KR20040107137A - A Method for measuring trench depth formed on semiconductor substrate - Google Patents

Abstract

PURPOSE: A method of measuring the depth of a trench in a semiconductor substrate is provided to prevent the substrate from being contaminated and scratched due to a metallic probe of a conventional alpha-step manner by using optical processing. CONSTITUTION: First and second laser beams are irradiated on a wafer(10) with a trench, wherein the first and second laser beams have a predetermined incident angle(θ) on the wafer. A first reflected laser point(50') of the first laser beam and a second reflected laser point(60') of the second laser beam are detected by a sensor(40). A distance(a) between the first and second reflected laser points is measured. A depth of the trench is calculated according to the measured distance and the predetermined incident angle of each laser beam.

Description

A method for measuring trench depth formed on semiconductor substrate

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to depth measurement of semiconductor substrates, and more particularly, to a method for measuring trench depth of a semiconductor substrate suitable for efficiently measuring trench depth.

In general, the LOCOS method has been used in the past as a method of insulation between transistors in semiconductor devices. However, as the degree of integration of semiconductor devices increases, a shallow trench isolation (STI) method is used.

However, in the STI method, since the trench is etched on the substrate, it is important to measure the depth, and the alpha step method has been used in the past.

1 is an explanatory diagram of a general alpha step method of measuring a depth by connecting a piezoelectric element to a probe 20.

As is well known, the alpha-step method connects a piezoelectric element to the probe 20 so that when the probe scratches a pattern, if the probe encounters a certain step, the probe is shocked and the shock is converted into an electrical signal using a piezoelectric element to measure the step depth. Measure

However, this method is more inaccurate than the optical method because the probe 20 is forced to contact the wafer 10 to scratch a portion of the wafer, but also causes scratches on the substrate or contamination of the wafer by the metal component of the probe. Could bring.

The alpha step method, which is a conventional method for measuring the depth of trenches of a semiconductor substrate, has the following problems.

First, because the probe scrapes the bottom to measure depth, it may cause scratches on the substrate and the wafer may be contaminated by the metal component of the probe.

Secondly, it is less accurate because it is a mechanical method.

The present invention has been made to solve the above problems, and proposes a method for measuring the depth of the trench in an optical method.

1 is an explanatory diagram of an alpha-step method for measuring depth by measuring a step by connecting a piezoelectric element to a probe and detecting an impact transmitted according to depth when the floor is scratched with an electrical signal.

2A is an explanatory diagram showing a process of scanning a laser beam at an angle of θ and capturing a reflected laser point to a sensor sensing the laser point;

2B is an explanatory diagram showing a process in which a distance difference occurs between a first laser point reflected first by a trench depth and a second laser point reflected later;

<Explanation of symbols for the main parts of the drawings>

10: semiconductor substrate 20: probe connected piezoelectric element

30: laser point incident on wafer 30 ': reflected laser point

40: Sensor for sensing the reflected laser point

50: first laser point projected on the wafer 50 ': reflected first laser point

60: second laser point projected on the wafer 60 ': second laser point having a distance difference from the point first reflected by the trench depth

In order to achieve the above object, the present invention provides a method for scanning a first laser beam on a wafer at a predetermined angle of incidence, wherein the first laser point is reflected on the wafer, and the second laser beam is Detecting a second laser point reflected on the wafer with a sensor, measuring a distance difference generated according to a trench depth between the first laser point reflected first on the wafer and the second laser point reflected later, Estimating the trench depth by the measured distance difference and the incident angle of the beam.

Referring to the accompanying drawings, a method of measuring a semiconductor substrate trench depth is as follows.

As shown in FIG. 2A, when a laser beam having a length of 0.5 to 2.0 μm is incident on the wafer 10 at an angle of θ, an image of the same length is applied to the sensor 40 sensing the laser point 30 because of the reflectivity of the wafer. Detects the formation of 30 '.

As shown in FIG. 2B, the first laser point 50 ′ first reflected by the trench depth and the second laser point 60 ′ reflected later are separated from each other at a predetermined distance a. As the trench depth b increases, Will be further away. Here, if the trench depth is b, using the incident angle θ and the distance a between the points,

b = (a * tan θ) / 2

You can get it through the formula As shown in the above formula, b is constant, so decreasing the angle of incidence θ increases the value of a, thereby reducing the measurement error. Therefore, the desired trench depth can be measured by measuring the a value with this optical method.

When the laser is used in the above manner, it is possible to prevent metal contamination or scratch generation of the wafer, which has been a problem in the conventional alpha-step method. Furthermore, according to the present invention, the trench depth can be measured more easily than in the conventional case by measuring a constant distance between points reflected by the trench depth.

In the present invention, in general, since b is constant, it is possible to reduce the error of measurement by decreasing the value of θ, and the length of the laser point used in the present invention is preferably 0.5 to 2.0 m.

As described in detail above, according to the trench depth measurement method of the semiconductor substrate using the laser of the present invention, it is possible to fundamentally solve the contamination of the wafer caused by the scratch and the metal component of the probe generated in the conventional alpha-step method. Since the trench depth b is constant, the measurement error can be reduced by increasing the distance difference a caused by the trench depth by decreasing the incident angle θ of the laser beam.

Claims (3)

Scanning the first and second laser beams on the wafer at a predetermined angle of incidence, Detecting, by a sensor, a first laser point at which the first laser beam is reflected on the wafer and a second laser point at which the second laser beam is reflected on the wafer; Measuring a distance difference generated according to a trench depth between the first laser point reflected first from the wafer and the second laser point reflected later; And estimating a trench depth by the measured distance difference and the incident angle of the beam. The method of measuring the trench depth of a semiconductor substrate according to claim 1, wherein the length of the laser point is 0.5 to 2.0 mu m. 2. The method of claim 1, wherein the laser beam is scanned at a small incident angle to reduce measurement errors.