KR100596882B1 - Method for forming polysilicon gate - Google Patents

Abstract

The present invention relates to a polysilicon gate formation method, and more particularly, to a polysilicon gate formation method of forming a gate by etching a polysilicon film in a simplified process while having a high selectivity and a good profile.

According to an aspect of the present invention, there is provided a method of forming a polysilicon gate by etching a polysilicon layer on a gate oxide layer, the method comprising: an initial etching step of removing a portion of an upper surface of the polysilicon layer; Stock angle step by the mixed gas of hydrogen bromide, chlorine, nitrogen and oxygen; And an overetching step with a mixed gas of hydrogen bromide, chlorine, nitrogen, and oxygen.

Therefore, the polysilicon gate forming method of the present invention has a high selectivity, but the process is simplified, and since there is no stabilization step, particles are not generated, thereby reducing defects.

Polysilicon Gate Etch, Equity Angle, Simplify Process

Description

Method for forming polysilicon gate             

1 is a flow chart of a polysilicon gate formation method according to the prior art.

2 is a flowchart of a polysilicon gate forming method according to the present invention;

Figure 3 (a) is a cross-sectional photograph of a polysilicon gate formed by the prior art.

Figure 3 (b) is a cross-sectional photograph of a polysilicon gate formed by the present invention.

The present invention relates to a polysilicon gate formation method, and more particularly, to a polysilicon gate formation method of forming a gate by etching a polysilicon film in a simplified process while having a high selectivity and a good profile.

As the degree of integration of semiconductor devices improves, chip sizes and circuit line widths become smaller and gate oxide films become thinner. Accordingly, it is increasingly difficult to obtain a polysilicon gate having a good profile even in a thin gate oxide film.

Hereinafter, a flowchart of a polysilicon gate forming method according to the related art will be described with reference to FIG. 1.

In order to form a polysilicon gate of a predetermined type, an isolation layer is first formed and a gate oxide layer is formed to electrically isolate the semiconductor substrate. Thereafter, polysilicon (gate) is deposited to a predetermined thickness (S101), and then a photoresist is applied and patterned.

The substrate is coated with the photoresist as described above is loaded into the chamber of the etching apparatus to perform an initial etching step of etching a portion of the upper surface of the polysilicon film (S102).

Next, a first stock angle step S103 and a second stock angle step S104 for main etching the polysilicon film by injecting a predetermined etching gas are performed. The reason why the stock step is separated and performed secondly is because the thickness of the gate oxide film is gradually thinned, so that a high selectivity with the polysilicon film is required.

The selectivity ratio is a ratio of the etching rate of the polysilicon film to the etching rate of the gate oxide film, and the higher the integration, the larger the selectivity value, and the larger the value, the greater the overetch.

The etching gas mainly used in the first and second stock angles is a mixed gas of hydrogen bromide (HBr), chlorine (Cl ₂ ) and oxygen (O ₂ ).

Next, after the stock etching, the first overetching step S105 and the second overetching step 106 are performed. The first overetching step is mainly performed using a mixed gas of hydrogen bromide, nitrogen (N ₂ ) and oxygen, and the second overetching step is mainly performed using a mixed gas of hydrogen bromide and oxygen.

As described above, the conventional polysilicon gate forming method is divided into various stock angles and over-etching stages in consideration of the selection ratio between the polysilicon and the gate oxide film as the gate oxide film becomes thinner. However, since the polysilicon etching step is composed of several steps as described above, there is a problem that a good profile is not obtained by forming a layer when the polysilicon is etched.

In addition, between each etching step, a stabilization step for changing the etching conditions is added. In other words, it is necessary to wait until the process condition of the next etching step is reached while the power is turned off. In this case, defects such as a pattern short may occur due to particles falling on the substrate and preventing the etching.

In order to solve this problem, it is necessary to perform the stock angle and the over etching in one etching step under the condition that the selectivity of the polysilicon and the gate oxide layer is 30: 1 or more.

