Method for measuring thickness of epitaxial layer

Abstract

The invention provides a method for measuring the thickness of an epitaxial layer. The method comprises the following steps: providing a substrate; forming a doped test region in the substrate through an ion implantation process; forming an epitaxial layer on the substrate, wherein a doping concentration difference exists between the epitaxial layer and the doping test region; and based on the doping concentration difference between the epitaxial layer and the doping test region, performing thickness detection on the epitaxial layer on the doping test region through a Fourier transform infrared spectrometer to obtain the thickness of the epitaxial layer. According to the method, the thickness of the epitaxial layer can be directly measured on the production line of the semiconductor manufacturing process, the doping testing area is formed by conducting ion implantation on the substrate, the doping concentration difference exists between the doping testing area and the epitaxial layer, and therefore the testing principle of a Fourier transform infrared spectrometer (FTIR) is met. According to the method, the thickness of the epitaxial layer can be accurately monitored in real time without damaging the wafer, and the stability of semiconductor production and manufacturing is greatly improved.

Description

Technical Field

[0001] The invention belongs to the field of semiconductor integrated circuit design and manufacture, and in particular relates to a method for measuring the thickness of an epitaxial layer. Background Art

[0002] Epitaxial technology is to grow a film layer with the same lattice orientation as the single crystal substrate on a single crystal substrate (Sub). The epitaxial process plays an important role in modern ICs. The quality of the epitaxial layer (EPI) is better than that of the substrate material (Sub), with good lattice structure integrity, few defects and uniform doping distribution. Growing an epitaxial layer on a single crystal substrate helps reduce device leakage (Leakage) and improve device performance.

[0003] Most devices in the BCD process are made of epitaxial layers. The drift of the epitaxial layer thickness (EPI THKshift) will mainly lead to a decrease in the breakdown voltage (BV) and insulation performance (Isolation) of the device, which will in turn affect the device performance.

[0004] There are two main methods for testing epitaxial layer thickness in the industry: mechanical slicing and Fourier transform infrared absorption spectrometer (FTIR). In order to promote the contact between the epitaxial layer and the substrate, BCD products use epitaxial layers with similar resistivity and lattice structure as the substrate. However, the similar film structure makes it difficult to distinguish the spectra by FTIR. Currently, there is no method to directly use FTIR to measure the thickness of the epitaxial layer online, and the offline slicing thickness measurement method has no directness and timeliness of monitoring. The measurement of epitaxial layer thickness has become an urgent problem to be solved in the BCD process.

[0005] It should be noted that the above introduction to the technical background is only for the convenience of providing a clear and complete description of the technical solutions of the present application and for the convenience of understanding by those skilled in the art. It cannot be considered that the above technical solutions are well known to those skilled in the art simply because they are described in the background technology section of the present application. Summary of the invention

[0006] In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a method for measuring the thickness of an epitaxial layer, so as to solve the problem in the prior art that it is difficult to strike a balance between the measurement accuracy and efficiency of the thickness of the epitaxial layer.

[0007] To achieve the above-mentioned purpose and other related purposes, the present invention provides a method for measuring the thickness of an epitaxial layer, the measuring method comprising: providing a substrate; forming a doping test area in the substrate through an ion implantation process; forming an epitaxial layer on the substrate, the epitaxial layer and the doping test area having a doping concentration difference; based on the doping concentration difference between the epitaxial layer and the doping test area, performing thickness detection on the epitaxial layer on the doping test area through a Fourier transform infrared spectrometer to obtain the thickness of the epitaxial layer.

[0008] Optionally, the thickness detection of the epitaxial layer is performed on a production line of a semiconductor process.

[0009] Optionally, the material of the epitaxial layer is the same as that of the substrate, and has the same electrical doping type and the same order of magnitude of doping concentration.

[0010] Optionally, the doping concentration of the doping test region is more than 50 times the doping concentration of the epitaxial layer.

[0011] Optionally, when forming the doping test area, the electrical doping type of the substrate is P-type, the P-type doping element is In, the resistivity is less than or equal to 0.29Ω·cm, and the ion implantation dose of the doping test area is greater than or equal to 6e16atoms / cm 2 .

[0012] Optionally, when forming the doping test area, the electrical doping type of the substrate is N-type, the N-doped element is As, the resistivity is less than or equal to 0.28Ω·cm, and the ion implantation dose of the doping test area is greater than or equal to 2e16atoms / cm 2 .

[0013] Optionally, the depth of the doped test region is greater than or equal to 1 micron.

