TW201318061A - Method for dynamically detecting etched end point - Google Patents

Abstract

The invention relates to a method for dynamically detecting an etched end point. The method comprises the steps of: acquiring the strength of a real-time optical signal from the start of etching to the finish of etching, wherein the process from the start of etching to the finish of etching comprises a delay time section, a stable etching time section and an etched end point-judging time section, and the strength of the optical signal with a specific wavelength corresponds to the concentration of an active ingredient or a product of a specific etching gas in an etching cavity; providing a reference threshold value of a predetermined delay time section; searching for an inflection point of the strength of the real-time optical signal in the delay time section; if finding out the inflection point in the delay time section, entering the stable etching time section; and if no inflection point is in the predetermined delay time section, entering the stable etching time section after reaching the reference threshold value. The delay time method provided by the invention is high in precision.

Description

Etching end point dynamic detection method

The invention relates to a semiconductor etching process, in particular to a method for dynamically detecting an etch end point.

The integrated circuit manufacturing process is a planar fabrication process that combines various processes such as photolithography, etching, deposition, ion implantation, etc., to form a large number of various types of complex devices on the same substrate surface, and interconnect them to have complete electrons. Features. As the feature size of the device of the integrated circuit is continuously reduced, the degree of integration is continuously improved, and higher requirements are imposed on the monitoring of each step process and the accuracy of the process result.

The etching process is one of the most complicated processes in the integrated circuit fabrication process. It is especially important to accurately monitor the etch end of the etch process. An etch end point monitoring method for determining a plasma etching process by optical emission spectroscopy (OES) is provided in U.S. Patent No. 5,568,423. An etch end point monitoring method using OES to determine a plasma etch process includes: determining a detected element, the element being a component of a film layer to be etched; collecting a light intensity of the element, the light intensity and the The concentration of the element is related; as the etching process proceeds, at the end of the etching, the film material is etched, the concentration of the element in the etching chamber is reduced, and the light intensity of the element detected in the reaction chamber begins. Reduced, at this time, is the end point of etching.

However, it has been found in the actual etching process that the existing monitoring method for determining the etching end point of the plasma etching process cannot accurately monitor the etching end point of the plasma etching process.

The problem solved by the present invention is to provide a method for dynamically detecting an etch end point which can accurately monitor a plasma etching process.

In order to solve the above problems, the present invention provides a method for dynamically detecting an etch end point, comprising: obtaining an intensity of an instant optical signal from the start of etching to completion of etching, wherein the etch starts from the completion of etching to include a delay period and is stable. Etching period and etching end point determining period, the intensity of the specific wavelength optical signal corresponds to the specific etching gas active component concentration or product concentration in the etching chamber; providing a preset delay period reference threshold; search delay time The inflection point of the instantaneous optical signal strength in the segment, if the inflection point is searched within the delay time period, the stable etching time period is entered, and if there is no inflection point within the preset delay time period, after reaching the reference threshold value Enter the stable etching period.

In an embodiment of the present invention, the method for determining the inflection point is: searching for the slope of the intensity and time of the specific wavelength instant optical signal, and the point corresponding to the slope of the intensity curve of the instant optical signal being 0 is an inflection point.

In an embodiment of the present invention, the determining method of the inflection point is: acquiring the intensity of the optical signal noise signal in the stable etching period, so that the variation amplitude of the adjacent two signals in the delay period is ΔI=In- When In-1 is less than 10 times of the signal noise intensity in the stable etching period, it enters a stable etching period, where In is the intensity of the nth instant optical signal, and In-1 is the n-1th instant optical signal. Intensity, n is a natural number greater than one.

In an embodiment of the present invention, the inflection point obtaining method is: providing adjacent sampling time intervals, the difference between the intensity of the optical signal and the optical signal strength of the previous time point ΔIn=In-In-1, when △In is greater than △In-1 When 80% of the value enters the stable etching period, where In is the intensity of the nth instant optical signal, where In-1 is the intensity of the n-1th instant optical signal, and n is a natural number greater than 1.

