Epitaxial layer thickness monitoring method

Abstract

The invention discloses a method for monitoring the thickness of an epitaxial layer, which comprises the following steps of: introducing a germanium-silicon injection layer before the preparation of the epitaxial layer, irradiating a laser beam to the surface of the epitaxial layer by utilizing the optical characteristic of the silicon-germanium injection layer and the characteristic that the epitaxial layer is different, and measuring the characteristic information reflected by the laser beam, so that the preparation thickness of the epitaxial layer can be monitored in real time.

Description

Technical Field

[0001] The invention relates to the field of semiconductor technology, and in particular to a method for monitoring the thickness of an epitaxial layer. Background Art

[0002] With the development of CMOS technology, epitaxial growth of doped silicon thin films has become increasingly important, and can be widely used in the fields of device source / drain regions, epitaxial functional layers, etc. The key point of the above applications is that a relatively low temperature growth process is required to avoid diffusion between adjacent regions, so that the device is not damaged during the manufacturing process.

[0003] At present, reduced pressure chemical vapor deposition (RPCVD or LPCVD) is usually used for epitaxial growth of doped silicon films, using raw material gases such as silane, dichlorodihydrosilane, germane, diborane, and phosphine to generate a doped epitaxial silicon layer on the silicon surface. It can also be combined with a selective deposition process, adding gases such as HCl as an etchant during the reaction, and deposition and etching are carried out simultaneously to achieve selective epitaxial growth of silicon. However, the epitaxial layer has controllable thickness and composition, so an accurate and instantaneous epitaxial layer thickness precision monitoring technology is urgently needed. Summary of the invention

[0004] Based on the above-described problem, the present invention proposes a method for monitoring the thickness of an epitaxial layer, comprising: A semiconductor substrate is provided; a Ge injection layer is formed in the semiconductor substrate; an epitaxial layer is formed on the Ge injection layer; a probe beam is provided on the epitaxial layer and the Ge injection layer, and the thickness of the epitaxial layer is determined by detecting the probe beam reflected by the Ge injection layer and the epitaxial layer.

[0005] Furthermore, the Ge-containing doping layer is formed on the surface of the silicon substrate by ion implantation.

[0006] Furthermore, the process of forming the epitaxial layer includes: forming an epitaxial layer on the surface of the substrate by epitaxial growth; the temperature of the epitaxial growth does not exceed 450° C., and the pressure does not exceed 40 Torr.

[0007] Furthermore, the method for preparing the epitaxial layer is to perform HCl and H2 surface treatment on the surface of the substrate on which a thick Ge injection layer has been formed under constant low pressure and constant low temperature conditions, deposit silane on the wafer surface, and simultaneously introduce an doping gas with a flow rate greater than that of the silicon source to obtain a highly doped single crystal film, wherein the low pressure is not more than 40 Torr, and the low temperature is not more than 550°C.

[0008] Furthermore, the probe beam is a laser light source.

[0009] Furthermore, the material of the epitaxial layer is SiB.

[0010] Furthermore, the silicon source in the preparation of the epitaxial layer is one or more of dichlorosilane, silane, disilane, and trisilane, and the doping gas is one or more of borane, diborane, phosphine, arsine, and ethylene.

[0011] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: On the one hand, by introducing a germanium-silicon injection layer before the preparation of the epitaxial layer, and utilizing the different optical properties of the silicon-germanium injection layer and the epitaxial layer, the laser beam is irradiated onto the surface of the epitaxial layer and the characteristic information reflected back is measured to monitor the thickness of the epitaxial layer in real time.

[0012] On the other hand, the introduction of the silicon germanium injection layer can significantly improve the crystal quality of doped epitaxial silicon, so that almost defect-free uniform highly doped single crystal films can be prepared under low-temperature preparation processes. The silicon germanium injection layer can improve the adsorption characteristics of the reaction precursor source gas on the substrate surface, making the epitaxial layer growth rate controllable. At the same time, the silicon germanium injection layer can also inhibit the diffusion of doped atoms in the epitaxial layer, forming a single crystal film with uniform doping concentration distribution.

[0013] In addition, an ion implantation method is used to form a germanium silicon implantation layer, and the hydrogen atmosphere in the subsequent epitaxial reaction is used to repair the lattice damage caused by the ion implantation of germanium. The preparation method is convenient and the material quality is good. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The accompanying drawings of the present invention constitute a part of this specification and are used to further understand the present invention. The drawings illustrate embodiments of the present invention and together with the description are used to explain the principle of the present invention.

[0015] Figure 1 This is a schematic structural diagram of a boron-doped epitaxial silicon single crystal film prepared by low-temperature epitaxy according to the present invention.

[0016] Figure 2 It is a schematic diagram of an epitaxial layer thickness monitoring system according to a specific embodiment. DETAILED DESCRIPTION

[0017] The following detailed descriptions are all illustrative and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0018] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention.

[0019] A method for monitoring the thickness of an epitaxial layer according to an embodiment of the present invention is as follows: Figure 1As shown, the method includes the following steps: providing a silicon substrate 101; forming a Ge injection layer 102 in the silicon substrate 101; forming a silicon epitaxial layer 103 on the Ge injection layer; and providing a probe beam (not shown in the figure) on the silicon epitaxial layer 103 and the Ge injection layer 102. Figure 2 As shown, the thickness of the epitaxial layer is determined by detecting the probe beams L2 and L3 reflected by the Ge injection layer and the epitaxial layer. In some other embodiments, the semiconductor substrate may be a conventional substrate material in the art, including one of Si, Ge and III-V materials, and a silicon substrate is preferably used in this embodiment.