[0014] Optionally, the doping test region is disposed in a scribe line region of the substrate.

[0015] Optionally, multiple ion implantations with different energies are performed multiple times to form multiple implantation regions with uniform doping concentration distribution at different depths, and the multiple implantation regions together form a doping test region to improve the doping uniformity of the doping test region.

[0016] Optionally, the thickness detection of the epitaxial layer on the doped test area by Fourier transform infrared spectrometer includes the following steps: an infrared light source emits interference light to the surface of the epitaxial layer; part of the interference light is reflected on the surface of the epitaxial layer to form a first reflected light, and part of the interference light penetrates the epitaxial layer and is emitted on the surface of the test doped area to generate a second reflected light; an optical receiver receives the first reflected light and the second reflected light, processes the signal by Fourier transform, obtains an infrared absorption spectrum graph in which the transmittance or absorbance varies with the wave number or wavelength, and obtains the thickness of the epitaxial layer by analyzing the infrared absorption spectrum graph.

[0017] Optionally, the wavelength of the infrared light source is 0.9 micrometers to 20 micrometers, and the angle of incidence on the epitaxial layer is 25 degrees to 45 degrees.

[0018] Optionally, before performing thickness detection on the epitaxial layer, the method also includes: forming an isolation buried layer in the epitaxial layer and the substrate; forming an isolation structure in the epitaxial layer; forming an active area in the epitaxial layer above the isolation buried layer; wherein the isolation buried layer, the isolation structure and the active area are arranged in an area outside the doping test area.

[0019] As described above, the method for measuring the thickness of an epitaxial layer of the present invention has the following beneficial effects:

[0020] The present invention realizes a method for directly measuring the thickness of an epitaxial layer on a production line of a semiconductor process, by forming a doping test area by ion implantation into a substrate, so that there is a doping concentration difference between the doping test area and the epitaxial layer, thereby satisfying the Fourier transform infrared spectrometer (FTIR) test principle. The present invention does not require wafer cutting, and can retain a complete wafer, thereby effectively reducing the test cost; the present invention can realize real-time and accurate epitaxial layer thickness monitoring without damaging the wafer, greatly improving the stability of semiconductor production and manufacturing. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The included drawings are used to provide a further understanding of the embodiments of the present application, which constitute a part of the specification, are used to illustrate the implementation of the present application, and together with the text description, explain the principles of the present application. Obviously, the drawings described below are only some embodiments of the present application.

[0022] Figure 1 to Figure 7 A schematic structural diagram showing the steps of the method for measuring the thickness of an epitaxial layer according to an embodiment of the present invention.

[0023] Figure 8 The graph is a depth-doping concentration relationship graph of forming multiple implantation regions with uniform doping concentration distribution at different depths through multiple ion implantations with different energies according to an embodiment of the present invention.

[0024] Component number description

[0025] 101 Substrate

[0026] 102 Doping test area

[0027] 103 Epitaxial layer

[0028] 104 Isolation buried layer

[0029] 105 Isolation Structure

[0030] 106 Active Area

[0031] 201 Infrared light source

[0032] 202 Optical Receiver

[0033] 203 Interference of light

[0034] 204 First reflected ray

[0035] 205 Second reflected ray DETAILED DESCRIPTION

[0036] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0037] It should be emphasized that the term “include / comprises” when used herein refers to the presence of features, integers, steps or components, but does not exclude the presence or addition of one or more other features, integers, steps or components.

[0038] Features described and / or illustrated with respect to one embodiment may be used in the same or similar manner in one or more other embodiments, combined with features in other embodiments, or substituted for features in other embodiments.

[0039] For example, when describing the embodiments of the present invention in detail, for the sake of convenience, the cross-sectional diagrams showing the device structure will not be partially enlarged according to the general scale, and the schematic diagrams are only examples, which should not limit the scope of protection of the present invention. In addition, in actual production, the three-dimensional dimensions of length, width and depth should be included.

[0040] For ease of description, spatially relative terms such as "under", "below", "below", "below", "above", "on", etc. may be used herein to describe the relationship of one element or feature shown in the drawings to other elements or features. It will be understood that these spatially relative terms are intended to encompass other orientations of the device in use or operation in addition to the orientation depicted in the drawings. In addition, when a layer is referred to as being "between" two layers, it can be the only layer between the two layers, or one or more intervening layers may also be present.

[0041] In the context of the present application, a structure in which a first feature is described as being "above" a second feature may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features are formed between the first and second features, such that the first and second features may not be in direct contact.

