The measuring method of reciprocal capacitance of diode
Technical field
The present invention relates to a kind of semicoductor capacitor measuring method, be specifically related to a kind of reciprocal capacitance of diode measuring method.
Background technology
As shown in Figure 1, it is the synoptic diagram of a diode, when the N-type district (N-Si) that gives diode when adding positive voltage, the diode reverse cut-off, the diode depletion layer of this moment and N-type district (N-Si) and the p type island region (P-Si) of both sides have just consisted of a plane-parallel capacitor, can carry out the test of reciprocal capacitance.Fig. 2 is a kind of structure of diode of reality, on P substrate 2, form p well region 3 by ion doping, shallow trench isolation region 5 is arranged in the p well region 3, in the P well region, form heavy doping N-type district 4 by Implantation between the adjacent shallow trench isolation region 5, p well region 3 and heavy doping N-type district 4 are connected to interconnecting metal layer 1 by contact (CT) 7, arrive at last pincushion (pad) 6, consist of a complete electricity loop.
In the process of carrying out the reciprocal capacitance of diode test, need a structure to eliminate the impact of the stray capacitances such as the central cable that uses of test, board, this structure device general and to be tested is identical, is exactly just passable the circuit breaker of one end, as shown in Figure 3.Individual problem is arranged here, and where the place of opening circuit can at will not selected, must consider the factors such as physical characteristics of manufacture craft, device.For diode capacitance, optimal trip point just is selected at CT7 and is connected the place that connects with heavy doping N-type district, so just can eliminate all parasitic electric capacity.But select like this, will add several technique during manufacturing, increased manufacturing cost and difficulty.So the selection of trip point generally is to connect on the circuit of CT7 at interconnecting metal, and the place of close diode capacitance.Such processing can make simplified manufacturing process, but but the accurate measurement of electric capacity and the accurate extraction of model has been brought difficulty.
Specifically, CT7 is a cone-shaped body that is made of metal, and itself just has electric capacity, and the CT7 that is connected to interconnecting metal layer 1 neither one, also has electric capacity between them, especially when the density ratio of CT7 was higher, the electric capacity of its generation be can not ignore especially.So when existing diode capacitance detection calibration structure is carried out capacity measurement calibration and test in Fig. 3, the stray capacitance that can inevitably cause with upper CT7, thereby cause the test result of diode junction capacitance inaccurate, the diode junction capacitance model that uses these data to extract is also accurate not.We study the Accurate measurement of reciprocal capacitance of diode, also has another prior purpose, in the model of MOSFET, we need to provide accurate reciprocal capacitance of diode model, because the source of MOSFET and drain region are exactly two diodes, and the numerical value of reciprocal capacitance of diode is the switching speed that can have influence on MOSFET.Therefore, can accurately measure and model extraction reciprocal capacitance of diode, can obviously have influence on circuit design and simulation.
Summary of the invention
Technical matters to be solved by this invention provides a kind of measuring method of reciprocal capacitance of diode, can eliminate the impact of contact capacitance, obtains more accurate reciprocal capacitance of diode numerical value, reduces error.
In order to solve above technical matters, the invention provides a kind of measuring method of reciprocal capacitance of diode, comprise the steps:
(1) chooses at least three area is identical, contact density is identical but reciprocal capacitance of diode that girth is different, extract the edge capacitance of reciprocal capacitance of diode;
(2) electric capacity that uses in the selecting step (1) is chosen at least two reciprocal capacitance of diode identical with girth from this capacitive touch dot density but that area is different again, extracts the area capacitance of reciprocal capacitance of diode in conjunction with the edge capacitance that obtains;
(3) the common electric capacity that uses of selecting step (1) and step (2), choose again at least two reciprocal capacitance of diode identical with girth from this capacity area but that electric shock density is different, in conjunction with the contact capacitance of the edge capacitance that obtains and area capacitance extraction reciprocal capacitance of diode;
(4) take contact capacitance and contact density as coordinate, according to the contact capacitance that obtains and the drawing of contact density data, and data are carried out match, obtain contact capacitance to the funtcional relationship of contact density;
(5) according to contact capacitance the funtcional relationship of contact density is removed contact capacitance, obtain reciprocal capacitance of diode numerical value, further extract the model of reciprocal capacitance of diode.
