Plasma etching of silicon using fluorinated gas mixtures

Details Plasma etching of silicon using fluorinated gas mixtures Plasma etching of silicon using fluorinated gas mixtures

1999-02-23

2001-05-22

Gulakowski, Randy (Department: 1746)

Etching a substrate: processes

Gas phase etching of substrate

Application of energy to the gaseous etchant or to the...

C216S079000, C438S714000, C438S719000, C252S079100

Reexamination Certificate

active

06235214

ABSTRACT:

BACKGROUND OF THE DISCLOSURE
1. Field of the Invention
The invention relates to a method of dry etching of semiconductor wafers and, more particularly, to a method of etching silicon using gas mixtures comprising fluorine (F) and oxygen (O).
2. Description of the Background Art
Trenches formed in semiconductor substrates have many uses in producing integrated circuits including isolation, capacitor formation, transistor formation, and the like. One important use of trenches is in the formation of gate structures for field effect transistors. In a conventional gate structure, trench walls are formed between a source region and a drain region. The walls and bottom of the trench are coated with a thin dielectric material, which is then conformally coated with polysilicon such that the polysilicon forms a gate electrode for a transistor.
Traditionally, gate trenches are formed using an anisotropic chemical or reactive ion etching of a masked silicon substrate. Etching chemistries utilize combinations of such chemicals as hydrogen bromide (HBr), chlorine (Cl
2
), oxygen (O
2
), nitrogen fluoride (NF
3
), sulfur hexafluoride(SF
6
), and nitrogen (N
2
). For example, an HBr/Cl
2
) chemistry can provide a silicon etch rate of about 5000 Å/min. with a photoresist selectivity (defined as the ratio of the etch rate of silicon to that of photoresist) of between 3:1 to 4:1. To improve the throughput for wafer processing, it is desirable to maximize the silicon etch rate, especially for applications such as trench etching. In general, however, an increase in the silicon etch rate also decreases the photoresist etch selectivity.
Therefore, a need exists in the art for a silicon etching process having an increased silicon etch rate and an enhanced mask selectivity.
SUMMARY OF THE INVENTION
The present invention solves the above problem by providing an etch process with an increased silicon etch rate while enhancing photoresist selectivity. In particular, the invention is a method of etching a silicon substrate using a gas (or gas mixture) comprising fluorine (F) and oxygen (O). Anisotropic etching of silicon trenches can be accomplished at a total pressure of greater than 100 mtorr, at an etch rate exceeding about 1 &mgr;m/min. with an etch uniformity of about ±5%. A photoresist mask selectivity as high as about 9:1 can be achieved.
The invention can be practiced in a M×P etch chamber from Applied Materials, Inc., using a gas comprising, for example, SF
6
at about 40-60 sccm, O
2
at about 40-60 sccm and CHF
3
up to about 50 sccm, at a total pressure of about 100-400 mtorr and a cathode power of about 150-500 W. Silicon trench etching can be accomplished in either a single-step using a mixture of SF
6
/O
2
/CHF
3
, or in two separate steps using first, a mixture of SF
6
/O
2
/CHF
3
, followed by a mixture of SF
6
/O
2
. By adjusting the gas composition, operating pressure and power in individual steps, the trench profile and dimension can be tailored to specific needs.
The present invention can be adapted for etching other forms of silicon, such as doped or undoped polysilicon and amorphous silicon, and may also be used with either photoresist mask or hardmask materials.


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