Abstract:
In a method of manufacturing a semiconductor device in which a capacitor having a storage electrode is formed on a semiconductor substrate, silicon films are formed on the semiconductor substrate and at the same time first and second endpoint marker layers for dividing the silicon films into three parts in the direction of thickness are formed by using a material different from the material of the silicon films. The silicon films including the first and second endpoint marker layers are etched. The etching depth of the silicon films is controlled based on the type of etched material, thereby forming the storage electrode.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a method of manufacturing a semiconductor device having a cylindrical capacitor. 
     To increase the memory capacity, a memory device having a cylindrical capacitor has conventionally been proposed in, e.g., Japanese Patent Laid-Open No. 5-218333. In this memory device, the lower electrode of the capacitor is formed into a cylindrical shape to increase the contact area between the upper and lower electrodes via a dielectric film without increasing the occupied area of the capacitor and to increase the integration degree while ensuring the capacitance of the capacitor. This cylindrical lower electrode is generally called a storage electrode. 
     FIGS. 4A to  4 E show a method of manufacturing a conventional cylindrical capacitor. 
     The step in FIG. 4A according to a general manufacturing method will be described briefly. A gate oxide film  2 , a gate electrode  3 , a diffusion layer  4 , and the like are selectively formed on a silicon substrate  1  to constitute an element. FIGS. 4A to  4 E show only one element on the substrate  1 , but a plurality of elements are practically manufactured. The elements are electrically isolated from each other by element isolation films  5 . 
     An interlevel insulating film  6  and an oxide film  7  are sequentially formed on these elements and the element isolation films  5 . Each contact hole  14  is formed in the diffusion layer  4  through the two films. An oxide film  8  is formed on the side surface in the contact hole  14  to improve electrical characteristics. 
     Simultaneously when the contact hole  14  is filled, a polysilicon film  9  having a predetermined thickness is formed on the oxide film  7 . An oxide film  30  having a predetermined width and a polysilicon film  13  are stacked on the silicon film  9 . Silicon oxide sidewalls  15   a  are formed on the sidewalls of the oxide film  30  and silicon film  13 . 
     As shown in FIG. 4B, while the silicon film  9  is etched using the oxide film  7  as an etching stopper, the silicon film  13  is etched using the oxide film  30  as an etching stopper. 
     As shown in FIG. 4C, the oxide film  30  is etched away to expose the silicon film  9 . 
     As shown in FIG. 4D, the silicon film  9  is etched to a predetermined thickness on the bottom using the sidewall  15   a  as an etching mask. Then, a recessed storage electrode  16  whose top is open is formed from the silicon film  9 . 
     As shown in FIG. 4E, a dielectric layer  18  is formed on the surface of the storage electrode  16 , and a cell plate electrode  19  is formed on the dielectric layer  18  to complete the cylindrical capacitor. 
     In this prior art, the thickness of the silicon film on the bottom of the storage electrode  16  cannot be stably controlled because the endpoint cannot be detected in etching the silicon film  9  in the step of FIG.  4 D. If the silicon film on the bottom is too thin, the resistance increases to generate a memory hold error; if the silicon film is too thick, the inner area of the storage electrode  16  decreases to decrease the capacitance of the capacitor. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a semiconductor device manufacturing method capable of easily controlling the etching depth. 
     To achieve the above object, according to the present invention, there is provided a method of manufacturing a semiconductor device in which a capacitor having a storage electrode is formed on a semiconductor substrate, comprising the steps of forming silicon films on the semiconductor substrate and at the same time forming when first and second endpoint marker layers for dividing the silicon films into three parts in a direction of thickness by using a material different from a material of the silicon films, etching the silicon films including the first and second endpoint marker layers, and controlling an etching depth of the silicon films based on the type of etched material, thereby forming the storage electrode. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A to  1 H are sectional views, respectively, showing the steps in manufacturing a semiconductor device according to the first embodiment of the present invention; 
     FIGS. 2A and 2B are sectional views, respectively, showing the steps in manufacturing a semiconductor device according to the second embodiment of the present invention; 
     FIG. 3 is a graph showing the thickness of the undoped amorphous silicon film and an erroneous shape of the HSG formed on it; and 
     FIGS. 4A to  4 E are sectional views, respectively, showing the steps in manufacturing a conventional semiconductor device. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will be described below with reference to the accompanying drawings. 
     FIGS. 1A to  1 H show a method of manufacturing a semiconductor device according to the first embodiment of the present invention. 
