Method of manufacturing semiconductor memory device

This application is a divisional application of U.S. patent application Ser. No. 15/227,986 filed Aug. 4, 2016, which is incorporated by reference in its entirety.

The present invention relates to a method of manufacturing semiconductor device, and more particularly to a method of manufacturing semiconductor memory device comprising a plurality of semiconductor memory cells.

Flash memories are popular in modern societies. A conventional flash memory is similar to a CMOS (Complementary Metal-Oxide-Semiconductor) transistor, in which the conventional flash memory includes two gates (also called “gate electrodes”) and a spacing film sandwiched between the gates. The spacing film is made of dielectric material and has to electrically isolate both gates from each other to prevent causing a short circuit between the gates, so that the spacing film prefers to have high breakdown voltage. Hence, the spacing film sandwiched between two gates is an important part of the flash memory.

The present invention provides a method of manufacturing a semiconductor memory device. In the method, a substrate is provided. Then, a plurality of gate structures and a plurality of dielectric caps are formed, wherein the gate structures are formed on the substrate and each comprise a first gate and a first gate dielectric layer between the first gate and the substrate, and the dielectric caps are formed atop the gate structures respectively. Next, a first dielectric layer and a second dielectric layer are formed. The first dielectric layer covers the dielectric caps and a plurality of sidewalls of the gate structures. The second dielectric layer covers the first dielectric layer. Then, partially remove the second dielectric layer to reveal a plurality of top parts of the first dielectric layer and to form a plurality of first spacing films. Then, a plurality of second gates is formed on the substrate. The second gates cover and contact the first dielectric layer and a top edge of the first spacing film. Next, the dielectric caps are removed to reveal the first gates. Then, drains and sources are formed in the substrate.

Based on the above, since the second gates cover the top edges of the first spacing films, the first spacing films can be protected by the second gates. Therefore, the breakdown voltage between the two gates (e.g. first gate and second gate) can be kept or increased

The present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which:

FIG. 1A to FIG. 1I are cross-sectional views of a method of manufacturing a semiconductor memory device in accordance with an embodiment of the present invention.

FIG. 2 is a plan view of the semiconductor memory device in FIG. 1I .

The present invention will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of embodiments of this invention are presented herein for the purpose of illustration and description only. It is not intended to be exhaustive or to be limited to the precise form disclosed.

FIG. 1A to FIG. 1H illustrate a method of manufacturing a semiconductor memory device in accordance with an embodiment of the present invention. Referring to FIG. 1A , in the method, first, provide a substrate 110 i, which may be a wafer. Then, an electric isolating structure 112 is formed in the substrate 110 i. The electric isolating structure 112 may be a shallow trench isolation (STI), a field oxide (FOX), or a doping region.

Referring to FIG. 1B and FIG. 1C , after the electric isolating structure 112 is completed, a plurality of gate structures 121 and a plurality of dielectric caps 123 are formed. The gate structures 121 are formed on the substrate 110 i, and the dielectric caps 123 are formed atop the gate structures 121 , respectively. The gate structures 121 and the dielectric caps 123 can be formed by thin-film deposition and photolithography.

In the formation of the gate structures 121 and the dielectric caps 123 , multiple films are formed on the substrate 110 i first, and the multiple films include a plurality of dielectric films S 21 , N 21 , S 22 , 123 i , and a semiconductor layer G 1 . The dielectric films S 21 , N 21 , and S 22 are formed on the substrate 110 i in sequence, where the dielectric film N 21 is sandwiched between the dielectric films S 21 and S 22 , and the dielectric film S 21 is in contact with the substrate 110 i. The semiconductor layer G 1 is formed between the dielectric films S 22 and 123 i, as shown in FIG. 1B .

The dielectric films S 21 and S 22 may be silicon oxide films (e.g. SiO 2 ), whereas the dielectric films N 21 and 123 i may be silicon nitride films (e.g. Si 3 N 4 ). The semiconductor layer G 1 may be made of poly silicon. The dielectric films S 21 , N 21 , S 22 , 123 i and the semiconductor layer G 1 can be formed by chemical vapor deposition (CVD). Afterward, photolithography is performed to remove parts of the abovementioned multiple film and to form the gate structures 121 and the dielectric caps 123 .