Accordingly, the present invention is to solve the problems of the prior art as described above, polysilicon gate formation having a simple etching process consisting of one step of stock angle step and over etching step while having high selectivity and good gate profile It is an object of the present invention to provide a method.

According to an aspect of the present invention, there is provided a method of forming a polysilicon gate by etching a polysilicon layer on a gate oxide layer, the method comprising: an initial etching step of removing a portion of an upper surface of the polysilicon layer; Stock angle step by the mixed gas of hydrogen bromide, chlorine, nitrogen and oxygen; And an overetching step with a mixed gas of hydrogen bromide, chlorine, nitrogen, and oxygen.

Details of the above object and technical configuration of the present invention and the effects thereof according to the present invention will be more clearly understood by the following detailed description with reference to the drawings showing preferred embodiments of the present invention.

2 is a flowchart of a polysilicon gate forming method according to the present invention. As shown in FIG. 2, the etching of the polysilicon film according to the present invention includes three steps of an initial etching step (S202), a stock engraving step (S203), and an overetching step (S204).

Before proceeding to the initial etching step (S202), a device isolation film such as shallow trench isolation (STI), a polysilicon film to be used as a gate oxide film and a gate electrode for electrical isolation from the semiconductor substrate is deposited (S201). Thereafter, a photoresist is applied on the polysilicon film, and exposed and developed to pattern the photoresist.

The gate oxide film is preferably a silicon oxide film by a thermal oxidation process, and the polysilicon film is preferably formed through a chemical vapor deposition method such as low pressure chemical vapor deposition (LPCVD).

Next, the semiconductor substrate including the gate oxide film, the polysilicon film, and the patterned photoresist is loaded into the etching chamber of the etching apparatus, and then an initial etching step S202 is performed. The initial etching step is to remove a part of the upper surface of the polysilicon film, it is preferable to use carbon tetrafluoride (CF ₄ ) to reduce the polymer generated by the reaction with the photoresist.

As a specific example, initial etching was performed for 10 seconds at a pressure of 4 mTorr, a source power of 500 W, a bias power of 40 W, and a carbon tetrafluoride flow rate of 50 sccm.

Next, the stock silicon step (S203) may be performed to etch the polysilicon film to substantially form a polysilicon gate pattern.

The stock angle step (S203) is to perform the etching using a mixed gas of hydrogen bromide, chlorine, nitrogen and oxygen. The flow rate of the mixed gas is preferably 120 to 170 sccm for hydrogen bromide, 20 to 70 sccm for chlorine, 1 to 10 sccm for nitrogen, and 0.5 to 5 sccm for oxygen.

In addition to the flow conditions of the mixed gas as described above, the chamber pressure is 8 to 15 mTorr, source power is 550 to 650W, it is preferable to use the process conditions of 60 to 100W.

As a specific example, a chamber pressure of 9 mTorr, a source power of 570 W, a bias power of 70 W, a hydrogen bromide flow rate of 150 sccm, a chlorine flow rate of 30 sccm, a nitrogen flow rate of 9 sccm, and an oxygen flow rate of 3 sccm were used.

After the stock angle step S203, an overetch step S204 of over-etching the polysilicon film is performed. The over-etching step (S204) is to perform the etching using a mixed gas of hydrogen bromide, chlorine, nitrogen and oxygen. Moreover, it is preferable to set chamber pressure high and bias power large compared with stock each step.

As a specific example, a chamber pressure of 50 mTorr, a source power of 570 W, a bias power of 100 W, a hydrogen bromide flow rate of 150 sccm, a chlorine flow rate of 30 sccm, a nitrogen flow rate of 9 sccm, and an oxygen flow rate of 3 sccm were used.

Cross-sectional photographs of the polysilicon gates formed by the prior art and cross-sectional photographs of the polysilicon gates formed by the etching method of the present invention are shown in FIGS. 3 (a) and 3 (b), respectively. As shown in FIG. 3, the present invention can form a polysilicon gate having an excellent profile by simplifying an etching process.

