# US 12,217,972 B2 · Multi-state pulsing for achieving a balance between bow control and mask selectivity

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- Number: US 12,217,972 B2
- Document ID: US12217972B2
- Status: Granted
- Kind: B2
- Application number: 17/779,520
- Filed: 2020-12-03
- Published: 2023-01-05
- Granted: 2025-02-04
- Earliest claimed: 2019-12-13
- Assignees: Lam Research Corporation
- Applicants: Lam Research Corporation
- Inventors: Nikhil Dole; Merrett Tinlok Wong; Eric Hudson; Sangheon Lee; Xiaoqiang Yao
- Web page: https://patentgrep.com/patent/US12217972B2

## CPC

- H10P 50/73: {using masks for insulating materials}
- H01J 37/32146: {Amplitude modulation, includes pulsing}
- H01J 37/32165: {Plural frequencies}
- H01J 37/32183: {Matching circuits}
- H10P 50/242: {of Group IV materials}
- H10P 50/283: {by chemical means}
- H01J 37/32174: {Circuits specially adapted for controlling the RF discharge}
- H01J 2237/334: Etching
- H01J 2237/3346: Selectivity
- H10P: GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
- H01J: ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS (spark-gaps H01T; electric arc lamps H05B31/00; particle accelerators H05H)

## Abstract

A method for multi-state pulsing to achieve a balance between bow control and mask selectivity is described. The method includes generating a primary radio frequency (RF) signal. The primary RF signal pulses among three states including a first state, a second state, and a third state. The method further includes generating a secondary RF signal. The secondary RF signal pulses among the three states. During the first state, the primary RF signal has a power level that is greater than a power level of the secondary RF signal. Also, during the second state, the secondary RF signal has a power level that is greater than a power level of the primary RF signal. During the third state, power levels of the primary and secondary RF signals are approximately equal.

## Claims

### Claim 1

A method for multi-state pulsing to achieve a balance between bow control and mask selectivity, comprising:
generating a primary radio frequency (RF) signal, wherein the primary RF signal pulses among three states including a first state, a second state, and a third state;
generating a secondary RF signal, wherein the secondary RF signal pulses among the three states,
wherein during the first state, the primary RF signal has a power level that is greater than a power level of the secondary RF signal;
wherein during the second state, the secondary RF signal has a power level that is greater than a power level of the primary RF signal,
wherein during the third state, power levels of the primary and secondary RF signals are within a pre-determined range.

### Claim 2 (depends on 1)

The method of claim 1, wherein a duty cycle of the first state is less than a duty cycle of the third state, wherein a duty cycle of the second state is less than the duty cycle of the third state.

### Claim 3 (depends on 2)

The method of claim 2, wherein the duty cycle of the first state ranges between three percent and twenty-five percent of a clock cycle of a clock signal.

### Claim 4 (depends on 3)

The method of claim 3, wherein the duty cycle of the second state ranges between three percent and fifty percent of the clock cycle of the clock signal.

### Claim 5 (depends on 4)

The method of claim 4, wherein the duty cycle of the third state ranges between twenty five percent and ninety four percent of the clock cycle of the clock signal, wherein a sum of the duty cycles of the first, second, and third states is equal to one-hundred percent of the clock cycle.

### Claim 6 (depends on 2)

The method of claim 2, wherein the power level of the primary RF signal during the first state, the power level of the secondary RF signal during the second state, the duty cycle of the first state, and the duty cycle of the second state facilitate achieving the balance between bow control and the mask selectivity.

### Claim 7 (depends on 1)

The method of claim 1, further comprising:
supplying the primary RF signal to an impedance matching network, wherein the impedance matching network is coupled to an electrode of a plasma chamber;
supplying the secondary RF signal to the impedance matching network.

### Claim 8 (depends on 1)

The method of claim 1, wherein the power level of the primary RF signal during the first state is greater than the power level of the secondary RF signal during the first state by at least six times and at most ten times.