[0042] It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and therefore the illustrations only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0043] like Figure 1 to Figure 7 As shown, this embodiment provides a method for measuring the thickness of an epitaxial layer, and the measuring method comprises the following steps:

[0044] like Figure 1 As shown, first, step 1) is performed to provide a substrate 101. In one embodiment, the substrate 101 may be a silicon substrate, a germanium substrate, a germanium silicon substrate, a silicon carbide substrate, a III-V substrate, etc. In a specific example, the substrate 101 may be a single crystal silicon substrate.

[0045] The substrate 101 may be undoped, P-type doped, or N-type doped. The P-type doped element may be, for example, boron (B) or indium (In), and the N-type doped element may be, for example, phosphorus (P) or arsenic (As). Figure 2 As shown, step 2) is then performed to form a doped test region 102 in the substrate 101 by an ion implantation process.

[0046] In one embodiment, the electrical doping type of the substrate 101 is P-type, and the resistivity of the substrate 101 is less than or equal to 0.29Ω·cm by setting the concentration of ion doping. At this time, the total ion implantation dose of the doping test area 102 is greater than or equal to 6e16atoms / cm 2 .

[0047] In another embodiment, the electrical doping type of the substrate 101 is N-type, and the resistivity of the substrate 101 is less than or equal to 0.28Ω·cm by setting the concentration of ion doping. At this time, the total ion implantation dose of the doping test area 102 is greater than or equal to 2e16atoms / cm 2 .

[0048] In a preferred example, the N-doped element may preferably be arsenic, and the P-type doped element may preferably be indium. Compared with doping with boron or phosphorus, the above-mentioned doping is not easy to diffuse during the process of forming an active area before thickness detection of the epitaxial layer 103, which facilitates a stable concentration difference between the epitaxial layer and the doping test area.

[0049] In one embodiment, the depth of the doping test region 102 is greater than or equal to 1 micron. For example, the depth of the doping test region 102 may be 1 micron, 2 microns, 3 microns, 5 microns, etc.

[0050] In one embodiment, the doping test area 102 is arranged in the cutting path area of ​​the substrate 101. Since the active area 106 will not be arranged in the cutting path area, the doping test area 102 is arranged in the cutting path area, which will not affect the subsequent device process and will not waste the additional use area of ​​the substrate 101, thereby effectively saving costs.

[0051] In one embodiment, multiple ion implantations with different energies may be performed to form multiple implantation regions with uniform doping concentrations at different depths, and the multiple implantation regions may together form the doping test region 102 to improve the doping uniformity of the doping test region 102. For example, multiple ion implantations may be performed on the substrate 101 while ensuring that the total ion implantation dose remains unchanged, and the energy of each ion implantation may be gradually reduced. In a specific example, Figure 8 As shown, a first injection region can be formed at a deeper position by an injection energy of 2900keV, and the main depth of ion doping in the first injection region is between 2000 nanometers and 4500 nanometers, and the dose distribution is relatively uniform. Then, a second injection region can be formed at a shallower position by an injection energy of 490keV, and the main depth of ion doping in the second injection region is between 0 nanometers and 2000 nanometers, and the dose distribution is also relatively uniform. At the same time, the ion doping dose of the first injection region is basically consistent with the ion doping dose of the second injection region. Therefore, after subsequent annealing, the uniformity of the ion doping concentration in the doping test region 102 superimposed by the first injection region and the second injection region can be greatly improved.

[0052] like Figure 3 to Figure 6 As shown, step 3) is then performed to form an epitaxial layer 103 on the substrate 101 , and the epitaxial layer 103 and the doping test region 102 have a doping concentration difference.

[0053] In one embodiment, the material of the epitaxial layer 103 is the same as that of the substrate 101, and has the same electrical doping type and the same order of magnitude of doping concentration. For example, in one embodiment, the material of the substrate 101 is N-type doped silicon, the material of the epitaxial layer 103 is also N-type doped silicon, and the ion doping concentration of the epitaxial layer 103 is substantially the same as or completely the same as that of the substrate 101.

[0054] In one implementation, the doping concentration of the doping test area 102 is more than 50 times the doping concentration of the epitaxial layer 103. It should be noted that the doping concentration difference between the doping test area 102 and the epitaxial layer 103 is based on the principle of Fourier transform infrared spectrometer (FTIR) testing, that is, the doping concentration difference can make the infrared light have sufficient reflectivity at the interface between the epitaxial layer 103 and the doping test area 102.

