIG. 5C , a structure  55  is thinned to a structure  56 . According to  FIG. 5D , a substrate having a top layer  57   a  and a bottom layer  57   b  is structured such that the top layer  58   a  only receives a pattern by etching, without breaking through the top layer  58   a . In  FIG. 5E , the starting situation is the same as in  FIG. 5D . During the etching step, however, structure  59   a  is provided to top layer  57   a  with break through the top layer. 
       FIG. 5F  shows a top view of etched lines and spaces, as provided, for example, by processes in accordance with  FIGS. 5A to 5E .  FIG. 5G  shows a top view of a structure having etched holes  63 . 
     In all of the structures shown in  FIGS. 5A to 5G , the structuring includes a change in volume process which may be monitored using X-ray fluorescence. 
     In the following, a further embodiment of a method for manufacturing a semiconductor device using X-ray fluorescence to measure a change in volume of at least one substrate layer is discussed. This method has already been indicated with respect to  FIG. 4A  according to which there is a top first layer  221  the volume of which is changed during the process and an underlying second layer  222  the layer of which is not changed during the process. The first layer comprises a first material A having a fluorescence radiation with a first wavelength and a second layer comprises a second material having a fluorescence radiation with a second wavelength, wherein both layers are subjected to X-ray radiation. 
     In this embodiment, other than in the embodiment previously described with respect to  FIG. 4A , the focus is on the signal of the underlying second layer. It is thus considered an X-ray radiation with a penetration depth that is suitable to penetrate also the second layer  222 . To this end, the angle of incidence a may be adjusted appropriately. 
     In such embodiment, the fluorescence signal of the second layer  222  may be evaluated to determine the end point of the change in volume process. For example, if a change in volume process is an etching process such as in  FIG. 4A , the fluorescence signal of the second layer is measured and an end point detected when the fluorescence signal of the second layer reaches a specific strength, such strength indicating a specific open area of the second layer produced by the etching of the first layer. 
     According to this embodiment, a fluorescence signal is detected which is representative of an open area of a substrate layer which is beneath the substrate layer that has been subject to an etching or other process. The intensity of the emission from the layer below the etched layer is a measure of the open area and, therefore, a measure of the etched critical dimension at the measuring spot. 
     Such measurement may be made for sample volumes by scanning an incident X-ray beam over the wafer as discussed before. Also, one averaging measurement for the complete wafer may be carried out. 
     In an embodiment, such open area fluorescence signal measurement is implemented for a spacer etch in the course of a double patterning process, for example below 40 nm half-pitch. With a spacer etch, the direction of the incident X-rays in one embodiment is parallel to the respective lines.  FIG. 4B  shows such embodiment. Apart from the direction of the incident X-rays,  FIG. 4B  is similar to  FIG. 4A . 
     With spacer etches, if the etch is too long, the spacer becomes too small, if it is too short, the spacer becomes too wide. Further, there is usually a non-uniformity over the wafer and the shape of the spacer can vary. Therefore, exact control during etch is required to provide for a desired critical dimension (CD). A measurement as discussed above provides end point detection that allows to control such etch. The integrated intensity over a defined dose and defined pattern is sufficiently precise to calibrate a critical dimension versus signal curve for, e.g., a sub-40 nm patterning, especially for sublithographic patterning techniques. 
     In one embodiment, this method provides for a kind of “0-1” transition, the “1-signal” occurring when the top layer has been partially etched through such that the fluorescence signal of the second layer gains importance. 
     The above embodiment similarly applies for deposition processes, in which the signal from an underlying layer is being reduced in the course of deposition, or the signal from the deposited layer is being increased. 
     As all methods described in this text, the method can be applied in in-situ but also ex-situ. 
       FIG. 12  shows a further example of a method for producing a semiconductor device. The method includes a first step  121  in which a semiconductor substrate is provided. There is further provided a second step  122  in which at least one structured layer in the semiconductor substrate is produced. Further, in step  123  a process which changes the volume of at least one layer of the semiconductor substrate or of at least on layer deposited on the semiconductor substrate is carried out. In step  124 , the change in volume of such at least one layer is measured using reflection of electromagnetic waves. Such electromagnetic waves may be, but are not limited to, X-Rays. 
     For example, the semiconductor substrate has a top first layer and a second layer beneath the first layer, the two layers having a different refractive index. When the top first layer has been etched away or partially been etched away, the X-rays are reflected at least partially by the second layer, this leading to a different signal. 