In an embodiment of the invention, the delay period reference threshold is an empirical value.

In an embodiment of the invention, the delay period reference threshold is less than 10 seconds.

In an embodiment of the invention, the delay period reference threshold is 5 seconds or 6 seconds.

In an embodiment of the invention, the etching is plasma etching.

Compared with the prior art, the present invention has the following advantages: the embodiment of the present invention obtains an accurate delay time by searching the inflection point of the intensity of the instant optical signal within the delay time reference threshold with respect to the etching time, avoiding the experience of the operator. The defect of the delay time of the etching end point is judged, so that the limitation of the etching apparatus can be overcome, and the delay time obtained by the embodiment of the present invention is used to monitor the etching end point of the plasma etching process with high precision.

It is known from the prior art that the method of monitoring the etching end point of the plasma etching process by monitoring the optical emission spectrum of the element contained in the etched film layer cannot accurately monitor the etching end point. The inventors have studied the above problems and found that the prior art generally obtains a curve of the light intensity and time of the elements detected by optical emission spectroscopy, and the light intensity of the element begins to decrease, that is, the etching end point.

However, due to the limitations of existing equipment, measurement equipment is used. When the light intensity versus time curve of the element is measured, the initial time of the obtained curve has a certain delay time from the time when the measuring device starts measuring. Therefore, the etching delay time is defined as: the plasma is usually started when etching is started. There is a stable process for the concentration of reactants and products in the chamber after ignition, so a delay time is set before the end of the etch is detected. If the delay time is not properly selected, it will affect the detection of the etch end point, and even the etch end point will not be detected.

In the prior art measurement method, the existing monitoring method for determining the etching end point of the plasma etching process usually determines the delay time of the etching end point by the experience of the operator, so that the etching end point of the plasma etching process is inaccurate. , affecting the accuracy of the etching.

To this end, the present invention proposes an optimized etch end point dynamic detection method to solve the defect of the prior art ignoring the delay time of the etch end point or determining the delay time of the etch end point by the experience of the operator, please refer to FIG. 1 , including The following steps are as follows: Step S101: Acquire an intensity of an instant optical signal from the start of the etching to the completion of the etching, wherein the etching from the beginning of the etching to the completion of the etching includes a delay period, a stable etching period, and an etching end determining period, The intensity of the specific wavelength optical signal corresponds to a specific etching gas active component concentration or product concentration in the etching cavity; step S102: providing a preset delay time period reference threshold; step S103: searching for an instant within the delay time period An inflection point of the optical signal strength enters a stable etching period if the inflection point is searched within the delay period, and if there is no inflection point within the preset delay period, the stable etching is performed after reaching the reference threshold period.

Embodiments of the present invention are obtained by etching from etching to etching The intensity curve of the instant light signal, and the inventors found that the delay time has an inflection point in the corresponding intensity curve, so that the delay time can be accurately determined.

The etch end point dynamic detection method of the present invention will be described in detail below with reference to a specific embodiment.

Step S101 is performed to obtain an intensity of the instant optical signal from the start of the etching to the completion of the etching, wherein the etching from the beginning of the etching to the completion of the etching includes a delay period, a stable etching period, and an etching end determining period, The intensity of the particular wavelength optical signal corresponds to the concentration of the particular etch gas active component or product concentration within the etch chamber.

In an embodiment, obtaining an intensity curve of the instant optical signal from the start of the etching to the completion of the etching specifically includes: providing an etching device, the etching device is a plasma etching device, and the etching device has etching a cavity, the wafer to be etched is placed on a carrier of the cavity; an etching gas is introduced into the etching cavity, and the wafer to be etched is etched by a plasma etching device; The detector in the plasma etching apparatus collects the optical signal in the etching cavity, and the optical signal refers to the light of different wavelengths emitted by the etching reactant and the etching product in the etching cavity at each moment. strength.

