A method and device for detecting steps on epitaxial wafer surface

Abstract

The present disclosure provides a method and device for detecting steps on the surface of an epitaxial wafer, the method comprising: using a laser to scan the surface of the epitaxial wafer to obtain a polishing haze signal of the epitaxial wafer surface; based on the polishing haze signal, obtaining a Bragg diffraction coordinate diagram corresponding to the steps with a periodic structure on the surface of the epitaxial wafer; using an atomic force microscope to measure a local area of ​​the surface of the epitaxial wafer to obtain a step height variation curve of all steps in the local area; based on the step height variation curve, determining the average step width w0; based on the step average width w0, the laser wavelength λ, the laser incident angle θ and the Bragg diffraction condition, calculating the average step height d0; based on the step height variation curve, selecting a number of step height samples, and calculating the true height of the step based on the weight of each step height sample and the step average height d0. The method and device for detecting steps on the surface of an epitaxial wafer provided by the present disclosure can detect the step height on the surface of an epitaxial wafer.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor manufacturing, and in particular to a method and a device for detecting steps on the surface of an epitaxial wafer. Background Art

[0002] In the process of semiconductor chip manufacturing, in order to prevent small-sized ions from directly penetrating the silicon wafer through the gaps between silicon atoms during ion implantation, resulting in uncontrollable ion diffusion depth, during the silicon wafer manufacturing process, the crystal rod is cut at a certain angle to the crystal plane, which is called off-orientation.

[0003] This bevel cutting method will form high-density atomic steps on the surface of the silicon wafer. During epitaxial growth, gas phase molecules are deposited on the substrate surface and migrate to the atomic steps. As the growth time increases, the surface atomic steps continue to extend, so the substrate crystal form is repeated during the epitaxial process. This results in the final epitaxial silicon wafer being affected by the steps and the surface polishing haze is very high. Polishing haze refers to the shallow defects left on the wafer surface after polishing.

[0004] At present, the polishing haze signal is generally only used to characterize the roughness of the silicon wafer surface, but the formation mechanism of polishing haze and the polishing haze signal have not been further applied. As for the steps on the surface of silicon wafers, only the local step morphology is characterized by AFM (atomic force microscope), but the step height and width are not fully measured. In addition, since the step height is very small, the step height error measured by AFM is large. Summary of the invention

[0005] The embodiments of the present disclosure provide a method and device for detecting steps on the surface of an epitaxial wafer, which can further utilize the polishing haze signal to detect the height of the steps on the surface of the epitaxial wafer.

[0006] The technical solutions provided by the embodiments of the present disclosure are as follows:

[0007] A method for detecting steps on the surface of an epitaxial wafer comprises the following steps:

[0008] Scan the surface of the epitaxial wafer with laser to obtain the polishing haze signal of the epitaxial wafer surface;

[0009] Based on the polishing haze signal, a Bragg diffraction coordinate diagram corresponding to the steps with a periodic structure on the surface of the epitaxial wafer is obtained, wherein the step width w, the step height d, the laser wavelength λ and the laser incident angle θ satisfy the Bragg diffraction condition represented by the Bragg diffraction diagram;

[0010] Measuring a local area of ​​the epitaxial wafer surface by using an atomic force microscope to obtain a step height variation curve of all steps in the local area of ​​the epitaxial wafer surface;

[0011] Based on the step height variation curve, determining the average step width w0;

[0012] Based on the average step width w0, the laser wavelength λ, the laser incident angle θ and the Bragg diffraction condition, the average step height d0 is calculated;

[0013] Based on the step height variation curve, a number of step height samples are selected, and based on the weight of each step height sample and the step average height d0, the real height of the step is calculated.

[0014] In some embodiments of the present disclosure, scanning the surface of the epitaxial wafer with an incident laser to obtain a polishing haze signal of the epitaxial wafer surface specifically includes:

[0015] Scanning the laser on the surface of the epitaxial wafer along a preset path, and the laser incident angle θ gradually changes from the scanning start point to the scanning end point as the scanning progresses;

[0016] The reflected light intensity signal of the epitaxial wafer surface during the scanning process is acquired to obtain the polishing haze signal.

[0017] In some embodiments of the present disclosure, obtaining a Bragg diffraction coordinate diagram corresponding to steps having a periodic structure on the surface of the epitaxial wafer based on the polishing haze signal specifically includes:

[0018] Based on the polishing haze signal, the laser incident angle θ from the scanning start point to the scanning end point is used as the horizontal coordinate, and the reflected light intensity signal obtained during the scanning process is used as the vertical coordinate to draw a coordinate diagram as the Bragg diffraction coordinate diagram.