     As shown in FIG. 1A, a gate oxide film  102  is selectively formed on a silicon substrate  101 , and a gate electrode  103  is formed on the gate oxide film  102 . Using the gate electrode  103  as a mask, diffusion layers  104  are formed on the two side regions of the gate electrode  103  in the silicon substrate  101 . The gate oxide film  102 , the gate electrode  103 , and the diffusion layer  104  constitute an element. 
     FIGS. 1A to  1 H show only one element, but a plurality of elements are practically formed. The elements are electrically isolated from each other by element isolation films  105 . 
     An interlevel insulating film  106  and an undoped oxide film  107  are sequentially formed on these elements and the element isolation films  105 . Each contact hole  114  is formed to a depth reaching the diffusion layer  104  through the two films  106  and  107 . An oxide film  108  is formed on the inner surface in the contact hole  114  to improve electrical characteristics. 
     After a native oxide film formed on the diffusion layer  104  at the bottom of the contact hole  114  is removed with dilute hydrofluoric acid, a silicon film  109  having a predetermined thickness is formed on the oxide film  107 . At this time, the contact hole  114  is filled with the silicon film  109 . An endpoint marker layer  110 , a silicon film  111 , an endpoint marker layer  112 , and a silicon film  113  are sequentially formed on the silicon film  109 . 
     When phosphorus-doped amorphous silicon is to be grown as the silicon films  109 ,  111 , and  113 , a gas containing silane gas and phosphine is applied at a growth temperature of 520 to 530° C., a growth pressure of 0.5 to 2.0 Torr, and a P concentration of 1.0e20 atoms/cc or more. The silicon film  113  may be formed from either doped or undoped amorphous silicon. The amorphous silicon film may be grown by PE-CVD (Plasma Enhanced-Chemical Vapor Deposition). When HSG (Hemi-Spherical Grain) is not formed in the succeeding step, the silicon films  109 ,  111 , and  113  may be formed from polysilicon. 
     The endpoint marker layers  110  and  112  are formed from a silicon oxide film or silicon nitride film about 1 to 2 nm thick by only applying O 2  or NH 3  gas during the growth of the underlying silicon films  109  and  111 . The endpoint marker layers  110  and  112  can also be obtained by introducing O 2  gas while stopping the growth of the silicon films  109  and  111 , and forming native oxide films on the surfaces of the silicon films  109  and  111 . Therefore, the silicon films  109 ,  111 , and  113  can be continuously grown. 
     As shown in FIG. 1B, the silicon film  113  is anisotropically dry-etched to leave it by only a predetermined width above the contact hole  114 . At this time, light emission of the etched material in the plasma is always monitored to stop etching in accordance with changes in light emission intensity of the material contained in the endpoint marker layer  112  or the like. 
     When the endpoint marker layer  112  is made of silicon oxide, light emission of oxygen is monitored. The endpoint may be detected by mass spectrometric analysis of the etched material, instead of monitoring the light emission intensity. 
     As shown in FIG. 1C, an oxide film  115  is formed on the silicon film  113  and endpoint marker layer  112  by atmospheric pressure CVD or PE-CVD at 500° C. or less. At this time, P or B is used as an impurity to form a BPSG (BoroPhosphoSilicate Glass) oxide film  15 . 
     As shown in FIG. 1D, the oxide film  115  is etched back by anisotropic dry etching to form a sidewall  115   a  on the sidewall of the silicon film  113 . 
     As shown in FIG. 1E, the silicon film  113 , endpoint marker layer  112 , and silicon film  111  are etched using the sidewall  115   a  as an etching mask. In etching the silicon film  111 , light emission of the etched material is always monitored to stop etching in accordance with the light emission intensity of the material contained in the endpoint marker layer  110 . At the same time, the silicon film  111 , endpoint marker layer  110 , and silicon film  109  outside the sidewall  115   a  are also etched away. As a result, a storage electrode  116  in which the silicon film  109  is left to a predetermined thickness at the bottom is formed. 
     When the endpoint marker layer  110  is made of silicon oxide, light emission of oxygen is monitored. The endpoint may be detected by mass spectrometric analysis instead of monitoring the light emission intensity. 
     As shown in FIG. 1F, the sidewall  115   a  is selectively removed. If the oxide film  107  is made of undoped oxide, and the sidewall  115   a  is made of BPSG, the sidewall  115   a  can be selectively removed with HF. 
