Method of controlling and improving SOG etchback etcher

[0002] (1) Field of the Invention

[0003] The invention relates to a method of removing polymer buildup on a wafer and on the etch chamber walls in the manufacture of integrated circuits, and more particularly, to a method of removing polymer buildup after spin-on-glass etchback in the manufacture of integrated circuits.

[0004] (2) Description of the Prior Art

[0005] In the current sub-micron technology of the manufacture of integrated circuit devices, the spin-on-glass etchback process has been adopted widely to improve planarization. However, spin-on-glass etchback causes the buildup of polymer on the upper electrode and the chamber wall of the etch chamber. The polymer buildup on the electrode results in an unstable etch rate and non-uniformity.

[0006] U.S. Pat. No. 5,679,211 to Huang discloses an oxygen-containing plasma treatment to remove a polymer formed on a spin-on-glass layer by the process of etching the spin-on-glass layer. U.S. Pat. No. 5,639,345 to Huang et al teaches a two-step SOG etchback process. These processes address polymer buildup on the wafer rather than the problem of polymer buildup in the etch chamber.

[0007] Accordingly, a principal object of the present invention is to provide an effective and very manufacturable method of removing polymer buildup from an etch chamber.

[0008] A further object of the invention is to provide a method for removing polymer buildup from the upper electrode and walls of an etch chamber after spin-on-glass etchback.

[0009] A still further object of the invention is to provide a method for removing polymer buildup from the upper electrode and walls of an etch chamber after spin-on-glass etchback to improve the etch rate and etch uniformity.

[0010] Yet another object is to provide a method for improving particle level, stability of etch rate, and etch uniformity by removing polymer buildup from the upper electrode and walls of an etch chamber after spin-on-glass etchback.

[0011] Yet another object of the invention is to provide a method for improving particle level, stability of etch rate, and etch uniformity by using a dry plasma clean to remove polymer buildup from the upper electrode and walls of an etch chamber after spin-on-glass etchback.

[0012] In accordance with the objects of this invention a new method for improving particle level, stability of etch rate, and etch uniformity by using a dry plasma clean to remove polymer buildup from the upper electrode and walls of an etch chamber after spin-on-glass etchback is achieved. An etching chamber having a lower electrode, upper electrode, and interior walls is provided. Spin-on-glass etchback is performed within the etching chamber whereby a polymer buildup forms on surfaces of the chamber. A dummy wafer is placed into the etching chamber and the polymer buildup within the chamber is removed using a dry plasma cleaning process.

[0013] In the accompanying drawings forming a material part of this description, there is shown:

[0014] FIG. 1 schematically illustrates in cross-sectional representation a spin-on-glass etchback chamber.

[0015] FIGS. 2 and 3 illustrate in cross-sectional representation a production wafer of the present invention.

[0016] FIG. 4 is a flowchart depicting the chamber cleaning process of the present invention.

[0017] Referring now more particularly to FIG. 1, there is illustrated an extremely simplified representation of an etch chamber 100 such as that used to etch back a spin-on-glass layer. The lower electrode 102 and upper electrode, or cathode, 104 are illustrated as well as clamps 106. The wafer 108 is placed onto the lower electrode 102.

[0018] FIG. 2 illustrates a portion of a partially completed integrated circuit device. There is shown a semiconductor substrate 10, preferably composed of monocrystalline silicon. Semiconductor device structures and insulating layers, not shown, may be formed in and on the semiconductor substrate. A layer of spin-on-glass 14 is coated on the surface of the substrate to a typical thickness of between about 5000 and 20,000 Angstroms.

[0019] The spin-on-glass layer is baked and cured as is conventional in the art. For example, the spin-on-glass layer is baked at a temperature of between about 20 and 300 ° C. for 1 to 5 minutes and then cured at a temperature of between about 300 and 450° C. for 30 to 100 minutes.

[0020] The spin-on-glass layer is now to be planarized by etchback. The wafer 108 is placed on the lower electrode 102, as illustrated in FIG. 1. Typically, the spin-on-glass layer is etched back using CF₄/CHF₃chemistry. For example, CF₄is flowed at 80 to 150 sccm, CHF₃is flowed at 40 to 100 sccm, and Ar is flowed at 100 to 300 sccm under pressure of 300 to 600 mTorr and power of 700 to 1000 watts for a duration of 80 to 200 seconds.

[0021] FIG. 3 illustrates the planarized surface 15 of the spin-on-glass layer 14 after etchback.

[0022] As wafers are processed through the etch chamber 100, polymer builds up on the surface of the cathode, as illustrated by 110, and on the walls of the chamber, as illustrated by 112. The CHF₃used in the spin-on-glass etchback recipe is a major source of the polymer problem. Etch chamber conditions become progressively worse; that is, unstable etch rate, bad etch rate uniformity, and higher particle levels. Non-uniformity of wafers and more down time of the etching equipment has been observed as well.

[0023] The process of the present invention provides a method for periodically cleaning the polymer from the etch chamber. FIG. 4 is a flowchart illustrating the process of the invention. According to the first step illustrated, 42, the etchback process is performed for “N” lots of production wafers. The number “N” can be determined experimentally in order to balance performance and cost control considerations. The preferred range of “N” is from 8 to 12 lots. In determining an optimum “N,” oxide and spin-on-glass etchrate and uniformity issues should be considered.

[0024] Polymer builds up on the cathode and the chamber walls, 44, during the course of performing the etchback process for “N” lots.

[0025] Now, after “N” lots of wafers have been etched back, the dry plasma clean process of the present invention is performed. According to step 46, a dummy wafer is placed into the etch chamber. The dummy wafer is preferably a bare-silicon wafer.

[0026] Next, the dry plasma cleaning step 48 is performed. Argon, O₂, and CF₄are passed into the etching chamber and plasma is turned on. Specifically, Ar is flowed at 300 to 500 sccm, O₂is flowed at 15 to 100 sccm, and CF₄is flowed at 40 to 100 sccm under a pressure of 200 to 600 mTorr and power of 500 to 1000 watts for a duration of 20 to 50 minutes.

[0027] The plasma cleaning process of the present invention removes the polymer buildup from the cathode surface and from the chamber walls of the etch chamber. The etching chamber condition is recovered after the cleaning step. The plasma dry clean process improves the particle level, etch rate stability, and etch uniformity of the etch chamber along with increasing the available for use time of the etching equipment.

[0028] The dummy wafer is removed from the etcher and production lots can again be run through the etcher. After another “N” lots of production wafers have been run, the cleaning process of the present invention is performed again.

[0029] The process of the present invention provides a simple and effective method of removing polymer buildup from the walls and from the upper electrode of an etching chamber. The dry plasma clean process of the invention uses Ar, O₂, and CF₄gases in plasma to remove the polymer buildup and hence improve the performance of the sin-on-glass etchback process.

[0030] 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 invention.