[0019] In some embodiments of the present disclosure, the step of obtaining a Bragg diffraction coordinate diagram corresponding to steps having a periodic structure on the surface of the epitaxial wafer based on the polishing haze signal specifically further includes:

[0020] The peak position of the reflected light signal is determined as the position where the reflected light is coherently enhanced. The step width w, step height d, laser wavelength λ and laser incident angle θ at the peak position meet the Bragg diffraction conditions represented by the Bragg diffraction pattern.

[0021] In some embodiments of the present disclosure, determining the average step width w0 based on the step height variation curve specifically includes:

[0022] The diffraction period in the step height variation curve is taken as y step widths, wherein the multiple y is determined according to a preset size level of the step height, and y is a positive integer greater than or equal to 1.

[0023] In some embodiments of the present disclosure, the step height variation curve is based on which a plurality of step height samples are selected, and the actual height of the step is calculated based on the weight of each step height sample and the average height d0 of the step, specifically including:

[0024] Selecting a step height in the step height variation curve as a reference height;

[0025] Count the height values ​​of all steps relative to the above reference height, and calculate the height difference d between two adjacent steps n , several height differences d of the same numerical value n Recorded as the same group, the height difference d contained in each group is counted n the number of

[0026] Select several groups of height difference values ​​d whose proportion is greater than the preset proportion n As the step height sample, and determining the weight Vn corresponding to the number of height difference values ​​dn contained in each group of the height difference values ​​dn in all groups of height difference values ​​dn as the step height sample, the following weighted formula (I) is obtained:

[0027] (d1*V1)+(d2*V2)+……+(d n *Vn)=d0;

[0028] According to the step height values ​​of all steps relative to the above-mentioned reference height, the measured height ratio between each group of height difference values ​​dn in the step height sample is determined to obtain the following formula (II):

[0029] d1:d2:……dn=K1:K2:……Kn

[0030] Wherein, K1:K2:...Kn represent the measured height ratios between each group of height difference values ​​dn in the step height sample;

[0031] Each set of height difference values ​​calculated based on the above formula (I) and formula (II) is taken as the actual height of the step.

[0032] An epitaxial wafer surface step detection device, comprising:

[0033] A first acquisition unit is used to scan the surface of the epitaxial wafer with a laser to obtain a polishing haze signal of the epitaxial wafer surface;

[0034] A second acquisition unit is used to acquire a Bragg diffraction coordinate diagram corresponding to the steps with a periodic structure on the surface of the epitaxial wafer based on the polishing haze signal, wherein the step width w, the step height d, the laser wavelength λ and the laser incident angle θ meet the Bragg diffraction condition represented by the Bragg diffraction diagram;

[0035] A third acquisition unit is used to measure the local area of ​​the epitaxial wafer surface by using an atomic force microscope to obtain a step height variation curve of all steps in the local area of ​​the epitaxial wafer surface;

[0036] A first calculation unit, configured to determine an average step width w0 based on the step height variation curve;

[0037] A second calculation unit is used to calculate the average step height d0 based on the average step width w0, the laser wavelength λ, the laser incident angle θ and the Bragg diffraction condition;

[0038] The third calculation unit is used to select a number of step height samples based on the step height variation curve, and calculate the real height of the step based on the weight of each step height sample and the average height d0 of the step.

[0039] In some embodiments of the present disclosure, the first acquisition unit is configured to be specifically used for:

[0040] Scanning the laser on the surface of the epitaxial wafer along a preset path, and the laser incident angle θ gradually changes from the scanning start point to the scanning end point as the scanning progresses;

[0041] The reflected light intensity signal of the epitaxial wafer surface during the scanning process is acquired to obtain the polishing haze signal.

[0042] In some embodiments of the present disclosure, the second acquisition unit is configured to be specifically used for:

[0043] Based on the polishing haze signal, the laser incident angle θ from the scanning start point to the scanning end point is used as the abscissa, and the reflected light intensity signal obtained during the scanning process is used as the ordinate, and a coordinate diagram is drawn as the Bragg diffraction coordinate diagram;

[0044] The peak position of the reflected light signal is determined as the position where the reflected light is coherently enhanced. The step width w, step height d, laser wavelength λ and laser incident angle θ at the peak position meet the Bragg diffraction conditions represented by the Bragg diffraction pattern.

[0045] In some embodiments of the present disclosure, the third computing unit is configured to be specifically the same as:

[0046] Selecting a step height in the step height variation curve as a reference height;

[0047] Count the height values ​​of all steps relative to the above reference height, and calculate the height difference d between two adjacent steps n , several height differences d of the same numerical value n Recorded as the same group, the height difference d contained in each group is counted n the number of

[0048] Select several groups of height difference values ​​d whose proportion is greater than the preset proportion n As the step height sample, and determining the weight Vn corresponding to the number of height difference values ​​dn contained in each group of the height difference values ​​dn in all groups of height difference values ​​dn as the step height sample, the following weighted formula (I) is obtained:

[0049] (d1*V1)+(d2*V2)+……+(d n *Vn)=d0;

[0050] According to the step height values ​​of all steps relative to the above-mentioned reference height, the measured height ratio between each group of height difference values ​​dn in the step height sample is determined to obtain the following formula (II):

[0051] d1:d2:……dn=K1:K2:……Kn;

[0052] Wherein, K1:K2:...Kn represent the measured height ratios between each group of height difference values ​​dn in the step height sample;

[0053] Each set of height difference values ​​calculated based on the above formula (I) and formula (II) is taken as the actual height of the step.

