Online detection method for epitaxial layer thickness of silicon single crystal light-doped thick epitaxial wafer for IGBT (Insulated Gate Bipolar Translator)

Abstract

The invention relates to the technical field of semiconductor manufacturing, in particular to an on-line detection method for the thickness of an epitaxial layer of a silicon single crystal light-doped thick epitaxial wafer for an IGBT (Insulated Gate Bipolar Translator), which comprises the following steps of: measuring the weight W < front > of a silicon wafer before epitaxy; measuring the weight W of the silicon wafer again after epitaxy; and calculating the thickness of the epitaxial layer, the thickness of the epitaxial layer = the weight difference before and after epitaxy / the density rho of silicon / the area S of the epitaxial surface, namely (W < rear >-W < front >) / rho / S. And the W front part and the W rear part are measured by adopting an online weighing instrument.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, and in particular to an online method for detecting the epitaxial layer thickness of a lightly doped silicon single crystal epitaxial wafer used in IGBTs. Background Technology

[0002] The common IGBT uses silicon single crystal lightly doped epitaxial wafers. The substrate dopant is usually phosphorus, and the conductivity type is N-type. The epitaxial layer is also lightly doped with phosphorus and the doping concentration is close to that of the substrate (such as a product that is widely used with a substrate resistivity of 10~16 ohm-cm and an epitaxial resistivity of 100±5 ohm-cm, and an epitaxial layer thickness of 95~100um).

[0003] The traditional mainstream method for measuring the thickness of epitaxial layers is the FTIR method (i.e., Fourier transform infrared spectroscopy). The principle is to use infrared light to irradiate the epitaxial wafer, forming interference at the interface between the epitaxial layer and the substrate. By analyzing the interference fringes of the reflection spectrum, the thickness of the epitaxial layer is calculated using Fourier transform.

[0004] While this method can measure the thickness of silicon epitaxial wafers at multiple points and calculate the uniformity of the epitaxial layer thickness, it has the following drawbacks: 1) The dopant concentration or resistivity of the epitaxial layer and the substrate need to be different by a sufficient factor (generally, a resistivity difference of more than 20 times is required); otherwise, the difference in refractive index between the epitaxial layer and the substrate is too small to be measured. 2) Because the silicon single crystal lightly doped thick epitaxial wafers commonly used in IGBTs have insufficient difference in doping concentration between the epitaxial layer and the substrate, the product cannot be directly measured. Substrates with different doping concentrations must be used as monitoring wafers for monitoring and measurement, which leads to higher online monitoring costs (on the one hand, additional substrate costs are required, and on the other hand, the epitaxial processing cost of the monitoring wafer is also higher due to the long epitaxial time of the thick epitaxial wafer). Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings in the above-mentioned background technology and provide an online detection method for the epitaxial layer thickness of a lightly doped silicon single crystal epitaxial wafer for IGBTs.

[0006] The technical objective of this invention is achieved as follows: A method for online detection of the epitaxial layer thickness of a lightly doped silicon single-crystal epitaxial wafer used in IGBTs, comprising: Before epitaxy, the weight W of the silicon wafer is measured. 前 ; The weight W of the silicon wafer was measured again after epitaxy. 后 ; Calculate the epitaxial layer thickness: Epitaxial layer thickness = Weight difference before and after epitaxy / Silicon density ρ / Epitaxial surface area S, i.e. (W 后 -W 前 ) / ρ / S.

[0007] In a further proposal, W 前 and W 后 All measurements were taken using online weighing instruments.

[0008] The beneficial effects of this invention are: 1. It can be directly and non-destructively measured on the actual product, which facilitates increasing the monitoring frequency or even 100% pre-inspection; 2. No substrate monitoring chip is required, which saves the cost of the substrate monitoring chip and also saves the cost of epitaxial processing of the monitoring chip; 3. With the development of weighing technology, the accuracy of weighing instruments is now very high. To achieve the same detection accuracy, the cost of weighing instruments is lower than that of FTIR measurement equipment.

[0009] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Detailed Implementation

[0010] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below.

[0011] This embodiment provides an online detection method for the epitaxial layer thickness of a lightly doped silicon single-crystal epitaxial wafer used in IGBTs. Based on the characteristics of single-crystal silicon, which has uniform texture and density, the increased epitaxial layer thickness is calculated by using the weight of the silicon wafer before and after epitaxy.

[0012] The steps of this method are as follows: Before epitaxy, the weight of the silicon wafer (denoted as W) is measured online using a weighing instrument. 前 After epitaxy, the weight of the silicon wafer is measured online again using a weighing instrument (denoted as W). 后 Then, the epitaxial layer thickness of the silicon wafer can be calculated using the following formula: weight difference before and after epitaxy / density of silicon (denoted as ρ) / epitaxial surface area (denoted as S), which is: (W 后 -W 前 ) / ρ / S.

[0013] For a specific silicon wafer, since both ρ and S are known, the amount to be removed can be calculated quickly.

[0014] This invention is mainly used to replace the existing FTIR method. It is not limited by the thickness of silicon wafers and mainly solves the problem of measuring the thickness of thicker silicon epitaxial layers (e.g., 95~100um). Although this method cannot measure the thickness of epitaxial layers at multiple points and cannot calculate the uniformity of epitaxial layer thickness, it can monitor the stability of the total epitaxial thickness directly on the actual product without damage for online monitoring and measurement.

[0015] The above description is merely a preferred embodiment of the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for online detection of the epitaxial layer thickness of a lightly doped silicon single-crystal epitaxial wafer for IGBTs, characterized in that, include: Before epitaxy, the weight W of the silicon wafer is measured. 前 ; The weight W of the silicon wafer was measured again after epitaxy. 后 ; Calculate the epitaxial layer thickness: Epitaxial layer thickness = weight difference before and after epitaxy / silicon density ρ / epitaxial surface area S, i.e. (W 后 -W 前 ) / ρ / S.

2. The method for online detection of epitaxial layer thickness of a lightly doped silicon single-crystal epitaxial wafer for IGBTs according to claim 1, characterized in that, W 前 and W 后 All measurements were taken using online weighing instruments.