     As shown in FIG. 1G, after the native oxide film on the storage electrode  116  is removed with dilute hydrofluoric acid as pre-processing of HSG growth, silane gas is applied at 550 to 600° C. and 1 mTorr or less to deposit nuclei  117  on the surface of the storage electrode  116 . 
     As shown in FIG. 1H, while the nuclei  117  are deposited on the surface of the storage electrode  116 , the resultant structure is annealed to grow projecting HSGs  117   a . A dielectric film  118  is formed on the surface of the storage electrode  116 , and a cell plate electrode  119  is formed to complete the cylindrical capacitor. 
     Note that HSGs need not always be grown. Like the prior art, the capacitor may be manufactured by forming the dielectric film and cell plate electrode on the storage electrode without growing any HSGs. In this case, the silicon film need not be made of amorphous silicon. 
     FIGS. 2A and 2B show a method of manufacturing a semiconductor device according to the second embodiment of the present invention. The same reference numerals as in FIGS. 1A to  1 H denote the same parts. In the second embodiment, silicon films  109 ,  111 , and  113  are made of doped amorphous silicon in order to decrease the contact resistance and the like. In addition, as shown in FIG. 2A, undoped amorphous silicon films  120  and  121  are respectively formed at the interfaces between endpoint marker layers  110  and  112  and the silicon film  111 . 
     The silicon film  109  has a thickness of 150 nm, the silicon film  111  has a thickness of 490 nm, and the silicon film  113  has a thickness of 430 nm. Each of the undoped amorphous silicon films  120  and  121  has a thickness of 30 nm. 
     If a heavily doped amorphous silicon film is directly formed on an oxide film, amorphous silicon is easily crystallized from the interface with the oxide film by high temperatures in processes such as film growth, HSG nucleus formation, and HSG annealing. More specifically, as shown in FIG. 2A, the doped amorphous silicon films  109 ,  111 , and  113  may crystallize. When HSGs are grown on the surface of the storage electrode, the silicon film crystallizing to the surface of the storage electrode stops the growth of HSGs. 
     For this reason, crystallization of particularly the silicon film  111  having the largest surface area in a storage electrode  116  must be prevented. 
     The present inventors have found that crystallization of the silicon film  111  can be prevented by respectively forming the undoped amorphous silicon films  120  and  121  at the interfaces between the endpoint marker layers  110  and  112  and the silicon film  111 . 
     Consequently, even if the silicon films  109  and  113  in contact with oxide films  107  and  115  may crystallize to polysilicon  122 , as shown in FIG. 2B, the silicon film  111  sandwiched between the undoped amorphous silicon films  120  and  121  do not crystallize. 
     Although the endpoint marker layer  110  is left in the storage electrode  116 , the thickness is as small as 1 to 2 nm. The thin endpoint marker layer  110  allows electrons to flow therethrough as a tunnel current, so no parasitic capacitor is formed. The endpoint marker layer  110  having a thickness of 1 nm or more can be reliably detected as an endpoint marker. 
     How to determine the thicknesses of the undoped amorphous silicon films  120  and  121  will be explained. 
     FIG. 3 shows the relationship between the thickness of the undoped amorphous silicon film and an erroneous shape of the HSG formed on it. As shown in FIG. 3, if the undoped amorphous silicon films  120  and  121  are formed with a thickness of about 30 nm or more depending on the P concentration of the doped amorphous silicon underlayer, the erroneous shape of the HSG can be prevented. 
     Examples according to the present invention will be explained. The silicon films  109  and  113  in examples 1 to 3 are formed by LP-CVD, whereas the silicon film  113  in example 4 is formed by plasma CVD. 
     [Example 1] 
     The materials and thicknesses of the respective layers were as follows. 
     Silicon film  113 : 
     doped amorphous silicon film (430 nm) 
     Endpoint marker layer  112 : 
     silicon oxide film (1 to 2 nm) 
     Undoped amorphous silicon film  121 : 
     undoped amorphous silicon film (30 nm) 
     Silicon film  111 : 
     doped amorphous silicon film (490 nm) 
     Undoped amorphous silicon film  120 : 
     undoped amorphous silicon film (30 nm) 
     Endpoint marker layer  110 : 
     silicon oxide film (1 to 2 nm) 
     Silicon film  109 : 
     doped amorphous silicon film (150 nm) 
     The method of monitoring the light emission intensity was as follows. Both the endpoint marker layers  110  and  112  could be detected by any one of methods (1) to (3). 