[0054] The beneficial effects brought by the embodiments of the present disclosure are as follows:

[0055] The method and device for detecting steps on the surface of an epitaxial wafer provided in the embodiment of the present disclosure further utilize the haze signal (Haze signal) of the polishing of the surface of the epitaxial wafer, obtain the Bragg diffraction coordinate diagram corresponding to the steps with periodic structure on the surface of the epitaxial wafer based on the Haze signal, and obtain the step height change curve on the surface of the epitaxial wafer through an atomic force microscope to determine the average width w0 of the step. Since the step width w, step height d, laser wavelength λ and laser incident angle θ meet the Bragg diffraction conditions represented by the Bragg diffraction diagram, the average height d0 of the step can be calculated; based on the step height change curve obtained by the atomic force microscope, a number of step height samples are selected, and based on the step height sample weight and the average step height d0, the real height of the step can be calculated according to the weighted formula. In this way, by further utilizing the Haze signal and combining it with the step height change curve obtained by the atomic force microscope, the real height of the step on the surface of the epitaxial wafer can be detected through a reasonable formula calculation. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 A flow chart showing a method for detecting steps on the surface of an epitaxial wafer provided by an embodiment of the present disclosure;

[0057] Figure 2 A schematic diagram showing the laser scanning path on the surface of the epitaxial wafer when measuring the Haze signal;

[0058] Figure 3 A schematic diagram showing the change of the laser incident angle on the epitaxial wafer surface when measuring the Haze signal;

[0059] Figure 4 It represents a Bragg diffraction coordinate diagram drawn based on the measured Haze signal, with the laser incident angle θ from the scanning start point to the scanning end point as the horizontal coordinate and the reflected light intensity signal obtained during the scanning process as the vertical coordinate;

[0060] Figure 5 The Bragg diffraction principle diagram showing the measured Haze signal;

[0061] Figure 6 It represents the step height variation information curve obtained by AFM measurement;

[0062] Figure 7 Indicates based on Figure 6 A table showing the number of different step height values ​​corresponding to the statistics in the curve shown;

[0063] Figure 8 Indicates based on Figure 6 A table showing the quantities corresponding to the different step height differences counted in the curve shown. DETAILED DESCRIPTION

[0064] In order to make the purpose, technical solution and advantages of the embodiments of the present disclosure clearer, the technical solution of the embodiments of the present disclosure will be clearly and completely described below in conjunction with the drawings of the embodiments of the present disclosure. Obviously, the described embodiments are part of the embodiments of the present disclosure, not all of the embodiments. Based on the described embodiments of the present disclosure, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present disclosure.

[0065] Unless otherwise defined, the technical terms or scientific terms used in the present disclosure should be understood by people with ordinary skills in the field to which the present disclosure belongs. The "first", "second" and similar words used in the present disclosure do not indicate any order, quantity or importance, but are only used to distinguish different components. Similarly, similar words such as "one", "one" or "the" do not indicate quantity restrictions, but indicate that there is at least one. Similar words such as "include" or "comprise" mean that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Similar words such as "connect" or "connected" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0066] Before describing in detail the epitaxial wafer surface step detection method and device provided by the embodiments of the present disclosure, the following description is made of the related technologies:

[0067] In the related art, the bevel cutting method with crystal orientation deviation will form high-density atomic steps on the surface of silicon wafers. During epitaxial growth, gas phase molecules are deposited on the substrate surface and migrate to the atomic steps. As the growth time increases, the surface atomic steps are continuously extended, so the substrate crystal form is repeated during the epitaxial process. This results in the final epitaxial silicon wafer being affected by the steps, and the surface polishing haze is very high. Polishing haze refers to the shallow defect damage left on the wafer surface after polishing.

[0068] If the polishing haze is too high, it will affect the surface particle control (particle counter), and it will be impossible to measure small-sized particles. Small-sized particle control is directly related to advanced processes. To some extent, the limit size that particle control can measure is the limit size of advanced processes. The current most advanced particle control (SP7) has a measurement limit of 12.5nm, but due to the high polishing haze of epitaxial silicon wafers, the measurement limit can only be measured to 17nm.