In one embodiment, when the yttrium oxide is etched with a fluorocarbon gas, there is CO in the by-product produced by the etching, and the corresponding spectral wavelength is 483 nm, and by detecting the peak intensity of 483 nm with time, It is possible to know the change in the CO concentration in the cavity; thereby inferring the case where SiO2 is etched.

In another embodiment, when SiN (tantalum nitride) is etched with a fluorocarbon gas, the by-product is CN, and the corresponding spectral wavelength is 387 nm, by detecting the peak intensity of 387 nm with time, The change in CN concentration in the cavity is known; thus the case where SiN is etched is inferred.

It should be noted that, when the type of the wafer to be etched is different from the type of the etching gas, the specific wavelength optical signal may be different, but the intensity of the specific wavelength optical signal is specific to the etching cavity. The etching gas active component concentration or the product concentration is corresponding, and those skilled in the art can select a corresponding specific wavelength optical signal according to the type of the etched wafer and the type of the etching gas, and acquire the optical signal of the specific wavelength. The strength, which is specifically stated herein, should not unduly limit the scope of the invention.

It should also be pointed out that due to the limitations of the device, when the measuring device measures the light intensity versus time curve of the element, the initial time of the obtained curve has a certain delay time from the time when the measuring device starts measuring, in the prior art. In the measurement method, the existing monitoring method for determining the etching end point of the plasma etching process usually ignores the delay time of the etching end point, or judges the delay time of the etching end point by the experience of the operator, so that the plasma etching The etch end of the process is inaccurate and affects the accuracy of the etch.

To this end, after performing step S101, the embodiment of the present invention performs step S102 to provide a preset delay period reference threshold.

The delay time reference threshold is used to determine whether there is an inflection point within the delay time reference threshold time, and the delay time reference threshold can be etched by the etched wafer multiple times under the same condition, and tested Obtaining the degree of over-etching of the etched wafer, and obtaining the intensity curve of the instantaneous optical signal from the start of etching to the completion of etching by the same condition, directly setting the time of the empirically obtained delay time to a slightly longer time as the delay time. Reference threshold.

In an embodiment, the delay period reference threshold is an empirical value, and the delay period reference threshold is less than 10 seconds, for example, the delay period reference threshold is 1 second, 2 seconds, 3 seconds, 4 seconds, 5 Second, 6 seconds, 7 seconds, 8 seconds, or 9 seconds, preferably, the delay period reference threshold is 5 seconds or 6 seconds.

In an embodiment, the delay time reference threshold is obtained by providing an intensity curve of an instant optical signal from the start of etching to the completion of etching, and the intensity curve of the instant optical signal may refer to the instant optical signal of step S101. The method for obtaining the intensity curve will not be described here.

Providing adjacent sampling time intervals, a is a natural number greater than or equal to 1 in a time interval of adjacent sampling interval time, searching for the absolute value of the slope of the intensity of the instantaneous optical signal relative to the sampling time, and obtaining the slope The difference between the intensity of the optical signal corresponding to the maximum value of the absolute value and the intensity of the optical signal of the previous time point ΔI, the reference value B is selected in the range of 0 to a ΔI; the value of In-a+B and In For comparison, when the curve is a rising curve and In-a+B>In, the time corresponding to In is the delay time reference threshold; the curve is the falling curve, and In-aB<In, the time corresponding to In is the delay time. Reference threshold; wherein In-a is the intensity of the nath instant optical signal, In is the first The intensity of n instantaneous light signals, n is a natural number.

Wherein, the rising curve is determined by: selecting P consecutive time segments, P is greater than 1, and collecting the etching signals at the end points of each time segment, which are sequentially recorded as I1, I2, ..., In, In+1, ... IP, If the selected P etch signal values are sequentially increased, it is determined that the time period is a rising curve.

