CN108899275B

CN108899275B - Plasma etching method

Info

Publication number: CN108899275B
Application number: CN201810809089.4A
Authority: CN
Inventors: 卫晶; 韦刚; 陈国动; 牛晨; 王桂滨; 杨京
Original assignee: Beijing Naura Microelectronics Equipment Co Ltd
Current assignee: Beijing Naura Microelectronics Equipment Co Ltd
Priority date: 2018-07-20
Filing date: 2018-07-20
Publication date: 2021-03-02
Anticipated expiration: 2038-07-20
Also published as: TW202008455A; CN108899275A; TWI695431B

Abstract

The plasma etching method comprises at least one etching step, wherein each etching step comprises a step of adjusting the phase difference between an upper electrode radio frequency power supply and a lower electrode radio frequency power supply so as to adjust the angular distribution state of plasma.

Description

Plasma etching method

Technical Field

The disclosure relates to the technical field of semiconductors, in particular to a plasma etching method.

Background

As the feature size of integrated circuits is continuously reduced, the required processing technology is more and more strict, one of the important requirements is the uniformity problem in the whole range of the workpiece to be processed, and the better the uniformity in the whole range of the workpiece to be processed is, the higher the yield of the product is, and the lower the relative production cost is. The inductively coupled plasma etching is the main etching method in the field of integrated circuits at present, and the structure of a reaction chamber cannot reach complete symmetry due to the requirement of the reaction chamber on functions of chip transmission, air extraction and the like, so that the etching uniformity is reduced due to the asymmetry.

The existing inductively coupled plasma equipment is shown in fig. 1, wherein an upper electrode radio frequency power supply 1 loads power to an outer ring 6 and an inner ring 7 of an inductively coupled coil through a matcher 2 and a current distribution unit 3, process gas enters a reaction chamber 13 through a nozzle 12 installed on a quartz dielectric window 8, meanwhile, radio frequency energy on the inductively coupled coil is coupled into the reaction chamber 13 through the dielectric window 8 to generate plasma 11, the plasma 11 acts on a workpiece 9 to be processed, the workpiece 9 to be processed is placed on an electrostatic chuck 10, a lower electrode radio frequency power supply 5 loads radio frequency energy to a radio frequency copper column located at the bottom of the electrostatic chuck through the matcher 4, so as to provide a radio frequency field, generate radio frequency bias voltage, form an ion acceleration sheath on the surface of the workpiece to be processed to etch the workpiece 9 to be processed, 14 in fig. 1 is a phase-locked cable (cable) with a fixed length, the upper electrode rf power source is usually defined as a main power source (Master), the lower electrode rf power source is defined as an auxiliary power source (Slave), the cable is a fixed length, and a Common EXcitation (CEX) phase-locking angle of the upper and lower electrode rf power sources is a fixed value, so as to lock a phase difference of output rf waveforms of the upper electrode rf power source 1 and the lower electrode rf power source 5.

The current commonly used method for solving the etching uniformity is to adjust the current proportion distribution unit 3 to distribute the power loaded on the outer coil 6 and the inner coil 7 in proportion, thereby realizing the uniformity of the plasma above the workpiece to be processed and further improving the etching rate.

In carrying out the present disclosure, applicants have discovered that the prior art suffers from the following drawbacks:

the method for adjusting the current ratio of the inner ring and the outer ring is limited by the coil structure and the current ratio adjusting unit, the adjustment of the current ratio under partial process gas has little contribution to the uniformity, and meanwhile, the method for adjusting the current ratio of the inner ring and the outer ring has obvious effect on the radial uniformity of the workpiece to be processed and has limited effect on the angular uniformity of the workpiece to be processed.

Disclosure of Invention

In view of the technical problems, the present disclosure provides a plasma etching method to solve the problem that the adjustment effect on the angular distribution of plasma is limited in a manner of adjusting the current ratio of the inner and outer rings.

According to one aspect of the disclosure, a plasma etching method is provided for etching a workpiece to be processed in a reaction chamber, and the plasma etching method comprises at least one etching step, wherein each etching step comprises a step of adjusting a phase difference between an upper electrode radio frequency power supply and a lower electrode radio frequency power supply so as to adjust an angular distribution state of plasma.