[0055] In one embodiment, in the epitaxial layer, the number of surface defects with a size larger than 0.12 micrometers is no more than 20, and the number of surface defects with a size larger than 0.2 micrometers is no more than 5.

[0056] like Figures 4 to 6 As shown, before the thickness detection of the epitaxial layer 103 is performed, the following steps are also included:

[0057] An isolation buried layer 104 is formed in the epitaxial layer 103 and the substrate 101, such as Figure 4 shown.

[0058] An isolation structure 105 is formed in the epitaxial layer 103, such as Figure 5 shown.

[0059] An active region 106 is formed in the epitaxial layer 103 above the isolation buried layer 104. Figure 6 As shown; wherein, the isolation buried layer 104, the isolation structure 105 and the active area 106 are arranged in the area outside the doped test area 102.

[0060] Determine the measurement position and select a specific area on the cutting path. After removing the surface oxide layer, the area forms a mark that can be recognized by the machine. The mark can be, for example, a pad (PAD), and other film structures will not be covered above the mark in the subsequent process to avoid interference of the film structure on the test results. In subsequent measurements, the machine can identify the mark and find the accurate measurement position for detection.

[0061] like Figure 4 to Figure 7 As shown, step 4 is then performed to detect the thickness of the epitaxial layer 103 on the doping test area 102 by Fourier transform infrared spectrometer based on the doping concentration difference between the epitaxial layer 103 and the doping test area 102 to obtain the thickness of the epitaxial layer 103.

[0062] In one embodiment, the thickness detection of the epitaxial layer 103 is performed on the production line of the semiconductor process. Preferably, the thickness detection of the epitaxial layer 103 can be performed in situ in the epitaxial cavity. The present invention can realize real-time and accurate monitoring of the thickness of the epitaxial layer 103 without damaging the wafer, greatly improving the stability of semiconductor production and manufacturing.

[0063] The Fourier Transform Infrared (FTIR) spectrometer is mainly composed of an infrared light source, a beam splitter, an interferometer, a sample cell, a detector, a computer data processing system, a recording system, etc. The Fourier Transform Infrared Spectrometer uses a Michelson interferometer to obtain the interference pattern of the incident light, and then transforms the time domain function interference pattern into a frequency domain function graph (ordinary infrared spectrum graph) through Fourier mathematical transformation. The basic principle of the Fourier Transform Infrared Spectrometer: The light emitted by the light source is divided into two beams by the beam splitter, one beam reaches the moving mirror through transmission, and the other beam reaches the fixed mirror through reflection. The two beams of light are reflected by the fixed mirror and the moving mirror respectively and then return to the beam splitter. The moving mirror moves in a straight line at a constant speed, so the two beams of light after being split by the beam splitter form an optical path difference and produce interference. The interference light passes through the sample cell after meeting in the beam splitter. After passing through the sample, the interference light containing the sample information reaches the detector, and then the signal is processed by Fourier transform, and finally the infrared absorption spectrum of transmittance or absorbance with wave number or wavelength is obtained.

[0064] like Figure 7 As shown, the thickness detection of the epitaxial layer 103 on the doped test area 102 by Fourier transform infrared spectrometer includes the following steps:

[0065] The infrared light source 201 emits interference light 203 to the surface of the epitaxial layer 103. The interference light includes interference light formed by being reflected by the fixed mirror and the moving mirror and then returning to the beam splitter to generate interference. The moving mirror moves linearly at a constant speed, so that the two beams of light reflected by the fixed mirror and the moving mirror have an optical path difference, which generates interference to form interference light.

[0066] Part of the interference light 203 is reflected on the surface of the epitaxial layer 103 to form a first reflected light 204, and part of the interference light 203 penetrates the epitaxial layer 103 and is emitted on the surface of the test doping region to generate a second reflected light 205;

[0067] The optical receiver 202 receives the first reflected light and the second reflected light, processes the signal by Fourier transform, obtains an infrared absorption spectrum showing the variation of transmittance or absorbance with wave number or wavelength, and obtains the thickness of the epitaxial layer 103 by analyzing the infrared absorption spectrum.

[0068] In one embodiment, the wavelength of the infrared light source 201 is 0.9 microns to 20 microns, and the angle of incidence to the epitaxial layer 103 is 25 degrees to 45 degrees. Different incident angles can be set according to different models of Fourier transform infrared spectrometers to meet the needs of thickness detection.