The judgment method of the falling curve is: selecting Q consecutive time segments, Q is greater than 1, and collecting the etching signals at the end points of each time segment, which are sequentially recorded as I1, I2, ..., In, In+1, ..., IQ. The selected Q etching signal values are sequentially decreased, and it is determined that the time period is a falling curve.

Specifically, the total duration of the P time periods and the duration of each time period may be selected according to an etching process, a signal to noise ratio of the etching signal, and the like. Referring to FIG. 2, it is a schematic diagram showing the relationship between the intensity of the etched signal and the time of an embodiment, wherein the vertical axis is the intensity of the etched signal and the horizontal axis is the time. In this embodiment, the peak of the etch signal according to the sample can be used. The duration P' corresponding to the rising edge is selected to monitor the total duration of the P time periods selected for the subsequent etch end of the same batch of samples. The total duration of P time periods may be greater than or equal to P'.

The value of P can also be selected according to the specific process, or FIG. 2 is taken as an example. In the case where the curve representing the etch signal is not smooth in FIG. 2, in the case where the total duration of the P time periods is determined, The value of the P may be slightly smaller to avoid interference of noise in the signal because the point is too dense, and the end point of each time period of the P time periods may be reasonably allocated according to the situation of the noise, for example, A noise wave appears every 0.01 s, and the length of each time period of the P time periods may be an integer multiple of 0.01 s. Preferably, the P time periods are equal, The equal length of the P time periods can improve the accuracy of the rising edge judgment and reduce the noise interference.

As shown in FIG. 3, after searching for I, I2, In, In+1, ... IP, a total of P successively increased etching signals, a rising edge is searched.

In another embodiment, a search for a falling edge is started in the etch signal, and the search process of the falling edge includes: selecting Q consecutive time segments, Q is greater than 1, and collecting an etch signal at an end point of each time segment, It is denoted as Ii+1, Ii+2, ...Ii+n, Ii+n+1...Ii+Q, and if the selected Q etching signal values are sequentially decreased, the falling edge of the etching signal is obtained. If Ii+n is less than or equal to Ii+n+1, then Q consecutive time segments are re-selected from Ii+n+1, and the etching signals at the end points of each time segment are collected and compared until Q is successively subtracted. A small etch signal is considered to result in a falling edge of the etch signal.

Specifically, the total duration of the Q time periods and the duration of each time period may be selected according to an etching process, a signal to noise ratio of the etching signal, and the like. Referring to FIG. 4, the vertical axis of FIG. 4 is the intensity of the etch signal, and the horizontal axis is time. In this embodiment, Q time can be selected according to the time length Q′ of the falling edge of the peak of the etch signal of the sample. The total length of the segment. The total duration of the Q time periods may be greater than or equal to Q'.

The value of Q can also be selected according to the specific process, or FIG. 4 is taken as an example. In the case where the curve representing the etched signal is not smooth in FIG. 4, in the case where the total duration of the Q time periods is determined, The value of the Q may be slightly smaller to avoid interference of noise in the signal because the point is too dense, and the end point of each time period of the Q time period may be reasonably allocated according to the situation of the noise, for example, , a noise wave appears every 0.02s, it can be every time period of Q time period The length is an integer multiple of 0.02 s. Preferably, the Q time periods are equal in length, and the equal lengths of the Q time segments can improve the accuracy of determining the falling edge and reduce noise interference.

As shown in FIG. 5, after searching for Ii+1, Ii+2, ... Ii+n, Ii+n+1, ... Ii+Q, successive Q successively falling etch signals, a falling edge is searched.

Step S103 is performed to search for an inflection point of the instantaneous optical signal strength in the delay period. If an inflection point is searched in the delay period, the stable etching period is entered, and if there is no inflection point in the preset delay period Then, after reaching the reference threshold, the stable etching period is entered.