[0069] At present, the polishing haze signal (Haze signal) is mainly used to characterize the roughness of the silicon wafer surface. However, in fact, the information represented by the light and dark stripes on the Haze signal (actually the stripes corresponding to the steps) is often not taken seriously, and the formation mechanism of the polishing haze and the polishing haze signal are not further used. For example, the current Haze signal is not used to calculate the height, width and other information of the steps. For the steps on the surface of the silicon wafer, AFM (atomic force microscope) can characterize the local step morphology, but the height and width of the overall steps on the silicon wafer surface cannot be fully measured. In addition, since the step height is very small, the step height error measured by AFM is large.

[0070] In summary, there is currently no good global testing solution for the stripes on the surface of epitaxial wafers, and the information reflected by the Haze signal is not fully utilized. Breakthroughs in advanced processes require the use of this previously ignored information to obtain and quantify the morphological information on the surface of epitaxial wafers, thereby providing a clear direction for process improvement.

[0071] Based on this, the present application provides a method and device for detecting steps on the surface of an epitaxial wafer, which can quantify the steps on the surface of the epitaxial wafer.

[0072] like Figure 1 As shown, a method for detecting steps on the surface of an epitaxial wafer provided in an embodiment of the present disclosure includes the following steps:

[0073] Step S01, scanning the surface of the epitaxial wafer with a laser to obtain a polishing haze signal (Haze signal) of the epitaxial wafer surface;

[0074] Step S02, based on the polishing haze signal, obtaining a Bragg diffraction coordinate diagram corresponding to the steps with a periodic structure on the surface of the epitaxial wafer, wherein the step width w, the step height d, the laser wavelength λ and the laser incident angle θ meet the Bragg diffraction conditions represented by the Bragg diffraction diagram;

[0075] Step S03, using an atomic force microscope (AFM) to measure a local area on the surface of the epitaxial wafer to obtain a step height variation curve of all steps in the local area on the surface of the epitaxial wafer;

[0076] Step S04, determining the average step width w0 based on the step height variation curve;

[0077] Step S05, calculating the average step height d0 based on the average step width w0, the laser wavelength λ, the laser incident angle θ and the Bragg diffraction condition;

[0078] Step S06: Based on the step height variation curve, select a number of step height samples, and calculate the real height of the step based on the weight V of each step height sample and the average height d0 of the step.

[0079] In the above scheme, the Haze signal on the surface of the epitaxial wafer is further applied. The Haze signal is not limited to characterizing the surface morphology. The Bragg diffraction coordinate diagram corresponding to the steps with periodic structure on the surface of the epitaxial wafer is obtained based on the Haze signal, and the step height change curve on the surface of the epitaxial wafer is obtained by atomic force microscopy to determine the average step width w0. Since the step width w, step height d, laser wavelength λ and laser incident angle θ meet the Bragg diffraction conditions represented by the Bragg diffraction diagram, the average step height d0 can be calculated; based on the step height change curve obtained by the atomic force microscope, a number of step height samples are selected, and based on the step height sample weight and the step average height d0, the real height of the step can be calculated according to the weighted formula. In this way, by further applying the Haze signal and combining it with the step height change curve obtained by the atomic force microscope, the real height of the step on the surface of the epitaxial wafer can be detected by a reasonable formula calculation.

[0080] The measurement principle of Haze signal is: the incident laser is reflected or scattered on the surface of the epitaxial wafer, and the scattered or reflected signal of the defective part is significantly different from that of the defect-free position. Based on this, the distribution of surface defects can be obtained by calculation.

[0081] In some embodiments of the present disclosure, the above step S01 specifically includes:

[0082] Step S011, scanning the laser on the surface of the epitaxial wafer according to a preset path, and the laser incident angle θ gradually changes from the scanning start point to the scanning end point as the scanning progresses;

[0083] Step S012: Acquire the reflected light intensity signal of the epitaxial wafer surface during the scanning process to obtain the polishing haze signal.

[0084] In the above scheme, the specific process of obtaining the Haze signal can be as follows: Figure 2 and Figure 3 As shown, when performing the Haze signal test, the sample stage supports the epitaxial wafer 10 and rotates, so that the incident laser scans the surface of the epitaxial wafer 10 from the inside to the outside in a spiral manner. At the same time, the incident angle θ between the incident laser and the surface of the epitaxial wafer 10 also changes continuously during the scanning process until the entire surface of the epitaxial wafer 10 is scanned. Figure 2 As shown, the scanning path of the laser on the epitaxial wafer 10 is a spiral path from inside to outside; Figure 3The figure shows a schematic diagram of the change of the incident angle θ of the laser on the surface of the epitaxial wafer 10. In one embodiment, the incident angle of the laser gradually increases from the inside to the outside of the epitaxial wafer surface, that is, θ2 is greater than θ1 in the figure. It should be understood that in other embodiments, the scanning method of the incident laser on the epitaxial wafer is not limited to this.