     (1) Light emission of oxygen was monitored, and a portion where the intensity increased was determined as an endpoint. The wavelengths of light to be monitored were 437, 497, 502, 533, 544, 605, 616, 646, 700, 725, and 777 nm. 
     (2) Light emission of SiO 2  was monitored, and a portion where the intensity increased was determined as an endpoint. The wavelengths of light to be monitored were 241, 234, and 249 nm. 
     (3) The difference in P concentration between the undoped layer and the doped layer was used. That is, light emission of P was monitored, and a portion where the intensity decreased was determined as an endpoint. The wavelengths of light to be monitored were 214 and 253 nm. 
     The monitoring method by mass spectrometric analysis was as follows. Both the endpoint marker layers  110  and  112  could be detected by any one of methods (1) to (4). 
     (1) The oxygen atom O was monitored with mass number “16”, and a portion where the intensity increased was determined as an endpoint. 
     (2) SiO 2  was monitored with mass number “60”, and a portion where the intensity increased was determined as an endpoint. 
     (3) The difference in P concentration between the undoped layer and the doped layer was used. That is, P was monitored with mass number “31”, and a portion where the intensity decreased was determined as an endpoint. 
     (4) The difference in SiP concentration between the undoped layer and the doped layer was used. That is, SiP was monitored with mass number “59”, and a portion where the intensity decreased was determined as an endpoint. 
     [Example 2] 
     The materials and thicknesses of the respective layers were as follows. 
     Silicon film  113 : 
     undoped amorphous silicon film (430 nm) 
     Endpoint marker layer  112 : 
     silicon oxide film (1 to 2 nm) 
     Undoped amorphous silicon film  121 : 
     undoped amorphous silicon film (30 nm) 
     Silicon film  111 : 
     doped amorphous silicon film (490 nm) 
     Undoped amorphous silicon film  120 : 
     undoped amorphous silicon film (30 nm) 
     Endpoint marker layer  110 : 
     silicon oxide film (1 to 2 nm) 
     Silicon film  109 : 
     doped amorphous silicon film (150 nm) 
     The method of monitoring the light emission intensity was as follows. 
     (1) Light emission of oxygen was monitored, and a portion where the intensity increased was determined as an endpoint. The wavelengths of light to be monitored were 437, 497, 502, 533, 544, 605, 616, 646, 700, 725, and 777 nm. 
     (2) Light emission of SiO 2  was monitored, and a portion where the intensity increased was determined as an endpoint. The wavelengths of light to be monitored were 241, 234, and 249 nm. 
     (3) The difference in P concentration between the undoped layer and the doped layer was used. That is, for detection of the endpoint marker layer  112 , light emission of P was monitored, and a portion where the intensity increased was determined as an endpoint. For detection of the endpoint marker layer  110 , light emission of P was monitored, and a portion where the intensity decreased was determined as an endpoint. The wavelengths of light to be monitored were 214 and 253 nm. 
     The monitoring method by mass spectrometric analysis was as follows. 
     (1) The oxygen atom O was monitored with mass number “16”, and a portion where the intensity increased was determined as an endpoint. 
     (2) SiO 2  was monitored with mass number “60”, and a portion where the intensity increased was determined as an endpoint. 
     (3) The difference in P concentration between the undoped layer and the doped layer was used. That is, for detection of the endpoint marker layer  112 , P was monitored with mass number “31”, and a portion where the intensity increased was determined as an endpoint. 
     (4) The difference in SiP concentration between the undoped layer and the doped layer was used. That is, for detection of the endpoint marker layer  110 , SiP was monitored with mass number “59”, and a portion where the intensity increased was determined as an endpoint. 
     [Example 3] 
     The materials and thicknesses of the respective layers were as follows. 
     Silicon film  113 : 
     undoped amorphous silicon film (430 nm) 
     Endpoint marker layer  112 : 
     silicon nitride film (1 to 2 nm) 
     Undoped amorphous silicon film  121 : 
     undoped amorphous silicon film (30 nm) 
     Silicon film  111 : 
     doped amorphous silicon film (490 nm) 
     Undoped amorphous silicon film  120 : 
     undoped amorphous silicon film (30 nm) 
     Endpoint marker layer  110 : 
     silicon nitride film (1 to 2 nm) 
     Silicon film  109 : 
     doped amorphous silicon film (150 nm) 
     The method of monitoring the light emission intensity was as follows. 