### Claim 9 (depends on 1)

The method of claim 1, wherein the power level of the primary RF signal during the second state is at least twenty percent and at most less than one hundred percent of the power level of the secondary RF signal during the second state.

### Claim 10 (depends on 1)

The method of claim 1, wherein the power levels of the primary and secondary RF signals during the third state are zero.

### Claim 11 (depends on 1)

The method of claim 1, wherein the primary RF signal pulses from the power level of the first state to the power level of the second state, pulses from the power level of the second state to the power level of the third state, and pulses from the power level of the third state to the power level of the first state.

### Claim 12 (depends on 1)

The method of claim 1, wherein the first RF signal pulses among the three power levels in synchronization with the three states of a digital pulsed signal.

### Claim 13

A method for etching a stack below a mask in a plasma processing chamber, comprising:
flowing an etch gas comprising a metal fluoride or a tungsten-containing passivant and an etch component into the plasma processing chamber; and
transforming the etch gas into a plasma, comprising:
generating a primary radio frequency (RF) signal at a first frequency range, wherein the primary RF signal pulses among at least three states including a first state, a second state, and a third state; and
generating a secondary RF signal at a second frequency range, wherein the secondary RF signal pulses among the at least three states and wherein the first frequency range is less than the second frequency range;
wherein during the second state, the primary RF signal has a power level that is less than 80% of a power level of the primary RF signal during the first state;
wherein during the third state, the primary RF signal has a power level that is less than 20% of the power level of the primary RF signal during the second state; and
wherein during the third state, a power level of the secondary RF signal is less than 20% of a power level of the secondary RF signal during the second state.

### Claim 14 (depends on 13)

The method of claim 13, wherein a duty cycle of the first state is less than a duty cycle of the third state, wherein a duty cycle of the second state is less than the duty cycle of the third state.

### Claim 15 (depends on 13)

The method of claim 13, wherein the duty cycle of the first state ranges between three percent and twenty-five percent of a clock cycle of a clock signal.

### Claim 16 (depends on 15)

The method of claim 15, wherein the duty cycle of the second state ranges between three percent and fifty percent of the clock cycle of the clock signal.

### Claim 17 (depends on 16)

The method of claim 16, wherein the duty cycle of the third state ranges between twenty-five percent and ninety-four percent of the clock cycle of the clock signal, wherein a sum of the duty cycles of the first, second, and third states is equal to one-hundred percent of the clock cycle.

### Claim 18 (depends on 13)

The method of claim 13, wherein the first frequency range is between 80 kHz and 14 MHz, inclusive, and wherein the second frequency range is between 15 MHz and 120 MHz, inclusive.

### Claim 19 (depends on 13)

The method of claim 13, wherein the metal fluoride or the tungsten-containing passivant is tungsten fluoride.

### Claim 20 (depends on 13)

The method of claim 13, wherein the metal fluoride or the tungsten-containing passivant is tungsten hexafluoride.

### Claim 21 (depends on 13)

The method of claim 13, wherein the stack comprises silicon.

### Claim 22 (depends on 21)

The method of claim 21, wherein the mask is a hardmask.

### Claim 23 (depends on 22)

The method of claim 22, wherein the hardmask comprises polysilicon.

### Claim 24 (depends on 23)

The method of claim 23, wherein the stack comprises at least one silicon oxide containing layer.

### Claim 25 (depends on 13)

The method, as recited in claim 13, wherein a ratio of the power level of the primary RF signal during the first state to the power level of the secondary RF signal during the first state is greater than 1, and a ratio of the power level of the primary RF signal during the second state to the power level of the secondary RF signal during the second state is less than 1.

### Claim 26 (depends on 13)

The method, as recited in claim 13, wherein when the primary RF signal is pulsed among the three states and the secondary RF signal is pulsed among the three states, a multi-state pulsing scheme is applied, wherein the multi-state pulsing scheme is tuned to minimize necking and bowing with the metal fluoride or the tungsten-containing passivant.