     Accordingly, in this embodiment, X-ray reflection is used for measurement instead of X-ray fluorescence. However, measurement of X-ray reflection may be combined with measurement of X-ray fluorescence as described above. Further, in other embodiments, instead of X-rays, electromagnetic waves of other wavelengths may be used for reflection such us UV light. 
       FIG. 13  shows a more detailed embodiment of a method for manufacturing a semiconductor device using X-ray reflection to measure a change in volume of a substrate layer. According to  FIG. 13 , in step  131 , a semiconductor substrate is provided. In step  132 , there is provided a top first layer of the semiconductor substrate and a second layer of the semiconductor substrate beneath the first layer, the two layers having a different refractive index for X-Ray radiation. In step  133 , the first layer of the semiconductor substrate is etched. The substrate is irradiated with X-Rays, step  134 , and the X-Rays reflected by the substrate are measured, step  135 . There is provided a signal indicative of the reflected X-rays, step  135 . A change in the signal is determined, step  136 , and an end point of the etching process is associated with the change in the signal, step  137 . The change in signal is caused by a changed reflectivity when the material of the first layer is at least partly etched away and the X-Rays are then at least partly reflected by the second layer. 
     In an embodiment of the method of  FIG. 13 , the material of the first layer is chosen such that it has a first critical grazing angle of total reflection for X-Ray radiation and the material of the second layer is chosen such that it has a second critical grazing angle of total reflection for X-Ray radiation, wherein the second critical angle is smaller than the first critical angle. X-Rays are irradiated at the substrate at a grazing angle of incidence that is smaller than the first critical angle of total reflection for the material of the first layer and larger than the second critical angle of total reflection for the material of the second layer. 
     Accordingly, before material of the first layer is etched away, total reflection of the incident X-Rays occurs at this material, and when material of the first layer has been etched away, the X-Rays are incident on the material of the second layer where they do not experience total reflection. This corresponds to a drop in reflected intensity which can be associated with an end point of the etch. 
     The method of  FIG. 13  provides for an in-situ control of a plasma etching process and the determination of an end point of the etching process by means of a reduction in reflected intensity due to a loss or reduction of total reflection after the top layer has been etched. 
     This embodiment will be better understood in the context of the examples of  FIGS. 6   a  to  10 . 
       FIG. 6A  shows the situation involved in total reflection. There are provided two materials having a refractive index of n 1  and n 2 , respectively. The boundary between the two materials is designated by reference sign  7 . In the present case, the material of refractive index nil is vacuum (or gas or plasma). The material of refractive index n 2  is a material subjected to a change in volume process. Due to the fact that for X-rays the real part of the refractive index in vacuum (as well as in gas and plasma) is greater than the real part of the refractive index of a solid material, nil (vacuum, gas, plasma) is larger than n 2  (solid). 
     Grazing angle θ C  indicates the angle of total refraction. X-ray X 1  irradiated with that angle on the boundary  7  runs parallel to the boundary  7  and is not refracted into material with refractive index n 2 . All X-rays with an angle of incidence smaller than the critical angle of incidence θ c , such as X-ray X 2  with angle of incidence β, are totally reflected at boundary  7 . 
     According to  FIG. 6B , the value of the critical angle θc varies with material density, wherein the material density is connected to the refractive index, such that the value of the critical angle θc varies with the refractive index of the respective material. The angle of incidence of the X-rays of X-ray source  3  (see  FIG. 1 ) is chosen such that it lies between the critical angles for material A of the first, top layer and for material B of the second, underlying layer. In other words, the material A of the first layer is chosen such that it has a first critical grazing angle of total reflection for X-ray radiation, the material B of the second layer is chosen such that it has a second critical grazing angle of total reflection for X-ray radiation, wherein the second critical angle is smaller than the first critical angle. X-rays are now irradiated at the substrate at a grazing angle of incidence that is smaller than the first critical angle of total reflection for the material of the first layer and larger than the second critical angle of total reflection for the material of the second layer. 
     Accordingly, incident X-rays are totally reflected as long as the second layer is covered by material of the first layer. Once the material of the first layer has been etched away, the prerequisites for total reflection are not present anymore such that total reflection is stopped in those areas in which the material of the first layer has been removed. This corresponds to a drop in reflected intensity, which may be sharp. This drop in reflected intensity is measured by the X-ray detection device  4  (see  FIG. 1 ). The drop in reflected intensity indicates the endpoint of the etching step. 