     (1) Light emission of SiN was monitored, and a portion where the intensity increased was determined as an endpoint. The wavelengths of light to be monitored were 441, 405, 409, 413, 420, and 424 nm. 
     (2) For detection of the endpoint marker layer  112 , light emission of CN was monitored, and a portion where the intensity increased was determined as an endpoint. The wavelengths of light to be monitored were 387, 418, 647, 693, 709, and 785 nm. Note that C in CN is supplied from the resist during the manufacture. 
     The monitoring method by mass spectrometric analysis was as follows. 
     (1) The nitrogen atom N was monitored, and a portion where the intensity increased was determined as an endpoint. 
     (2) SiN was monitored, and a portion where the intensity increased was determined as an endpoint. 
     (3) The difference in SiP concentration between the undoped layer and the doped layer was used. That is, for detection of the endpoint marker layer  112 , SiP was monitored, and a portion where the intensity decreased was determined as an endpoint. 
     (4) The difference in P concentration between the undoped layer and the doped layer was used. That is, for detection of the endpoint marker layer  112 , P was monitored, and a portion where the intensity increased was determined as an endpoint. 
     [Example 4] 
     The materials and thicknesses of the respective layers were as follows. 
     Silicon film  113 : 
     plasma-CVD undoped amorphous silicon film (430 nm) 
     Endpoint marker layer  112 : 
     native oxide film (1 to 2 nm) 
     Undoped amorphous silicon film  121 : 
     undoped amorphous silicon film (30 nm) 
     Silicon film  111 : 
     doped amorphous silicon film (490 nm) 
     Undoped amorphous silicon film  120 : 
     undoped amorphous silicon film (30 nm) 
     Endpoint marker layer  110 : 
     silicon oxide film (1 to 2 nm) 
     Silicon film  109 : 
     doped amorphous silicon film (150 nm) 
     The method of monitoring the light emission intensity was as follows. 
     (1) Light emission of oxygen was monitored, and a portion where the intensity increased was determined as an endpoint. The wavelengths of light to be monitored were 437, 497, 502, 533, 544, 605, 616, 646, 700, 725, and 777 nm. 
     (2) Light emission of SiO 2  was monitored, and a portion where the intensity increased was determined as an endpoint. The wavelengths of light to be monitored were 241, 234, and 249 nm. 
     (3) The difference in P concentration between the undoped layer and the doped layer was used. That is, for detection of the endpoint marker layer  112 , light emission of P was monitored, and a portion where the intensity increased was determined as an endpoint. For detection of the endpoint marker layer  110 , light emission of P was monitored, and a portion where the intensity decreased was determined as an endpoint. The wavelengths of light to be monitored were 214 and 253 nm. 
     The monitoring method by mass spectrometric analysis was as follows. 
     (1) The oxygen atom O was monitored with mass number “16”, and a portion where the intensity increased was determined as an endpoint. 
     (2) SiO 2  was monitored with mass number “60”, and a portion where the intensity increased was determined as an endpoint. 
     (3) The difference in P concentration between the undoped layer and the doped layer was used. That is, for detection of the endpoint marker layer  112 , P was monitored with mass number “31”, and a portion where the intensity increased was determined as an endpoint. 
     (4) The difference in SiP concentration between the undoped layer and the doped layer was used. That is, for detection of the endpoint marker layer  110 , SiP was monitored with mass number “59”, and a portion where the intensity increased was determined as an endpoint. 
     In Example 4, since the undoped amorphous silicon film is formed by plasma CVD, it can be grown at a lower temperature than in LP-CVD, the thermal hysteresis is small in forming the silicon film  113  serving as a sacrificial silicon film, and crystallization hardly occurs in the storage electrode  116 . 
     Etching conditions in Examples 1 to 4 are as follows. 
     Etching apparatus: 
     parallel plate reactive ion etching apparatus 
     Pressure: 100 mTorr 
     Inter-electrode gap: 80 mm 
     Cl 2 : 150 sccm 
     HBr: 450 sccm 
     O 2 : 5 sccm 
     Top-side power: 500 W 
     Bottom-side power: 300 W 
     As has been described above, according to the present invention, since the endpoint marker layer is formed inside the storage electrode in HSG growth, the etching depth can be stably controlled. 
     Since the endpoint marker layer is etched away together with the silicon film in processing the storage electrode, no additional removal step is required. 
     By forming undoped amorphous silicon films at two portions inside the silicon film, crystallization of the amorphous silicon film sandwiched between the two films can be prevented to avoid an erroneous shape of the HSG.