Contact hole etching process for the lower electrode of phase change memory for plasma Surface processor

Contact hole etching process for the lower electrode of phase change memory for plasma Surface processor:

The size of the "heater" in the storage unit of the PHASE-change memory is critical to the performance of the device, and the smaller size means that the lower electrode contact has a higher current density, higher heating efficiency, and a smaller area of the phase-change material. The structure and process flow of the knife-edge silicon nitride electrode contact with GST as phase change material, which can form the lower electrode contact with the size of less than 20nm along the direction of the position line.

According to the cutting sequence of Titanium nitide in U-shaped groove, lithographic segmentation and plasma surface processor etched after etching in the contact hole of the lower electrode are two technological processes. The lithography segmentation process uses the distance between the two ends of the photoresist to define the segmentation zone. Then, the lower layer of the film is removed successively. The upper surface and side wall of the U-shaped groove are removed, and the bottom layer is also cut accordingly. The process is simple and the cost of the hood is low, but the limitations of lithography may lead to the Shortening of the Line End (LES), which can lead to lateral parietal titanium loss. When the graph is further miniaturized, the effect becomes more significant and even causes the graph to fail. The lithographic pattern of etching and cutting process is a complete straight line, and the bottom nitriding will not be cut, so it is necessary to add additional silicon nitride cutting process after etching by plasma surface processor of plasma cleaning machine with contact hole of the lower electrode. This method requires at least two masks, which is of high cost. The advantage is that the lithography process window is large, and the control ability of the size of the lower electrode contact along the direction of the word line is strong, which facilitates the further reduction of the size of the lower electrode contact.

The requirements of the two processes for the etching of plasma surface processor in the plasma cleaning machine with lower electrode contact holes are appropriate contact size, vertical TI nitriding profile shape and no TI nitriding residue at the bottom of u-shaped groove. After the organic substrate in the trench is removed by the plasma surface treatment with the plasma cleaning machine, there are two schemes of isotropic and anisotropic plasma etching for the titanium nitride silicon oxide in the lower layer. If isotropic etching is adopted (such as high pressure strength, low rf power combined with high ratio CF4 for silicon oxide etching or high ratio Cl2 for titanium nitridation etching), the lithographic segmentation process can effectively ensure that there is no titanium nitridation residue at the side wall and bottom of the groove, but it also brings side effects such as oblique profile shape and serious CD loss. In addition to the above problems, there are titanium nitride and even silicon oxide residues on the side wall in the cutting method after the plasma surface processor etching in the plasma cleaning machine. After the etching time is prolonged, the residue is removed but the top of the titanium nitride is seriously damaged. If anisotropic etching is used (e.g., low pressure strength, high bias power combined with C4F8/Ar for silicon oxide etching or Cl2/N2 for titanium nitide etching), both processes have better CD loss and profile shape, with serious substrate material loss as a side effect. Organic substrate material are removed, the oxidation of anisotropic silicon etching will remove groove at the top, but at the bottom of the film in the lateral wall with residual, especially the corner if the silica/titanium nitride choice than below 15:1, the plasma cleaning machine plasma surface treatment machine increase etching time will open at the bottom of the titanium nitride cause severe loss of substrate materials. However, the plasma etching process of plasma surface processing machine with too high selection ratio will cause more inclined slope shape and the uniformity is more difficult to control.

The two etching schemes have their own advantages and disadvantages. Because CD control is important for the further miniaturization of graphics and mass production, the industry tends to adopt the anisotropic etching scheme of plasma surface processor in plasma cleaning machine. Therefore, in order to resolve the conflict between titanium nitrite residue and selection ratio, a partial removal scheme of organic substrate was proposed. In this scheme, by controlling the opening time of organic substrate, enough organic matter is left in the trench to protect the titanium nitrite at the bottom, so as to avoid the conflict between the two demands of etching directivity and selection ratio. Therefore, CF4/CHF3, an etching formula with a low selectivity, can then be used to simultaneously etch down the silicon oxide, the titanium nitrite on the side wall, and the organic matter in the trench in the uncovered area of light resistance, followed by the over-etching step of the gas etching dominated by the plasma surface processor Cl2 in the plasma cleaning machine to remove the possible residual titanium nitrite. The optimization scheme achieves less bottom substrate material and CD loss, straighter profile shape and no titanium nitide residue in U-shaped groove. The significant difference between this scheme and the above two schemes is that the silicon oxide on both sides of the trench is not covered by the photoresist. This side effect can be addressed by refilling the silicon oxide.