The rest of the dielectric films S 21 , N 21 , S 22 and the semiconductor layer G 1 become the gate structures 121 , and the rest of the dielectric film 123 i becomes the dielectric caps 123 . The gate structures 121 each include a first gate MG 1 and a first gate dielectric layer GD 1 between the first gate MG 1 and the substrate 110 i. The first gate MG 1 is formed from the semiconductor layer G 1 , and the first gate dielectric layer GD 1 is formed from the dielectric films S 21 , N 21 , S 22 .

In addition, the first gate dielectric layer GD 1 includes a charge-trap layer CT 1 , which is formed from the dielectric film N 21 . That is, the charge-trap layer CT 1 is a silicon nitride film. Moreover, the substrate 110 i, the first gate dielectric layer GD 1 , and the first gate MG 1 can form a SONOS structure when the charge-trap layer CT 1 is silicon nitride film; the dielectric films S 21 and S 22 are silicon oxide films; and the first gate MG 1 is made of poly silicon.

Referring to FIG. 1D , a first dielectric layer 125 a and a second dielectric layer 125 b are formed. The first dielectric layer 125 a covers the dielectric caps 123 and a plurality of sidewalls SW 1 of the gate structures 121 , whereas the second dielectric layer 125 b covers the first dielectric layer 125 a. That is, the first dielectric layer 125 a is formed between the second dielectric layer 125 b and the substrate 110 i.

The first dielectric layer 125 a and the second dielectric layer 125 b also can be formed by thin-film deposition, such as CVD. Both the first dielectric layer 125 a and the second dielectric layer 125 b which are formed by CVD can conformally cover the gate structures 121 and the dielectric caps 123 . Moreover, the first dielectric layer 125 a may be a silicon oxide film, and the second dielectric layer 125 b may be a silicon nitride film. In other words, the materials (e.g. silicon oxide and silicon nitride) of both the first dielectric layer 125 a and the second dielectric layer 125 b are different.

Referring to FIG. 1D and FIG. 1E , then, the second dielectric layer 125 b is partially removed to reveal a plurality of top parts of the first dielectric layer 125 a and to form a plurality of first spacing films 126 a (as shown in FIG. 1E ). Partial removal of the second dielectric layer 125 b includes performing a plasma etching. That is, the part of the second dielectric layer 125 b can be removed by plasma.

The etching rate of the second dielectric layer 125 b is different from the etching rate of the first dielectric layer 125 a because the materials of both the first dielectric layer 125 a and the second dielectric layer 125 b are different. During the plasma etching, the etching rate of the second dielectric layer 125 b is higher than the etching rate of the first dielectric layer 125 a, so that the removed part of the second dielectric layer 125 b is more than the removed part of the first dielectric layer 125 a. Even, the whole first dielectric layer 125 a can be almost remained after the plasma etching according to the embodiment illustrated in FIG. 1E . After the part of the second dielectric layer 125 b is removed, the rest of the second dielectric layer 126 forms the first spacing films 126 a.

Referring to FIG. 1F and FIG. 1G , subsequently, a plurality of second gates CG 2 is formed on the substrate 110 i. The second gates CG 2 can be formed by thin-film deposition. Specifically, in the formation of the second gates CG 2 , a semiconductor film 131 is formed on the substrate 110 i at first, in which the semiconductor film 131 can be formed by CVD, and the materials of both the semiconductor layer G 1 (referring to FIG. 1B ) and the semiconductor film 131 may be the same. In addition, the (completed) semiconductor film 131 may fill a depression R 1 and cover two adjacent first spacing films 126 a, where the depression R 1 is defined by the two adjacent first spacing films 126 a and the substrate 110 i.

After the semiconductor film 131 is completed, the semiconductor film 131 is partially removed to form the second gates CG 2 . The second gate CG 2 covers and contacts the first dielectric layer 125 a and a top edge 126 t of the first spacing film 126 a. Accordingly, each first spacing film 126 a is sandwiched between the second gate CG 2 and the first dielectric layer 125 a, and covered by the second gate CG 2 and the first dielectric layer 125 a, as shown in FIG. 1G . The removal of the part of the semiconductor film 131 and the formation of the second gates CG 2 may be performed by self aligned etching, and the part of the semiconductor film 131 can be removed by dry etching, such as plasma etching.