In some embodiments of the present disclosure, the step of adjusting the phase difference between the rf power supply for the upper electrode and the rf power supply for the lower electrode includes adjusting a phase angle of an output waveform of the rf power supply for the upper electrode and/or adjusting a phase angle of an output waveform of the rf power supply for the lower electrode.

In some embodiments of the disclosure, the step of adjusting the phase difference between the upper electrode rf power supply and the lower electrode rf power supply includes periodically varying the phase difference between a first angle and a second angle.

In some embodiments of the present disclosure, the phase difference gradually changes from the first angle to the second angle or gradually changes from the first angle to the second angle and then gradually changes from the second angle to the first angle in each change period.

In some embodiments of the present disclosure, the phase difference varies discretely by a predetermined step size in each variation cycle.

In some embodiments of the present disclosure, the predetermined step sizes are all the same.

In some embodiments of the present disclosure, the phase difference is continuously varied in each variation period.

In some embodiments of the present disclosure, the phase difference varies linearly and continuously.

In some embodiments of the present disclosure, the change slopes of the phase difference are the same.

According to the plasma processing method, the CEX phase locking angle of the radio frequency power supply of the upper electrode and the lower electrode is adjusted in the etching process, the plasma distribution above the workpiece to be processed can be fully adjusted, the limitation of the adjustment effect of the current proportion of the inner ring and the outer ring on the angular distribution of the plasma is avoided, the uniform angular distribution of the plasma in the etching time is favorably realized, and the etching uniformity is improved. In the method, the change period and the change rate of the CEX phase-locked angle can be adjusted, so that the defects caused by current proportion adjustment can be compensated to the greatest extent, and the etching uniformity is further optimized.

Drawings

Fig. 1 is a schematic structural diagram of a conventional inductively coupled plasma apparatus.

FIG. 2 is a schematic diagram illustrating the effect of different CEX phase lock angles on etch rate at different locations of the edge of a workpiece to be processed according to the present disclosure.

FIG. 3 is a schematic diagram of an etching process and a corresponding CEX angle setting according to an embodiment of the disclosure.

FIG. 4 is a flow chart of a method of plasma etching according to the embodiment of the disclosure shown in FIG. 3.

FIG. 5 is a schematic diagram of an etching process and a corresponding CEX angle setting according to another embodiment of the present disclosure.

FIG. 6 is a flow chart of a method of plasma etching according to the embodiment of the disclosure shown in FIG. 5.

FIG. 7 is a flow chart of a method for plasma etching according to another embodiment of the present disclosure.

Description of the symbols

1-upper electrode radio frequency power supply; 2, 4-matcher; 3-a current distribution unit; 5-lower electrode radio frequency power supply; 6-outer ring of inductive coupling coil; 7-inner ring of inductive coupling coil; 8-a quartz dielectric window; 9-a workpiece to be processed; 10-an electrostatic chuck; 11-plasma; 12-a nozzle; 13-a reaction chamber; 14-phase locked cable.

Detailed Description

For the purpose of promoting a better understanding of the objects, aspects and advantages of the present disclosure, reference is made to the following detailed description taken in conjunction with the accompanying drawings.

For convenience of description, the rf power source of the upper electrode refers to the rf power source of the upper electrode structure, and the rf power source of the lower electrode refers to the rf power source of the lower electrode structure.

The method adopted by the disclosure is realized based on adjusting the phase difference of the output waveforms of the upper electrode radio frequency power supply and the lower electrode radio frequency power supply, namely the phase-locked angle of the CEX.