[0085] In some embodiments of the present disclosure, the above step S02 specifically includes:

[0086] Step S021, based on the polishing haze signal, taking the laser incident angle θ from the scanning start point to the scanning end point as the abscissa and the reflected light intensity signal obtained during the scanning process as the ordinate, and drawing a coordinate diagram as the Bragg diffraction coordinate diagram;

[0087] Step S022: determine the peak position of the reflected light signal as the position where the reflected light is coherently enhanced, and the step width w, step height d, laser wavelength λ and laser incident angle θ at the peak position meet the Bragg diffraction condition represented by the Bragg diffraction pattern.

[0088] In the above scheme, for the measured Haze signal on the surface of the epitaxial wafer, the laser incident angle from the scanning start point to the scanning end point is selected as the horizontal coordinate, and the reflected light intensity signal obtained during the scanning process is selected as the vertical coordinate to draw a Bragg diffraction coordinate diagram. The Bragg diffraction coordinate diagram can be compared to the Bragg diffraction image of the laser under the step of the periodic structure on the surface of the epitaxial wafer. Among them, the peak position of the curve in the Bragg diffraction coordinate diagram can be regarded as the coherent enhancement position of the reflected light. At this position, the step height d, step width w, laser wavelength λ, and laser incident angle θ theoretically meet the Bragg diffraction conditions. Since the laser wavelength λ and the laser incident angle θ are both known parameters, when the step width is known, the step height can be calculated based on the Bragg diffraction condition. Since the step average width W0 can be determined based on the step height change curve obtained by the atomic force microscope in step S04, the step average height d0 can be calculated based on the Bragg diffraction condition.

[0089] Specifically, combined Figure 5 and Figure 6 As shown in the figure, the formation mechanism of the Haze signal can be compared to the Bragg crystal diffraction theorem. The step height d and step width w are periodic structures, which can cause the laser to produce optical path difference in the direction of the step height d and the step width w. When the total optical path difference is an integer multiple of the laser wavelength λ, the reflected light is coherently enhanced, and the enhanced position is the position where the reflected light signal in the Haze signal is the strongest. In the Bragg diffraction coordinate diagram, the peak position of the curve is the position where the reflected light is coherently enhanced. At this position, the step height d, step width w, laser wavelength λ, and laser incident angle θ theoretically meet the following Bragg diffraction conditions:

[0090]

[0091] Wherein, d represents the step height, y represents the multiple, w represents the step width, θ represents the laser incident angle, and λ represents the laser wavelength.

[0092] It should be noted that the atomic force microscope (AFM) has a limited measurement range and cannot measure globally. It can only measure local areas, such as the range of 1*1μm. Therefore, in the above steps S03 to S04, the average step width W0 is measured in a local area of ​​the epitaxial wafer using an atomic force microscope. In this embodiment, the overall mean is replaced by the sample mean in the local area. This is because, in the atomic force microscope test, the step width changes very little in the entire epitaxial wafer and has good periodicity. Therefore, the average step height d0 calculated by the sample mean is roughly equal to the overall mean of the epitaxial wafer surface, that is, the sample mean can replace the overall mean.

[0093] In some embodiments of the present disclosure, the above step S04 specifically includes: taking the diffraction period in the step height variation curve as y step widths, wherein the multiple y is determined according to a preset size level of the step height, and y is a positive integer greater than or equal to 1.

[0094] In the above step S04, it should be noted that the incident angle of the obliquely incident laser is small, so the measurement model generally belongs to small-angle diffraction. From the perspective of the step width w, the diffraction period may be a single step width w or an integer multiple of the step width (y*w). When determining the multiple y, an appropriate multiple can be selected to make the step height within the preset size level and ensure that the Bragg diffraction equation for calculating the step width w conforms to physical common sense.

[0095] In some embodiments of the present disclosure, the above step S05 specifically includes:

[0096] Step S051, selecting a step height in the step height variation curve and recording it as a reference height;

[0097] Step S052: Count the height values ​​of all steps relative to the reference height, and calculate the height difference d between two adjacent steps. n , several height differences d of the same numerical value n All step height differences are divided into multiple groups, and the height difference values ​​d contained in each group are counted. n the number of

[0098] Step S053: select several groups of height difference values ​​d whose proportion is greater than a preset proportion nAs the step height sample, and determining the weight Vn corresponding to the number of height difference values ​​dn contained in each group of the height difference values ​​dn in all groups of height difference values ​​dn as the step height sample, the following weighted formula (I) is obtained:

[0099] (d1*V1)+(d2*V2)+……+(d n *Vn)=d0;

[0100] Step S054: Determine the measured height ratio between each group of height difference values ​​dn in the step height sample according to the step height values ​​of all steps relative to the reference height, and obtain the following formula (II):

[0101] d1:d2:……dn=K1:K2:……Kn;

[0102] Wherein, K1:K2:...Kn represent the measured height ratios between each group of height difference values ​​dn in the step height sample;

[0103] Step S055: taking each set of height difference values ​​calculated based on the above formula (I) and formula (II) as the actual height of the step.