The present invention is than existing reciprocal capacitance of diode measuring technique, owing to considered the impact of CT electric capacity, CT electric capacity is removed from reciprocal capacitance of diode, obtained high-precision reciprocal capacitance of diode model, for circuit designers, when carrying out circuit design and breadboardin, can obtain more accurate reciprocal capacitance of diode numerical value, more accurate reciprocal capacitance of diode numerical value is brought into obtains the more accurate switching speed of MOSFET in the MOSFET model, thereby effectively reduced the error of analog computation, increased work efficiency.And for a factory, its technique has very high stability, therefore, has obtained the funtcional relationship of CT electric capacity to CT density, just has widely purposes, can also be used to the stability of monitoring process flow process.
Description of drawings
Below in conjunction with the drawings and specific embodiments the present invention is described in further detail.
Fig. 1 is the diode junction capacitance synoptic diagram;
Fig. 2 is the basic structure of reciprocal capacitance of diode;
Fig. 3 is the test electric capacity calibration structure of existing reciprocal capacitance of diode;
Fig. 4 is the process flow diagram of reciprocal capacitance of diode measuring method of the present invention;
Fig. 5 is the CT electric capacity of one embodiment of the invention and the funtcional relationship of CT density.
Reference numeral among the figure is: 1, metal level; 2, P substrate; 3, p well region; 4, heavy doping N-type district; 5, shallow trench isolation region; 6, pincushion; 7, CT.
Embodiment
The present invention proposes a kind of measuring method of reciprocal capacitance of diode, can eliminate the impact of contact capacitance, obtain more accurate reciprocal capacitance of diode numerical value, reduce error, as shown in Figure 4, the present invention need to carry out following step in the measurement of carrying out reciprocal capacitance of diode:
Step S1 chooses electric capacity M1, M2 and M3, has identical area, CT density is identical but girth different, is used for extracting the edge capacitance of reciprocal capacitance of diode;
Step S2 chooses electric capacity M1, and M4 and M5 have identical girth, identical CT density, and different areas is used for extracting the area capacitance of reciprocal capacitance of diode;
Step S3 chooses electric capacity M1, M6 ..., Mn, minimum will have three electric capacity, has identical area, identical girth, different CT density, according to step 1, area capacitance and edge capacitance in 2 are calculated CT electric capacity;
Step S4 is figure with the CT electric capacity that obtains to CT density, and data are fitted, and obtains CT electric capacity to the funtcional relationship of CT density;
Step S5 removes contact capacitance according to CT electric capacity to the funtcional relationship of CT density, obtains reciprocal capacitance of diode numerical value, further extracts the model of reciprocal capacitance of diode.
Technique take operating voltage as 1.8V is example, and implementation step of the present invention is as follows:
1. use electric capacity M1, M2 and M3, they have identical area, CT density, different girths is used for extracting the edge capacitance of reciprocal capacitance of diode.Computing formula is as follows:
Total capacitance C=C_area*S+C_f*P+C_ct, C_area wherein, C_f, and C_ct represents respectively area capacitance, edge capacitance and CT electric capacity, S and P are respectively the area and perimeters of reciprocal capacitance of diode.The C_ct=S*f here (DCT); Wherein, C_ct is contact capacitance; S is the area of reciprocal capacitance of diode, and DCT is the contact density on the diode capacitance, and f (DCT) is that contact capacitance described in the step (4) is to the functional relation of contact density.
2. electric capacity M1, M4 and M5 have identical girth, identical CT density, different areas uses above-mentioned formula, just can calculate the area capacitance of reciprocal capacitance of diode
3. electric capacity M1, M6 ..., Mn, minimum will have three electric capacity, has identical area, identical girth, different CT density according to the area capacitance in step 1 and 2 and edge capacitance, is calculated CT electric capacity.
4. according to the CT electric capacity that obtains, make CT electric capacity to the image of CT density, by data fitting, obtain the funtcional relationship between CT electric capacity and the CT density.
5.C_area C_f is exactly the accurate numerical value of reciprocal capacitance of diode, can extract based on this reciprocal capacitance of diode model, obtains simultaneously the central necessary reciprocal capacitance of diode data of MOSFET model.