As described above, various experiments have been conducted to obtain a simplified etching process including an initial etching step, a stock etching step, and an overetching step, which will be described below.

Table 1 is a table for briefly showing the process conditions and Table 2 is a table showing the experimental results of the etching process of the polysilicon film tested under various process conditions.

Pr (mTorr) Pw (W) H / C N / O □ 39 150 160/20 10/2 ○ 26 100 150/30 9/3 ◇ 13 50 130/50 7/5

Pr Pw H / C N / O Properties ER _P ER _OX Selectivity T / B One □ □ □ □ 1131 39 29 0.80 2 □ □ ◇ ◇ 1426 24 59 0.95 3 □ ◇ □ ◇ 780 8 92 0.91 4 □ ◇ ◇ □ 909 11 85 1.10 5 ◇ □ □ ◇ 2025 59 34 0.80 6 ◇ □ ◇ □ 2055 212 10 0.82 7 ◇ ◇ □ □ 1300 27 48 1.12 8 ◇ ◇ ◇ ◇ 1749 36 48 1.39 Baseline ○ ○ ○ ○ 1231 25 49 1.00

In Table 1 and Table 2, Pr is chamber pressure, Pw is bias power, H / C is hydrogen bromide flow / chlorine flow, N / O is nitrogen flow / oxygen flow, ER _P is poly The etching rate of silicon, ER _OX is the etching rate of the gate oxide, T / B is the ratio of the top and bottom length of the gate.

Based on the above results, it was found that the bias power and the chamber pressure were the most influential factors in the selection ratio. This results in polysilicon when the process conditions for each stock stage are 9mTorr chamber pressure, 570W source power, 70W bias power, 150sccm hydrogen bromide flow, 30sccm chlorine flow, 9sccm nitrogen flow, and 3sccm oxygen flow. The etch rates of the and gate oxides were 1561 and 34 Å / min, respectively, indicating a selectivity of about 46.

That is, using the conditions as described above, it is possible to etch the polysilicon formed on the gate oxide film of 40 占 Å or less by using only one stock angle step.

Although the present invention has been shown and described with reference to preferred embodiments as described above, it is not limited to the above-described embodiments and those skilled in the art without departing from the spirit of the present invention. Various changes and modifications will be possible.

Therefore, the polysilicon gate forming method of the present invention uses a mixed gas of hydrogen bromide, chlorine, nitrogen, and oxygen, and adjusts process conditions such as chamber pressure and bias power to provide a simple process with high selectivity and good gate profile. The polysilicon layer may be etched to form a gate.

In addition, since there is no stabilization step during etching of the polysilicon film, particles do not occur, thereby reducing the defects.

Claims (6)

In the method of forming a polysilicon gate by etching a polysilicon film present on the gate oxide film, An initial etching step of removing a part of the upper surface of the polysilicon film; Stapling each polysilicon film with a mixed gas of hydrogen bromide, chlorine, nitrogen, and oxygen; And Overetching of the remaining film of the polysilicon film by a mixed gas of hydrogen bromide, chlorine, nitrogen and oxygen Polysilicon gate forming method comprising a. The method of claim 1, The initial etching step is a polysilicon gate forming method characterized in that using the carbon tetrafluoride (CF ₄ ) gas. The method of claim 1, The stock angle step is a method of forming a polysilicon gate, characterized in that is carried out while applying a source power of 550 to 650W and a bias power of 60 to 100W. The method of claim 1, Wherein each stock step is polysilicon gate forming method characterized in that carried out in a pressure range of 8 to 15mTorr. The method of claim 1, The stock each step is a polysilicon gate forming method characterized in that the flow rate of hydrogen bromide, chlorine, nitrogen and oxygen gas is performed in the range of 20 to 70 sccm, 120 to 170 sccm, 1 to 10 sccm and 0.5 to 5 sccm, respectively. The method of claim 1, And the bias power and the chamber pressure of the over-etching step are respectively greater than the bias power and the chamber pressure of the stock-etching step, respectively.

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