Method for forming opening in a semiconductor device

[0002] 1. Field of Invention

[0003] The present invention relates to a method for forming a semiconductor device. More particularly, the present invention relates to a method for forming an opening in a semiconductor device.

[0004] 2. Description of Related Art

[0005] The conventional method for forming an opening in a semiconductor device includes the following steps. A photoresist layer is formed on a material layer. Then, the photoresist layer is patterned by the photolithographic process. An etching process is performed to form an opening in the material layer with the patterned photoresist layer.

[0006] As the shrinkage in the size of the semiconductor device, the control of critical dimension (CD) in the photolithographic process is the bottleneck in the process due to the limitation of light resolution and depth of focus (DOF). This bottleneck in the photolithographic process limits the formation of a small-size opening. Even with some advance technology such as phase shift mask (PSM), it is still difficult to form a small-size opening.

[0007] The invention provides a method for forming an opening in a semiconductor device to form a small-size opening.

[0008] As embodied and broadly described herein, the invention provides a method for forming an opening in a semiconductor device. A silicon-oxy-nitride layer is formed on a dielectric layer, and then a photoresist layer with a first opening is formed on the silicon-oxy-nitride layer. A polymer film is formed on sidewalls of the first opening. A second opening narrower than the first opening is formed in the dielectric layer with the photoresist layer and the polymer film as a mask.

[0009] In accordance with the aspect of this invention, a method for forming an opening in a semiconductor device is provided. A silicon-oxy-nitride layer is formed on a dielectric layer and then a photoresist layer with a first opening is formed on the silicon-oxy-nitride layer. By utilizing a gas etchant including C₄F₈, CO, Ar and O₂, a polymer film is formed on sidewalls of the first opening. Next, a second opening is formed in the dielectric layer by using the photoresist layer and the polymer film as a mask; the second opening is narrower than the first opening.

[0010] In this invention, the silicon-oxy-nitride layer is formed on the dielectric layer to be a stop layer; thus, the polymer film can be formed on the sidewalls of the first opening. The second opening is formed by using the photoresist layer and the polymer film as a mask. So that the second opening is narrower than the first opening. A small-size opening is obtained.

[0011] It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.

[0012] The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings,

[0013] FIGS. 1A, 1B and 1C are schematic, cross-sectional views of a method according to this invention of forming an opening in a semiconductor device.

[0014] In the preferred embodiment of the invention, a polymer film is formed on sidewalls of an opening in a photoresist layer. An opening is formed in a dielectric layer by using the photoresist layer and the polymer film as a mask while patterning the dielectric layer; thus, the opening in the dielectric layer is narrower than the opening in the photoresist layer.

[0015] To form the polymer film, a silicon-oxy-nitride layer as a stop layer is first formed on the dielectric layer. The dielectric layer is not etched while forming the polymer film due to the silicon-oxy-nitride layer; thus, no oxygenic radicals are released from the dielectric layer to affect the formation of the polymer film.

[0016] FIGS. 1A through 1C are schematic, cross-sectional views of a method according to this invention of forming an opening in a semiconductor device.

[0017] Referring to FIG. 1A, a silicon-oxy-nitride (SiO_xN_y) layer 104 whose thickness is about 100-900 Å is formed on a dielectric layer 102 on a substrate 100 by, for example, chemical vapor deposition. The dielectric layer 102 includes silicon dioxide. Then, a photoresist layer 106 is formed on the silicon-oxy-nitride layer 104. An opening 108 is formed in the photoresist layer 106 to expose a portion of the silicon-oxy-nitride layer 104.

[0018] The substrate 100 is then placed in a chamber, and a gas etchant at least includes C₄F₈and Ar flows into the chamber; the flow rate of C₄F₈is larger than 10 sccm and the flow rate of Ar is larger than 300 sccm. The gas etchant further includes CO, O₂and CH_xF_ysuch as CHF₃, CH₂F₂or CH₃F; the flow rate of CO is about 0-500 sccm and the flow rate of O₂is about 0-3 sccm. A plasma generator such as radio frequency (RF) is utilized to generate plasma and a polymer film 110 is in-situ deposited on sidewalls of the opening 108 as shown in FIG. 1B. The power of the plasma generator is set to about 1600W, and the temperature of the bottom electrode of the plasma generator is about 10° C.

[0019] Since the material of the dielectric layer 102 is generally silicon dioxide, oxygenic radicals are released from the dielectric layer 102 while etching the dielectric layer 102 to form an opening with the gas etchant containing fluorine ions. At the same time, polymer is also produced. However, the polymer is uneasily deposited on the sidewalls of the opening 108 due to the oxygenic radicals. In this embodiment, the silicon-oxy-nitride layer 104 with a sufficient thickness is as a stop layer to prevent the dielectric layer 102 from etching; thus, no oxygenic radicals are released from the dielectric layer 102. The polymer can be deposited on the sidewalls of the opening 108.

[0020] Carbon contained in C₄F₈reacts with hydrogen contained in the photoresist layer 106 to produce the polymer film 110. CH_xF_ycan assist the formation of the polymer film 110. As a result, the thickness of the polymer film 110 is controlled by the flow rate of C₄F₈in the gas etchant, and the ratio of hydrogen contained in CH_xF_ycontrols the densification of the polymer film 110. When the ratio of hydrogen contained in CH_xF_yis high, the polymer film 110 is thicker but is loose. However, the densification of the polymer film 110 is not related to the use of the polymer film 110.

[0021] While the polymer film 110 is deposited on the sidewalls of the opening 108, the polymer deposited on the silicon-oxy-nitride layer 104 is bombarded away at the time due to sufficient argon in the gas etchant. So that no polymer is deposited on the silicon-oxy-nitride layer 104 exposed by the opening 108.

[0022] After the polymer film 110 is deposited on the sidewalls of the opening 108, an etching process is performed with the photoresist layer 106 and the polymer film 110 as a mask to remove a portion of the silicon-oxy-nitride layer 104 and a portion of the dielectric layer 102 by changing the flow rate of the gas etchant; thus, an opening 112 is formed in the dielectric layer 102. The gas etchant preferably includes C₄F₈, CO, Ar and O₂; for example, the flow rate of C₄F₈is about 12 sccm, the flow rate of CO is about 50 sccm, the flow rate of Ar is about 250 sccm and the flow rate of O₂is about 5 sccm. The pressure in the chamber is about 30 mtorr.

[0023] Since the polymer film 110 is as a spacer on the sidewalls of the opening 108, the opening 112 is narrower than the opening 108. As a result, a small-size opening is obtained. In addition, the silicon-oxy-nitride layer 104 on the dielectric layer 102 is also used as an anti-reflective-coating layer (ARC) to avoid misalignment during the patterning process. Next, the photoresist layer 106 is removed.

[0024] In this invention, the silicon-oxy-nitride layer is formed on the dielectric layer to be a stop layer; thus, the polymer film can be formed on the sidewalls of the opening in the photoresist layer. The photoresist layer and the polymer film are used as a mask to form the opening in the dielectric layer, which is narrower than the opening in the photoresist layer. So that a small-size opening is obtained.

[0025] It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.