The energy coupled into the reaction chamber by the upper electrode radio frequency power supply structure of the inductively coupled plasma equipment can be divided into two parts of capacitive coupling and inductive coupling, wherein about 1/3 is capacitive coupling, 2/3 is inductive coupling, the energy coupled into the reaction chamber by the lower electrode radio frequency power supply is mainly capacitive coupling energy, and the phase difference between the capacitive coupling energy of the upper electrode radio frequency power supply and the capacitive coupling energy of the lower electrode radio frequency power supply can be adjusted by adjusting the CEX phase-locking angle, so that the ion energy and the sheath potential above the workpiece to be processed are influenced, the angular distribution state of the plasma is adjusted, the etching Rate and Map distribution of the workpiece to be processed are further changed, and therefore, the difference of the CEX phase-locking angle can directly influence the process etching Rate (ER, Etch Rate) and Map distribution.

Taking the etching result of the edge circumference of the workpiece to be processed as an example, the 12 o' clock direction of the workpiece to be processed is 0 degree, the points rotating clockwise for one circle respectively correspond to the points of 0-360 degrees of the measurement position in fig. 2, the change conditions of the etching rate of the edge circumference of the workpiece to be processed under different CEX phase-locked angles are listed in the figure, when the CEX phase-locked angles change, the position corresponding to the minimum value of the etching rate deviates along with the change of the CEX phase-locked angles, and the distribution of the etching rate Map is directly influenced. Relative to the position corresponding to the minimum etching rate value when the CEX phase-locked angle is zero, when the CEX phase-locked angle is lambda/8, the position corresponding to the minimum etching rate value is shifted by about 45 degrees, when the CEX phase-locked angle is lambda/4, the position corresponding to the minimum etching rate value is shifted by about 90 degrees, when the CEX phase-locked angle is lambda/2, the position corresponding to the minimum etching rate value is shifted by about 180 degrees, and therefore when the CEX phase-locked angle changes along one wavelength angle, the map of the etching rate is correspondingly rotated and changed by one period.

The method provided by the disclosure is to perform cyclic change of the CEX phase locking angle in the etching process, so that the plasma state in the etching process is continuously changed, and the ion energy above the workpiece to be processed and the potential of the sheath layer are periodically and continuously changed, thereby realizing the improvement of the etching uniformity.

As shown in fig. 3, an embodiment of the present disclosure provides a plasma etching method, which is suitable for the following etching processes. The etching process includes etching step1, etching step2, etching step3, … …, etching step stepN, the etching time of each etching step is T1, T2, T3 … … TN, the CEX phase-locked angle is changed from 0 ° to 360 ° and is defined as a change period, in this embodiment, multiple change periods of the CEX phase-locked angle are realized in each etching step, if the number of the change periods of the CEX phase-locked angle in the etching step1 is a, the change rate of the CEX phase-locked angle is K1 ═ 360a/T1, the number of the change periods of the CEX phase-locked angle in the etching step2 is b, the change rate of the CEX phase-locked angle in the etching step2 is K2 ═ 360b/T2, the number of the change periods of the CEX phase-locked angle in the etching step3 is c, the change rate of the CEX phase-locked angle in the etching step3 is K3 ═ c/T3942, and the number of the change rate of the CEX phase-locked angle in the etching step3 is c/T3, the change rate of the CEX phase-locked angle of the etching step N is KN (360 m/TN), when each etching step is carried out, the CEX phase-locked angle changes the corresponding set change period number, when each etching step is carried out, after the CEX phase-locked angle passes through a change period, the plasma energy above each point on the workpiece to be processed and the sheath layer potential change by a period, and the etching rate of each point in the circumferential direction undergoes a periodic change from the maximum value to the minimum value. Over a plurality of cycles, the average level of the etch rate at each point in the circumferential direction is equivalent over the etch time, thus improving the azimuthal uniformity of the etch rate.