The inventors have found that the intensity of the luminescence of the substance in the etch chamber continues to change during the delay period, but at the end of the delay time, the rate of change of the luminescence intensity of the substance in the etch chamber has an inflection point. Please refer to FIG. 6. FIG. 6 is a graph showing the relationship between the peak intensity of the wavelength of 483 nm corresponding to the by-product CO generated by etching when etching yttrium oxide, and in the embodiment of etching yttrium oxide. The delay time is referenced to the threshold, and a delay time is obtained at an inflection point of the intensity of the instant optical signal within the delay time reference threshold relative to the etch time.

Specifically, the inflection point of the instantaneous optical signal strength in the delay period can be obtained by:

Method 1:

The inflection point is determined by searching for the slope of the intensity and time of the specific optical signal of the specific wavelength, and the point corresponding to the slope of the intensity curve of the instant optical signal is 0 is the inflection point.

Taking the intensity curve of the instant light signal of the etched yttrium oxide of FIG. 6 as an example, the horizontal axis is the detection time, and the vertical axis is the intensity of the instantaneous light signal. The intensity curve of the instantaneous light signal of the etched yttrium oxide is obtained to obtain the slope of the peak intensity of 483 nm and the time. When the slope of the 483 nm spectral peak intensity curve is 0, the point corresponding to the inflection point, and the time corresponding to the inflection point is the delay time.

Method 2:

The method for judging the inflection point is: obtaining the intensity of the optical signal noise signal when the plasma etching is stable, and setting ΔI=In-In-1, if the absolute value of ΔI is less than 10×light when the plasma etching is stable When the signal noise signal intensity is strong, the time point corresponding to In is the inflection point, where In is the intensity of the nth instant optical signal, In-1 is the intensity of the n-1th instant optical signal, and n is a natural number greater than 1. .

Please refer to FIG. 7. FIG. 7 is an intensity curve of an etched SiN (tantalum nitride) instant light signal. The horizontal axis is the detection time, the vertical axis is the intensity of the instantaneous light signal, the by-product is CN, and the corresponding wavelength of the CN is 387 nm. ΔI=In-In-1 is set in the intensity curve of the etched SiN instant optical signal, and the time corresponding to In when the absolute value of ΔI is <10×the optical signal noise intensity when the plasma etching is stable The point is an inflection point, where In is the intensity of the nth instant optical signal, In-1 is the intensity of the n-1th instant optical signal, and n is a natural number greater than 1.

Mode 3

Providing adjacent sampling time intervals, the difference between the intensity of the optical signal and the intensity of the optical signal at the previous time point ΔIn=In-In-1, and when ΔIn is greater than 80% of the value of ΔIn-1, it enters a stable engraving The eclipse period, where In is the intensity of the nth instant optical signal, wherein In-1 is the intensity of the n-1th instant optical signal, and n is a natural number greater than 1.

It should also be noted that, in other embodiments, the intensity of the instantaneous optical signal within the delay time reference threshold is relative to the inflection point of the etch time. There may be multiple, for example: 2, 3, 4... In this embodiment, the etch time corresponding to the first inflection point searched is the delay time corresponding to the etch; if the delay time is referenced There is no inflection point within the threshold, and the delay time reference threshold is defined as the delay time of the etch.

Preferably, in order to reduce the misjudgment of the inflection point caused by interference such as signal noise, after the first inflection point occurs within the delay time reference threshold, multiple inflection points appear consecutively, and the time corresponding to the first inflection point is selected as Delay time; for example, after the first inflection point, each point within 10 seconds of the first inflection point satisfies the inflection point requirement.

It should be noted that if there is an inflection point in the reference threshold within the delay period, the stable etching period is entered; if there is no inflection point in the preset delay period, the stable etching time is entered after reaching the reference threshold. segment.

