KR-102964767-B1 - Large particle monitoring using laser power control for defect inspection

KR102964767B1KR 102964767 B1KR102964767 B1KR 102964767B1KR-102964767-B1

Abstract

A semiconductor wafer is inspected using a main laser beam and an auxiliary laser beam. The auxiliary laser beam leads the main laser beam and has a lower power than the main laser beam. Using the auxiliary laser beam, particles on the semiconductor wafer having a size that meets a threshold are detected. In response to the detection of particles, the power of the main laser beam and the power of the auxiliary laser beam are reduced. The particles pass through the main laser beam with reduced power. After the particles pass through the main laser beam with reduced power, the power of the main laser beam and the power of the auxiliary laser beam are restored in a controlled manner slower than a single step.

Inventors

로마노브스키 아나톨리
수 지웨이
유디츠키 유리
쿠이 이펭
파란자페 만다르

Assignees

케이엘에이 코포레이션

Dates

Publication Date: 20260513
Application Date: 20210902
Priority Date: 20210407

Claims (20)

In a method for inspecting defects on a semiconductor wafer, A step of inspecting the semiconductor wafer using a main laser beam and an auxiliary laser beam - the auxiliary laser beam leads the main laser beam and has a lower power than the main laser beam - ; A step of detecting particles on the semiconductor wafer having a size that satisfies a threshold value using the above auxiliary laser beam; In response to detecting the particle, a step of reducing the power of the main laser beam and the power of the auxiliary laser beam - the particle passes through the main laser beam with the reduced power - ; and After the particle passes the main laser beam with the reduced power, a step of restoring the power of the main laser beam and the power of the auxiliary laser beam in a controlled manner having a restoration speed slower than the single-stage restoration speed. A method for inspecting defects on a semiconductor wafer, comprising
In claim 1, A method for inspecting defects on a semiconductor wafer, wherein the step of restoring the power of the main laser beam and the power of the auxiliary laser beam in the above-mentioned controlled manner includes the step of restoring the power of the main laser beam and the power of the auxiliary laser beam in a series of steps.
In claim 2, A method for inspecting defects on a semiconductor wafer, wherein the above series of steps consists of 3 to 7 steps.
In claim 2, A method for inspecting defects on a semiconductor wafer, wherein the above series of steps comprises at least three steps.
In claim 1, A method for inspecting defects on a semiconductor wafer, wherein the step of restoring the power of the main laser beam and the power of the auxiliary laser beam in the above-mentioned controlled manner includes the step of ramping up the power of the main laser beam and the power of the auxiliary laser beam in a gentle curve.
In claim 1, A method for inspecting defects on a semiconductor wafer, wherein the step of restoring the power of the main laser beam and the power of the auxiliary laser beam in the above-mentioned controlled manner includes the step of ramping up the power of the main laser beam and the power of the auxiliary laser beam with a linear ramp.
In claim 1, The method further includes the step of splitting the third laser beam into the main laser beam and the auxiliary laser beam. The step of reducing the power of the main laser beam and the power of the auxiliary laser beam includes the step of reducing the power of the third laser beam, and A method for inspecting defects on a semiconductor wafer, wherein the step of restoring the power of the main laser beam and the power of the auxiliary laser beam in the above-mentioned controlled manner includes the step of restoring the power of the third laser beam in the above-mentioned controlled manner.
In claim 7, A method for inspecting defects on a semiconductor wafer, wherein the step of splitting the third laser beam comprises providing the third laser beam to a diffraction optical element that splits the third laser beam into the main laser beam and the auxiliary laser beam.
In claim 7, A method for inspecting defects on a semiconductor wafer, further comprising the step of generating the third laser beam, wherein the step of generating the third laser beam includes the step of converting a portion of the fourth laser beam into the third laser beam using a harmonic generator, and wherein the third laser beam is a harmonic of the fourth laser beam.
In claim 9, The step of reducing the power of the third laser beam includes the step of reducing the power of the fourth laser beam, and A method for inspecting defects on a semiconductor wafer, wherein the step of restoring the power of the third laser beam in the above-mentioned controlled manner includes the step of restoring the power of the fourth laser beam in the above-mentioned controlled manner.
In claim 10, A method for inspecting defects on a semiconductor wafer, wherein the step of restoring the power of the fourth laser beam in the above-mentioned controlled manner includes the step of restoring the power of the fourth laser beam in a series of steps.
In claim 11, A method for inspecting defects on a semiconductor wafer, wherein the above series of steps consists of 3 to 7 steps.
In claim 11, A method for inspecting defects on a semiconductor wafer, wherein the above series of steps comprises at least three steps.
In claim 10, A method for inspecting defects on a semiconductor wafer, wherein the step of restoring the power of the fourth laser beam in the above-mentioned controlled manner includes the step of ramping up the power of the fourth laser beam in a gentle curve.
In claim 10, A method for inspecting defects on a semiconductor wafer, wherein the step of restoring the power of the fourth laser beam in the above-mentioned controlled manner includes the step of ramping up the power of the fourth laser beam with a linear ramp.
In claim 10, It further includes the step of asserting a signal in response to detecting the above particle, and The step of reducing the power of the fourth laser beam includes the step of increasing the radio-frequency (RF) power provided to an acousto-optic modulator (AOM) in the path of the fourth laser beam, and A method for inspecting defects on a semiconductor wafer, wherein the step of restoring the power of the fourth laser beam in the above-mentioned controlled manner includes the step of reducing the RF power provided to the AOM.
In a defect inspection system on a semiconductor wafer, An optical system for providing a main laser beam and an auxiliary laser beam to the semiconductor wafer above—the auxiliary laser beam precedes the main laser beam and has a lower power than the main laser beam—; and A detector for detecting particles on the semiconductor wafer having a size that satisfies a threshold using the above auxiliary laser beam Includes, The optical system includes a modulator, and the modulator responds to detecting the particle: When the above particle passes through the above main laser beam, the power of the above main laser beam and the power of the above auxiliary laser beam are reduced, and A defect inspection system on a semiconductor wafer, wherein, after the particle passes through the main laser beam, the power of the main laser beam and the power of the auxiliary laser beam are restored in a controlled manner having a restoration speed slower than a single-stage restoration speed.
In claim 17, A defect inspection system on a semiconductor wafer, wherein the modulator is for restoring the power of the main laser beam and the power of the auxiliary laser beam in a series of steps.
In claim 18, A defect inspection system on a semiconductor wafer, wherein the above series of steps consists of 3 to 7 steps.
In claim 18, A defect inspection system on a semiconductor wafer, wherein the above series of steps includes at least three steps.

