METHOD FOR MAKING A HIGH ASPECT RATIO TRENCH

1 . A method, comprising:

providing a semiconductor substrate having an upper surface; and

forming a first trench extending into the semiconductor substrate from the upper surface;

wherein forming the first trench comprises:

in a first etch phase, performing a plurality of repeated alternating etching and deposition cycles to open a first portion of the first trench in the semiconductor substrate, said first portion of the first trench having a first depth; and

in a second etch phase, subsequent to the first etch phase, performing a reactive ion etch to open a second portion of the first trench, extending from a bottom of the first portion of the first trench, in the semiconductor substrate, said second portion of the first trench having a second depth.

2 . The method of claim 1 , further comprising:

lining sidewalls and a bottom of the first trench with an insulating layer; and

then filling the first trench with a conductive material.

3 . The method of claim 1 , wherein the repeated alternating etching and deposition cycles of the first etch phase are part of one of a Bosch etching process or a rapid alternating parameters (RAP) etching process for trench formation.

4 . The method of claim 1 , wherein performing the reactive ion etch comprises:

supplying a noble gas in a gas mixture for the reactive ion etch; and

applying a negative bias voltage to the semiconductor substrate during the reactive ion etch.

5 . The method of claim 4 , wherein the noble gas is Ar.

6 . The method of claim 4 , wherein the negative bias voltage is in a range of 200-400 Volts.

7 . The method of claim 4 , wherein the gas mixture comprises a mixture of SF 6 , O 2 and Ar.

8 . The method of claim 7 , wherein the gas mixture comprises 35-55% SF 6 , 25-40% O 2 and 15-30% Ar.

9 . The method of claim 4 , wherein performing the reactive ion etch comprises an initial phase including flowing the gas mixture that includes CHF 3 , O 2 and Ar but where no plasma power is applied.

10 . The method of claim 9 , further comprising applying a 0 Volts bias voltage to the semiconductor substrate during the initial phase.

11 . The method of claim 1 , wherein the first trench has an aspect ratio of at least 10:1.

12 . The method of claim 1 , further comprising forming a second trench, separate from the first trench, extending into the semiconductor substrate from the upper surface.

13 . The method of claim 12 , forming the second trench comprises:

in a respective first etch phase, performing a plurality of repeated alternating etching and deposition cycles to open a first portion of the second trench in the semiconductor substrate, said first portion of the second trench having a respective first depth; and

in a respective second etch phase, subsequent to the respective first etch phase, performing a reactive ion etch to open a second portion of the second trench, extending from a bottom of the first portion of the second trench, in the semiconductor substrate, said second portion of the second trench having a respective second depth.

14 . The method of claim 13 , wherein first etch phase and the respective first etch phase are simultaneously performed, and wherein the second etch phase and the respective second etch phase are simultaneously performed.

15 . The method of claim 12 , wherein an overall depth of the first trench is smaller than an overall depth of the second trench.

16 . A manufacturing method of an electronic device comprising a semiconductor substrate having an upper surface and a first trench and second trench extending into the semiconductor substrate from the upper surface, wherein the second trench has a second depth in the semiconductor substrate greater than a first depth of the first trench in the semiconductor substrate, wherein the method comprises:

providing the semiconductor substrate;

in a first etch phase, performing a plurality of repeated alternating etching and deposition cycles to open a respective first portion of each of the first and second trenches, said respective first portion having a respective first depth;

in a second etch phase, subsequent to the first etch phase, performing a reactive ion etch to open a respective second portion of each of the first and second trenches, extending from a bottom of the respective first portion, said respective second portion having a respective second depth;

lining sidewalls and a bottom of each of the first and second trenches with an insulating layer;

removing the insulating layer from the bottom of the second trench, while leaving the insulating layer in place on the bottom of the first trench; and

then, filling each of the first and second trenches with a conductive material.

17 . The method of claim 16 , wherein, in the first etch phase, the respective first portions of the first and second trenches are formed at the same time, and wherein, in the second etch phase, the respective second portions of the first and second trenches are formed at the same time.

18 . The method of claim 16 , wherein the repeated alternating etching and deposition cycles of the first etch phase are part of one of a Bosch etching process or a rapid alternating parameters (RAP) etching process.

19 . The method of claim 16 , wherein performing the reactive ion etch comprises:

supplying a noble gas in a gas mixture for the reactive ion etch; and

applying a negative bias voltage to the semiconductor substrate during the reactive ion etch.

20 . The method of claim 20 , wherein the negative bias voltage is in a range of 200-400 Volts, and the gas mixture comprises 35-55% SF 6 , 25-40% O 2 and 15-30% Ar.