[0104] In order to more clearly explain the above step S05, a specific embodiment is used as follows:

[0105] Figure 6 The figure shows the height variation information of the stripes on the surface of the epitaxial wafer measured by atomic force microscopy on the local area of ​​the epitaxial wafer, that is, the step height variation information of all steps in the local area. The height of one of the steps is set as the reference height and recorded as 0.

[0106] like Figure 6 to Figure 7 As shown in , all step height values ​​are counted and the number of steps with different height values ​​is obtained. Figure 6 and Figure 7 , the number of steps with a step height value of the base height 0 is 5; the number of steps with a step height value of -3 is 2; the number of steps with a step height value of -2 is 2; the number of steps with a step height value of -1 is 5; the number of steps with a step height value of 1 is 1; the number of steps with a step height value of 2 is 5; the number of steps with a step height value of 3 is 2.

[0107] See also Figure 6 and Figure 8 , calculate the height difference between two adjacent steps in the local area, and perform statistics on the height difference. The statistical results are as follows Figure 8As shown. The number of height difference values ​​with a value of 0 is 2; the number of height difference values ​​with a value of 1 is 8; the number of height difference values ​​with a value of 2 is 4; the number of height difference values ​​with a value of 3 is 3; the number of height difference values ​​with a value of 4 is 1; and the number of height difference values ​​with a value of 5 is 1.

[0108] Among all the height difference values ​​mentioned above, several height difference values ​​with a large proportion are selected, for example, there are 8 height difference values ​​with a value of 1; there are 4 height difference values ​​with a value of 2; there are 3 height difference values ​​with a value of 3; these 15 height difference values ​​are selected as step height samples. Since the height of the step is much smaller than the width of the step, these three height difference values ​​mainly contribute to the optical path difference in the height direction during diffraction through weighting.

[0109] The proportion of each height difference value in the step height samples in the above local area is taken as the proportion of each height difference step in the overall epitaxial wafer. For example, a step with a height difference of 1 is recorded as a step of level 1, a step with a height difference of 2 is recorded as a step of level 2, and a step with a height difference of 3 is recorded as a step of level 3. Then, in this embodiment, there are 8 steps of level 1, and the weight is 8 / (8+4+3)=8 / 15; there are 4 steps of level 2, and the weight is 4 / 15; there are 3 steps of level 3, and the weight is 3 / 15. Therefore, according to the weighted formula (I), the following formula (I') can be obtained: d1*(8 / 15)+d2*(4 / 15)+d3*)(3 / 15)=d0.

[0110] From the measurement results of the atomic force microscope, it can also be obtained that for each step with a height difference, the ratio between the measured step height values, for example, in this embodiment, the average step height of the 1st step is about 18pm, the average step height of the 2nd step is about 130pm, and the average step height of the 3rd step is about 170pm. Therefore, the following formula (II') is obtained: d1:d2:d3=9:65:85.

[0111] According to the above formulas (I') and (II'), the actual height of the step corresponding to each height difference can be calculated respectively.

[0112] Another embodiment of the present disclosure provides an epitaxial wafer surface step detection device, comprising:

[0113] A first acquisition unit is used to scan the surface of the epitaxial wafer with a laser to obtain a polishing haze signal of the epitaxial wafer surface;

[0114] A second acquisition unit is used to acquire a Bragg diffraction coordinate diagram corresponding to the steps with a periodic structure on the surface of the epitaxial wafer based on the polishing haze signal, wherein the step width w, the step height d, the laser wavelength λ and the laser incident angle θ meet the Bragg diffraction condition represented by the Bragg diffraction diagram;

[0115] A third acquisition unit is used to measure the local area of ​​the epitaxial wafer surface by using an atomic force microscope to obtain a step height variation curve of all steps in the local area of ​​the epitaxial wafer surface;

[0116] A first calculation unit, configured to determine an average step width w0 based on the step height variation curve;

[0117] A second calculation unit is used to calculate the average step height d0 based on the average step width w0, the laser wavelength λ, the laser incident angle θ and the Bragg diffraction condition;

[0118] The third calculation unit is used to select a number of step height samples based on the step height variation curve, and calculate the real height of the step based on the weight of each step height sample and the average height d0 of the step.

[0119] In some embodiments of the present disclosure, the first acquisition unit is configured to be specifically used for:

[0120] Scanning the laser on the surface of the epitaxial wafer along a preset path, and the laser incident angle θ gradually changes from the scanning start point to the scanning end point as the scanning progresses;

[0121] The reflected light intensity signal of the epitaxial wafer surface during the scanning process is acquired to obtain the polishing haze signal.