[0069] As described above, the method for measuring the thickness of an epitaxial layer of the present invention has the following beneficial effects:

[0070] The present invention realizes a method for directly measuring the thickness of the epitaxial layer 103 on the production line of the semiconductor process, by performing ion implantation on the substrate 101 to form a doping test area 102, so that there is a doping concentration difference between the doping test area 102 and the epitaxial layer 103, thereby satisfying the Fourier transform infrared spectrometer (FTIR) test principle. The present invention does not need to cut the wafer, and can retain the complete wafer, thereby effectively reducing the test cost; the present invention can realize real-time and accurate monitoring of the thickness of the epitaxial layer 103 without damaging the wafer, greatly improving the stability of semiconductor production and manufacturing.

[0071] Therefore, the present invention effectively overcomes various shortcomings in the prior art and has high industrial utilization value.

[0072] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A method for measuring the thickness of an epitaxial layer, characterized in that: The measuring method comprises: providing a substrate; forming a doped test region in the substrate by an ion implantation process; forming an epitaxial layer on the substrate, wherein the epitaxial layer and the doping test region have a doping concentration difference; Based on the doping concentration difference between the epitaxial layer and the doping test area, the thickness of the epitaxial layer on the doping test area is detected by Fourier transform infrared spectrometer to obtain the thickness of the epitaxial layer.

2. The method for measuring the thickness of an epitaxial layer according to claim 1, characterized in that: The thickness detection of the epitaxial layer is performed on a production line of a semiconductor process.

3. The method for measuring the thickness of an epitaxial layer according to claim 1, characterized in that: The material of the epitaxial layer is the same as that of the substrate, and has the same electrical doping type and the same order of magnitude of doping concentration.

4. The method for measuring the thickness of an epitaxial layer according to claim 1, characterized in that: The doping concentration of the doping test area is more than 50 times the doping concentration of the epitaxial layer.

5. The method for measuring the thickness of an epitaxial layer according to claim 1, characterized in that: When forming the doping test area, the electrical doping type of the substrate is P type, the P type doping element is In, the resistivity is less than or equal to 0.29Ω·cm, and the ion implantation dose of the doping test area is greater than or equal to 6e16atoms / cm 2 .

6. The method for measuring the thickness of an epitaxial layer according to claim 1, characterized in that: When forming the doping test area, the electrical doping type of the substrate is N-type, the N-doped element is As, the resistivity is less than or equal to 0.28Ω·cm, and the ion implantation dose of the doping test area is greater than or equal to 2e16atoms / cm 2 .

7. The method for measuring the thickness of an epitaxial layer according to claim 1, characterized in that: The depth of the doping test area is greater than or equal to 1 micron.

8. The method for measuring the thickness of an epitaxial layer according to claim 1, characterized in that: The doping test area is arranged in a scribe line area of ​​the substrate.

9. The method for measuring the thickness of an epitaxial layer according to claim 1, characterized in that: Multiple ion implantations with different energies are performed to form multiple implantation regions with uniform doping concentration distribution at different depths. The multiple implantation regions together form a doping test region to improve the doping uniformity of the doping test region.

10. The method for measuring the thickness of an epitaxial layer according to claim 1, characterized in that: The thickness detection of the epitaxial layer on the doped test area by Fourier transform infrared spectrometer comprises the following steps: An infrared light source emits interference light toward the surface of the epitaxial layer; Part of the interference light is reflected on the surface of the epitaxial layer to form a first reflected light, and part of the interference light penetrates the epitaxial layer and is emitted on the surface of the test doping region to generate a second reflected light; The optical receiver receives the first reflected light and the second reflected light, processes the signal by Fourier transform, obtains an infrared absorption spectrum showing that the transmittance or absorbance varies with the wave number or wavelength, and obtains the thickness of the epitaxial layer by analyzing the infrared absorption spectrum.

11. The method for measuring the thickness of an epitaxial layer according to claim 10, characterized in that: The wavelength of the infrared light source is 0.9 micrometers to 20 micrometers, and the angle of incidence on the epitaxial layer is 25 degrees to 45 degrees.

12. The method for measuring the thickness of an epitaxial layer according to claim 1, characterized in that: Before measuring the thickness of the epitaxial layer, the method further comprises: forming an isolation buried layer in the epitaxial layer and the substrate; forming an isolation structure in the epitaxial layer; forming an active region in the epitaxial layer above the isolation buried layer; Wherein, the isolation buried layer, the isolation structure and the active area are arranged in an area outside the doping test area.

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