Photoresist adhesion improvement on metal layer after photoresist rework by extra N2O treatment

[0002] The present invention relates generally to semiconductor fabrication and more specifically to a method of improving the adhesion of photoresist after reworking.

[0003] During fabrication of semiconductor integrated circuit (IC) devices, it may become necessary to rework, or remove and reapply, metal photoresist. However, metal photoresist rework leads to yield loss due to the reapplied photoresist peeling inducing metal shorting. This is especially true for 0.18 μm logic products.

[0004] U.S. Pat. No. 6,143,666 to Lin et al. describes a method for forming a via through a dielectric layer within a microelectronics fabrication. A silicon oxide dielectric layer is formed over a substrate and is then treated with an oxygen plasma to enhance adhesion to a photoresist layer formed over the oxygen plasma treated silicon oxide dielectric layer.

[0005] U.S. Pat. No. 6,143,670 to Cheng et al. describes a method for forming a composite dielectric layer with enhanced adhesion upon a substrate by treating with ion implantation methods.

[0006] U.S. Pat. No. 6,096,662 to Ngo et al. describes a method of manufacturing a semiconductor device with improved adhesion between the local interconnect etch stop layer and the thermal oxide in an isolation region.

[0007] U.S. Pat. No. 5,714,037 to Puntambekar et al. describes methods for improving adhesion between various materials utilized in the fabrication of integrated circuits. In one method, the surface of a silicon dioxide (oxide) layer is treated with a nitrogen plasma in a reactive ion etching process prior to depositing a silicon nitride film upon the treated oxide layer.

[0008] U.S. Pat. No. 4,330,569 to Gulett et al. describes a method of conditioning a nitride surface by treating it with ionized oxygen.

[0009] U.S. Pat. No. 6,153,512 to Chang et al. describes a process to improve adhesion of hydrogen silsesquioxane (HSQ) MD layer to underlying materials. A series of plasma treatments performed in a nitrogen containing ambient are used to improve the adhesion of the hydrogen silsesquioxane (HSQ) IMD layer.

[0010] U.S. Pat. No. 5,795,821 to Bacchetta et al. describes a method for improved adhesion between dielectric materials at their interface by interposing a thin oxide layer between a first and second dielectric layer.

[0011] Accordingly, it is an object of the present invention to provide a method of improving adhesion between an inorganic anti-reflective coating (ARC) layer and photoresist after a metal photoresist rework

[0012] Other objects will appear hereinafter.

[0013] It has now been discovered that the above and other objects of the present invention may be accomplished in the following manner. Specifically, a semiconductor structure having an upper exposed metal layer is provided. An ARC layer is formed over the upper exposed metal layer. The ARC layer having an upper surface. A first photoresist layer is formed upon the ARC layer. The first photoresist layer is removed by a rework process. The ARC layer upper surface is roughened to form a roughened ARC layer upper surface. A second photoresist layer is formed upon the roughened ARC layer upper surface whereby adhesion of the second photoresist layer to the ARC layer is improved.

[0014] The present invention will be more clearly understood from the following description taken in conjunction with the accompanying drawings in which like reference numerals designate similar or corresponding elements, regions and portions and in which:

[0015] FIGS. 1 to 3 illustrate a preferred embodiment of the present invention.

[0016] FIG. 4 is a chart illustrating the results of experiments conducted using the method of the present invention compared to the current method.

[0017] Unless otherwise specified, all structures, layers, steps, methods, etc. may be formed or accomplished by conventional steps or methods known in the prior art.

[0018] The inventors have discovered that photoresist peeling inducing metal shorting occurs during the current 0.18 μm logic metal layer photoresist rework procedure (as noted above) because of poor adhesion between the inorganic silicon oxynitride (SiON) anti-reflective coating (ARC) layer and the photoresist after the metal photoresist rework. The current 0.18 μm logic metal layer photoresist rework procedure uses a PRS tool (with an ACT solvent treatment)+Mattson(90C plasma dry ashing)+deionized water(DIW).

[0019] The inventors have discovered that by including an additional treatment of the exposed ARC layer during the metal photoresist rework process that roughens the surface of the ARC layer, adhesion between the treated SiON ARC layer and the reapplied photoresist is dramatically improved. This reduces/avoids yield loss by metal shorts otherwise due to the peeling of the reapplied photoresist.