[0122] In some embodiments of the present disclosure, the second acquisition unit is configured to be specifically used for:

[0123] Based on the polishing haze signal, the laser incident angle θ from the scanning start point to the scanning end point is used as the abscissa, and the reflected light intensity signal obtained during the scanning process is used as the ordinate, and a coordinate diagram is drawn as the Bragg diffraction coordinate diagram;

[0124] The peak position of the reflected light signal is determined as the position where the reflected light is coherently enhanced. The step width w, step height d, laser wavelength λ and laser incident angle θ at the peak position meet the Bragg diffraction conditions represented by the Bragg diffraction pattern.

[0125] In some embodiments of the present disclosure, the third computing unit is configured to be specifically the same as:

[0126] Selecting a step height in the step height variation curve as a reference height;

[0127] Count the height values ​​of all steps relative to the above reference height, and calculate the height difference d between two adjacent steps n , several height differences d of the same numerical value nRecorded as the same group, the height difference d contained in each group is counted n the number of

[0128] Select several groups of height difference values ​​d whose proportion is greater than the preset proportion n As the step height sample, and determining the weight Vn corresponding to the number of height difference values ​​dn contained in each group of the height difference values ​​dn in all groups of height difference values ​​dn as the step height sample, the following weighted formula (I) is obtained:

[0129] (d1*V1)+(d2*V2)+……+(d n *Vn)=d0;

[0130] According to the step height values ​​of all steps relative to the above-mentioned reference height, the measured height ratio between each group of height difference values ​​dn in the step height sample is determined to obtain the following formula (II):

[0131] d1:d2:……dn=K1:K2:……Kn;

[0132] Wherein, K1:K2:...Kn represent the measured height ratios between each group of height difference values ​​dn in the step height sample;

[0133] Each set of height difference values ​​calculated based on the above formula (I) and formula (II) is taken as the actual height of the step.

[0134] There are a few points to note:

[0135] (1) The drawings of the embodiments of the present disclosure only relate to the structures related to the embodiments of the present disclosure, and other structures may refer to the general design.

[0136] (2) For the sake of clarity, in the drawings used to describe the embodiments of the present disclosure, the thickness of layers or regions is exaggerated or reduced, that is, these drawings are not drawn according to the actual scale. It is understood that when an element such as a layer, film, region or substrate is referred to as being "on" or "under" another element, the element may be "directly" "on" or "under" the other element or there may be intermediate elements.

[0137] (3) In the absence of conflict, the embodiments of the present disclosure and the features therein may be combined with each other to obtain new embodiments.

[0138] The above are only specific implementations of the present disclosure, but the protection scope of the present disclosure is not limited thereto, and the protection scope of the present disclosure shall be based on the protection scope of the claims.

Claims

1. A method for detecting steps on the surface of an epitaxial wafer, characterized in that: The steps include: Scan the surface of the epitaxial wafer with laser to obtain the polishing haze signal of the epitaxial wafer surface; Based on the polishing haze signal, a Bragg diffraction coordinate diagram corresponding to the steps with a periodic structure on the surface of the epitaxial wafer is obtained, wherein the step width w, the step height d, the laser wavelength λ and the laser incident angle θ satisfy the Bragg diffraction condition represented by the Bragg diffraction diagram; Measuring a local area of ​​the epitaxial wafer surface by using an atomic force microscope to obtain a step height variation curve of all steps in the local area of ​​the epitaxial wafer surface; Based on the step height variation curve, determining the average step width w0; Based on the average step width w0, the laser wavelength λ, the laser incident angle θ and the Bragg diffraction condition, the average step height d0 is calculated; Based on the step height variation curve, a number of step height samples are selected, and based on the weight of each step height sample and the average step height d0, the real height of the step is calculated; The method of selecting a plurality of step height samples based on the step height variation curve and calculating the actual height of the step based on the weight of each step height sample and the average step height d0 specifically includes: Selecting a step height in the step height variation curve as a reference height; Count the height values ​​of all steps relative to the above reference height, and calculate the height difference d between two adjacent steps n , several height differences d of the same numerical value n Recorded as the same group, the height difference d contained in each group is counted n the number of Select several groups of height difference values ​​d whose proportion is greater than the preset proportion n As the step height sample, and determining the weight Vn corresponding to the number of height difference values ​​dn contained in each group of the height difference values ​​dn in all groups of height difference values ​​dn as the step height sample, the following weighted formula (I) is obtained: (d1*V1)+(d2*V2)+……+(d n *Vn)=d0; According to the step height values ​​of all steps relative to the above-mentioned reference height, the measured height ratio between each group of height difference values ​​dn in the step height sample is determined to obtain the following formula (II): d1:d2:……dn=K1:K2:……Kn; Wherein, K1:K2:...Kn represent the measured height ratios between each group of height difference values ​​dn in the step height sample; The actual height of the step corresponding to each height difference is calculated according to the above formulas (I) and (II).