     Accordingly, as long as there is material A on the surface, total reflection occurs. When material A is removed, e.g. by plasma etching, the reflected intensity will drop down significantly, because the radiation will now enter material B where no total reflection happens. The corresponding signal indicative of the reflected X-rays will thus experience a change as well. In particular, such signal may experience a sharp (non-gradual) reduction or drop-off that can be associated with an end point of the etching process. 
       FIG. 7  shows an example application indicating an in-situ process for monitoring the etching of the lines and spaces. There are provided three layers in a sample volume, a top layer  231  comprising a first material A, an intermediate layer  232  comprising a material B and a bottom layer  233  comprising a material C. In the top layer  231 , lines  231   a  and spaces  231   b  are etched.  FIG. 7  shows the top layer  231  after the etching process has been finished. 
     The direction of the incident X-rays is parallel to the lines  231   a  and spaces  231   b , as indicated by arrows X. Before the material A of layer  231  has been etched away in the spaces  231   b , total reflection in these areas occurred. After the spaces  231   b  have been etched, incident X-rays are not further totally reflected in these areas but will at least partly enter material B of layer  232 , this corresponding with a change in the reflected intensity which can be evaluated to identify the endpoint of the etching process. 
       FIG. 8  shows another embodiment regarding an in-situ process for monitoring a liner etch in the course, e.g., of double patterning. 
     Again, there is provided a top layer  241 , an intermediate layer  242  and a bottom layer  243 . The top layer  241  includes lines  241   a  which comprise material B. At the sides of the lines, spacers  242   b  of material A are formed. Between the lines  241   a  and the spacers  241   b  spaces  242   c  are present. The intermediate layer  242  comprises material C and the bottom layer  243  comprises material D. 
     Again, in  FIG. 8 , the situation when the etching process has ended is shown. As in  FIG. 7 , there is a decline in reflected intensity when material previously in the area of spaces  242   c  has been etched away such that total reflection does not occur anymore in these areas. 
     Examples for the materials A, B, C and D in  FIGS. 7 and 8  are as follows: Material A may be TiN, Ge, GeO 2 , Ta, TaN, TaO x , W, WO x , TiO x , MoSi, CoSi and Cu. Material B may be Si, SiO x N y , polymer and Ge. Material C may be Si 3 N 4 , TiN, Al 2 O 3 , Al, Cu or Si. Material D may be C. 
       FIG. 9  shows the reflected intensity in dependence on the incident angle for two different materials. With an assumed angle of incidence θ c  of 0.3 deg, the reflected intensity is considerably higher for the material of dashed line  91  compared to the material of solid line  92 . The material of dashed line  91  is material A of  FIG. 7 . Solid line  92  represents material B of  FIG. 7 . Accordingly, if incident X-rays are reflected at material A (along the lines  231   a  of  FIG. 7 ), the reflected intensity is more than ten times higher compared to when the incident X-rays are reflected at material B (along spaces  231   b  of  FIG. 7 ). 
       FIG. 10  shows the reflected intensity in dependence of the thickness of a layer which is deposited on an underlying layer. Again, the reflected intensity is measured at an angle of incidence θ c  of 0.3 deg. As the thickness of the layer grows, the reflected intensity grows as well, as the newly deposited layer now provides for total reflection of the incident X-rays. 
       FIG. 14  shows a further embodiment of a method for manufacturing a semiconductor device using X-ray reflection to measure a change in volume of a substrate layer. In step  141 , there is provided a semiconductor substrate. In step  142 , there is provided a process which etches a top first layer of the semiconductor substrate or produces such layer, wherein a second layer of the semiconductor substrate is located beneath the first layer. In step  143 , the materials of the first and second layers and the angle of incidence of the incident X-Rays are chosen such that total reflection of the incident X-Rays occurs or disappears when material of at least a part of the first layer has been processed (e.g., completely etched or deposited). The occurrence or disappearance of total reflection corresponds to an increase or drop in the intensity of the reflected X-Rays and indicates an end point of the etch or deposition process. 
     The person skilled in the art will recognize that the embodiments described above are just examples and that other variations in the use of fluorescence and/or reflection may be implemented to measure a change in volume of a semiconductor substrate layer and/or to provide for endpoint detection of etching or depositing processes. For example, other parts of the electromagnetic spectrum than X-rays may be used for fluorescence and reflection such as ultraviolet (UV) light. Also, etching may be implemented by any etching apparatus and method such as plasma etching, ion beam etching and electron-induced reactive etching.