PE-silane oxide particle performance improvement

[0002] (1) Field of the Invention

[0003] The present invention relates to the fabrication of integrated circuit devices, and more particularly, to a method of reducing the number of particles formed on a wafer during PE-silane oxide film formation in the fabrication of integrated circuits.

[0004] (2) Description of the Prior Art

[0005] Silicon oxide films are widely used in semiconductor processing as interlevel and intermetal dielectrics. Silicon oxide films are often formed by plasma-enhanced chemical vapor deposition (PECVD). FIG. 1 illustrates a typical CVD chamber 20. The wafer is placed into the chamber. Gases are flowed into the chamber whereby the silicon oxide film is formed on the surface of the wafer. Typically, silane (SiH₄) is flowed from the Mass Flow Controller (MFC) of one gas inlet 22 while N₂O is flowed from the MFC of a second gas inlet 24. The reaction of the two gases forms SiO₂.

[0006] In the typical silicon oxide PE-silane reaction, the SiH₄and N₂O gases are flowed into the CVD chamber with no radio frequency power as a stabilization step. Then the radio frequency, for example 280 watts, is applied while the two gases continue to flow to form the silicon oxide film.

[0007] After the silicon oxide film was formed according to the conventional recipe, the inventors obtained a particle count on the wafer. Unexpectedly, they found an extremely high particle count of more than 20,000 particles of a size 0.2 μm and larger. It is desirable to find a method of forming a silicon oxide film without this extremely high particle count.

[0008] U.S. Pat. No. 5,279,865 to Chebi et al teaches a method of forming a silicon oxide layer using silane flow. U.S. Pat. No. 5,525,550 to Kato teaches a method of forming silicon oxide by CVD using silane and water as the main feed gases. U.S. Pat. No. 5,576,076 to Slootman et al teaches forming an silicon dioxide layer by subjecting a wafer to an electrical discharge in the presence of silane and N₂O. U.S. Pat. No. 5,214,952 to Leggett et al teaches the use of a series of highly accurate mass flow controllers to deliver a high purity calibration gas mixture to a gas analyzer. None of these references address the particle problem.

[0009] Accordingly, it is a primary object of the invention to provide a process for greatly reducing the particle count in the formation of a PE-silane oxide film.

[0010] In accordance with the object of the invention, a method of forming a PE-silane oxide layer with a greatly reduced particle count is achieved. A semiconductor substrate is provided over which a silicon oxide film is to be formed. The silicon oxide film is formed by the steps of: 1) pre-flowing a non-silane gas into a deposition chamber for at least two seconds whereby the pre-flowing step prevents formation of particles on the silicon oxide film, and 2) thereafter depositing a silicon oxide film by chemical vapor deposition by flowing a silane gas into the deposition chamber to complete formation of a silicon oxide film using plasma-enhanced chemical vapor deposition in the fabrication of an integrated circuit.

[0011] In the accompanying drawings forming a material part of this description, there is shown:

[0012] FIG. 1 is a cross-sectional representation of chemical deposition chamber.

[0013] FIG. 2 is a cross-sectional representation of an embodiment of the present invention.

[0014] FIG. 3 is a flow chart of the process flow of a first embodiment of the present invention.

[0015] FIG. 4 is a flow chart of the process flow of a second embodiment of the present invention.

[0016] Referring now more particularly to FIG. 2, there is shown a semiconductor substrate 10, preferably composed of monocrystalline silicon. Semiconductor device structures, not shown, may be formed in and on the semiconductor substrate, such as in layer 14. Alternatively, layer 14 may be a metal layer. An interlevel or intermetal dielectric layer 18 of silicon dioxide is to be formed by plasma-enhanced chemical vapor deposition (PECVD) overlying layer 14.

[0017] The inventors conducted a series of tests to determine the cause of the particle spiking observed after conventional PECVD silicon dioxide film deposition and to determine a solution to this problem. First, the inventors conducted a hardware check of the transfer mechanism and the gas flow inlets. These tests showed a particle count of less than 10 each. Next, the inventors checked the reaction parameters of the deposition step. Particle counts of greater than 20,000 were found after SiH₄+N₂O gas flow and after SiH₄gas flow without N₂O. However, a particle count of less than 10 was found after a gas flow of N₂O without SiH₄.

[0018] The inventors have determined a possible mechanism for the particle formation sequence. Excess SiH₄is flowed into the chamber due to overshooting or bad timing by the Mass Flow Controller (MFC). The SiH₄is adsorbed by the wafer surface. Abnormal nucleation sites are formed by the SiH₄on the wafer surface resulting in the particle spiking disaster observed by the inventors.

[0019] The solution found by the inventors is a simple and ingenious one. The abnormal nucleation sites can be reduced by adding a non-SiH₄gas pre-flow before stabilization. This will result in good nucleation sites and good particle performance.

[0020] FIG. 3 illustrates the process flow of the first preferred embodiment of the present invention. Steps 32 and 34 are the conventional stabilization and deposition steps. Step 31 is the new non-SiH₄gas pre-flow step of the present invention. N₂O and/or N₂gas should be flowed for at least 2 seconds before the conventional stabilization step. It has been found that N₂O and/or N₂plasma works as well as gas.

[0021] The following Example is given to show the important features of the invention and to aid in the understanding thereof. Variations may be made by one skilled in the art without departing from the spirit and scope of the invention.

[0022] The following table summarizes the results of testing various gas flow rates and times for the new pre-flow step of the invention along with the resulting particle counts.

[0023] It can be seen from Table 1 that the pre-flow step of the present invention drastically reduces the particle count from over 20,000 to less than 15, and in most cases, to 3 or fewer. N₂O gas was flowed at 1400 and 1100 sccm for 2, 10, or 30 seconds. In one case (3), the pre-flow step was performed followed immediately by deposition without the stabilization step. However, without the stabilization step, the thickness of the resulting film may be unstable. N₂pre-flow was also satisfactory alone (5) or in combination with N₂O (6).

[0024] The last table entry (7) refers to the second embodiment of the present invention. This is a new stabilization step including N₂and SiH₄flow before the N₂O and SiH₄deposition step. The particle counts were also satisfactory for this case.

[0025] FIG. 4 illustrates the process flow of the second preferred embodiment of the present invention. Step 34 is the conventional deposition step. Step 33 is the new stabilization step of the present invention. N₂and SiH₄gases are flowed together in the new stabilization step.

[0026] The process of the present invention provides a method of PE-silane oxide deposition with dramatically reduced particle counts. The inventive process in the first embodiment is a pre-flow step inserted before the N₂O+SiH₄stabilization step. N₂O gas or N₂gas, or a combination of the two, is flowed, preferably for at least 2 seconds. The flow rate of the gases is preferred to be the same as the flow rate of the N₂O gas in the deposition step.

[0027] In an alternative according to the second embodiment, a new stabilization step is inserted in place of the N₂O+SiH₄stabilization step. The new step flows N₂gas and SiH₄gas using no radio frequency followed by conventional deposition Particle performance was found to be good when this new stabilization step was substituted for the conventional stabilization step. It is surmised that the N2 and SiH4 gases together changed the nucleation conditions.

[0028] Both embodiments of the present invention are simple and effective methods of providing dramatically reduced particle counts. However, to keep film thickness and film quality the same as in the conventional process, it is preferred to use the first embodiment of the invention in which a non-silane gas pre-flow step is used before the conventional stabilization and deposition steps.

[0029] While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the a invention.