2. The method according to claim 1, characterized in that The method of scanning the surface of the epitaxial wafer with an incident laser to obtain a polishing haze signal of the surface of the epitaxial wafer specifically includes: Scanning the laser on the surface of the epitaxial wafer along a preset path, and the laser incident angle θ gradually changes from the scanning start point to the scanning end point as the scanning progresses; The reflected light intensity signal of the epitaxial wafer surface during the scanning process is acquired to obtain the polishing haze signal.

3. The method according to claim 1, characterized in that The step of obtaining a Bragg diffraction coordinate diagram corresponding to steps having a periodic structure on the surface of the epitaxial wafer based on the polishing haze signal specifically includes: Based on the polishing haze signal, the laser incident angle θ from the scanning start point to the scanning end point is used as the horizontal coordinate, and the reflected light intensity signal obtained during the scanning process is used as the vertical coordinate to draw a coordinate diagram as the Bragg diffraction coordinate diagram.

4. The method according to claim 3, characterized in that The step of obtaining a Bragg diffraction coordinate diagram corresponding to steps having a periodic structure on the surface of the epitaxial wafer based on the polishing haze signal specifically includes: The peak position of the reflected light signal is determined as the position where the reflected light is coherently enhanced. The step width w, step height d, laser wavelength λ and laser incident angle θ at the peak position meet the Bragg diffraction conditions represented by the Bragg diffraction pattern.

5. The method according to claim 1, characterized in that Determining the average step width w0 based on the step height variation curve specifically includes: The diffraction period in the step height variation curve is taken as y step widths, wherein the multiple y is determined according to a preset size level of the step height, and y is a positive integer greater than or equal to 1.

6. An epitaxial wafer surface step detection device, characterized in that: include: A first acquisition unit is used to scan the surface of the epitaxial wafer with a laser to obtain a polishing haze signal of the epitaxial wafer surface; A second acquisition unit is used to acquire a Bragg diffraction coordinate diagram corresponding to the steps with a periodic structure on the surface of the epitaxial wafer based on the polishing haze signal, wherein the step width w, the step height d, the laser wavelength λ and the laser incident angle θ meet the Bragg diffraction condition represented by the Bragg diffraction diagram; A third acquisition unit is used to measure the local area of ​​the epitaxial wafer surface by using an atomic force microscope to obtain a step height variation curve of all steps in the local area of ​​the epitaxial wafer surface; A first calculation unit, configured to determine an average step width w0 based on the step height variation curve; A second calculation unit is used to calculate the average step height d0 based on the average step width w0, the laser wavelength λ, the laser incident angle θ and the Bragg diffraction condition; a third calculation unit, configured to select a plurality of step height samples based on the step height variation curve, and calculate a real height of the step based on a weight of each step height sample and the average height d0 of the step; The third computing unit is configured to be specifically used for: Selecting a step height in the step height variation curve as a reference height; Count the height values ​​of all steps relative to the above reference height, and calculate the height difference d between two adjacent steps n , several height differences d of the same numerical value n Recorded as the same group, the height difference d contained in each group is counted n the number of Select several groups of height difference values ​​d whose proportion is greater than the preset proportion n As the step height sample, and determining the weight Vn corresponding to the number of height difference values ​​dn contained in each group of the height difference values ​​dn in all groups of height difference values ​​dn as the step height sample, the following weighted formula (I) is obtained: (d1*V1)+(d2*V2)+……+(d n *Vn)=d0; According to the step height values ​​of all steps relative to the above-mentioned reference height, the measured height ratio between each group of height difference values ​​dn in the step height sample is determined to obtain the following formula (II): d1:d2:……dn=K1:K2:……Kn; Wherein, K1:K2:...Kn represent the measured height ratios between each group of height difference values ​​dn in the step height sample; The actual height of the step corresponding to each height difference is calculated according to the above formulas (I) and (II).

7. The device according to claim 6, characterized in that The first acquisition unit is configured to be specifically used for: Scanning the laser on the surface of the epitaxial wafer along a preset path, and the laser incident angle θ gradually changes from the scanning start point to the scanning end point as the scanning progresses; The reflected light intensity signal of the epitaxial wafer surface during the scanning process is acquired to obtain the polishing haze signal.

8. The device according to claim 6, characterized in that The second acquisition unit is configured to be specifically used for: Based on the polishing haze signal, the laser incident angle θ from the scanning start point to the scanning end point is used as the abscissa, and the reflected light intensity signal obtained during the scanning process is used as the ordinate, and a coordinate diagram is drawn as the Bragg diffraction coordinate diagram; The peak position of the reflected light signal is determined as the position where the reflected light is coherently enhanced. The step width w, step height d, laser wavelength λ and laser incident angle θ at the peak position meet the Bragg diffraction conditions represented by the Bragg diffraction pattern.

Images