The plasma etching method corresponding to this embodiment is as shown in fig. 4, where an upper electrode rf power supply is set as a main power supply, and a lower electrode rf voltage is set as an auxiliary power supply. After the etching starts, the CEX angle of the upper electrode radio frequency power supply and the lower electrode radio frequency power supply is set to be 0 degrees, the CEX angle of the upper electrode radio frequency power supply is kept unchanged in the subsequent etching process, and the phase difference of the upper electrode radio frequency power supply and the lower electrode radio frequency power supply is changed only by changing the phase angle of the output waveform of the lower electrode radio frequency power supply, namely the CEX angle. After the start of the etch step1, the CEX angle is changed at a rate of 360 a/T1K 1 during a change period, i.e., during the entire etch time T1, to

Sending an instruction to the lower electrode radio frequency power supply at the time interval, sequentially setting the CEX angle of the lower electrode radio frequency power supply to be 0 degrees, 1 degrees, … … 360 degrees, 0 degrees, 1 degrees, … … 360 degrees and … … at each time point respectively until the etching step1 is finished, restoring the CEX angle of the lower electrode radio frequency power supply to be 0 degrees after the etching step1 is finished, continuing to perform the next etching step, and when the etching step stepN is performed, periodically changing the CEX phase-locking angle at the speed of KN 360m/TN, namely, periodically changing the CEX phase-locking angle at the speed of KN 360m/TN

And sending an instruction to the lower electrode radio frequency power supply at the time interval, and enabling the CEX angle of the lower electrode radio frequency power supply to be respectively set to be 0 degrees, 1 degrees, … … 360 degrees, 0 degrees, 1 degrees, … … 360 degrees and … … degrees in sequence, and repeating the steps until the etching step stepN is finished, and recovering the CEX angle of the lower electrode radio frequency power supply to be 0 degrees when the whole etching process is finished.

In this embodiment, the CEX phase-lock angle is changed in steps of 1 ° for each change period. The number of the variation cycles of each etching step is not limited, and can be adjusted according to actual requirements and the conditions of etching results. It will be understood by those skilled in the art that the number of the variation cycles is at least one, but in general, the number of the variation cycles is relatively large for the etching step with longer etching time.

As shown in fig. 5, a difference of the plasma etching method according to another embodiment of the present disclosure from the previous embodiment is that a variation period is defined by a variation of the CEX lock angle from 0 ° to 360 °, and further a variation of 360 ° to 0 °.

When the number of the change cycles of the CEX phase-locked angle in the etching step1 is a, the change rate is K1 ═ 360a/T1 × 2, the number of the change cycles of the CEX phase-locked angle in the etching step2 is b, the change rate of the CEX phase-locked angle in the etching step2 is K2 ═ 360b/T2 × 2, the number of the change cycles of the CEX phase-locked angle in the etching step3 is c, the change rate of the CEX phase-locked angle in the etching step3 is K3 ═ 360c/T3 × 2, the number of the change cycles of the CEX phase-locked angle in the etching step stepN is m, the change rate of the CEX phase-locked angle in the etching step n is KN ═ 360m/TN × 2, and when each etching step is performed, the CEX phase-locked angle changes by the corresponding set number of change cycles, thereby improving the overall uniformity.

As shown in fig. 6, after the etching starts, the CEX angle of the rf power supply for the upper electrode and the CEX angle of the rf power supply for the lower electrode are set to 0 °, the CEX angle of the rf power supply for the upper electrode is kept unchanged during the subsequent etching, and the phase difference between the rf power supplies for the upper electrode and the lower electrode is changed only by changing the CEX angle of the rf power supply for the lower electrode. After the etching step1 started, CEX lock was performed by applying a rate of K1 ═ 360a/T1 × 2Periodic variation of phase angle, i.e. in

Sending an instruction to the lower electrode radio frequency power supply at the time interval, sequentially setting the CEX angle of the lower electrode radio frequency power supply to be 0 degrees, 1 degrees, … … 360 degrees, 359 degrees, 358 degrees, … … 0 degrees and … … degrees respectively until the etching step1 is finished, recovering the CEX angle of the lower electrode radio frequency power supply to be 0 degrees after the etching step1 is finished, continuing to perform the next etching step, and when the etching step stepN is performed, periodically changing the CEX phase-locking angle at the rate of KN (360 m/TN) 2, namely, periodically changing the CEX phase-locking angle at the rate of KN (360 m/TN) 2

The CEX angle of the lower electrode radio frequency power supply is respectively set to be 0 degrees, 1 degrees, … … 360 degrees, 359 degrees, 358 degrees, … … 0 degrees and … … degrees in sequence, and the CEX angle of the lower electrode radio frequency power supply is recovered to be 0 degrees after the etching step stepN is finished and the whole etching process is finished.