Since the second gates CG 2 can be formed by dry etching (e.g. plasma etching), a top of each second gate CG 2 may form an inclined surface, where one inclined surface is opposite to and faces to the other inclined surface, as illustrated in FIG. 1G . In addition, except for the first spacing films 126 a, the rest of the second dielectric layer 126 may be removed by etching (e.g. dry etching or wet etching) after the second gates CG 2 are completed.

Referring to FIG. 1G and FIG. 1H , afterwards, the dielectric caps 123 are removed to reveal the first gates MG 1 , in which the removal of the dielectric caps 123 can include performing a wet etching. Because phosphoric acid (H 3 PO 4 ) can dissolve silicon nitride, the wet etching can use phosphoric acid as etchant when the material of the dielectric caps 123 is silicon nitride. However, phosphoric acid basically can't dissolve silicon and silicon oxide, so that the first dielectric layer 125 a (e.g. silicon oxide) and the first gate MG 1 (e.g. poly silicon) can be remained.

The second gates CG 2 cover both the top edges 126 t and sidewalls 126 s of the first spacing films 126 a, and each first spacing film 126 a is sandwiched between the second gate CG 2 and the first dielectric layer 125 a and covered by the second gate CG 2 and the first dielectric layer 125 a, so that the second gates CG 2 (e.g. poly silicon) and the second dielectric layer 125 b (e.g. silicon oxide) can protect the first spacing films 126 a from phosphoric acid, thereby remaining entire first spacing films 126 a.

In addition, before the dielectric caps 123 are removed, the first dielectric layer 125 a can be partially removed to reveal the dielectric caps 123 and the substrate 110 i by etching, such as dry etching (e.g. plasma etching). Therefore, the dielectric caps 123 can be in contact with etchant (e.g. phosphoric acid) and be removed.

Moreover, after the first dielectric layer 125 a is partially removed, the rest of the first dielectric layer 125 a forms a plurality of second spacing films 127 b and a plurality of second gate dielectric layers GD 2 . Each second spacing film 127 b is between the first spacing film 126 a and the first gate MG 1 , whereas each second gate dielectric layer GD 2 is between the second gate CG 2 and the substrate 110 i. Furthermore, the first gate MG 1 and the second gate CG 2 do not cover a top edge 127 t of the second spacing film 127 b.

Refer to FIG. 1I and FIG. 2 , where FIG. 1I . is the cross-sectional view taken along the line I-I in FIG. 2 . After the first gates MG 1 are revealed by removing the dielectric caps 123 , a plurality of drains D 11 and a plurality of sources S 11 are formed by doping. The substrate 110 i becomes a substrate 110 a after doping, so that the substrate 110 a has the drains D 11 and the sources S 11 . That is, the drains D 11 and the sources S 11 are formed in the substrate 110 a. In addition, a plurality of contacts T 1 and contacts T 2 can be formed on the drains D 11 and the sources S 11 , respectively, for electric connection.

After the drains D 11 and the sources S 11 are formed, a semiconductor memory device 10 including a plurality of semiconductor memory cells 100 and the electric isolating structure 112 is basically completed. Each of the semiconductor memory cells 100 includes the substrate 110 a, the first gate MG 1 , the second gate CG 2 , the first gate dielectric layer GD 1 , the second gate dielectric layer GD 2 , the first spacing film 126 a, and the second spacing film 127 b, in which the first gate MG 1 is a memory gate, and the second gate CG 2 is a select gate. Moreover, the substrate 110 a, the first gate dielectric layer GD 1 , and the first gate MG 1 can form a SONOS structure.

In one semiconductor memory cell 100 , the first gate MG 1 and the second gate CG 2 are both formed on the substrate 110 a, and between the drain D 11 and the source S 11 . The first gate dielectric layer GD 1 is disposed between the first gate MG 1 and the substrate 110 a , whereas the second gate dielectric layer GD 2 is disposed between the second gate CG 2 and the substrate 110 a. The first spacing film 126 a is disposed between the first gate MG 1 and the second gate CG 2 , where the second gate CG 2 covers the sidewall 126 s and the top edge 126 t. In addition, a level H 1 of the top edge 126 t relative to the substrate 110 a is higher than a level H 2 of the top edge 127 t relative to the substrate 110 a.

Based on the above, since the second gates cover the top edges of the first spacing films, the first spacing films can be protected by the second gates during the manufacturing process. Therefore, the breakdown voltage between the two gates (e.g. first gate and second gate) can be kept or increased.

While the invention has been described in terms of what is presently considered to be the most practical and embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.