Description

Large particle monitoring using laser power control for defect inspection Related applications This application claims priority to U.S. Provisional Patent Application No. 63/082,484 filed September 24, 2020, the entirety of which is incorporated by reference for all purposes. Technology field The present disclosure relates to laser power modulation, and more specifically to laser power modulation for large-particle monitoring. As semiconductor design rules become stricter, the size of defects shrinks accordingly. Defect inspection tools, also referred to as particle inspection tools or simply inspection tools, must be able to detect small particles at advanced design layers (e.g., design layers with the most stringent design rules). For laser scattering-based inspection tools, laser power density requirements will continue to increase to enable the detection of increasingly smaller particles. Consequently, new inspection tools feature higher laser power densities and smaller focus spot sizes. However, laser heating of particle defects can cause the particles to explode (i.e., induce particle ablation). Increasing the laser power density reduces the threshold size at which particle ablation occurs. Particle ablation can cause particle contamination by breaking a single large particle into hundreds of small particles in the peripheral region of the semiconductor wafer. Higher laser power densities can also damage films deposited on the wafer and possibly the wafer itself (e.g., when high power density is combined with long exposure times). This problem can be mitigated by dynamically adjusting the laser power during wafer inspection. Dynamic adjustment of laser power can be referred to as laser power modulation (LPM). Therefore, an improved method and system for laser power modulation during wafer inspection is required. In some embodiments, the method includes the step of inspecting a semiconductor wafer using a main laser beam and a secondary laser beam. The secondary laser beam leads the main laser beam and has a lower power than the main laser beam. The method also includes the step of detecting a particle on the semiconductor wafer having a size that satisfies a threshold using the secondary laser beam, and the step of reducing the power of the main laser beam and the power of the secondary laser beam in response to the detection of the particle. The particle passes through the main laser beam with the reduced power. The method further includes the step of restoring the power of the main laser beam and the power of the secondary laser beam in a controlled manner slower than a single step after the particle has passed through the main laser beam with the reduced power. In some embodiments, the system includes an optical system for providing a main laser beam and an auxiliary laser beam to a semiconductor wafer. The auxiliary laser beam leads the main laser beam and has a lower power than the main laser beam. The system also includes a detector for using the auxiliary laser beam to detect particles on the semiconductor wafer having a size that meets a threshold. The optical system includes a modulator, the modulator being intended to reduce the power of the main laser beam and the power of the auxiliary laser beam when the particle passes through the main laser beam in response to the detection of a particle, and to restore the power of the main laser beam and the power of the auxiliary laser beam in a controlled manner slower than a single step after the particle has passed through the main laser beam. To better understand the various described implementations, refer to the detailed description below in conjunction with the following drawings. The drawings may not be drawn to actual scale. FIG. 1 is a drawing of a component of a system for inspecting a semiconductor wafer according to some embodiments. FIG. 2 illustrates, according to some embodiments, the positions of the spot of the auxiliary beam and the spot of the main beam for the particle, the main beam and auxiliary beam signals for detecting the particle, and stepwise beam power reduction and restoration to avoid particle ablation. FIG. 3 illustrates various ways in which, according to some embodiments, the power of the main beam and the power of the auxiliary beam can be restored in a controlled manner slower than a single step. Figure 4 is a graph showing the modeled minimum ablation size and auxiliary beam sensitivity versus laser power. FIG. 5 is a drawing illustrating a laser beam power modulation system having an acousto-optic modulator (AOM) according to some embodiments. FIG. 6 is a flowchart of a method for modulating the power of a main laser beam and an auxiliary laser beam while inspecting a semiconductor wafer to avoid large particle ablation according to some embodiments. Throughout the drawings and specifications, similar reference numbers refer to corresponding parts. Various embodiments illustrated in the accompanying drawings wi