The plasma etching method according to another embodiment of the present disclosure, as shown in fig. 7, is different from the above embodiment in that the present embodiment is not limited to the step change by 1 °. After the start of the etch step1, the CEX phase lock angle is periodically varied by changing the phase lock angle at a rate of K1 ═ 360a/T1, i.e., at a rate of zero-delta

Sending an instruction to the lower electrode radio frequency power supply at a time interval, sequentially setting the CEX angle of the lower electrode radio frequency power supply to be a cycle of 0 degrees, q degrees, 2 xq degrees, … … 360 degrees, 0 degrees, q degrees, 2 xq degrees, … … 360 degrees and … … degrees (at this time, q is a submultiple of 360 degrees, namely, 360 degrees is an integral multiple of q), until the etching step1 is finished, restoring the CEX angle of the lower electrode radio frequency power supply to 0 degrees after the etching step is finished, continuing to perform the next etching step, and when the etching step stepN is performed, similarly, setting KN to a speed of 360m/TN to perform etching on the CEX angle of the lower electrode radio frequency power supplyWith periodic variation of the CEX angle, i.e. with

The CEX angle of the lower electrode radio frequency power supply is respectively set to be 0 degrees, q degrees, 2 xq degrees … … 360 degrees, 0 degrees, q degrees, 2 xq degrees … … 360 degrees and … … cycles (at this time, q is a submultiple of 360 degrees, namely 360 is an integral multiple of q), until the etching step stepN is finished, and when the whole etching process is finished, the CEX angle of the lower electrode radio frequency power supply is recovered to be 0 degrees. That is, for this embodiment, the change in CEX during etching is not limited to being performed in steps of 1 °, and may be increased by any angle value q, e.g., 5 °, 10 °, etc., according to the time interval.

The plasma etching method according to still another embodiment of the present disclosure is different from the above embodiments in that, in each variation period, the CEX lock angle is continuously varied, and the CEX lock angle is continuously varied from the first angle to the second angle, or continuously varied from the first angle to the second angle and then continuously varied from the second angle to the first angle, which is defined as a variation period.

During the etching process, if an etching step1, an etching step2, an etching step3 and an etching step … … are adopted, the etching time of each etching step is T1, T2 and T3 … … TN respectively, for any etching step, a plurality of change cycles can be included, the CEX phase-locked angle is changed from a first angle to a second angle or from the first angle to the second angle in each change cycle, and then from the second angle to the first angle, and the CEX phase-locked angle change slopes of each change cycle in the same etching step can be different. For any change period, the CEX phase-locked angle is continuously changed from the first angle to the second angle with a change slope or from the first angle to the second angle with a change slope and then continuously changed from the second angle to the first angle with a change slope, that is, the change mode of the CEX phase-locked angle in the etching process can also be expanded to continuously change along a certain slope, that is, the CEX phase-locked angle is linearly and continuously changed.

In this embodiment, the change slopes of the CEX lock phase angle in each change period of the same etching step may also be the same, and in this case, the change slopes of the CEX angle in each etching step may be the same or different. The first angle is preferably 0 deg., and the second angle is preferably 360 deg. to improve etch uniformity.

The plasma etching method according to another embodiment of the present disclosure is different from the above embodiments in that the upper electrode rf power source is set as an auxiliary power source, and the lower electrode rf power source is set as a main power source. In this embodiment, after the etching starts, the CEX angle of the lower electrode rf power supply is set to 0 °, the CEX angle of the lower electrode rf power supply is kept unchanged in the subsequent etching process, and the change of the phase difference between the upper and lower electrode rf power supplies is realized only by changing the CEX angle of the upper electrode rf power supply.

The plasma etching method of another embodiment of the present disclosure is different from the above embodiments in that the rf settings of the upper electrode and the lower electrode in this embodiment are not primary and secondary, after the etching starts, the CEX angle of the rf power of the upper electrode and the CEX angle of the rf power of the lower electrode can be set to 0 ° at the same time, and the phase difference between the rf power of the upper electrode and the rf power of the lower electrode can be changed at the same time during the subsequent etching process.