In the subsequent steps, the etching end point of the plasma etching process can be monitored in various ways by inputting the delay time period obtained by using the various embodiments of the present invention, specifically, the etching end point of the plasma etching process. The manner of obtaining can refer to the etching end point judgment mode of the existing plasma etching process, and details are not described herein again.

The embodiment of the present invention obtains an accurate delay time by searching the inflection point of the intensity of the instant optical signal in the delay time reference threshold with respect to the etching time, thereby avoiding the defect of the delay time of the etching end point by the experience of the operator, thereby being able to Overcoming the limitations of the etching apparatus, the delay time obtained by the embodiment of the present invention is used to monitor the etching end point of the plasma etching process with high accuracy.

The present invention has been disclosed in the above preferred embodiments, but it is not intended to limit the invention, and any person skilled in the art will not depart from the invention. In the spirit and scope of the present invention, possible changes and modifications may be made to the technical solutions of the present invention by using the methods and technical contents disclosed above. Therefore, the above embodiments are in accordance with the technical essence of the present invention without departing from the technical solution of the present invention. Any simple modifications, equivalent changes, and modifications made by the present invention are within the scope of the present invention.

1 is a schematic flow chart of a method for dynamically detecting an etch end point according to an embodiment of the present invention; FIG. 2 is a schematic diagram showing relationship between an intensity of an etch signal and time according to an embodiment of the present invention; FIG. 3 is a search in the embodiment of FIG. FIG. 4 is a schematic diagram showing the relationship between the intensity of an etch signal and the aging signal according to another embodiment of the present invention; FIG. 5 is a schematic diagram of searching for an etch signal in the embodiment of FIG. 4; In the case of 矽, the intensity of the peak intensity of the wavelength of 483 nm corresponding to the CO produced by the etching changes with time; FIG. 7 is the intensity curve of the instant light signal of the etched SiN.

Claims (8)

A method for dynamically detecting an etch end point includes: obtaining an intensity of an instant optical signal from the start of etching to completion of etching, wherein the etching from the beginning of the etching to the completion of the etching includes a delay period, a stable etching period, and an etching end point Determining the time period, the intensity of the specific wavelength optical signal corresponds to the specific etching gas active component concentration or product concentration in the etching cavity; providing a preset delay time period reference threshold; searching for the instantaneous optical signal intensity within the delay time period The inflection point enters a stable etching period if the inflection point is searched within the delay period. If there is no inflection point within the preset delay period, the stable etching period is entered after reaching the reference threshold. The etch end point dynamic detecting method according to claim 1, wherein the inflection point is determined by searching for a slope of the intensity and time of the specific optical signal of the specific wavelength, and the slope of the intensity curve of the instant optical signal is 0. For the turning point. The etch end point dynamic detection method as described in claim 1, wherein the inflection point is determined by: obtaining an optical signal noise signal strength during a stable etching period, so that two adjacent signals in the delay period The variation amplitude ΔI=In-In-1 is less than 10 times of the signal noise intensity in the stable etching period, and enters the stable etching period, where In is the intensity of the nth instant optical signal, and In-1 is the first The intensity of n-1 instant optical signals, where n is a natural number greater than one. The method for dynamically detecting an etch end point according to claim 1, wherein the inflection point is obtained by providing an adjacent sampling time interval, a difference between an intensity of the optical signal and an optical signal intensity at a previous time point. In=In-In-1, when ΔIn is greater than 80% of the value of ΔIn-1, it enters a stable etching period, where In is the intensity of the nth instant optical signal, where In-1 is the n-1th The intensity of an instant optical signal, where n is a natural number greater than one. The etch endpoint dynamic detection method according to claim 1, wherein the delay period reference threshold is an empirical value. The etch end point dynamic detection method according to claim 1, wherein the delay period reference threshold is less than 10 seconds. The etch end point dynamic detection method according to claim 6, wherein the delay period reference threshold is 5 seconds or 6 seconds. The etch end point dynamic detecting method according to claim 1, wherein the etching is plasma etching.