[0020] As shown in FIG. 1, semiconductor structure 10 includes an overlying dielectric layer 12. Semiconductor structure 10 is also understood to possibly include a semiconductor wafer or substrate, active and passive devices formed within the wafer, conductive layers and dielectric layers (e.g., inter-poly oxide (IPO), intermetal dielectric (IMD), etc.) formed over the wafer surface. The term “semiconductor structure” is meant to include devices formed within a semiconductor wafer and the layers overlying the wafer.

[0021] Dielectric layer 12 is preferably formed of silicon oxide (SiO₂or oxide).

[0022] Metal layer 14 is formed over dielectric layer 12 and may be a metal 1, metal 2 or metal 3 layer, for example. Metal layer 14 may be composed of copper, aluminum, titanium (Ti) or TiN.

[0023] A bottom anti-reflective coating (ARC) layer 16 is formed over metal layer 14 to a thickness of preferably from about 100 to 1000 Å and more preferably about 200 to 600 Å. ARC layer 16 having an upper exposed surface 32.

[0024] ARC layer 16 is preferably formed of SiON, SiN, TiN or SiO₂and is more preferably formed of SiON.

[0025] First metal photoresist layer 18 is formed over ARC layer 16. First metal photoresist layer 18 may be patterned as shown. Due to any number of problems with first patterned metal photoresist layer 18, it must be removed (by reworking) and another (patterned) metal photoresist layer 30 reapplied.

[0026] As shown in FIG. 2, first patterned metal photoresist layer 18 is removed by a rework process as is known to one skilled in the art, for example by the sequential steps:

[0027] a PRS using an ACT solvent treatment;

[0028] a Mattson asher using a plasma dry ashing at a temperature of about 90° C.; and

[0029] a deionized water (DIW) treatment.

[0030] In a key step of the invention, exposed surface 32 of ARC layer 16 is roughened 20 that creates roughened ARC layer surface 32′. The ARC surface 32 roughening 20 is conducted preferably with N₂O gas at the following parameters:

[0031] (1) an N₂O gas flow of preferably from about 500 to 3000 sccm and more preferably from about 1200 to 2000 sccm;

[0032] (2) a temperature of preferably from about 350 to 450° C. and more preferably from about 380 to 420° C.;

[0033] (3) a pressure of preferably from about 1 to 15 Torr and more preferably from about 2 to 8 Torr; and

[0034] (4) for a time of from about 20 to 100 seconds and more preferably from about 20 to 60 seconds.

[0035] The inventors have discovered that by roughening the surface 32 of ARC layer 16 to create roughened ARC layer surface 32′, the adherence of subsequently formed reapplied photoresist layer/patterned photoresist layer 30 is substantially improved.

[0036] As shown in FIG. 3, second metal photoresist layer 30 is formed over the roughened surface 32′ of ARC layer 16. Second metal photoresist layer 30 may be patterned as shown. The roughening of ARC layer 16 surface 32 to form roughened ARC layer surface 32′ dramatically improves the adhesion of second patterned metal photoresist layer 30 to ARC layer 16 and thus reduces the problem of second patterned photoresist layer 30 from lifting off causing metal shorts and loss of yield.

[0037] FIG. 4 illustrates the results of sets of three wafers with 0.18 logic devices reworked in accordance with the additional ARC layer 16 surface 32 roughening step of the present invention (A (1-3), B (4-6) and C (7-9)) as compared to reworking without the ARC layer 16 surface 32 roughening step of the present invention (D (14-16) and E (17-19)) showing the yield tile percent for each wafer.

[0038] As shown, the average yield tile % for the three sets of wafer reworking with the roughening step of the present invention are:

[0039] As demonstrated, using the additional ARC layer 16 surface 32 roughening step of the present invention dramatically increases the yield tile % after reworking.

[0040] The advantages of the present invention include:

[0041] (1) improved adhesion between the second photoresist layer and the ARC layer;

[0042] (2) reduced second photoresist layer peeling;

[0043] (3) reduced metal shorting; and

[0044] (4) improved yields.

[0045] While particular embodiments of the present invention have been illustrated and described, it is not intended to limit the invention, except as defined by the following claims.