Up to this point, the present embodiment has been described in detail with reference to the accompanying drawings. From the above description, those skilled in the art should clearly recognize that the plasma control method of the present disclosure is applicable.

The present disclosure is applicable not only to inductively coupled plasma apparatuses but also to capacitively coupled plasma apparatuses, microwave plasma apparatuses, ECR plasma apparatuses.

The above-mentioned embodiments are intended to illustrate the objects, aspects and advantages of the present disclosure in further detail, and it should be understood that the above-mentioned embodiments are only illustrative of the present disclosure and are not intended to limit the present disclosure, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present disclosure should be included in the scope of the present disclosure.

It should also be noted that directional terms, such as "upper", "lower", "front", "rear", "left", "right", and the like, used in the embodiments are only directions referring to the drawings, and are not intended to limit the scope of the present disclosure. Throughout the drawings, like elements are represented by like or similar reference numerals. Conventional structures or constructions will be omitted when they may obscure the understanding of the present disclosure.

Unless otherwise indicated, the numerical parameters set forth in the specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by the present disclosure. In particular, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about". Generally, the expression is meant to encompass variations of ± 10% in some embodiments, 5% in some embodiments, 1% in some embodiments, 0.5% in some embodiments by the specified amount.

Furthermore, the word "comprising" does not exclude the presence of elements or steps not listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

The use of ordinal numbers such as "first," "second," "third," etc., in the specification and claims to modify a corresponding element is not itself intended to imply any ordinal numbers for the element, nor the order in which an element is sequenced or methods of manufacture, but are used to distinguish one element having a certain name from another element having a same name, but rather, to distinguish one element having a certain name from another element having a same name.

Similarly, it should be appreciated that in the foregoing description of exemplary embodiments of the disclosure, various features of the disclosure are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various disclosed aspects. However, the disclosed method should not be interpreted as reflecting an intention that: that is, the claimed disclosure requires more features than are expressly recited in each claim. Rather, as the following claims reflect, disclosed aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this disclosure.

Claims

1. A plasma etching method is used for etching a workpiece to be processed in a reaction chamber and comprises at least one etching step, wherein each etching step comprises the step of continuously adjusting the phase difference between an upper electrode radio frequency power supply and a lower electrode radio frequency power supply according to a preset number of change cycles so as to adjust the angular distribution state of plasma;

wherein the step of adjusting the phase difference between the upper electrode RF power supply and the lower electrode RF power supply comprises periodically varying the phase difference between zero degrees and 360 degrees; in each etching step, the variation rate of the phase difference is equal to 360 × the number of variation cycles/etching time of each etching step, or the variation rate of the phase difference is equal to 360 × the number of variation cycles/etching time of each etching step × 2.

2. The plasma etching method of claim 1, wherein the step of adjusting the phase difference between the rf power supply for the upper electrode and the rf power supply for the lower electrode comprises adjusting a phase angle of an output waveform of the rf power supply for the upper electrode and/or adjusting a phase angle of an output waveform of the rf power supply for the lower electrode.

3. A plasma etching method according to claim 1, wherein the phase difference is gradually changed from the first angle to the second angle or from the first angle to the second angle and then from the second angle to the first angle in each change period;

when the angle is gradually changed from the first angle to the second angle, the change rate of the phase difference is equal to 360 multiplied by the number of change cycles/etching time of each etching step;

when the phase difference is gradually changed from the first angle to the second angle and then from the second angle to the first angle, the change rate of the phase difference is equal to 360 times the number of change cycles/etching time of each etching step x 2.

4. A plasma etching method according to claim 3, wherein the phase difference is varied discretely in predetermined steps in each variation period.

5. The plasma etching method of claim 4, the predetermined steps all being the same.

6. A plasma etching method according to claim 3, wherein the phase difference is continuously changed in each change period.

7. The plasma etching method of claim 6, wherein the phase difference varies linearly and continuously.