[0020] In the above steps, the Ge implantation layer 102 can be prepared by conventional preparation methods in the art, such as vapor deposition, ion implantation, etc. When the substrate of the present invention is silicon, it is preferred to use an ion implantation method with a relatively low temperature and a simple preparation process to implant germanium atoms into the silicon substrate to form a silicon germanium implantation layer, and the thickness of the implantation layer is 10nm~10μm, preferably 30~50nm. Annealing can also be selected after ion implantation for activation.

[0021] In the above steps, the preparation temperature of the epitaxial layer does not exceed 550°C, optionally, such as 100°C, 150°C, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, and the pressure of the epitaxial chamber is 0.1~80Torr, optionally, such as 10Torr, 20Torr, 30Torr, 40Torr. Under constant pressure and temperature conditions, HCl and H2 are introduced successively. 2 Surface treatment, then H 2 The single crystal film is obtained by introducing a silicon source gas and a doping source gas into the carrier gas, and depositing the single crystal film. The single crystal film is p-type doped silicon or n-type doped silicon, and the dopant includes at least one of carbon, germanium, phosphorus, arsenic or boron, preferably boron, wherein the boron doping concentration can reach 1×10 20 ~1×10 21 cm -1 .

[0022] In a specific embodiment, (001) single crystal silicon is used as the silicon substrate 101, and germanium ions are first implanted and annealed to form a 44nm germanium silicon implantation layer. Then, at 525°C, 10Torr constant pressure and temperature conditions, HCl and H2 are introduced in sequence. 2 Surface treatment, then H 2 Silane, disilane, or trisilane is introduced as a carrier gas, and diborane is introduced at the same time, wherein the flow rate of diborane is greater than the flow rate of the silane, disilane, or trisilane, so that the resistivity of the silicon epitaxial film is reduced, and a boron-doped epitaxial silicon single crystal film is deposited, and its growth rate can reach 8Å / S. The hydrogen atmosphere during epitaxial deposition can also repair the lattice damage caused by germanium ion implantation.

[0023] like Figure 2 FIG. 1 is a schematic diagram of an optical path for monitoring the thickness of an epitaxial layer used in the first embodiment.

[0024] The laser beam L1 irradiates the surface of the silicon epitaxial layer 103 at a certain angle, and a part of the beam is reflected on the surface of the epitaxial layer to form the L2 beam, while a part of the beam passes through the epitaxial layer with a lower carrier concentration and is reflected at the interface of the silicon epitaxial layer 103 and the Ge injection layer 102 to form the L3 beam. The detector receives the beam to determine the thickness of the epitaxial layer.

[0025] The specific epitaxial layer thickness d is

[0026] Where N is the number of selected interference fringes, n is the refractive index of the epitaxial layer 103 to be measured, a is the incident angle of the laser near the measuring point, and v 1 and v 2 Calculate the starting and ending wave values ​​of the selected interference fringes respectively.

[0027] Having described the basic concepts, it is obvious to those skilled in the art that the above detailed disclosure is merely an example and does not constitute a limitation of the present invention. Although not explicitly stated herein, those skilled in the art may make various modifications, improvements and amendments to the present invention. Such modifications, improvements and amendments are suggested in the present invention, so such modifications, improvements and amendments still belong to the spirit and scope of the exemplary embodiments of the present invention.

[0028] It should be understood that the embodiments described in the present invention are only used to illustrate the principles of the embodiments of the present invention. Other variations may also fall within the scope of the present invention. Therefore, as examples and not limitations, alternative configurations of the embodiments of the present invention may be considered consistent with the teachings of the present invention. Accordingly, the embodiments of the present invention are not limited to the embodiments explicitly introduced and described in the present invention.

Claims

1. A method for monitoring the thickness of an epitaxial layer, characterized in that: include: Providing a semiconductor substrate; forming a Ge implantation layer in the semiconductor substrate; forming an epitaxial layer on the Ge-implanted layer; A probe beam is provided on the epitaxial layer and the Ge-implanted layer, and the thickness of the epitaxial layer is determined by detecting the probe beam reflected by the Ge-implanted layer and the epitaxial layer.

2. The method according to claim 1, characterized in that The Ge implantation layer is formed on the surface of the silicon substrate by ion implantation.

3. The method according to claim 1, characterized in that The formation process of the epitaxial layer includes: An epitaxial layer is formed on the surface of the substrate by epitaxial growth; the temperature of the epitaxial growth does not exceed 550° C. and the pressure does not exceed 40 Torr.

4. The method according to claim 3, characterized in that The preparation method of the epitaxial layer is to perform HCl and H2 surface treatment on the surface of the substrate on which a thick Ge injection layer has been formed under constant low pressure and constant low temperature conditions, and then deposit a silicon source on the surface of the wafer and introduce a doping gas with a flow rate greater than that of the silicon source to obtain a highly doped single crystal film, wherein the low pressure is no more than 40 Torr and the low temperature is no more than 550°C.

5. The method according to claim 1, characterized in that The probe beam is a laser light source.

6. The method according to claim 1, characterized in that The material of the epitaxial layer is one or more of SiB, SiP, SiAs and SiC.

7. The method according to claim 4, characterized in that The silicon source in the preparation of the epitaxial layer is one or more of dichlorosilane, silane, disilane, and trisilane, and the doping gas is one or more of borane, diborane, phosphine, arsine, and ethylene.

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